WO1990007350A1

WO1990007350A1 - Disposable hypodermic syringe

Info

Publication number: WO1990007350A1
Application number: PCT/NO1990/000001
Authority: WO
Inventors: Odd Gerhard MÜLLER; Per Gunnar Werner
Original assignee: Mueller Odd Gerhard
Priority date: 1989-01-04
Filing date: 1990-01-02
Publication date: 1990-07-12
Also published as: NO890027L; CN1043876A; NO890027D0; ZA9030B; AU4821190A

Abstract

Disposable hypodermic syringe for the injection of liquid into body tissue, comprising a cylindrical main part (32), a piston (31) with an associated piston rod (34), an actuating member (35) at the free end of the piston rod, and a cannula (37) for injecting liquid when the piston is depressed by means of the actuating member. The cannula (37) is adapted to be retractable into the main part (32), but in a normal condition is retained against such retraction by means of a releasable blocking member (36a). Drive means (39) is provided for causing said retraction, and a releasing device (40, 41) is adapted to release the blocking member (36a) when presssure on the actuating member (35) is removed after an initiated injection.

Description

Disposable hypodermic syringe

It is well known that hypodermic syringes represent a serious risk of infection in various ways, including repeated use among drug addicts. Significant efforts have been made all over the world in an attempt to design hypodermic syringes which cannot be used more than once. Until now, however, no satisfactory solution has been found. An example of designs which have been tried, is based on the breaking of the piston rod of the syringes when an injection has been completed, and another example simply consists therein that the user himself can actively retract the cannula into the syringe after the injection. Experience has shown that these and other solutions attempted are insufficient in relation to the risk of infection represen¬ ted by an infected syringe or cannula tip.

An object of this invention is to provide a hypodermic syringe for use only once and with- a substantially complete elimination of the risk of infection which can arise from abuse of syringes or from inadvertant perforation of the skin during handling or contact with a used syringe.

Thus the invention takes as a basis the form of a hypodermic syringe for injecting a liquid into body tissue, which comprises a cylindrical main part, a piston with an associated piston rod, an actuating member at the free end of the piston rod, and a cannula for liquid injection when the piston is pressed down by means of the actuating member.

What is novel and specific in the syringe according to the invention, in the first place consists therein that the cannula is adapted to be retractable into the main part, but is retained in a normal condition against such retraction by means of a releasable blocking member, that there is provided drive means for effecting said retraction, and that a releasing device is adapted to release the blocking member on cessation of pressure on the actuating member after an initiated injection.

With this solution the cannula including the pointed tip thereof will immediately disappear into the main part of the syringe as soon as the user's finger is removed from the actuating member, for example a push button on the piston rod. Thereby the syringe is automatically rendered harm¬ less, not only as soon as the injection is completed, but also immediately in the case of an interrupted injection. This will prevent drug addicts from sharing a dose, which often occurs, with the transfer of infection as a result. As will appear from the following description the design described here will also prevent the user from putting the automatic security system of the syringe out of operation. In other respects the syringes according to the invention may be utilised in the same manner as earlier commonly known hypodermic syringes as regards filling, venting, applying and injecting.

The invention as well as additional particular features and advantages obtained thereby, will be explained more closely in the following description with reference to the drawings, in which:

Fig. 1 in longitudinal section shows a first embodi¬ ment of the hypodermic syringe according to the invention in its normal or usual condition of use,

Fig. 2. shows in a similar section the same syringe as in fig. 1 after having been rendered harmless by retrac¬ tion of the cannula into the main part of the syringe,

Fig. 3 shows at an enlarged scale certain details of a releasing device incorporated in the syringe of figs. 1 and 2,

Fig. 4 shows at an enlarged scale other details of the releasing device,

Fig. 5 shows a second and more preferred embodiment of the syringe according to the invention, in longitudinal section,

Fig. 6 shows an enlarged sectional view of the lower portion of the syringe in fig» 5,

Fig. 7 shows the details at one end of a pulling element provided between the releasing device and the blocking member in the syringe shown in fig. 5,

Fig. 8 shows important details at the opposite end of the pulling element,

Figs. 9 - 12 in enlarged cross-sectional view show the releasing device and the actuating member at the top of the syringe according to fig. 5 in various steps of operation,

Figs. 13A-D show an additional embodiment of the releasing device in various steps of operation,

Fig. 14 shows in plane view a membrane element incorporated into the device in figs. 13A-D,

Fig. 15 can be considered as an enlarged cross- section of the lower half of the syringe in fig. 5, with retracted cannula and a specific sealing element at the lower end or opening,

Fig. 16 shows the lower portion of the syringe in fig. 15 when the sealing element has acquired its final shape,

Fig. 17 in an enlarged cross-sectional view shows the lower portion of a syringe in its normal condition, having specific design features associated with a sealing element, and

Fig. 18 shows the lower portion of a syringe as in fig. 17 but with its cannula retracted.

The hypodermic syringe shown in figures 1 and 2 comprises a main part in the form of an outer tube 15 and an inner tube 16 with an intermediate piston 4 and an associa¬ ted tubular piston rod 11, the upper free end of which is provided with an actuating member in the form of a push button 9. A cannula 8 projects through a lower opening 21.

On movement of the annular piston 4 towards the bottom of the main part 15 of the syringe, liquid in the space 19 in front of the piston will be pressed through slits 7 out into the cannula 8 in the usual way, the upper portion of the latter having a perforation for liquid inflow.

The cannula 8 can be retracted into the syringe main part 15, i.e. more particularly into the inner tube 16, but in its normal position as illustrated in fig. 1, is blocked against inward retraction by means of a blocking member in the form of an ampulla 5 filled with a pressurised medium and retained against an abutment element in the form of a flange 17 in the interior of the tube 16. A compression spring 6 constitutes drive means urging the cannula 8 in the upwards direction in the figure, i.e. against the under side of the ampulla 5. A disc 18 or a similar engagement piece for this purpose is attached to the upper end of the cannula 8. The disc 18 is shaped so as to be able to pass through the opening delimited by the flange 17.

Puncture or destruction of the ampulla 5 will release the cannula 8 for movement upwards and into the tube 16 under the influence of the compression spring 6. This release of the blocking takes place by means of a needle 3 which can be shot downwards from its releasing device at the top of the piston rod 11, the needle 3 being brought to move by an upper spring 10 after releasing. At the top of the tube 16 there is formed a cone 13 with an enlarged flat bottom 14, the cone serving to catch the point of the needle 3 and guide it in a correct direction against the ampulla 5 even if the whole of the needle should initially be located above the cone-shaped opening 13.

The releasing device for the needle 3 as shown at an enlarged scale in figs. 3 and 4 with main components 1 and 2, can be considered similar to the conventional activating mechanism in ballpoint pens. A round plate 2 is mounted at the upper portion of the needle 3 and is adapted to co¬ operate with notches in the interior of a sleeve-shaped part 1, lb which accommodates the spring 10. When the plate 2 is rotated incisions through it will make it possible for the plate, and thereby the needle 3, to move downwards under the influence of the spring 10. This release takes place when the actuating button 9 is depressed for injection and is then released, which can for example be the case when the injection has been completed and the syringe is empty, or when the user attempts to change hands on the syringe, or if two drug addicts try to share a dose from the same syringe.

The syringe is provided with a top plate 12 which among other things makes it impossible to disassemble the syringe.

Figure 2 shows the syringe after use, i.e. with the blocking member in the form of the ampulla 5 destroyed and both springs 6 and 10 having performed their function. The cannula 8 has been retracted into the inner tube 16 and has stopped against the cone bottom 14 with the point of the cannula located at or immediately inside the opening 21 at the lower end of the syringe. In this area and possibly also at a sealing member 20 about the cannula 8, there can with advantage be provided a sealing element which prevents leakage along the cannula 8 out through the opening 21. The hypodermic syringe thus has been rendered harmless and can never be used again. Remaining liquid in the space 19 in front of the piston 4 cannot leak out.

In the embodiment of figures 5 and 6 some main features of the design are similar to those in the embodiment described above, namely a main part 32, an inner tube 33, an annular piston 31 adapted to move between these and an associated piston rod 34. As best seen in figure 6, injection liquid from the space 38 in front of the piston 31 can be pressed out into a cannula 37 through channels 33b and 36b, provided respectively at the bottom of the main part 32 and in a mounting member 36 for the cannula 37 which penetrates through an opening 32a at a projecting bottom portion of the main part 32. The tubular parts 32 and 33 with the associated annular piston 31 can have circular, hexagonal or other cross-sectional shapes.

At its upper end the piston rod 34 is enlarged and shaped so as to accommodate a portion of a releasing device 40. This device is also partly enclosed by an actuating member in the form of a flexible cap 35 which is made to be elastically resilient to a compressive load, for example from a user's thumb. A plug-shaped part 41 of the releasing device is pressed into the upper end portion of the piston rod 34 and serves an important function which will be explained more closely in connection with figures 9 - 12 below. From the releasing device 40 a pulling element 42 is extended centrally down through the piston rod and the inner tube 33 to a blocking member on the mounting 36. The releasing device 40 has an engagement member 45 adapted to co-operate with toothing or the like on the pulling^*element 42.

Figure 6 shows in more detail the mounting or blocking member 36 the top of which is attached to the lower end of the pulling element 42 and forms a plate- or yoke-like transverse piece with edges 36a adapted to abut against, and being blocked by flanges 33a in the interior of the inner tube 33. Accordingly these flanges constitute projecting small abutments which in the normal condition secure against any movement of the blocking and mounting member 36 upwards through the inner tube 33. As seen from figures 5 and 6 the cannula 37 in this normal condition or position is located so as to project from the main part 32 ready for normal use, i.e. an injection operation.

A compression spring 39 is provided in the tube part 33 between the bottom thereof and shoulders around the outer periphery of the upper enlarged portion of the blocking and mounting member 36. The spring 39 seeks to push this member upwards, but this is without any effect as long as the blocking between the co-operating blocking elements 36a and 33a is present. This blocking effect is adapted to be removed at the occurrence of only a relatively weak upwardly directed tensional force in the pulling element 32, as such a force will deform the transverse piece of the member 36 between the abutment flanges 33a, i.e. by a certain bulging upwards of the middle portion and thereby a reduction of the lateral dimension. Thus the projections 36a can move past the flanges 33a, and the spring 39 with a comparatively large force may throw not only the mounting member 36 as a whole, but also the pulling element 42 upwards through the inner tube 33. At the same time the cannula 37 is retracted into the main parts 32-33 of the syringe through the lower opening 32a. This retractive movement continues until the whole cannula 37 has been displaced through the opening 32a and is brought into a secure and protected position inside the main parts of the syringe.

Figure 7 shows in elevation the design of the blocking and mounting member 36 with blocking projections 36a and the pulling element 42. This string-shaped pulling element can be moulded as one piece with the mounting member 36 and is flexible, but has a certain stiffness which makes it possible to push it upwards through the inner tube part 33 and the piston rod 34 during the upward movement caused by the spring 39, as explained above.

How the mentioned upwardly directed force in the pulling element 42 is generated, will now be explained with reference to figure 8 and figures 9-12.

Figure 8 shows in elevation the upper end of the pulling element 42, the release member 41 and a portion of the actuating member 35 which is formed by an elastic cap. To the inside of this cap there is attatched a release arm 35a being directed downwards and provided with two hooks 47a and 47b adapted to co-operate with an oppositely directed hook 41a on the moveable engagement piece 45 which is incorporated in the release member 41. In its initial or non-actuated position as shown in fig. 9, the hook 47b is ready to engage the hook 41a. If anybody should attempt to destroy the releasing system of the syringe, for example by cutting away the top of the cap 35 or removing the cap as a whole, there will be exerted an upwardly directed force in the release arm 35 which results in triggering of the blocking member as will be explained in the following description referring to the normal function of the syringe.

When the syringe is to be used in a normal manner, i.e. for an injection operation, a pressure is exerted with a finger on top of the cap so that this will bulge downwards as shown in fig. 10 and simultaneously this will cause a movement of the release arm 35a downwards. At this the hook 47a will engage the hook 41a (fig. 8).

When an injection has been made in part or completely, the finger pressure on the cap 45 is terminated and the cap by itself will seek to return to its unstrained condition, i.e. the bulging down will decrease as shown in figure 11. This elastic movement of the top surface of the cap 35 through the release arm 35a gives a small movement of the engagement piece 45, so that the projection 45a thereof will engage the toothing of the pulling element 42.

Continued movement of the top surface of the cap 35 towards a completely relieved condition as in fig. 12 brings about a small upward pull of the whole releasing member 41 in relation to the piston rod 34. This initial small movement is sufficient for the clamping force from the end portion of the piston rod 34 against the plug-shaped member 41 to obtain its full effect and with a relatively great force to push the whole releasing device upwards until the top of this device abuts against the inside of the cap 35. The conically narrowed shape of the member 41 into the end portion of the piston rod 34 is intended to provide for this pushing force. This is the same force which is exerted through the pulling element 42 for causing the above described deformation of the blocking member at the lower end of the pulling element 42.

As mentioned before this release of the blocking member will also have the consequence that the pulling element or string 42 is pushed upwards, and this string accordingly must be accommodated in the upper portion of the syringe arrangement. As shown in fig. 12 this takes place by means of a chamber 43 being in principle circular and provided in the upper portion of the releasing device 40. Thus, after release the engagement piece 45 is moved back from its engagement with the toothing of the string 42 and makes it possible for the string to be pushed upwards through the passage shown and into the chamber 43. The previously mentioned flexibility combined with a certain stiffness of the string 42, permits of this pushing and storing of the string somewhat like a coil withing the chamber 43, which is sufficiently large to accommodate the necessary length of the string 42. It should be noted that the toothing of the string is provided along substantially the whole length of the string, so that the above engagement and the actual releasing function can take place irrespective of how far down the piston has been pressed during an injection operation.

From the above description with reference to fig. 8 and figs. 9-12 it appears that the engagement piece 45 of the releasing device is set into an activated condition when there is exerted a pressure e.g. a finger on the cap-shaped actuating member 35, as the respective hooks 47a and 47b are brought into an active position in relation to the hook 41a (fig. 8). When the pressure on the cap 35 is removed the elastic restoration thereof will bring the engagement piece 45 with projections 45a to engage the toothing of the toothing element 42 and cause an initial displacement which in its turn leads to complete releasing and retraction as illustrated in figs. 9-12.

Figures 13A-D and figure 14 show an alternative and simpler embodiment of the releasing device. Here also there is included a cap-shaped and elastic actuating member 55 which is attached to an extension of the piston rod 54 and has a release arm 53 serving a quite similar function to the release arm 35a in fig. 8. Moreover in figs. 13A-D there is shown a pulling element 52 having a hook-like toothing. An essential component in this embodiment is a membrane 51 mounted around the inner circumference of the piston rod 54. As also seen from fig. 14 the membrane 51 has a hole 51a for the release arm 53 and another opening 51b through which the pulling element 52 is extended. A tongue 51c directed towards the opening 51b is adapted to co-operate with the toothing of the pulling element 52.

The function of this releasing device is as follows, taking the normal condition shown in fig. 13A as a starting point:

The membrane 51 bulges downward and a first hook-like projection 53b on the release arm 53 is located on the under side of the membrane.

On depressing the cap 55 as shown in fig. 13B, i.e. by normal use of the syringe during an injection, the release arm 53 is displaced downwards and the second hook 53a thereon passes through the hole 51a and takes a position at the underside of the membrane. Thereby the releasing device is activated.

If now the elastic cap 55 is permitted to return towards its normal condition via an intermediate position as shown for example in fig. 13C, the hook 53a will move the membrane 51 towards a neutral position at the same time as the tongue 51cengages the toothing of the pulling element and exerts an initial tensional force on the pulling element. In the next moment the membrane 51 will quickly snap through or be transformed from a condition of bulging downwards to a condition of bulging upwards and thereby exert a significant tensional force in the pulling element, so that a quick and strong upward movement of the pulling element 52 is obtained. Thereby the blocking member is released as described above, in particular in connection with fig. 6, and the pulling element 52 is pushed into a circular chamber 56 in the form of a coil.

The clamped membrane element 51 thus preferrably covers substantially the whole interior cross-sectional area of the piston rod 54 and has two stable positions bulging out to respectively opposite axial directions within the piston rod (fig.ι3A and 13D) . By a suitable choice of material and dimensions of the membrane, the function described will be attained.

A hypodermic syringe having an automatic retraction of the cannula after use, as described above, will reduce to a very substantial degree the risks of spreading infection and the like. It can occur, however, that for example children put a used syringe in the mouth and suck. Then the child may be infected by some of the substance which still may be present in or on the syringe, e.g. a drug, and can be contaminated by infectious substances which may be located within and around the opening for the cannula.

Already in fig. 5 of the drawings there is indicated means for eliminating the problem mentioned here, i.e. a sealing element 60 arranged to be releasable in relation to the opening for retracting the cannula into the syringe. In various ways such a sealing element can be adapted to be released by this retraction, for the purpose of enclosing the cannula point in the completely retracted position and besides, preferrably to seal the opening completely.

Figure 15 shows in more detail such a sealing element 60a in the situation where the cannula 67 is fully retracted and the point thereof is located inside the opening 61. For example the sealing element 60a can be an elastic material which in the situation shown will in the first place tightly enclose the point of the cannula and in the second place expand or be subjected to a change of shape so that the whole space around the cannula point and the opening 61 will be filled. Figure 16 shows this final condition of the sealing element 60b, which has been partially extruded through the opening 61 so that this has become more or less completely sealed.

A suitable material for this sealing element may be polyurethane foam which is easily shaped and can expand or alternatively contract to a sufficient degree for effect¬ ively sealing the opening. A foam-like porous material will also be able to absorb injection liquid or the like, of which remains usually are present in the syringe itself and in the cannula. Also a cellulose-basefd material or textile fibres may be able to have a similar effect by giving a relatively efficient sealing by swelling or taking up liquid or moisture. Besides, polyurethane foam as mentioned, or other cellular materials may be mixed with a substance which reacts chemically when brought into contact with water or another liquid, and which brings the cells to swell or foam and to form a hard surface when the chemical reaction has been terminated. Such materials are known inter alia from adhesive technology, from which polyurethane and epoxy adhesives may be mentioned as examples.

Other types of adhesive of interest in this connection can for example comprise a hardening agent and an adhesive substance which both are separately chemically stable until they are mixed with one another. Adhesives of this type are available in which the hardening agent is encapsuled in microscopic spheres which break up on light mechanical influence so that the hardening agent will come into contact with the adhesive substance and the surrounding sphere particles. This starts a process which will spread so that the whole mass gradually will be transformed into a rigid adhesive substance. The sealing element for the cannula point and opening 61 in fig. 15 can be based on such materials or types of adhesive. Further in this connection it is possible to combine such materials with agents for chemically disinfecting the area around the lower portion of the syringe, in particular around the opening 61. Disinfec¬ tant's of interest may be included in liquid or solid form. The agent can be activated by mechanical influence or in a similar manner and, besides, the disinfectant may be mixed with the activating liquid utilised for the foaming and hardening as explained above.

In the particular and modified embodiment shown in fig. 17, a mounting or a supporting piece 66 for the cannula 67a is provided with activating elements 66d such as lugs or hooks adapted to .activate or release a sealing element 60c mechanically upon retraction of the cannula 67a through the opening 61a. In order to prevent the sealing element 60c being pulled upwards together with the cannula 67a, there can be provided interior ribs 69 which keep the sealing element in place.

Figure 18 shows the sealing element 60c after swelling or forming so as to result in the desired sealing effect.

An additional specific feature is illustrated at the point of the cannula 37 in fig. 6. This cannula point is provided with a removable filter tip consisting of a sleeve¬ like clamp 71 adapted to co-operate with the cannula dimension concerned, and a filter material 72 at the end of the sleeve or clamp. In this way it can be ensured by simple and handy means that liquid being sucked into the syringe for later injection, does not contain undesired particles or foreign matter.

It is obvious that a hypodermic syringe according to the present invention can be designed with various modifica¬ tions in relation to what is described above with reference to the drawings, and moreover it is clear that a variety of materials may be employed. It is preferred, however, to manufacture the parts of the syringe from plastic materials in order to make possible a fully automatic, efficient and inexpensive production. In this connection it is to be mentioned that the plastic material in the region of the syringe tip can be so chosen that it will be destroyed or atomised by heating, without the cannula being thereby fixed by fusion in its normal position. Attempts to make the automatic retraction function inoperative by such heating, therefore, will not be successful. Syringes according to the invention can be supplied with ready mounted cannulas or with separate cannulas intended for mounting by the user himself. Sealing elements as discussed particularly with reference to figs. 15-18 can also be provided in hypodermic syringes based on possible different means for retracting the cannula, than described here.

Claims

C l a i m s

1. Disposable hypodermic syringe for the injection of liquid into body tissue, comprising a cylindrical main part (15,32), a piston (4,31) with an associated piston rod (11, 34), an actuating member (9,35) at the free end of the piston rod, and a cannula (8,37) for injecting liquid when the piston is depressed by means of the actuating member, c h a r a c t e r i z e d in that the cannula (8,37) is adapted to be retractable into the main part (15,32), but in a normal condition is retained against such retraction by means of a releasable blocking member (5,36a), that drive means (6,39) is provided for causing said retraction, and that a releasing device (1,2,3,10,40,41) is adapted to release the blocking member (5,36a) when pressure on the actuating member (9,35) is removed after an initiated injection.

2. Hypodermic syringe according to claim 1 c h a r a c t e r i z e d in that an inner tubular part (16,33) is provided within the main part, that the piston (4,31) is annular and located between the main part and the tubular part, and that the piston rod (11,34) is tubular.

3. Hypodermic syringe according to claim 2 c h a r a c t e r i z e d in that the blocking member (5,36a) is provided in the tubular part (16,33) and the releasing device is located substantially within the tubular piston rod (11,34), preferrably adjacent the free end of the piston rod.

4. Hypodermic syringe according to claims 1, 2 and 3 c h a r a c t e r i z e d in that said drive means is a spring element (6,39).

5. Hypodermic syringe according to claim 4 c h a r a c t e r i z e d in that the spring element is in the form of a helical compression spring (6,39) located adjacent to the cannula end of the main part (15,32) and that the cannula (8,37) is adapted to move axially at least in part through the spring during said retraction.

6. Hypodermic syringe according to claim 3, 4 or 5 c h a r a c t e r i z e d in that in the interior of the tubular part (16,33) there is provided an abutment element (17,33a) which in said normal condition keeps the blocking member (5,36a) in place, and that the blocking member is deformable under the influence of the releasing device (1, 2,3,10,40,41) so that the blocking effect with respect to the abutment element (17,33a) can be removed.

7. Hypodermic syringe according to any one of claims 1 - 6 c h a r a c t e r i z e d in that the releasing device (1,2,3,10,40,41) is adapted to be set into an activated condition as soon as an injection movement has been initia¬ ted by depressing the actuating member (9,36).

8. Hypodermic syringe according to any. one of claims 1 - 7 c h a r a c t e r i z e d in that a string-shaped pulling element (42) having toothing, perforation or the like along a substantial portion of its length, is provided between the releasing device (40) and the blocking member (36a) for releasing the blocking member by means of a tensional force exerted through the pulling element (42).

9. Hypodermic syringe according to claim 8, c h a r a c t e r i z e d in that the pulling element (42) is sufficiently flexible in order to be gathered as a coil in a chamber (43) being preferrably of a generally circular shape and provided in association with the releasing device (40.41), and that the pulling element also has a certain degree of stiffness which enables it to be pushed into the chamber .

10. Hypodermic syringe according to claim 8 or 9, c h a r a c t e r i z e d in that the releasing device (40) has an engagement piece (45) adapted to be set into an activated condition by depressing the actuating member (35) and to engage the pulling element (42) immediately upon termination of pressure on the actuating member, the actuating member preferrably then by itself exerting a tensional force which moves the engagement piece (45) from its activated condition to engagement with the pulling element (42) .

11. Hypodermic syringe according to claim 8, 9 or 10, c h a r a c t e r i z e d in that a plug-shaped part (41) of the releasing device (40) is pressed into an end portion of the tubular piston rod (34) with a certain degree of slip in relation thereto so that a radial inwardly directed clamping force from the end portion of the piston rod will push the whole releasing device (40) partially out from said end portion and thereby exert said tensional force through the pulling element (42), when a releasing movement has been initiated.

12. Hypodermic syringe according to claim 8 or 9, c h a r a c t e r i z e d in that the releasing device comprises a membrane-like element (51) which substantially covers the whole interior cross-sectional area of the piston rod (54) and has two stable positions bulging out to respective opposite axial directions of the inner tube, that the membrane element (51) has two openings (51a,51c) for co¬ operation with a hook element (53) attached to the actuating member (55) and with the pulling element (52) respectively, the membrane element being from an activated middle position (fig. 13C) adapted to perform a quick snap-over movement with bulging in the direction towards the actuating member, to thereby exert said tensional force through the pulling element (52) .

13. Hypodermic syringe according to any one of claims

1-12 c h a r a c t e r i z e d in that the point of the cannula is provided with a removable filter tip (71, 72).

14. Hypodermic syringe for the injection of liquid into body tissue, comprising a cylindrical main part (15,32), a piston (4,31) with an associated piston rod (11,34), an actuating member (9,35) at the free end of the piston rod, and a cannula (8,37) for injecting liquid when the piston is depressed by means of the actuating member c h a r a c t e r i z e d in that the cannula (8,37) is adapted to be retractable into the main part (15,32) and that a releasable sealing element (60) is provided at the end of the main part (32) in association with an opening (61) for said retraction of the cannula (37), and is adapted to be released by said retraction so as to enclose (60a) the point of the cannula in its fully retracted position and preferrably to seal (60b) said opening (61).

15. Hypodermic syringe according to claim 14, c h a r a c t e r i z e d in that the sealing element (60) as an essential constituent comprises a material or a mixture which under the influence of liquid remains from an injection, is subjected to a change of volume and/or shape (60b), and preferrably comprises a disinfectant.

16. Hypodermic syringe according to claim 14, c h a r a c t e r i z e d in that actuating elements (66d) are provided adjacent a supporting part (66) for the cannula, and adapted to release the sealing element (60c) on retraction of the cannula (67a).