Manually inserted power injector and method of use

Abstract

The automatic injector includes a front housing that holds a syringe and an actuation cap that covers the syringe needle, and a rear housing that includes a drive assembly for automatically delivering one or more medicaments from the syringe when the device is actuated. The rear housing includes a gas canister and an opener mechanism for opening the canister to a set of chambers in an inner housing within the outer housing. When the contact surface of the actuation cap is pressed against the subject's skin and a needle is inserted, the actuation cap retracts into the outer housing and activates the opener mechanism to release pressurized gas from the canister into the chambers, thereby advancing a plunger in the inner housing and delivering one or more medicaments from the syringe into the subject's body. Once the injection is complete and the device is withdrawn from the skin, the actuation cap automatically advances to cover the needle.

Description

[Technical Field]

[0001] The present application relates generally to devices and methods for delivering medication into the body of a subject, and more particularly to automatic injectors and / or gas-actuated drive systems for injection devices, and methods of making and using such devices.

[0002] Related application data This application claims the benefit of co-pending U.S. Provisional Application No. 63 / 394,235, filed August 1, 2022, the entire disclosure of which is expressly incorporated herein by reference. [Background technology]

[0003] Many applications involve delivering drugs or other agents into a patient's body subcutaneously, intramuscularly, or otherwise. For example, auto-injectors are available that contain a preset dose of medication that can be automatically administered into a patient's body after application to the patient's skin and activation. Typically, such auto-injectors are spring-loaded syringes that, upon activation, release the spring to generate sufficient force to cause the needle to penetrate the skin and deliver the dose in the syringe. For viscous fluids, the force required to generate fluid flow can be greater than what a spring-powered system can provide. When springs are used, relatively large forces must be generated, necessitating a spring with a large mass. As a result, such auto-injectors can be loud, produce pressure spikes in the syringe that can lead to glass breakage, vibrate, and / or drive the needle into the patient's skin, which can cause pain and / or frighten the user, especially if the patient is administering the medication themselves.

[0004] Therefore, improved devices and methods for delivering pharmaceutical agents into the body of a patient would be useful. Summary of the Invention

[0005] The present application relates generally to devices and methods for delivering medication into the body of a subject, and more particularly to automatic injectors and / or gas-actuated drive systems for injection devices, and methods of making and using such devices.

[0006] According to one example, an injection device for delivering one or more medicaments into a body of a subject is provided, the injection device comprising: an outer housing including a proximal portion terminating in a proximal end and a distal portion terminating in an open distal end; a syringe having a barrel containing one or more medicaments, a needle extending distally from the barrel with a tip of the needle disposed in the distal portion adjacent the distal end; and a piston disposed within the proximal end of the barrel; an inner housing within the outer housing, the inner housing including a first chamber adjacent the proximal end of the outer housing and a second chamber between the first chamber and the proximal end of the barrel; and a piston disposed at the distal end of the housing. the actuation cap includes an actuation cap attached to the barrel, the actuation cap having a contact surface disposed distal to the distal end of the outer housing and an actuation cap extension extending proximally around the barrel; a pressurized gas source within the first chamber; a release cap within the outer housing adjacent the proximal end of the outer housing, the release cap carrying an opening pin disposed adjacent the pressurized gas source; a spacer within the outer housing adjacent the inner housing, the spacer including a distal end adjacent the proximal end of the actuation cap extension and a proximal end adjacent the release cap; and a plunger having a proximal end within the second chamber and a distal end coupled to the piston of the syringe. The actuation cap is axially movable relative to the outer housing, and is configured such that when a contact surface of the actuation cap is pressed against the subject's skin, the actuation cap moves proximally to guide the spacer proximally, such that the spacer guides the release cap proximally, thereby releasing the release pin, which in turn opens the pressurized gas source to release pressurized gas into the first chamber and the second chamber, which in turn advances the plunger and guides the piston distally to deliver one or more medicaments through the needle. Further, the spacer can be biased to advance distally, such that after delivering the one or more medicaments, when the contact surface is guided away from the subject's skin to release the actuation cap, the spacer guides the actuation cap distally to cover the needle, and the spacer includes one or more locking members to prevent subsequent proximal movement of the spacer and the actuation cap.

[0007] According to another example, there is provided a device for delivering one or more medicaments into a body of a subject, the device comprising: an outer housing including a proximal portion terminating in a proximal end and a distal portion terminating in an open distal end; a syringe having a barrel containing the one or more medicaments, a needle extending distally from the barrel with a tip of the needle disposed in the distal portion adjacent the distal end; a piston within the proximal end of the barrel; and an inner housing within the outer housing, having a first chamber adjacent the proximal end of the outer housing and a second chamber between the first chamber and the proximal end of the barrel. the plunger includes an inner housing including a first chamber, an actuation cap disposed at a distal end of the housing, the actuation cap having a contact surface disposed distal to the distal end of the outer housing, a pressurized gas source within the first chamber, a release cap disposed within the outer housing adjacent the proximal end of the outer housing, the release cap carrying an opening pin disposed adjacent the pressurized gas source, the release cap operably coupled to the actuation cap so as to be guided proximally by proximal movement of the actuation cap, and a plunger having a proximal end within the second chamber and a distal end coupled to a piston of the syringe. The actuation cap is axially movable relative to the outer housing, and is configured such that when the contact surface of the actuation cap is pressed against the skin of a subject, the actuation cap retracts proximally into the distal end, thereby guides the release cap proximally and releases the opening pin, which in turn opens the pressurized gas source to release pressurized gas into the first chamber and the second chamber, which in turn advances the plunger and guides the piston distally to deliver one or more medicaments through the needle.

[0008] According to yet another example, a method for delivering one or more medicaments into a body of a subject is provided, the method including the steps of: providing an injection device, the injection device comprising: an outer housing; an inner housing within the outer housing; and a pressurized gas source, the outer housing holding a syringe including a barrel containing one or more medicaments and a needle extending distally from the barrel such that a tip of the needle is positioned adjacent to an actuation cap at a distal end of the outer housing; the inner housing including first and second chambers, the pressurized gas source being provided in the first chamber; pressing a contact surface of the actuation cap against the skin of the subject to insert the needle into the skin, thereby retracting the actuation cap proximally into the outer housing and releasing and advancing a carriage carrying an opening pin, thereby opening an outlet of the pressurized gas source into the first and second chambers and advancing a plunger in the outer housing by pressure of the pressurized gas, thereby delivering the one or more medicaments from the barrel through the needle into the body of the subject; and withdrawing the needle from the skin of the subject, wherein the actuation cap automatically advances to cover the needle.

[0009] According to yet another example, a method for assembling an injection device is provided, the method including the steps of providing a front housing including a proximal end and a distal end, and an actuation cap provided at the distal end such that a contact surface is located distal to the distal end; providing a rear housing and a plunger, the rear housing having proximal and distal ends and an interior extending therebetween, the rear housing including: a release cap provided adjacent to the proximal end of the rear housing and carrying an opening pin located adjacent to a pressurized gas source; and an inner housing provided within the interior including first and second chambers, the plunger having a proximal end within the second chamber; loading a syringe into the front housing such that a needle of the syringe is located within the front housing proximal to the contact surface; and coupling the distal end of the rear housing to the proximal end of the front housing, thereby coupling the plunger to a piston in the syringe. The actuation cap is axially movable relative to the outer housing, and when the contact surface of the actuation cap is pressed against the subject's skin, the actuation cap moves proximally, directing the release cap proximally and releasing the release pin, which then opens the pressurized gas source to release pressurized gas into the first chamber and the second chamber, which in turn advances the plunger and directs the piston distally to deliver one or more medicaments through the needle.

[0010] Other aspects and features of the present invention will become apparent from consideration of the following description taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0011] The present invention will be better understood from the following description of specific embodiments taken in conjunction with the accompanying drawings, in which like reference numerals indicate the same elements, and in which: [Figure 1] FIG. 1 is a perspective view of an exemplary autoinjector device including front and rear housings and a safety cap. [Figure 2]2A and 2B are longitudinal cross-sectional views of the device of FIG. 1 taken along orthogonal planes 2A-2A and 2B-2B, respectively, showing the internal components of the device, including a syringe that holds one or more medicaments. [Figure 3] 3A and 3B are detailed views of the distal end of the device of FIGS. 1-2B prior to use, showing how the safety cap covers the device's actuation cap and needle. [Figure 4] 4A-4C are cross-sectional views of the device of FIGS. 1-2B illustrating the operation of the device, showing how, when the device is pressed against the subject's skin and the needle pierces the skin, the actuation cap moves proximally, displacing the syringe spacer and release cap proximally, thereby releasing the carriage holding the opening pin and advancing the opening pin distally, thereby opening the gas canister and releasing pressurized gas into the flow path within the device. [Figure 5] 5A-5C are detailed views of the proximal end of the device shown in FIGS. 4A-4C, respectively. [Figure 6] 6A and 6B are cross-sectional views of the device of FIGS. 1-6 after pressurized gas is released, showing how the pressurized gas advances a plunger in the device, delivering one or more medicaments in the syringe through the needle and advancing the actuation cap as the needle is withdrawn from the subject's skin. FIG. 6C is a detailed view of the device shown in FIG. 6B, showing how a tab locks the actuation cap after advancement.

[0012] The drawings are not intended to be limiting in any sense, and it is envisioned that various examples of the invention may be embodied in a variety of other ways, including those not necessarily shown in the drawings. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several aspects of the invention and, together with the detailed description, serve to explain the principles of the invention. It should be understood, however, that the invention is not limited to the precise arrangements shown. DETAILED DESCRIPTION OF THE INVENTION

[0013] Before describing the examples, it is to be understood that this invention is not limited to particular examples described, as such may, of course, vary. Also, it is to be understood that the terminology used herein is for the purpose of describing particular examples only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.

[0014] Where a range of values is given, each intervening value between the upper and lower limits of that range, to the tenth of the unit of the lower limit, is understood to be specifically disclosed unless the context clearly dictates otherwise. Each smaller range between any stated value or intervening value in a stated range and any other stated value or intervening value in that stated range is encompassed within the invention. The upper and lower limits of such smaller ranges may each independently be included or excluded, and whether both or neither are included in the smaller range, each range is encompassed within the invention, subject to any specifically excluded limit in the stated range. When a stated range includes one or both of the limits, ranges excluding either or both of those included limits are also intended to be included within the invention.

[0015] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, some potential exemplary methods and materials are described herein.

[0016] It should be noted that, as used herein and in the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, a reference to a "compound" includes a plurality of such compounds, and a reference to a "polymer" includes a reference to one or more polymers and equivalents thereof known to those skilled in the art.

[0017] In this specification, certain ranges are presented with the term "about" before the numerical values. The term "about" is used herein to provide literal support for the exact numerical value that follows the term, as well as a numerical value that is close to or approximate to the numerical value that follows the term. In determining whether a numerical value is close to or approximate to a specifically stated numerical value, the unstated near or approximate numerical value may be a numerical value that, in the context in which it is presented, provides a substantial equivalent to the specifically stated numerical value.

[0018] Referring to the drawings, FIG. 1 illustrates an example of an automatic injection device 6 having an outer housing 8 including a front housing 10 that holds a syringe 70 containing one or more medications within a medication chamber 73, and a rear housing 12 that includes a drive assembly for automatically delivering one or more medications from the syringe 70 when the device 6 is actuated. As shown, to prevent premature actuation of the device 6, the front housing 10 is provided with a safety cap 86, which can be removed immediately prior to injection, as described further elsewhere herein. Additionally, when the device 6 is actuated, one or more internal components of the device 6 can move axially, i.e., proximally and / or distally relative to the longitudinal axis 18, as described further elsewhere herein.

[0019] In one example, syringe 70 may be a pre-filled syringe formed, for example, from glass or plastic, and filled with a preset amount of medication, e.g., corresponding to a single patient dose. Alternatively, the medication chamber and needle may be integrated with front housing 10, if desired (not shown). In a further example, syringe 70 (or an integrated medication chamber) may include a needleless distal port (not shown), and a separate needle (also not shown) may be coupled to the port immediately prior to injection or as needed, e.g., using a luer fitting, mating threads, and / or other cooperating connector. As used herein, "medication" may include one or more flowable therapeutic and / or diagnostic compounds, drugs, or substances, e.g., in liquid or gas form, in solution or suspension, e.g., in a viscous fluid.

[0020] 2A and 2B, syringe 70 includes a barrel 72 containing one or more medicaments within medicament chamber 73, a needle 78 extending from a distal end 72a of barrel 72, and a piston or stopper 74 slidable within a proximal end 72b of barrel 72 for directing the one or more medicaments through needle 78 and into a subject's body (not shown). Device 6 also includes a gas canister or pressurized gas source 40 for powering device 6, e.g., to advance plunger 50 coupled to piston 74 to deliver one or more medicaments. Device 6 also includes an actuation cap 80 and opener mechanism 60 for opening canister 40 and releasing the pressurized gas within canister 40 into the set of chambers of device 6. For example, inner housing 20 is mounted within outer housing 8, which includes a first or proximal chamber 22 within which gas canister 40 is mounted, e.g., and a second or distal chamber 24 within which plunger 50 is slidably received, e.g.,

[0021] Typically, device 6 is configured so that when contact surface 84 of actuation cap 80 is pressed against the subject's skin to insert needle 78, actuation cap 80 retracts proximally into outer housing 8 and opener mechanism 60 is automatically activated to release pressurized gas from canister 40 into first and second chambers 22, 24, which generates a distally directed force to advance plunger 50 and deliver one or more medicaments from syringe 70 into the subject's body. Once injection is complete and device 6 is withdrawn from the skin, actuation cap 80 can automatically advance to cover needle 78.

[0022] For example, as described further elsewhere herein, a spacer 30 can be provided extending between the actuation cap 80 and the release cap 34 adjacent the opener mechanism 60, such that proximal movement of the actuation cap 80 is transferred by the spacer 30 to direct the release cap 34 proximally within the rear housing 12, thereby releasing the opener mechanism 60. The spacer 30 can be biased distally, for example, by a spring 32, which can bias the actuation cap 80 distally after an injection is completed, as described further elsewhere herein.

[0023] Generally, outer housing 8 includes a proximal end 8a, e.g., at rear housing 12, an open distal end 8b, e.g., at front housing 10, and an inner wall extending therebetween to enclose the interior of device 6. The outer surface between proximal and distal ends 8a, 8b can be sized and / or shaped to facilitate manipulation of device 6, such as to facilitate placing and pressing actuation cap 80 against a subject's skin to activate device 6 and inject one or more medicaments. For example, the outer surface can have a generally cylindrical shape, optionally including one or more textures or gripping features, to facilitate an operator (the subject or a third party) holding device 6 in one hand and pressing actuation cap 80 against the subject's skin, as further described elsewhere herein. As shown, the proximal end 8a of the housing 8 may include a wall 8c surrounding the proximal end 8a and, optionally, one or more pockets or other features 8d for locking the release cap 34, as further described elsewhere herein.

[0024] The outer housing 8 may be formed from multiple separate components, e.g., clamshell halves, formed from metals such as stainless steel, aluminum, plastics, and / or composites, e.g., by one or more of cold drawing, molding, casting, machining, etc., that are substantially permanently joined together, e.g., by one or more of welding, soldering, fusion bonding, adhesive bonding, interference fit, etc. As shown, the outer housing 8 is formed as separate front and rear housings 10, 12 that are assembled separately with their respective internal components and then joined together, e.g., after loading a syringe 70 into the front housing 10.

[0025] For example, during manufacturing, front housing 10 can be assembled with activation cap 80 and safety cap 86, and syringe 70 can be loaded into front housing 10 any time before an injection is made, e.g., during manufacturing or assembly of device 6. Optionally, as shown in FIGS. 3A and 3B , syringe 70 can include a rigid needle shield 79, e.g., formed from a conventional material, which can be removably secured to distal end 72 a of barrel 72 to protect the needle and prevent accidental needle sticks. Safety cap 86 can include a feature 86 a that engages with needle shield 79 such that needle shield 79 is removed when safety cap 86 is removed. For example, as shown, the proximal end of the safety cap 86 may include one or more fingers 86a that fit into one or more corresponding notches, recesses or other features of the needle shield 79 when the syringe 70 is inserted into the front housing 10, thereby allowing the needle shield 79 to be coupled to the safety cap 86, as described elsewhere herein.

[0026] The rear housing 12 can be assembled with the inner housing 20, spacer 30, release cap 34, gas canister 40, plunger 50, and opener mechanism 60 (and other associated components), and the rear housing 12 can be coupled to the front housing 10 at any time. For example, during manufacturing, a syringe 70 can be loaded inside the front housing 10, and the assembled rear housing 12 can be immediately coupled to the front housing 10. When the rear housing 12 is attached to the front housing 10, the distal end 54 of the plunger 50 is coupled to a piston 74 within the syringe 70, such that distal movement of the plunger 50 is transferred to the piston 74, e.g., as further described elsewhere herein.

[0027] As shown in FIGS. 2A and 2B , the outer housing 8 can include a mount 11, e.g., on one of the front and rear housings 10, 12, for guiding and / or securing the syringe 70 during loading. Optionally, the proximal end 72b of the barrel 72 can include one or more flanges, e.g., a radial flange or a pair of opposing flanges, that can abut and / or be received within the mount 11 to secure the syringe 70 relative to the front housing 10. Additionally or alternatively, the front housing 10 can be provided with one or more detents, ridges, or other features (not shown) to secure the syringe 70. Optionally, the front housing 10 can include one or more windows 10c in a sidewall to facilitate observation of the syringe 70 during injection, e.g., to visually confirm when the piston 74 is fully advanced.

[0028] Optionally, device 6 can include a syringe spacer or adapter 75 that provides an interface between distal end 54 of plunger 50 and piston 74, e.g., to provide a connector therebetween and / or to ensure proper spacing so that piston 74 advances in conjunction with plunger 50. For example, spacers 75 of various lengths can be provided to allow syringes of various lengths to be loaded into front housing 10 while still properly positioning needle 78 adjacent distal end 8b of outer housing 8 and allowing plunger 50 to properly couple to piston 74.

[0029] During manufacture or assembly, a syringe 70 can be selected that is inserted into housing 8 through an opening in distal end 8b and coupled to distal end 16 of drive assembly 12, for example. A syringe spacer 75 can be selected and its distal end 75a can be coupled to piston 74, for example, by one or more cooperating threads, one or more detents, or other connectors, as shown. The distal end 54 of plunger 50 can be inserted into recess 75b of syringe spacer 75 when rear housing 12 is coupled to front housing 10. Optionally, distal end 54 and recess 75b of plunger 50 can include cooperating locking features, for example, one or more threads, detents, or the like (not shown), or distal end 54 can simply be inserted into recess 75b to couple subsequent distal movement of piston 74 to plunger 50, as further described elsewhere herein.

[0030] Alternatively, the assembled housings 10, 12 can be packaged, stored, and / or otherwise prepared for later assembly. For example, the housings 10, 12 can be shipped or otherwise provided to a manufacturer of syringe 70, who can load the syringe 70 and couple the housings 10, 12 together to provide the completed device 6. In a further alternative, the assembled housings 10, 12 can be provided to a hospital, physician, or other medical professional to complete final assembly just prior to administering the injection and load the syringe with a particular medication prior to the injection.

[0031] The proximal end 10a of the front housing 10 and the distal end 12b of the rear housing 12 may include one or more cooperating connectors (not shown) for coupling the housings 10, 12 to one another to provide a fully assembled device 6. For example, the housings 10, 12 may include one or more mating threads, detents, etc. that may permanently couple the housings 10, 12 to one another. Alternatively, the connectors may allow the housings 10, 12 to be later separated, e.g., after an injection has been performed, so that the syringe 70 can be removed and the device 6 can be cleaned and reused with a new syringe, for example.

[0032] Additionally or alternatively, housings 10, 12 may be permanently attached to one another by one or more of an interference fit between ends 10a, 12b, adhesive bonding, fusion bonding, sonic welding, etc. In another alternative, outer housing 8 may be formed as a single, integral component into which the components of device 6 are assembled. In such an alternative (or even in a two-part housing), device 6 may be a disposable device, discarded after a single injection.

[0033] In the example shown in FIGS. 2A and 2B , the inner housing 20 includes a proximal cylinder 20a including a first chamber 22 and a distal cylinder 20b including a second chamber 24. Each of the proximal and distal cylinders 20a, 20b can have an elongated cylindrical wall or other cross-sectional shape along their length. The proximal and distal cylinders 20a, 20b can be permanently attached to one another, for example, by one or more of cooperating threads as shown, detents or other connectors, a force fit, adhesive bonding, sonic welding, fusion bonding, etc., to provide the inner housing 20. Alternatively, the inner housing 20 can be formed as a single, integral structure including the first and second chambers 22, 24. The proximal and distal cylinders 20a, 20b can be formed from the same or different materials as the outer housing 8.

[0034] The inner housing 20 may be mounted within the outer housing 8 such that the inner housing 20 remains substantially stationary within the outer housing 8. Similarly, the gas canister 40 may be mounted within the inner housing 20, e.g., within the first chamber 22, such that the gas canister 40 also remains substantially stationary relative to the outer housing 8. For example, one or more struts, supports, or other structures (not shown) may be provided on the inner housing 20 and / or outer housing 8 to fix the inner housing 20 and / or gas canister 40 relative to the outer housing 8.

[0035] In the illustrated example, the proximal cylinder 20a can include an annular wall surrounding a first chamber 22, which includes a first region 22a of uniform diameter in which the gas canister 40 is mounted, and second and third regions 22b, 22c in which the opener mechanism 60 is slidably mounted, as further described elsewhere herein. The distal cylinder 20b can have a length such that a distal end 21b of the distal cylinder 20b abuts the syringe 70 when the device 6 is assembled.

[0036] Optionally, distal end 21b may include one or more features that contact proximal end 72b of syringe 70, such as an O-ring 20d secured on or around distal end 21b formed from a resilient and / or relatively flexible material. O-ring 20d may prevent distal end 21b from damaging syringe 70, for example, if barrel 72 is made of glass.

[0037] 2A and 2B, canister 40 includes a body 42 including a first closed end 42a, a second outlet end 42b, and a cap 44 welded or otherwise attached to outlet end 42b, thereby providing a sealed cavity 48 filled with a fluid including a pressurized gas, such as carbon dioxide or a fluorocarbon gas, compressed to a pressure sufficient to at least partially liquefy the gas within cavity 48. Alternatively, a fluid that remains in a gaseous state can be stored within cavity 48, including gases such as argon, nitrogen, helium-argon, or other combinations thereof. As described elsewhere herein, the pressurized fluid contained within cavity 48 can be used to generate a force to operate device 6, for example, to inject one or more medicaments into a subject's body from syringe 70.

[0038] In one example, the body 42 and the cap 44 may be formed from stainless steel or other desired or suitable metal, plastic, or composite material by, for example, one or more of drawing, stamping, machining, casting, molding, etc. For example, the body 42 may be deep drawn from a round sheet metal blank, e.g., type 305 stainless steel, using one or more dies and punches (not shown) to form a main barrel region, a closed end 42a, an optional tapered shoulder region, and an outlet end 42b that defines an opening into which the cap 44 is attached.

[0039] As shown, the canister 40 can be oriented so that the outlet end 42b is more proximal than the closed end 42a, and the opener mechanism 60 can be located proximal to the outlet end 44. In the illustrated example, the cap 44 can be a closed cap that includes a septum or other weakened area (not shown) that can be opened by the opener mechanism. In this example, the opener mechanism can include a puncture pin 62 configured to puncture or preferentially tear the septum, as described elsewhere herein. Additional information regarding usable canisters and methods of making them can be found in U.S. Publication No. 2017 / 0258583, the entire disclosure of which is expressly incorporated herein by reference.

[0040] Alternatively, cap 44 may include another closure mechanism, such as a ball or other member (not shown), that is biased or otherwise configured to close the outlet in cap 44, but that can be directed by opener mechanism 60 away from cap 44, for example, into canister 40, to thereby open the outlet and release pressurized gas within cavity 48. In this alternative, opening pin 62 may include a tapered tip (not shown) sized to enter the outlet and push the closure mechanism out of the outlet.

[0041] Plunger 50, which may be an elongated rod or other member, includes a proximal end 52 slidably disposed within second chamber 24, e.g., initially immediately adjacent first chamber 22, and a distal end 54 coupled to piston 74. Plunger 50 is movable from an initial or retracted position (e.g., as shown in FIGS. 2A and 2B) to a final or extended position (e.g., as shown in FIGS. 7A and 7B), e.g., with distal end 54 extending from second end 16 of drive assembly 12 into drug chamber 73 of syringe 70.

[0042] The proximal end 52 of the plunger 50 is provided with a flange or other guide member 53 that slidably engages the wall of the second chamber 24. As a result, when pressurized gas enters the second chamber 24 (via the first chamber 22), the pressure generates a distal force that directs the plunger 50 distally from an initial position toward a final position, advancing the piston 74 and delivering one or more medicaments from the medicament chamber 73 through the needle 78 and into the subject's body, as further described elsewhere herein.

[0043] Optionally, a wall, orifice, or intermediate passage (not shown) can be provided between the first and second chambers 22, 24. The intermediate passage can have a relatively small diameter to provide a restrictor for shortening the pressure buildup time in the second chamber 24. For example, the intermediate passage can i) slow the transient flow of gas, slowing the buildup of pressure on the plunger 50, e.g., to provide a soft start to the injection, reducing / eliminating pressure shock waves in the fluid being injected in the syringe, and reducing pain to the patient due to a gradual start to the drug injection, and / or ii) slow the steady-state flow of gas, reducing other pressures on the plunger 50, providing a limiting effect on the flow rate of the drug being injected into the patient's body.

[0044] Optionally, plunger 50 may also include a plunger chamber 56, as shown, extending, for example, from an open proximal end 52 to a closed distal end 54 of plunger 50. Plunger chamber 56 may taper inwardly from proximal end 52 to distal end 54, as shown, or may have a uniform diameter or other cross-sectional shape along its length. Alternatively, proximal end 52 of plunger 50 may include a closed wall and / or plunger 50 may be a solid rod extending between proximal end 52 and distal end 54.

[0045] Optionally, flange 53 at proximal end 52 of plunger 50 may include one or more passages (not shown) extending between the proximal and distal faces of flange 53. For example, flange 53 may include a plurality of circular or other enclosed passages spaced apart from one another around the circumference of flange 53, each extending between the proximal and distal faces.

[0046] In this case, flange 53 may be sized and / or shaped to slidably engage the inner wall of second chamber 24 to, for example, allow plunger 50 to move from an initial position to an extended position, but does not require an O-ring or other seal. Instead, one or more O-rings or other seals may be provided within and / or adjacent inner housing 10 to seal first and second chambers 22, 24 and / or otherwise seal the flow path from gas canister 40 to plunger 50. For example, a first O-ring 58a may be provided between inner housing 10 and opener mechanism 60, a second O-ring 58b may be provided between distal end 21b of inner housing 10 and plunger 50, and / or a third O-ring 58c may be provided between proximal and distal cylinders 10a, 10b (if provided as separate components secured to one another).

[0047] In one example, plunger 50 includes a flange 53 formed as a cylindrical head having a larger outer diameter than plunger 50, which may be integrally molded or otherwise formed with plunger 50 or separately manufactured and permanently attached thereto, and which may have one or more passages (not shown) extending between the proximal and distal faces of flange 53. When canister 40 is opened to release the pressurized gas, the initial volume that must be filled with gas (including first chamber 22 around canister 40, second chamber 24 around plunger 50, and optional plunger chamber 56) may result in an initial pressure drop as the gas fills the vacant volume. However, as plunger 50 advances, the change in volume that must be filled with gas increases only minimally (e.g., the volume occupied by plunger 50 in second chamber 24 as it is pushed out of distal end 16 of drive assembly 12). As a result, because the change in volume is minimized, the force exerted by the pressure on plunger 50 remains substantially constant or only decreases slightly, thereby minimizing the drop in force exerted on plunger 50 and providing a more uniform delivery rate of medication from syringe 70. Additional information regarding plungers capable of reducing pressure drop is provided in co-pending U.S. application Ser. No. 17 / 965,707, the entire disclosure of which is expressly incorporated herein by reference.

[0048] Optionally, the proximal end 52 of the plunger 50 can have a larger diameter or other cross-section than the distal end 54 of the plunger 50. For example, the outer diameter or cross-section can be tapered between the proximal end 52 and the distal end 54 of the plunger 50. Such a taper can increase the cross-sectional area of the plunger 50 as it advances from its initial position toward its final position, thereby minimizing changes in distal force applied to the syringe stopper due to changes in volume. This is particularly useful in applications requiring a constant delivery rate. It will be understood that any of these features associated with the plunger 50 can be combined with or omitted as desired.

[0049] 2A and 2B, the opener mechanism 60 includes a spring perch or carriage 64 slidably coupled to the rear housing 12, e.g., within the second and third regions 22b, 22c of the first chamber 24. The carriage 64 carries an opening pin 62, which is mounted, e.g., along the axis 18 and pointed distally toward the cap 44. The carriage 64 and release cap 34 include one or more features that disengage when the release cap 34 is directed proximally (by the actuation cap 80 and spacer 30), and when released, the carriage 64 is biased to move distally to direct the opening pin distally, thereby opening the outlet of the cap 44 of the canister 40.

[0050] For example, the rear housing 12 and the carriage 64 may include cooperating features that prevent the carriage 64 from moving until the device 6 is actuated. For example, as best seen in FIGS. 5A-5C , the carriage 64 includes a locking tab or other feature 64a at its proximal end that engages the proximal end 13a of the rear housing 12, and a flange 64b at its distal end that is slidable within the second region 22b of the first chamber 24. A spring 66, such as a coil spring that is initially compressed between the rear housing 12 and the flange 64b, is also provided within the second region 22b around the carriage 64. As a result, the spring 66 biases the carriage 64 to move distally until the locking feature 64a engages the proximal end 13a of the rear housing 12.

[0051] The release cap 34 and carriage 64 include cooperating features that release the locking feature 64a from the rear housing 12 when the device 6 is actuated. For example, as shown in FIGS. 5A-5C , the release cap 34 includes a cylindrical body that surrounds a portion of the rear housing 12, e.g., around the second and third regions 22b, 22c of the first chamber 24. The release cap 34 may also include a surrounded proximal end 34a that is proximal to the proximal end 13a of the rear housing 12 and a distal end 34b that includes one or more features for limiting axial movement of the release cap 34. For example, one or more flanges on the distal end 34b may slide proximally, e.g., along the inner surface of the outer housing 8, until they abut a ridge on the outer housing 8 to prevent further proximal movement of the release cap 34, as further described elsewhere herein.

[0052] As shown, the proximal end 34a of the release cap 34 includes a central hub 36 aligned along the axis 18 distally toward the opening pin 62. The carriage 64 includes a plurality of tabs 65, e.g., concentrically arranged about the axis 18, such that the tabs 65 slide along the hub 36 when the release cap 34 is guided proximally. When the hub 36 moves proximally past the tabs 65, the tabs 65 are biased to move radially inward (toward the central axis 18), thereby directing the locking feature 64a inward. When the locking feature 64a passes the proximal end 13a of the rear housing 12, as shown in FIG. 5C, for example, a spring 66 automatically guides the carriage 64 distally, thereby directing the opening pin 62 distally to pierce (or otherwise open) a septum in the cap 44 of the canister 40.

[0053] During use, the device 6 can initially be provided with a safety cap 86 attached to the distal end 8b of the housing 8, as shown, for example, in FIGS. 1-2B . Just prior to performing an injection, the safety cap 86 can be removed, for example, by simply pulling the safety cap 86 distally away from the outer housing 8 to expose the contact surface 84 of the actuation cap 80, as shown, for example, in FIG. 4A . For example, as best seen in FIGS. 3A and 3B , the safety cap 86 can include inner and outer cylindrical members, with the proximal end 86a of the inner member coupled to the needle shield 79 and the proximal end 86b of the outer member slidably received on the distal end 8b of the outer housing 8. Alternatively, the safety cap 86 and / or the outer housing 8 can include one or more connectors, locks, or the like (not shown) that can be disengaged prior to removing the safety cap 86.

[0054] As described elsewhere herein, the safety cap 86 can prevent the actuation cap 80 from being guided proximally, for example, by preventing the actuation cap 80 from being touched. Additionally or alternatively, the safety cap 86 can include features that engage with the needle shield 79 such that the needle shield 79 is removed when the safety cap 86 is removed. The safety cap 86 and needle shield 79 can prevent the needle 78 from being exposed from the housing 8 prior to use. Once the safety cap 86 and needle shield 79 are removed, the device 6 is ready for use to perform an injection.

[0055] 4A-4C, the needle 78 can be inserted by placing the contact surface 84 against the subject's skin (not shown) and then pressing the device 6 against the skin, and as the needle 78 is inserted into the subject's skin, the actuation cap 80 can be slid proximally from the initial position shown in FIG. 4A to the retracted position shown in FIG. 4B. As described further below, this action activates the opener mechanism 60, causing the opening pin 62 to open the outlet of the gas canister 40, thereby releasing pressurized gas into the first chamber 22, which advances the plunger 50 and therefore the piston 74, thereby delivering one or more medicaments through the needle 78 and into the subject's body.

[0056] 4A , initially, the proximal end 82 of the actuation cap 80 may abut or otherwise engage the distal end 30a of the spacer 30, and the proximal end 30b of the spacer 30 may abut or otherwise engage the distal end 34b of the release cap 34. As a result, as the actuation cap 80 is retracted proximally within the outer housing 8, its proximal end 82 presses against the distal end 30a of the spacer 30, thereby directing the spacer 30 proximally, and the proximal end 30b of the spacer 30 presses against the distal end 34b of the release cap 34, thereby directing the release cap 34 proximally, until, for example, the proximal end 34a of the release cap 34 contacts the proximal end 8c of the outer housing 8.

[0057] As the actuation cap 80, spacer 30, and release cap 34 move proximally, the inner housing 20 (and canister 40 within first chamber 22) may remain substantially stationary. As shown in FIGS. 4A and 4B , as the spacer 30 is guided proximally, the spring 32 may be compressed, for example, between a feature at the distal end 30 a of the spacer 30 and the inner housing 20, thereby biasing the spacer 30 for subsequent distal movement. However, with the operator pressing the contact surface 84 of the actuation cap 80 against the subject's skin, the spacer 30 cannot move distally.

[0058] Because carriage 64 is secured relative to inner housing 20 by locking feature 64a, carriage 64 also remains substantially stationary, and therefore, as best seen in FIGS. 5A-5C , release cap 34 moves proximally relative to carriage 64, causing tab 65 of carriage 64 to slide along hub 36 of release cap 34. When release cap 34 reaches its proximal-most position, shown in, for example, FIGS. 4C and 5C , hub 36 has already moved proximally beyond the end of tab 65, and the inward bias of tab 65 releases and automatically moves tab 65 inward. Because tab 65 is coupled to locking feature 64a of carriage 64, the inward movement of tab 65 causes locking feature 64a to move inward, thereby disengaging locking feature 64a from proximal end 21a of inner housing 20.

[0059] The spring 66 then releases the carriage 64, urging it to move distally, thereby advancing the opening pin 62 distally and opening the outlet of the canister 40, as shown in Figures 4C and 5C. The release cap 34 may include one or more tabs or other features 34c that correspond, for example, to pockets 8d in the outer housing 8, so that when the release cap 34 reaches its distal-most position, the tabs 34c are received within the respective pockets 8d, as shown. Thus, the tabs 34c may prevent the release cap 34 from moving distally as the spring 66 advances the carriage 64 distally.

[0060] As carriage 64 moves distally, release pin 62 advances and pierces (or otherwise opens) the septum of cap 44, thereby releasing the pressurized gas within canister 40. The released pressurized gas then enters first chamber 22, e.g., around canister 40, and travels to second chamber 24, thereby pressurizing second chamber 24 and generating a distal force that directs plunger 50 distally from an initial position toward a final position to deliver one or more medicaments from syringe 70 through needle 78 and into the subject's body, e.g., as shown in FIG. 6A .

[0061] During injection, the operator can monitor syringe 70, for example, through one or more windows 8c, to verify that piston 74 has fully advanced distally within barrel 72, administering the full dose to the subject. Once injection is complete, device 6 can be moved away from the subject, and needle 78 can be withdrawn from the subject's skin. Once device 6 is withdrawn from the subject's skin, actuation cap 80 is free to move distally, and the distal bias of spring 32 automatically advances spacer 30 distally, thereby directing actuation cap 80 distally to cover the withdrawn needle 78.

[0062] As best seen in FIG. 6C , as the spacer 30 advances distally, the proximal end 30b of the spacer can move distally past a feature 34d at the distal end 34b of the release cap 34. For example, the feature 34b can include one or more fingers or tabs that slide along the interior of the spacer 30 until the proximal end 30b has passed distally, at which point the tab 34d can resiliently move radially outward, e.g., to a position more proximal than the proximal end 30b of the spacer 30, thereby preventing further proximal movement of the spacer 30. Blocking the spacer 30 from moving proximally prevents the actuation cap 80 from retracting again, thereby locking the actuation cap 80 in a position extending over the needle 78 and preventing accidental exposure of the needle 78.

[0063] Thereafter, if the device 6 is a disposable device, it can be discarded. Alternatively, if the device is reusable, e.g., if the front and rear housings 10, 12 are separable, the rear housing 12 can be separated from the front housing 10 and the syringe 70 can be removed. For reusable devices, one or more features can be provided within the device to release residual pressure within the first and second chambers 22, 24. For example, as shown in FIGS. 6A and 6B , a gas valve and / or shaft member can be provided within the plunger 50 that can be operated to release the pressurized gas before the plunger 50 is separated from the piston 74. The separate housings 10, 12 can then be cleaned and / or sterilized, and a new gas canister 40 can be loaded into the inner housing 20 before reassembling the device.

[0064] While the invention is susceptible to various modifications and alternative forms, specific examples thereof have been shown in the drawings and are herein described in detail. It should be understood, however, that the invention is not limited to the particular forms or methods disclosed, but rather the invention is intended to cover all modifications, equivalents, and alternatives falling within the scope of the appended claims.

Claims

1. 1. A device for delivering one or more agents into a subject's body, comprising: an outer housing including a proximal portion terminating in a proximal end and a distal portion terminating in an open distal end; a syringe having a barrel containing one or more medicaments, a needle extending distally from the barrel with a needle tip disposed within the distal portion adjacent the distal end, and a piston disposed within the proximal end of the barrel; an inner housing within the outer housing, the inner housing including a first chamber adjacent a proximal end of the outer housing and a second chamber between the first chamber and the proximal end of the barrel; an actuation cap disposed at the distal end of the housing, the actuation cap having a contact surface located distal to the distal end of the outer housing and an actuation cap extension extending proximally around the barrel; a source of pressurized gas within the first chamber; a release cap within the outer housing adjacent a proximal end of the outer housing, the release cap carrying an opening pin positioned adjacent the source of pressurized gas; a spacer within the outer housing adjacent the inner housing, the spacer including a distal end adjacent the proximal end of the actuation cap extension and a proximal end adjacent the release cap; a plunger having a proximal end within the second chamber and a distal end coupled to a piston of the syringe; the actuation cap is axially movable relative to the outer housing, and is configured to move proximally to guide the spacer proximally when a contact surface of the actuation cap is pressed against the skin of the subject, such that the spacer guides the release cap proximally, thereby releasing the release pin, which then opens the pressurized gas source to release pressurized gas into the first chamber and the second chamber, whereby the pressurized gas advances the plunger and guides the piston distally to deliver the one or more medicaments through the needle; The device is characterized in that the spacer is biased to advance in a distal direction, and after delivering the one or more drugs, when the contact surface is directed away from the subject's skin and the actuating cap is released, the spacer guides the actuating cap distally to cover the needle, and the spacer includes one or more locking members to prevent subsequent proximal movement of the spacer and the actuating cap.

2. 10. The device of claim 1, The device, wherein the inner housing is axially fixed within the outer housing such that the proximal and distal chambers do not move relative to the outer housing.

3. 10. The device of claim 1, the proximal portion comprising a rear housing that retains the inner housing, the release cap, the spacer, the pressurized gas source, and the plunger, the plunger being disposed adjacent a distal end of the rear housing.

4. 4. The device of claim 3, the distal portion includes a front housing that carries the actuation cap and includes a proximal end having an opening for inserting the syringe into the front housing; a proximal end of the front housing and a distal end of the rear housing including cooperating connectors for securing the front and rear housings together to provide the outer housing after the syringe is inserted.

5. 5. The device of claim 4, the piston and plunger include cooperating connectors such that when the front and rear housings are secured together, distal movement of the plunger directs the piston distally.

6. 6. The device of claim 5, The device further comprises a syringe spacer between the plunger and the piston.

7. 10. The device of claim 1, the inner housing includes a proximal cylinder including the first chamber and a distal cylinder including the second chamber, the proximal and distal cylinders including cooperating connectors for securing the proximal and distal cylinders to one another to provide the inner housing.

8. 8. The device of claim 7, 10. A device wherein said cooperating connectors include one or more cooperating male and female threads.

9. 10. The device of claim 1, The device, wherein the inner housing is a one-piece cylindrical housing containing the first and second chambers.

10. 10. The device of claim 1, The device, wherein the source of pressurized gas includes a canister having an outlet, and the opening pin is axially movable to open the outlet and release the pressurized gas.

11. 11. The device of claim 10, The gas canister includes a pierceable septum initially spaced from the opening pin, and when the release cap is directed proximally, the opening pin is released, causing the opening pin to resiliently move axially through the septum and release the pressurized gas.

12. 12. The device of claim 11, The device, wherein a septum of the gas canister is oriented proximally within the proximal chamber and the opening pin is oriented distally toward the septum.

13. 11. The device of claim 10, the gas canister initially includes a ball spaced from the opening pin to seal the outlet, and when the release cap is directed proximally, the opening pin is released, causing the opening pin to resiliently move axially and push against the ball, thereby opening the outlet and releasing the pressurized gas.

14. 14. The device of claim 13, 10. A device comprising: an opening pin including one or more features configured to prevent the opening pin from moving away from the gas canister after opening the outlet.

15. The device according to any one of claims 10 to 14, a carriage releasably coupled to the release cap, the opening pin extending axially from the carriage, the release cap and carriage including one or more features that disengage when the release cap is guided proximally by the actuation cap and spacer, and the carriage being biased to move axially so as to move the opening pin when released to open the outlet.

16. 16. The device of claim 15, The device, wherein the inner housing and the carriage include cooperating features that prevent the carriage from moving proximally when the release cap is directed proximally.

17. 16. The device of claim 15, The device further comprising a spring mounted between the carriage and the inner housing to bias the carriage toward axial movement.

18. 16. The device of claim 15, the one or more features include a central hub on the release cap and a plurality of tabs on the carriage, the tabs sliding along the hub as the release cap is directed proximally until the hub moves proximally past the tabs, the tabs being biased to move radially inward to release the carriage.

19. 20. The device of claim 18, the carriage includes one or more locking features that engage the inner housing to prevent movement of the carriage relative to the inner housing, the locking features coupled to the plurality of tabs such that when the tabs move radially inward, the one or more locking features disengage from the inner housing, thereby releasing the carriage to move axially.

20. The device according to any one of claims 1 to 14, The device further includes a spring coupled to the spacer, wherein when the actuation cap is initially moved proximally, the potential force of the spring increases as the spacer is guided proximally, and when the actuation cap is released, the potential force of the spring increases to bias the spacer distally.

21. The device according to any one of claims 1 to 14, The device, wherein the spacer comprises a cylinder slidably mounted around the inner housing.

22. The device according to any one of claims 1 to 14, The device further comprises a safety cap connected to the distal end of the housing distal to the actuation cap to prevent the actuation cap from being guided in a proximal direction.

23. The device according to any one of claims 1 to 14, The device further comprises a safety cap removably connected to the distal end of the housing distal to the actuation cap, thereby preventing the needle from being exposed from the housing before the safety cap is removed.

24. The device according to any one of claims 1 to 14, 10. A device comprising: a plunger having a plunger chamber extending from an opening at a proximal end that communicates with the second chamber; and pressurized gas entering the second chamber fills the plunger chamber.

25. The device according to any one of claims 1 to 14, The device, wherein the outer housing includes a window that allows observation of the piston of the syringe.

26. 1. A device for delivering one or more agents into a subject's body, comprising: an outer housing including a proximal portion terminating in a proximal end and a distal portion terminating in an open distal end; a syringe having a barrel containing one or more medicaments, a needle extending distally from the barrel with a needle tip disposed within the distal portion adjacent the distal end, and a piston within the proximal end of the barrel; an inner housing within the outer housing, the inner housing including a first chamber adjacent a proximal end of the outer housing and a second chamber between the first chamber and the proximal end of the barrel; an actuation cap provided at a distal end of the housing, the actuation cap having a contact surface located distal to the distal end of the outer housing; a source of pressurized gas within the first chamber; a release cap disposed within the outer housing adjacent a proximal end thereof, the release cap carrying an opening pin disposed adjacent the source of pressurized gas, the release cap operatively coupled to the actuation cap so as to be directed proximally by proximal movement of the actuation cap; a plunger having a proximal end within the second chamber and a distal end coupled to a piston of the syringe; the actuation cap is axially movable relative to the outer housing, and is configured to retract proximally into the distal end when a contact surface of the actuation cap is pressed against the subject's skin, thereby directing the release cap proximally to release the opening pin, which in turn opens the pressurized gas source to release pressurized gas into the first chamber and the second chamber, which in turn advances the plunger and directs the piston distally to deliver the one or more medicaments through the needle.

27. 27. The device of claim 26, The device is characterized in that the actuating cap is biased to retract proximally and then advance distally, and after delivering the one or more drugs, when the contact surface is directed away from the subject's skin and the actuating cap is released, the actuating cap advances distally to cover the needle.

28. 27. The device of claim 26, a spacer disposed between the outer housing and the inner housing and extending between the actuation cap and the release cap, wherein when the actuation cap is retracted proximally, the actuation cap guides the spacer to guide the release cap proximally until the opening pin is released.

29. 29. The device of claim 28, The device is characterized in that the spacer is biased distally so that when the actuation cap is retracted proximally, the spacer is guided proximally, and when the needle is withdrawn from the subject's skin, the spacer automatically moves distally to guide the actuation cap distally and cover the needle, and the spacer comprises one or more locking members to prevent subsequent proximal movement of the spacer and actuation cap.

30. The device according to any one of claims 26 to 29, a carriage releasably coupled to the release cap, the opening pin extending axially from the carriage, the release cap and carriage including one or more features that disengage when the release cap is guided proximally by the actuation cap and spacer to release the carriage, the carriage being biased to move axially and configured, when released, to move the opening pin and thereby open the outlet.

31. 1. A method for delivering one or more agents into a subject's body, comprising: providing an injection device comprising an outer housing, an inner housing within the outer housing, and a pressurized gas source, the outer housing holding a syringe including a barrel containing one or more medicaments and a needle extending distally from the barrel such that a tip of the needle is positioned adjacent an actuation cap at a distal end of the outer housing, the inner housing including first and second chambers, the pressurized gas source being disposed within the first chamber; pressing a contact surface of the actuation cap against the skin of the subject to insert the needle into the skin, thereby retracting the actuation cap proximally into the outer housing to release and advance a carriage carrying an opening pin, thereby opening an outlet of the pressurized gas source into the first and second chambers, whereby pressure from the pressurized gas in the second chamber advances a plunger in the outer housing to deliver one or more medicaments from the barrel through the needle and into the body of the subject; and withdrawing the needle from the subject's skin, the actuation cap automatically advancing to cover the needle.

32. 32. The method of claim 31 , the pressurized gas source includes a canister having an outlet, and when the carriage is released, the opening pin moves axially to open the outlet, thereby releasing the pressurized gas.

33. 33. The method of claim 32, the gas canister includes a pierceable partition initially spaced from the opening pin, and when the carriage is released, the opening pin resiliently moves axially to pierce the partition, thereby releasing the pressurized gas.

34. 32. The method of claim 31 , When the actuation cap is retracted proximally, the actuation cap directs a release cap proximally to release the carriage.

35. 35. The method of claim 34, the release cap and carriage include one or more features that disengage when the release cap is guided proximally by the actuation cap to release the carriage, and the carriage is biased to move axially, and when released, moves the release pin to open the outlet.

36. 36. The method of claim 35, the inner housing and the carriage including cooperating features that prevent the carriage from moving proximally when the release cap is directed proximally.

37. 36. The method of claim 35, the one or more features include a central hub on the release cap and a plurality of tabs on the carriage, the tabs sliding along the hub as the release cap is directed proximally until the hub moves proximally past the tabs, the tabs being biased to move radially inward to release the carriage.

38. 38. The method of claim 37, the carriage comprises one or more locking features that engage the inner housing to prevent movement of the carriage relative to the inner housing, the locking features coupled to the plurality of tabs such that when the tabs move radially inward, the one or more locking features disengage from the inner housing, thereby releasing the carriage to move axially.

39. 32. The method of claim 31 , the device further includes a spacer disposed between the outer housing and the inner housing and extending between the actuation cap and a release cap adjacent the carriage, wherein when the actuation cap is retracted proximally, the actuation cap guides the release cap proximally until the carriage is released, and the carriage is biased to move axially and, when released, moves the release pin to open the outlet.

40. 40. The method of claim 39, wherein the spacer is biased distally such that when the actuation cap is retracted proximally, the spacer is guided proximally, and when the needle is withdrawn from the subject's skin, the spacer automatically moves distally to guide the actuation cap distally to cover the needle.

41. The method according to any one of claims 31 to 40, The method further comprises removing a safety cap coupled to a distal end of the outer housing to expose the activation cap before pressing the contact surface against the subject's skin.

42. 1. A method for assembling an infusion device, comprising: providing a front housing including a proximal end and a distal end, and an actuation cap disposed on the distal end such that a contact surface is located distal to the distal end; providing a rear housing and a plunger, the rear housing having proximal and distal ends and an interior extending therebetween, the rear housing including a release cap disposed within the interior adjacent the proximal end of the rear housing, the release cap carrying an opening pin disposed adjacent a source of pressurized gas, and an inner housing disposed within the interior including first and second chambers, the plunger having a proximal end within the second chamber; loading the syringe into the front housing such that the needle of the syringe is located within the front housing proximal to the contact surface; and coupling a distal end of the rear housing to a proximal end of the front housing, thereby coupling the plunger to a piston within the syringe; the actuation cap is axially movable relative to the outer housing, and when a contact surface of the actuation cap is pressed against the subject's skin, the actuation cap moves proximally, directing the release cap proximally and releasing the opening pin, which then opens the pressurized gas source to release pressurized gas into the first chamber and the second chamber, which in turn advances the plunger and directs the piston distally to deliver the one or more medicaments through the needle.

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