Surgery – Means for introducing or removing material from body for... – Treating material introduced into or removed from body...
Reexamination Certificate
2002-10-16
2004-07-06
Casler, Brian L. (Department: 3763)
Surgery
Means for introducing or removing material from body for...
Treating material introduced into or removed from body...
C604S068000
Reexamination Certificate
active
06758829
ABSTRACT:
The technical field of the invention is that of prefilled and disposable needleless syringes functioning with a gas generator and used for intradermal, subcutaneous and intramuscular injections of liquid active principle for therapeutic use in human or veterinary medicine.
For the injection devices according to the invention, a liquid active principle consists of a more or less viscous liquid, or a mixture of liquid, or a gel. The active principle can be a solid dissolved in a suitable solvent for injection. It can also be represented by a powdered solid in more or less concentrated suspension in a suitable liquid. The particle size of the principle must be compatible with the diameter of the conduits in order to avoid blockages.
The needleless syringes according to the invention have the particular feature of functioning with a pyrotechnic gas generator which involves a pyrotechnic charge consisting of the mixture of two powders, the main benefit of this being to control, over the course of time, the pressure of the liquid active principle as it leaves the nozzle, in such a way that each phase of the injection is effected under the required conditions.
In the field of needleless syringes for injection of liquid active principles, it transpires that there is no patent relating to the use of a pyrotechnic gas generator involving the mixture of two powders. By contrast, the use of a single pyrotechnic charge for this type of syringe already exists and is the subject of several patents. By way of example, mention may be made of the patent U.S. Pat. No. 2,322,244 which relates to a hypodermic needleless injector functioning with a blank cartridge. The liquid to be injected, placed in contact with the cartridge, is expelled from the injector under the effect of the pressure generated by the combustion gases. Another patent, WO 98/31409, describes a hypodermic injection system involving a pyrotechnic charge which consists of an explosive or a powder. The specific feature of this injector is that it is designed to attempt to control the problems associated with the kinetics of expulsion of the liquid active principle, not by acting on the characteristics of the pyrotechnic composition, but by having a specific geometry defining in particular an adjoining gas expansion chamber which is provided with a vent. The pyrotechnic charge, which is located in immediate proximity to the liquid active principle, acts directly and instantaneously on said principle by giving it a very high initial speed, while the gases invade the main chamber and the adjoining chamber. The pressure exerted on the active principle then decreases and eventually fixes at an almost constant value, which is sufficient to cause it to penetrate the patient's skin. The adjoining chamber makes it possible to regulate this pressure. Finally, the patent U.S. Pat. No. 2,704,542 relates to a method of injection by liquid jet. This method does not specifically involve a pyrotechnic charge but uses a device intended to control the pressure profiles. In this case, the method used to achieve this objective is based on the two-stage sliding movement of a two-part piston formed by a central cylinder of small cross section housed in a hollow cylinder. An upstream pressure first causes a displacement of low amplitude of the central cylinder in order to communicate a brief but very intense impulse to the liquid which is to be expelled, then the whole of the piston displaces in order to continue to expel said liquid at the appropriate pressure, so as to ensure proper penetration.
The needleless syringes according to the invention are designed to ensure penetration, through the skin, of all of the liquid active principle, without causing any losses of said liquid on account of insufficient speed, since said losses could prove to be detrimental to the quality of the injection. The method used to control the pressure of the liquid, as a function of time, at the nozzle outlet lies in using a pyrotechnic charge consisting of the mixture of two powders, one called “fast-burning” and the other called “slow-burning”, the dimensional and chemical characteristics of these two powders being conditioned by the geometry and dimensions of the syringes, and also by the injection system including the reservoir of liquid active principle, if appropriate a piston for thrusting said active principle, and a nozzle comprising expulsion orifices. The fast-burning powder, when combusted, has the main function of communicating almost instantaneously to the liquid active principle a level of pressure such that the latter instantaneously acquires a speed of several hundreds of meters per second, allowing it to penetrate the patient's skin as it is expelled from the syringe. The slow-burning powder, which is combusted simultaneously, is able to guarantee the active principle a minimum level of pressure throughout the duration of the injection and sufficient to continue the diffusion through the orifice created in the skin by the effect of the fast-burning powder. The concepts of fast-burning powder and slow-burning powder will be explained later.
Thus, the needleless syringes according to the invention, while retaining their geometry and their reduced size, make it possible to ensure reliable and correct injection, in contrast to the injection devices described in the prior art, and in which the search for an optimized pressure profile involves a modification of their structure, illustrated by the addition of supplementary parts or attached volumes, thereby increasing their size and making the mechanism of their functioning more complex.
Moreover, irrespective of the syringe configuration, which may be dictated by imperatives linked to the specificity of an injection, it is still possible to determine a mixture of powders suitable for ensuring a satisfactory injection without in any way having to modify said syringe. This is because the liquid active principle can be present in a greater or lesser quantity, in more or less viscous form, in a syringe of linear or compact architecture. The powder mixture will be defined taking into consideration all of these constraints.
The needleless syringes according to the invention ensure correct and reliable injection and permit a very high degree of flexibility of use on account of the great variability of the pyrotechnic charges which can be used for the mixture, and all this without adding to their size.
The subject of the present invention is a needleless syringe comprising, in succession, a pyrotechnic gas generator, at least one piston, a reserve of liquid active principle, and an ejection nozzle, characterized in that the pyrotechnic gas generator comprises a pyrotechnic charge consisting of the mixture of at least two powders.
The pyrotechnic charge preferably consists of the mixture of a first powder and of a second powder.
The powders are characterized, on the one hand, by their chemical formulation and, on the other hand, by their geometry. The chemical formulation integrates all of the components included in the powder and to which there must be added a weighting coefficient corresponding to the fraction by mass of said component. The geometry of the powder reflects the geometry of each particle which it comprises. A particle is defined by its shape, its dimensions and the number of holes it has, said holes contributing to determining a burning thickness.
When it is stated that the pyrotechnic charge consists of the mixture of a first powder and of a second powder, this signifies that the two powders are different from one another and that this difference may lie in only one of the parameters mentioned above. In other words, the two powders can, for example, have the same chemical composition but have particles of slightly different geometry.
The pyrotechnic charge advantageously consists of a mixture of two powders in loose form, that is to say the two powders are in a state in which the particles are mixed haphazardly, without any particular order, the resulting powder matching the shape of the cont
Alexandre Patrick
Cognot Patrick
Lafforgue Joel
Roller Denis
Casler Brian L.
Crossject
Han Mark K
Oliff & Berridg,e PLC
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