Abstract:
An auto-injector confines all functional components inside an enclosed housing, to keep its needle out-of-sight, at all times. Within the housing, a needle holder positions a needle at a location. A drive mechanism then simultaneously engages the needle with a fluid source and accelerates it with a predetermined momentum for insertion into a patient. After fluid delivery, the withdrawn needle is moved to storage within the housing for subsequent disposal.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention pertains generally to systems and devices for using a needle to inject fluid medicaments into the body of a patient. More particularly, the present invention pertains to auto-injectors that can be used by a caregiver, or used individually by a patient to self-administer a fluid medicament. The present invention is particularly, but not exclusively, useful as a system and method for conveniently self-administering an injection without ever subjecting the user to a visual confrontation with the needle. 
       BACKGROUND OF THE INVENTION 
       [0002]    Injectable drugs are necessary for numerous medical reasons, and they are typically used in a wide variety of applications. Consequently, various types of drug delivery systems have been developed to meet the many diverse needs of particular medical procedures. With any injectable drug delivery system, however, both physical and psychological implications are involved. Both are important, and both deserve consideration. 
         [0003]    In general, all injectable drug delivery systems require some mechanical device or system that will drive or force a liquid into the body of a person or animal. Typically, this can be done in either of two ways. One way is to use a hypodermic needle. The other requires the use of a so-called needleless injector that relies on a liquid jet to create a hole in the skin. The liquid (i.e. fluid medicament) is then forced through the hole and into the body. Although needleless injectors are particularly efficacious for subcutaneous injections, they typically require excessive power to achieve the depth normally required for many intramuscular injections. With the above in mind, the focus here is on drug delivery systems that require the use of a hypodermic needle. 
         [0004]    The physical implications that are involved when a hypodermic needle is used with an injectable drug delivery system pertain primarily to the needle itself. The length, the diameter and the needlepoint characteristics of a hypodermic needle are all obvious considerations in this context. Collectively, during the development of an injectable drug delivery system, these considerations must be engineered to: 1) establish the proper depth of an injection; 2) avoid a tissue compression, that will either cause a deep injection or result in needlepoint deformation due to bone contact (i.e. “fish hook”); 3) minimize the dangers of handling needles; and 4) allow for effective insertion of the needle into the body. An improper engineering of some, or all, of these considerations may affect drug absorption rates or cause pain. Apart from these considerations, however, the psychological implications that result from using a hypodermic needle may be even more profound. This is particularly so when the fluid medicament is to be self-administered. 
         [0005]    Like the physical implications noted above, the psychological implications that are involved when a hypodermic needle is used with an injectable drug delivery system pertain primarily to the needle. Needle anxiety is real. For instance, many patients have a natural aversion to even the sight of a needle. Further, this aversion frequently evokes fear of injection site reactions (e.g. pain and bruising) that may, or may not, be real. And, when the injection needs to be self-administered, the task itself will often cause a hesitation or paralysis on the part of the user that prevents accomplishing a proper injection. In this context, it is known that “needle anxiety” has caused some patients to unnecessarily delay the beginning of a therapy regime for extended periods of time (e.g. several years). 
         [0006]    Several attempts have been made to overcome many of the aforementioned implications that are associated with injectable drug delivery systems. For one, there have been efforts to provide so-called auto-injectors that will automatically drive a needle attached to a syringe into the skin to perform an injection. Typically, this is a push-button operation that is accomplished without any direct manipulation of the injectors drive mechanism. Nevertheless, prior to use, auto-injectors invariably involve many complicated steps for set-up. And, after use, they require special disposal procedures for the needle. Unfortunately, these operations typically expose the user to a visual contact with a needle that can trigger “needle anxiety.” Also, injections with an auto-injector can be perceived to be more painful than a regular syringe injection due to the auto-injector&#39;s response to the drive mechanism actuation. Further, auto-injectors are typically not configured to conveniently provide for the sequence of multi-dose injections that may be required for many treatment regimes. 
         [0007]    In light of the above, it is an object of the present invention to provide an auto-injector that is convenient to use and that requires minimal manipulation before, during, and after an injection. Another object of the present invention is to provide an auto-injector that overcomes needle anxiety by keeping the needle(s) hidden from patient-view at all times. Still another object of the present invention is to provide an auto-injector that conveniently uses a “clip” or “magazine” of sterile needles to eliminate operating steps, and to allow a patient to follow a multi-dose treatment regime wherein a new sterile needle is automatically provided for each injection. Yet another object of the present invention is to provide an auto-injector that automatically captures used needles and stores them out-of-sight for a subsequent safe and simple disposal with regular trash. Another object of the present invention is to provide an auto-injector that is easy to use, is relatively simple to manufacture, and is comparatively cost effective and provides a comfortable injection. 
       SUMMARY OF THE INVENTION 
       [0008]    In accordance with the present invention, an auto-injector is provided that is effectively self-contained inside the interior of a housing. The intent here is to keep all operational components of the auto-injector, and most importantly its needle, out-of-sight and hidden from the view of the user. As envisioned for the present invention, this concealment of the needle is accomplished before, during and after an injection. To do this, the needles that are to be used with the auto-injector can be preloaded and supplied inside a casement (magazine, drum, etc.) for insertion into or for attachment to the auto-injector. The needle casement can then be used, and subsequently discarded as a unit without the user ever seeing or handling any of the needles. Some additional benefits of the present invention are also noteworthy. Specifically, with a completely enclosed operation, there is increased safety when using the auto-injector of the present invention. Moreover, each needle is used only once. This fact, alone, helps prevent contamination and insures that the structural integrity and lubricity of each needle are maintained until there is an actual use of the needle. 
         [0009]    Structurally, the auto-injector of the present invention is characterized by an external housing that encloses many operational components in its interior. In particular, a replaceable fluid reservoir (e.g. cartridge) can be mounted on the housing to provide a fluid medicament for injections into the user. As intended for the present invention, the fluid reservoir may contain either a single dose of the desired fluid medicament, or multiple doses of the medicament. Also mounted onto the housing is a magazine, or clip, that holds a plurality of sterile needles. Further, a drive mechanism for inserting a needle into the patient is mounted in the interior of the housing. These components then interact with each other inside the housing via a connector and a needle holder. Specifically, the needle holder is used to operationally position the needle for connection with the connector, and the connector is used to connect the needle in fluid communication with the fluid reservoir. The needle/connector combination then cooperates with the drive mechanism to insert the needle into the user. 
         [0010]    As envisioned for the present invention, the needle will typically be an elongated hypodermic needle that has both a sharp distal end and a sharp proximal end. Additionally, the needle will include a circular collar that is mounted on the needle between its proximal and distal ends. More specifically, the collar will preferably be disk shaped and will extend radially from the axis of the hypodermic needle. 
         [0011]    In detail, the connector of the present invention includes a fluid transfer section that is formed with a fluid chamber that has an input port and an output port. A septum, that is preferably made of an elastomeric material, is used to cover the output port and provide for fluid communication with the fluid chamber when it is penetrated. On the other hand, the input port is connected to a flexible hose that is provided to join the fluid chamber of the transfer section in fluid communication with the fluid medicament reservoir. 
         [0012]    The needle holder that is used for the present invention can generally have either of three embodiments. In one embodiment, the holder is positioned in the interior of the housing and it is substantially cylindrical-shaped. It will also define at least three separate stations and, as the holder is rotated inside the housing, it will assume three different operational orientations. Specifically, during a rotation, each station will sequentially move from a position where it retrieves a sterile needle from the magazine, to a second position where the needle is presented for engagement with the connector, and then to a third position where the used needle is placed in storage. In another embodiment, the holder is positioned inside the housing to move a sterile needle along predetermined paths. Specifically, this involves moving a needle from the magazine, along a first path, and into a position for engagement with the connector. After the needle has been used, the holder then moves the needle along a second path to a storage location inside the housing. With this embodiment, the holder sequentially handles each needle individually. In yet another embodiment, the holder can be a cassette that is pre-loaded with a plurality of needles. The cassette can then be loaded onto the housing and rotated to sequentially position a needle for engagement with the connector. 
         [0013]    In operation, the user of the auto-injector (i.e. patient) positions the housing of the auto-injector against his/her body at the desired injection site. The user then pushes a button and waits a few seconds while the injection is performed. The housing is then removed from the injection site. At no time does the user see a needle during this operation. 
         [0014]    Inside the housing, before the user pushes the button to initiate operation of the auto-injector, the needle holder positions a sterile needle at a location in the housing for engagement with the fluid transfer section of the connector. Once the needle is so positioned, the user pushes the button to initiate operation and the drive mechanism releases a drive rod that is accelerated into contact with the fluid transfer section. The consequent transfer of momentum causes the proximal end of the needle to penetrate through the septum of the transfer section to establish fluid communication between the needle and the fluid reservoir. Further, in addition to the momentum that is transferred from the drive mechanism, forces from the drive rod can also cause the needle to be inserted into the patient for performing the injection. Once the needle is inserted into the patient (user), a plunger is advanced into the fluid reservoir to expel a dose of fluid medicament therefrom through the connector and needle, and into the patient. The needle is then subsequently withdrawn from the patient (user) and is moved by the needle holder for storage. At this point, another needle can be positioned at the location for another injection operation. 
         [0015]    It is to be appreciated that the collar on the needle can be caused to interact with the housing during an operation of the auto-injector to limit the depth to which the needle will penetrate into the patient (user). It is also to be appreciated that the auto-injector of the present invention may include a vacuum system that can be activated to stabilize the skin of the patient at the injection site, to thereby provide for a more predictable injection. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which: 
           [0017]      FIG. 1  is a view of a patient using an auto-injector in accordance with the present invention; 
           [0018]      FIG. 2  is a schematic diagram of the operational components of the auto-injector of the present invention; 
           [0019]      FIG. 3  is a perspective view of a needle in accordance with the present invention; 
           [0020]      FIG. 4  is a top plan view of an embodiment of a needle holder for use with the present invention; 
           [0021]      FIG. 5  is a top plan view of an alternate embodiment of a needle holder for use with the present invention; 
           [0022]      FIG. 6  is a perspective view of another alternate embodiment of a needle holder for use with the present invention; 
           [0023]      FIG. 7  is a cross-section view of a connector for use with the present invention; 
           [0024]      FIG. 8A  is an elevation view of the drive mechanism, needle and connector, in combination with the fluid reservoir of the present invention (with portions shown in cross-section for clarity) prior to an injection; and 
           [0025]      FIG. 8B  is an elevation view of the same components shown in  FIG. 8A  during an injection. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]    Referring initially to  FIG. 1 , an auto-injector  10  in accordance with the present invention is shown being used by a patient (user)  12  for a self-administration of a fluid medicament. As can be seen in  FIG. 1 , the auto-injector  10  includes a push-button  14  that extends from the external housing  16  of the auto-injector  10  to be depressed by the user  12  to initiate an injection. As envisioned for the present invention, all of the operational components of the auto-injector  10  are maintained out-of-sight, inside the housing  16 . 
         [0027]    Referring now to  FIG. 2  it will be seen that the internal components located in the interior  17  of the housing  16  of the auto-injector  10  include a controller  18  that is connected with the push-button  14 . In turn, the controller  18  is connected to a drive mechanism  20 , to a fluid reservoir (e.g. a fluid medicament cartridge)  22  and, optionally, to a vacuum system  24 . As envisioned by the present invention, the controller  18  may be an electronic micro-computer of a type well known in the pertinent art. In any event, the purpose of the controller  18  is to coordinate the respective operations of the drive mechanism  20 , the fluid reservoir  22 , the vacuum system  24  and the needle holder  28 . 
         [0028]      FIG. 2  also shows that the drive mechanism  20  is directly involved with the operations of a connector  26  and a needle holder  28 . To understand the structure and inter-cooperation of these components, however, it is necessary to structurally understand the needle unit (i.e. needle)  30  that is to be manipulated by these components. For this purpose, refer to  FIG. 3 . There it will be seen that a needle unit  30  includes an elongated, hollow hypodermic tube  32  that has a sharp proximal end  34  and a sharp distal end  36 . Further, the needle unit  30  also includes a collar  38  that is positioned and affixed on the tube  32  intermediate the ends  34  and  36 . More specifically, the collar  38  is generally disk-shaped, and it extends in a radial direction from the axis that is defined by the hypodermic tube  32 .  FIG. 3  also shows that the distal end  36  of the tube  32  is located at a distance “l” from the collar  38 . 
         [0029]    In  FIG. 4  an embodiment of the needle holder  28  is shown, and is generally designated  40 . This particular embodiment  40  of the needle holder  28  is provided to move a needle unit  30  from a magazine  42 , and to then subsequently move it to a storage location  44 . To do this, the embodiment  40  includes an arm  46  that rotates about a point  47 . A grip  48  is located at one end of the arm  46 . Thus, as the arm  46  is rotated back and forth in the direction of the arrows  50 , the grip  48  can, in sequence, retrieve a needle unit  30  from the magazine  42  and then move it along a path  52  to a location (shown as needle unit  30 ′). At this location, the needle unit  30 ′ is positioned to cooperate with the connector  26 . After its cooperation with the connector  26 , needle unit  30 ′ is then moved by the grip  48  along a path  54  to the storage location  44  (i.e. needle unit  30 ″) where it will be stored for subsequent disposal. 
         [0030]      FIG. 5  shows another embodiment of the needle holder  28  that is generally designated  56 . For the embodiment  56  of the needle holder  28 , a carousel  58  is employed to move the needle unit  30  into location for cooperation with the connector  26 . More specifically, for the embodiment  56  a needle unit  30  is retrieved from the magazine  42  and moved along path  52  onto the carousel  58 . The carousel  58  then rotates in the direction of the arrow  60  to the location of needle unit  30 ′ where it cooperates with the connector  26  (see  FIG. 7 ). After its cooperation with the connector  267  the needle unit  30 ′ is then moved by the carousel  58  for further movement along a path  54  to the storage location  44  (shown as needle unit  30 ″). There it will be stored for subsequent disposal. 
         [0031]    In  FIG. 6 , a cassette  61  is shown as yet another embodiment of the needle holder  28 . Specifically, the cassette  61  is generally cylindrical shaped, as shown, and it is formed with a plurality of receptacles  63 . As intended for the present invention, individual needle units  30  can be pre-loaded into respective receptacles  63  of the cassette  61 , prior to engaging the cassette  61  with the housing  16 . When used, the cassette  61  is rotated about the axis  65  to present an individual needle unit  30  at the location for cooperation with the connector  26 . Thus, the cassette  61  effectively combines the functionality of the needle holder  28 , the magazine  42  and the storage  44  into a single structure. It is to be appreciated that all of the embodiments of the needle holder  28  (i.e. embodiments  40  and  56 , as well as cassette  61 ) are unitary components of the auto-injector  10 . As such, they can be selectively engaged with the auto-injector  10  and, along with the spent needle units  30 , individually disposed of after they have been used. 
         [0032]    Respective structures for the fluid reservoir  22 , for the drive mechanism  20 , and for the connector  26  will be best appreciated with reference to both  FIG. 7  and  FIG. 8A . Considering the fluid reservoir  22  first, it will be seen that the reservoir  22  includes a vial  62  for holding a fluid medicament  64  therein. A septum  66 , at one end of the vial  62 , is provided to establish fluid communication with the reservoir  22  whenever it (i.e. the septum  66 ) is penetrated. It will be appreciated, however, that any other mechanism well known in the pertinent art for establishing a fluid connection can be used for this purpose, such as a Luer fitting. The fluid reservoir  22  also includes a bung  67  that can be advanced by a plunger  68  into the vial  62  for purposes of expelling fluid medicament  64  from the reservoir  22  through a penetrated septum  66 . As envisioned for the present invention, the fluid reservoir  22  can be a pre-filled cartridge that can hold either one, or multiple doses of the fluid medicament  64 . Further, the plunger  68  can be calibrated to establish a specific dosage of fluid medicament  64 , each time it advances the bung  67 . 
         [0033]    The drive mechanism  20  for the auto-injector  10  is shown in  FIG. 8A  to include a drive rod  70  that is selectively propelled by a compressed spring  72  in a linear direction indicated by the arrow  74 . It will be appreciated by the skilled artisan that the actual mechanism for propelling the drive rod  70  can vary. In this context, the spring  72  is only exemplary. It is important for the present invention, however, that the propulsion of the drive rod  70  by the drive mechanism  20  develops a predetermined momentum for the drive rod  70  (see OPERATION below). 
         [0034]    Referring specifically to  FIG. 7 , it will be seen that the connector  26  includes a fluid transfer section  76  that is formed with a fluid chamber  78 . Further, the fluid transfer section  76  has an input port  80  to the fluid chamber  78 , and it has an output port  82  that is covered by a septum  84 .  FIG. 7  also shows that the connector  26  includes a flex hose  86  that has one end connected for fluid communication with the input port  80  of the fluid transfer section  76 . As also shown, the other end of the flex hose  86  is fitted with a spike  88  that can be used to penetrate the septum  66  of the fluid reservoir  22 . For another aspect of the present invention,  FIG. 8A  shows that the housing  16  of auto-injector  10  can be formed with a vacuum depression  90  that is placed in fluid communication with the vacuum system  24  (see  FIG. 2 ) via a vacuum hose  92 . 
       Operation 
       [0035]    In the operation of the auto-injector  10  of the present invention, after setting a desired dose of the fluid medicament  64  to be delivered, the user (patient)  12  will position the housing  16  against an injection site  94 . The user  12  then depresses the push-button  14 . After a predetermined time interval, the user  12  removes the auto-injector  10  from the injection site  94 , and the injection of fluid medicament  64  into the user (patient)  12  has been completed. At no time, either before, during or after an injection, is any part of a needle unit  30  ever visible to the user  12 . Furthermore, other than an earlier loading of the fluid reservoir  22 , engaging the reservoir  22  with connector  26 , and loading a magazine  42  of needle units  30 , only a dose setting may be required before the auto-injector  10  is used. There is nothing for the user  12  to do after the injection has been completed except, perhaps, to put a cover (not shown) over the housing  16 . 
         [0036]    Referring back to  FIG. 2 , it will be appreciated that as the user  12  depresses the push-button  14 , several mechanisms inside the housing  16  are sequentially activated by the controller  18 . For one, the needle holder  28  (with either embodiment  40  or, alternatively, embodiment  56 ) retrieves a needle unit  30  from the magazine  42 . The needle holder  28  then moves the needle unit  30  into the position indicated in the drawings as needle unit  30 ′ (see  FIG. 8A  in particular). Prior to this, the connector  26  has been connected in fluid communication with the fluid reservoir  22 . Specifically, this connection is made by inserting the spike  88  on flex hose  86  through the septum  66 . At this point, with the needle unit  30 ′ in position, the drive mechanism  20  comes into play. 
         [0037]    It is an important aspect of the operation of the auto-injector  10  of the present invention, that the drive mechanism  20  propels the drive rod  70  toward the connector  26  (e.g. fluid transfer section  76 ) with a predetermined momentum. Specifically, in accordance with well known impulse and momentum considerations, this predetermined momentum will be determined by the mass of the drive rod  70  and its velocity (predetermined momentum=m rod v rod ). As intended for the present invention, when the drive rod  70  impacts with the connector  26 , its momentum (m rod v rod ) is then transferred to the fluid transfer section  76  of the connector  26 . Note: the flex hose  86  mechanically isolates the transfer of momentum to only the fluid transfer section  76 . This transfer of momentum will then immediately accomplish several functions. For one, part of the momentum is used to establish fluid communication between the fluid transfer section  76  of the connector  26  and the needle unit  30 . This is accomplished as the proximal end  34  of the hypodermic tube  32  penetrates through the septum  84 . The remaining momentum that is now determined by the velocity (v f ) of the combined mass (m combined ) of the fluid transfer section  76  and the needle unit  30 . Importantly, the velocity term (v f ) of this remaining momentum must be sufficient to cause the distal end  36  of the needle unit  30  to penetrate into the user (patient)  12  at the injection site  94  (see  FIG. 8B ). As appreciated by the present invention, the velocity that is necessary for generating the necessary predetermined momentum of the drive rod  70  need not result in an excessively high velocity for the needle unit  30 . To the contrary, the intent here is to generate a so-called “light touch” that will guarantee only that an effective penetration of the needle unit  30  is achieved. A benefit here is that the possibility of creating pain or bruising at the injection site  94  is minimized. Additional benefits are that by minimizing the final momentum there is less shock to the user  12 , due to reduced recoil, and there is a reduced need for energy input. 
         [0038]    Once the needle unit  30  has penetrated the user (patient)  12  at the injection site  94 , the controller  18  will then activate the fluid reservoir  22 . Specifically, with this activation, the bung  67  is advanced into the vial  62  to expel fluid medicament  64  into the injection site  94 . When doing this, the fluid medicament  64  traverses the flex hose  86 , and enters the hypodermic tube  32  of needle unit  30  through the fluid transfer section  76 . Once the injection has been completed, the needle unit  30  is withdrawn from the injection site  94 . The needle holder  28  then moves the needle unit  30  to storage  44 . At this point, the auto-injector  10  is rearmed and another cycle can then be performed. Once the magazine  42  is empty of needle units  30 , it can be disposed of. Likewise, when the fluid reservoir  22  has been emptied of fluid medicament  64 , it is ready for disposal. In some instances it may also be desirable to dispose of the connector  26 . 
         [0039]    Further to the above disclosure, it will be appreciated that the vacuum system  24  can be activated during a use of the auto-injector  10  to help stabilize the auto-injector  10  at the injection site  94  and avoid tissue compression. Specifically, when a partial vacuum is created in the vacuum depression  90  that is established as housing  16  is positioned against the injection site  94 , skin from the user (patient)  12  will be drawn into the depression  90  (see  FIG. 8B ). This will help stabilize the auto-injector  10  during an injection without the need to push the auto-injector  10  against the skin and, thereby, compress tissue. Further, the depth to which the distal end  36  of needle unit  30  will penetrate into the user (patient)  12  can be controlled, and varied as desired. In general, penetration depths of up to around one and a half inches are considered typical. In each case, a precise penetration depth is achieved by establishing the distance “e” between the collar  38  and distal end  36  of the needle unit  30  (see  FIG. 3 ). More specifically, this distance “l” of needle unit  30 , and the location of an adjustable abutment  96  on the housing  16  will establish a travel limit for the collar  38  and needle unit  30 . Consequently, a precise penetration depth can be established for the hypodermic tube  32  of the needle unit  30 . 
         [0040]    Referring again to  FIG. 8A , it will be seen that the auto-injector  10  includes a recoil mechanism  98 , such as a spring, that is positioned on the abutment  96  substantially as shown.  FIG. 8A  also shows that the auto-injector  10  includes a cocking mechanism  100  that responds to instructions from the controller  18  and is used to rearm the auto-injector  10  in preparation for a subsequent injection cycle. In operation, the recoil mechanism  98  and the cocking mechanism  100  interact with the needle unit  30  in different ways. These different operations are, perhaps, best appreciated by first considering  FIG. 8B . 
         [0041]    With reference to  FIG. 8B  it will be seen that during an injection (i.e. after an injection cycle has been started) the spring  98  is depressed between the abutment  96  and the collar  38  of needle unit  30  ( 30 ′). While it is depressed, the spring  98  reacts against the force that is being applied by the drive spring  72  and by the drive rod  70 . The depressed spring  98 , however, does not overcome the combined forces that are applied by spring  72  and drive rod  70 . Therefore, during an injection, the distal end  36  of needle unit  30  remains inserted at the injection site  94 . Indeed, it may be desirable for the distal end  36  to remain inserted at the injection site  94 , even after the injection of fluid medicament  64  is completed. If so, the controller  18  can be programmed to delay the activation of cocking mechanism  100  for the withdrawal of the distal end  36  of needle unit  30  from the injection site  94 . This delay can be for any predetermined period of time (e.g. five seconds). 
         [0042]    As indicated above, the cocking mechanism  100  is used to return the drive rod  70  and its drive spring  72  from their respective positions shown in  FIG. 8B  (i.e. during an injection) to those shown in  FIG. 8A  (i.e. preparatory to an injection). It also happens that this action returns the fluid transfer section  76  and the needle unit  30  to their positions shown in  FIG. 8A . To help insure that this withdrawal is accomplished without complication, the depressed spring  98  assists in lifting the distal end  36  of needle unit  30  from the injection site  94 . The needle unit  30  can then be separated from the fluid transfer section  76 . Importantly, the now-used needle unit  30  can be removed from its location between the fluid transfer section  76  and the abutment  96 , and replaced with a new sterile needle unit  30 . The sequence of operation can then be repeated, until the supply of needle units  30  that has been loaded into the auto-injector  10  is exhausted. 
         [0043]    While the particular Injection System with Hidden Needles as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.