Abstract:
An auto-injector for injecting a fluid medicament into a patient from a pre-filled syringe requires a disposable cassette that is selectively engageable with the reusable injector. The syringe is latched onto the cassette, and the cassette is then engaged with the injector. Activation of the injector causes a first motor to move the syringe so its needle is extended from a concealed position inside the cassette for injection of the medicament. A second motor on the injector is then activated to expel fluid medicament from the syringe. Then, the first motor is again activated to withdraw the syringe into the cassette for disposal of the cassette/syringe after an injection.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention pertains generally to systems and methods for injecting fluid medicaments into a patient from a syringe. More particularly, the present invention pertains to auto-injectors that conceal the injection needle of a hypodermic syringe before, and after an injection. The present invention is particularly, but not exclusively, useful as a system and method that employs a bifurcated drive mechanism wherein one motor moves the entire syringe for an injection, and another motor moves the syringe plunger for expelling a fluid medicament from the syringe. 
       BACKGROUND OF THE INVENTION 
       [0002]    In order to inject a fluid medicament into a patient when using a hypodermic syringe, three separate and distinct tasks must be performed. These are: 1) insertion of the needle into the patient; 2) injection of the fluid medicament from the syringe into the patient; and 3) withdrawal of the needle after the injection has been completed. For each task, the magnitude and direction of forces on the syringe, as well as the location of their application, are different from the other tasks. For instance, compare the task of inserting the needle, with the task of injecting the fluid medicament. Insertion of the needle requires that only minimal forces be applied on the syringe, and that they be applied for only a very short period of time. On the other hand, injection of the medicament requires a much greater force be applied. Further, this force must be applied on the plunger of the syringe for what will typically be a relatively longer period of time. In comparison with both of these tasks, needle withdrawal requires the application of a force in the opposite direction. These, and other similar considerations, become important when the injection process is to be automated. 
         [0003]    Springs for generating forces on a syringe in an automated process have been used heretofore for various purposes. A characteristic of springs, however, is that the magnitude and direction of a spring force are not variable. Consequently, springs do not lend themselves for so-called “multi-tasking” operations. This is particularly so where precise control over a syringe injection operation is required, and different magnitude forces are sequentially required in the same direction (e.g. needle insertion and medicament injection). 
         [0004]    In addition to the mechanical considerations mentioned above, the design of an auto-injector also requires “user-friendly” considerations. In particular, it is desirable that the injection needle of a syringe be operationally concealed from the view of a user. Preferably, this concealment can be maintained before, during and after an injection procedure. Further, it is desirable that operation of the syringe be limited to only those times when the syringe is properly positioned for an injection. 
         [0005]    In light of the above, it is an object of the present invention to provide a two-motor device for performing the injection of a fluid medicament into a patient wherein each motor generates different forces on a hypodermic syringe for different purposes. Another object of the present invention is to provide a reusable injector that can be operationally engaged with a disposable, pre-filled syringe. Still another object of the present invention is to provide an auto-injector system wherein the needle of a pre-filled syringe is operationally concealed and the system is operable only when the injector is properly positioned against the skin of a patient for an injection. Another object of the present invention is to provide a system and a method for automatically injecting a fluid medicament from a pre-filled syringe that is relatively simple to manufacture, is easy to use and is comparatively cost effective. 
       SUMMARY OF THE INVENTION 
       [0006]    In accordance with the present invention an autoinjector system includes a disposable cassette that operates in combination with a reusable injector. Prior to an engagement of the cassette with the injector, however, a pre-filled syringe is mounted and latched onto the cassette. When latched, the syringe is held on the cassette in a so-called “home position”. For the present invention, this pre-filled syringe may be of any type syringe well-known in the pertinent art that has a fluid chamber with an injection needle at its distal end, and a plunger that can be advanced into the fluid chamber. When the cassette, with syringe, is engaged with the injector, the system is ready for use. 
         [0007]    Operation of the system of the present invention requires two separate motors that are individually mounted on the injector. Though they are mechanically independent of each other, the respective operations of these two motors must be coordinated. Specifically, a first motor is used to effect movements of the entire syringe assembly (i.e. syringe chamber, injection needle and plunger are all moved together). On the other hand, a second motor is employed to advance the plunger into the fluid chamber for performing an injection of a fluid medicament. 
         [0008]    In a duty cycle of the system, the first motor moves a drive rod into engagement with the syringe. With this engagement, the drive rod also releases the latch that otherwise holds the syringe in its “home position.” After the syringe has been released, the first motor then advances the syringe in a distal direction on the cassette. This movement inserts the injection needle into a patient. Further, the first motor can be used to abruptly stop the needle when a specified needle depth has been achieved. The first motor can then be used to help stabilize the needle during an injection of the medical medicament from the syringe. 
         [0009]    As mentioned above, the injection of medical medicament from the syringe is accomplished using the second motor. In detail, once the needle has been properly inserted into the patient, the second motor moves a pusher to urge against the plunger of the syringe to advance the plunger into the fluid chamber of the syringe. Importantly, the second motor can be programmed to advance the plunger into the fluid chamber at a predetermined rate(s) for compliance with an injection protocol. 
         [0010]    After the injection has been completed, the second motor withdraws the pusher. The first motor is then used again. Specifically, the first motor is now used to withdraw the injection needle from the patient, and to return the syringe to its “home position” on the cassette, where it is re-latched onto the cassette. The cassette can then be removed from the injector and discarded. 
         [0011]    In order to control the concerted operations of the first and second motors, the system includes a microcomputer that is mounted on the injector. Importantly, the microcomputer operates the motors with different forces, and at different speeds for different purposes. More specifically, the first motor must operate quickly to insert the needle (e.g. 0.1 to 1 m/s), but it does not require much force to do so. Similarly, needle withdrawal by the first motor requires a minimal force. Unlike the first motor, however, the second motor will typically be required to generate greater forces for the injection of fluid medicament. And, accordingly, it will also typically operate at slower speeds. Further, and most importantly, different injections (i.e. advancements of the syringe plunger by the second motor) may require different injection rates. Thus, the second motor requires speed control provided by the microcomputer. 
         [0012]    Together with the components mentioned above, the system of the present invention may, optionally, employ a capacitance skin sensor of a type well known in the pertinent art. If used, such a sensor will allow the user to ascertain whether the system has been properly positioned for an injection. In detail, a metal foil is positioned at the extreme distal end of the injector to establish a capacitance signal whenever the foil is in contact with a skin surface of the patient. The function of this signal is actually two-fold. First, it can be used to prevent initial operation, if the system is not properly positioned. And, second, it can be used to interrupt operation of the system, if it becomes improperly positioned during an injection. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    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: 
           [0014]      FIG. 1  is a perspective view of an autoinjector system showing a cassette engaged with an injector in accordance with the present invention; 
           [0015]      FIG. 2  is an exploded perspective view of the cassette and its component elements for use with the present invention; 
           [0016]      FIG. 3A  is a perspective view of a cassette and a drive assembly of the system in position at the beginning and at the end of a duty cycle; 
           [0017]      FIG. 3B  is a view of the components shown in  FIG. 3A  with the syringe in the cassette being advanced by a first motor of the drive assembly for insertion of the syringe needle into a patient; and 
           [0018]      FIG. 3C  is a view of the components shown in  FIG. 3B  with the plunger in the syringe being advanced by a second motor of the drive assembly for injection of a fluid medicament from the syringe into the patient. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    Referring initially to  FIG. 1 , an autoinjector system in accordance with the present invention is shown and is generally designated  10 . As shown, the system  10  essentially includes a disposable cassette  12  and a re-useable injector  14 . Further, as shown in phantom in  FIG. 1 , a drive assembly  16  and a microcomputer  18  are mounted inside the injector  14 . As intended for the present invention, the microcomputer  18  is activated by depression of the button  20  on the injector  14 . And, when activated, the microcomputer  18  controls the operation of the drive assembly  16  for its interaction with the cassette  12 . 
         [0020]    In  FIG. 2  it will be seen that the cassette  12  includes a housing  22 , a sleeve member  24  and a syringe assembly  26 . More specifically, the syringe assembly  26  is of a type well-known in the pertinent art that has a syringe chamber  28  for holding a fluid medicament. The syringe assembly  26  will also have an injection needle  30 , and a plunger  32  that is moveable within the syringe chamber  28  to expel fluid medicament from the syringe chamber  28  through the injection needle  30 .  FIG. 2  also shows that the syringe assembly  26  is formed with an orifice  34  that allows for contact with the plunger  32  for the stated purpose. As intended for the present invention, the syringe assembly  26  is fixedly joined with the sleeve member  24  and this combination (i.e. syringe assembly  26  and sleeve member  24 ) is incorporated with the housing  22  to establish the cassette  12 . 
         [0021]    Still referring to  FIG. 2 , it will be seen that the sleeve member  24  includes a protrusion  36 . Further, it will be seen that the housing  22  is formed with a fixation member  38  that is dimensioned for engagement with the injector  14  (see  FIG. 1 ). As is to be appreciated by the skilled artisan, the fixation member  38  engages with the injector  14  to position the cassette  12  in an operational alignment with the drive assembly  16 . Importantly, the cassette  12  can be fixedly held on the injector  14  during an operation duty cycle of the system  10 , and selectively removed from the injector  14  after its use. 
         [0022]      FIG. 2  also shows that the housing  22  is formed with a latch mechanism  40 . In detail, the latch mechanism  40  includes a pair of opposed, resilient arms  42   a  and  42   b  that are respectively formed with a detent  44   a  and  44   b . As shown, the resilient arms  42   a  and  42   b  straddle a slot  46  that extends along the side  48  of the housing  22 . 
         [0023]    An important aspect of the present invention involves the assembly of the cassette  12  into an integral unit. When assembled, it is to be appreciated that the cassette  12  is intended for use only so long as there is fluid medicament in the syringe chamber  28  and, it is thereafter disposable. Prior to assembly, the syringe assembly  26  will have a pre-filled syringe chamber  28  holding a defined dose. The pre-filled syringe assembly  26  is then inserted into the sleeve member  24  where it is fixedly held. Movements of the sleeve member  24  will thus result in a corresponding movement of the syringe assembly  26 . The combination (i.e. syringe assembly  26  and sleeve member  24 ) is then joined with the housing  22 . When so joined, the protrusion  36  on sleeve member  24  fits in the detents  44   a  and  44   b  between the resilient arms  42   a  and  42   b . Accordingly, the syringe assembly  26  is held on the cassette  12  in a so-called “home position”. Importantly, with the syringe assembly  26  in the “home position”, the injection needle  30  of the syringe assembly  26  is held, and concealed within the housing  22 . In this configuration, the cassette  12  can be engaged with the injector  14  substantially as shown in  FIG. 1 . 
         [0024]    For an operation of the system  10 , reference is directed collectively to  FIGS. 3A ,  3 B and  3 C. Although the injector  14  is not shown in these Figs., it is to be appreciated that the cassette  12  and the drive assembly  16  are to be considered as being operationally mounted on the injector  14  (i.e. cross-reference  FIGS. 3A ,  3 B and  3 C with  FIG. 1 ). Further, in greater detail, the drive assembly  16  is shown in  FIG. 3A  to include a first motor  50  that is used to move a drive rod  52 . Also, a second motor  54  is shown that is used to move a pusher  56 . For purposes of the present invention, the motors  50  and  54  can be of any type well known in the pertinent art. Furthermore, the respective movements of drive rod  52  and pusher  56  can be provided by any well known mechanical device such as a lead screw or a rack-and-pinion. As noted above, the operations of the first motor  50  and the second motor  54  are both controlled by the microcomputer  18 . 
         [0025]    In overview, a duty cycle for the system  10  can be envisioned as a series of sequential changes in the configuration of cassette  12 . For system  10 , these configuration changes are caused by separate operations of the first motor  50  and the second motor  54 . In compliance with these operations, a complete duty cycle for the system  10  will constitute, in order, configurations shown from  FIG. 3A , to  FIG. 3B , to  FIG. 3C , and then in reverse order from  FIG. 3C , back to  FIG. 3B  and  FIG. 3A . 
         [0026]      FIG. 3A , shows the cassette  12  with the syringe assembly  26  in its “home position.” Importantly, in this “home position” the protrusion  36  on sleeve member  24  is held by the latch mechanism  40  on housing  22 . And, consequently, the injection needle  30  of the syringe assembly  26  is held and concealed within the cassette  12 .  FIG. 3B  shows the cassette  12  with the syringe assembly  26  moved into an advanced position wherein the injection needle  30  has been extended from the cassette  12  through a hole  58  at the distal end  60  of the system  10  (see  FIG. 1 ). It is to be appreciated that during the movement from  FIG. 3A  to  FIG. 3B , the first motor  50  advances the drive rod  52 . Specifically, with this advancement, the drive rod  52  interacts with latch mechanism  40  to release protrusion  36 , and to thereby allow a distal movement of the now “unlatched” syringe assembly  26  and sleeve member  24  on the housing  22 . Specifically, this movement is controlled by the microcomputer  18  and is performed with sufficient force to allow the injection needle  30  to penetrate into the tissue of a patient. Preferably, this movement of the syringe assembly  26  from the “home position” ( FIG. 3A ) to the advanced position ( FIG. 3B ) is accomplished at a speed of approximately 0.1 to 1 m/s. Further, the first motor  50  can be pre-programmed to stabilize the syringe assembly  26  in its advanced position. 
         [0027]    With the syringe assembly  26  in its advanced position ( FIG. 3B ), microcomputer  18  then activates second motor  54  to move pusher  56  against the plunger  32  in syringe chamber  28  (see  FIG. 2 ). Again, microcomputer  18  is in control and, in this case, can be pre-programmed to advance the plunger  32  at an appropriate speed for injection of the fluid medicament from the syringe chamber  28 . At the completion of the injection, the respective configurations of the cassette  12  and the drive assembly  16  are as shown in  FIG. 3C . As mentioned above, completion of the injection duty cycle requires the pusher  56  be withdrawn. This withdrawal of the pusher  56  is accomplished by the second motor  54 . Once the pusher  56  has been withdrawn (see  FIG. 3B ), the first motor  50  is again activated to withdraw the drive rod  52 . The drive rod  52  then pulls the protrusion  36  back for engagement with the latch mechanism  40 , and the syringe assembly  26  is thus returned to its “home position.” The cassette  12  can then be removed from the injector  14  and discarded. 
         [0028]    As an additional feature of the system  10 , a sensor  62  can be provided at the distal end of the injector  14 . In particular, the sensor  62  should be positioned adjacent the hole  58  of cassette  12 . For purposes of the present invention, the sensor  62  is preferably of a type that will react to capacitance that can be measured between the sensor  62  and the skin of the patient. The purpose of this sensor  62  is to establish that the system  10  is in physical contact with the patient. Specifically, the microcomputer  18  will operate a duty cycle for the system  10  only when such contact is indicated. Otherwise, there can be no operation of the system  10 . 
         [0029]    While the particular System and Method for an Injection Using a Syringe Needle 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.