Abstract:
A needle-less injector suitable for injecting fluid through a surface includes a housing, a driver, an engine and a trigger. The housing contains a fluid and the engine contains a compressed gas. Upon application of sufficient force to the trigger, the compressed gas is released from the engine forcing the driver through the interior of the housing, expelling the liquid from the housing at a speed sufficient to pierce an injection surface. In one embodiment, the needle-less injector includes a mechanism for mitigating the kickback associated with releasing compressed gas from the engine. In another embodiment, the housing includes finger rests that provide stability and resistance to activate the device. In another embodiment, the engine is fitted with a reusable valve. In another embodiment, a safety clamp is included on the housing, preventing accidental activation of the device.

Description:
RELATED APPLICATIONS  
       [0001]    This application is related to U.S. patent application Ser. No. 09/566,928, filed May 6, 2000. Further, this application generally relates to U.S. patent application Ser. No. 09/215,769, filed Dec. 19, 1998, now U.S. Pat. No. 6,063,053, which is a continuation of U.S. patent application Ser. No. 08/727,911, filed Oct. 9, 1996, now U.S. Pat. No. 5,851,198, which is a continuation-in-part of U.S. patent application Ser. No. 08/719,459, filed Sep. 25, 1996, now U.S. Pat. No. 5,730,723, which is a continuation-in-part of U.S. patent application Ser. No. 08/451,470, filed Oct. 10, 1995, now abandoned. This application is also generally related to U.S. patent application Ser. No. 09/192,079, filed Nov. 14, 1998, now U.S. Pat. No. 6,080,130, and to U.S. patent application Ser. No. [attorney docket No. 69816-0250782], filed Mar. 14, 2001. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to needle-less injectors, and in particular, modular gas-pressured needle-less injectors and methods of performing needle-less injections using the same.  
         BACKGROUND OF THE INVENTION:  
         [0003]    Traditionally, fluids such as medications are injected into patients, either subdermally or intradermally, using hypodermic syringe needles. The body of the syringe is filled with the injectable fluid and, once the needle has pierced the patient&#39;s skin, the syringe plunger is depressed so as to expel the injectable fluid out of an opening in the needle. The person performing the injection is usually a trained medical services provider, who manually inserts the hypodermic needle between the layers of a patient&#39;s skin for an intradermal injection, or beneath the skin layers for a subcutaneous injection.  
           [0004]    Intradermal or subdermal delivery of a medication through the use of a hypodermic needle requires some skill and training for proper and safe administration. In addition, the traditional method of intradermal injections requires actual physical contact and penetration of a needle through the skin surface of the patient, which can be painful for the patient. Traditional needle injectors, such as hypodermic syringes, are also expensive to produce and difficult to use with prepackaged medication doses. Needle injectors also suffer from increased danger of contamination exposure to health care workers administering the injections, and to the general public when such injectors are not properly disposed of.  
           [0005]    Jet injectors are generally designed to avoid some or all of these problems. However, not only are conventional jet injectors cumbersome and awkward, but, existing conventional jet injectors are only capable of subcutaneous delivery of a medication beneath the skin layers of a patient. Conventional jet injectors are also somewhat dangerous to use, since they can be discharged without being placed against the skin surface. With a fluid delivery speed of about 800 feet per second (fps) and higher, a conventional jet injector could injure a person&#39;s eye at a distance of up to 15 feet. In addition, jet injectors that have not been properly sterilized are notorious for creating infections at the injection site. Moreover, if a jet injector is not positioned properly against the injection site, the injection can result in wetting on the skin surface. Problems associated with improper dosage amounts may arise as well, if some portion of the fluid intended for injection remains on the skin surface following an injection, having not been properly injected into and/or through the skin surface.  
           [0006]    Typically, needle-less medication injectors use either an expansion spring or a compressed inert gas to propel the fluid medication (via a push rod plunger) through a small orifice (an injector nozzle) which rests perpendicular to and against the injection site. The fluid medication is generally accelerated at a high rate to a speed of between about 800 feet per second (fps) and 1,200 fps (approximately 244 and 366 meters per second, respectively). This causes the fluid to pierce through the skin surface without the use of a needle, resulting in the medication being deposited in a flower pattern under the skin surface.  
           [0007]    It should be noted, however, that compression spring propelled jet injectors do not offer linear delivery speeds (constant speed of the fluid being injected). In addition to this problem, spring propelled jet injectors with weak (e.g., deteriorated) springs often slow fluid delivery speed down while an injection is being administered, resulting in improper fluid penetration. Reduced speed of the fluid can cause improper dosing and bruising at the injection site when the injection surface is the skin of a human recipient.  
           [0008]    In a jet injector, if the inert gas is not quickly and properly expelled, fluid may be improperly injected, as with those devices employing a compression spring. Conventional disposable needle-less injectors, such as those shown in U.S. Pat. No. 4,913,699 to Parsons and U.S. Pat. No. 5,009,637 to Newman et al. show a gas-containing, breakable tube that is shattered or cracked open by a side mounted trigger. Difficulties arise in the need to maintain tight tolerances on the breakable member, since minor changes in thickness can dramatically effect the pressure needed to deploy the gas from the gas chamber of the device. In addition, the broken shards of the breakable member are ejected at high speed when the gas is expelled and these shards can occasionally jam between the plunger driver and the housing, thereby preventing proper operation of the needle-less injector. Attempts to prevent small shards from being formed would obviate some of this potential, but tend to make activation of the device more difficult.  
           [0009]    U.S. Pat. No. 6,080,130, U.S. Pat. No. 6,063,053, U.S. Pat. No. 5,851,198 and U.S. Pat. No. 5,730,723 describe needle-less injectors incorporating a gas power source, thus obviating some of the limitations inherent in compression spring injectors and addressing many of the concerns of conventional jet injectors. The injectors described therein have a pre-filled and self-contained compressed gas for providing pressure to inject medication into the skin surface of a patient without the use of a needle.  
           [0010]    Gas power sources for needle-less injectors that employ either pop valves or breakaway tab valves to release the inert gas stored in their respective gas chambers, however, may only be opened once, thereby presenting difficulty with regard to quality control testing measures. Further, operation of many injectors requires a user to depress a trigger, relying mainly on resistance force from the injection surface to initiate an injection. Where the underlying surface is sensitive, applying such pressure may not be advantageous. Further, if the injection surface is slippery such a device may slide out of place during an injection rendering its use potentially injurious and possibly resulting in improper fluid delivery.  
         SUMMARY OF THE DISCLOSURE  
         [0011]    It is therefore an object of an embodiment of the instant invention to provide gas-pressured needle-less injectors that obviate, for practical purposes, the above-mentioned limitations.  
           [0012]    In one embodiment of the instant invention, a needle-less injector suitable for injecting fluid through an injection surface includes a housing, a trigger, an engine, and a driver. The housing contains a fluid and the engine contains a compressed gas. Upon application of a sufficient amount of force to the trigger, the compressed gas is released from the engine forcing the driver through the interior of the housing, expelling the liquid from the housing at a speed sufficient to pierce an injection surface.  
           [0013]    In another embodiment of the instant invention, the needle-less injector includes a mechanism for mitigating the kickback associated with releasing compressed gas from the engine. Grips may be included on the engine, mechanically coupling the engine to an element of the needle-less injector that is affixed to the housing, thereby preventing the engine from separating from the housing upon release of compressed gas from the engine. Also, retainer hooks on the interior of the trigger corresponding to latch retainer mechanisms on the exterior of the housing further prevent the engine from separating from the housing.  
           [0014]    In yet another embodiment of the instant invention, the housing of the needle-less injector includes finger rests that provide stability in administering an injection and provide resistance to activate the needle-less injector. Thus, a user need not rely solely on resistance from the injection surface to initiate the administration of an injection. The finger rests may be included on opposing sides of the housing, designed to comfortably receive the fingers of a user without substantial slippage.  
           [0015]    In yet another embodiment of the instant invention, the engine of the needle-less injector is fitted with a reusable valve. The valve may contain a rubber head that is held against a fixed element of the engine such that depression of the trigger separates the head from the fixed element, releasing the compressed gas from the engine and, further, forcing the driver to expel liquid from the housing. A spring may be included in the valve to help maintain a proper airtight seal with the canister holding the compressed gas.  
           [0016]    In yet another embodiment of the instant invention, a safety clamp is included on the exterior of the housing of the needle-less injector, preventing accidental activation of the device. The safety clamp must be removed prior to use and may be made of a sufficiently elastic material such that a user need only deform the clamp, aided by grips included thereon, to remove the clamp from the housing. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIGS. 1 a - 1   e  illustrate a needle-less injector in accordance with an embodiment of the instant invention. FIG. 1 a  is a side perspective view prior to administration of an injection, shown at 0° rotation about the central axis of the injector, FIG. 1 b  is a side cross-sectional view, the injector having been rotated 90° about the central axis, FIG. 1 c  is a side perspective view at 0° rotation about the central axis, FIG. 1 d  is a side perspective view after administration of an injection, shown at 180° rotation about the central axis of the injector and FIG. 1 e  is a side partial cross-sectional view after administration of an injection, the injector having been rotated 90° about the central axis.  
         [0018]    [0018]FIGS. 2 a - 2   c  illustrate the housing of a needle-less injector in accordance with an embodiment of the instant invention. FIG. 2 a  is a side perspective view at 180° rotation about the central axis of the injector, FIG. 2 b  is a proximate end perspective view and FIG. 2 c  is a distal end perspective view.  
         [0019]    [0019]FIGS. 3 a - c  illustrate the ampoule cap of a needle-less injector in accordance with an embodiment of the instant invention. FIG. 3 a  is a side perspective view, FIG. 3 b  is a side cross-sectional view and FIG. 3 c  is a proximate end perspective view.  
         [0020]    [0020]FIGS. 4 a - c  illustrate the plunger of a needle-less injector in accordance with an embodiment of the instant invention. FIG. 4 a  is a side perspective view, FIG. 4 b  is a side cross-sectional view and FIG. 4 c  is a proximate end perspective view.  
         [0021]    [0021]FIGS. 5 a - d  illustrate the piston of a needle-less injector in accordance with an embodiment of the instant invention. FIG. 5 a  is a side perspective view, FIG. 5 b  is a side cross-sectional view, FIG. 5 c  is a proximate end perspective view and FIG. 5 d  is a distal end perspective view.  
         [0022]    [0022]FIGS. 6 a - d  illustrate the diffuser of a needle-less injector in accordance with an embodiment of the instant invention. FIG. 6 a  is a side perspective view, FIG. 6 b  is a side cross-sectional view, FIG. 6 c  is a proximate end perspective view and FIG. 6 d  is a distal end perspective view.  
         [0023]    [0023]FIGS. 7 a - i  illustrate various configurations of channels in the diffuser of a needle-less injector in accordance with embodiments of the instant invention.  
         [0024]    [0024]FIGS. 8 a - d  illustrate the trigger of a needle-less injector in accordance with an embodiment of the instant invention. FIG. 8 a  is a side perspective view at 0° rotation about the central axis of the trigger, FIG. 8 b  is a side cross-sectional view at 90° rotation, FIG. 8 c  is a proximate end perspective view and FIG. 8 d  is a distal end perspective view.  
         [0025]    [0025]FIGS. 9 a - b  illustrate the safety clamp of a needle-less injector in accordance with an embodiment of the instant invention. FIG. 9 a  is a proximate end perspective view and FIG. 9 b  is a side perspective view.  
         [0026]    [0026]FIGS. 10 a - d  illustrate the engine housing of a needle-less injector in accordance with an embodiment of the instant invention. FIG. 10 a  is a side perspective view, FIG. 10 b  is a side cross-sectional view, FIG. 10 c  is a proximate end perspective view and FIG. 10 d  is a distal end perspective view.  
         [0027]    [0027]FIGS. 11 a - d  illustrate the valve body of a needle-less injector in accordance with an embodiment of the instant invention. FIG. 11 a  is a side perspective view, FIG. 11 b  is a side cross-sectional view and FIG. 11 c  is a proximate end perspective view.  
         [0028]    [0028]FIGS. 12 a - c  illustrate the closing ferrule of a needle-less injector in accordance with an embodiment of the instant invention, prior to the closing ferrule being mechanically fitted around a valve body and an engine housing. FIG. 12 a  is a side perspective view, FIG. 12 b  is a side cross-sectional view and FIG. 12 c  is a proximate end perspective view.  
         [0029]    [0029]FIGS. 13 a - d  illustrate the threaded valve stem guide of a needle-less injector in accordance with an embodiment of the instant invention. FIG. 13 a  is a side perspective view in partial cross-section, FIG. 13 b  is a side cross-sectional view, FIG. 13 c  is a proximate end perspective view and FIG. 13 d  is a distal end perspective view.  
         [0030]    [0030]FIGS. 14 a - c  illustrate the valve stem of a needle-less injector in accordance with an embodiment of the instant invention. FIG. 14 a  is a side perspective view, FIG. 14 b  is a side cross-sectional view prior to the distal end being shaped and FIG. 14 c  is a proximate end perspective view.  
         [0031]    [0031]FIGS. 15 a - b  illustrate the valve spring of a needle-less injector in accordance with an embodiment of the instant invention. FIG. 15 a  is a side perspective view in the relaxed state, FIG. 15 b  is a side perspective view in the compressed state.  
         [0032]    [0032]FIG. 16 is a graph depicting the velocity of the driver of an embodiment of the instant invention during administration of an injection.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]    As shown in the drawings for purposes of illustration, the invention is embodied in a gas-pressured needle-less injector. In preferred embodiments of the present invention, the gas-pressured needle-less injector is pre-loaded with medication and is adapted for a single use. Preferably, the needle-less injector is for use with human beings or other animals. However, it will be recognized that further embodiments of the invention may be used in other applications requiring needle-less injection, such as passing injectable materials through a porous membrane or the like.  
         [0034]    Also, embodiments of the present invention may be used to inject other fluids or injectants such as proteins, vitamins, hormones, drugs, vaccines, medications, lyophilized medications, medication cocktails, or the like, and such are contemplated as being within the scope of the term “liquid” as used herein. In preferred embodiments, the liquids used in accordance with the present invention are de-gassed prior to filling into the needle-less injector or are of sufficient chemical properties such that the liquids de-gas immediately upon or soon after filling, as described in U.S. patent application Ser. No. [attorney docket No. 69816-0250782], filed Mar. 14, 2001. In either of such preferred embodiments, substantially no gas pocket develops in the interior cavity where the liquid resides during storage of the needle-less injector, prior to use.  
         [0035]    For ease in describing the various elements of the instant invention, the following spatial coordinate system will apply thereto. As depicted in FIG. 1 c,  a central axis is defined through the length of a gas-pressured needle-less injector  100 . This central axis  1  has one terminus at the proximate end  2  of the needle-less injector  100 , defined as that end of the device in contact with an injection surface during normal operation of the injector. The other terminus of the central axis is at the distal end  3  of the injector  100 , defined as that end of the device furthest from the injection surface when the injector is positioned perpendicular to the injection surface. Thus, various elements of the device of the instant invention may be described with reference to their respective proximate and distal portions, as well as their central axes.  
         [0036]    As depicted in FIG. 1, a gas-pressured needle-less injector  100  includes a housing  201 . The housing  201  may be of any suitable shape, though in preferred embodiments it is roughly cylindrical about the central axis. The housing  201  preferably has a varying interior diameter along its length to accommodate the elements that reside and operate therein when the injector  100  is fully assembled. The housing  201  depicted in FIG. 2 a  has four such interior diameters: an ampoule diameter  202 , a piston diameter  203 , a diffuser diameter  204  and an engine diameter  205 , respectively. Embodiments of the instant invention preferably do not have an ampoule that is a mechanical element separate and distinct from the housing  201 , yet the housing  201  may act as an ampoule for various purposes such as filling with liquid.  
         [0037]    The exterior portion  206  of the proximate end surface of the housing  201  may be flat, though in preferred embodiments it is of a shape that maximizes injector efficacy. Efficacy is optimal when substantially all liquid contained in the injector  100  is delivered through the injection surface, leaving substantially no liquid on either the injection surface or the exterior portion  206  of the proximate end surface of the housing  201  after an injection is complete (see FIGS. 1 d  and  1   e ). To that end, in the embodiment depicted in FIG. 2 a,  the exterior portion  206  of the proximate end of the housing  201  is adapted to pinch and stretch the surface through which an injection is to be administered, as the exterior portion  206  of the proximate end surface of the housing  201  is brought into contact with an injection surface. Thus, the exterior portion  206  of the proximate end of the housing  201  preferably has a conical shape about the central axis, and further possesses an elevated rim  207  around its circumference.  
         [0038]    The interior portion  208  of the proximate end of the housing  201  may be of any appropriate shape. It may conform roughly to the shape of the exterior portion  207 , or have a design independent thereof. In one embodiment, the interior portion  208  is flat, though preferably, as depicted in FIG. 2 a  the interior portion  208  is roughly conical, with at least one orifice  209  at or near the vertex  210 . The needle-less injector  100  depicted in FIG. 1 is shown with only one orifice.  
         [0039]    The at least one orifice  209  provides fluid communication between the interior  214  of the housing  201  and the surface through which an injection is administered. The number of orifices  209  may be varied depending on the delivery parameters of the liquid to be injected. One such parameter is the depth to which a liquid must penetrate a recipient&#39;s tissue, when the device is used for the injection of a medicament into a human being. For example, in one embodiment it may be desirable to inject a liquid just beneath the outermost skin layers of a recipient, and multiple orifices may best suit that end. Alternatively, a single orifice may be most desirable for an injection that requires deeper penetration for maximum drug efficacy.  
         [0040]    An exhaust passage  211  may be created through the housing  201 , from the interior wall  212  to the exterior wall  213 , preferably within the section of the housing  201  of ampoule diameter  202 . The exhaust passage  211  allows gas to vent from the interior  214  of the housing  201  preferably only after an injection has been administered. Thus, most preferably, the exhaust passage  211  is located at a point in the housing  201  at or immediately distal to the location of the piston  500  (see FIGS. 1 d  and  1   e ) after administration of an injection. In these most preferred embodiments, gas may not vent from the interior  214  of the housing  201  through the exhaust passage  211  until after substantially all liquid contained in the housing  201  has been discharged from the needle-less injector  100 , with the piston  500  at rest in its final position.  
         [0041]    Liquid stored in the needle-less injector  100 , prior to administration of an injection, is preferably contained in the interior  214  of the housing  201  in the region bounded by the interior portion  208  of the proximate end of the housing  201 , the interior wall  212  of the housing  201  and the proximate end  403  of the plunger  400  (see FIG. 1 a  and  2   a ).  
         [0042]    As depicted in FIG. 2 a,  the housing  201  may further include finger rests  215 . In preferred embodiments, two such finger rests  215  are formed on the exterior wall  213  of the housing  201  at opposing locations. Most preferably, the finger rests  215  are located directly opposite one another. In preferred embodiments, each finger rest  215  has an arc  216  on the proximate side thereof to accommodate proper finger placement for either self-administration of an injection or assisted administration by a health care professional or the like. In the most preferred embodiments, the arcs  216  of the finger rests  215  further contain a non-slip, textured surface  217 .  
         [0043]    When the needle-less injector  100  is used by an individual performing self-administration of an injection, the individual&#39;s thumb and middle finger may be placed in the arcs  216  of the finger rests  215  on opposing sides of the housing  201  for stabilization of the device, with the index finger operably placed against the trigger  800  at the distal end of the injector  100 . Another manner in which a user may perform self-administration of an injection, which is also the manner preferred when the needle-less injector  100  is operated by an individual other than the recipient of an injection, involves the index and middle fingers being placed in the arcs  216  of the finger rests  215  on opposing sides of the housing  201  for stabilization of the device, with the thumb operably placed against the trigger  800  at the distal end of the injector  100 .  
         [0044]    The housing  201  may further contain at least one latch retainer mechanism  218  near the distal end. The at least one latch retainer mechanism  218  may be comprised of a single set of saw tooth ridges that encircle the exterior wall  213  of the housing  201  around its central axis. More preferably, there are two latch retainer mechanisms  218  comprising two sets of saw tooth ridges  219 , disposed opposite one another on the exterior wall  213  of the housing  201 , though any appropriate number of latch retainer mechanisms  218  may be utilized. Preferably, as shown in FIG. 1 b,  the housing  201  further contains a clamp indentation  220  that is defined on its proximate end by a ridge  221  and on its distal end by the at least one latch retainer mechanism  218  and the proximate end of the trigger  800 .  
         [0045]    The proximate end of the housing  201  may further be fit with an ampoule cap  300 , as depicted in FIG. 3, which serves to maintain sterility of the exterior portion  206  of the proximate end surface of the housing  201  while the needle-less injector  100  is stored. Further, when de-gassed liquids are used in accordance with the present invention, the ampoule cap  300  provides the requisite airtight seal between the at least one orifice  209  in the proximate end of the housing  201  and the local atmosphere, such that the de-gassed liquids may remain gas-free during storage. Referring again to FIG. 3, the interior  301  of the ampoule cap  300  is preferably designed to conform substantially to the exterior surface  206  of the proximate end of the housing  201 , while the exterior  302  of the ampoule cap  300  may be of any convenient configuration.  
         [0046]    As depicted in FIG. 4, the housing  201  may be fit with a plunger  400 . Preferably, the plunger  400  is pressure-fit within the housing  201 , as its diameter is equivalent to or slightly greater than the ampoule diameter  202  of the housing  201 . The plunger  400  is preferably constructed of a sufficiently elastic material such that the pressure-fit creates an air and liquid-tight seal with the interior wall  212  of the housing  201 . The plunger  400  is preferably cylindrical to mirror the shape of the interior wall  212  of the housing  201 , though other shapes may be suitable especially where the interior wall  212  of the housing  201  is not cylindrical. Moreover, the wall  401  of the plunger  400  may have multiple ridges  402  disposed thereupon. Preferably, there are at least two such ridges  402 , and most preferably there are three ridges  402 . These ridges  402  provide stability to the plunger  400  such that its direction of travel during administration of an injection remains substantially linear along the central axis, without rotational motion around any axis other than the central axis.  
         [0047]    The proximate end  403  of the plunger  400  may be of any suitable shape, including a flat surface, though in preferred embodiments it roughly mirrors the shape of the interior wall  208  of the proximate end of the housing  201 . However, the elastic properties of the plunger material may allow the proximate end  403  of the plunger  400  to conform to the shape of a surface different than its own when mechanically forced against such a surface. Thus, the shape of the proximate end  403  of the plunger  400  need not mirror the shape of the interior wall  208  of the proximate end of the housing  201 , yet the plunger proximate end  403  may conform to the shape of the interior wall  208  when forced against it during or after an injection is administered. In most preferred embodiments, however, the proximate end  403  of the plunger  400  is roughly conical in shape.  
         [0048]    The distal end  404  of the plunger  400  may similarly be of any suitable shape, and is received by the proximate end of the piston  500 . In preferred embodiments, the plunger  400  is symmetrical in shape along a plane perpendicular to the central axis. Thus, in preferred embodiments, the distal end  404  of the plunger  400  is roughly conical in shape.  
         [0049]    The housing  201  may be fit with a piston  500 , as depicted in FIG. 5. The piston  500  preferably is of roughly cylindrical shape along the length of its central axis with a flared portion  501  toward its distal end, though other shapes may be appropriate especially in those embodiments where the interior wall  212  of the housing  201  is non-cylindrical. Preferably, the proximate end  502  of the piston  500  is shaped such that it mechanically receives the distal end  404  of the plunger  400 . Thus, in most preferred embodiments, the proximate end  502  of the piston  500  is a roughly conical indentation. In preferred embodiments, the piston  500  further includes a chamber  503  that extends from the vertex of the conical indentation  502  along the central axis of the piston  500 .  
         [0050]    The exterior of the distal section of the piston is preferably a flared portion  501 , terminating in an expansion cup rim  504 . In most preferred embodiments, the distal section of the piston further has a hollow expansion cup  505 . This expansion cup  505  is not in gaseous communication with the chamber  503  that extends from the proximate end  502  of the piston  500  along the piston central axis, as the chamber  503  does not extend entirely through the piston  500  to the expansion cup  505 .  
         [0051]    Referring to FIGS. 2 a  and  5 , the distal section of the piston  500  may be pressure-fit within the portion of the housing  201  of piston diameter  203 , such that the diameter of the expansion cup rim  504  of the piston  500  is substantially equivalent to the piston diameter  203  of the housing  201 . Alternatively, the diameter of the expansion cup rim  504  may be slightly less than the piston diameter  203  of the housing  201 . During use of the needle-less injector  100 , the expansion cup  505  may expand radially due to the force of compressed gas pushing upon it. This serves to optimize the performance of the piston  500 , as a substantially airtight seal is thus formed between the expansion cup rim  504  and the interior wall  212  of the housing  201 .  
         [0052]    The housing  201  may be fit with a diffuser  600 , as depicted in FIG. 6. The diffuser  600  is preferably affixed to the housing  201  along the interior wall  212  thereof at the portion of diffuser diameter  204 . Affixing may be performed by high frequency welding or other suitable means. Most preferably, the diffuser  600  is affixed to the housing  201  only after the plunger  400  and piston  500  have been fit within the housing  201 .  
         [0053]    The diffuser  600  preferably further contains at least one channel  601  that provides gaseous communication between the distal end  602  of the diffuser  600  and the base of the diffuser cup  603 . The at least one channel  601  is sized and positioned to optimize the injection delivery parameters of a particular liquid. In preferred embodiments, as illustratively depicted in FIG. 7, the diffuser  600  may contain between two and eight channels  601 , which may be of the same or different diameter, and may be symmetrically or non-symmetrically oriented about the central axis of the diffuser  600 . Selection of various combinations of channels  601  in the diffuser  600  will affect the delivery performance of the needle-less injector  100 , altering, for example, the initial acceleration of the driver of the needle-less injector  100 . The velocity of the driver of the preferred embodiment of the instant invention is depicted in FIG. 16. Notably, the compressed gas engine of the instant invention allows for a substantially constant delivery velocity during the bulk of the injection.  
         [0054]    Referring to FIG. 6 b,  a valve stem support depression  604  may further be included on the distal end  602  of the diffuser  600 , located at the diffuser central axis. The diffuser  600  may further contain a locking ring  605  around its outer circumference. Preferably the locking ring  605  is angled on its distal surface  606 , but is flat on its proximate surface  607 .  
         [0055]    The housing  201  may further be fit with a trigger  800 , as depicted in FIG. 8. The trigger  800  is preferably roughly cylindrical, to match the shape of the exterior wall  213  of the housing  201 . The distal end of the trigger  800  may have a depression  801  therein, and in preferred embodiments this depression  801  may further be textured for non-slip finger placement during operation of the needle-less injector  100 .  
         [0056]    The trigger  800  preferably contains at least one retainer hook mechanism  802  used both for securing the trigger  800  to the housing  201  and for mitigating the kickback associated with deploying the compressed gas stored in the engine housing  1000 . Without such a safety feature, the force created by release of gas stored in the engine housing  1000  may cause the engine assembly to separate from the remainder of the needle-less injector  100 , potentially resulting in both an improper injection and injury to the user.  
         [0057]    The at least one retainer hook mechanism  802  operably mates with the at least one latch retainer mechanism  218  located near the distal end of the housing  201  as the retainer hook  803  at the proximate end of the retainer hook mechanism  802  locks around consecutive saw tooth ridges  219  that preferably comprise the latch retainer mechanism  218 . In preferred embodiments, there are two retainer hook mechanisms  802 , located opposite one another on the trigger  800 , that spatially correspond to two latch retainer mechanisms  218  on the exterior wall  213  of the housing  201 .  
         [0058]    The at least one retainer hook mechanism  802  and at least one latch retainer mechanism  218  preferably prevent the trigger  800  from rotating about its central axis. In a most preferred embodiment, the sides  804  of the at least one retainer hook mechanism  802  fit around the sides  222  of the at least one latch retainer mechanism  218 , preventing such rotation.  
         [0059]    The housing  201  may further be fit with a safety clamp  900 , as depicted in FIG. 9. The safety clamp  900  prevents the needle-less injector  100  from being discharged accidentally. The safety clamp  900  is preferably roughly semi-cylindrical in shape to conform to the exterior wall  213  of the housing  201 , and resides around the exterior wall  213  of the housing  201  in the clamp indentation  220  that is defined on its proximate end by a ridge  221  and on its distal end by the at least one latch retainer mechanism  218  and the proximate end of the trigger  800  (see FIG. 1 b ). The safety clamp  900  preferably does not completely encircle the housing  201 , but rather encircles only at least half of the housing  201 , allowing for easy removal while preventing the clamp  900  from simply falling off of the injector  100 . Most preferably, the safety clamp  900  is constructed of a sufficiently elastic material such that temporarily deforming the clamp  900  permits removal thereof from the exterior wall  213  of the housing  201 . To aid in this removal, a grip  901  and feet  902  may be included on the safety clamp  900 .  
         [0060]    The housing  201  is preferably fit with an engine assembly  101 , as depicted in FIG. 1 b.  The engine assembly  101  may further contain an engine housing  1000 , as depicted in FIG. 10. The engine housing  1000  is preferably constructed of a material impermeable to a compressed gas stored therein, and has a hollow interior chamber  1003 . Most preferably, the engine housing  1000  is comprised of stainless steel or a similar metal. A compressed inert gas is preferably used to drive the needle-less injector  100  and is stored within the engine housing  1000  prior to use. The most preferred gas is carbon dioxide, though other suitable gases may be employed, as well. In most preferred embodiments, the engine assembly  101  is overcharged (i.e., excess compressed gas is stored therein) to allow for use at variable altitudes without hampering the performance characteristics of the needle-less injector  100 .  
         [0061]    The engine housing  1000  is preferably roughly cylindrical in shape to match the interior wall  212  of the housing  201 , though alternate configurations may be utilized. Referring to FIG. 10, the engine housing  1000  may have a portion of wide diameter  1001  and a portion of small diameter  1002 , wherein the portion of small diameter  1002  is proximate to the portion of wide diameter  1001 . The distal end of the engine housing  1000  may contain a circular depression  1004  and may rest against the trigger  800  (see FIG. 1 b ). The proximate end of the engine housing  1000  contains an opening  1005 , and in preferred embodiments, a closing ridge  1006  encircles the opening  1005 .  
         [0062]    The engine assembly  101  preferably further contains a valve body  1100 , as depicted in FIG. 11. The valve body  1100  is preferably roughly cylindrical in its overall shape, and more preferably resides at least partially within the engine housing  1000 . The valve body  1100  most preferably has a closing rim  1101  around its outer circumference that rests against the closing ridge  1006  encircling the opening  1005  of the proximate end of the engine housing  1000 . Most preferably, a closing ferrule  1200  is wrapped around both the closing rim  1101  and closing ridge  1006  to secure the valve body  1100  and engine housing  1000  to one another (see FIG. 1 b ).  
         [0063]    The closing ferrule  1200  is shown in FIG. 12 prior to its distal portion  1201  being mechanically bent around the closing rim  1101  and closing ridge  1006 . The proximate portion  1202  of the closing ferrule  1200  is of substantially the same diameter as the exterior of the valve body  1100 , such that solely bending the distal portion mechanically couples the valve body  1100  to the engine housing  1000 . In FIG. 1, the distal portion  1201  of the closing ferrule  1200  is shown in the bent state. The valve body  1000  preferably has a depression  1102  around its circumference adapted to fit a gasket  1103  (shown in FIG. 1 b ). The gasket  1103  helps ensure that an airtight seal is maintained between the interior of the engine housing  1000  which contains the gas and the internal atmosphere of the needle-less injector  100 .  
         [0064]    Referring to FIG. 11, the interior of the valve body  1100  is preferably hollow and comprised of several distinct portions. The distal interior portion  1104  of the valve body  1100  may contain a screw thread engagement  1105 , preferably extending from the distal end of the valve body  1100  to the distal end of a first axial cavity  1106 . The first axial cavity  1106  may be bounded on its proximate end by a shoulder  1107  that separates this first axial cavity  1106  from a second axial cavity  1108 , which is preferably of smaller diameter than the first axial cavity  1106 . In preferred embodiments, the shoulder  1107  is an angled edge. Also in preferred embodiments, at least one valve stem guide  1109  protrudes from the wall of the second axial cavity  1108 . In a most preferred embodiment, there are at least three such valve stem guides  1109  that serve to substantially prevent the valve stem  1400  from moving in any direction other than along the central axis of the needle-less injector  100  during administration of an injection.  
         [0065]    The proximate end of the second axial cavity  1108  preferably terminates at a diffuser-receiving chamber  1110  that is of sufficient diameter such that it encircles a distal end  602  of the diffuser  600 . After administration of an injection with the needle-less injector  100 , the distal end  602  of the diffuser  600  is most preferably at rest within the diffuser-receiving chamber  1110 .  
         [0066]    The proximate end of the diffuser-receiving chamber  1110  preferably has at least one grip  1111  extending therefrom. Preferably, the at least one grip  1111  locks around another suitable element of a needle-less injector  100  as the gripping element  1112  is situated on the interior side of the grip  1111 . In alternative embodiments, however, the at least one grip  1111  may lock within another element as the gripping element  1112  may be disposed on the exterior side of the grip  1111 . In most preferred embodiments, there are two grips  1111  disposed opposite one another each of which contains a gripping element  1112  situated on the interior side of the grip  1111  . In these most preferred embodiments, the two grips  1111  are slid over and lock around the locking ring  605  of the diffuser  600  upon administration of an injection. The combination of a locking ring  605  and grips  1111  assists in mitigating the kickback associated with deploying the compressed gas stored in the engine assembly  101  and ensures that a user fully and properly depresses the trigger  800 , since an injection is preferably not deployed until the grips  1111  slip past the locking ring  605 .  
         [0067]    The valve body  1100  preferably further contains a threaded valve guide  1300 , as depicted in FIG. 13. The threaded valve guide  1300  is preferably cylindrical in shape and threaded around its exterior wall  1301 , such that it may be screwed into the distal interior portion  1104  of the valve body  1100  by interacting with the screw thread engagement  1105 . Most preferably, the threading on the exterior wall  1301  of the threaded valve guide  1300  extends along the entirety of the exterior wall  1301  from the distal to the proximate end of the threaded valve guide  1300 . The threaded valve guide  1300  may also contain a cylindrical interior cavity  1302  that is unobstructed at the proximate end. The distal end, however, is preferably partially covered with a valve stem guide pane  1303 . The valve stem guide pane  1303  preferably provides at least one vent  1304  allowing gaseous communication between the interior cavity  1302  of the threaded valve guide  1300  and the hollow interior chamber  1003  of the engine housing  1000  at the distal end of the threaded valve guide  1300 . Also preferably, the valve stem guide pane  1303  includes a hole  1305  at the central axis slightly larger in diameter than the valve stem  1400  that resides therein. Most preferably, the valve stem guide pane  1303  further includes a spring seat  1306  on its proximate surface that is comprised of at least one ridge  1307  that maintains the valve spring  1500  in proper position.  
         [0068]    The valve body  1100  preferably further contains a valve stem  1400 , as depicted in FIG. 14. The valve stem  1400  is preferably comprised of a substantially cylindrical rod  1401  having a proximate end  1402  which is flat and a distal end  1403  which is preferably pressed or hammer-forged. The distal end  1403  is shown after hammer-forging in FIG. 14 a  and prior to hammer-forging in FIG. 14 b.  Most preferably, there is also included a spring ridge  1404  that extends radially from the rod  1401 , and a roughly conical valve head  1405  affixed to the proximate and exterior surfaces of the spring ridge  1404  as well as that portion of the rod  1401  immediately proximate to the spring ridge  1404 . Most preferably, the valve head  1405  is comprised of a rubber material such as semi-permeable, silicon-based rubber that is sufficiently malleable for use in accordance with the needle-less injector  100 . In most preferred embodiments, the angle between the proximate surface of the valve head  1405  and the central axis is substantially similar to the angle of the shoulder  1107  located between the first axial cavity  1106  and second axial cavity  1108  of the valve body  1100 .  
         [0069]    The valve body  1100  may further contain a valve spring  1500 , as depicted in FIG. 15. The valve spring  1500  is preferably composed of wire and semi-conical in shape, wherein the proximate end  1501  is smaller in diameter than the distal end  1502 . The proximate end  1501  of the valve spring  1500  preferably rests against the distal surface of the spring ridge  1404  on the valve stem  1400 , while the distal end  1502  of the valve spring  1500  preferably rests against the proximate surface of the valve stem guide pane  1303  and is held in place radially by the spring seat  1306 .  
         [0070]    Furthermore, the valve of the instant invention may be repeatedly opened and closed without being destroyed, thus it may be inspected for quality control determinations by opening and closing at least one time prior to the engine assembly  101  being filled with compressed gas. A faulty valve is a concern in any device employing such a mechanism, though it is of particular import in the context of a needle-less injector useful in medical applications, where such a faulty valve may result in the improper dosage of medication.  
         [0071]    During the administration of an injection with the needle-less injector, several mechanisms act to mitigate the kickback associated with releasing compressed gas from the engine housing. The grips on the valve body operatively couple with the locking ring on the exterior surface of the diffuser and the retainer hooks on the retainer hook mechanisms operatively lock at each successive saw tooth of the latch retainer mechanisms. Such safety features not only function to avoid potential injury, but further insure proper delivery of liquid through an injection surface.  
       EXAMPLE  
     Operation of a Needle-less Injector  
       [0072]    Prior to use, a needle-less injector is assembled in accordance with the instant invention, all elements thereof being gamma sterilized with the exception of the engine assembly. The engine assembly is checked for quality control purposes by opening and closing the valve, and thereafter the engine housing is filled with a suitable compressed gas. The interior portion of the housing between the proximate end of the housing and the proximate end of the plunger is then filled with 0.5 ml. of liquid. The needle-less injector is then assembled and stored for a prolonged period of time.  
         [0073]    When ready for use (see FIG. 1 a ), the ampoule cap is removed from the proximate end of the housing by the user. Subsequently, the user also removes the safety clamp by bending and/or distorting the clamp. The user is performing self-administration of an injection and elects to employ the following configuration: the user&#39;s index and middle fingers are placed in the arcs of the finger rests for stabilization of the device, with the thumb operably placed against the trigger. The proximate end of the needle-less injector is then positioned roughly perpendicular to the injection surface.  
         [0074]    The user then depresses the trigger until the proximate end of the trigger comes to rest against the ridge defining the proximate end of the clamp indentation. During this movement of the trigger, the retainer hook mechanisms and latch retainer mechanisms interact as the retainer hooks lock past consecutive saw teeth that comprise the latch retainer mechanisms.  
         [0075]    Forward, axial movement of the trigger causes the engine housing, valve body and threaded valve guide to move, as well. Thus, the grips at the proximate end of the valve body proceed to lock around the locking ring of the diffuser as the distal portion of the diffuser concurrently slides into and partially through the diffuser-receiving cavity of the valve body, coming to rest therein. Simultaneously, the valve stem moves along with the trigger, however, once it comes into mechanical contact with the valve stem support depression in the diffuser it remains stationary relative to the housing. The valve stem and diffuser reach such mechanical contact approximately when the grips slide over and past the locking ring of the diffuser.  
         [0076]    When the valve stem and diffuser come into mechanical contact, the valve spring is compressed and the valve opens as the valve head is separated from the shoulder residing between the first and second axial cavities of the valve body. Compressed gas (previously stored in the engine housing, the interior cavity of the threaded valve guide and the first axial cavity of the valve body) may then rush through the gap created between the valve head and the shoulder. The gas rushes through the second axial cavity, past the valve stem guides, through the diffuser-receiving chamber and through the at least one channel in the diffuser. The gas then fills the space defined by the diffuser cup and the expansion cup of the piston, which rest near or against one another prior to gas forcing the two elements apart. The introduction of gas into this space forces the piston in the proximate direction, pushing the plunger through the interior of the housing and correspondingly forcing the liquid from the injector through the at least one orifice in the proximate end of the injector and into and/or through the injection surface. The piston and plunger act in concert as a driver. Once the plunger comes to rest against the proximate end of the housing, excess gas may escape through the exhaust passage in the housing. The user may then dispose of the needle-less injector, the injection having been completed.  
         [0077]    While the description above refers to particular embodiments of the present invention, it should be readily apparent to people of ordinary skill in the art that a number of modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true spirit and scope of the invention. The presently disclosed embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than the foregoing description. All changes that come within the meaning of and range of equivalency of the claims are intended to be embraced therein.