WO2025175060A1

WO2025175060A1 - Gas canister puncture systems for auto-injectors, auto-injector devices and methods for using them

Info

Publication number: WO2025175060A1
Application number: PCT/US2025/015862
Authority: WO
Inventors: Jack R. Auld; Matthew MCCAWLEY; John C. DUNNE, Jr.; Eric Anderfaas; Cho Kin CHIU; Gavin Li; Quinton A. QUINTANA
Original assignee: Altaviz LLC
Current assignee: Altaviz LLC
Priority date: 2024-02-13
Filing date: 2025-02-13
Publication date: 2025-08-21
Anticipated expiration: 2026-08-13

Abstract

Drive modules for injectors are provided that include an inner housing comprising a proximal end, a distal end, a first chamber adjacent the proximal end and a second chamber; a source of pressurized gas within the first chamber; a release cap surrounding the proximal end; and a. carriage within the first chamber carrying an opener pin located adjacent the source of pressurized gas and releasably coupled to the release cap. The release cap and carriage comprising features that disengage when the release cap is directed proximally by an actuator, the carriage biased to move axially when released to move the opener pin thereby causing the opener pin to open the source of pressurized gas to release the pressurized gas into the first chamber and into the second chamber such that the pressurized gas advances a plunger extending from the second chamber and the distal end of the inner housing.

Description

GAS CANISTER PUNCTURE SYSTEMS FOR AUTO-INJECTORS, AUTO-INJECTOR DEVICES AND METHODS FOR USING THEM RELATED APPLICATION DATA [0001] The present application claims benefit of co-pending U.S. provisional application Serial No. 63/553,113, filed February 13, 2024, the entire disclosure of which is expressly incorporated by reference herein. The present application is also related to U.S. application Serial No. 18/229,103, filed August 1, 2023, published as U.S. Publication No. 2024/ 0033434, the entire disclosure of which is expressly incorporated by reference herein. TECHNICAL FIELD [0002] The present application relates generally to devices and methods for delivering agents into a subject’s body and, more particularly, to auto-injectors and/or gas- powered drive systems for injection devices, and to methods for making and using such devices. BACKGROUND [0003] There are many applications involving delivery of a medicament or other agent subcutaneously, intramuscularly, or otherwise into a patient’s body. For example, auto-injectors are available that include a predetermined dose of the agent that may be delivered automatically into the patient’s body, e.g., after placement against the patient’s skin and activation. Generally, such auto-injectors are spring-loaded syringes that are activated to release the spring, which generates sufficient force to penetrate the skin with a needle and deliver the dose within the syringe. For viscous fluids, the forces required to develop fluid flow can be higher than spring-powered systems can provide. When springs can be used, they must generate a relatively high force that requires springs of high mass. Consequently, such auto-injectors may make substantial noise, create pressure spikes in the syringe leading to glass breakage, vibrate, and/or may drive the needle forcefully into the patient’s skin, which may cause pain and/or may startle the user, particularly when the patient is administering the injection themselves. [0004] Therefore, improved devices and methods for delivering agents into a patient’s body would be useful. SUMMARY [0005] The present application relates generally to devices and methods for delivering agents into a subject’s body and, more particularly, to auto-injectors and/or gas- powered drive systems for injection devices, and to methods for making and using such devices. [0006] In accordance with one example, a drive module is provided for an injector that includes an inner housing comprising a proximal end, a distal end, a first chamber adjacent the proximal end and a second chamber between the first chamber and the distal end; a source of pressurized gas within the first chamber; a release cap surrounding the inner housing proximal end; and a carriage within the first chamber carrying an opener pin located adjacent the source of pressurized gas and releasably coupled to the release cap, the release cap and carriage comprising one or more features that disengage when the release cap is directed proximally by an actuator, the carriage biased to move axially when released to move the opener pin thereby causing the opener pin to open the source of pressurized gas to release the pressurized gas into the first chamber and into the second chamber such that the pressurized gas advances a plunger extending from the second chamber and the distal end of the inner housing. The one or more features may include one or release fingers, release balls, and/or other features provided on one or more of the release cap, carriage, and the inner housing. [0007] In accordance with another example, a drive module is provided for an injector that includes an inner housing comprising a proximal end, a distal end, a first chamber adjacent the proximal end and a second chamber between the first chamber and the distal end; a source of pressurized gas within the first chamber; a release cap surrounding the inner housing proximal end; and a carriage within the first chamber carrying an opener pin located adjacent the source of pressurized gas and releasably coupled to the release cap, the release cap and carriage comprising one or more features that disengage when the release cap is directed distally by an actuator, the carriage biased to move axially when released to move the opener pin thereby causing the opener pin to open the source of pressurized gas to release the pressurized gas into the first chamber and into the second chamber such that the pressurized gas advances a plunger extending from the second chamber and the distal end of the inner housing, the one or more features comprise a central hub on the release cap and a plurality of fingers on the carriage that slide along the hub as the release cap is directed proximally until the hub moves proximally beyond the tabs, the fingers biased to move radially inwardly to release the carriage. [0008] In accordance with still another example, a drive module is provided for an injector that includes an inner housing comprising a proximal end, a distal end, a first chamber adjacent the proximal end and a second chamber between the first chamber and the distal end; a source of pressurized gas within the first chamber; a release cap surrounding the inner housing proximal end; and a carriage within the first chamber carrying an opener pin located adjacent the source of pressurized gas and releasably coupled to the release cap, wherein the proximal end of the carriage, inner housing, and the release cap comprise one or more features that disengage when the release cap is directed proximally by an actuator to release the carriage, the carriage biased to move axially when released to move the opener pin thereby causing the opener pin to open the source of pressurized gas to release the pressurized gas into the first chamber and into the second chamber such that the pressurized gas advances a plunger extending from the second chamber and the distal end of the inner housing. [0009] In accordance with yet another example, a drive module is provided for an injector that includes an inner housing comprising a proximal end, a distal end, a first chamber adjacent the proximal end and a second chamber between the first chamber and the distal end; a source of pressurized gas within the first chamber; a release cap surrounding the inner housing proximal end; a carriage within the first chamber carrying an opener pin located adjacent the source of pressurized gas; a plurality of release balls provided on one of a proximal end of the inner housing and the carriage; and one or more recesses on the other of the proximal end of the inner housing and the carriage configured to receive the release balls. When the release cap is in an initial position, the release balls are constrained to prevent the release balls from moving out of the one or more recesses, thereby preventing axial movement of the carriage, and, when the release cap is directed axially, the release balls are released to move out of the one or more recesses, thereby releasing the carriage. When the release cap is directed proximally by an actuator, the release balls are released to move out of the one or more recesses, thereby releasing the carriage, and the carriage is biased to move axially when released to move the opener pin thereby causing the opener pin to open the source of pressurized gas to release the pressurized gas into the first chamber and into the second chamber such that the pressurized gas advances a plunger extending from the second chamber and the distal end of the inner housing. [00010] In accordance with still another example, a drive module is provided for an injector that includes an inner housing comprising a proximal end, a distal end, a first chamber adjacent the proximal end and a second chamber between the first chamber and the distal end; a source of pressurized gas within the first chamber; a release cap surrounding the inner housing proximal end; a carriage within the first chamber carrying an opener pin located adjacent the source of pressurized gas and releasably coupled to the release cap; a central tab comprising a stem extending axially from the release cap and terminating at a distal tip, the tab comprising a relatively large region adjacent the distal tip having a cross- section larger than the stem; and a plurality of fingers extending proximally from the carriage and disposed around the central tab, the fingers comprising inner shoulders that contact the relatively large region when the release cap is in an initial position to constrain the fingers against a surrounding bore of the inner housing to prevent axial movement of the carriage. The release cap is movable axially relative to inner housing when the drive module is activated such that the inner shoulders slide off the relative larger region onto the stem to allow the fingers to move radially inwardly to release the carriage, and the carriage is biased to move axially when released to move the opener pin thereby causing the opener pin to open the source of pressurized gas to release the pressurized gas into the first chamber and into the second chamber such that the pressurized gas advances a plunger extending from the second chamber and the distal end of the inner housing. [00011] In accordance with another example, a device is provided for delivering one or more agents into a subject’s body that includes an outer housing comprising a proximal portion terminating in a proximal end and a distal portion terminating in an open distal end; a syringe comprising a barrel containing one or more agents, a needle extending distally from the barrel such that a tip of the needle is disposed within the distal portion adjacent the distal end, and a piston within a proximal end of the barrel; a drive module; and a plunger comprising a proximal end within the second chamber and a distal end coupled to the piston of the syringe such that the plunger is advanced when pressurized gas is released from the source and enters the second chamber to advance the piston to deliver the one or more agents through the needle. The drive module may include an inner housing comprising a proximal end, a distal end, a first chamber adjacent the proximal end and a second chamber between the first chamber and the distal end; a source of pressurized gas within the first chamber; a release cap surrounding the inner housing proximal end; and a carriage within the first chamber carrying an opener pin located adjacent the source of pressurized gas and releasably coupled to the release cap. The release cap and carriage may include one or more features that disengage when the release cap is directed proximally by an actuator, the carriage biased to move axially when released to move the opener pin thereby causing the opener pin to open the source of pressurized gas to release the pressurized gas into the first chamber and into the second chamber such that the pressurized gas advances the plunger. [00012] 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 DESCRIPTION OF THE DRAWINGS [00013] It is believed the present invention will be better understood from the following description of certain examples taken in conjunction with the accompanying drawings, in which like reference numerals identify the same elements and in which: [00014] FIGS. 1A and 1B are side and end views, respectively, of an exemplary gas puncture system or drive module that may be provided in an auto-injector. [00015] FIG. 1C is an exploded view of the system of FIGS. 1A and 1B showing internal components. [00016] FIG. 1D is a longitudinal cross-section of the system of FIGS. 1A and 1B taken along D-D. [00017] FIGS. 1E and 1F are side and perspective views, respectively, of a spring perch assembly that may be included in the system of FIGS. 1A and 1B. [00018] FIG. 1G is a longitudinal cross-section of the spring perch assembly of FIGS. 1E and 1F. [00019] FIGS. 2A and 2B are longitudinal cross-sections of an exemplary auto- injector device including a front and rear housing, and a safety cap. showing internal components of the device including a syringe carrying one or more agents. [00020] FIGS. 3A and 3B are details of the distal end of the device of FIGS. 2A and 2B before use, showing a safety cap covering an activation cap and needle of the device. [00021] FIGS. 4A-4C are cross-sections of the device of FIGS. 2A and 2B, showing activation of the device when the activation cap is displaced proximally when the device is pressed against a subject’s skin to puncture the skin with the needle, the activation cap causing a syringe spacer and release cap to also displace proximally to release a carriage carrying an opener pin, causing the opener pin to advance distally to open a gas canister to release pressurized gas into a flow path within the device. [00022] FIGS. 5A-5C are details of the proximal end of the device as shown in FIGS. 4A-4C, respectively. [00023] FIGS. 6A and 6B are cross-sections of the device of FIGS. 2A and 2B after the pressurized gas is released, showing the pressurized gas advancing a plunger within the device to deliver one or more agents within the syringe through the needle, and advancing the activation cap when the needle is withdrawn from the subject’s skin. [00024] FIG. 6C is a detail of the device as shown in FIG. 6B, showing a tab locking the activation cap after being advanced. [00025] FIG. 7 is a side view of another example of a gas puncture system or drive assembly for an auto-injector. [00026] FIG. 8 is an exploded view of the gas puncture system of FIG. 7 showing internal components. [00027] FIG. 9A is an end view of the gas puncture system of FIG. 7. [00028] FIG. 9B is a longitudinal cross-section of the gas puncture system of FIGS. 7-9 taking along E-E. [00029] FIGS. 10A and 10B are details of a spring perch of the gas puncture system of FIGS. 7-9, showing release angles Θ and γ. [00030] FIGS. 11 and 12 are side and perspective views, respectively, of an exemplary spring perch assembly that may be included in the gas puncture system of FIGS. 7-9. [00031] FIG. 13 is a longitudinal cross section of the spring perch assembly of FIGS. 11 and 12. [00032] FIG. 14 is a detail of a cross section side illustrating flex in a release finger of the spring perch assembly of FIGS. 11 and 12. [00033] FIG. 15 is a side view of still another example of a gas puncture system or drive assembly for an auto-injector. [00034] FIG. 16 is an exploded view of the system of FIG. 15 showing internal components. [00035] FIG. 17A is an end view of the system of FIG. 15. [00036] FIG. 17B is a longitudinal cross-section of the gas puncture system of FIGS. 7-9 taking along F-F. [00037] FIG. 17C is a perspective view of an exemplary release cap that may be included in the system of FIG. 15. [00038] FIG. 18 is a detail showing a release angle Q. [00039] FIGS. 19A-19C are details of a spring perch assembly and release cap of the system of FIGS. 15 and 16, showing fingers being released from the perch during activation of the system. [00040] FIGS. 20A and 20B are end and cross-sectional views of still another example of a gas puncture system or drive assembly. [00041] FIGS. 21A-21C are details of a spring perch assembly and release cap of the system of FIGS. 20A and 20B, showing release of the spring perch during activation of the system. [00042] FIGS. 22A and 22B are end and cross-sectional views of another example of a gas puncture system or drive assembly. [00043] FIGS. 23A and 23B are details of a spring perch assembly and release cap of the system of FIGS. 22A and 22B, showing release of the spring perch during activation of the system. [00044] FIGS. 24A and 24B are perspective views of another example of a front cylinder with release fingers and a spring perch assembly that may be included in another example of a gas puncture system or drive assembly. [00045] FIGS. 25A and 25B are end and cross-sectional views of yet another example of a gas puncture system or drive assembly. [00046] FIGS. 26A and 26B are details of a spring perch assembly (with external balls) and release cap of the system of FIGS. 25A and 25B, showing release of the spring perch during activation of the system. [00047] FIGS. 27A and 27B are perspective views of another example of a front cylinder with external balls and a spring perch assembly that may be included in another example of a gas puncture system or drive assembly. [00048] FIGS. 28A and 28B are end and cross-sectional views of still another example of a gas puncture system or drive assembly. [00049] FIGS. 29A and 29B are details of a spring perch assembly (with internal balls) and release cap of the system of FIGS. 28A and 28B, showing release of the spring perch during activation of the system. [00050] FIGS. 30A and 30B are perspective views of another example of a front cylinder and a spring perch assembly with internal ball release features that may be included in another example of a gas puncture system or drive assembly. [00051] FIGS. 31A and 31B are end and cross-sectional views of another example of a gas puncture system or drive assembly. [00052] FIGS. 32A and 32B are details of a spring perch assembly and release cap of the system of FIGS. 31A and 31B, showing release of the spring perch during activation of the system. [00053] FIGS. 33A and 33B are end and cross-sectional views of still another example of a gas puncture system or drive assembly. [00054] The drawings are not intended to be limiting in any way, and it is contemplated that various examples of the invention may be carried out in a variety of other ways, including those not necessarily depicted in the drawings. The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention; it being understood, however, that this invention is not limited to the precise arrangements shown. DETAILED DESCRIPTION [00055] Before the examples are described, it is to be understood that the invention is not limited to particular examples described, as such may, of course, vary. It is also 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. [00056] Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither or both limits are included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention. [00057] Unless defined otherwise, 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 and exemplary methods and materials are now described. [00058] It must 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, reference to “a compound” includes a plurality of such compounds and reference to “the polymer” includes reference to one or more polymers and equivalents thereof known to those skilled in the art, and so forth. [00059] Certain ranges are presented herein with numerical values being preceded by the term “about.” The term “about” is used herein to provide literal support for the exact number that it precedes, as well as a number that is near to or approximately the number that the term precedes. In determining whether a number is near to or approximately a specifically recited number, the near or approximating unrecited number may be a number which, in the context in which it is presented, provides the substantial equivalent of the specifically recited number. [00060] Turning to the drawings, FIGS. 1A-1G show an exemplary gas-powered device or drive assembly A, which uses energy stored in a gas canister E to power a device, such as the auto-injector 10 shown in FIGS. 2-6, e.g., for delivering one or more agents and the like. As shown in FIGS. 1A-1C, the device A generally includes a front cylinder H, a rear cylinder B, and a release cap I. The front cylinder H includes the gas canister E, a gas canister stop C, and a puncture assembly including a spring perch assembly F. As shown in FIG. 1C, generally, the device A is actuated by sliding the release cap I proximally (e.g., to the right as shown in FIG. 1C), which pulls a release cap pin feature J, such as that as shown in FIG. 1D, from between spring perch release fingers K, e.g., as best seen in FIG. 1F. This proximal movement of the release cap I allows the release fingers K to be pushed into a bore of the front cylinder H by the force provided by a puncture spring G. [00061] With the spring perch release fingers K release, the spring perch assembly F pushes a puncture or opener pin M into the gas canister E, which is held in position by the gas canister stop C, releasing pressurized gas (not shown) stored in the canister E to power the device A. O-rings, e.g., cylinder O-ring D and spring perch O-ring L seal the gas within chambers of the rear cylinder B and the front cylinder H, which may push on a plunger or similar element to power the device A. If slight increases in puncture spring G are desired, then a spring shim O may be used to increase the deflection of the puncture spring G and hence the spring force. [00062] Testing with a device similar to device A has shown less release reliability than desired for a typical use of the device. The present application discloses various examples of drive assemblies or modules that may provide various advantages over the device A, e.g., providing improved reliability and/or functionality. For example, the forces associated with pulling the release cap pin feature J may be higher than desired for a given application since the spring perch release fingers K push on the release cap pin feature J, which may increase the release forces due to friction. The exemplary devices herein may allow for reductions or increases in this pinching force as desired for a given application. [00063] For clarity, FIG. 1E shows a side view of the spring perch assembly F, while FIG. 1F shows an isometric view of the spring perch assembly F and the shape of the release fingers K both on the inside, which interfaces with the release pin feature J as well as the outside interfaces which interface with the front cylinder H. The associated elements of the spring perch assembly are best seen in FIG. 1G, such as the spring perch O-ring L, the spring perch N, and the puncture pin M, which may be pressed into or otherwise attached to the spring perch N. The spring shim O may be included or omitted depending on the desired spring force. [00064] Turning to FIGS 2A and 2B, an exemplary auto-injector device 6 is shown that may include a drive assembly similar to the device A shown in FIGS. 1A-1G. Alternatively, the drive assembly may be replaced with any of the other exemplary drive assemblies, as described elsewhere herein. As shown, the device 6 includes an outer housing 8 including a front housing 10 carrying a syringe 70 containing one or more agents within an agent chamber 73, and a rear housing 12 including a drive assembly for automatically delivering the agent(s) from the syringe 70 when the device 6 is activated. As shown, a safety cap 86 is provided on the front housing 10 to prevent premature activation of the device 6, which may be removed immediately before an injection, as described further elsewhere herein. One or more internal components of the device 6 may move axially, i.e., proximally and/or distally relative to the longitudinal axis 18 when the device 6 is activated, as described further elsewhere herein. [00065] In one example, the syringe 70 may be a pre-filled syringe, e.g., formed from glass, plastic, and the like, filled with a predetermined volume of agent, e.g., corresponding to a single dose for a patient. Alternatively, the agent chamber and needle may be integrated into the forward housing 10 if desired (not shown). In a further alternative, the syringe 70 (or integral agent chamber) may include a distal port (not shown) without a needle, such that a separate needle (also not shown) may be coupled to the port, e.g., using a Luer fitting, mating threads, and/or other cooperating connectors, immediately before an injection or otherwise as desired. As used herein, “agent” may include one or more flowable therapeutic and/or diagnostic compounds, medicaments, or materials, e.g., in liquid or gaseous form, in solution or suspension, and the like, such as viscous fluids. [00066] With continued reference to FIGS. 2A and 2B, the syringe 70 includes a barrel 72 containing the agent(s) within agent chamber 73, a needle 78 extending from a distal end 72a of the barrel 72, and a piston or stopper 74 slidable within a proximal end 72b of the barrel 72 for directing the agent(s) through the needle 78 into the subject’s body (not shown). The device 6 also includes a gas canister or other source of pressurized gas 40 to power the device 6, e.g., to advance a plunger 50 coupled to the piston 74 to deliver the agent(s). The device 6 also includes an activation cap 80 and an opener mechanism 60 for opening the canister 40 to release pressurized gas within the canister 40 into a set of chambers of the device 6. For example, an inner housing 20 may be mounted within the outer housing 8 that includes a first or proximal chamber 22, e.g., within which the gas canister 40 is mounted, and a second or distal chamber 24, e.g., in which the plunger 50 is slidably received. [00067] Generally, the device 6 is configured such that, when a contact surface 84 of the activation cap 80 is pressed against a subject’s skin to insert the needle 78, the activation cap 80 retracts proximally into the outer housing 8 and automatically activates the opener mechanism 60 to release the pressurized gas from the canister 40 into the first and second chambers 22, 24, which generates a distal force to advance the plunger 50 to deliver the agent(s) from the syringe 70 into the subject. After the injection is completed and the device 6 is withdrawn away from the skin, the activation cap 80 may automatically advance to cover the needle 78. [00068] For example, a spacer 30 may be provided that extends between the activation cap 80 and a release cap 34 of the opener mechanism 60, e.g., such that proximal movement of the activation cap 80 is translated by the spacer 30 to the direct the release cap 34 proximally within the rear housing 12, which releases a spring perch assembly or carriage 64 of the opener mechanism 60, as described further elsewhere herein. The spacer 30 may be biased distally, e.g., by spring 32, which may, in turn, bias the activation cap 80 distally after completing the injection, also as described further elsewhere herein. [00069] Generally, the outer housing 8 includes a proximal end 8a, e.g., provided on the rear housing 12, an open distal end 8b, e.g., provided on the forward housing 10, and an inner wall extending therebetween to enclose the interior of the device 6. The outer surface between the proximal and distal ends 8a, 8b may be sized and/or shaped to facilitate manipulation of the device 6, e.g., to facilitate placing and pressing the activation cap 80 against a subject’s skin to activate the device 6 and inject the agent(s). For example, the outer surface may have a generally cylindrical shape optionally including one or more textures or grip features to facilitate an operator (the subject themselves or a third party) holding the device 6 in one hand and pressing the activation cap 80 against the subject’s skin, as described further elsewhere herein. As shown, the proximal end 8a of the housing 8 may include a wall 8c enclosing the proximal end 8a and, optionally, one or more pockets or other features 8d for locking the release cap 34, as described further elsewhere herein. [00070] The outer housing 8 may be formed from multiple, separate components, e.g., clamshell halves, e.g., formed from metal, such as stainless steel, aluminum, and the like, plastic, and/or composite material, by one or more of cold drawing, molding, casting, machining, and the like, that are substantially permanently attached together, e.g., by one or more of welding, soldering, fusing, bonding with adhesive, interference fit, and the like. As shown, the outer housing 8 is formed as separate forward and rear housings 10, 12, which may be assembled separately with respective internal components, and then coupled together, e.g., after loading a syringe 70 into the forward housing 10. [00071] For example, during manufacturing, the forward housing 10 may be assembled with the activation cap 80 and safety cap 86, and a syringe 70 may be loaded into an interior of the forward housing 10, e.g., during manufacturing or during assembly of the device 6 any time before performing an injection. Optionally, as shown in FIGS. 3A and 3B, the syringe 70 may include a rigid needle shield 79, e.g. formed from conventional materials, that may be removably secured to the distal end 72a of the barrel 72 to protect the needle and prevent accidental sticks. The safety cap 86 may include features 86a that engage the needle shield 79 such that, when the safety cap 86 is removed, the needle shield 79 is also removed. For example, as shown, the proximal end of the safety cap 86 may include one or more fingers 86a that fall into one or more corresponding cutouts, recesses, or other features on the needle shield 79 when the syringe 70 is inserted into the forward housing 10, thereby coupling the needle shield 79 to the safety cap 86, as described elsewhere herein. [00072] The rear housing 12 may be assembled with the inner housing 20, the spacer 30, the release cap 34, the gas canister 40, the plunger 50, and the opener mechanism 60 (and any other incidental components), and the rear housing 12 may be coupled to the forward housing 10 at any time. For example, during manufacturing, a syringe 70 may be loaded into the interior of the forward housing 10, and the assembled rear housing 12 may be immediately coupled to the forward housing 10. When the rear housing 12 is attached to the forward housing 10, a distal end 54 of the plunger 50 may be coupled to the piston 74 within the syringe 70, e.g., such that distal movement of the plunger 50 is translated to the piston 74, as described further elsewhere herein. [00073] As shown in FIGS. 2A and 2B, the outer housing 8 may include a mount 11, e.g., on one of the forward and rear housings 10, 12, for guiding and/or securing the syringe 70 during loading. Optionally, the proximal end 72b of the barrel 72 may include one or more flanges, e.g., a radial flange or a pair of opposing flanges, that may abut and/or be received within the mount 11 to secure the syringe 70 relative to the forward housing 10. In addition or alternatively, one or more detents, ridges, or other features (not shown) may be provided on the forward housing 10 for securing the syringe 70. Optionally, the forward housing 10 may include one or more windows 10c in the sidewall, which may facilitate observing the syringe 70 during an injection, e.g., to allow visual confirmation when the piston 74 is fully advanced. [00074] Optionally, the device 6 may include a syringe spacer or adapter 75 that may provide an interface between a distal end 54 of the plunger 50 and the piston 74, e.g., to provide connectors therebetween and/or ensure proper spacing such that the piston 74 is advanced in conjunction with the plunger 50. For example, different length spacers 75 may be provided to allow different length syringes to be loaded into the forward housing 10 while properly positioning the needle 78 adjacent the distal end 8b of the outer housing 8 and allowing the plunger 50 to be properly coupled to the piston 74. [00075] During manufacturing or assembly, a syringe 70 may be selected that may be inserted into the housing 8, e.g., through the opening in the distal end 8b and coupled to the distal end 16 of the drive assembly 12. A syringe spacer 75 may be selected and its distal end 75a may be coupled to the piston 74, e.g., by one or more cooperating threads, as shown, one or more detents or other connectors, and the like. The distal end 54 of the plunger 50 may be inserted into a recess 75b in the syringe spacer 75 when the rear housing 12 is coupled to the forward housing 10. Optionally, the distal end 54 of the plunger 50 and the recess 75b may include cooperating locking features, e.g., one or more threads, detents, and the like (not shown) or the distal end 54 may simply be inserted into the recess 75b to coupled subsequent distal movement of the piston 74 to the plunger 50, as described further elsewhere herein. [00076] Alternatively, the assembled housings 10, 12 may be packaged, stored, and/or otherwise prepared for subsequent assembly. For example, the housing 10, 12 may be shipped or otherwise provided to a manufacturer of the syringe 70, who may load the syringe 70 and couple the housings 10, 12 together to provide the finished device 6. In a further alternative, the assembled housings 10, 12 may be provided to a hospital, physician, or other medical professional, and final assembly may be completed immediately before performing an injection, which may allow a syringe including a specific agent to be loaded before an injection. [00077] The proximal end 10a of the forward housing 10 and the distal end 12b of the rear housing 12 may include one or more cooperating connectors (not shown) to couple the housings 10, 12 together to provide the fully-assembled device 6. For example, the housings 10, 12 may include one or mating threads, detents, and the like, which may permanently couple the housings 10, 12 together. Alternatively, the connectors may allow the housings 10, 12 to be subsequently separated, e.g., after performing an injection, to remove the syringe 70, e.g., to allow the device 6 to be cleaned and reused with a new syringe. [00078] In addition or alternatively, the housings 10, 12 may be permanently attached together by one or more of an interference fit between the ends 10a, 12b, bonding with adhesive, fusing, sonic welding, and the like. In another alternative, the outer housing 8 may be formed as a single, integral component into which the components of the device 6 may be assembled. In these alternatives or even with a two-part housing, the device 6 may be a single use device, which may be disposed of after a single injection. [00079] In the example shown in FIGS. 2A and 2B, the inner housing 20 includes a proximal cylinder 20a including the first chamber 22 and a distal cylinder 20b including the second chamber 24. Each of the proximal and distal cylinders 20a, 20b may have an elongate cylindrical wall or other cross-sectional shape along their lengths. The proximal and distal cylinders 20a, 20b may be permanently attached together to provide the inner housing 20, e.g., by one or more of cooperating threads, as shown, detents or other connectors, force fit, bonding with adhesive, sonic welding, fusing, and the like. Alternatively, the inner housing 20 may be formed as a single, unitary structure including the first and second chambers 22, 24. The proximal and distal cylinders 20a, 20b may be formed from materials similar to or different from the outer housing 8. [00080] The inner housing 20 may be mounted within the outer housing 8 such 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 and/or outer housings 20, 8 to secure the inner housing 20 and/or the gas canister 40 relative to the outer housing 8. [00081] In the example shown, the proximal cylinder 20a may include an annular wall surrounding the first chamber 22 that includes a uniform diameter first region 22a within which the gas canister 40 is mounted, and second and third regions 22b, 22c within which the carriage 64 is slidably mounted, as described further elsewhere herein. The distal cylinder 20b may have a length such that a distal end 21b of the distal cylinder 20b may abut the syringe 70 when the device 6 is assembled. [00082] Optionally, the distal end 21b may include one or more features that contact the proximal end 72b of the syringe 70, e.g., an O-ring 20d secured on or around the distal end 21b formed from resilient and/or relatively flexible material. The O-ring 20d may prevent the distal end 21b from damaging the syringe 70, e.g., if the barrel 72 is made from glass. [00083] With continued reference to FIGS. 2A and 2B, the 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 the outlet end 42b to provide an enclosed cavity 48 filled with a fluid containing pressurized gas, such as carbon dioxide or fluorocarbon gases, compressed to sufficient pressure to least partially liquefy the gas within the cavity 48. Alternatively, fluids containing gases such as argon, nitrogen, helium argon, or other combinations thereof that remain in gaseous form may be stored within the cavity 48. As described elsewhere herein, the pressurized fluid contained within the cavity 48 may be used to generate the forces to operate the device 6, e.g., to inject one or more agents from the syringe 70 into a subject’s body. [00084] In one example, the body 42 and cap 44 may be formed from stainless steel or other desired or suitable metal, plastic, or composite material, e.g., formed by one or more of drawing, stamping, machining, casting, molding, and the like. For example, the body 42 may be deep drawn from sheet metal, e.g., a round sheet metal blank of Type 305 stainless steel, using one or more dies and punches (not shown), to form a main barrel region, the enclosed end 42a, an optional tapered shoulder region, and the outlet end 42b defining an opening to which the cap 44 is attached. [00085] As shown, the canister 40 may be oriented with the outlet end 42b proximal to the enclosed end 42a, and the carriage 64 may be provided proximal to the outlet end 44. In the example shown, the cap 44 may be an enclosed cap including a septum or other weakened region (not shown) that may be opened by the opener mechanism. In this example, the carriage 64 may include an opener pin 62 configured to puncture or preferentially tear the septum, as described elsewhere herein. Additional information regarding canisters that may be used and methods for making them may be found in U.S. Publication No. 2017/ 0258583, the entire disclosure of which is expressly incorporated by reference herein. [00086] Alternatively, the cap 44 may include other closer mechanisms, such as a ball or other member (not shown) that may be biased or otherwise configured to close an outlet in the cap 44 yet may be directed away from the cap 44, e.g., into the canister 40, by the carriage 64 to open the outlet and release the pressurized gas within the cavity 48. In this alternative, the opener pin 62 may include a tapered tip (not shown) sized to enter the outlet and push the closure away from the outlet. [00087] The plunger 50 may be an elongate rod or other member including a proximal end 52 that is slidably disposed within the second chamber 24, e.g., initially immediately adjacent the first chamber 22, and a distal end 54 coupled to the piston 74. The plunger 50 is movable from an initial or retracted position (e.g., shown in FIGS. 2A and 2B) to a final or extended position (e.g., shown in FIGS. 6A and 6B), e.g., wherein the distal end 54 extends from the second end 16 of the drive assembly 12 into the agent chamber 73 of the syringe 70. [00088] A flange or other guide member 53 may be provided on the proximal end 52 of the plunger 50 that slidably engages a wall of the second chamber 24. Consequently, when pressurized gas enters the second chamber 24 (via the first chamber 22), the pressure generates a distal force to direct the plunger 50 distally from the initial position towards the final position to advance the piston 74 and deliver the one or more agents from the agent chamber 73 through the needle 78 into the subject, as described further elsewhere herein. [00089] Optionally, a wall, orifice, or intermediate passage (not shown) may be provided between the first and second chambers 22, 24. The intermediate passage may have a relatively small diameter to provide a restrictor to reduce pressure rise time within the second chamber 24. For example, the intermediate passage may i) slow down the transient flow of gas, slowing the rise of pressure imparted to the plunger 50, e.g., providing a soft-start to the injection, reducing/eliminating pressure shock waves in the fluid to be injected in the syringe and possibly reducing patient pain as the drug injection is gently initiated; and/or ii) slow down the steady state flow of gas, reducing the otherwise pressure imparted to the plunger 50, providing a limiting effect to the flow rate of the drug injected into the patient. [00090] Optionally, as shown, the plunger 50 may also include a plunger chamber 56, e.g., extending from an open proximal end 52 of the plunger 50 to a closed distal end 54. The plunger chamber 56 may taper inwardly from the proximal end 52 to the distal end 54, as shown, or may have a uniform diameter or other cross-sectional shape along its length. Alternatively, the proximal end 52 of the plunger 50 may include a closed wall and/or the plunger 50 may be a solid rod between the proximal and distal ends 52, 54. [00091] Optionally, the flange 53 on the proximal end 52 of the plunger 50 may include one or more passages (not shown) that extend between proximal and distal surfaces of the flange 53. For example, the flange 53 may include a plurality of circular or other enclosed passages spaced apart from one another around a circumference of the flange 53, each extending between the proximal and distal surfaces. [00092] In this option, the flange 53 may be sized and/or shaped to slidably engage an inner wall of the second chamber 24, e.g., to allow the plunger 50 to move from the initial to the extended position, but may not require O-rings or other seals. Instead, one or more O-rings or other seals may be provided within and/or adjacent the inner housing 20 to seal the first and second chambers 22, 24 and/or otherwise a flow path from the gas canister 40 to the plunger 50. For example, a first O-ring 58a may be provided between the inner housing 20 and the carriage 64, a second O-ring 58b may be provided between a distal end 21b of the inner housing 20 and the plunger 50, and/or a third O-ring 58c may be provided between the proximal and distal cylinders 10a, 10b, if provided as separate components secured together. [00093] In one example, the plunger 50 includes a flange 53 formed as a cylindrical head having a larger outer diameter than the plunger 50, which may be integrally molded or otherwise formed with the plunger 50, or that is manufactured separately and permanently attached to the plunger 50, with one or more passages (not shown) extending between proximal and distal surfaces of the flange 53. When the canister 40 is opened to release the pressurized gas, the initial volume that the gas must fill the first chamber 22 around the canister 40, the second chamber 24 around the plunger 50 and, optionally, the plunger chamber 56, which may result in an initial pressure drop as the gas fills the available volume. However, as the plunger 50 advances, the change in volume that the gas must fill increases only minimally (e.g., the volume the plunger 50 occupies within the second chamber 24 that is displaced out of the distal end 16 of drive assembly 12). Consequently, because the volume change is minimized, the resulting force applied by the pressure on the plunger 50 may remain substantially constant or reduce only slightly. Thus, the resulting force drop applied to the plunger 50 may be minimized, which may provide a more uniform delivery rate of the agent from the syringe 70. Additional information regarding plungers that may provide reduced pressure drop can be found in co-pending U.S. application, Serial Nos. 17/965,707, the entire disclosure of which is expressly incorporated by reference herein. [00094] Optionally, the proximal end 52 of the plunger 50 may 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 may taper between the proximal and distal ends 52, 54 of the plunger 50. Such a tapered shape may increase the cross-sectional area of the plunger 50 as it advances from the initial position towards the final position, which may minimize the change in the distal force applied to the syringe stopper due to volume change, which may be particularly useful for applications where consistent rates of delivery are desired. It will be appreciated that any of these optional features related to the plunger 50 may be combined together or omitted, as desired. [00095] Returning to FIGS. 2A and 2B, the opener mechanism 60 includes a release cap 34 and a spring perch assembly 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 the opener pin 62, e.g., mounted along the axis 18 and oriented distally towards 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 activation cap 80 and spacer 30), and the carriage 64 may be biased to move distally, when released, to direct the opener pin distally to open the outlet in the cap 44 of the canister 40. [00096] 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 activated. For example, as best seen in FIGS. 5A-5C, the carriage 64 includes locking tabs or other features 64a on its proximal end that engage the proximal end 13a of the rear housing 12, and a flange 64b on its distal end slidable within the second region 22b of the first chamber 24. A puncture spring 66 is also provided within the second region 22b around the carriage 64, e.g., a coil spring provided in an initially compressed state between the rear housing 12 and the flange 64b. Consequently, the spring 66 biases the carriage 64 to move distally, but for the locking features 64a engaging the proximal end 13a of the rear housing 12. [00097] The release cap 34 and carriage 64 include cooperating features that release the locking features 64a from the rear housing 12 when the device 6 is activated. For example, as shown in FIGS. 5A-5C, the release cap 34 includes a cylindrical body surrounding 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 an enclosed proximal end 34a proximal to the proximal end 13a of the rear housing 12, and a distal end 34b that includes one or more features to limit axial movement of the release cap 34. For example, one or more flanges on the distal end 34b may slide proximally along the inner surface of the outer housing 8, e.g., until they abut a ridge on the outer housing 8 to prevent further proximal movement of the release cap 34, as described further elsewhere herein. [00098] As shown, a central hub 36 is provided on the proximal end 34a of the release cap 34 aligned along the axis 18 distally towards the opener pin 62. The carriage 64 includes a plurality of tabs or release fingers 65, e.g., arranged concentrically around the axis 18 such that the tabs 65 may slide along the hub 36 as the release cap 34 is directed proximally. Once the hub 36 moves proximally beyond the tabs 65, the tabs 65 are biased to move radially inwardly (towards the central axis 18), thereby directing the locking features 64a inwardly. Once the locking features 64a clear the proximal end 13a of the rear housing 12, e.g., as shown in FIG. 5C, the spring 66 may automatically direct the carriage 64 distally, thereby directing the opener pin 62 distally to penetrate the septum in the cap 44 of the canister 40 (or otherwise opening the outlet). [00099] During use, the device 6 may be provided initially with the safety cap 86 attached to the distal end 8b of the housing 8, e.g., as shown in FIGS. 1-2B. Immediately before performing an injection, the safety cap 86 may be removed, e.g., by simply pulling the safety cap 86 distally away from the outer housing 8, to expose the contact surface 84 of activation cap 80, e.g., as shown in FIG. 4A. For example, as best seen in FIGS. 3A and 3B, the safety cap 86 may include inner and outer cylindrical members with the proximal end 86a of the inner member coupled to the needle shield 79 and a proximal end 86b of the outer member slidably received over the distal end 8b of the outer housing 8. Alternatively, the safety cap 86 and/or outer housing 8 may include one or more connectors, locks, and the like (not shown) that may be disengaged before removing the safety cap 86. [000100] As described elsewhere herein, the safety cap 86 may prevent the activation cap 80 from being directed proximally, e.g., by preventing the activation cap 80 from being contacted. In addition or alternatively, the safety cap 86 may include features that engage the needle shield 79 such that, when the safety cap 86 is removed, the needle shield 79 is also removed. The safety cap 86 and needle shield 79 may 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 to be used to perform an injection. [000101] Turning to FIGS. 4A-4C, the contact surface 84 may be placed against a subject’s skin (not shown) and then the device 6 may be pressed against the skin to insert the needle 78, thereby causing the activation cap 80 to slide proximally from the initial position shown in FIG. 4A to the retracted position shown in FIG. 4B as the needle 78 enters the subject’s skin. As described further below, this action may activate the opener mechanism 60 to cause the opener pin 62 to open the outlet of the gas canister 40 to release pressurized gas into the first chamber 22, whereupon the pressurized has may advance the plunger 50 and, consequently, the piston 74 to deliver the agent(s) through the needle 78 into the subject. [000102] For example, as shown in FIG. 4A, initially, the proximal end 82 of the activation cap 80 may abut or otherwise engage a distal end 30a of the spacer 30, and a proximal end 30b of the spacer 30 may abut or otherwise engage the distal end 34b of the release cap 34. Consequently, when the activation cap 80 is retracted proximally within the outer housing 8, its proximal end 82 pushes the distal end 30a of the spacer 30, thereby directing the spacer 30 proximally, and, in turn, the proximal end 30b of the spacer 30 pushes the distal end 34b of the release cap 34, thereby directing the release cap 34 proximally, e.g., until the proximal end 34a of the release cap 34 contacts the proximal end 8c of the outer housing 8. [000103] As the activation cap 80, spacer 30, and release cap 34 move proximally, the inner housing 20 (and canister 40 within the first chamber 22) may remain substantially stationary. As can be seen in FIGS.4A and 4B, as the spacer 30 is directed proximally, the spring 32 may be compressed, e.g., between features on the distal end 30a of the spacer 30 and the inner housing 20, thereby biasing the spacer 30 subsequently to move distally. However, with the operator pressing the contact surface 84 of the activation cap 80 against the subject’s skin, the spacer 30 is unable to move distally. [000104] Since the carriage 64 is secured relative to the inner housing 20 by the locking features 64a, the carriage 64 also remains substantially stationary, such that the release cap 34 moves proximally relative to the carriage 64 and the tabs 65 on the carriage 64 slide along the hub 36 on the release cap 34, as best seen in FIGS. 5A-5C. When the release cap 34 reaches its proximal-most position, e.g., shown in FIGS. 4C and 5C, the hub 36 has moved proximally beyond the ends of the tabs 65 and, given the inward bias of the tabs 65, the tabs 65 are released and automatically move inwardly. Given that the tabs 65 are coupled to the locking features 64a on the carriage 64, the inward movement of the tabs 65 causes the locking features 64a to move inwardly, thereby disengaging the locking features 64a from the proximal end 21a of the inner housing 20. [000105] Due to the spring 66, the carriage 64 is then released and biased to move distally, thereby advancing the opener pin 62 distally to open the outlet of the canister 40, as shown in FIGS. 4C and 5C. The release cap 34 may include one or more tabs or other features 34c, e.g., corresponding to the pockets 8d in the outer housing 8, such that, when the release cap 34 reaches its distal-most position, the tabs 34c are received in respective pockets 8d, as shown. Thus, the tabs 34c may prevent the release cap 34 from moving distally as the carriage 64 advances distally due to the spring 66. [000106] When the carriage 64 moves distally, it causes the opener pin 62 to advance and penetrate the septum in the cap 44 (or otherwise open the outlet), thereby releasing the pressurized gas within the canister 40. The released pressurized gas then enters the first chamber 22, e.g., around the canister 40, and passes to the second chamber 24, thereby pressurizing the second chamber 24 to generate a distal force to direct the plunger 50 distally from the initial position towards a final position to deliver the one or more agents from the syringe 70 through the needle 78 into the subject, e.g., as shown in FIG. 6A. [000107] The operator may monitor the syringe 70 during the injection, e.g., via the window(s) 8c to confirm that the piston 74 has fully advanced distally within the barrel 72 to deliver the entire dose into the subject. Once the injection is completed, the device 6 may be directed away from the subject, thereby withdrawing the needle 78 from the subject’s skin. As the device 6 is directed away from the subject’s skin, the activation cap 80 is free to move distally and, due to the distal bias of the spring 32, the spacer 30 automatically advances distally, thereby directing the activation cap 80 distally to cover the needle 78 as it is withdrawn. [000108] As best seen in FIG. 6C, as the spacer 30 advances distally, the proximal end 30b of the spacer may pass distally beyond features 34d on the distal end 34b of the release cap 34. For example, the features 34b may include one or more fingers or tabs that slide along the interior of the spacer 30 until the proximal end 30b passes distally, whereupon the tabs may resiliently move radially outwardly, e.g., such that the tabs 34d are located proximal to the proximal end 30b of the spacer 30, thereby preventing the spacer 30 from subsequently moving proximally. With the spacer 30 prevented from moving proximally, the activation cap 80 is unable to retract again, thereby locking the activation cap 80 extended over the needle 78 and preventing accidental exposure of the needle 78. [000109] If the device 6 is a single-use device, the device 6 may then be disposed of. If the device is reusable, e.g., if the forward and rear housings 10, 12 are separable, the rear housing 12 may subsequently be separated from the forward housing 10, and the syringe 70 may be removed. For a reusable device, one or more features may be provided within the device to release any 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 may be provided within the plunger 50, which may be manipulated to release the pressurized gas before removing decoupling the plunger 50 from the piston 74. The separate housings 10, 12 may then be cleaned and/or sterilized and a new gas canister 40 may be loaded into the inner housing 20 before reassembling the device. [000110] Turning to FIGS. 7-14, another example of a gas puncture system or drive assembly 100 is shown that may be included in an auto-injector, e.g., to replace the drive assembly of the injector 10 shown in FIGS. 2-6, e.g., in place of the release cap 34, inner housing 20, and their related components. For example, a spacer 30 and outer housing 8 may be provided around the system 100 and a front housing 10 carrying a syringe 70, e.g., similar to that shown in FIGS. 2-6, may be mounted to the device to provide an assembled injector (not shown). [000111] Generally, the system 100 includes a front cylinder 114 and a rear cylinder 102, which may be attached together, e.g., by one or more of mating threads and/or other connectors, interference fit, bonding with adhesive, sonic welding, and the like (or, alternatively, integrally formed together) to provide an inner housing that may be mounted within an outer housing of an injector, e.g., within the outer housing 12 shown in FIGS. 2A and 2B, which may, in turn, be coupled to the front housing 10 containing the syringe 70 (or other source of one or more agents intended for delivery to a subject). [000112] As shown in FIG. 8, a gas canister 108 and spring perch assembly or carriage 112 may be provided within the front cylinder 114 with the carriage 112 carrying an opener pin (not shown) configured to open a septum of the gas canister 108, similar to other devices herein. For example, the carriage 112 may include an annular distal region that may at least partially surround the gas canister 108, e.g., a proximal or neck region including a septum (not shown). [000113] In addition, a gas canister stop 104 may be provided, e.g., between the front and rear cylinders 114, 102, thereby dividing the interior into a first or proximal chamber within the front cylinder 114 (within which pressurized gas from the gas canister 108 is initially released), and a second or distal chamber within the rear cylinder 102 (within which a plunger or other actuator member (not shown) may be provided, e.g., similar to the plunger 50 in the injector 6 and into which the released gas flows around or through the stop 104). The gas canister stop 104 may prevent axial movement of the gas canister 108, while the carriage 112 is movable axially relative to the gas canister 108, e.g., from an initial or proximal position where the opener pin is spaced from the gas canister 108 and a final or distal position where the opener pin opens the septum during activation of the system 100, as described elsewhere herein. [000114] Most of the elements of the system 100 may include features similar to the device 6 shown in FIGS. 2-6, e.g., including a hub or release cap pin feature 118 within the release cap 116,e.g., extending distally from an enclosed proximal end of the release cap 116 (e.g., as best seen in FIG. 9B) and a plurality of release fingers or tabs 120 on the carriage 110 surrounding an inner passage 132 (best seen in FIG. 13). As with the injector 6, the fingers 120 may be provided initially on the hub 118 (e.g., as shown in FIG. 9B) and may be released, when the release cap 116 is directed proximally during activation of the system 100, whereupon a spring 112 may direct the carriage 110 distally to open the gas canister 108 and release the pressurized gas. [000115] One difference from the drive assembly of the injector 6 is that the carriage 112 has longer and more flexible spring perch release fingers 120, which allow the fingers 120 to be deflected or otherwise moved into a relatively narrow proximal bore of the front cylinder 114 more easily. In addition, to help move the spring perch release fingers 120 into the bore within a proximal region 114a of the front cylinder 114, each finger 120 may include one or more lateral bump features 130 extending radially outwardly from each release finger 120. For example, as shown in FIGS. 11 and 13, each release finger 120 may include two bumps 130 spaced apart from one another between fixed and free ends of the release finger 120. As shown, the bumps 130 may extend circumferentially around the fingers 120 at the same axial locations, e.g., to define a discontinuous annular ridge or ring around the spring perch 112, as best seen in FIGS. 11 and 12. [000116] As shown in FIG. 14, these bump features 130 force the spring perch release fingers 120 to flex at intermediate locations between the fixed and free ends (e.g., represented by the dotted line) once the release cap hub 118 has been inserted into the proximal bore to lock the spring perch release fingers 120 with the tips 130 against the hub 118. When the release cap hub 118 has been removed from between the fingers 120 during activation of the system 100 (when the release cap 116 is directed proximally away from the spring perch 112), the release finger lateral bump features 130 apply forces to pull tips of the fingers 120 inwardly into the inner passage 132. The size, number, and location of these bumps 130 may be tailored to adjust release of the spring perch release fingers 120 release from the hub 118, e.g., depending on the potential energy stored within the puncture spring 112 force and/or other design parameters. [000117] As with other devices herein, e.g., the injector 6 in FIGS. 2-6, one or more O-rings may be provided for sealing released gas from the gas canister 108 within the chambers of the system 10. For example, O-ring 106 may be provided around the gas canister stop 104 and O-ring 122 may be provided around the carriage 110, which may sealingly engage an inner wall of the front and/or rear cylinder 114, 102, to seal the chambers and prevent pressurized gas released from the gas canister 108 from escaping, e.g., such that pressurized gas passes into the distal chamber within the rear cylinder 102 to advance the piston (not shown) therein. In this example, the carriage O-ring 122 has been moved to the larger bore in the front cylinder 114 for sealing on the released gas. [000118] Optionally, as shown in FIG. 10A, a proximal edge of the front cylinder 114 may have a chamfer, defining an angle theta (Q). By increasing this angle, the force applied by the puncture spring 112 onto the carriage 110 may help to pull the release fingers 120 away from the bore edge of the front cylinder 114, which may improve releasing the fingers 120 during activation. For example, by redirecting the pull force, this angle may tend to make the release fingers 120 pinch the release cap hub 118 with a greater force, thereby increasing the friction force acting on the release cap hub 118. Optionally, as shown in FIG. 10B, to counterbalance this increased pinching force, the angle gamma γ between the release cap hub 118 and the release fingers 120 may be used to reduce the release force since the squeezing of the release fingers 120 may tend to push the release cap hub 118 out of engagement. [000119] Turning to FIGS. 15-19C, another example of a gas puncture system or drive assembly 200 is shown that may include components generally similar to the system 100 (with like components increased by 100 to 2xx), as shown in FIGS. 15 and 16. For example, as best seen in FIGS. 19A-19C, the system 200 includes a spring perch assembly or carriage 210 with release fingers 220 that include tips 232 that slidably engage a release cap hub 218 on a release cap 216, generally similar to the system 100. Optionally, the release fingers 220 may include lateral bumps 230 extending outwardly, e.g., to provide a discontinuous annular ring or otherwise similar to the bumps 130. [000120] In addition, one or more (e.g., all) of the release fingers 220 include release finger extensions 234 that extend proximally from the tips 232. The release cap 216 includes respective release cap slots 236 (best seen in FIGS. 17C, 19A-19C) through the proximal end wall of the release cap 216 around the release cap hub 218 through which respective release finger extensions 234 initially extend, e.g., as shown in FIG. 19A. [000121] During activation, as shown in FIGS. 19A-19C, as the release cap 216 is directed proximally relative to the front cylinder 214 (e.g., moved to the right in FIGS. 19A- 19C), the extensions 234 act on the release cap 216 as they transit through the slots 236. For example, FIG. 19A shows the release cap 216 in an initial “locked” position in which the release cap 216 provides an “active hold” by holding the release fingers 220 radially outwardly, thereby locking them to the surrounding bore 214a of the front cylinder 214. In FIG. 19B, the release cap 216 has moved proximally, pulling the release cap hub 218 out from the release fingers 220, allowing them to move inwardly away from the to the surrounding bore 214a of the front cylinder 214 in a passive fashion, similar to the system 100. With further motion, as shown by FIG. 19C, the release finger extensions 234 slide within the slots 236 in the release cap 216 and, given the enlarged ends of the extensions 234, the slots 236 actively push the spring perch release fingers 220 away from the surrounding bore 214a of the front cylinder 214, i.e., radially inwardly towards one another, thereby positively causing release of the spring perch assembly 210 in an “active release” mode. Thus, the potential energy in the puncture spring 212 may act against the carriage 210 without any resistance from the release fingers 220. [000122] Optionally, as with the system 100, the angles theta Q and gamma γ may be adjusted as desired to increase or decrease the force required to move the release cap 216. In addition to those design parameters, the geometry of the release finger extensions 234 and the release cap slots 236 may be adjusted to provide a desired active release sequence. [000123] Turning to FIGS. 20A-21C, still another example of a gas puncture system or drive assembly 300 is shown that includes components generally similar to the other systems herein, e.g., including a housing, e.g., including front cylinder 314, a spring perch assembly or carriage 310, a release cap 316, and a gas canister (not shown for clarity). Unlike the systems 100, 200, in this example, the release cap 316 is configured to move distally during activation (e.g., to the left in FIGS. 21A-21C or pushed towards the front cylinder 314) for release. This is in the opposite direction from the systems 100, 200 described previously, which require the release cap 116, 216 to move proximally (to the right or pulled away from the front cylinder 114, 214) for release. [000124] As shown, the release cap 316 may include a release cap feature 318, e.g., a tab or spline that includes a relatively large distal tip or end region 318a at or adjacent a distal tip of the release cap feature 318, and a relatively narrow segment or stem 318b proximal to the distal tip 318a. In an initial position before the system 300 is activated, the end region 318a may engage inwardly extending shoulders or regions 320a of the release fingers 320, thereby constraining the release fingers 320 outwardly against the surrounding bore of a proximal region 314a of the front cylinder 314, e.g., as shown in FIG. 21A. [000125] FIGS. 21A-21C show progression of the system 300 from being fully locked to release. In FIG. 21A, the release cap feature 318 is initially positioned in its locked position with the end region 318a holding the release fingers 320 out, locking the carriage 310 from axial movement within the bore of a proximal region 314a of the front cylinder 314. As the release cap 316 begins to move distally (to the left, as shown in FIG. 21B), the release cap feature 318 is configured to unlock the release fingers 320, allowing a passive unlock mode. For example, the relatively large end region 318a may pass distally beyond the shoulders 320a on the release fingers 320, thereby releasing the release fingers 320 to move radially inwardly away from the surrounding bore. [000126] For example, the release fingers 320 may unlock or, due to friction etc., may stay locked in this passive mode. With further distal motion of the release cap 316 as shown in FIG. 21C, the tapered proximal edge of the release cap 316 may push release finger extensions 330, and consequently, the release fingers 320 radially inwardly away from the surrounding bore of the front cylinder 314, thereby releasing the carriage 310, whereupon the puncture spring 312 may push the carriage 310 distally to open the septum of the gas canister (not shown). [000127] In FIG. 21C, the overlap / interference between the spring perch release finger extensions 330 and the tapered bore on the release cap 316 imply this motion. This provides an “active release” of the spring perch assembly 310. [000128] Turning to FIGS. 22-24, another example of a gas puncture system or drive assembly 400 is shown that generally includes a front cylinder 414, a release cap 416, a spring perch assembly or carriage 410, and a gas canister (not shown for clarity), generally constructed similar to other examples herein. In this system 400, however, a plurality of release fingers 420 are included on a proximal region 414a of the front cylinder 414, e.g., as best seen in FIG. 24A, rather than on the carriage 410. To lock the spring perch assembly 410, a bore or recess 418 is provided in the release cap 416, which is configured to hold the release fingers 420 in their initially locked position. [000129] For example, the carriage 410 may include an annular groove 411 into which inner shoulders on the release fingers 420 may be received such that the outer diameter of the release fingers 420 is slightly smaller than the inner diameter of the bore 418 such that the release fingers 420 may be positioned within the groove 411 and bore 418, thereby constraining the release fingers 420 from moving radially outwardly out of the groove 411. The release fingers 420 and/or groove 411 may include tapered or ramped distal surfaces, e.g., ramped surface 411a shown in FIG. 24B, which are configured to allow the release fingers 420 to move radially outwardly as the release cap 416 moves proximally. [000130] The release fingers 420 may be constructed from flexible material, such as plastic, metal or composite material. One skilled in the art may appreciated that the carriage 410 may be constructed similarly to other spring perch assemblies or carriages described elsewhere herein (but with the groove 411 instead of release fingers). The system 400 may include one or more O-rings or other seals to prevent pressurized gas from escaping from the system 400, once activated, similar to other examples herein. For example, as shown, a spring perch O-ring 422 may be provided in the larger bore of the front cylinder 414. As with some of the other examples described herein, the system 400 may be configured for passive release or, alternatively, the system 400 may be configured for active release, e.g., using similar features to systems 200, 300. [000131] FIGS. 23A and 23B show the system 400 in locked and released modes, respectively. For example, when the system 400 is activated and the release cap 416 moves proximally (e.g., to the right as shown), thereby moving the bore 418 until the release fingers 420 are no longer constrained, thereby allowing the release fingers 420 to move radially outwardly as the release cap 416 moves, e.g., allowing the release fingers 420 to slide along the tapered distal surface 411a of the groove 411 in the spring perch assembly 410. This radially outward spread of the release fingers 420 then releases the carriage 410, allowing the opener pin 424 to puncture or otherwise open the septum of the gas canister (not shown). [000132] In this example, the moment applied to the release fingers 420 by the force of the puncture spring 412 may tend to pull the release fingers 420 into the bore of the front cylinder 414, locking the carriage 410. Optionally, to remove this tendency, the angle theta Q may be increased, e.g., by providing a larger chamfer on the proximal edge of release fingers 420. The forces created by this larger chamfer angle may then overcome the moments applied to the front cylinder release fingers 420. [000133] Turning to FIGS. 25A-27B, yet another example of a gas puncture system or drive assembly 500 is shown that generally includes a front cylinder 514, a release cap 516, a spring perch assembly or carriage 510, and a gas canister (not shown for clarity), generally constructed similar to other examples herein. However, in this example, rather than release fingers, the system 500 includes a set of release balls 528 to hold and release the spring perch assembly 510. [000134] For example, similar to the system 400, the carriage 510 may include an annular groove or other recess 511 (or a plurality of recesses for respective release balls) in a proximal end of the carriage 510 configured to receive the release balls 528. The release cap 516 includes a bore or recess 518 having an inner diameter that is slightly larger than an outer diameter of a proximal region 514a of the front cylinder 514. The proximal region 514a may include a plurality of ball reliefs or other apertures 520 that may receive respective release balls 528, which may be configured to limit radially inward movement of the release balls 528 to allow the proximal region 514a to be slidably received within the bore 518. In this initial position, the release balls 528 may extend radially inwardly from the proximal region 514a and be received in the annular groove 511, thereby preventing axial movement of the spring perch assembly 510. Thus, with the proximal region 514a positioned in the bore 518, the bore 518 constrains the release balls 528 in the front cylinder ball reliefs 520 and locks the carriage 510 from axial movement, as shown in FIG. 26A. [000135] When the release cap 516 moves proximally (e.g., to the right as shown in FIGS. 26A and 26B), the proximal region 514a and the ball reliefs 520 are exposed from the bore 518, and the release balls 528 are free to roll and/or move radially outwardly within the ball reliefs 520, i.e., out of the annular groove 511, thereby releasing the carriage 510, whereupon the puncture spring 512 directs the carriage 510 distally to release pressurized gas from the gas canister (not shown), similar to the other systems herein. The spherical shape of the release balls 528 may provide an outer surface that facilitates movement radially outwardly once release and/or may provide an interface that facilitates subsequent movement of the carriage 510. In a similar fashion to other systems herein, a chamfer angle theta Q, the diameter of the release balls 528, and/or a depth of the groove 511 in the spring perch assembly 510 may be adjusted, as desired, to alter the contact angle at the interface, which may be used to adjust the release forces. [000136] Turning to FIGS. 28-30, still another example of a gas puncture system or drive assembly 600 is shown that generally includes a front cylinder 614, a release cap 616, a spring perch assembly or carriage 610, and a gas canister (not shown for clarity), generally constructed similar to other examples herein. The system 600 also uses release balls 628 to lock and release the carriage 610; however, in this example, the release balls 628 move toward the inside of the proximal region 614a of the front cylinder 614, rather than the outside as with the system 500. [000137] In this example, the release cap 616 includes an internal boss or hub 620 instead of the bore 518. For example, as shown in FIG. 30A, the front cylinder 614 includes an annular groove 618 within the proximal region 614a sized to receive release balls 628 provided on a proximal end of the spring perch assembly 610. For example, as shown in FIG. 30B, the carriage 610 includes a plurality of ball reliefs or recesses 630 (or alternatively may include a single annular bearing slot) spaced apart from one another around the circumference of the carriage 610 within which respective release balls 628 may be received. [000138] Initially, the release cap hub 620 may be provided coaxially with the ball reliefs 630, thereby constraining the release balls 628 outwardly into the groove 618 in the proximal region 614a of the front cylinder 614. [000139] FIG. 29A shows the example in the locked position while FIG. 29B shows the release cap 616 moved proximally (e.g., to the right) with the spring perch assembly 610 released. For example, when the system 600 is activated, the release cap 616 may move proximally, thereby directing the release cap hub 620 proximally until the release balls 628 are released. The release balls 628 may then be free to roll and/or move radially inwardly, i.e., out of the groove 618, thereby releasing the spring perch assembly 610 to move distally (based on the potential energy in the puncture spring 612) to release pressurized gas from the gas canister. [000140] In this example, some care may be required to ensure that there is adequate clearance in the spring perch 626 for the release balls 628 to move out of the locking groove 618 in the front cylinder 614 instead of being jammed in the spring perch 626 internal bore. As with the system 500, the diameter of the release balls 628 and/or the depth of the locking groove 618 in the front cylinder 614 may be used to control the interface contact angle and the forces associated with release of the release balls 628. [000141] Turning to FIGS. 31-33, another example of a gas puncture system or drive assembly 700 is shown that generally includes a front cylinder 714, a release cap 716, a spring perch assembly or carriage 710, and a gas canister (not shown for clarity), generally constructed similar to other examples herein. The system 700 may be constructed and function generally similar to the systems 500 and 600 and shows how the concepts described herein may be used to create a wide range of puncture releases systems. In the example shown, the carriage 710 includes a plurality of long flexible release fingers 720, e.g., similar to the release fingers 120 of the system 100 and including ball-shaped features 718, which may be shaped similar to release balls 628 in the system 600. [000142] This example also shows how different geometries may be used as the holding feature such as a lip type holding feature on the spring perch release finger 120 of system 100 to the ball shaped holding feature 720 of this example. One skilled in the art would readily recognize that various shaped features may be provided that function well as combinations of those shown. [000143] In addition to the different geometries present in this application, the materials used may be optimized for cost and operation of the device. Metal, plastic and/or filled plastics may be used based on the material suitability of stress, strain, creep and friction properties. Optionally, besides materials, different coatings may be used to adjust the friction characteristics between the different elements interfacing. [000144] Another aspect of the functioning of the system 700 (and the other gas puncture systems herein) is the forces required to puncture the gas canister of the systems. High-puncture-force down to low-puncture-force gas canisters would require different examples for optimal cost and function. [000145] It will be appreciated that any of the devices herein may include any combination of the different elements described in any of the examples. [000146] 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 to be limited to the particular forms or methods disclosed, but to the contrary, the invention is to cover all modifications, equivalents and alternatives falling within the scope of the appended claims.

Claims

WE CLAIM: 1. A drive module for an injector, comprising: an inner housing comprising a proximal end, a distal end, a first chamber adjacent the proximal end and a second chamber between the first chamber and the distal end; a source of pressurized gas within the first chamber; a release cap surrounding the inner housing proximal end; and a carriage within the first chamber carrying an opener pin located adjacent the source of pressurized gas and releasably coupled to the release cap, the release cap and carriage comprising one or more features that disengage when the release cap is directed proximally by an actuator, the carriage biased to move axially when released to move the opener pin thereby causing the opener pin to open the source of pressurized gas to release the pressurized gas into the first chamber and into the second chamber such that the pressurized gas advances a plunger extending from the second chamber and the distal end of the inner housing.

2. The drive module of claim 1, wherein the inner housing and the carriage comprise cooperating features that prevent the carriage from moving proximally when the release cap is directed proximally.

3. The drive module of claim 1, further comprising a spring mounted between the carriage and the inner housing to bias the carriage to move axially when released from the release cap.

4. The drive module of claim 1, wherein the one or more features comprise a central hub on the release cap and a plurality of fingers on the carriage that slide along the hub as the release cap is directed proximally until the hub moves proximally beyond the tabs, the fingers biased to move radially inwardly to release the carriage.

5. The drive module of claim 4, wherein the carriage comprises one or more locking features that engage the inner housing to prevent the carriage from moving relative to the inner housing, the locking features coupled to the plurality of fingers such that, when the fingers move radially inwardly, the one or more locking features disengage from the inner housing, whereupon the carriage is released to move axially.

6. The drive module of claim 4, wherein the fingers comprise one or more features configured to cause the fingers to flex to facilitate releasing the carriage from the release cap.

7. The drive module of claim 6, wherein the one or more features comprise bumps configured to cause an intermediate region of the fingers to flex inwardly when the fingers are secured around the hub.

8. The drive module of claim 6, wherein the one or more features comprise outward bumps on the fingers aligned to define a discontinuous annular ring.

9. The drive module of claim 8, wherein each finger includes two bumps spaced apart axially from one another between fixed and free ends of each respective finger, thereby defining two discontinuous annular rings.

10. The drive module of claim 4, further comprising a spring mounted between the carriage and the inner housing to bias the carriage to move axially when released from the release cap, and wherein the proximal end of the inner housing and the fingers comprise features that interact to prevent movement of the carriage until released by the release cap.

11. The drive module of claim 10, wherein the features comprise a chamfer on the proximal end of the inner housing and fingers comprise features that slidably engage the chamfer to facilitate release of the carriage.

12. The drive module of claim 4, wherein one or more of the fingers comprise a finger extension slidably received in an opening in the release cap that lock the carriage until the release cap is directed proximally.

13. The drive module of claim 12, wherein each finger extension and release cap are configured to release the fingers from the hub as the release cap is directed proximally and actively release the carriage.

14. The drive module of claim 4, wherein each finger of the plurality of the fingers comprises a finger extension that is slidably received through a respective slot in the release cap that lock the carriage until the release cap is directed proximally.

15. The drive module of claim 4, wherein one or both of the fingers and the central hub include ramped surfaces that facilitate the fingers sliding off the central hub as the release cap moves proximally to provide active release of the carriage.

16. [device 300] The drive module of claim 1, wherein: the one or more features comprise a central tab comprising a stem extending distally from a proximal end the release cap and a relatively large region adjacent a distal tip of the tab, a plurality of fingers on the carriage that include inner shoulders that contact the relatively large region to constrain the fingers against a surrounding bore of the inner housing to prevent axial movement of the carriage, and wherein the release cap is movable axially relative to inner housing when the drive module is activated such that the inner shoulders slide off the relative larger region onto the stem to allow the fingers to move radially inwardly to release the carriage.

17. The drive module of claim 16, wherein the fingers comprise features that engage corresponding features on the surrounding bore when the fingers are constrained against the surrounding bore to prevent axial movement of the carriage.

18. The drive module of claim 17, wherein the features comprise an outward shoulder on each finger that engages a proximal end wall of the surrounding bore to prevent the axial movement.

19. The drive module of claim 18, wherein one or both of the outward shoulder and the proximal wall comprise a ramped surface to facilitate allowing the fingers to move radially inwardly when the fingers slide off the relatively large region.

20. [device 500, 600] The drive module of claim 1, wherein: the one or more features comprise a plurality of release balls provided on one of a proximal end of the inner housing and the carriage and one or more recesses on the other of the proximal end of the inner housing and the carriage configured to receive the release balls, and when the release cap is in an initial position, the release balls are constrained to prevent the release balls from moving out of the one or more recesses, thereby preventing axial movement of the carriage, and, when the release cap is directed axially, the release balls are released to move out of the one or more recesses, thereby releasing the carriage.

21. The drive module of claim 20, wherein the release balls are spaced about circumferentially from one another.

22. The drive module of claim 21, wherein the one or more recesses comprises an annular groove on the other of the proximal end of the inner housing and the carriage.

23. The drive module of claim 22, wherein the groove comprises a ramped or tapered distal edge to facilitate the release balls moving out of the grove when the release cap is directed axially to provide active release of the carriage.

24. [device 500] The drive module of one of claims 20-23, wherein the one or more recesses are provided in a proximal end of the carriage, and the release balls are received within respective reliefs in a proximal end of the inner housing such that the release balls are constrained inwardly by the release cap in the initial position into the one or more recesses to prevent axial movement of the carriage.

25. The drive module of claim 24, wherein the proximal end of the inner housing is received within an annular bore within the release cap in the initial position to constrain the release balls inwardly, and wherein, when the release cap is directed axially, the proximal end of the inner housing exits the bore to allow the release balls to move radially outwardly out of the one or more recesses.

26. [device 600] The drive module of one of claims 20-23, wherein the release cap comprise a central hub that extends into a proximal end of the carriage, and wherein the one or more recesses are provided within a proximal end of the inner housing, and the release balls are received within respective reliefs in the proximal end of the carriage such that the release balls are constrained outwardly by the central hub in the initial position into the one or more recesses to prevent axial movement of the carriage.

27. The drive module of claim 26, wherein, when the release cap is directed axially, the central hub moves proximally beyond the release balls to allow the release balls to move radially inwardly out of the one or more recesses.

28. [device 500, 600] A drive module for an injector, comprising: an inner housing comprising a proximal end, a distal end, a first chamber adjacent the proximal end and a second chamber between the first chamber and the distal end; a source of pressurized gas within the first chamber; a release cap surrounding the inner housing proximal end; a carriage within the first chamber carrying an opener pin located adjacent the source of pressurized gas; a plurality of release balls provided on one of a proximal end of the inner housing and the carriage; and one or more recesses on the other of the proximal end of the inner housing and the carriage configured to receive the release balls, wherein, when the release cap is in an initial position, the release balls are constrained to prevent the release balls from moving out of the one or more recesses, thereby preventing axial movement of the carriage, and, when the release cap is directed axially, the release balls are released to move out of the one or more recesses, thereby releasing the carriage, and wherein, when the release cap is directed proximally by an actuator, the release balls are released to move out of the one or more recesses, thereby releasing the carriage, the carriage biased to move axially when released to move the opener pin thereby causing the opener pin to open the source of pressurized gas to release the pressurized gas into the first chamber and into the second chamber such that the pressurized gas advances a plunger extending from the second chamber and the distal end of the inner housing.

29. The drive module of claim 28, wherein the release balls are spaced about circumferentially from one another.

30. The drive module of claim 29, wherein the one or more recesses comprises an annular groove on the other of the proximal end of the inner housing and the carriage.

31. The drive module of claim 30, wherein the groove comprises a ramped or tapered distal edge to facilitate the release balls moving out of the grove when the release cap is directed axially to provide active release of the carriage.

32. [device 500] The drive module of one of claims 28-31, wherein the one or more recesses are provided in a proximal end of the carriage, and the release balls are received within respective reliefs in a proximal end of the inner housing such that the release balls are constrained inwardly by the release cap in the initial position into the one or more recesses to prevent axial movement of the carriage.

33. The drive module of claim 32, wherein the proximal end of the inner housing is received within an annular bore within the release cap in the initial position to constrain the release balls inwardly, and wherein, when the release cap is directed axially, the proximal end of the inner housing exits the bore to allow the release balls to move radially outwardly out of the one or more recesses.

34. [device 600] The drive module of one of claims 28-31, wherein the release cap comprise a central hub that extends into a proximal end of the carriage, and wherein the one or more recesses are provided within a proximal end of the inner housing, and the release balls are received within respective reliefs in the proximal end of the carriage such that the release balls are constrained outwardly by the central hub in the initial position into the one or more recesses to prevent axial movement of the carriage.

35. The drive module of claim 34, wherein, when the release cap is directed axially, the central hub moves proximally beyond the release balls to allow the release balls to move radially inwardly out of the one or more recesses.

36. [device 300] A drive module for an injector, comprising: an inner housing comprising a proximal end, a distal end, a first chamber adjacent the proximal end and a second chamber between the first chamber and the distal end; a source of pressurized gas within the first chamber; a release cap surrounding the inner housing proximal end; a carriage within the first chamber carrying an opener pin located adjacent the source of pressurized gas and releasably coupled to the release cap; a central tab comprising a stem extending axially from the release cap and terminating at a distal tip, the tab comprising a relatively large region adjacent the distal tip having a cross-section larger than the stem; and a plurality of fingers extending proximally from the carriage and disposed around the central tab, the fingers comprising inner shoulders that contact the relatively large region when the release cap is in an initial position to constrain the fingers against a surrounding bore of the inner housing to prevent axial movement of the carriage, wherein the release cap is movable axially relative to inner housing when the drive module is activated such that the inner shoulders slide off the relative larger region onto the stem to allow the fingers to move radially inwardly to release the carriage, the carriage biased to move axially when released to move the opener pin thereby causing the opener pin to open the source of pressurized gas to release the pressurized gas into the first chamber and into the second chamber such that the pressurized gas advances a plunger extending from the second chamber and the distal end of the inner housing.

37. The drive module of claim 36, wherein the central tab extends distally from a proximal end of the release cap and wherein the release cap is movable distally when the drive module is activated.

38. The drive module of claim 37, wherein the fingers comprise features that engage corresponding features on the surrounding bore when the fingers are constrained against the surrounding bore to prevent axial movement of the carriage.

39. The drive module of claim 38, wherein the features comprise an outward shoulder on each finger that engages a proximal end wall of the surrounding bore to prevent the axial movement.

40. The drive module of claim 39, wherein one or both of the outward shoulder and the proximal wall comprise a ramped surface to facilitate allowing the fingers to move radially inwardly when the fingers slide off the relatively large region.

41. A drive module for an injector, comprising: an inner housing comprising a proximal end, a distal end, a first chamber adjacent the proximal end and a second chamber between the first chamber and the distal end; a source of pressurized gas within the first chamber; a release cap surrounding the inner housing proximal end; and a carriage within the first chamber carrying an opener pin located adjacent the source of pressurized gas and releasably coupled to the release cap, the release cap and carriage comprising one or more features that disengage when the release cap is directed distally by an actuator, the carriage biased to move axially when released to move the opener pin thereby causing the opener pin to open the source of pressurized gas to release the pressurized gas into the first chamber and into the second chamber such that the pressurized gas advances a plunger extending from the second chamber and the distal end of the inner housing, the one or more features comprise a central hub on the release cap and a plurality of fingers on the carriage that slide along the hub as the release cap is directed proximally until the hub moves proximally beyond the tabs, the fingers biased to move radially inwardly to release the carriage.

42. A drive module for an injector, comprising: an inner housing comprising a proximal end, a distal end, a first chamber adjacent the proximal end and a second chamber between the first chamber and the distal end; a source of pressurized gas within the first chamber; a release cap surrounding the inner housing proximal end; a carriage within the first chamber carrying an opener pin located adjacent the source of pressurized gas and releasably coupled to the release cap, wherein the proximal end of the carriage, inner housing, and the release cap comprise one or more features that disengage when the release cap is directed proximally by an actuator to release the carriage, the carriage biased to move axially when released to move the opener pin thereby causing the opener pin to open the source of pressurized gas to release the pressurized gas into the first chamber and into the second chamber such that the pressurized gas advances a plunger extending from the second chamber and the distal end of the inner housing.

43. The drive module of claim 42, wherein the one or more features comprise a plurality of fingers on the carriage that engage the release cap to prevent axial movement of the carriage, the release cap constraining the fingers until the release cap is directed proximally, whereupon the fingers move radially outwardly to release the carriage.

44. The drive module of claim 42, wherein the one or more features comprise release balls received between the release cap and the carriage to prevent axial movement of the carriage, the release balls moveable when the release cap is directed proximally to release cap.

45. The drive module of claim 44, wherein the release cap comprises a bore that is aligned with the release balls as the release cap is directed proximally such that the release balls move outwardly into the bore to release the carriage.

46. The drive module of claim 44, wherein the release cap comprises a central hub and wherein the release balls are slidable along the hub when the release cap is directed proximally, the hub comprising recesses configured to receive the release balls once the release cap has moved a predetermined distance to allow the release balls to move inwardly to release the carriage.

47. device for delivering one or more agents into a subject’s body, comprising: an outer housing comprising a proximal portion terminating in a proximal end and a distal portion terminating in an open distal end; a syringe comprising a barrel containing one or more agents, a needle extending distally from the barrel such that a tip of the needle is disposed within the distal portion adjacent the distal end, and a piston within a proximal end of the barrel; a drive module according to any one of claims 1-23, 28-31, and 36-46 received within the outer housing adjacent the syringe; and a plunger comprising a proximal end within the second chamber and a distal end coupled to the piston of the syringe such that the plunger is advanced when pressurized gas is released from the source and enters the second chamber to advance the piston to deliver the one or more agents through the needle.