FIELD OF INVENTION

The present invention related to methods and devices for medicinal product administration. In particular, the present invention relates to the manufacture of a syringe using cartridges pre-filled with a medicinal product.

BACKGROUND

The present invention relates methods and devices configured to accept medicinal fluid containing cartridges and to dispense said medicinal product through a needle.

WO0172362 discloses a hypodermic needle syringe comprising a retraction mechanism, and configured to accept and use needle equipped cartridges. The document discloses three distinct embodiments, which embodiments differ in the type of energy storage and in how retraction force. In the first embodiment, energy to be converted into a retraction force is stored by means of vacuum inside the proximal end of a piston rod. In a second embodiment, the same energy is stored by means of a spring inside the proximal end of a piston rod. In the third embodiment, energy used for the retraction movement is stored in a compression spring located around the cartridge and acting directly upon a radial protrusion located at the proximal end of said cartridge. In all three embodiments, the position of the cartridge in the injector is held by a flexible tab. In all three embodiments the cartridge is provided with hooking means configured to interact with a compatible radial extension on the piston rod. In all three embodiments, the piston rod is contained within a cylindrical button, which cylindrical button is configured to block the rearward motion of the piston rod until the piston is fully inserted into the syringe cartridge, after which, the syringe cartridge and piston are then allowed to retract, hiding the needle.

W003097133 discloses an injection device with automatically retractable needle configured to use cartridges. The disclosed device includes a spring loaded plunger mechanism and a spring loaded needle retraction mechanism. The plunger mechanism is first provided with a loaded spring, which spring is stronger than a spring provided in the needle retraction mechanism. Upon release, said plunger spring compresses the retraction mechanism spring, exposing the needle, injecting the medicinal product contained in a cartridge, after which, the plunger mechanism is disengaged. The cartridge is then allowed to retract by action of the retraction mechanism spring, which spring is located around the body of the cartridge and acting upon a radial extension at the proximal end of said cartridge.

In both of the abovementioned documents, the devices described therein require the use of modified capsules in order to work effectively. Furthermore, due to their complexity, the disclosed devices are not easily loadable with a cartridge and are therefore more suitable to be provided as an assembled device rather than a kit.

W02001024852 discloses a retractable dental syringe, which syringe includes a hollow body configured to accept a cartridge, a push ring and a spring loaded spring assembly configured to enter the body of said cartridge. Upon injection of the contents of the cartridge, said cartridge is pushed against an exposed proximal end of the needle, piercing the a seal at the distal end of the cartridge, a piston rod pushes a piston contained within the cartridge, thereby pushing the fluid contents of the cartridge through the needle. Further pressure exerted by the piston rod displaces the needle from the push ring, pushing the seal of the cartridge inwards and letting the needle retract into the body of the cartridge by action of spring pressure.

The device disclosed in W02001024852 still requires the use of capsules having non-standard elements. Furthermore, once the needle is retracted through the opening at the distal end of the capsule, said opening is no longer sealed, thereby allowing any residual fluids still in the capsule to leak.

US20150065955A1 discloses a syringe for injecting medicament having automatic needle extension and retraction the syringe includes a first body with a cylindrical cross-section, which includes a front end and a rear end. The front end is provided with a means of transport smaller in diameter than the first body, which is fastened to same with a first fastening protrusion. The means of transport include a male frustoconical element which in turn includes conduits to transport said medicament, the front end further including a sealing protrusion and, located above said first fastening protrusion and said first sealing protrusion, a first alignment protrusion, inside said first body there is also a first elastic element which is fastened to said rear end of said first body with a posterior spring clip, and to said means of transport with an anterior spring clip, the rear end of said first body includes a handle. The syringe of US '955, similarly to WO '852, disadvantageously leaves the distal end of the syringe open upon retraction of the needle, thereby allowing any residual fluids still in the capsule to leak.

US5324265A1 discloses a syringe having a retractable needle and a retraction mechanism inside a hollow plunger, the distal end of which retraction mechanism has coupling features complementary to coupling features on the proximal end of the retractable needle. The retraction mechanism and the needle are configured to engage when the hollow plunger nears its end of travel inside the syringe barrel. Further displacement of said plunger in a distal direction causes the retraction mechanism to travel towards the proximal end of the syringe under action of a retraction spring. In this last displacement, the retraction mechanism pulls the retractable spring which moves in solidarity with the distal end of the retraction mechanism, and in this way becoming completely encased by the hollow plunger. Upon retraction of the needle, the distal end of the syringe is disadvantageously left open, leading to possible leakage of leftover medicinal fluid and/or blood backflow.

US9233209B2 discloses an injection device for injecting a medicament from a cartridge through a needle cannula. The injection device includes an actuator for driving a piston driver and includes an end of stroke limiter. When the piston driver is arrested by the end of stroke limiter a shielding driver is automatically triggered to actively shift the needle cannula into a shielded state. The injection device may also include a fluid dispensing interruption mechanism that automatically interrupts fluid flow when the piston driver has moved a predetermined stroke length. The injection device may also include a single pre-stressed spring acting exclusively in a linear compression mode or exclusively in a torsion mode and adapted to sequentially drive the device to enable fully automatic operation.

US20180353709A1 discloses a medicament injection device comprising: a main body configured to receive a medicament cartridge, a needle sleeve axially movable with respect to the main body, a needle holder holding a needle, and a displacement element coupled to the needle holder and disengageably coupled to the needle sleeve; wherein, upon axial displacement of the needle sleeve by a predefined distance in a proximal direction, the needle carrier and needle are displaced axially in a proximal direction. The device, and more in particular, the coupling of the needle to the medicament cartridge requires the user or a spring to overcome the resistance offered by the engagement elements of the needle holder, thereby creating a snapping effect when engagement between the needle holder and the cartridge is attained.

In both US '209 and US '709, the cartridge is disadvantageously subject to sudden deceleration after engaging with the proximal end of the needle. This sudden deceleration, besides being potentially damaging to one or more elements of the syringe, may result in undesired loss of medicinal fluid.

The abovementioned limitations prove the need for a device and method which is compatible with a wide range of capsules already in common use. In particular, a device suitable for the use of said capsules and which device comprises smooth engagement of the cartridge with the needle as well as self-retraction of the needle into the body of the device by manipulation of a sliding element.

SUMMARY OF INVENTION

The present invention and embodiments thereof serve to provide a solution to one or more of above-mentioned disadvantages. To this end, the present invention relates to a syringe-cartridge assembly according to claim 1, having the advantage that the syringe is intuitively operable for a healthcare worker, or any other individual.

The syringe can be operated like a regular cartridge using syringe, wherein the retraction mechanism is allowed to be engaged in one fluid motion which does not differ from normal operation of a regular syringe. Consequently, the syringe according to the present invention does not leave the operator in doubt about whether or not retraction has been correctly and/or completely engaged, nor does the operator have the possibility to re-use the syringe. Furthermore, the present syringe being configured to use cartridges, the volumetric accuracy of injection is optimally preserved.

Preferred embodiments are shown in any of the claims 2 to 10. An assembly including such syringe and cartridges is presented in any of the claims from 11 to 13. A method of using the syringe is disclosed in any of the claims 14 to 17. Two possible kits including both syringes and/or cartridges are shown in both claim 18 and claim 19. FIGURES

Figure 1 illustrates a syringe with a straight walled outer plunger before cartridge activation.

Figure 2 illustrates a syringe with a straight walled outer plunger with an activated cartridge.

Figure 3 illustrates a syringe with an outer plunger having a threaded interface before cartridge activation.

Figure 4 illustrates a syringe with an outer plunger having a threaded interface and with an activated cartridge.

Figure 5 illustrates the syringe after all the medicinal fluid has been pushed out of the cartridge.

Figure 6 illustrates the syringe after all the medicinal fluid has been pushed out of the cartridge and said cartridge has been retracted together with the needle.

Figure 7 illustrates another embodiment of the invention wherein a proximal plunger cap is comprised of two parts that can be separated from each other.

DETAILED DESCRIPTION

The present invention relates to a syringe - cartridge assembly.

Unless otherwise defined, all terms used in disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, term definitions are included to better appreciate the teaching of the present invention.

As used herein, the following terms have the following meanings: "A", "an", and "the" as used herein refers to both singular and plural referents unless the context clearly dictates otherwise. By way of example, "a compartment" refers to one or more than one compartment.

"Comprise", "comprising", and "comprises" and "comprised of" as used herein are synonymous with "include", "including", "includes" or "contain", "containing", "contains" and are inclusive or open-ended terms that specifies the presence of what follows e.g. component and do not exclude or preclude the presence of additional, non-recited components, features, element, members, steps, known in the art or disclosed therein.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order, unless specified. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

The recitation of numerical ranges by endpoints includes all numbers and fractions subsumed within that range, as well as the recited endpoints.

Whereas the terms "one or more" or "at least one", such as one or more or at least one member(s) of a group of members, is clear per se, by means of further exemplification, the term encompasses inter alia a reference to any one of said members, or to any two or more of said members, such as, e.g., any >3, >4, >5, >6 or >7 etc. of said members, and up to all said members.

A first aspect of the invention relates to a syringe having a needle retraction mechanism and designed to receive a cartridge having a medicinal product, said syringe comprises: a. a barrel comprising a hollow body and a hollow nose end, said barrel is able to retrieve a cartridge in said hollow body, preferably through an open proximal end of the barrel; b. a needle holder positioned in said nose end, wherein said needle holder comprises an internal cavity configured to receive the distal end of a cartridge, and into which the proximal end of the needle extends, by preference, the needle holder comprises a needle, more preferably, the needle holder is provided with hooking means configured to connect to a cartridge shoulder; c. a plunger, insertable in said barrel, preferably though an open distal end of the barrel; said plunger includes a retraction mechanism comprising a hollow inner plunger within a hollow outer plunger, wherein said inner plunger comprises a retraction spring, said spring is connecting a proximal plunger cap attached to a proximal end of said outer plunger and an distal plunger cap attached to the distal end of said inner plunger, said spring being positioned along the axis of both the outer plunger and inner plunger.

In the context of the present invention, the term "syringe" relates to a simple reciprocating pump consisting of a "plunger" or "piston" that fits tightly within a cylindrical tube. The plunger can be linearly pulled and pushed along the inside of said cylindrical tube, allowing the syringe to take in and expel liquid through a discharge orifice located at distal end of the syringe. According to the invention, the nose end is fitted with a needle holder, which needle holder comprises a needle, e.g. a hypodermic needle. Syringes as described herein are frequently used in clinical medicine to administer injections, or to infuse intravenous therapy into the bloodstream.

The term "retraction mechanism" indicates any mechanism which allows the automatic retraction of the needle holder including the needle inside the syringe, in order to prevent re-use of the syringe and/or to lower the risk of needle-stick injury. In an embodiment the distal plunger cap relates to a specific element of the retraction mechanism which extracts the needle and pulls it inside the syringe. According to the present invention, actual retraction is achieved by means of a "retraction spring", indicating that the spring is under tension during operation of the syringe, and retracts to its resting state upon engagement of the retraction mechanism, thereby retracting the inner plunger, distal plunger cap, cartridge and the needle holder coupled thereto.

The distal plunger cap can be comprised of one single part or of one or more separate parts that together form a functional plunger cap.

In some embodiments the needle holder may comprise a needle only on its proximal end in order to engage the distal end of a cartridge, the distal end of which needle holder being a luer cone configured to receive a standard hypodermic needle. In this way, the syringe is made more versatile because the choice of the needle is done just before the injection instead of during the syringe procurement process.

In an embodiment, said proximal plunger cap relates to a specific element of the retraction mechanism which covers the proximal end of the plunger and provides at least two substantially cylindrical sections, preferably three cylindrical sections. At least one such cylindrical section is configured to provide support upon which the proximal end of said retraction spring can be attached. Similar to the distal plunger cap, said proximal plunger cap may be provided as a single part or in two or more parts that together form a proximal plunger cap. In the latter case a plunger cap cylinder configured to support the return spring is further provided separate from a rear cover, which plunger cap cylinder is equipped with a plurality of radially extending hooking means, said hooking means being configured to engage the proximal end of the outer plunger. Preferably, said hooking means are bendable hooking means. More preferably, the plunger cap cylinder is provided with three or more bendable hooking means. Still more preferably, said bendable hooking means are configured to bend between -40° and 5° relative to the axis of the plunger cap cylinder. A two or more part proximal plunger cap permits, very advantageously, to assemble the retraction spring onto the plunger cap cylinder and distal plunger cap before pre-tensioning the spring. In this way, assembling of the plunger is greatly facilitated.

The terminology "hooking means" relates to any means which reversable interconnect two or more elements to each other. Specific hooking means comprise complementary protrusions and/or indentations, areas of higher friction or adhesion etc.

An embodiment wherein, the proximal end of said inner plunger is defined by a plurality of bendable flanges, said plurality of bendable flanges comprises at least two bendable flanges, preferably at least three bendable flanges.

The wording "bendable flanges" herein relates to any bendable parts extending from the plunger in the direction of the needle holder, wherein their bendable nature is the result of e.g. provision of a deformable material, provision of a certain thinness to the flanges etc.

The syringe according to the present invention comprises a vastly improved needle retraction mechanism, having the advantage that the syringe is intuitively operable for a healthcare worker, or any other individual. The invention can be operated like a regular syringe, wherein the retraction mechanism is automatically engaged as soon as the syringe has been emptied. Self-locking syringes known in the art commonly require the operator to perform multiple and/or additional steps in order to engage the mechanism, i.e. the plunger has to be pushed further forward although the syringe has already been emptied, the coupling of the needle holder to the distal plunger cap and the decoupling of the distal plunger cap from the plunger taking place in separate movements etc. The present invention comprising bendable flanges on the plunger however allows the retraction mechanism to be engaged in one fluid motion which does not differ from normal operation of a regular syringe. Consequently, the syringe according to the present invention does not leave the operator in doubt about whether or not retraction has been correctly and/or completely engaged, nor does the operator have the possibility to re-use the syringe. As a result, any risk of needle-stick injuries has been eliminated and re-use has been effectively prevented. Furthermore, as the syringe is configured to use cartridges, the volumetric accuracy of injection is optimally preserved.

In an embodiment, the inner plunger has, relative to the outer plunger, an advanced position A and a retracted position B, in which position said inner plunger is fully retracted into said outer plunger. This retracted position B avoids, advantageously, the return of the inner plunger to the extended position A. In this way, reuse of the syringe is advantageously avoided.

By preference, the plurality of bendable flanges are bendable over an angle of between 5° and 45°, more preferably between 5 and 40° relative to the axial centerline of the syringe. This bending range of the bendable flanges permits, advantageously, for said bendable flanges to provide sufficient tension for the inner plunger to remain in the advanced position A. Furthermore, the bending range of the bendable flanges is such that it permits said bendable flanges to easily bend under side pressure. Said pressure being directed towards the axis of the of the inner plunger as the bendable flanges contact the opening at the proximal end of the cartridge. This permits the unseating of said bendable flanges from the annular abutment, allowing the inner plunger to retract into the outer plunger.

In an embodiment, the outer plunger is a hollow cylinder comprising an inner annular abutment upon which the bendable flanges rest as the inner plunger is in the advanced position A. Said annular abutment provides a resting surface which advantageously permits a safe and reliable transmission of the force applied to the plunger to the inner plunger without the risk that said inner plunger slips under said tension.

In an embodiment, the needle holder is provided with hooking means configured to connect to a cartridge shoulder. Preferably, the hooking means of the needle holder are a plurality of bendable grippers. More preferably, said plurality of bendable grippers are at least two, preferably at least three bendable grippers. The presence of a plurality of hooking means allow for a firmer grip around the shoulder of the cartridge. This permits, very advantageously, the extraction of the needle holder along with the cartridge without the need for further extraction means other than those already included in the plunger. Additionally to safety, two other characteristics that are essential to any medical material are functional reliability and ease of manufacture. One skilled in the art will appreciate, in particular, the use of bendable flanges with which the proximal end of the inner plunger is equipped. These flanges advantageously reduce the number of moving parts necessary for the effective operation of the syringe, while making the inner plunger easier to manufacture and assemble.

By preference, the plurality of bendable grippers are bendable over an angle of between 30° and -30° relative to the axial centerline of the syringe. This bending range, advantageously permits the hooking means to override the distal end of the cartridge and engage the shoulder of said cartridge.

A common issue with syringes configured to use cartridges relates to the initial activation of the syringe where the user has to press a plunger, building up pressure until the cartridge sear is punctured by a proximal extensions of the needle. During this step, significant pressure upon the plunger is often required, which pressure is often suddenly released after the puncture of the cartridge seal, resulting in spilling of some of the drug contained in the syringe. In an embodiment, the outer surface of the outer plunger has a thread, which thread is complimentary to a second thread on the inner surface of the barrel. The threads present in both the outer plunger and barrel permit a safer handling of the syringe as the threads permit a better control of the advance of the plunger into the barrel. Furthermore, said threads permit, advantageously, a reduction of the force the user needs to exert in order to press the cartridge against the needle holder and to override the hooking means of said needle holder. This advantageously permits the use of stronger hooking means on the needle holder, which in turn ensure a reliable retraction of the needle. Another aspect of the invention relates to an assembly, comprising a syringe and a cartridge having a medicinal product, said cartridge is contained in the barrel of the syringe, and between the needle holder and the plunger. In an embodiment, the inner plunger is able to extend into the cartridge through its proximal end, the distal plunger cap on the distal end of said inner plunger being configured to rest against the rear seal inside said cartridge. This permits advantageously to align the proximal end of the cartridge with the axis of the syringe. More importantly, this permits, very advantageously, to transfer of the force applied to the plunger and onto the rear seal of the cartridge, allowing the fluid contained in the cartridge to be pushed out the distal end of said cartridge and through the needle.

Preferably, the cartridge comprises a hollow body sealed on both ends by a rear seal near its proximal end and a front seal on its distal end, which distal end is further provided with a shoulder and which cartridge is configured to air-tightly contain an amount of fluid within its hollow body, between said rear seal and said front seal. In this way, it is possible to provide the user with a pre-dosed amount of a medicinal fluid, thereby, preventing any dosing errors during the administration of said medicinal fluid.

In some embodiments the distal cap can present a protrusion to connect with the plunger stopper. This allows, advantageously, for an operator to be able to perform a negative pressure at the beginning of the injection (Lesser maneuver).

The present invention is also reached by a plurality of methods of delivering a medicinal product to a subject by means of a syringe. A first said method comprising the steps of: a. introducing a cartridge into a barrel of a syringe comprising a needle holder, by preference, the cartridge is inserted via the proximal end of the outer barrel; b. introducing the distal end of the plunger into the barrel, by preference, the plunger is inserted into the barrel through the proximal end of the outer and into the proximal end of the barrel; c. engaging the needle holder onto a cartridge having a medicinal product preferably by engaging an outer plunger thread with a barrel thread, then turning the plunger until the bendable grippers snap around the cartridge shoulder, and; d. administering the medicinal fluid to said subject. Yet another method of delivering a medicinal product to a subject by means of a syringe comprises the steps of: a. introducing a cartridge into a barrel of a syringe comprising a needle holder, by preference, the cartridge is inserted via the proximal end of the outer barrel; b. introducing the distal end of the plunger into the barrel, by preference, the plunger is inserted into the barrel through the proximal end of the outer and into the proximal end of the barrel; and c. engaging the needle holder onto a cartridge, preferably by engaging an outer plunger thread with a barrel thread, then turning plunger until the bendable grippers snap around the cartridge shoulder.

In an embodiment the needle holder is engaged onto the cartridge by pressing onto the plunger until the bendable grippers snap around the cartridge shoulder. In this way, the cartridge seals remain intact until the time of use.

Preferably, the needle holder is engaged onto the cartridge by engaging an outer plunger thread with a barrel thread, then turning plunger until the bendable grippers snap around the cartridge shoulder. The above mentioned method permits, advantageously, a more controlled rupture of the front seal of the cartridge and to avoid excessive advance of the plunger, thereby avoiding the spillage of any medicinal fluid. In this way, fluid communication between the inside of the cartridge and the open distal end of the needle is established, making the syringe quickly and easily ready for administering the contents of the cartridge.

The present invention is suitable to be made available in a kit comprising a plurality of syringes, said kit further including a plurality of cartridges. The present invention can also be made available in another kit, wherein each syringe is provided in two parts, a plunger and a barrel equipped with a needle holder.

FIGURE DESCRIPTION

Figures 1 to 6 illustrates a syringe (1) according to an embodiment of the current invention. Said syringe comprises a straight walled outer plunger before cartridge activation. A needle holder (4) is presented against the inner surface of the hollow nose of the barrel (2). A cartridge (5) is shown within the same barrel (2), the distal end of each cartridge is resting against the proximal end of the bendable grips (16) of the needle holder (4). A plunger (18) is shown inserted into the barrel (2), said plunger being comprised of hollow outer plunger (3) and inner plunger (8). The inner plunger (8) is shown in its advanced position which position it holds by having its bendable flanges (13) expanded and resting against the annular abutment inside the outer plunger (3). The position of the inner plunger (8) relative to the outer plunger (3) holds the retraction spring (7) under tension. The proximal end of said spring is here shown attached to a proximal plunger cap (6) at the proximal end of the outer plunger (3). The distal end of the retraction spring (7) is here shown attached to the distal plunger cap (9), which distal plunger cap (9) and part of the inner plunger (8) are shown extending into the cartridge (5) and pressing upon the rear seal (10).

Figure 2 illustrates a syringe with a straight walled outer plunger with an activated cartridge. In this figure the plunger (18) is shown inserted further into the barrel (2), having acted upon cartridge (5) by intermediate of the distal plunger cap (9) upon the rear seal (10). Said cartridge is shown pressed against the needle holder (4) and having a piercing the front seal (11). Said cartridge (5) is shown engaged to the needle holder (4) by means of the bendable grippers (16) which are now shown engaging the cartridge shoulder (17).

Figure 3 illustrates the syringe (1) with an outer plunger (3) having a threaded interface before cartridge activation. A needle holder (4) is presented against the inner surface of the hollow nose of the barrel (2). A cartridge (5) is shown within the same barrel (2), the distal end of each cartridge is resting against the proximal end of the bendable grips (16) of the needle holder (4). A plunger (18) is shown partially inserted into the barrel (2). Said plunger being comprised of a hollow outer plunger (3) and an inner plunger (8). In this figure, both the barrel and outer plunger are shown engaged by the barrel threads (15) and the outer plunger threads (14). The inner plunger (8) is shown in its advanced position which position it holds by having its bendable flanges (13) expanded and resting against the annular abutment inside the outer plunger (3). The position of the inner plunger (8) relative to the outer plunger (3) holds the retraction spring (7) under tension. The proximal end of said spring is here shown attached to a proximal plunger cap (6) at the proximal end of the outer plunger (3). The distal end of the retraction spring (7) is here shown attached to the distal plunger cap (9), which distal plunger cap (9) and part of the inner plunger (8) are shown extending into the cartridge (5) and pressing upon the rear seal (10).

Figure 4 illustrates a syringe with an outer plunger having a threaded interface and with an activated cartridge. In this figure the plunger (18) is shown positioned farther into the barrel (2) by action of the outer plunger threads (14) and the barrel threads (15). Cartridge (5) is shown pressed against the needle holder (4) and having a pierced the front seal (11). Said cartridge (5) is shown engaged to the needle holder (4) by means of the bendable grippers (16) which are now shown engaging the cartridge shoulder (17).

Different positions of the syringe according to Figure 1 or 2 with cartridge are shown in Figures 3 to 6. Figure 5 illustrates the syringe (1) after all the medicinal fluid has been pushed out of the cartridge (5) by action of the plunger (18) upon the rear seal (10) of the cartridge (5). The inner plunger (8) is here shown in its froward position and with its bendable flanges (12) in contact with the proximal end of the cartridge (5) immediately before retraction of said inner plunger (8), cartridge (5) and needle holder (4).

Figure 6 illustrates the syringe (1) after all the medicinal fluid has been pushed out of the cartridge (5) and said cartridge has been retracted together with the needle. In this figure, the cartridge (5) is shown fully retracted into the plunger (18). The inner plunger (8) is here shown with its bendable flanges (12) resting against the proximal plunger cap (6). The full length of needle is shown completely shrouded by the hollow nose of the barrel (2), thereby rendering the whole device safe.

Figure 7 illustrates another embodiment of the invention wherein a proximal plunger cap is comprised of two parts that can be separated from each other, one part being a plunger cap cylinder (19) and the other being a cover (21). In this figure, the proximal end of the retraction spring (7) is shown with a plurality of its coils wrapped around said proximal plunger cap cylinder (19), thereby forming a rigid attachment between retraction spring (7) and the plunger cap cylinder (19). Said plunger cap cylinder (19) is here provided with a plurality of bendable hooks (20) extending from its proximal end. Said bendable hooks (20) are shown engaged to a hole in the center of the proximal end of the outer plunger (3). A cover (21) is shown here placed onto the proximal end of the outer plunger (3), said cover (21) covering the tips of said bendable hooks (20).

1 syringe

2 barrel

3 outer plunger

4 needle holder 5 cartridge

6 proximal plunger cap

7 retraction spring

8 inner plunger 9 distal plunger cap

10 rear seal

11 front seal

12 bendable flanges

13 annular abutment 14 outer plunger thread

15 barrel thread

16 bendable grippers

17 cartridge shoulder

18 plunger 19 plunger cap cylinder

20 bendable hooks

21 cover