Abstract:
The disclosed embodiment relates to an injection device that is a single patient use, disposable device containing a needle and a cartridge containing a drug or pharmaceutical product. The device is initially provided in a pre-armed configuration wherein the needle sheath maintains cantilever locking tabs on the housing in a position to the maintain the needle in a position separated from the septum of a cartridge. To arm the device, the practitioner removes the needle sheath and pushes down the plunger assembly. The cantilever locking tabs flex outwardly thereby allowing the cartridge-to-housing interface and the cartridge to move forward whereby the butt end of the needle punctures the septum of the cartridge. Additionally, the cantilever locking tabs form a stop configuration with the housing of the device. The disclosed embodiment is particularly adaptable to dental anesthetic applications, as well as other medical and veterinary applications.

Description:
[0001]    This application claims priority under 35 U.S.C. 119(e) of U.S. Provisional Patent Application Serial No. 61/875,274, filed on Sep. 9, 2013, the disclosure of which is incorporated by reference herein in its entirety. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates to a syringe or similar injection device, which is configured to inject an injectable agent from a pre-loaded cartridge, in a single-use configuration. 
         [0003]    Conventionally, syringes for the sterile injection of injectable agents in the medical, dental or veterinary fields are filled with the injectable agent by a medical professional just prior to use. However, conventional prior art syringes may be problematic in that they may place the medical professional at a higher risk for an accidental needle stick due to the handling before and after the injection. 
       SUMMARY 
       [0004]    It is therefore an object of the present disclosure to provide improvements in syringe-type injection devices, particularly pre-loaded single-use, disposable devices containing a needle and a cartridge containing an injectable agent, wherein the injection device has an armed and a pre-armed state. 
         [0005]    It is therefore a further object of the present disclosure to provide improvements in syringe-type injection devices which are particularly adaptable to sterile injection of injectable agents, wherein the injection device has an armed and a pre-armed state. 
         [0006]    These and other objects are attained by providing a sterile injector assembly, pre-loaded with an injectable agent. The sterile needle assembly includes a stainless steel cannula set within a hub with a needle sheath, bulk packaged and sterilized by gamma ray or ultra-violet irradiation or a similar process as appropriate to the design. 
         [0007]    More particularly, taught herein is a disposable and sterile pre-loaded injection device comprising a cartridge with a closed first cartridge end and a second cartridge end including a cartridge plunger, a housing enclosing the cartridge, the housing including cantilevered locking tabs, a needle, an adapter engaging the first cartridge end and further including an adapter engagement element, wherein the adapter is movable with respect to the cantilevered locking tabs, between a pre-armed position wherein the needle is separated from the cartridge and an armed position wherein the needle penetrates the septum of the cartridge. 
         [0008]    Additionally, taught herein is a method of manufacture of an injection device including the steps of engaging a sterile cartridge to a sterile adapter, loading the sterile cartridge with the sterile adapter into a housing, and securing the sterile cartridge with the sterile adapter within the housing. 
         [0009]    In order to use the device, the medical professional (which may include a dental, veterinary or similar professional) removes the device from the packaging, engages the plunger rod in some embodiments, removes the needle sheath (thereby removing the constraints on the outward flexure of the cantilevered locking tabs) and depresses the plunger rod. Movement of the plunger rod causes the cartridge assembly to move forward relative to a fixed or stationary housing thereby flexing the cantilevered locking tabs outwardly and advancing the septum into the butt end of the cannula thereby reaching the armed or detent position, creating a sterile fluid path for the injectable agent and allowing the injectable agent of the cartridge to be dispensed. In this armed or detent position, the cartridge assembly is locked in place by the cantilevered locking tabs and cannot be detached or retracted during aspiration. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Further objects and advantages of the disclosure will become apparent from the following description and from the accompanying drawings, wherein: 
           [0011]      FIG. 1A  is a cross-sectional view of the assembled injection device of the present disclosure in the pre-armed configuration, including cross-sectional areas of detail along plane A-A and plane B-B. 
           [0012]      FIG. 1B  is a cross-sectional view of the assembled injection device of the present disclosure in the armed configuration. 
           [0013]      FIG. 1C  is a perspective view of the various disassembled elements of the injection device of the present disclosure. 
           [0014]      FIG. 2A  is a perspective cut-away view in detail, showing the cartridge-to-housing interface and its relation to the surrounding components in the pre-armed configuration of the injection device of the present disclosure. 
           [0015]      FIG. 2B  is a perspective cut-away view in detail, showing the cartridge-to-housing interface and its relation to the surrounding components in the armed configuration of the injection device of the present disclosure. 
           [0016]      FIG. 3  is a perspective view of a partially assembled injection device of the present disclosure, prior to the insertion of the cartridge and plunger assembly. 
           [0017]      FIG. 4  is a partially cut-away view corresponding to  FIG. 2 . 
           [0018]      FIG. 5  is a perspective partially exploded view illustrating the attachment of the cartridge-to-housing interface to the cartridge of the present disclosure. 
           [0019]      FIG. 6  is a perspective view of the assembly of the cartridge-to-housing interface and the cartridge of the present disclosure. 
           [0020]      FIG. 7A  illustrates the insertion of the assembled cartridge-to-housing interface and cartridge of  FIGS. 5 and 6  into the partially assembled injection device of  FIG. 3 , of the present disclosure. 
           [0021]      FIG. 7B  is a perspective view of the partially assembled injection device of the present disclosure, containing the cartridge-to-housing interface and cartridge of  FIGS. 5 and 6 . 
           [0022]      FIG. 7C  is a perspective cut-away view corresponding to  FIG. 7B . 
           [0023]      FIG. 8  is a perspective view of the plunger assembly of the present disclosure. 
           [0024]      FIG. 9  is a perspective cut-away view of the plunger assembly of the present disclosure. 
           [0025]      FIG. 10A  illustrates the insertion of the plunger rod assembly of  FIGS. 7 and 8  into the partially assembly injection device of  FIG. 9A ,  9 B and  9 C of the present disclosure. 
           [0026]      FIG. 10B  is a perspective view of the fully assembled injection device of the present disclosure in the pre-armed configuration. 
           [0027]      FIG. 10C  is a perspective cut-away view corresponding to  FIG. 10B . 
           [0028]      FIG. 11A  is a further perspective cut-away view, showing the cartridge-to-housing interface and its relation to the surrounding components in the pre-armed configuration of the injection device of the present disclosure. 
           [0029]      FIG. 11B  is a perspective view of the needle sheath and surrounding components of the injection device of the present disclosure, the needle sheath constraining the injection device to the pre-armed configuration. 
           [0030]      FIG. 12A  is a perspective cut-away view, showing the cartridge-to-housing interface and its relation to the surrounding components in the armed or detent configuration of the injection device of the present disclosure, with the septum of the cartridge punctured. 
           [0031]      FIG. 12B  is a perspective view corresponding to  FIG. 12A . 
           [0032]      FIGS. 13A and 13B  are cross-sectional views of the cap and septum of the present disclosure. 
           [0033]      FIG. 14  is a flowchart of the assembly of the injection device of the present disclosure. 
           [0034]      FIG. 15  is a chart of force versus time for a thumb ring and plunger of an embodiment of the present disclosure. 
           [0035]      FIG. 16  is a diagram of a plunger assembly strip which may be used in the assembly of an embodiment of the present disclosure. 
           [0036]      FIG. 17  is a cross-sectional view of an alternative embodiment of the assembled injection device of the present disclosure in the pre-armed configuration. 
           [0037]      FIG. 18  is a cross-sectional view of an alternative embodiment the assembled injection device of the present disclosure in the armed configuration. 
           [0038]      FIG. 19  is an exploded view of the components of the alternative embodiment of the injection device of  FIGS. 17 and 18 . 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    Disclosed herein are pre-loaded syringe assemblies with a plurality of sterility barriers and aseptic methods of manufacturing the same. The pre-loaded syringe assemblies include a plurality of sterility barriers to maintain the sterility of certain components of the syringe assemblies during packaging, shipping and storage until use by a medical professional. The pre-loaded syringe assemblies taught herein are shipped to a medical professional in a pre-armed state while maintaining sterility of the contents of a pre-loaded cartridge and the surfaces of components that will come into contact with the contents of the cartridge. Prior to use of the pre-loaded syringe assemblies taught herein a medical professional places the assembly in an armed state by forming a sterile fluid pathway between a needle tip and the contents of the cartridge. Placement of the assembly into the armed state occurs by placing pressure on a terminal end of a plunger to move the cartridge toward a distal end of the assembly and cause a butt end of the needle to pierce a septum attached to the cartridge. During arming, the cartridge and the plunger move distally relative to a fixed housing. 
         [0040]    Referring now to the drawings in detail wherein like numerals indicate like elements throughout the several views, one sees that the injection device  200  is a single-patient, single-use, disposable, sterile injection device pre-loaded with an injectable agent. As used herein, the term “injectable agent” refers to, but is not limited to, local anesthetics, therapeutic or pharmaceutical agents, cosmetic agents or other liquids, gels or powders in the medical, dental, veterinary or cosmetic fields. Further, one sees that  FIG. 1A  is a cross-sectional view of the fully assembled injection device  200 , with a proximal end  202  and a distal end  204 , in a pre-armed state (i.e., a sterility barrier of the cartridge  82  has not been pierced by the butt end  44  of the needle cannula  40  prior to the formation of a continuous sterile pathway from the cartridge  82  to the tip  42  of needle cannula  40  to inject the injectable agent), with a cartridge  82  concentrically surrounded by housing  10 . The cartridge  82  includes a cartridge plunger  86  on one end and a cap or band  88  on the other end that secures a septum  89  thereto. The septum  89  forms one sterility barrier to maintain sterility of a liquid held in the cartridge  82 . A cartridge-to-housing interface  90  engages the cap  88  of the cartridge  82 . The housing  10  includes first and second cantilevered locking tabs  18 ,  20  which are constrained from outward flexure by the outward concentric engagement of the needle sheath  70 . The cantilevered first and second locking tabs  18 ,  20 , in this constrained position, prevent the forward movement of the cartridge-to-housing interface  90  and the cartridge  82  thereby maintaining a separation between the butt end  44  of the cannula  40  and the septum  89  of cartridge  82  held in place by cap or band  88  Often, the harpoon  160  is visible through the housing, allowing the medical professional visualization of the harpoon  160 . Moreover, the length of housing  10  which provides for the visibility of the harpoon  160  further often provides for improved axial control of the injection device  200  during operation. 
         [0041]    In the armed state (i.e., piercing of the sterility barrier by the butt end  44  of the needle cannula  40  to form a continuous sterile pathway from the cartridge  82  to the tip  42  of cannula  40  to inject the injectable agent) of injection device  200 , which is illustrated in  FIG. 1B , the needle sheath  70  has been removed thereby allowing outward flexure of the first and second locking tabs  18 ,  20  and further allowing the cartridge  82  and cartridge-to-housing interface  90  to be moved forward toward the distal end  204  by motion on the plunger rod  130  so that the butt end  44  of the cannula  40  penetrates the septum  89  of the cartridge  82 . As the cartridge  82  and cartridge-to-housing interface  90  are moved forward relative to the fixed housing  10 , first and second latching bosses  26 ,  28  engage the annular notch  100  of the cartridge-to-housing interface  90 . In this armed state, the injection device  200  is ready for use by a medical professional. It should be noted that while the first and second latching bosses  26 ,  28  are illustrated as being inwardly extending, that it is envisioned that this disclosure, particularly regarding latching and engagement elements, could encompass many different equivalent structures, for example, detents, stops, latches, catches and the like. 
         [0042]      FIG. 1C  illustrates the various components for the assembly of injection device  200 . The housing  10 , which can be seen in further detail in cut-away in  FIGS. 1A  (including areas of cross-sectional detail A-A and B-B),  1 B,  2 A,  2 B,  4 ,  7 C,  10 C,  11 A, and  12 A, is made from hard polyethylene or polypropylene, but is not limited thereto, and includes a cylindrical body  12  with a forward nose  14  and a mounting hub  12 A of somewhat increased diameter on its proximal end. a passageway  63  of reduced diameter passing therethrough for receiving the plunger rod assembly  120  as shown in  FIGS. 8 and 9 . Mounting hub  12 A further includes radially oriented internal fins  69 A between the interior wall of mounting hub  12 A and the exterior wall of passageway  63  (see cross-sectional area of detail B-B of  FIG. 1A ). Mounting hub  12 A further includes an annular lip  16  with an annular groove  16 A formed thereon for mounting or rotatably engaging the finger flange assembly  60  (see the area of cross-sectional detail A-A of  FIG. 1A  as well as  FIGS. 7A-7C ). The finger flange assembly is often rotatably mounted, but other embodiments include a finger flange assembly which is fixed. 
         [0043]    The forward nose  14  of cylindrical body  12  includes a section  19  of reduced diameter which further includes the first and second cantilevered locking tabs  18 ,  20 . As shown in  FIG. 2A , the first and second cantilevered locking tabs  18 ,  20  are formed from and integral with the wall of section  19  of reduced diameter and defined by first and second channels  22 ,  24  cut on three sides of the first and second cantilevered locking tabs  18 ,  20  thereby forming respective first and second cantilevered integral connections  21 ,  23  with the section  19  of reduced diameter. Additionally, as shown in detail in  FIGS. 2A and 2B , the interior forward end of first and second cantilevered locking tabs  18 ,  20  include first and second latching bosses  26 ,  28 . As shown in the cut-away views of  FIGS. 2A and 2B , the first and second latching bosses  26 ,  28  each include a ramped portion  25 , a flat distal portion  27  and a transverse orthogonal wall  29 . The forward nose  14  further includes a frustoconical section  30  leading to first cylindrical portion  32  which, in turn, leads to cylindrical wall  34  forming cannula passageway  35 . Four support wall segments  36 ,  37 ,  38 ,  39  radially extend from cylindrical wall  34 . 
         [0044]    Needle cannula  40  is of conventional structure, made from stainless steel or a similar material, but not limited thereto, with a beveled pointed forward end  42  for insertion into a patient or other injection point, a rear or butt end  44  for receiving an injectable agent, and a central passageway  46 . 
         [0045]    Cannula crimp insert  50 , made from stainless steel or a similar material, but not limited thereto, includes a rearward rimmed base  52  along with first and second cylindrical portions  54 ,  56 , wherein first cylindrical portion  54  has a slightly greater diameter than second cylindrical portion  56  in order to seat within the interior of nose  14  of housing  10 . Cannula crimp insert  50  further includes central passageway  58  for receiving and engaging needle cannula  40 . 
         [0046]    Finger flange assembly  60  is formed from injection molded plastic, but is not limited thereto, and may have no sterility requirement. Finger flange assembly  60  has two finger flanges  62 ,  64  for use by the medical practitioner during injection and further has a central bore  66  with an internal annular ridge  68  for engaging annular groove  16 A of annular lip  16  of mounting hub  12 A of housing  12  thereby providing for a snap fit with rotatable engagement between the finger flange assembly  120  and the mounting hub  12 A which allows the user or medical practitioner to orient the bevel  42  of the needle cannula  40  during use. Bevel orientation can be achieved in other ways, such as, but not limited to, a fixed finger flange assembly in combination with either a rotating plunger rod or a plunger rod with a rotating harpoon. 
         [0047]    Needle sheath  70  includes a generally cylindrical wall  72  with a closed end  74  and an open end  76 . The sheath  70  is formed from polyethylene or polypropylene, but is not limited thereto. The interior of cylindrical wall  72  immediately inwardly adjacent from open end  76  includes an internal contour  78  to outwardly concentrically engage the following portions of housing  10 , section  19  of reduced diameter, frustoconical section  30 , first cylindrical portion  32  and wall segments  36 ,  37 ,  38 ,  39 . While the needle sheath  70  is mounted on housing  10  thereby forming first sterile barrier  168  extending circumferentially around the outer diameter of section  19  of reduced diameter as it contacts the inner diameter of sheath  70  as shown in  FIG. 2A , the concentric engagement of internal contour  78  of needle sheath  70  to section  19  of reduced diameter of housing  10  prevents the outward flexure of the first and second cantilevered locking tabs  18 ,  20  of the housing  10 . 
         [0048]      FIGS. 3 and 4  illustrate the axial relationship and configuration of housing  10 , needle cannula  40 , cannula crimp insert  50 , finger flange assembly  60  and needle sheath  70  in order to achieve initial subassembly  80 . The needle cannula  40  is inserted into cannula crimp insert  50 . Thereafter, the cannula crimp insert  50 , with the needle cannula  40  therein, is inserted through the rear opening  17  of housing  10  and inserted so as to be engaged within cannula passageway  35  within the forward nose  14  of housing  10 . Alternatively, the needle cannula  40  may be directly secured to the housing  10  by an adhesive bond or a similar method thereby eliminating the cannula crimp insert  50 . The needle sheath  70  is mounted on housing  10  so as to outwardly concentrically engage section  19  of reduced diameter, frustoconical section  30 , first cylindrical portion  32  and wall segments  36 ,  37 ,  38 ,  39  of housing  10 . Finger flange assembly  60  is mounted on housing  10  by engaging annular ridge of  68  of finger flange assembly  60  to annular groove  16 A of annular lip  16  of mounting hub  12 A. The initial subassembly  80  of 
         [0049]      FIGS. 3 and 4  is bulk sterilized either before or after assembly, by ultra-violet, gamma ray or a similar method as appropriate to the design. 
         [0050]      FIGS. 5 and 6 , as well as  FIG. 1C , illustrate the axial relationship and configuration of the cartridge  82  and the cartridge-to-housing interface  90 . As shown in the cut-away view of  FIG. 7C , the cartridge  82  includes cylindrical glass wall  84 , containing the injectable agent therein, and further includes a cartridge plunger  86  at one end and an aluminum cap or band  88  at the other end, holding a septum  89  in place. 
         [0051]    The cartridge-to-housing interface  90  is formed from hard polyethylene or polypropylene, but is not limited thereto, and includes a first end  92  with cylindrical wall  94  for forming a tight fit around the cap  88  of cartridge  82 , holding septum  89  in place. As shown in  FIGS. 13A and 13B , the cap  88  holds the septum  89  in place ( FIG. 13A  discloses a single layer septum  89  while  FIG. 13B  discloses a dual layer septum  89 ), exposed through opening  91  in cap  88 . The combination of the cap  88  and the septum  89  form a piercable sterility barrier to maintain sterility of the contents of the pre-loaded cartridge  82 . Cartridge-to-housing interface  90  further includes a central passageway  96  for communication between the first end  92  and second end  98 . Second end  98  includes outwardly flared edge  99 . Immediately inwardly adjacent from second end  98 , annular notch  100  is formed. As shown in the cut-away views of  FIGS. 2A and 2B , annular notch  100  has a ramped portion  102 , an interior flat portion  104  and a transverse annular wall section  106  to correspond or to be complementary to the ramped portion  25 , flat distal portion  27  and transverse orthogonal wall  29  of first and second latching bosses  26 ,  28  of housing  10 . Additionally, as shown in  FIGS. 2A and 2B , an annular ridge  108  is formed interiorly adjacent from annular notch  100  in order to form a seat for the cap  88  of cartridge  82 . Similarly, annular lip  110  is formed on the interior of cylindrical wall  94 , immediately inwardly adjacent from first end  92  to snap engage the cap  88  of cartridge  82 . 
         [0052]    As shown in  FIGS. 5 and 6 , the cartridge-to-housing interface  90  (which has been bulk sterilized by gamma ray, ultra-violet or a similar method as appropriate to the design) and cartridge  82  are brought into a controlled area (laminar airflow ISO class air supply). During bulk sterilization, the cartridges  82  are oriented vertically with the cap  88  on top and have their top surface sterilized with pulsed ultra-violet light or by a similar method. The cartridge-to-housing interface  90  is then pressed onto the cap  88  as shown in  FIGS. 5 and 6  whereby the interior of cylindrical wall  94  of the first end  92  of the cartridge-to-housing interface  90  forms a friction fit with the cap  88  of cartridge  82  thereby forming second sterile barrier  170 , extending circumferentially around the cap  88  as it contacts the interior of cylindrical wall  94  (see  FIGS. 2A and 2B ) of the cartridge-to-housing interface  90  providing a maximum insertion, and a seat for the cartridge  82  while annular lip  110  of the cartridge-to-housing interface  90  snap engages the cap  88  of cartridge  82 . This results in second subassembly  118 . 
         [0053]    As shown in  FIGS. 7A ,  7 B, and  7 C, the cartridge subassembly  118 , comprising the cartridge  82  with the cap  88  engaged by the cartridge-to-housing interface  90 , is inserted into the initial subassembly  80  through the rear opening  17  of housing  10  thereby achieving the configuration of the injector subassembly  119  of  FIGS. 7B and 7C . In the configuration of  FIG. 7C , and as shown in detail in  FIG. 2A , the first and second latching bosses  26 ,  28  of first and second cantilevered locking tabs  18 ,  20 , which are prevented from outward deflection by the needle sheath  70 , provide a stop for the maximum insertion of the cartridge-to-housing interface  90  in this pre-armed configuration. Further, this maximum insertion of the cartridge-to-housing interface  90  provides for the butt end  44  of needle cannula  40  to be separated from the cap  88  and septum  89  of cartridge  82 . Additionally, as shown in  FIGS. 2A and 2B , third sterile barrier  172  is formed circumferentially around the cartridge-to-housing interface  90  as it the inner diameter of the housing  10 . 
         [0054]      FIGS. 8 and 9  are illustrations of plunger rod assembly  120  which includes plunger rod  130  and harpoon  160 . The plunger rod  130  is made from hard polyethylene or polypropylene, but are not limited thereto while the harpoon  160  is made from stainless steel or a similar material, but is not limited thereto. Plunger rod  130  includes circular thumb ring  132  and shaft  134 . Shaft  134  includes proximal end  136  attached to circular thumb ring  132  and distal end  138  which includes annular retention channel  117  between annular ring  117 A and distal annular terminating ridge  117 B. Harpoon  160  extends from longitudinal blind bore  142  and, as shown in  FIG. 10C , is separated from the cartridge plunger  86  when injection device is in the pre-armed configuration, but engages the cartridge plunger  86  when the injection device  200  is in the armed state and when the injection is being administered. The assembly of the harpoon  160  into the shaft  134  can be done in many different ways. For example, as depicted in  FIGS. 8 and 9  the harpoon  160  may be press fit into a terminal end of the shaft  134 . In another example depicted in  FIG. 16 , the harpoon  160  is insert molded as part of molding the shaft  134 . 
         [0055]    The plunger rod assembly  120  of  FIGS. 8 and 9  is engaged within the mounting hub  12 A as illustrated in the areas A-A and B-B of cross-sectional detail of  FIG. 1A . An internal annular retention ring  95  is formed on the interior of passageway  63  for engaging with a corresponding external annular retention channel (see element  118 ,  FIG. 8A ) on the plunger rod assembly  120 . The internal annular retention ring  95  has a cross section with a sloped surface  95 A facing toward the proximal end or user end, in order to facilitate insertion of the plunger rod assembly  120 , but with an abrupt orthogonal surface  95 B toward the distal end in order to capture the plunger rod assembly  120  once it is inserted, and to resist any subsequent withdrawal of the plunger rod assembly  120 . The annular retention channel  117  is formed on shaft  134  of plunger rod assembly  120  between annular ring  117 A and distal annular terminating ridge  117 B. When the shaft  134  of plunger rod assembly  120  is initially inserted into passageway  63 , the distal end of plunger rod assembly  120  slides over the sloped surface  95 A of internal annular retention ring  95  so that internal annular retention ring  95  is captured within annular retention channel  117  between annular ring  117 A and distal annular terminating ridge  117 B. Similarly, the relationship or contact between the opposing orthogonal surfaces of distal annular terminating ridge  117 B and orthogonal surface  95 B resists any subsequent withdrawal of the plunger rod assembly  120  from the passageway  63 . Likewise, the relationship or contact between the sloped surface  95 A of internal annular retention ring  95  and the annular ring  117 A causes a snap detent engagement of the plunger rod assembly  120  which holds the plunger rod assembly  120  in place, but which allows the medical professional to press against the plunger rod assembly  120  to overcome the snap detent engagement, thereby often causing both audible and tactile feedback, with the plunger rod assembly  120  being driven into passageway  63 . 
         [0056]    As shown in  FIGS. 10A ,  10 B and  10 C, the plunger rod assembly  120  is inserted into injector subassembly  119 . In this inserted configuration of  FIG. 10C , the configuration shown in the cross-sectional area of  FIG. 1A  is achieved. This configuration of the external annular channel  117  and the internal annular retention ring  95  often provides a tactile snap, as well as audible feedback, for the user while pushing the plunger rod assembly  120  to operate the injection device  200 .  FIG. 15  illustrates that as force or energy is applied, the snap detent configuration of internal annular retention ring  95  and external annular channel  117  holds the energy until approximately fifteen pounds-force is applied as shown on the Y-axis, whereas the X-axis is sample number, at a sampling rate of 24,000 samples per second. Then, disengagement of the detent configuration occurs, the momentum is momentarily released to allow the harpoon  160  to travel at a faster speed and force than would occur without the snap detent configuration. This is particularly a benefit for users who are not as likely to use an aggressive slap style of activation. 
         [0057]      FIGS. 10B and 10C  illustrate the injection device  200  in the pre-armed state as it is often provided to the customer in a flow wrapper package (not shown). In this pre-armed state, as shown in  FIGS. 2A and 10C , the butt end  44  of needle cannula  40  is separated from the cap  88  and septum  89  of cartridge  82  and the harpoon  160  is separated from the cartridge plunger  86 . In particular, as shown in  FIG. 2A , this separation of the butt end  44  of the needle cannula  40  from the septum  89  of cartridge  82  is caused by the rigid positioning of first and second latching bosses  26 ,  28  of first and second cantilevered locking tabs  18 ,  20 , as constrained by the needle sheath  18 , providing a stop to the forward movement of the cartridge subassembly  118  comprising the cartridge-to-housing interface  90  and cartridge  82 . 
         [0058]      FIGS. 17 ,  18  and  19  illustrate an alternative embodiment of the injection device  200  of the present disclosure, wherein the housing  12  does not include the mounting hub  12 A. 
         [0059]    The embodiment of  FIGS. 17 ,  18  and  19  includes some different elements from the other embodiment. For instance, the finger flange assembly  60  includes first and second notches  65 ,  67  and further includes central bore  66  which with an internal annular snap ring  69  which is snap engaged between the first and second external snap ridges  153 ,  155  of the plunger cap  150 . This forms a sandwiched engagement between the rear annular rim  16  of housing  10  between the finger flange assembly  60  and the plunger cap  150 . This sandwiched engagement is sufficiently tight to ensure structural stability but retains the ability of the finger flange assembly  60  to rotate with respect to the housing  10 . Furthermore, a snap detent engagement is formed between an annular snap ring ridge  140  on the shaft  134  of plunger rod  130  and an annular snap notch of the plunger cap  150 . 
         [0060]    In order to arm the injection device  200  for an injection, the user removes the injection device  200  from the flow wrapper package. The user then removes the needle sheath  70  from the housing  10  of injection device  200 . The removal of needle sheath  70  from the housing  10  removes the constraint on the outward flexure of first and second cantilevered locking tabs  18 ,  20 . The user then manually engages the finger flanges  62 ,  64  and the circular thumb ring  132  in the conventional manner and depresses the circular thumb ring  132 . This releases, overcomes, or disengages the detent or snap-fit engagement between the annular retention channel shaft  134  of the plunger rod assembly and the annular retention ring  95  of mounting hub  12 A (often producing audible feedback) and drives the harpoon  160  into engagement with the cartridge plunger  86  of cartridge  82 . Further movement of the plunger rod  30  urges the cartridge  82  and the cartridge-to-housing interface  90  (i.e., the cartridge subassembly  118 ) forward. It is noted that while the cartridge  82  is sealed with the cap  88  intact, the cartridge plunger  86  cannot move within the cylindrical wall  84  of cartridge  82  and insertion of the plunger rod  30  is translated into forward movement of the cartridge  82  and the cartridge-to-housing interface  90  toward the distal end  204 . This forward movement further causes the outward flexure of the first and second cantilevered locking tabs  18 ,  20  as the second end  98  of cartridge-to-housing interface  90  is urged against the ramped portions  25  of first and second latching bosses  26 ,  28  of first and second cantilevered locking tabs  18 ,  20 . As second end  98  of cartridge-to-housing interface  90  passes over the first and second latching bosses  26 ,  28  and abuts against an interior of the frustoconical section  30 , the first and second cantilevered locking tabs  18 ,  20  snap back into place whereby first and second latching bosses  26 ,  28  are engaged within annular notch  100  of cartridge-to-housing interface  90 . Further, outwardly flared edge  99  of second end  98  of cartridge-to-housing interface  90  is engaged between the interior of the frustonical section  30  and the transverse orthogonal wall  29  of first and second latching bosses  26 ,  28 . Additionally, this forward movement of the cartridge  82  causes the butt end  44  of cannula  40  to pierce the septum  89  of cartridge  82  thereby providing a sterile fluid pathway between the cartridge  82  and the cannula  40 . Often, audible feedback is generated when the injection device  200  goes from the first engagement or pre-armed position ( FIG. 1A ) to the second engagement or armed position ( FIG. 1B ). The audible feedback provides the medical professional with an indication that the needle or cannula  40  is engaged to fully connect the fluid pathway. With the position of the cartridge  82  stabilized by the engagement between the first and second cantilevered latching tabs  18 ,  20  and the cartridge-to-housing interface  90 , and with the septum  89  pierced, further depression or insertion of the plunger rod  130  drives the cartridge plunger  86  further into the cartridge  82  thereby causing the ejection of the injectable agent out of the cartridge  82  through the central passageway  46  of cannula  40  for injection into a patient. 
         [0061]      FIG. 14  illustrates an exemplary assembly or manufacturing method for injection device  200 , but the assembly or manufacture of injection device  200  is not limited thereto. The order of steps presented is merely illustrative and may be performed in a different order or in parallel operations. 
         [0062]    In step  602 , which is performed in an aseptic environment at least with respect to the needle  40  and any elements which form the sterile fluid pathway, the cannula crimp insert  50 , with the needle  40  inserted therein, is inserted into the forward nose  14  of housing  10 . Additionally, the needle sheath  70  is mounted on the housing  10  and the finger flange assembly  60  is positioned on the mounting hub  34  of housing  10  thereby resulting in the initial subassembly  80  of  FIGS. 3 and 4 . In step  604 , which is performed in an aseptic environment at least with respect to the septum  89  and the cartridge-to housing interface  90  to the extent that they form the sterile fluid pathway, the cartridge  82  is inserted into the cartridge-to-housing interface  90  thereby resulting in the cartridge subassembly  118  of  FIGS. 5 and 6 . In step  606 , which is performed in an aseptic environment, the cartridge subassembly  118  of  FIGS. 5 and 6  is inserted into the initial subassembly  80  of  FIGS. 3 and 4  thereby resulting in the injector subassembly  119  of  FIGS. 7A ,  7 B and  7 C. In step  608 , which is not necessarily performed in an aseptic environment, the plunger rod assembly  120  is attached to the injector subassembly  119  as shown in  FIGS. 10A ,  10 B and  10 C thereby resulting in the pre-armed injection device  200  of  FIG. 10C  as well as  FIG. 1A . In step  610 , the resulting injection device  200  may be packaged, which is not necessarily performed in an aseptic environment. 
         [0063]    Thus the several aforementioned objects and advantages are most effectively attained. Although preferred embodiments of the invention have been disclosed and described in detail herein, it should be understood that this invention is in no sense limited thereby and its scope is to be determined by that of the appended claims.