Patent Publication Number: US-10765812-B2

Title: Convertible plungers and methods for assembling the same in a medical barrel

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Phase of International Application No. PCT/US2016/042167, filed Jul. 13, 2016, which claims priority to U.S. Provisional Application Ser. Nos. 62/192,192, filed Jul. 14, 2015, 62/269,600, filed Dec. 18, 2015 and 62/343,536, filed May 31, 2016, all of which are incorporated by reference herein in their entireties for all purposes. 
    
    
     FIELD OF INVENTION 
     The invention relates generally to plungers and their use in drug delivery devices, such as (prefilled, filled before use or empty) syringes, cartridges or auto-injectors. More particularly, the invention relates to convertible plungers that provide and maintain container closure integrity and gas-tight seal in a storage mode (during the shelf life of, e.g., a prefilled syringe) and then are convertible to a dispensing mode. The dispensing mode facilitates relatively low and smooth/consistent plunger force when dispensing syringe contents. 
     BACKGROUND 
     The present disclosure predominantly describes use of convertible plungers according to the present invention in connection with prefilled syringes. However, a skilled artisan would readily appreciate that the invention is not limited to prefilled syringes, but may include other drug delivery devices, such as (prefilled, filled before use, or empty) syringes, cartridges and auto-injectors as well as prefilled syringes or other barrels used for diagnostics applications. 
     Prefilled parenteral containers, such as syringes or cartridges, are commonly prepared and sold so that the syringe does not need to be filled by the patient or caregiver before use. The syringe, and more specifically the barrel of the syringe, may be prefilled with a variety of different injection products, including, for example, saline solution, a dye for injection, or a pharmaceutically active preparation, among other items. 
     Prefilled parenteral containers are typically sealed with a rubber plunger, which provides closure integrity over the shelf life of the container&#39;s contents. To use the prefilled syringe, the packaging and cap are removed, optionally a hypodermic needle or another delivery conduit is attached to the distal end of the barrel, the delivery conduit or syringe is moved to a use position (such as by inserting it into a patient&#39;s tissue or into apparatus to be rinsed with the contents of the syringe), and the plunger is advanced in the barrel to inject contents of the barrel to the point of application. 
     Seals provided by rubber plungers in the barrel typically involve the rubber of the plunger being pressed against the barrel. Typically the rubber plunger is larger in diameter than the internal diameter of the barrel. Thus, to displace the rubber plunger when the injection product is to be dispensed from the syringe requires overcoming this pressing force of the rubber plunger. Moreover, not only does this pressing force provided by the rubber seal typically need to be overcome when initially moving the plunger, but this force also needs to continue to be overcome as the rubber plunger is displaced along the barrel during the dispensing of the injection product. The need for relatively elevated forces to advance the plunger in the syringe may increase the user&#39;s difficulty in administering the injection product from the syringe. This is particularly problematic for auto injection systems where the syringe is placed into the auto injection device and the plunger is advanced by a fixed spring. Accordingly, primary considerations concerning the use of a plunger in a prefilled parenteral container include: (1) container closure integrity (“CCI”, defined below) and gas-tightness; and (2) plunger force (defined below) required to dispense syringe contents. 
     In practice, maintaining CCI/gas-tightness and providing desirable plunger force tend to be competing considerations. In other words, absent other factors, the tighter the fit between the plunger and the interior surface of the container to maintain adequate CCI/gas-tightness, the greater the force necessary to advance the plunger in use. In the field of medical syringes, it is important to ensure that the plunger can move at a substantially constant speed and with a substantially constant and relatively low force when advanced in the barrel. In addition, the force necessary to initiate plunger movement and then continue advancement of the plunger should be low enough to enable comfortable administration by a user and prevent jolting or unnecessarily high pressing force that can cause patient discomfort. 
     Plunger force is essentially a function of the coefficients of friction of each of the contacting surfaces (i.e., the plunger surface and interior syringe wall surface) and the normal force exerted by the plunger against the interior wall of the syringe. The greater the respective coefficients of friction and the greater the normal force, the more force required to advance the plunger. Accordingly, efforts to improve plunger force should be directed to reducing friction and lowering normal force between contacting surfaces. However, such efforts are preferably tempered by the need to maintain adequate CCI and gas-tightness, as discussed above. 
     To reduce friction and thus improve plunger force, lubrication is traditionally applied to the barrel-contacting engagement surface of the plunger, the interior surface of the barrel, or both. Liquid or gel-like flowable lubricants, such as free silicone oil (e.g., polydimethylsiloxane or “PDMS”), may provide a desired level of lubrication between the plunger and the barrel to optimize plunger force. PDMS is, in fact, a standard flowable lubricant used in the industry. However, for preferred embodiments of the invention, use of flowable lubricant between the plunger and the barrel is not desired. One reason is that a flowable lubricant can mix and interact with the drug product in a syringe, potentially degrading the drug or otherwise affecting its efficacy and/or safety. Degradation is particularly an issue in the case of protein compositions and polypeptide compositions, which occupy a market with tremendous growth potential. Further, such lubricants may in some cases be problematic if they are injected into the patient along with the drug product. In addition, flowable lubricants, when used with prefilled syringes, may migrate away from the plunger over time, resulting in spots between the plunger and the interior surface of the container with little or no lubrication. This may cause a phenomenon known as “sticktion,” an industry term for the adhesion between the plunger and the barrel that needs to be overcome to break out the plunger and allow it to begin moving. For these reasons, there is an industry need for an “oil free” solution, i.e., a plunger that is entirely or at least substantially free of flowable lubricant between the plunger and the barrel and wherein such flowable lubricant is absent from the drug product stream. 
     As an alternative (or in addition) to flowable lubricants, plungers may be made from materials having lubricious properties or include friction-reducing coatings or film laminates on their exterior surfaces. Examples of such plungers include, for example: the i-COATING by TERUMO, which is disclosed in Canadian Patent No. 1,324,545, incorporated by reference herein in its entirety; W.L. Gore extended ETFE film on a rubber plunger; and the CZ plunger by WEST. However, film coated plungers alone are considered to provide inadequate CCI or gas-barrier properties. For example, while fluoropolymer films on plungers provide excellent lubricious properties, they are known to provide poor gas barriers. Accordingly, a conventional fluropolymer film laminated plunger alone may not be a viable solution for a prefilled syringe that houses product which is sensitive to certain gases. 
     Thus, there is a need for plungers that balance desirable plunger force in a parenteral container with maintaining adequate CCI and (as the case may be) gas-tight sealing to prevent drug leakage, protect the drug product and attain sufficient product shelf life. In addition, there is a need to provide adequate lubricity to achieve a desired plunger force while preventing adverse effects of flowable lubricant-generated particles and interaction with the drug product held by the container. There is a further need to optimize these factors while reducing manufacturing costs and complexity. The subject invention preferably addresses those needs, and others. 
     SUMMARY OF THE INVENTION 
     One aspect of this invention is a convertible plunger. The convertible plunger has an internal portion and a generally cylindrical exterior surface that surrounds at least part of the internal portion. The generally cylindrical exterior surface includes a compressible and resilient storage sealing section that is maintained in an expanded state by outward radial pressure provided by the internal portion. The internal portion is comparatively more rigid than the storage sealing section. The expanded state is reducible to a constricted state by an operation that is applied to the internal portion of the plunger to reduce or eliminate the outward radial pressure. The storage sealing section, in the constricted state, has a reduced maximum diameter or cross-sectional width than the storage sealing section in the expanded state and/or is less resistant to inward radial compression compared to the storage sealing section in the expanded state. The storage sealing section is configured to be set in the expanded state through application of a setting force onto the convertible plunger in a distal direction, optionally when the convertible plunger is disposed in a medical barrel. The operation is application of an actuation force onto the convertible plunger in the distal direction, optionally when the convertible plunger is disposed in a medical barrel. 
     Another aspect of this invention is a pre-filled syringe having a convertible plunger according to any embodiment disposed therein. The pre-filled syringe, according to an optional embodiment, includes a medical barrel having an inner wall and an injectable drug product, optionally a liquid composition, disposed in a product containing area of the medical barrel. The medical barrel has a distal dispensing end for dispensing the injectable drug product and an open proximal end configured for receipt of a convertible plunger. 
     Optionally in any embodiment of a syringe according to the invention, the convertible plunger provides a break loose force and glide force below 15 N, optionally below 10 N, optionally below 9 N, optionally below 8 N, optionally below 7 N, optionally below 6 N, optionally between 2.5 N and 5.5 N, entirely without the presence of a flowable lubricant between the inner wall of the medical barrel and the convertible plunger&#39;s barrel-contacting surfaces. 
     Optionally in any embodiment of a convertible plunger according to the invention, a plunger head is provided at a distal end of the convertible plunger. The plunger head includes a liquid sealing section configured to provide a liquid tight seal and optionally a CCI seal against an inner wall of a medical barrel. The plunger head comprises a first component. The storage sealing section is mounted to and axially movable about a second component or integral with the second component. The first component and second component are separate components that are assembled to form the convertible plunger. 
     Optionally in any embodiment of a pre-filled syringe according to the invention, the injectable drug product, optionally a liquid composition, disposed in a product containing area of the medical barrel, includes a polypeptide composition or protein composition. In this optional embodiment, desirable plunger forces are achieved entirely without the presence of a flowable lubricant between the inner wall of the medical barrel and the convertible plunger&#39;s barrel-contacting surfaces. In addition, flowable lubricant-generated particles are absent from the drug product. 
     In an optional aspect, the invention is a method for assembling a convertible plunger into a medical barrel to form a syringe. Such a method may include providing a medical barrel, inserting a convertible plunger through an open proximal end of the barrel, disposing the plunger within the medical barrel proximal to the product containing area. The method includes applying a setting force onto the convertible plunger in a distal direction in order to set the storage sealing section in the expanded state, thereby placing the convertible plunger in the storage mode. A convertible plunger, as may be used in this method, may include an internal portion and a generally cylindrical exterior surface that surrounds at least part of the internal portion. The generally cylindrical exterior surface has a compressible and resilient storage sealing section that is maintained in an expanded state by outward radial pressure provided by the internal portion, thereby rendering the convertible plunger in storage mode. The internal portion is comparatively more rigid than the storage sealing section. The expanded state is reducible to a constricted state by an operation that is applied to the internal portion of the plunger to reduce or eliminate the outward radial pressure to transition the convertible plunger from the storage mode to a dispensing mode. The storage sealing section in the constricted state has a reduced maximum diameter or cross-sectional width than the storage sealing section in the expanded state and/or is less resistant to inward radial compression compared to the storage sealing section in the expanded state. Optionally, according to this method, the convertible plunger in the storage mode is configured to transition to the dispensing mode upon providing an actuation force onto the convertible plunger in a distal direction. Optionally, according to this method, the syringe is pre-filled in a manufacturing filling process with a drug product in the product containing area. Optionally, according to this method, flowable lubricant is absent from the product containing area. 
     Optionally, according to any embodiment of a syringe according to the invention, the barrel is made from an injection moldable thermoplastic resin, optionally COP or COC. 
     Optionally, according to any embodiment of a syringe according to the invention, the barrel has an organo-siloxane coating or layer on the interior wall of the barrel, optionally wherein the organosiloxane coating or layer is a pH protective coating, optionally as a top layer of a tri-layer coating set. 
     Optionally, according to any embodiment of a pre-filled syringe according to the invention, the storage sealing section in the expanded state forms a liquid-tight, CCI and gas-tight interface with the interior wall of the barrel, optionally wherein the gas-tight interface is substantially impermeable to oxygen, nitrogen, water vapor and/or ethylene oxide. 
     Optionally, according to any embodiment of a pre-filled syringe according to the invention, the storage sealing section in the expanded state forms a CCI and gas-tight seal over a product shelf-life of 6 months, one year, optionally 18 months, optionally 24 months, optionally three years. 
     Optionally, according to any embodiment of a pre-filled syringe according to the invention, the plunger provides a differential between break loose force and glide force of optionally below 20%, optionally below 15%, optionally below 12%, optionally below 10%, optionally below 8%, optionally between 2.5% and 6% entirely without the presence of a flowable lubricant between the barrel and the plunger&#39;s barrel-contacting surfaces. 
     Optionally, according to any embodiment, the convertible plunger is secured to a plunger rod, forming a plunger assembly, wherein the plunger rod is configured to be pressed in a distal direction to actuate the plunger and dispense drug product. 
     Optionally, according to any embodiment of a pre-filled syringe according to the invention, the drug product is an injectable liquid selected from the group consisting of: a small molecule pharmaceutical drug product, a biologic, a vaccine, a peptide-based drug, a protein-based drug, sterile water or saline solution for injection and a diagnostic medium. 
     Optionally, according to any embodiment of a pre-filled syringe according to the invention, the drug product is selected from group consisting of: diagnostic agents (e.g., dyes or contrast agents), vaccines, injections for research purposes (e.g., placebos), chemotherapeutic agents, contrast agents, immunogens, antigens, interferons, polyclonal antibody preparations, monoclonal antibodies, anesthetics, interfering RNAs, gene vectors, insulins, carriers, excipients, diluents and combinations of two or more of the foregoing. 
     Optionally, according to any embodiment of a pre-filled syringe according to the invention, a drug product disposed in the syringe is selected from the group of biopharmaceutical products set forth in BIOPHARMA: Biopharmaceutical Products in the U.S. and European Markets-Recent U.S. Approvals, Jul. 13, 2016, pp. 1-20, http://www.biopharma.com/approval.htmI, which is incorporated by reference herein in its entirety for all purposes. It is contemplated that at least some of these biopharmaceutical products are susceptible to one or more negative effects from interaction with particles generated from a flowable lubricant. Such negative effects may include: denaturing of proteins in the composition, agglomeration of proteins in the composition, degradation of proteins in the composition, triggering an undesired immune response in a patient who is administered the drug product and degrading efficacy of the drug product. In an optional embodiment of the invention, flowable-lubricant generated particles are absent from the biopharmaceutical drug product such that the drug product is not subject to the one or more of the aforementioned negative effects from flowable-lubricant generated particles. 
     Optionally, according to any embodiment of a syringe according to the invention, the medical barrel is made from glass. 
     Optionally, according to any embodiment of a syringe according to the invention, the convertible plunger includes a liquid sealing section that is located distal to the storage sealing section. The liquid sealing section includes a film coating having a lower coefficient of friction than a substrate to which the film coating is applied. The film coating is optionally a fluoropolymer film. The liquid sealing section preferably provides a liquid tight seal against the inner wall of the barrel. 
     Optionally, according to any embodiment of a plunger or pre-filled syringe according to the invention, the storage sealing section includes at least two annular ribs separated by an annular valley therebetween. 
     Optionally, any embodiment of a pre-filled syringe according to the invention may be a component of an auto injector. 
     Optionally, any embodiment of a syringe according to the invention is a 0.5 mL syringe. Optionally, any embodiment of a syringe according to the invention includes a barrel having an inner diameter of from 2.5 mm to 4.6 mm. Applicants have successfully reduced to practice a functional convertible plunger in a 0.5 mL syringe. It is a notable achievement that a convertible plunger, with small separate cooperating components, is workable in such small syringe dimensions. 
     Optionally, for any embodiment of a syringe according to the invention, the storage sealing section is on an outer storage ring disposed about the convertible plunger. The convertible plunger is configured to axially translate distally relative to the storage ring when transitioning from storage mode to dispensing mode. 
     Optionally, for any embodiment of a pre-filled syringe according to the invention, the injectable drug includes a polypeptide composition or protein composition that is susceptible to one or more negative effects from interaction with particles generated from a flowable lubricant. Such negative effects may include: denaturing of proteins in the composition, agglomeration of proteins in the composition, degradation of proteins in the composition, triggering an undesired immune response in a patient who is administered the drug product and degrading efficacy of the drug product. 
     In one aspect, the invention is optionally directed to a method for using any syringe embodiment disclosed herein for ophthalmic applications. The syringe for such applications contains 5-50 microliters, optionally 10-30 microliters, optionally 10-20 microliters of ophthalmic drug in the product-containing space. The barrel has an inner diameter of from 2.5 mm to 4.6 mm. The method includes inserting a needle into a patient&#39;s eye tissue wherein the needle provides fluid communication from the product-containing area through the dispensing end of the barrel and actuating the convertible plunger to transition from storage mode to dispensing mode. The “inserting” step may precede the “actuating” step or vice versa. Further, the method includes injecting the ophthalmic drug into the patient&#39;s eye tissue. 
     In another optional embodiment, the invention is a convertible plunger for disposition within a barrel of a medical container. The barrel is configured for receipt of an injectable product therein and having a central axis and an interior wall surrounding the axis. The plunger is configured to be moved within the barrel along the axis from a storage mode to a dispensing mode. The plunger includes a ring carrier having a compressible and resilient storage ring disposed thereon. The ring is configured to displace axially, optionally by sliding, along the ring carrier from an engagement position to a release position. In the engagement position, the storage ring is disposed about a storage platform of the ring carrier. In the release position, the storage ring is disposed about a dispensing platform having a narrower maximum cross-sectional width or diameter than the storage platform. The storage platform is optionally comparatively more rigid than the storage ring. The storage ring includes a storage sealing section configured to apply outward radial pressure on the interior wall when the storage sealing section is in the engagement position. The storage sealing section is configured in the release position to provide reduced or no outward radial pressure on the interior wall. The plunger further includes a plunger head mounted at a distal end of the plunger, the plunger head having a liquid sealing section configured to contact and provide a seal against the interior wall. The plunger head is a separate component assembled with the ring carrier, directly or indirectly, to form the convertible plunger. 
     In another optional embodiment, the invention is a convertible plunger. The plunger includes first and second subassemblies secured to each other. The first subassembly includes an optionally polymeric and optionally generally cylindrical connector body having a distal end and a proximal end. The first subassembly further includes a plunger head, which is a separate component that is assembled to the distal end of the connector body. The plunger head has a liquid sealing section configured to contact and provide a seal against an interior wall of a medical barrel when disposed therein. The second subassembly includes an elongate ring carrier, which is optionally polymeric, having a distal end and a proximal end. The distal end of the ring carrier is secured to the proximal end of first subassembly. The proximal end of the ring carrier is configured to be secured to a plunger rod. The ring carrier comprises, from its proximal end, an annular dispensing platform and an annular storage platform distal to the dispensing platform. The annular storage platform has a larger maximum diameter or cross-sectional width than the dispensing platform. The second subassembly further includes a compressible and resilient storage ring, which is optionally elastomeric, disposed about the ring carrier and configured to displace axially thereon, optionally to slide axially thereon. The storage platform is optionally comparatively more rigid than the storage ring. Optionally, the proximal end of the connector body includes a recess or axial channel, the ring carrier further including an annular insertion platform distal to the annular storage platform. The annular insertion platform has a smaller maximum diameter or cross-sectional width than the storage platform. The insertion platform is disposed in the recess or axial channel so as to fixedly secure the first subassembly to the second subassembly. 
     Optionally, according to any embodiment of a convertible plunger according to the invention, there is a fluoropolymer film wrapped about the liquid sealing section. 
     Optionally, according to any embodiment of a convertible plunger according to the invention, the storage ring includes at least two annular ribs separated by an annular valley therebetween. Optionally, the storage ring includes exactly three annular ribs with exactly two annular valleys respectively separating the ribs. 
     Optionally, according to any embodiment of a convertible plunger according to the invention, the storage ring in an uncompressed state includes a rib on an inside surface of the storage ring and an opposing rib on the outer surface of the storage sealing section. The opposing ribs have peaks that are preferably aligned along the same radial plane. 
     Optionally, according to any embodiment of a convertible plunger according to the invention, the storage ring includes an outer surface facing generally radially outward away from the ring carrier. When the storage ring is in an uncompressed state, the outer surface comprises a proximal end, a distal end and a radial plane of symmetry between the proximal and distal ends, optionally equidistant from the proximal and distal ends, wherein the outer surface is symmetrical on either side of the radial plane of symmetry. 
     Optionally, according to any embodiment, the convertible plunger may be disposed in a pre-filled syringe. When the storage ring is disposed about the storage platform, the storage sealing section is maintained in an expanded state by outward radial pressure provided by the storage platform to create compression between the storage sealing section and the inner wall of the barrel. This renders the convertible plunger in storage mode. The expanded state is reducible to a constricted state upon transitioning the storage ring to being disposed about the dispensing platform whereupon the compression between the storage sealing section and the inner wall of the barrel is reduced or eliminated, thereby rendering the convertible plunger in dispensing mode. Optionally, the entire storage ring is disposed about the storage platform when the plunger is in storage mode. Optionally, the entire storage ring is disposed about the dispensing platform when the plunger is in dispensing mode. Optionally, the storage sealing section is configured to be set in the expanded state through application of a setting force onto the convertible plunger in a distal direction. Optionally, the convertible plunger in storage mode is configured to transition to dispensing mode upon providing an actuation force onto the convertible plunger in a distal direction. 
     In an optional embodiment, the invention is an assembly including a plunger head that has a compressible and resilient material, optionally an elastomer or thermoplastic elastomer. The plunger head is configured for providing a seal, optionally a liquid tight seal when disposed in a medical barrel. The plunger includes a distal product-facing surface, a proximal end and a sidewall therebetween configured for contacting an inner wall of a medical barrel to form the seal when disposed in the medical barrel. The assembly further includes a rigid component or rigid subassembly, optionally a ring carrier, a central core and/or a connector body, fixedly secured at a distal end of the rigid component or rigid subassembly, to the proximal end of the plunger head. A fluoropolymer film piece is wrapped about the plunger head, entirely covering the product-facing surface and sidewall. The fluoropolymer film piece has an edge about its perimeter, wherein the edge is not exposed on the assembly. For example, the edge may be sandwiched between the plunger head and the rigid component or rigid subassembly. 
     In an optional embodiment, the invention is a method for making a fluoropolymer film coated liquid sealing section for a plunger, optionally as a component of a convertible plunger, according to various process steps disclosed herein. Optionally, the plunger head comprises an elastomer disposed over a polymer support. The plunger head is optionally made through two-shot injection molding. Optionally, the elastomer of the plunger head comprises a polyolefin based thermoplastic elastomer and the polymer support comprises a polyolefin, optionally polypropylene, cyclic olefin polymer or cyclic olefin copolymer. 
     In an optional embodiment, the invention is a method for making an assembly. The method includes providing a plunger head comprising a compressible and resilient material, optionally an elastomer, disposed over a comparatively more rigid polymer support. The plunger head includes a distal product-facing surface, a proximal end and a sidewall therebetween configured for contacting an inner wall of a medical barrel to form a seal, optionally a liquid tight seal, when disposed in a medical barrel. Optionally, a fluoropolymer film is wrapped about the plunger head, entirely covering the product-facing surface and sidewall. The method further includes providing a polymeric and optionally generally cylindrical connector body having a distal end and a proximal end, the proximal end of the plunger head being assembled to the distal end of the connector body and optionally secured thereto by joining, optionally by welding (e.g., ultrasonic welding), the rigid support of the plunger head to the distal end of the connector body. Respective materials of the rigid support and connector body are configured to be compatible with each other for ultrasonic welding. The method further includes providing an elongate polymeric ring carrier having a distal end and a proximal end. The distal end of the ring carrier is assembled to the proximal end of the connector body. The ring carrier comprises a material having lower gas permeability, optionally lower oxygen permeability, nitrogen permeability, water vapor permeability and/or ethylene oxide permeability, than the connector body. Optionally, as part of the method, an elastomeric storage ring is disposed about the ring carrier. The ring carrier is configured to displace axially relative to the storage ring. However, broadly, this embodiment is not limited to convertible plungers and the storage ring may be omitted in appropriate cases, e.g., for non-prefilled syringe applications. 
     Optionally, in any embodiment, the storage ring is an elastomer. 
     Optionally, in one embodiment, the invention is a method for assembling a convertible plunger into a pre-filled syringe. The method includes providing a syringe barrel having a central axis and an interior wall surrounding the axis, the barrel including a dispensing end, an open top and a product containing area therebetween. The product containing area is pre-filled to a desired amount with an injectable drug product, optionally a liquid composition. A first subassembly is provided and includes a rigid and generally cylindrical connector body having a distal end and a proximal end. The proximal end has a recess or axial channel. The first subassembly further includes a plunger head, which is a separate component that is assembled to the distal end of the connector body. The plunger head has a liquid sealing section configured to contact and provide a seal against the interior wall of the barrel when disposed therein. A second subassembly is provided. The second subassembly has a rigid elongate ring carrier having a distal end and a proximal end. The distal end is configured to be secured to the first subassembly. The proximal end is configured to be secured to a plunger rod. The ring carrier includes, from its proximal end, an annular dispensing platform, and an annular storage platform distal to the dispensing platform. The annular storage platform has a larger maximum diameter or cross-sectional width than the dispensing platform. There is an annular insertion platform distal to the annular storage platform, the annular insertion platform having a smaller maximum diameter or cross-sectional width than the storage platform. The second subassembly further includes a compressible and resilient storage ring, which is optionally elastomeric, disposed about the ring carrier and configured to displace axially thereon, optionally to slide axially thereon. The first subassembly is loaded into the syringe barrel, with the plunger head located distally in the barrel with respect to the connector body, the loading step optionally being achieved through a vent tube, vacuum or vacuum assist loading method. The method further includes positioning the storage ring about the insertion platform and axially aligning the second subassembly with the recess or axial channel of the connector body, the distal end of the ring carrier facing the recess or axial channel. After positioning and aligning, the method includes moving the first subassembly toward the second subassembly and/or vice versa to dispose the second subassembly into the syringe barrel, whereupon the insertion platform is inserted into the recess or axial channel while the storage ring contacts the proximal end of the connector body. As the insertion platform is further inserted into the storage ring, the storage ring is pushed off the insertion platform and is disposed about the storage platform, creating a compression seal between the storage ring and the interior wall of the barrel and fixedly securing the first subassembly to the second subassembly. In this way, convertible plunger may optionally be assembled. Optionally by this method, a pressure zone is not created between the storage ring and the first subassembly or the plunger head. Optionally, the convertible plunger in storage mode is configured to transition to a dispensing mode upon providing an actuation force onto the convertible plunger in a distal direction. 
     In an optional embodiment, the invention is a convertible plunger assembly configured to be disposed within a syringe barrel and advanced in a dispensing direction to dispense the contents of the syringe barrel. The plunger assembly includes a plunger having an axial cavity and at least two axially spaced generally annular ribs. Each rib has an inner diameter and an outer diameter, joined by an intermediate sleeve portion of reduced outer diameter. The plunger assembly further includes a sliding shaft that is received in the axial cavity and displaceable along its axis. The sliding shaft includes at least one annular cylindrical ring and at least one reduced diameter portion axially displaced from the ring. 
     Additional methods for making plunger assemblies and inserting them into prefilled syringes are disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in conjunction with the following drawings in which like reference numerals designate like elements and wherein: 
         FIG. 1  is an axial sectional view of one exemplary syringe constructed in accordance with this invention. 
         FIG. 1A  is an enlarged sectional view of a first alternative embodiment of the inner surface of the syringe of  FIG. 1 , comprising a tri-layer coating set disposed thereon. 
         FIG. 1B  is an enlarged sectional view of a second alternative embodiment of the inner surface of the syringe of  FIG. 1 , comprising an organo-siloxane coating disposed thereon. 
         FIG. 2A  is an enlarged axial sectional view of a portion of a convertible plunger forming a portion of the syringe shown in  FIG. 1 , with the plunger being shown in its engagement position in the syringe, wherein its storage sealing section forms a liquid-tight and gas-tight interface with the interior wall of the syringe and its liquid sealing section forms a liquid-tight interface and preferably a CCI seal with the interior wall of the syringe. 
         FIG. 2B  is an enlarged sectional view, similar to  FIG. 2A , but showing the convertible plunger as it is moved from its engagement position to a release position wherein its storage sealing section no longer forms a liquid-tight and gas-tight interface with the interior wall of the syringe but its liquid sealing section still forms a liquid-tight interface and preferably CCI seal with the interior wall of the syringe. 
         FIG. 2C  is an enlarged sectional view similar to  FIGS. 2A and 2B  but showing the convertible plunger in its most fully released position. 
         FIG. 3A  is an enlarged, exploded, axial sectional view of the exemplary embodiment of the convertible plunger of  FIG. 1  in the process of being assembled. 
         FIG. 3B  is an enlarged axial sectional view of the exemplary embodiment of the convertible plunger of  FIG. 3A  but shown after it has been assembled. 
         FIG. 4A  is an enlarged axial sectional view of another exemplary embodiment of a convertible plunger constructed in accordance with this invention, and which convertible plunger can be used in any application that the convertible plunger shown in  FIG. 1  can be used. 
         FIG. 4B  is a sectional view taken along line  4 B- 4 B of  FIG. 4A . 
         FIG. 5A  is an enlarged axial sectional view of still another exemplary embodiment of a convertible plunger constructed in accordance with this invention shown in the process of assembling the plunger. 
         FIG. 5B  is an enlarged axial sectional view, similar to  FIG. 5A , but showing the plunger after it has been assembled, whereupon it can be used in any application that the convertible plunger shown in  FIG. 1  can be used. 
         FIGS. 6A-6E  constitute a series of enlarged isometric views of a portion of the syringe shown in  FIG. 1  during the assembly of its convertible plunger. 
         FIG. 7  is an axial sectional view of an exemplary plunger constructed in accordance with this invention, illustrating an optional configuration for applying film thereto. 
         FIG. 8  is an exploded axial sectional view of an exemplary plunger constructed in accordance with this invention, illustrating another optional configuration for applying film thereto. 
         FIG. 9  is an exploded axial section view of an exemplary plunger constructed in accordance with this invention, illustrating yet another optional configuration for applying film thereto. 
         FIG. 10  is a perspective view of an exemplary convertible plunger constructed in accordance with this invention, illustrating a three-ribbed storage sealing section. 
         FIG. 11  is a side view of the convertible plunger of  FIG. 10 . 
         FIG. 12  is an axial sectional view of the convertible plunger of  FIG. 10 . 
         FIG. 12A  is an axial sectional view of an alternative geometry and dimensions for a plunger head of a liquid sealing section according to an optional embodiment. 
         FIG. 13  is a schematic illustration of an embodiment of a plunger insertion apparatus for inserting the plunger of  FIG. 10  into a medical barrel. 
         FIG. 14A  is a partial schematic illustration of an alternative embodiment of a plunger insertion apparatus, according to an aspect of the invention, for inserting the plunger of  FIG. 10  into a medical barrel, wherein the storage ring is in a pre-storage sealing mode. 
         FIG. 14B  is the same partial schematic illustration as  FIG. 14A , except that the storage ring is set in storage sealing mode. 
         FIG. 14C  is a more complete schematic illustration of  FIG. 14A , showing additional components of the plunger insertion apparatus. 
         FIG. 15A  is a partial schematic illustration of an alternative embodiment of a plunger insertion apparatus, according to an aspect of the invention, for inserting the plunger of  FIG. 10  into a medical barrel, wherein the storage ring is set in storage sealing mode. 
         FIG. 15B  is a more complete schematic illustration of  FIG. 15A , showing additional components of the plunger insertion apparatus, wherein the storage ring is in a pre-storage sealing mode. 
         FIG. 16A  is a sectional schematic illustration of a plunger insertion apparatus, according to an aspect of the invention, for an exemplary embodiment of an insert and sleeve convertible plunger. 
         FIG. 16B  is a partial schematic illustration of the plunger insertion apparatus of  FIG. 16A , oriented 90 degrees from the view shown in  FIG. 16A . 
         FIG. 17A  is a partial cross-sectional view of an alternative plunger insertion apparatus, according to an aspect of the invention, for another exemplary embodiment of an insert and sleeve convertible plunger. 
         FIG. 17B  is a perspective view of the plunger insertion apparatus and plunger of  FIG. 17A . 
         FIG. 18  is a cross-sectional view of an alternative embodiment of a convertible plunger according to an aspect of the invention with an optional plunger insertion apparatus assembling the plunger into a medical barrel. 
         FIG. 19A  is a chart detailing the average plunger force profile of plungers according to an embodiment of the present invention, as discussed in Example 1 herein. 
         FIG. 19B  is a chart of the raw data for plunger force of the eighteen plungers that were tested, as discussed in Example 1 herein. 
         FIG. 20  is a chart of plunger force, discussed also in Example 1, for another set of similarly configured plungers and syringes as those tested and described with respect to  FIGS. 19A and 19B . 
         FIG. 21  is an axial sectional view of an alternative convertible plunger embodiment comprising a connector, which at a distal end thereof, is secured to the liquid sealing section and at a proximal end thereof, is secured to the central core. 
         FIGS. 22A and 22B  are schematic drawings illustrating the manner in which the convertible ring of  FIG. 21  may be assembled. 
         FIGS. 23A-23C  are schematic drawings illustrating the manner in which the convertible plunger components of  FIG. 21  may be loaded into and assembled within a syringe barrel. 
         FIG. 24  is an axial sectional view of an alternative convertible plunger identical to the plunger of  FIG. 21 , except that the cross-section of the storage ring of  FIG. 24  is an alternative geometry compared to that of  FIG. 21 . 
         FIG. 24A  is an enlarged partial view of the plunger of  FIG. 24  highlighting the alternative geometry of the cross-section of the storage ring. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described more fully with reference to the accompanying drawings, in which several embodiments are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth here. Rather, these embodiments are examples of the invention, which has the full scope indicated by the language of the claims. Like numbers refer to like elements throughout. 
     Definitions 
     For purposes of the present invention, an “organosilicon precursor” is a compound having at least one of the linkages: 
                         
which is a tetravalent silicon atom connected to an oxygen or nitrogen atom and an organic carbon atom (an organic carbon atom being a carbon atom bonded to at least one hydrogen atom). A volatile organosilicon precursor, defined as such a precursor that can be supplied as a vapor in a plasma enhanced chemical vapor deposition (PECVD) apparatus, is an optional organosilicon precursor. Optionally, the organosilicon precursor is selected from the group consisting of a linear siloxane, a monocyclic siloxane, a polycyclic siloxane, a polysilsesquioxane, an alkyl trimethoxysilane, a linear silazane, a monocyclic silazane, a polycyclic silazane, a polysilsesquiazane, and a combination of any two or more of these precursors.
 
     Values of w, x, y, and z are applicable to the empirical composition Si w O x C y H z  throughout this specification. The values of w, x, y, and z used throughout this specification should be understood as ratios or an empirical formula (for example for a coating or layer), rather than as a limit on the number or type of atoms in a molecule. For example, octamethylcyclotetrasiloxane, which has the molecular composition Si 4 O 4 C 8 H 24 , can be described by the following empirical formula, arrived at by dividing each of w, x, y, and z in the molecular formula by 4, the largest common factor: Si 1 O 1 C 2 H 6 . The values of w, x, y, and z are also not limited to integers. For example, (acyclic) octamethyltrisiloxane, molecular composition Si 3 O 2 C 8 H 24 , is reducible to Si 1 O 0.67 C 2.67 H 8 . Also, although SiO x C y H z  is described as equivalent to SiO x C y , it is not necessary to show the presence of hydrogen in any proportion to show the presence of SiO x C y . 
     The term “barrel” refers to a medical barrel, as may be used, e.g., as part of a medical device for containing and dispensing liquid product, such as a syringe. 
     The terms “plunger” or “plunger assembly” when used with reference to any embodiment of the present invention (as opposed to with reference to conventional plungers in the art) refers to a convertible plunger according to the present invention. 
     “Frictional resistance” can be static frictional resistance and/or kinetic frictional resistance. 
     The “plunger sliding force” (synonym to “glide force,” “maintenance force”, or F m , also used in this description) in the context of the present invention is the force required to maintain movement of a plunger tip in a syringe barrel, for example during aspiration or dispense. It can advantageously be determined using the ISO 7886-1:1993 test known in the art. A synonym for “plunger sliding force” often used in the art is “plunger force” or “pushing force”. 
     The “plunger breakout force” (synonym to “breakout force”, “break loose force”, “initiation force”, F i , also used in this description) in the context of the present invention is the force required to initiate movement of the plunger tip in a syringe, for example in a prefilled syringe. 
     Both “plunger sliding force” and “plunger breakout force” and methods for their measurement are described in more detail in subsequent parts of this description. These two forces can be expressed in N, lbs or kg and all three units are used herein. These units correlate as follows: 1N=0.102 kg=0.2248 lbs (pounds). 
     “Slidably” means that the plunger tip, closure, storage ring, convertible plunger or other removable part is permitted to slide axially, e.g. in a medical barrel. 
     “Container closure integrity” or “CCI” refers to the ability of a container closure system, e.g., a plunger disposed in a prefilled syringe barrel, to provide protection and maintain efficacy and sterility during the shelf life of a sterile product contained in the container. 
     The term “outward radial pressure,” as used with respect to a plunger according to the invention or elements thereof, refers to pressure applied or exerted in a direction outward from (or away from) the plunger&#39;s central axis. 
     The term “syringe” is broadly defined to include cartridges, injection “pens,” and other types of barrels or reservoirs adapted to be assembled with one or more other components to provide a functional syringe. “Syringe” is also broadly defined to include related articles such as auto-injectors, which provide a mechanism for dispensing the contents. Optionally, “syringe” may include prefilled syringes. A “syringe” as used herein may also apply to vaccine dispensing syringes comprising a product space containing a vaccine. A “syringe” as used herein may also have applications in diagnostics, e.g., a sampling device comprising a medical barrel prefilled with a diagnostic agent (e.g., contrast dye) or the like. 
     One or two openings, like the openings of a sample tube or vial (one opening) or a syringe barrel (two openings) are preferred. If the vessel has two or more openings, they can be of same or different size. 
     Though the invention is not necessarily limited to syringes of a particular volume, syringes are contemplated in which the lumen has a void volume of, for example, from 0.5 to 50 mL, optionally from 1 to 10 mL, optionally from 0.5 to 5 mL, optionally from 1 to 3 mL. 
     “PECVD” refers to plasma enhanced chemical vapor deposition. 
     A “lubricant” is a material or substance introduced to reduce friction between surfaces in mutual contact. A “flowable lubricant” is a lubricant that is deposited on a surface as a fluid (liquid or vapor). This definition encompasses such lubricants that are not treated or modified upon or after deposition, e.g., PDMS or silicone oil, in liquid form, applied to a surface. This definition also encompasses a liquid or vapor applied lubricant that is condensed, cross-linked, plasma-treated, reacted, heated, irradiated, or otherwise treated or modified upon deposition or subsequent to deposition. A common characteristic of flowable lubricants is that they tend to generate particles, e.g., in the form of droplets or micelles. 
     References to “pharmaceutical agent,” “pharmaceutically active,” “pharmaceutical,” “drug,” “medicament,” “active agent,” “active drug,” “drug product” and the like, refer in a general sense to substances useful in the medical and scientific arts as suitable for delivery via a syringe, including, for example, drugs, biologics, diagnostic agents (e.g., dyes or contrast agents) or other substances used for therapeutic, diagnostic, or preventative (e.g., vaccines), or research purposes. Example pharmaceutical agents or drug products include biologics, vaccines, chemotherapeutic agents, contrast agents, small molecules, immunogens, antigens, interferons, polyclonal antibody preparations, monoclonal antibodies, anesthetics, interfering RNAs, gene vectors, insulins, or combinations of any of these. “Inactive” substances refer to carriers, excipients, diluents, and the like, which are well-known in the art, although such substances may have beneficial function in the mixed injectable, such as, for example, adjuvants, isotonic or buffering agents. These active or inactive substances may also include substances having immediate, delayed or sustained release characteristics. It is contemplated that “drug products” may broadly include active and inactive substances configured for storage and injection by a syringe. 
     Syringe Barrel Materials 
     Optionally, syringes according to any embodiment of the present invention may be made from one or more injection moldable thermoplastic materials including, but not limited to: an olefin polymer; polypropylene (PP); polyethylene (PE); cyclic olefin copolymer (COC); cyclic olefin polymer (COP); polymethylpentene; polyester; polyethylene terephthalate; polyethylene naphthalate; polybutylene terephthalate (PBT); PVdC (polyvinylidene chloride); polyvinyl chloride (PVC); polycarbonate; polymethylmethacrylate; polylactic acid; polylactic acid; polystyrene; hydrogenated polystyrene; poly(cyclohexylethylene) (PCHE); nylon; polyurethane polyacrylonitrile; polyacrylonitrile (PAN); an ionomeric resin; Surlyn® ionomeric resin. For applications in which clear and glass-like polymers are desired (e.g., for syringes and vials), a cyclic olefin polymer (COP), cyclic olefin copolymer (COC) or polycarbonate may be preferred. Such materials may be manufactured, e.g., by injection molding or injection stretch blow molding, to very tight and precise tolerances (generally much tighter than achievable with glass). Alternatively, syringes according to embodiments of the present invention may be made from glass. 
     Syringe and Convertible Plunger Embodiments 
     In  FIG. 1 , one exemplary embodiment of a syringe  10  including a plunger assembly  20  constructed in accordance with one aspect of this invention is shown. As a brief aside, the terms “distal” and “proximal” are used throughout this specification. The terms “distal” and “proximal” refer generally to a spatial or positional relationship relative to a given reference point, wherein “proximal” is a location at or comparatively closer to that reference point and “distal” is a location further from that reference point. As applied herein to syringe barrels, for example, the relevant reference point is the back end of the barrel (for example, the flange at the top of the barrel  12  as shown in  FIG. 1 ), near where the plunger rod  22  and the convertible plunger  24  are joined. The distal end is at the bottom or dispensing end of the barrel  12 , where the needle  18  is mounted. “Proximal” and “distal” may also be used to refer to the direction of application of force. For example, the pushing force to dispense syringe contents would be applied in a “distal direction” or “distally,” i.e., a force pushing the plunger head  30  down in  FIG. 1  to advance the liquid sealing section  36  down toward the dispensing end or distal end of the syringe. 
     The syringe  10  is of generally conventional construction and includes a hollow barrel  12  having a central longitudinal axis A. The barrel has an inner surface  14  and is configured to hold an injectable liquid  16  therein. A needle  18  is located at the distal end of the barrel and is in fluid communication therewith. The plunger assembly  20  is disposed so that a distal portion of it is located in the proximally located portion of the barrel, like shown in  FIG. 1 , whereupon the syringe  10  is ready for use. To that end, when the plunger assembly  20  is actuated, e.g., pushed in the distal direction, it forces the injectable liquid within the barrel out through the needle  18 . 
     The plunger assembly  20  basically comprises a plunger rod  22  and a convertible plunger  24 . The convertible plunger  24  constitutes a subassembly of components which are configured to provide sufficient compressive force against the inner surface of the sidewall of a prefilled syringe or cartridge barrel to effectively seal and preserve the shelf-life of the contents of the barrel during storage. When a convertible plunger, such as that of the subject invention, provides container closure integrity (CCI) and gas-tight sealing (e.g., providing a barrier to oxygen, moisture and/or optionally additional gases), adequate to effectively seal and preserve the shelf-life of the contents of the barrel during storage, the convertible plunger (or at least a portion of its exterior surface) may alternatively be characterized as being in an “expanded state” or “storage mode.” The expanded state or storage mode may be a product of, for example, an expanded outer diameter or profile of at least a portion of the syringe barrel-contacting surface of the plunger and/or the normal force that the plunger exerts on the inner wall of the syringe barrel in which it is disposed. The convertible plunger (or at least a portion of its exterior surface) is reducible to what may alternatively be characterized as a “constricted state” or a “dispensing mode,” wherein the compressive force against the sidewall of the barrel is reduced or eliminated in part, allowing a user to more easily advance the plunger in the barrel and thus dispense the contents of the syringe or cartridge. The constricted state or dispensing mode may be a product of, for example, a reduced outer diameter or cross-sectional width (relative to that of the expanded state) of at least a portion of the syringe barrel-contacting surface of the plunger and/or reduced normal force against the inner wall of the syringe barrel exerted by the plunger and/or reduced resistance to inward radial compression. 
     As used herein, the term “convertible plunger” broadly includes a plunger, configured for use in a medical barrel, wherein the plunger is convertible from a storage mode to a dispensing mode, as generally described above. This specification focuses primarily (albeit not exclusively) on convertible plunger embodiments having a liquid sealing section that translates axially in a medical barrel, independently of a separate storage sealing section component, when the plunger transitions from storage mode to dispensing mode (for short, “independent storage sealing section plunger”). An alternative type of convertible plunger, which is the subject of applications assigned to the same assignee as the present Application, is optionally described as having an insert positioned within a cavity of the plunger sleeve to provide outward radial pressure of an adjacent storage sealing section against a medical barrel wall (to provide a storage mode). The insert, which is preferably more rigid than the plunger sleeve, is then movable to a different cavity (e.g., a cavity that is distal to the storage cavity) within the plunger sleeve to release such radial compression and thus transition the plunger to a dispensing mode. Such “insert and sleeve” plungers are described in PCT Publication No. WO 2015/054282, which is incorporated by reference herein in its entirety. While insert and sleeve plungers are not the primary focus of the present application, some embodiments are described herein particularly to illustrate methods and apparatus, according to aspects of the invention, for assembling such plungers into medical barrels. It should be understood, moreover, that the invention, in one aspect, may cover at least both independent storage sealing section and insert and sleeve types of convertible plungers. 
     Features common to both the independent storage sealing section type of plunger and insert and sleeve type of plunger are as follows. Generally speaking, they both comprise an internal portion and a generally cylindrical exterior surface that surrounds at least part of the internal portion. The generally cylindrical exterior surface includes a compressible and resilient storage sealing section (optionally an elastomer) that is maintained in an expanded state by outward radial pressure provided by the internal portion. The internal portion is comparatively more rigid than the storage sealing section. The expanded state is reducible to a constricted state by an operation that is applied to the internal portion of the plunger to reduce or eliminate the outward radial pressure. The storage sealing section, in the constricted state, has a reduced maximum diameter or cross-sectional width than the storage sealing section in the expanded state and/or is less resistant to inward radial compression compared to the storage sealing section in the expanded state. With the insert and sleeve type plunger, the internal portion comprises the insert and storage sealing section is the portion of the sleeve surrounding and adjacent to the insert. With the independent storage sealing section plunger type, the internal portion is the ring carrier and the storage sealing section is on the storage ring. In both cases, the plungers are preferably actuated by applying a force to the plungers in a distal direction. Such actuation force may apply the aforementioned operation to the internal portion of the plunger. In the case of the insert and sleeve type plunger, the operation may displace the insert from a proximal cavity to a distal cavity in the sleeve. In the case of the independent storage sealing section plunger type, the operation includes axial displacement of the ring carrier relative to the storage ring when transitioning from storage mode to dispensing mode. 
     Accordingly, in one aspect, as shown in  FIGS. 1 and 2A-3B , the invention is a convertible plunger  24  comprising a central core  32  having a longitudinal axis which is coaxial with the central axis A of the barrel  12 , a storage sealing section  34  and a liquid sealing section  36 . The central core  32  is preferably rigid, optionally made from a polymer material. The storage sealing section  34  and the liquid sealing section  36  each have a respective generally cylindrical exterior surface. As used herein, a “generally cylindrical” exterior surface may include minor interruptions or variations in geometry (e.g., due to ribs, valleys, etc.) to the otherwise cylindrical shape of the external surface of a given component, e.g., the liquid sealing section. As will be described in detail later, the generally cylindrical exterior surface of the storage sealing section includes one or more annular ribs or outwardly projecting surfaces for engagement with the inner wall of the syringe barrel when the storage sealing section is in its expanded state. The expanded state is reducible to a constricted state by the relative movement of the storage sealing section along the longitudinal axis A with respect to the liquid sealing section or vice versa. As used herein, “expanded state” and “constricted state” may refer to comparative dimensional measurements (e.g., expanded state being wider than constricted state) and/or comparative resistance to inward compression of the plunger (the “expanded state” being more resistant to inward compression and the “constricted state” being less resistant to inward compression) and/or comparative outward radial pressure exerted by at least a portion of the plunger&#39;s exterior surface (the plunger&#39;s exterior surface in the “expanded state” exerting more outward radial pressure and in the “constricted state” exerting less outward radial pressure). 
     The convertible plunger  24 , preferably at a proximal end of the central core  32 , is mounted on a distal end of the plunger rod  22 . The plunger rod  22  is an elongated member having a central longitudinal axis extending coaxially with the central axis A of the barrel of the syringe. The distal end of the plunger rod is optionally in the form of a threaded projection  26  ( FIG. 2A ) extending distally from the distal end of the rod  22  and centered on the axis A. The threaded projection  26  is configured to be threadedly received within a mating threaded bore or hole  28  in the proximal end of the convertible plunger  24  to mount the convertible plunger on the distal end of the plunger rod  22 . Alternatively, the plunger  24  may be mounted to the distal end of the plunger rod  22  through other means, such as by snap fit or press fit. The proximal end of the plunger rod  22  is in the form of an enlarged flanged head  30  ( FIG. 1 ), which is configured to be pressed by a user to eject the liquid  18  from the syringe. 
     The convertible plunger  24  is configured for operating in two modes. One mode is a sealing mode, like shown in  FIGS. 1 and 2A , in which the storage sealing section  34  of the plunger is in its “engagement” position wherein it is compressed between a first portion of the central core of the plunger and the internal wall of the syringe&#39;s barrel to form a gas-tight, liquid-tight and CCI level interface therebetween. The other mode is a gliding mode in which the storage sealing section is shifted to a different portion on the central core, e.g., a “release” position, when the plunger assembly is slid in the barrel so that the storage sealing section is no longer in engagement (or is in reduced engagement) with the internal wall of the barrel. However, in the gliding mode the liquid sealing section of the plunger will be in sliding engagement with the internal wall of the barrel to form a liquid-tight interface therebetween. Moreover, owing to the inherent lubricity of liquid sealing section, no liquid or other flowable lubricants (e.g., silicone oil) are necessary to be used between the plunger and the barrel to facilitate sliding of the plunger in the barrel. This feature constitutes a considerable advantage over the prior art, since the use of a flowable lubricant between the plunger and the barrel to facilitate sliding of the plunger may have the effect of contaminating the injectable liquid if the lubricant disassociates from the syringe or plunger into that liquid. The liquid sealing section itself, in addition to providing a liquid tight seal, preferably also provides a CCI-level seal, to comply with prevailing industry concerns and to provide CCI redundancy with the storage sealing section. 
     As best seen in  FIGS. 2A-2C , the liquid sealing section  36  is mounted on the distal end of the plunger&#39;s central core  32 , while the storage sealing section  34  is located proximally of the liquid sealing section. The storage sealing section  34  is in the form of at least one ring mounted around a portion of the central core and configured so that when the plunger assembly is in the engagement position like shown in  FIGS. 1 and 2A , the at least one ring of the storage sealing section  34  forms the heretofore mentioned liquid-tight and gas-tight interface with the interior wall  14  of the syringe&#39;s barrel  12 . Thus, when the plunger assembly is in that position the storage sealing section provides CCI and a gas-tight seal for the syringe. In the exemplary embodiment shown in  FIG. 1  the storage sealing section is in the form of a single “O-ring”  38  of circular cross-section. Other single rings of various cross-sectional shapes may be provided to form the storage sealing section. In fact, multiple rings of various cross-sectional shapes may be provided to form the storage sealing section. For example, optionally, the O-ring has more than one rib or lobe; e.g., 2 ribbed or 3 ribbed O-rings are contemplated. Some of those alternative embodiments for the storage sealing section are discussed below. 
     The central core  32  of the convertible plunger  24  is an elongated rigid member, optionally having a cylindrically shaped mounting projection  40  at the distal end thereof. The projection  40  can be of any suitable shape. In the exemplary embodiment shown it is semi-spherical. The projection  40  serves as the means for mounting the liquid sealing section  36  on the distal end of the central core  32 . A flange  42  projects radially outward from the central core immediately proximally of the projection  40 . An annular storage platform  44  is provided on the central core  32  immediately proximally of the flange  42 . The storage platform  44  is configured to receive and hold the at least one ring  38  thereon in a “holding” position when the plunger assembly  24  is in the storage mode, i.e., the state shown in  FIG. 1 . 
     The ring  38  is formed of a resilient material or one or more resilient materials, including, but not limited to, a thermoset rubber (e.g., butyl rubber), a thermoplastic elastomer (TPE), liquid silicone rubber and fluoro-liquid silicone rubber. The diameter of the central core  32  at the location of the storage platform  44  is greater than the normal internal diameter of the ring  38 . Thus, when the ring  38  is disposed around the storage platform  44  it is stretched from its normal outer diameter (i.e., its “constricted” state) to its “expanded” state. In that expanded state the outermost portion of the periphery of the ring will be in intimate engagement with the inner surface  14  of the barrel, thereby forming the heretofore mentioned gas-tight, CCI-tight and liquid-tight interface therebetween. As should be appreciated by those skilled in the art, when the ring  38  is in such engagement with the inner surface of the barrel “sticktion,” can result. Thus, the convertible plunger of this invention is constructed to enable the central core  32  to move with respect to the ring  38  (which initially adheres to the barrel through sticktion) to enable the plunger assembly  24  to be moved to the release position wherein it operates in the heretofore mentioned gliding mode. When in that mode, the ring  38  will be in a constricted state, wherein the outside diameter of the ring is optionally less than the inner diameter of the interior surface  14  of the barrel&#39;s wall  12  so that the ring does not engage that interior surface and hence will not interfere with the sliding movement of the plunger assembly into the barrel. 
     In order to enable the O-ring  38  to move from its engagement position (wherein it will be retained about the storage platform  44 ) to the release position (wherein it is transitioned from the storage platform  44 ), the central core  32  includes a conically tapering section  46  located immediately adjacent the storage platform  44 . The proximal end of the conically tapering section  46  terminates in a cylindrical section  48 , the external diameter of which is less than the external diameter of the storage platform  44 . Thus, when the plunger assembly  20  is pressed to cause it to move in the distal direction (i.e., applying an operation to the internal portion of the plunger comprising application of an actuation force on the plunger in the distal direction) shown by the arrow in  FIG. 2A  within the barrel  12 , the frictional engagement between the O-ring and the inner wall of the barrel will tend to hold the O-ring at that longitudinal position in the barrel, while the central core  32  moves distally. In other words, the O-ring  38  preferentially adheres to the inner surface  14  of the barrel over the outer surface of the central core  32 . Thus, there will be relative movement between the O-ring  38  and the central core  32  in the axial direction. That relative axial movement causes the O-ring  38  to move from its holding position about the storage platform  44 , so the O-ring slides in the proximal direction with respect to the central core  32  in the direction of the arrows  50  in  FIG. 2A , whereupon the radially outer-most surface of the O-ring will no longer be in engagement (or optionally will be in reduced engagement or apply reduced outward radial pressure) with inner surface  14  of the barrel. As such, the plunger assembly  20  can be slid smoothly down the barrel with minimal force. Continued pressing of the plunger assembly distally will ultimately bring the O-ring into engagement with the undersurface of a projecting flange  52  forming the proximal end of the central core  32 , such as shown in  FIG. 2C . 
     As mentioned above, when the plunger assembly  20  is in the glide mode, the liquid sealing section  36  will be in sliding engagement with the inner surface  14  of the barrel to result in a good liquid-tight interface therebetween. To that end, the liquid sealing section  36  basically comprises an elastomeric body or head  54  having an exterior surface portion having a lubricity that is greater than the lubricity of the interior wall  14 . The first surface portion may be in the form of a film  56  which extends about the entire exterior surface of the head  54 . The film may have an optional thickness in any embodiment of under approximately 100 micrometer (μm), optionally from 25-50 μm. A variety of different materials may be employed for the film, such as, for example, an inert fluoropolymer, including, fluorinated ethylene propylene (FEP), ethylene tetrafluoroethylene (ETFE), polytetrafluoroethylene (PTFE), ethylene perfluoroethylenepropylene (EFEP), ethylene chlorotrifluoroethylene (ECTFE), Polychlorotrifluoroethene (PCTFE), perfluoroalkoxy (PFA), among other coatings. Optionally, CPT fluoropolymer may be used. CPT is a modified perfluoroalkoxy (PFA) commercially available from Daikin America, Inc. and generally comprises the addition of PCTFE side chains to a PFA main chain during polymerization, thereby increasing gas and/or liquid barrier properties of standard PFA. Optionally, the exterior surface of the head  54  may be in the form of a rigid cap (not shown) formed of a perfluoropolyether oil, such as DEMNUM which is commercially available from Daikin America, Inc., which may be mixed with resin and extruded into a film, mold or cap. Additionally, according to certain embodiments, the material used for the film coating may not be an expanded fluoropolymer. Further, according to certain embodiments, additives may be added to the material for the film or cap, such as additives that may improve the adhesion of the film or cap to the underlying portion of the plunger making up the liquid sealing section and/or decrease the friction between that section and the sidewall of the barrel. Additionally, according to certain embodiments, an adhesion promoting coating or process may be employed, such as, for example, a corona treatment. For some applications, it may be desirable to coextrude different materials to form the film. For example, coextruded film combinations may include a cyclic olefin copolymer (COC) with Aclar, Polyethylene (PE) with Aclar and FEP with PE, among other combinations. 
     Optionally, after the film material has been inserted into the mold, the plunger material is injected into the mold. Thus, in the final product, the liquid sealing section of the plunger may comprise a plunger core, a polymer head disposed on the tip of the plunger core and a film covering the head. Alternatively, a high durometer, lubricious TPE material without any film disposed thereon may be used as the liquid sealing section. 
     In the case where a film  56  is used to provide the lubricious outer surface of the liquid sealing section, the film may be secured to the head  54  in various ways. For example, as shown in  FIG. 3A  a sheet of film  56  may be wrapped about the head  54 , so that the portions  58  of the sheet of film contiguous with its edges are located within a recess  60  in the head  54 , like shown in  FIGS. 2A-2C and 3A . The recess  60  is of a mating shape to the shape of the projection  40 . Thus, when the projection  40  is inserted into the recess to mount the head  54  on the distal end of the central core  32 , the edge portions  58  of the film  56  will be trapped therein. The securement of the head  54  to the central core  32  can be achieved by means of a press fit, compression ribs, or any other suitable means for fixedly securing the head to the central core with the edge portions of the film trapped therebetween. 
       FIGS. 4A and 4B  illustrate another convertible plunger  124  constructed in accordance with this invention. The plunger  124  basically comprises a cylindrical central core  132  having a distal end  135  to which a head  154  is fixedly secured. The head  154  is similar to the head  54  and serves to form a portion of the liquid sealing section  136  of this embodiment. A sheet of film  156 , similar to the film  56  described above is wrapped about the head  154 , with the portions of the film at its edges being trapped between the core  132  and a cylindrical sleeve  160 . The sleeve  160  is an elongated rigid tubular member, the inside diameter of which is just slightly larger than the outside diameter of the central core  132 . The inner surface of the sleeve at its distal end includes an annular inner recess  162 . The outer surface of the sleeve at its distal end includes an annular storage platform  144 . The inner recess  162  is configured to receive and trap the edge portions of the film  156 . The storage platform  144  is similar in function to the storage platform  44 , i.e., it is arranged to receive and hold the storage sealing section  134  of the convertible plunger  124  when the plunger  124  is in storage mode. That storage sealing section  134  comprises a ring  138  formed of a similar material as the O-ring  38 , but the ring  138  has a generally rectangular cross-section with a slightly concave outer surface  140 . The top and bottom edges of the outer surface  140  of the ring  138  are in the form of a pair of annular ribs  142 , each of which forms an engagement surface to tightly engage the inner surface of the barrel when a plunger assembly composed of the convertible plunger  124  is located within the barrel  12  of the syringe in the engagement position. That engagement results in a good gas-tight and liquid-tight interface between the ring  138  and the inner surface of the barrel. 
     The ring  138 , like the O-ring  38 , is arranged to be moved from the engagement position to the release position, whereupon it no longer engages the inner surface of the barrel. To that end, the sleeve  160  includes a conically tapering section  146  located immediately proximately of the storage platform  144 . The proximal end of the conically tapering section  146  terminates in a cylindrical section  148 , the external diameter of which is less than the external diameter of the recess  144 . Thus, when the plunger assembly including the convertible plunger  124  is pressed to cause it to move in the distal direction within the barrel  12  of the syringe, the O-ring  138  will move from the storage platform  144  and slide in the proximal direction with respect to the central core, whereupon the ribs  142  of the ring  138  will no longer be in engagement with (or at least will be in reduced engagement with) the inner surface  14  of the barrel. As such, the plunger assembly can be slid smoothly down the barrel with minimal force. The liquid sealing section of the convertible plunger  124  operates in the same manner as discussed with reference to the convertible plunger  24 , and hence will not be reiterated in the interest of brevity. 
     In order to facilitate the assembly of the components making up the convertible plunger  124 , the central core  132  includes a plurality of elongated venting grooves or channels  170  extending longitudinally therealong and being equidistantly spaced about the periphery of the central core. The grooves or channels  170  enable any air that would be trapped between the sleeve  160  and the central core  132  when the sleeve is mounted on the central core to exit or vent out the bottom of the sleeve. Alternatively, the venting slots or channels may be provided in the inner surface of the sleeve  160  rather than the outer surface of the central core  132 . In fact, the venting slots may be provided in both the inner surface of the sleeve and the outer surface of the central core. In any case, by venting any air between the sleeve and the central core one is able to trap the edge portions of the film  156  between the sleeve and the central core within the inner annular recess  162  expeditiously and neatly. 
     Still another embodiment of a convertible plunger is shown in  FIGS. 5A and 5B  and will be discussed now. That convertible plunger is designated by the reference number  224  and is similar in construction to the plunger  24  described heretofore, except for the manner in which the edge portions of the film  56  are trapped with respect to the central core so as not to be exposed. In the interest of brevity those features of the convertible plunger  224  which are common to the convertible plunger  24  will be given the same reference numbers and the details of their construction and operation will not be reiterated. Thus, as can be seen, the convertible plunger  224  includes a central core  32  on which the storage sealing section  34  and the liquid sealing section  36  are mounted. The portions of the film  56  contiguous with the edges thereof are not, however, trapped between the projection  40  and the recess  60  in the head  54 . Instead those edge portions are trapped between a retainer ring  162  and the flange  42 . The retainer ring is formed by molding it about the edge portions of the sheet of film  56 . To that end, a mold member  170  having an annular cavity  172  of generally L-shape in cross-section is disposed about the portion of the central core  32  at the location of the flange  42 , with the edge portions of the sheet of film  56  located within the cavity  172 . Then any suitable plastic material is injected into the cavity  172  to form the retaining ring  162 . Once that has been accomplished the mold member  170  can be removed, leaving the edge portions of the film trapped under the retaining ring and hence not exposed. 
       FIGS. 7-9  show three alternative configurations for applying film to plungers according to any embodiment of the invention. The film in these configurations would function the same as film applied in other configurations disclosed herein; so much of the disclosure elsewhere in the specification suffices for purposes of describing the embodiments of  FIGS. 7-9  and will not be repeated, for the sake of brevity. Differences, however, are noted here. To minimize the chances of film wrinkling when wrapping the film  56  about the head  54 , the film may be cut into a pattern enabling it to fold neatly into the recess  60  in the head  54 . Optionally, a rigid polymer support  61  is disposed within the recess  60  to provide a mating surface with portions of the film  56 . As shown in  FIG. 7 , portions of the film  56  bend into the rigid polymer support  61  and are sandwiched between the core  32  and the rigid polymer support  61 . Optionally in any embodiment, the film mates with the rigid polymer support  61  via ultrasonic welding or an adhesive. 
     In the plunger embodiments shown in  FIGS. 8 and 9 , the rigid polymer support  61  has an annular rim  61   a  that extends outward towards the outer diameter of the head  54 . The core  32  also includes a radially extending annular rim  32   a . The rims  32   a  and  61   a  are configured to mate to one another. As shown in  FIG. 8 , the rim  32   a  on the core  32  includes a plurality of radially spaced micro needles  63 , adapted to pierce the film  56  section covering the rim  61   a  and stake into the rim  61   a . Thus, when assembled, the film  56  is sandwiched between the rims  32   a ,  61   a  and secured to the head  54 . The configuration in  FIG. 9  is similar to that of  FIG. 8 , except that the rim  32   a  on the core  32  includes a plurality of radially spaced protrusions  63  adapted to mate with a plurality of radially spaced receptacles  65  on the flange  61   a , thereby securing the film  56  to the head  54 . Ribs or grooves can be incorporated on the core or rigid polymer support to provide friction for holding the core and for venting, as described elsewhere in this specification regarding other embodiments. An optional advantage to including a rigid polymer support  61  is that it allows for the option of ultrasonic welding or staking the components. 
     Referring now to  FIGS. 10-12 , there is shown an alternative embodiment of a convertible plunger  324  according to an aspect of the present invention. The convertible plunger  324  is, to some extent, structurally and functionally similar to the plunger  24  of  FIGS. 1 and 2A-3B , although there are important differences. Like its counterpart in  FIGS. 1 and 2A-3B , the convertible plunger  324  is configured for operating in sealing mode (wherein the storage sealing section in an engagement position) and gliding mode (wherein the storage sealing section is shifted to a release position), substantially as described above. Also, the convertible plunger  324 , like the plunger  24  of  FIGS. 1 and 2A-3B , is of the independent storage sealing section plunger type. Further, the plunger  324  may be secured to a plunger rod to form a plunger assembly, e.g., much like the embodiment of the assembly  20  shown in  FIG. 1 . For the sake of brevity, similar features as between the two embodiments (e.g., material of storage ring, the manner in which the plunger is secured to a plunger rod, the basic function of the plunger etc.) will not be discussed in great depth here. However, differences may be noted. 
     The convertible plunger  324  comprises a rigid central core  332 , which would be coaxial with the central axis of a syringe barrel when assembled into a syringe (e.g., the syringe barrel  12  of  FIG. 1 ). The central core  332  is preferably made from a rigid injection moldable thermoplastic polymer, more preferably from a polyolefin such as polypropylene (PP), cyclic olefin copolymer (COC) or cyclic olefin polymer (COP). The liquid sealing section  336  is mounted on the distal end of the plunger&#39;s central core  332 , while the storage sealing section  334  is located proximally of the liquid sealing section  336 . The storage sealing section  334  is provided in the form of a unitary storage ring  338  mounted on a portion of the central core  332 . The central core  332  in this embodiment (and others disclosed herein) functions as a rigid ring carrier, which is preferably more rigid than the ring  338 . The storage ring  338  comprises an inner surface  339  facing generally radially inward toward the central core  332  and an outer surface  341  facing generally radially outward away from the central core  332 . Preferably, when the storage ring  338  is in an uncompressed state, the inner surface  339  is symmetrical about a plane of symmetry across the width W 338  (between proximal and distal ends) of the storage ring  338 . Also, when the storage ring  338  is in an uncompressed state, the outer surface  341  is preferably symmetrical about a plane of symmetry across the width W 338  of the storage ring  338 . This symmetrical configuration provides stability to the storage ring  338  when the convertible plunger  324  is in storage mode and when the plunger  324  transitions to dispensing mode. A non-symmetrical configuration could result in the ring tilting or wobbling axially, potentially compromising the ring&#39;s sealing function and its ability to facilitate the plunger&#39;s smooth transition from storage mode to dispensing mode. While serving essentially the same purpose as the O-ring  38  of convertible plunger  24 , the storage ring  338  of convertible plunger  324  is not round in cross-section and thus is more appropriately referred to as a storage ring (indicating its basic function and structure), rather than specifically as an O-ring (referring to a storage ring having a generally round cross-sectional structure, such as shown in  FIGS. 1 and 2A-3B ). An O-ring is merely a type or shape of storage ring. 
     The outer surface  341  of the storage ring  338  in the illustrated embodiment ( FIGS. 10-12 ) includes three hills or ribs  338   a , wherein the middle rib is separated from neighboring ribs  338   a  by valleys  338   b  on either side of the middle rib. Multiple ribs  338   a  are configured to provide redundancy in storage sealing. An additional consideration is that change in pressure within a syringe (e.g., during transport at high altitudes) may cause an air bubble in the liquid contents of the syringe to compress or expand, causing a plunger to slightly move. Multiple ribs  338   a  on the storage ring  338  helps to reduce the risk that the plunger  324  will move into an unsterile area of the syringe. Optionally, the contours of the inner surface  339  are mirror images of the contours of the outer surface  341  of the storage ring. For example, the ribs  338   a  on the outer surface  341  are directly opposed by corresponding ribs  338   c  on the inner surface  339  located 180° from the ribs  338   a.    
     Notably, the storage ring  338  is configured to provide, when in the engagement position, a gas-tight seal between both: (1) the storage ring  338  and the syringe barrel; and (2) between the inner surface of the storage ring  338  and the central core  332  (the same applies to the O-ring  38  and the syringe barrel  12  and central core  32  of  FIGS. 1 and 2A-3B ). The storage ring  338  is configured to optimize the sealing and releasing of the seal and minimize or preferably prevent unintended contact with the syringe barrel&#39;s inner surface as the plunger travels down the barrel during dispensing of syringe contents. The durometer of the rubber of the storage ring  338  may factor in to such optimization. 
     It is further preferred that the storage ring  338  preferentially adhere to the syringe barrel over the central core  332  or ring carrier. This is to ensure that the seal between the storage ring  338  and central core  332  releases first (while the storage ring  338  initially continues to adhere to the barrel), allowing the storage ring  338  to move to an unsealed position so that the convertible plunger  324  smoothly transitions to glide mode. Preferential adherence of the storage ring  338  to the syringe barrel also advantageously resists movement of the plunger  324  towards the proximal (and potentially unsterile) end of the syringe. Preferential adherence of the storage ring  328  to the syringe barrel may optionally be achieved, e.g., with a flowable lubricant coating on the central core  332 . Such lubricants may include, e.g., PDMS in the form of free silicone oil, cross-linked silicone oil (e.g., through plasma cross-linking), or baked on silicone. Alternatively, the central core  332  may be coated with or embedded with fluorinated lubricants, e.g., Teflon, parylenes or any fluorinated polymer disclosed herein for use as a plunger film or cap material. Alternatively, the central core  332  may be provided with a lubricity coating applied by plasma enhanced chemical vapor deposition (PECVD), optionally using octamethylcyclotetrasiloxane (OMCTS) as a precursor. Such a coating may have the chemistries of a pH protective coating or a lubricity coating as described in U.S. Pat. No. 7,985,188, which is incorporated herein by reference in its entirety. Any of the aforementioned lubricating means may be provided between the storage ring and the ring carrier to facilitate sliding of the storage ring axially along the ring carrier while the ring preferentially adheres to the interior wall of the medical barrel. Notably, however, it is highly preferred that neither the medical barrel-contacting surfaces of the plunger  324  (storage sealing section  334  and liquid sealing section  336 ) nor the inner surface of the medical barrel are coated with flowable lubricant such as free silicone oil. In this preferred aspect of the invention, the convertible plunger  324  provides an “oil-free” solution for prefilled syringe applications, which is advantageous for reasons explained above. 
     The central core  332  is an elongated rigid member comprising, from the distal end thereof, a flange  342  which projects radially outward from the central core  332 . Proximal to the flange  342  is an annular storage platform  344 , which supports the storage ring  338  when the plunger  324  is in storage sealing mode. Proximal to the storage platform  344  is a conically tapering section or gradual transition region  346  which terminates in a cylindrical section or dispensing platform  348 , the external diameter of which is less than that of the storage platform  344 . The dispensing platform  348  terminates at a flange  352 . 
     The convertible plunger  324  operates largely in the same way as its counterpart in  FIGS. 1 and 2A-3B  to transition from storage sealing mode to a dispensing mode. These details will be summarized here in the context of the plunger  324  of  FIGS. 10-12 . As shown in  FIGS. 10-12 , the storage ring  338  is disposed on the storage platform  344 . In this position, the storage ring  338  is configured to provide sufficient compression against a medical barrel in which it is disposed, so as to provide a gas-tight and liquid-tight seal, thus providing CCI and protecting sterility of the barrel&#39;s contents over a desired shelf life. At the time of actuation/use, when plunger  324  begins to advance in a distal direction in a medical barrel, the central core  332  slides distally with respect to the storage ring  338 , causing the ring  338  to transition to the conically tapering section or gradual transition region  346  and then ultimately end at the dispensing platform  348 . The gradual transition region  346  is shown in a conical shape, but may be in other configurations, e.g., curved. 
     When disposed on the dispensing platform  348 , the storage ring  338  provides either reduced compression or no compression whatsoever against the medical barrel, thus putting the plunger  324  in dispensing mode. The flange  352  catches the storage ring  338 , preventing it from disassociating itself from the proximal end of the central core  332 . This also blocks plunger movement in a proximal direction in the event the storage ring fails to release from the barrel, thus reducing the risk of the storage ring  338  contacting an unsterile area within the syringe barrel. 
     As mentioned above, the liquid sealing section  336  is disposed on the plunger  324  distal to the flange  342  and storage sealing section. The liquid sealing section  336  provides a liquid-tight seal with the barrel sidewall and preferably also provides CCI for barrel contents. The liquid sealing section  336  optionally comprises a head  354  having a film  356  wrapped thereon, as substantially described above with respect to other embodiments. As shown in  FIG. 12 , the head  354  comprises a resilient material such as an elastomer  355  that is disposed over a rigid support  361 , preferably a polymer support. The rigid support  361  advantageously provides a rigid surface to secure or bond the liquid sealing section  336  to the central core  332 . The rigid support  361  may include a stem  363  that is secured within a central mating recess  360  of the central core  332 , e.g., by ultrasonic welding, an adhesive, a press-fit, a snap-fit or through threaded engagement. Particularly if ultrasonic welding is used, the rigid support  361  is preferably the same material as the central core  332  (e.g., a desired polyolefin). Optionally, the film  356  edge terminates within the central mating recess  360  of the central core  332  and is secured therein, rendering the film edge unexposed after assembly, thus strengthening the bond between the film  356  and the head  354 . 
     Optionally, the head  354  may be made through two-shot injection molding, wherein a first shot injects the rigid support  361  within a mold and the second shot injects the elastomer  355  within the mold, or vice versa. Such a method advantageously avoids the need for assembling separate components to make the head  354 . If a two-shot molding process is used, the materials must be compatible to enable the elastomer  355  and rigid polymer support  361  to bond together, thus forming a unitary structure. For example, if the elastomer  355  is a polyolefin based thermoplastic elastomer, the rigid support  361  is preferably a polyolefin, such as PP, COP or COC. 
     This plunger configuration provides several advantages. For example, the film  356  may be wrapped tightly over the head  354  without distorting the shape of the film or head, due to the rigid internal structure. Moreover, the rigid central core  332  facilitates automation, while still providing an elastomer  355  that is sufficiently resilient enough to provide adequate liquid sealing. In addition, this construction minimizes the amount of elastomeric material that may be subject to compression setting. 
     Optionally, the film may be wrapped about the plunger head according to the following process. The process comprises any combination of one or more of the following steps: (a) optionally loading film onto rollers; (b) optionally loading a plunger head in tooling; (c) optionally heating the film to a temperature for a length of time configured to render the film formable into a preform, wherein the controller is optionally set to heat the film to very high temperature (e.g., a controller set point of at least 1000° C., preferably above 1200° C., optionally about 1275° C.); (d) optionally applying a vacuum to pull film into preform tooling, wherein the preform is smaller than the plunger head; (e) optionally cutting out a film disk with the preform and transfer the disk to a forming station; (f) optionally clamping the cut disk with the preform rigidly at the perimeter, inverting the preform using a vacuum and push the plunger head up through the inverted preform stretching the preform to conform to the plunger head; (g) optionally pushing the plunger head and preform through an opening to gather the excess film behind the plunger head, holding film and plunger head on circumference with a first gripper and clamping the excess film behind the plunger head with a second gripper and rotating the first gripper at least 180°, optionally at least 270°, optionally up to about 720° rotation, wherein such rotation tightens the film about the plunger head; (h) optionally trimming the excess film away and rotating the plunger head to break the plunger free from the film; and (i) optionally finishing the film edge by using a heated tamping die to tamp cut the edge to back surface of the plunger head. This process is an alternative to traditional methods of laminating the film during a molding process. 
     Dimensions of the plunger may vary depending on specific needs, applications and syringe barrel diameters. Applicants have found that certain specific dimensions may be advantageous. The plunger head  354  needs to provide a liquid tight seal to prevent liquid contents of the syringe from leaking past the plunger head  54 , a phenomenon Applicants refer to as “blowback.” An embodiment with a sealing height H 336  of the liquid sealing section  336  of 3.0 mm and a diameter of 6.50 mm in a 6.48 mm syringe underwent testing, described in Example 2, below. That embodiment successfully blocked a 40 N load, without any leakage, wherein that load was applied distally, i.e., in a direction for dispensing liquid contents (although the needle was blocked to prevent the liquid from exiting the syringe). Also, Applicants have found that the wall thickness T 355  of the elastomer  355  of the plunger head  354  impacts glide force. For example a T 355  of 1.00 mm has a higher glide force than a T 355  of 1.45 mm. Also, Applicants have found a rigid support width W 361  of 3.7 mm to be beneficial for some applications. 
     Optionally, an alternative geometry is shown in  FIG. 12A , which aims to reduce the interference area between the liquid sealing section and syringe barrel.  FIG. 12A  illustrates a height of 0.75 mm at the maximum diameter. 
     Preferably, a liquid sealing section may be configured, according to an aspect of the invention, to provide a CCI level of sealing, although not gas (e.g., oxygen) sealing. 
     As discussed herein, the terms “central core” (e.g.,  32  or  332 ) or “sleeve” (in the case of the sleeve  160  of the embodiment shown in  FIGS. 4A and 4B ), have a storage ring or O-ring disposed directly thereon. The central core, sleeve or any other element on which the ring or storage sealing section is disposed may be referred to herein generically as a “ring carrier.” The ring carrier, in whichever form it takes, should be rigid. A rigid ring carrier provides necessary support and dimensional tolerances for the storage ring to reach desired and precise levels of compression when the plunger is in storage mode and to release smoothly (with little to no perception to the user) when the plunger transitions to dispensing mode. It should be borne in mind that the storage ring and the plunger in general will typically be tiny. Since the plunger components need to operate smoothly in what is typically a small-diameter syringe barrel, tight dimensional tolerances are needed. A rigid ring carrier does not compress when the storage ring disposed thereon compresses. In this way, the storage ring is the only variable that must be accounted for in designing a ring that is configured to provide an adequate seal on the one hand when the plunger is in storage mode and a smooth transition and plunger force on the other when the plunger is transitioned to dispensing mode. This configuration is much preferred to a compressible ring carrier, since that would add a level of complexity and difficulty (i.e., another variable) to achieving adequate seal and desirable plunger force. 
     Optionally, in any embodiment, the liquid sealing section is a separate component and made of a different composition, from the ring carrier. For example, the ring carrier may be made from a polyolefin while the liquid sealing section may be a fluoropolymer-covered injection molded TPE over a rigid polymeric skeleton. In such a case, the liquid sealing section is more flexible (and resilient) compared to the rigid ring carrier. In any embodiment of plungers according to the invention, the liquid sealing section may be more flexible and resilient than the rigid ring carrier. 
     The inventors have learned that the manner in which the storage ring is inserted into a syringe barrel is consequential. For example, it has been discovered that sliding the storage ring (e.g., using a shaft/sleeve) onto the storage platform once the plunger head has been inserted into the syringe barrel may cause torsional and circumferential distortion of the storage ring and/or create an unwanted “pressure zone” between the storage ring and the liquid sealing section. Such a pressure zone, which traps pressurized air between the two sealing sections, may have the tendency to push the storage ring back over time and can result in unwanted pressure against the liquid contents of a prefilled syringe. 
     To address these problems, the inventors have developed the alternative embodiment of a convertible plunger  724  shown in  FIGS. 21-23C . The plunger  724  is, to some extent, structurally and functionally similar to the plunger  324  of  FIGS. 10-12 , although there are important differences to the construction and assembly of the plunger  724 . Like its counterpart in  FIGS. 10-12 , the convertible plunger  724  is configured for operating in a sealing mode (wherein the storage sealing section in an engagement position) and gliding mode (wherein the storage sealing section is shifted to a release position), substantially as described above. Also, the convertible plunger  724  is of the independent storage sealing section plunger type. For the sake of brevity, similar features as between the two embodiments (e.g., material and configuration of the storage ring, the manner in which the plunger is secured to a plunger rod, the basic function of the plunger, etc.) will not be discussed in great depth here. However, differences may be noted. The convertible plunger comprises a ring carrier in the form of a rigid central core  732 , which would be coaxial with the central axis of a syringe barrel when assembled into a syringe (e.g., the syringe barrel  12  of  FIG. 1 ). The storage sealing section  734 , in the form of a storage ring  738 , is mounted on a portion of the central core  732 . The central core  732  is an elongated rigid member comprising, from the proximal end thereof, a flange  752  (which may be secured to a plunger rod, e.g., via threaded engagement or snap fit) which is adjacent to an annular dispensing platform  748 . Distal to the dispensing platform  748  is an annular steep transition region  746  which leads to the annular storage platform  744 . It has been found that the more steep or abrupt the transition region, the more smoothly the plunger transitions from storage mode to dispensing mode. The outer diameter of the central core  732  narrows distally to the storage platform  744  to form two resilient prongs  772  of an annular insertion platform  770 , the function of which is described below. 
     Unlike the embodiment of  FIGS. 10-12 , the central core  732  is mounted to the proximal end of a connector body  780  (as opposed to the proximal end of a storage sealing section  336 ). The connector body  780  is a preferably rigid (e.g., polymeric) and generally cylindrical member, the proximal end of which receives and connects to the resilient prongs  772  of the central core  732 . The liquid sealing section  736  is mounted to the distal end of the connector body  780  in essentially the same way as the liquid sealing section  336  mounts to the central core  332  of  FIGS. 10-12 . The description above with respect to the liquid sealing section  336  will suffice for description of the same vis-à-vis the plunger  724  of  FIGS. 21-23C . It will only be briefly noted that the liquid sealing section  736  optionally comprises a head  754  having a film  756  wrapped thereon. Notably, the film  756  is wrapped entirely around the head  754  and continues along an underside of the head  754 , wherein the film  756  is sandwiched between the head  754  and the connector body  780 . The head  754  comprises a stem  763  that is assembled and secured into a central mating recess  760  of the connector body  780 , e.g., by ultrasonic welding, an adhesive, a press-fit, a snap-fit or through threaded engagement. 
     The connector body  780  comprises an axial channel  784  leading to a wider opening  776  that optionally bores entirely through a center portion of the connector body  780 , in a direction perpendicular to the central axis of the axial channel  784 . This configuration simplifies injection molding of the connector body  780 . The opening  776  comprises a ridge section  782  adjacent to where the axial channel  784  meets the opening  776 . The prongs  772 , at their distal ends, comprise radially outward projecting abutments  774 . The abutments  774  are retained underneath the ridge section  782  to secure the central core  732  to the connector body  780 . 
     To assemble the central core  732  to the connector body  780 , the two components should be aligned and axially centered. The prongs  772  of the central core  732  are then inserted into the axial channel  784  of the connector body  780 . The axial channel  784  is configured to facilitate the insertion of the prongs  772 , e.g., with an annular chamfer  786  at the proximal end of the axial channel  784 . When the prongs  772  contact the chamfer  786 , the prongs  772  are urged to resiliently flex or compress radially inward so that the prongs  772  and abutments  774  fit entirely within the axial channel  784  as the prongs  772  are moved distally into the axial channel  784 . Once the abutments  774  fully reach the wider opening  776 , the prongs  772  are released from their compressed state and the abutments  774  are retained underneath the ridge section  782 , preventing the central core  732  from being separated from the connector body  780 . In short, the prongs  772  secure the central core  732  to the connector body  780  in a snap-fit configuration. This provides advantages during assembly of the plunger  724  into a syringe barrel, as explained now. 
       FIGS. 22A and 22B  are schematic drawings illustrating the manner in which the storage ring  738  via the central core  732  are assembled onto the connector body  780  and liquid sealing section  736  subassembly, thus forming a completed convertible plunger  724 .  FIG. 22A  shows the components just prior to fully assembling them to form the plunger  724 . As shown, the distal end of the central core  732  is protruding slightly into the axial channel  784  of the connector body  780  and is thus not yet secured thereto. Notably, in this position, the storage ring  738  is disposed on the annular insertion platform  770  of the central core  732  or ring carrier. The annular insertion platform  770  has a narrower outer diameter than the annular storage platform  744 . As such, the outer diameter of the storage ring  738  is correspondingly less than the ring&#39;s  738  outer diameter when disposed on the storage platform  744 , as shown in  FIG. 22B . The comparatively small outer diameter of the storage ring  738 , when disposed about the insertion platform  770 , is configured to facilitate insertion of the ring  738  into a syringe barrel in such a way that the ring  738  does not contact the barrel wall or has only minimal contact with it. When on the insertion platform  770 , the sealing ring  738  is in a “load position” wherein the ring  738  slides easily into the proximal end of the syringe barrel. As the prongs  772  are urged downward into the axial channel  784  of the connector body  780  to ultimately secure the central core  732  thereto (as shown in  FIG. 22B ), the storage ring  738  transitions from load position on the insertion platform  770  to engagement position, wherein the ring is disposed about the storage platform  744 . Optionally, as shown in  FIG. 22B , the entire ring  738 , when the plunger is in storage mode, is disposed about the storage platform  744 . In other words, no part of the ring  738  contacts the dispensing platform when in storage mode. This helps facilitate stability of the storage ring  738 . Likewise, as shown in  FIG. 21 , the entire ring  738  is optionally disposed about the dispensing platform  748  when the plunger  724  is in dispensing mode, which facilitates stability during dispensing. 
     Notably, with the aforementioned process, the ring  738  is not separately urged or pushed with a device to set the ring  738  into engagement mode. Rather, the ring  738  is inserted into the syringe barrel with little or no barrel sidewall resistance by placing the ring in load position on the central core  732  before mounting the central core  732  to the connector body  780 . As seen in both  FIGS. 22A and 22B , the ring  738  is flush against the proximal end of the connector body when the ring is in load position and in engagement position. In other words, the ring  738  remains in a fixed position during loading while central core  732  moves relative to the ring. With no space between the ring  738  and the connector body  728  both before and after the ring  738  compresses against the barrel sidewall, there is no “pressure zone” between the storage ring  738  and the liquid sealing section  736 . This design, therefore, addresses the problems identified above with loading the storage ring without distorting it or creating an unwanted pressure zone. 
     The schematic drawings of  FIGS. 23A-23C  more fully illustrate the manner in which the components of the convertible plunger  724  may be loaded into a prefilled syringe and assembled. As shown in  FIG. 23A , the liquid sealing section  736  and connector body  780  subassembly may be loaded into the plunger via traditional methods to load plungers. These include vent tube, vacuum loading and vacuum assist, all of which are described, below. Next, the storage ring  738  and central core  732  subassembly is created by disposing the ring  738  in load position  738  on the prongs  772  of the central core  732 . As shown in  FIG. 23C , the storage ring  738  and central core  732  subassembly is inserted, e.g., by push-rod or by a plunger rod assembled thereto, until the snap-fit is established with the connector body  780  to form the fully assembled convertible plunger, loaded in engagement mode. It is contemplated that liquid prefilled in the barrel provides resistance necessary to oppose the downward force applied when assembling the central core  732  to the connector body  780 . The plunger  724  then may be used, just as described with other embodiments, to convert the plunger  724  from engagement position (shown in  FIG. 23C ) to release position (shown in  FIG. 21 ). It should be noted that the expanded state of the plunger  724  is reducible to a constricted state by an operation that is applied to the internal portion of the plunger to reduce or eliminate the outward radial pressure provided by a comparatively rigid internal portion, in this case, the storage platform  744  of the ring carrier  732 . The ring  738  is set in the expanded state through application of a setting force onto the convertible plunger  724  in a distal direction. The operation to reduce the plunger to the constricted state comprises application of an actuation force onto the convertible plunger  724  in the distal direction. With such a preferred embodiment, the plunger  724  does not need to be pulled back or primed to set it in, or remove it from engagement mode, before transitioning to dispensing mode and then dispensing product. 
       FIG. 24  is an axial sectional view of an alternative convertible plunger identical to the plunger of  FIG. 21 , except that the cross-section of the storage ring of  FIG. 24  is an alternative geometry compared to that of  FIG. 21 .  FIG. 24A  is an enlarged partial view of the plunger of  FIG. 24  highlighting the alternative geometry of the cross-section of the storage ring. As shown, the alternative storage ring  738   i  includes an outer surface facing generally radially outward away from the ring carrier. In its uncompressed state, the ring  738   i  includes a proximal end  738   p , a distal end  738   d  and a radial plane of symmetry PS between the proximal  738   p  and distal  738   d  ends. Optionally, radial plane of symmetry PS is equidistant from the proximal  738   p  and distal  738   d  ends. The outer surface of the ring  738   i  is symmetrical on either side of the radial plane of symmetry PS. Optionally, the ring  738   i  is configured such that, in its uncompressed state, a given rib on the inside surface opposes a rib on the outside surface of the storage sealing section  734   i . These features may help to facilitate stable seating and translation of the ring  738   i . Further, the distal end of the ring  738   b  contacts the proximal end  785  of the connector body  780 , without being disposed in or pressing against the annular chamfer  786 . 
     Additional Methods and Apparatus for Assembling Convertible Plunger into Syringe Barrel 
     Given the novel configuration of the convertible plunger, as represented by exemplary embodiments described herein, traditional methods for assembling a conventional plunger into a prefilled syringe barrel after a filling operation, are not alone sufficient to assemble the convertible plunger into a syringe barrel. Traditional methods, however, may be incorporated into aspects of novel methods for assembling the convertible plunger into a syringe barrel. 
     There are three traditional methods for assembling a conventional plunger into a prefilled syringe. The first is use of a vent tube, wherein the plunger is pushed through a tube that is placed into the syringe and exits out the bottom of the tube into its final position within the syringe barrel. The second is use of a vacuum, which is created in the syringe and the plunger is introduced into the opening thereof. Differential pressure forces the plunger down into the barrel into a final position. A third method, known as vacuum assist, creates a vacuum and further includes a mechanical element to assist the plunger into its final position. Again, these traditional methods may be used to some extent to effectuate assembly of a convertible plunger into the syringe barrel. However, since the convertible plunger requires not only the plunger head to be disposed within the syringe barrel (which may be done, e.g., via one of the traditional methods recited above), but also setting the storage sealing section into an engagement position, traditional methods/apparatus are not equipped to adequately assemble convertible plungers into a medical barrel, such as a syringe. This section of the specification describes various methods and apparatus for assembling a convertible plunger into a syringe barrel.  FIGS. 6A-6E, 13-16B and 18  illustrate apparatus for assembling independent storage sealing section plunger type embodiments into a syringe barrel.  FIGS. 16A-17B  illustrate apparatus for assembling insert and sleeve plunger type embodiments into a syringe barrel. 
     Independent storage sealing section plunger embodiments present the issue that the storage ring, if initially positioned in engagement mode (i.e., at its largest diameter), can render it difficult or impossible to effectuate automated plunger insertion into a syringe barrel. Applicants have therefore determined that it is preferred that such embodiments are not initially inserted into a syringe with the storage ring in (expanded) engagement position, but instead in (constricted) release position. Once the plunger is initially inserted in the barrel, e.g., through a traditional method, the storage ring may be displaced from release position and set in engagement position for commercial use. 
     Turning now to  FIGS. 6A to 6E  the details of the assembly of the components making up the plunger assembly  20  within the barrel  12  of the syringe will now be described. To that end, the convertible plunger  24  is provided in the state wherein its O-ring  38  is located immediately under the flange  52 . Thus the O-ring will be in its constricted state so that it will not engage the interior surface of the barrel when introduced therein. With the convertible plunger  24  in that state it is introduced into the proximal open end of the barrel  12  and freely slid to the longitudinal position it will be when in the plunger assembly is in its engagement position, like shown in  FIG. 6A . A tubular tool  180  whose inner diameter is slightly larger than the outer diameter of the flange  52  of the central core  32  is then slid over that portion of the central core to engage a portion of the O-ring  38  disposed thereunder, such as shown in  FIG. 6B . The tool  180  is then pushed downward to cause the O-ring to slide along the central core in the distal direction, whereupon it will ride up over the conical section  46  and thus be stretched radially outward, like shown in  FIG. 6C . Continued pressing on the tool will eventually slide the O-ring into the annular recess  44 , like shown in  FIG. 6D  whereupon it will snap into place in the holding position. Once that has been accomplished the tool  170  can be removed and the plunger rod  22  can then be connected to the convertible plunger  24 . To that end the threaded projection  26  at the distal end of the plunger rod  22  can be screwed into the threaded hole or bore  28  in the central core, thereby completing the assembly of the plunger assembly within the syringe&#39;s barrel. 
     Referring to  FIG. 13 , there is shown an optional embodiment of a plunger insertion apparatus  1000 , used, e.g., to set the convertible plunger  324  of  FIGS. 10-12  in a syringe barrel. As a first step in a method of assembly, as discussed above, one of the traditional methods (e.g., vent tube, vacuum or vacuum assist) may be employed to initially dispose the plunger  324  within a syringe barrel. The apparatus  1000  may be used in a second step to set the ring  338  into engagement mode by displacing it from an initial position on the dispensing platform  348  to a position on the storage platform  344  of the central core  332 . 
     The apparatus  1000  includes a mount  1010  which initially drives the entire plunger  324  distally in direction D using the plunger positioning rod  1004  until flanged end  1006  of the positioning rod  1004  is blocked by stops  1012 , at which point plunger movement ceases. The continued downward movement collapses a spring  1008  affixed to a proximal end of the plunger positioning rod  1004 , which causes an insertion tube  1002  that is axially driven distally in direction D by the mount  1010  continues to move distally to displace the storage ring  338  into the engagement position or storage sealing mode. 
     Referring to  FIGS. 14A-C , there is shown an alternative optional embodiment of a plunger insertion apparatus  1020 , used, e.g., to set the convertible plunger  324  of  FIGS. 10-12  in a syringe barrel. As a first step in a method of assembly, as discussed above, one of the traditional methods (e.g., vent tube, vacuum or vacuum assist) may be employed to initially dispose the plunger  324  within a syringe barrel. The apparatus  1020  may be used in a second step to set the ring  338  into engagement mode by displacing it from an initial position on the dispensing platform  348  to a position on the storage platform  344  of the central core  332 . 
     The apparatus  1020  includes a mount  1030  which actuates a tubular structure (similar to a vent tube) that includes an inner and outer component. Namely, an insertion tube  1022  is configured to drive the storage ring  338  distally in direction D while the outer constriction tube  1023  initially surrounds and constrains the outer diameter of the ring  338 . Once the ring  338  is disposed about the storage platform  344  of the central core  332 , the tube structure retracts (see  FIG. 14B ) such that the constriction tube  1023  releases the ring  338 , enabling the ring  338  contact the barrel wall in the engagement position. The apparatus  1020  further includes a spring  1028 , stops  1032  and a plunger positioning rod  1024  which function substantially as described above with respect to like components of the apparatus  1000  of  FIG. 13 . The mount  1030  initially drives the entire plunger  324  distally in direction D using the plunger positioning rod  1024  until the rim  1026  at the proximal end of the insertion tube  1022  is blocked by the stops  1032 , at which point plunger movement ceases. However, the spring  1028  allows the constriction tube  1023  to continue past that point. The constriction tube  1023  first captures the outer diameter of the ring  338  and then moves down to the final position. The insertion tube  1022  moves independently of the mount  1030  to allow for the insertion tube  1022  to engage the storage ring  338  to support it during the phase when the constriction tube  1023  is capturing the sealing ring  338 . The insertion tube  1022  remains in place to retain the sealing ring  338  in an engagement position while retracting the constriction tube  1023 . 
     Referring to  FIGS. 15A and 15B , there is shown an alternative optional embodiment of a plunger insertion apparatus  1040 , used, e.g., to set the convertible plunger  324  of  FIGS. 10-12  in a syringe barrel. As a first step in a method of assembly, as discussed above, one of the traditional methods (e.g., vent tube, vacuum or vacuum assist) may be employed to initially dispose the plunger  324  within a syringe barrel. The apparatus  1040  may be used in a second step to set the ring  338  into engagement mode by displacing it from an initial position on the dispensing platform  348  to a position on the storage platform  344  of the central core  332 . 
     The outer diameter of the storage ring  338  is initially constrained by the constriction portion  1043  of a removable tubular component  1042 . The component  1042  may be placed in position when the plunger  324  is manufactured or at the point of use before insertion into a syringe. If the removable tubular component  1042  is placed in position when the plunger is manufactured, the component  1042  may be disposable. If the removable tubular component  1042  is placed in position at the point of use, the component  1042  may be reusable. Once the storage ring  338  is placed onto the storage platform  344 , the removable tubular component  1042  retracts and the storage ring  338  can expand into the engagement position. 
     As with other embodiments discussed above, the apparatus  1040  includes a mount  1050 , spring  1048  and plunger positioning rod  1044 . Optionally, the rod  1044  is telescoping to position the plunger  324  and engage the removable tubular component  1042  to remove it. There is further an outer frame  1045  that passes through the removable tubular component  1042  to engage the storage ring  338 . An independent motion retains the sealing ring in a desired position while the removable tubular component  1042  is retracted. 
     Referring now to  FIG. 18 , there is shown an alternative embodiment of a convertible plunger  624 . The plunger  624 , like the embodiment of  FIGS. 10-12 , includes a film  656  on a plunger head  654  that is secured to an internal rigid support  661 . The plunger  624  also includes a central core  632 , but unlike other embodiments disclosed herein, the central core  632  is not exposed to ambient conditions, such as moisture, oxygen or unsterile conditions. In this embodiment, the storage ring  638  covers the proximal end of the central core  632  and also provides gas-tight sealing to protect syringe contents from the ambient environment. The ring  638  includes three ribs  638   a  with valleys  638   b  on either side of the middle rib  638   a . Such multi ribbed configuration is advantageous for reasons provided above. An internal seal actuator  655  is positioned around a proximal portion of the central core  632  and is surrounded, in part, by the storage ring  638 . The seal actuator  655  is configured to slide on the central core  632 . The outer profile of the actuator  655  includes two ramped sections (a,c) and a flat section (b) therebetween. 
     The internal actuator  655  may be assembled onto the central core  632  and the material of the central core  632  may be displaced (e.g., via peening, ultrasonic energy, melting, etc.) over to retain the actuator  655 . At that point, the storage ring  338  may be assembled onto the central core  632 . The ramp (a) may retain the storage ring  338 . 
     The plunger  624  may be inserted in a barrel initially by vacuum or vacuum assist. To set the ring  638  in engagement position, the ring  638  is displaced distally, which in turn moves the internal seal actuator  655  distally so that the flat section (b) compresses the ribs  638   a  against the barrel wall. If vacuum assist is used as a method step in assembling the plunger, a telescoping element such as that shown in  FIG. 16A  (discussed below) may be used to displace the ring  338  in the center initially to position the plunger  624  and then the larger diameter tube to move the actuator  655  into position. 
     In use, the convertible plunger  624  may be actuated simply by pushing it distally to dispense the syringe contents. The initial movement displaces the actuator  655  further to release the storage ring  638  from engagement position and transition it to dispensing position. Continued movement displaces the plunger distally  624  down the barrel. 
     As mentioned above, methods and apparatus are also described in this specification for assembling insert and sleeve plunger type embodiments into a syringe barrel. One such apparatus is shown in  FIGS. 16A and 16B . The insert and sleeve convertible plunger  424  includes a preferably elastomeric plunger sleeve  423  having a storage sealing section  434  and liquid sealing section  436 . The plunger sleeve  423  further comprises internal cavities  447 ,  448 ,  450 , which are in communication with each other and are configured to receive movable insertion of an insert  442 . Cavity  448  is adjacent to the storage sealing section  434 . When the plunger  424  is in engagement position, the insert  442  is disposed in the cavity  448  to provide compression of the storage sealing section  434  against a syringe barrel wall. To transition to dispensing mode, the insert  442  is advanced from cavity  448  to cavity  450 . 
     The proximal most cavity or pre-load cavity  447  is the initial location of the insert  442  when assembling the plunger  424  into a syringe barrel. In this position, the plunger does not provide gas-tight compression against the syringe barrel, enabling the plunger  424  to advance distally to a desired point within the syringe. Such insertion may be effectuated with the plunger insertion apparatus  1060 . The apparatus includes a mount  1070 , spring  1068 , central rod  1064 , outer sleeve  1062 , flanged end  1066  of the central rod  1064  and stops  1072 . The rod  1064  may place the plunger  424  in the proper location with a syringe. A collapsing sleeve  1062  continues to move distally after the plunger is positioned. The continued movement moves the insert  442  into cavity  448  where the storage sealing section  434  becomes set in the engagement position for commercial distribution. 
     Referring to  FIGS. 17A and 17B , there is shown a plunger insertion apparatus  1080  for an insert and sleeve convertible plunger  524 . The plunger  524  includes a preferably elastomeric plunger sleeve  523  having a storage sealing section  534  and liquid sealing section  536 . The plunger sleeve  523  further comprises internal cavities  547 ,  548  and  550 , which are in communication with each other and are configured to receive movable insertion of an insert  542 . Cavity  548  is adjacent to the storage sealing section  534 . When the plunger  524  is in engagement position, the insert  542  is disposed in the cavity  548  to provide compression of the storage sealing section  534  against a syringe barrel wall. To transition to dispensing mode, the insert  542  is advanced from cavity  548  to cavity  550 . 
     When initially disposing the plunger  524  within a syringe barrel, the insert  542  is initially positioned in the distal most cavity,  550 . In this position, the insert may be advanced in the barrel with the plunger positioning rod  1084  that is disposed with a sleeve  1082  of the apparatus. A gripper  1083  is then used to grasp the proximal end of the insert and retract the insert so that it is positioned within cavity  548 , thus generating compression of the storage sealing section  534  against the syringe barrel to put the plunger  524  in an engagement position. 
     Optionally in any embodiment of convertible plunger according to the invention, the plunger provides a break loose force and glide force below 15 N, optionally below 10 N, optionally below 9 N, optionally below 8 N, optionally below 7 N, optionally below 6 N, optionally between about 2.5 N and about 5.5 N, substantially or entirely without the presence of a flowable lubricant between the barrel and the plunger&#39;s barrel-contacting surfaces. Optionally in any embodiment of convertible plunger according to the invention, the plunger provides a differential between break loose force and glide force of optionally below 2 N, optionally below 1.5 N, optionally below 1.0 N, optionally below 0.5 N, optionally below 0.4 N, optionally below 0.25 N. Optionally in any embodiment of convertible plunger according to the invention, the plunger provides a differential between break loose force and glide force of optionally below 20%, optionally below 15%, optionally below 12%, optionally below 10%, optionally below 8%, optionally between 2.5% and 6%. These differentials between break loose force and glide force are provided substantially or entirely without the presence of a flowable lubricant between the barrel and the plunger&#39;s barrel-contacting surfaces. 
     In any embodiment, the liquid sealing section (via the plunger head) provides a liquid tight seal and optionally (albeit preferably) CCI. If a CCI level seal for the liquid sealing section is to be provided, the sterile barrier provided by the liquid sealing section may be verified by using both of the following two tests: (1) microbial ingress testing using a liquid immersion technique; and (2) the dye penetration test. The microbial ingress test using a liquid immersion technique involves providing a challenge organism provided in a liquid, immersing the sample container in the liquid while a vacuum is applied to the contents section of the container, and after a designated time, testing to see if the challenge organism migrated past the liquid sealing section. The dye penetration test involves placing a sample container, with the plunger head disposed therein, into a dye bath, applying a vacuum to obtain a manometer reading lower than 635 mmHg for two minutes and visually or using an ultraviolet reading technique, determining whether any of the dye passed through the liquid sealing section. Ultimately, both tests should be passed in order to verify CCI provided by the liquid sealing section. 
     Absence of Flowable Lubricant in Injectable Drug Product 
     It has been observed that protein-based drugs can denature or otherwise degrade. A principal way the drug denatures is to unfold and then to cause aggregates to form in the drug product. The primary container can cause protein to denature. One factor that can cause such denaturing is the presence of silicone oil lubricant (a type of flowable lubricant). Droplets of silicone oil can detach from the container wall and interact with the drug. These droplets cause proteins in the liquid to unfold. 
     A big problem with biologic drugs is the possibility of an immune response by the patient. An immune response can be caused by aggregates (particles) in the drug that are injected into the patient. These aggregates may cause the production of antibodies in the patient that: (1) render the drug ineffective or (2) cause a severe autoimmune response. A small quantity of particles can cause an immune response. The % of proteins that have aggregated in the drug may be very, very small but can cause an immune response. For example, drugs taken by MS and Crohn&#39;s Disease patients develop an immune response within 2 years. This requires the patient to stop taking the drug and/or switch drugs. 
     The number of protein-based drugs has increased significantly over the past five years and this trend will continue. Drug therapies are being used to treat more chronic indications. This means that patients are taking the drugs longer and are more prone to side effects caused by the drug. Previously, protein drugs were taken for acute indications and side effects were limited. 
     The amount of contaminants in the drug may increase over the shelf life. The threshold for measuring contaminants is at the detection limit of the instrumentation—so the concentrations are going lower and lower. The concentration of these particles is low ppb/ml, but this may still be enough to cause an immune response. Accordingly, the need to avoid use of flowable lubricants is particularly pressing with biologic drugs, i.e., polypeptide compositions or protein compositions that are provided in prefilled syringes. 
     In an optional aspect of the invention, a convertible plunger according to any embodiment disclosed herein, which does not require the use of a flowable lubricant between the syringe barrel wall and the barrel-contacting surfaces of the plunger, is particularly beneficial for prefilled syringes containing a polypeptide composition or protein composition. In this way, flowable lubricant, e.g., silicone oil, will not migrate into the drug (and ultimately into the patient) and therefore will not denature the biologic components of the drug composition. As such, shelf life of the biologic drug may be optimized. Moreover, in this way, undesired immune responses by the patient otherwise caused by silicone oil giving rise to aggregates in the drug can be avoided. Thus an “oil-free solution” is particularly desirable for biologics. 
     Accordingly, in an optional embodiment, the invention is directed to use of a convertible plunger according to any embodiment disclosed herein, disposed in a prefilled syringe. The syringe includes a medical barrel having an inner wall and an injectable drug product, optionally a liquid composition, disposed in a product containing area of the medical barrel, the injectable drug product comprising a polypeptide composition or protein composition that is susceptible to denaturing from interaction with particles generated from a flowable lubricant. The medical barrel has a distal dispensing end for dispensing the injectable drug product and an open proximal end configured for receipt of the convertible plunger. According to an optional embodiment of the invention, the polypeptide composition or protein composition is susceptible to one or more of the following negative effects from interaction with particles generated from a flowable lubricant: denaturing of proteins in the composition; agglomeration of proteins in the composition; degradation of proteins in the composition; triggering an undesired immune response in a patient; and degrading efficacy of the drug product. Flowable lubricant-generated particles are absent from the drug product such that the drug product is not subject to any of the aforementioned negative effects that may otherwise result from interaction with flowable lubricant-generated particles. 
     The present embodiments are particularly useful for the administration of lyophilized pharmaceuticals, including small molecules and biologicals, such as those presently marketed as lyophilized or powdered drugs for injection. These include, by way of non-limiting examples, ActHIB® vaccine, Aldesleukin, ampicillin, asparaginase, amphotericin B (Amphotec, Amphocin, others), ATryn antithrombin, Bendamustine, Bleomycin, Bortezomib, Carboplatin, Carmustine, Caverject Powder (Alprostadil), Certolizumab (CIMZIA®), Cefazolin, Cefonicid, Ceftazidime, Ceftriaxone sodium, Cisplatin, Cytarabine, Cytoxan (cyclophosphamide), Dacarbazine, Daunorubicin, Degarelix, Desferrioxamine Mesilate, Doxorubicin (Adriamycin), Epirubicin, Erythrocin lactobionate, estrogen, Gemcitabine, glucagon, human chorionic gonadotropin, human growth hormone, human menopausal gonadotropin (HMG, menotrpin), human plasma, HcG 5000 IU-5 ml, immune globulin (Carimune, Gammagard®), Interferon beta la (Avonex), Intron A (interferon alfa-2b), Kogenate FS (recombinant factor VII) Leucovorin calcium, leuproreline, methylprednisolone, Leukine (sargramostim), Menomune® vaccine, MMR and MMRV vaccines, Peginterferon alfa-2b (Peglntron), Remicade® infliximab, Sermorelin/GHRH6-5 ml, somatropin (Genotropin, Saizen®), Sincalide (Kinevac), thiotepa, Vecuronium bromide, Vfend (voriconazole), Vincristine, Varicella vaccines, and Zostavax. 
     Some excipients are included in powdered or lyophilized products, such as solubilizers or buffers, may be considered functional excipients. Excipients used in various lyophilized formulations include bulking agents, buffering agents, tonicity modifiers, antimicrobial agents, surfactants and co-solvents, and are well-known in the art. See, e.g., Baheti et al., Excipients Used in Lyophilization of Small Molecules, 1 J. Excipients &amp; Food Chem. 41 (2010). Similarly, diluents are well-known in the art, such as water for injection, and often include excipients, e.g., saline or Ringer&#39;s solution. 
     Industry Standards for Testing Aspects of Plunger 
     Testing of compression setting properties of the plunger assembly may be conducted using methods known in the art, for example, ASTM D395. 
     Testing of adhesive properties or bonding strength between the film and the plunger may be conducted using methods known in the art, for example, according to ASTM D1995-92(2011) or D1876-08. 
     Plunger sliding force is the force required to maintain movement of a plunger in a syringe or cartridge barrel, for example during aspiration or dispense. It can advantageously be determined using, e.g., the ISO 7886-1:1993 test known in the art, or to the currently pending published test method to be incorporated into ISO 11040-4. Plunger breakout force, which may be tested using the same method as that for testing plunger sliding force, is the force required to start a stationary plunger moving within a syringe or cartridge barrel. Machinery useful in testing plunger sliding and breakout force is, e.g., an Instron machine using a 50 N transducer. 
     Testing for extractables, i.e., amount of material that migrates from the plunger into the liquid within the syringe or cartridge, may be conducted using methods set forth in Ph. Eur. 2.9.17 Test for Extractable Volume of Parenteral Preparations, for example. 
     Testing of container closure integrity (CCI) may be done using a vacuum decay leak detection method, wherein a vacuum his maintained inside of a test volume and pressure rise is measured over time. A large enough pressure rise is an indication that there is flow into the system, which is evidence of a leak. Optionally, the vacuum decay test is implemented over two separate cycles. The first cycle is dedicated to detecting large leaks over a very short duration. A relatively weak vacuum is pulled for the first cycle because if a gross leak is detected, a large pressure differential is not necessary to detect a large pressure rise. Use of a first cycle as described helps to shorten total test time if a gross leak exists. If no leak is detected in the first cycle, a second cycle is run, which complies with ASTM F2338-09 Standard Test Method for Nondestructive Detection of Leaks in Packages by Vacuum Decay Method. The second cycle starts out with a system evaluation to lower the signal to noise ratio in the pressure rise measurements. A relatively strong vacuum is pulled for a long period of time in the second cycle to increase the chance of detecting a pressure rise in the system. 
     Testing of air leakage past the syringe piston during aspiration may be conducted using methods known in the art, for example, ISO 7886-1:1993. 
     Testing of liquid leakage at syringe piston under compression may be conducted using methods known in the art, for example, ISO 7886-1:1993. 
     Convertible Plungers Used in PECVD-Coated Syringe Barrels 
     In another aspect, the present invention includes use of any embodiments (or combination of embodiments) of plungers according to the invention in syringes having a PECVD coating or PECVD coating set. The syringes may be made from, e.g., glass or plastic. Optionally, the syringe barrel according to any embodiment is made from an injection moldable thermoplastic material that appears clear and glass-like in final form, e.g., a cyclic olefin polymer (COP), cyclic olefin copolymer (COC) or polycarbonate. Such materials may be manufactured, e.g., by injection molding, to very tight and precise tolerances (generally much tighter than achievable with glass). This is a benefit when trying to balance the competing considerations of seal tightness and low plunger force in plunger design. 
     This section of the disclosure focuses primarily on prefilled syringes as a preferred implementation of optional aspects of the invention. Again, however, it should be understood that the present invention may include any parenteral container that utilizes a plunger, such as syringes, cartridges, auto-injectors, prefilled syringes, prefilled cartridges or vials. 
     For some applications, it may be desired to provide one or more coatings or layers to the interior wall of a parenteral container to modify the properties of that container. For example, one or more coatings or layers may be added to a parenteral container, e.g., to improve the barrier properties of the container and prevent interaction between the container wall (or an underlying coating) and drug product held within the container. Such coatings or layers may be constructed in accordance with the teachings of co-pending PCT Application PCT/US2014/023813, filed on Mar. 11, 2014, which is incorporated by reference herein in its entirety. 
     For example, as shown in  FIG. 1A , which is a first alternative embodiment of an enlarged sectional view of the barrel  12  of the syringe  10  of  FIG. 1 , the inner surface  14  of the barrel  12  may include a coating set  400  comprising one or more coatings or layers. The barrel  12  may include at least one tie coating or layer  402 , at least one barrier coating or layer  404 , and at least one organo-siloxane coating or layer  406 . The organo-siloxane coating or layer  406  preferably has pH protective properties. This embodiment of the coating set  400  is referred to herein as a “tri-layer coating set” in which the the barrier coating or layer  404  of SiO x  is protected against contents having a pH otherwise high enough to remove it by being sandwiched between the pH protective organo-siloxane coating or layer  406  and the tie coating or layer  402 . The contemplated thicknesses of the respective layers in nanometers (preferred ranges in parentheses) are given in the following Tri-layer Thickness Table: 
     
       
         
           
               
            
               
                   
               
               
                 Tri-layer Thickness Table 
               
            
           
           
               
               
               
            
               
                 Adhesion (nm) 
                 Barrier (nm) 
                 Protection (nm) 
               
               
                   
               
               
                  5-100 
                 20-200 
                  50-500 
               
               
                 (5-20) 
                 (20-30)  
                 (100-200) 
               
               
                   
               
            
           
         
       
     
     Properties and compositions of each of the coatings that make up the tri-layer coating set are now described. 
     The tie coating or layer  402  has at least two functions. One function of the tie coating or layer  402  is to improve adhesion of a barrier coating or layer  404  to a substrate (e.g., the inner surface  14  of the barrel  12 ), in particular a thermoplastic substrate, although a tie layer can be used to improve adhesion to a glass substrate or to another coating or layer. For example, a tie coating or layer, also referred to as an adhesion layer or coating can be applied to the substrate and the barrier layer can be applied to the adhesion layer to improve adhesion of the barrier layer or coating to the substrate. 
     Another function of the tie coating or layer  402  has been discovered: a tie coating or layer  402  applied under a barrier coating or layer  404  can improve the function of a pH protective organo-siloxane coating or layer  406  applied over the barrier coating or layer  404 . 
     The tie coating or layer  402  can be composed of, comprise, or consist essentially of SiO x C y , in which x is between 0.5 and 2.4 and y is between 0.6 and 3. Alternatively, the atomic ratio can be expressed as the formula Si w O x C y . The atomic ratios of Si, O, and C in the tie coating or layer  402  are, as several options:
         Si 100: O 50-150: C 90-200 (i.e. w=1, x=0.5 to 1.5, y=0.9 to 2);   Si 100: O 70-130: C 90-200 (i.e. w=1, x=0.7 to 1.3, y=0.9 to 2)   Si 100: O 80-120: C 90-150 (i.e. w=1, x=0.8 to 1.2, y=0.9 to 1.5)   Si 100: O 90-120: C 90-140 (i.e. w=1, x=0.9 to 1.2, y=0.9 to 1.4), or   Si 100: O 92-107: C 116-133 (i.e. w=1, x=0.92 to 1.07, y=1.16 to 1.33).       

     The atomic ratio can be determined by XPS. Taking into account the H atoms, which are not measured by XPS, the tie coating or layer  402  may thus in one aspect have the formula Si w O x C y H z  (or its equivalent S i O x C y ), for example where w is 1, x is from about 0.5 to about 2.4, y is from about 0.6 to about 3, and z is from about 2 to about 9. Typically, a tie coating or layer  402  would hence contain 36% to 41% carbon normalized to 100% carbon plus oxygen plus silicon. 
     The barrier coating or layer  404  for any embodiment defined in this specification (unless otherwise specified in a particular instance) is a coating or layer, optionally applied by PECVD as indicated in U.S. Pat. No. 7,985,188. The barrier coating preferably is characterized as a “SiO x ” coating, and contains silicon, oxygen, and optionally other elements, in which x, the ratio of oxygen to silicon atoms, is from about 1.5 to about 2.9. The thickness of the SiO x  or other barrier coating or layer can be measured, for example, by transmission electron microscopy (TEM), and its composition can be measured by X-ray photoelectron spectroscopy (XPS). The barrier layer is effective to prevent oxygen, carbon dioxide, or other gases from entering the container and/or to prevent leaching of the pharmaceutical material into or through the container wall. 
     Preferred methods of applying the barrier  404  layer and tie layer  402  to the inner surface  14  of the barrel  12  is by plasma enhanced chemical vapor deposition (PECVD), such as described in, e.g., U.S. Pat. App. Pub. No. 20130291632, which is incorporated by reference herein in its entirety. 
     The Applicant has found that barrier layers or coatings of SiO x  are eroded or dissolved by some fluids, for example aqueous compositions having a pH above about 5. Since coatings applied by chemical vapor deposition can be very thin—tens to hundreds of nanometers thick—even a relatively slow rate of erosion can remove or reduce the effectiveness of the barrier layer in less time than the desired shelf life of a product package. This is particularly a problem for fluid pharmaceutical compositions, since many of them have a pH of roughly 7, or more broadly in the range of 5 to 9, similar to the pH of blood and other human or animal fluids. The higher the pH of the pharmaceutical preparation, the more quickly it erodes or dissolves the SiO x  coating. Optionally, this problem can be addressed by protecting the barrier coating or layer, or other pH sensitive material, with a pH protective organo-siloxane coating or layer. 
     Optionally, the pH protective organo-siloxane coating or layer  406  can be composed of, comprise, or consist essentially of Si w O x C y H z  (or its equivalent SiO x C y ) or Si w N x C y H z  or its equivalent SiN x C y ). The atomic ratio of Si:O:C or Si:N:C can be determined by XPS (X-ray photoelectron spectroscopy). Taking into account the H atoms, the pH protective coating or layer may thus in one aspect have the formula Si w O x C y H z , or its equivalent SiO x C y , for example where w is 1, x is from about 0.5 to about 2.4, y is from about 0.6 to about 3, and z is from about 2 to about 9. 
     Typically, expressed as the formula Si w O x C y , the atomic ratios of Si, O, and C are, as several options:
         Si 100: O 50-150: C 90-200 (i.e. w=1, x=0.5 to 1.5, y=0.9 to 2);   Si 100: O 70-130: C 90-200 (i.e. w=1, x=0.7 to 1.3, y=0.9 to 2)   Si 100: O 80-120: C 90-150 (i.e. w=1, x=0.8 to 1.2, y=0.9 to 1.5)   Si 100: O 90-120: C 90-140 (i.e. w=1, x=0.9 to 1.2, y=0.9 to 1.4)   Si 100: O 92-107: C 116-133 (i.e. w=1, x=0.92 to 1.07, y=1.16 to 1.33), or   Si 100: O 80-130: C 90-150.       

     Alternatively, the organo-siloxane coating or layer can have atomic concentrations normalized to 100% carbon, oxygen, and silicon, as determined by X-ray photoelectron spectroscopy (XPS) of less than 50% carbon and more than 25% silicon. Alternatively, the atomic concentrations are from 25 to 45% carbon, 25 to 65% silicon, and 10 to 35% oxygen. Alternatively, the atomic concentrations are from 30 to 40% carbon, 32 to 52% silicon, and 20 to 27% oxygen. Alternatively, the atomic concentrations are from 33 to 37% carbon, 37 to 47% silicon, and 22 to 26% oxygen. 
     Optionally, the atomic concentration of carbon in the pH protective coating or layer  406 , normalized to 100% of carbon, oxygen, and silicon, as determined by X-ray photoelectron spectroscopy (XPS), can be greater than the atomic concentration of carbon in the atomic formula for the organosilicon precursor. For example, embodiments are contemplated in which the atomic concentration of carbon increases by from 1 to 80 atomic percent, alternatively from 10 to 70 atomic percent, alternatively from 20 to 60 atomic percent, alternatively from 30 to 50 atomic percent, alternatively from 35 to 45 atomic percent, alternatively from 37 to 41 atomic percent. 
     Optionally, the atomic ratio of carbon to oxygen in the pH protective coating or layer  406  can be increased in comparison to the organosilicon precursor, and/or the atomic ratio of oxygen to silicon can be decreased in comparison to the organosilicon precursor. 
     An exemplary empirical composition for a pH protective coating according to the present invention is SiO 1.3 C 0.5 H 3.6 . 
     Optionally in any embodiment, the pH protective coating or layer  406  comprises, consists essentially of, or consists of PECVD applied silicon carbide. 
     Optionally in any embodiment, the pH protective coating or layer  406  is applied by employing a precursor comprising, consisting essentially of, or consisting of a silane. Optionally in any embodiment, the silane precursor comprises, consists essentially of, or consists of any one or more of an acyclic or cyclic silane, optionally comprising, consisting essentially of, or consisting of any one or more of silane, trimethylsilane, tetramethylsilane, Si2-Si4 silanes, triethyl silane, tetraethyl silane, tetrapropylsilane, tetrabutylsilane, or octamethylcyclotetrasilane, or tetramethylcyclotetrasilane. 
     Optionally in any embodiment, the pH protective coating or layer  406  comprises, consists essentially of, or consists of PECVD applied amorphous or diamond-like carbon. Optionally in any embodiment, the amorphous or diamond-like carbon is applied using a hydrocarbon precursor. Optionally in any embodiment, the hydrocarbon precursor comprises, consists essentially of, or consists of a linear, branched, or cyclic alkane, alkene, alkadiene, or alkyne that is saturated or unsaturated, for example acetylene, methane, ethane, ethylene, propane, propylene, n-butane, i-butane, butane, propyne, butyne, cyclopropane, cyclobutane, cyclohexane, cyclohexene, cyclopentadiene, or a combination of two or more of these. Optionally in any embodiment, the amorphous or diamond-like carbon coating has a hydrogen atomic percent of from 0.1% to 40%, alternatively from 0.5% to 10%, alternatively from 1% to 2%, alternatively from 1.1 to 1.8%. 
     Optionally in any embodiment, the pH protective coating or layer  406  comprises, consists essentially of, or consists of PECVD applied SiNb. Optionally in any embodiment, the PECVD applied SiNb is applied using a silane and a nitrogen-containing compound as precursors. Optionally in any embodiment, the silane is an acyclic or cyclic silane, optionally comprising, consisting essentially of, or consisting of silane, trimethylsilane, tetramethylsilane, Si2-Si4 silanes, triethylsilane, tetraethylsilane, tetrapropylsilane, tetrabutylsilane, octamethylcyclotetrasilane, or a combination of two or more of these. Optionally in any embodiment, the nitrogen-containing compound comprises, consists essentially of, or consists of any one or more of: nitrogen gas, nitrous oxide, ammonia or a silazane. Optionally in any embodiment, the silazane comprises, consists essentially of, or consists of a linear silazane, for example hexamethylene disilazane (HMDZ), a monocyclic silazane, a polycyclic silazane, a polysilsesquiazane, or a combination of two or more of these. 
     Optionally in any embodiment, the PECVD for the pH protective coating or layer  406  is carried out in the substantial absence or complete absence of an oxidizing gas. Optionally in any embodiment, the PECVD for the pH protective coating or layer  406  is carried out in the substantial absence or complete absence of a carrier gas. 
     Optionally an FTIR absorbance spectrum of the pH protective coating or layer  406  SiOxCyHz has a ratio greater than 0.75 between the maximum amplitude of the Si—O—Si symmetrical stretch peak normally located between about 1000 and 1040 cm-1, and the maximum amplitude of the Si—O—Si asymmetric stretch peak normally located between about 1060 and about 1100 cm-1. Alternatively in any embodiment, this ratio can be at least 0.8, or at least 0.9, or at least 1.0, or at least 1.1, or at least 1.2. Alternatively in any embodiment, this ratio can be at most 1.7, or at most 1.6, or at most 1.5, or at most 1.4, or at most 1.3. Any minimum ratio stated here can be combined with any maximum ratio stated here, as an alternative embodiment. 
     Optionally, in any embodiment the pH protective coating or layer  406 , in the absence of the medicament, has a non-oily appearance. This appearance has been observed in some instances to distinguish an effective pH protective coating or layer  406  from a lubricity layer (e.g., as described in U.S. Pat. No. 7,985,188), which in some instances has been observed to have an oily (i.e. shiny) appearance. 
     The pH protective coating or layer optionally can be applied by plasma enhanced chemical vapor deposition (PECVD) of a precursor feed comprising an acyclic siloxane, a monocyclic siloxane, a polycyclic siloxane, a polysilsesquioxane, a monocyclic silazane, a polycyclic silazane, a polysilsesquiazane, a silatrane, a silquasilatrane, a silproatrane, an azasilatrane, an azasilquasiatrane, an azasilproatrane, or a combination of any two or more of these precursors. Some particular, non-limiting precursors contemplated for such use include octamethylcyclotetrasiloxane (OMCTS). 
     Optionally, an FTIR absorbance spectrum of the pH protective coating or layer  406  of composition SiOxCyHz has a ratio greater than 0.75 between the maximum amplitude of the Si—O—Si symmetrical stretch peak between about 1000 and 1040 cm-1, and the maximum amplitude of the Si—O—Si asymmetric stretch peak between about 1060 and about 1100 cm-1. 
     Other precursors and methods can be used to apply the pH protective coating or layer  406  or passivating treatment. For example, hexamethylene disilazane (HMDZ) can be used as the precursor. HMDZ has the advantage of containing no oxygen in its molecular structure. This passivation treatment is contemplated to be a surface treatment of the SiOx barrier layer with HMDZ. To slow down and/or eliminate the decomposition of the silicon dioxide coatings at silanol bonding sites, the coating must be passivated. It is contemplated that passivation of the surface with HMDZ (and optionally application of a few mono layers of the HMDZ-derived coating) will result in a toughening of the surface against dissolution, resulting in reduced decomposition. It is contemplated that HMDZ will react with the —OH sites that are present in the silicon dioxide coating, resulting in the evolution of NH3 and bonding of S—(CH3)3 to the silicon (it is contemplated that hydrogen atoms will be evolved and bond with nitrogen from the HMDZ to produce NH3). 
     Another way of applying the pH protective coating or layer is to apply as the pH protective coating or layer an amorphous carbon or fluorocarbon coating, or a combination of the two. 
     Amorphous carbon coatings can be formed by PECVD using a saturated hydrocarbon, (e.g. methane or propane) or an unsaturated hydrocarbon (e.g. ethylene, acetylene) as a precursor for plasma polymerization. Fluorocarbon coatings can be derived from fluorocarbons (for example, hexafluoroethylene or tetrafluoroethylene). Either type of coating, or a combination of both, can be deposited by vacuum PECVD or atmospheric pressure PECVD. It is contemplated that that an amorphous carbon and/or fluorocarbon coating will provide better passivation of an SiOx barrier layer than a siloxane coating since an amorphous carbon and/or fluorocarbon coating will not contain silanol bonds. 
     It is further contemplated that fluorosilicon precursors can be used to provide a pH protective coating or layer over a SiOx barrier layer. This can be carried out by using as a precursor a fluorinated silane precursor such as hexafluorosilane and a PECVD process. The resulting coating would also be expected to be a non-wetting coating. 
     Yet another coating modality contemplated for protecting or passivating a SiOx barrier layer is coating the barrier layer using a polyamidoamine epichlorohydrin resin. For example, the barrier coated part can be dip coated in a fluid polyamidoamine epichlorohydrin resin melt, solution or dispersion and cured by autoclaving or other heating at a temperature between 60 and 100° C. It is contemplated that a coating of polyamidoamine epichlorohydrin resin can be preferentially used in aqueous environments between pH 5-8, as such resins are known to provide high wet strength in paper in that pH range. Wet strength is the ability to maintain mechanical strength of paper subjected to complete water soaking for extended periods of time, so it is contemplated that a coating of polyamidoamine epichlorohydrin resin on a SiOx barrier layer will have similar resistance to dissolution in aqueous media. It is also contemplated that, because polyamidoamine epichlorohydrin resin imparts a lubricity improvement to paper, it will also provide lubricity in the form of a coating on a thermoplastic surface made of, for example, COC or COP. 
     Even another approach for protecting a SiOx layer is to apply as a pH protective coating or layer a liquid-applied coating of a polyfluoroalkyl ether, followed by atmospheric plasma curing the pH protective coating or layer. For example, it is contemplated that the process practiced under the trademark TriboGlide® can be used to provide a pH protective coating or layer  406  that is also provides lubricity. 
     Thus, a pH protective coating for a thermoplastic syringe wall according to an aspect of the invention may comprise, consist essentially of, or consist of any one of the following: plasma enhanced chemical vapor deposition (PECVD) applied silicon carbide having the formula SiOxCyHz, in which x is from 0 to 0.5, alternatively from 0 to 0.49, alternatively from 0 to 0.25 as measured by X ray photoelectron spectroscopy (XPS), y is from about 0.5 to about 1.5, alternatively from about 0.8 to about 1.2, alternatively about 1, as measured by XPS, and z is from 0 to 2 as measured by Rutherford Backscattering Spectrometry (RBS), alternatively by Hydrogen Forward Scattering Spectrometry (HFS); or PECVD applied amorphous or diamond-like carbon, CHz, in which z is from 0 to 0.7, alternatively from 0.005 to 0.1, alternatively from 0.01 to 0.02; or PECVD applied SiNb, in which b is from about 0.5 to about 2.1, alternatively from about 0.9 to about 1.6, alternatively from about 1.2 to about 1.4, as measured by XPS. 
     PECVD apparatus suitable for applying any of the PECVD coatings or layers described in this specification, including the tie coating or layer, the barrier coating or layer or the organo-siloxane coating or layer, is shown and described in U.S. Pat. No. 7,985,188 and U.S. Pat. App. Pub. No. 20130291632. This apparatus optionally includes a vessel holder, an inner electrode, an outer electrode, and a power supply. A vessel seated on the vessel holder defines a plasma reaction chamber, optionally serving as its own vacuum chamber. Optionally, a source of vacuum, a reactant gas source, a gas feed or a combination of two or more of these can be supplied. Optionally, a gas drain, not necessarily including a source of vacuum, is provided to transfer gas to or from the interior of a vessel seated on the port to define a closed chamber. 
     It is contemplated that syringes having a plunger-contacting inner surface comprising an organo-siloxane coating, without a separate discrete lubricity coating or substantially without the presence of a flowable lubricant, may still provide adequate lubricity for plunger advancement. As used herein, “substantially without the presence of a flowable lubricant,” means that a flowable lubricant (e.g., PDMS) is not provided to a syringe barrel in amounts that would contribute to the lubricity of the plunger-syringe system. Since it is sometimes the practice to use a flowable lubricant when handling plungers prior to assembling them into syringes, “substantially without the presence of a flowable lubricant” in some cases may contemplate the presence of trace amounts of such lubricant as a result of such handling practices. 
     Accordingly, in one aspect, the invention is directed to an organo-siloxane coating on the inner surface of a parenteral container which provides lubricious properties conducive to acceptable plunger operation. The organo-siloxane coating may, for example, be any embodiment of the pH protective coating discussed above. The organo-siloxane coating may be applied directly to the interior wall of the container or as a top layer on a multi-layer coating set, e.g., the tri-layer coating set discussed above. Preferably, this embodiment would obviate the need for a discrete lubricity coating, e.g., as described in U.S. Pat. No. 7,985,188 or a flowable lubricant, e.g., silicone oil. 
     The organo-siloxane coating can optionally provide multiple functions: (1) a pH resistant layer that protects an underlying layer or underlying polymer substrate from drug products having a pH from 4-10, optionally from 5-9; (2) a drug contact surface that minimizes aggregation, extractables and leaching; (3) in the case of a protein-based drug, reduced protein binding on the container surface; and (4) a lubricating layer, e.g., to facilitate plunger advancement when dispensing contents of a syringe. 
     Use of an organo-siloxane coating on a polymer-based container as the contact surface for a plunger provides distinct advantages. Plastic syringes and cartridges may be injection molded to tighter tolerances than their glass counterparts. It is contemplated that the dimensional precision achievable through injection molding allows optimization of the inside diameter of a syringe to provide sufficient compression to the plunger for CCI and gas-tightness on the one hand, while not over-compressing the plunger so as to provide desired plunger force upon administration of the drug product. Optimally, this would eliminate or dramatically reduce the need for lubricating the syringe or cartridge with a flowable lubricant or a discrete lubricity coating, thus reducing manufacturing complexity and avoiding problems associated with silicone oil. 
     Various aspects of the invention will be illustrated in more detail with reference to the following Examples, but it should be understood that the present invention is not deemed to be limited thereto. 
     EXAMPLES 
     Example 1: Low and Consistent F i  and F m    
     In this example, it is demonstrated how convertible plungers according to an aspect of the present invention achieved extraordinarily low and consistent breakout force F i  and maintenance force F m  with only a very slight difference in average F i  versus F m . Most notably, these forces were achieved without the presence of flowable lubricant between the syringe barrel and barrel-contacting surfaces of the plunger. These results are especially surprising since the plunger provides robust CCI and gas-tight sealing configured to protect the sterility and quality of contents within the syringe over a typical shelf-life of a prefilled syringe (see Example 2, below). 
     A group of eighteen plungers having the configuration of the convertible plunger  324  of  FIGS. 10-12  were assembled and set into storage sealing mode within plastic syringes having tri-layer coating sets  400  ( FIG. 1A ) deposited on the inner surfaces thereof. The syringes were filled with water for injection. Each of the plungers were actuated to transition from storage sealing mode to dispensing mode and then were advanced distally down each syringe barrel to dispense the water. 
       FIGS. 19A and 19B  graphically illustrate the plunger force results of these tests.  FIG. 19B  provides the raw data points comparing F i  (left) to F m  (right). As that chart shows, the forces between F i  versus F m  were substantially similar and very low. Even the highest force readings on both sides were under 7N and the average forces were approximately 5N. Moreover, the average difference between F i  and F m  was only about 0.5N. In practical terms, such a differential between F i  and F m  is virtually unnoticeable to a syringe handler or a patient receiving an injection therefrom.  FIG. 19A  illustrates the average plunger force profile along a 30 mm travel distance in the syringe barrel, again showing an average force of about 5N, which remained very consistent between initiation and glide over the length of the barrel. 
     In terms of percentages, the average breakout force being about 5.5 N with the average glide force being about 5.0 N, that equates to less than a 10% differential between average F i  and F m . 
     A separate group of eight plungers and syringes having essentially the same configuration as their counterparts described with respect to  FIGS. 19A and 19B , except without liquid in the syringe (i.e., dry) were also subjected to the same plunger force testing. This separate group of plungers demonstrated plunger forces generally between 4.3 N to 7.5 N in empty or dry syringes, as shown in  FIG. 20 . 
     The foregoing results demonstrate that the invention can be used to deliver injectable medications to a patient without applying too much pressure and without dramatic changes in the amount of force necessary from initial actuation of the plunger through completion of delivery. Moreover, this may be achieved without flowable lubricant between the plunger and syringe wall. This is a notable achievement. 
     Example 2: CCI Testing Using Vacuum Decay 
     The previous example demonstrated the surprisingly low and consistent plunger force that plungers, according to an aspect of the invention, are capable of providing. The present example tested the “competing consideration” of CCI (“competing’ with respect to plunger force, as discussed in the Background section above). CCI was tested using the vacuum decay method, as discussed above under the subsection heading, “Industry Standards for Testing Aspects of Plunger.” 
     Plungers subjected to this test had the configuration of the convertible plunger  324  of  FIGS. 10-12  and were assembled and set into storage sealing mode within plastic syringes having tri-layer coating sets  400  ( FIG. 1A ) deposited on the inner surfaces thereof. The particular focus with this test—aside from testing plunger CCI generally—was to determine any correlation between plunger shaft diameter and CCI. The plunger shaft diameter refers to (see  FIG. 12 ) diameter of the annular storage platform  344  of the central core  332 , supporting the storage ring  338  in the engagement position. 
     Five sets of plungers respectively having shaft diameters of 3.25 mm, 3.29 mm, 3.43 mm, 3.51 mm, 3.56 mm, 3.61 mm, 3.68 mm and 3.71 mm were tested in standard 6.48 mm syringe barrels using the vacuum decay method. The results demonstrated that every plunger passed except for one plunger out of four having a 3.25 mm shaft diameter. While thicker shaft diameter may increase the likelihood of providing CCI, it may simultaneously affect plunger force. Thus, a balance must be struck to manage these competing considerations. 
     Example 3: High Altitude Testing of Convertible Plunger 
     When prefilled syringes are filled with liquid contents, a gas bubble is typically formed therein. One concern with prefilled syringes is that in their transport, shifts in temperature and pressure (e.g. from changes in altitude) present a possible risk of undesirably displacing the plunger proximately, causing it to potentially contact unsterile portions of the syringe. For example, reduced pressure at high altitudes (e.g., when the product is in a plane or truck driving through a mountain pass) may cause plunger movement and provide a pathway for microbial ingress as the plunger returns to its original position when the reduced pressure is removed. 
     As altitude increases and pressure drops, this risk of plunger movement and resulting contamination increases. A cabin in a commercial aircraft is typically pressurized to replicate pressure at 8,000 feet altitude. Trucks driving through a mountain pass may be exposed to altitudes as high as 12,000 feet. Packaged products in non-pressurized holds, such as in feeder aircraft, can be exposed to altitudes as high as 16,000-19,000 feet. 
     In this example, seal movement of the plunger was assessed using vacuum pressure. A plunger was placed into a syringe, the storage ring was set into engagement position and then placed on the test fixture. A vacuum was generated at the flange end of the syringe to replicate air shipment. The test reproduced conditions of 20,000 feet altitude for a period of 16 hours. These would be regarded as exceptionally severe conditions for transport. Surprisingly, no movement of the plunger or the storage ring was observed under such conditions. This test provided results that substantially exceed the ASTM Standard D6653/D6653M-13 Standard Test method for Determining the Effects of High Altitude on Package System by Vacuum Method, which requires positive results at 14,000 to 16,000 feet for a period of one hour. 
     While the invention has been described in detail and with reference to specific examples thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.