Single use syringe

#The present invention relates to a single use syringe that is rendered inoperative after a single injection without requiring any deliberate action on the part of the user.

#In conventional syringes, including those intended to be disposable after a single usage, it is mechanically possible to re-load and discharge the instrument repeatedly. Such re-use of syringes has been identified as a source for spreading blood-transmitted infectious agents, including hepatitis viruses and the human immunodeficiency virus (HIV), which is believed to play a role in the causation of acquired immunodeficiency syndrome (AIDS).

#Various health agencies, including the World Health Organization, have recently expressed an interest in the development of an inexpensive, non-reusable syringe to prevent patient-to-patient HIV transmission, particularly in the third world or other development countries.

#FIG. 1 of the drawings is a side perspective view of a preferred embodiment of non-reusable hypodermic syringe according to the present invention in its approximate initial configuration.

#FIG. 2 of the drawings is a side elevational view of the syringe of FIG. 1, shown partly in cross section, and illustrating the device in the same configuration as shown in FIG. 1.

#FIG. 3 of the drawings is a view similar to FIG. 2, with the syringe in an intermediate configuration explained more fully below.

#Referring now to the Figures, there will be seen a non-reusable hypodermic syringe 10 having an elongated cylinder 12 open at one end 14 and substantially closed at the opposite other end 16. A hollow member 18 is integrally formed on said other end 16 and defines an internal duct 20 communicating with the interior 22 of the cylinder 12. The axis of the internal duct 20 is substantially aligned with the axis of the cylinder. The hollow member 18 is configured and dimensioned to accept a standard hypodermic needle 24 in releasable frictionally engaged relation, with the duct 20 in communication with the lumen (not shown) of the needle 24. The cylinder 12 and the hollow member 18 are preferably integrally moulded of a substantially rigid plastics material, such as polyethylene. As thus far described under this heading, the components of the hypodermic syringe of the invention are conventional in terms of materials, dimensions and construction, which are well-known in the art.

#A plunger means 26 is provided, which plunger means 26 is comprised of a substantially rigid shaft member 28 and a resilient piston member 30 releasably attached to a first end 31 of the shaft member 28. The piston member 30 is dimensioned and adapted to fit into the interior 22 of the cylinder 12 in longitudinally sliding, frictional sealing engagement therewith.

#The piston member 30 shown is of generally conventional design, preferably having two substantially parallel sealing ring members 42, 42', integrally formed on the circumference of the piston member 30 at opposite axial ends thereof in generally transverse planar orientation to the axis of the cylinder 12. The sealing ring members 42, 42' preferably have flattened outer edges (as illustrated) for effecting said frictional sealing engagement between the piston member 30 and the interior wall 23 of the cylinder 12, although any other conventional ring profiles may be used, so long as they effectively seal against fluid leakage in use. The leading face 44 of the piston member 30 is shaped to present a generally frusto-conical profile, such that its apex 45 is substantially aligned with the axis of the cylinder 12 when inserted into the cylinder 12. The inside wall 17 of the other end 16 of the cylinder 12 is formed with a complimentary frusto-conical profile to facilitate mating with the leading face 44 of the piston member 30 when fully inserted into the cylinder 12, thereby to substantially discharge liquid from the interior of the cylinder. Such full discharge is also facilitated by the alignment and mating of the apex 45 of the leading face 44 with the interior opening of the proximal end 21 of the internal duct 20 upon said full insertion of the piston member 30.