Medical device

Description of the invention

The present invention relates to an injection device.

Devices are known in the art for injecting medical liquids through the skin surface or mucosa of humans or animals under sufficiently high pressure in order to introduce the liquid into the tissue to a predetermined depth below the skin surface.

US Pat. No. 2,821,981 discloses a reusable injection device which uses the jet injection principle. In this known device, the injected fluid is loaded into the distal pressure chamber, the ampoule, from the proximal chamber containing the fluid medicament, for example in the form of a conventional syringe. A mechanism is used to transfer fluid from the fluid chamber to the pressure chamber, and then another mechanism is used to perform the injection. One-way valves are used in the loading port to prevent backflow. This rather mechanically complicated structure of the injection device is quite expensive to manufacture. Another disadvantage of such complex mechanical devices is the difficulty of assembling the device in a sterile environment. There is sometimes a need for parts that can become contaminated during injection to be disposable. This demand is very difficult to satisfy for the device disclosed in US-2,821,981 or in general for mechanically complex devices of this type due to the large number of different components making up such a device.

Application US-3,138,257 discloses an injection device similar to that known in US-2,821,981.

US Patent No. 4,447,225 discloses a multi-dose jet injection device adapted to receive a drug bottle or vial from which liquid drug is delivered to a pressure chamber. The drug is then pumped through a non-return valve into the drug collection chamber via the cannula. The drug is then ready to be injected by applying pressure to the liquid and forcing it through the nozzle of the jet injection device. One of the drawbacks of the jet injection device disclosed in US-4,447,225 is that it is structurally complicated, for example as regards the two-stage loading of liquid medicament prior to injection, and hence expensive to manufacture.

WO-92/01485 discloses a two-chamber syringe with a barrel, for example made of plastic, including a distal and a proximal segment. A cartridge made of some material, such as glass, which is compatible with the solvent or liquid drug, is inserted into the proximal section of the sleeve. The solvent is supplied to the distal end where the liquid dissolves the lyophilized powder via a bypass unit and the syringe is then ready for use with a simple hypodermic needle injection. It should be noted that the syringe disclosed in WO-92/01485 is intended for traditional needle injection, i.e. there is no suggestion that the distal end could withstand the higher pressures required for high pressure injection, e.g. units, designed to withstand high pressures. This design is only adapted to the step of dissolving the lyophilisate in the liquid carrier which occurs in the front compartment.

U.S. Patent No. 2,591,046 discloses a hypodermic syringe assembly with two chambers separated by a bypass section. The liquid drug enters the distal chamber via a bypass section. There are no separate chambers capable of imparting different properties, for example resistance to high pressures.

Liquid drugs for injection are usually stored in glass containers before being loaded into a syringe. The glass container is closed by a rubber gasket. The drug is therefore only in contact with glass and rubber. The main rationale behind the inadequacy of rubber in drug storage containers is that this type of plastic does not form a completely tight barrier to ingress of oxygen or components leaking from the container. Components from the manufacturing process that affect the liquid stored in the container may also be present in the plastic. Another reason is that the plastic can release trace amounts of ingredients that are unacceptable in injectables. The above-mentioned disadvantages related to the plastic used in the drug storage containers are only relevant

When using plastic containers for typical drug storage times, for example up to two years. When using plastics, for example in syringes and the like, where the liquid drug comes into contact with the plastic only at the time of injection, the above-mentioned disadvantages are not significant.

In jet injection devices using glass containers, this type of container must withstand the high pressure used to force the liquid out of the container. The glass container is then preferably manufactured from toughened glass, which makes it expensive. On the other hand, plastics can easily acquire the properties necessary for the pressure chamber, such as strength and elasticity, with little risk of breakage. Glass materials in storage containers and plastics in pressure chambers are also suitable for use in disposable items.

The object of the invention is to provide an injection device that is easy to use, which is less expensive to manufacture than devices known in the art and does not have the drawbacks of sterile handling of the device components.

It is also an object of the invention to provide an injection device capable of being prefilled with drug and allowing the drug to be stored for extended periods prior to injection, wherein all surfaces of the device and parts thereof coming into contact with the drug can be kept sterile during manufacture, storage and storage. and use, and having sterile components, which, in principle, cannot be reused to prevent unauthorized sterilization and the re-sale of devices that have already been used, which could be hazardous to the health of patients.

An injection device for delivering a liquid from a high pressure source, including a housing housing a pressure chamber and a storage chamber assembly, the pressure chamber including a pressure tube of substantially constant cross-section, slidably receiving at least one piston, and having a front bore. the final one, designed to push the liquid out, the pressure chamber being characterized by resistance to the pressure of the liquid, and the storage chamber for the liquid or liquid precursor ingredients is provided with a storage sleeve having at least a section of substantially constant cross-section in which at least one piston is disposed, and a fluid connection is provided between the pressure chamber and the storage chamber to allow liquid to flow from the storage chamber. to the pressure chamber, the axis of the pressure chamber and the axis of the storage chamber substantially coincide, the pressure sleeve and the storage sleeve have internal diameters close enough to allow the resilient piston to leak tightly from the storage sleeve to the pressure sleeve, and the storage chamber is separate from the pressure chamber and the pressure sleeve contains a vacuum or is filled with air or other gas according to the invention characterized in that the casing is provided with a compression mechanism containing means for applying pressure, directly or indirectly to the front piston while it is in the pressure sleeve, to create a liquid pressure in the pressure chamber above 25 atm. (2.5 MPa).

The front bore of the pressure sleeve is designed to generate a liquid jet.

The front opening of the pressure sleeve is covered with a removable or peelable closure or gasket.

The pressure sleeve has an open rear end and the storage sleeve has an open front end.

The fluid connection between the pressure chamber and the storage chamber comprises a bypass section leading from the storage chamber to the pressure chamber around the front piston.

The pressure chamber and the storage chamber are made of different materials, preferably plastic and glass, respectively.

There is a gasket between the pressure chamber and the storage chamber.

A second piston is movably placed in the storage chamber, delimiting the storage chamber with the front piston.

The storage chamber is a two-chamber storage chamber, provided with a bypass section and at least a third piston, dividing the storage chamber into two sub-chambers.

The pressure chamber has a larger volume than the volume of the storage chamber.

The bypass section includes bypass channels located on the inner surface of the bypass section.

The compression mechanism has a plunger acting on the rear piston.

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The compression mechanism consists of a spring loaded or pressurized gas.

A front piston and a rear piston are displaceably disposed in the pressure sleeve and, respectively, in the storage sleeve to form a chamber assembly, and the compression mechanism includes an axially movable plunger.

The device according to the invention has means for triggering a manual reverse movement of the chamber assembly, preferably in the form of a thread.

The device according to the invention has means for triggering the forward movement of the plunger, preferably being a compressed gas or a tension spring.

The front opening has a connection for attaching a hypodermic needle.

The idea of ​​the invention can be used in any injection device requiring high pressure of the injected fluid. High pressures may be needed to administer a high viscosity product, such as oil, gel, amorphous paste or suspension products, for example for dental purposes or to form a slow-shedding body deposit. Another major type of injection devices requiring high pressure are jet injection devices designed for needle-free penetration of liquid through the skin under pressure, which will be discussed below.

The invention provides an injection device that is easy to use, has few moving parts and is easy to manufacture. The injection device can be used to perform any type of high pressure injection, can be pre-filled with drug and stored without spoiling the drug, and can be manufactured, stored and used under sterile conditions. The device is also suitable for use as a disposable device.

The subject of the invention is illustrated in exemplary embodiments in the accompanying drawing, in which Figs. 1a-1e show a schematic illustration of an injection procedure with the injection device according to the invention, Fig. 2 - a cross-sectional view along the line AA of Fig. 3, Fig. 3. - a schematic illustration of the pressure chamber of the device according to the invention, fig. - 4a-4d - schematic illustration of the injection procedure using the injection device according to the second preferred embodiment of the invention, fig. 5 - schematic illustration of the pressure chamber of the device according to the alternative embodiment of the invention, fig. 6a-6b - schematic illustration of an alternative embodiment in which the pressure chamber and storage chamber assembly is movably arranged with respect to the housing containing the injection mechanism, and fig. 7a-7b - schematically modification of the plunger assembly, aimed at reducing the resultant elasticity of the system.

Figures 1a-1e show an illustration of the injection procedure using the injection device according to the invention. The injection device comprises a housing 2 in which there is a pressure chamber 4, a storage chamber 6 and a compression mechanism 8.

The pressure chamber 4, shown separately in Fig. 3, comprises a pressure sleeve 10 of substantially constant cross-section defining the axis 12 of the pressure chamber for receiving at least one piston therein and having a front opening 14 for fluid ejection. The pressure chamber 4 is strong enough to withstand the pressure of the liquid during the ejection procedure. The pressure sleeve 10 has an open rear end 26 (in Fig. 3).

The pressure chamber 4 is sterilized before assembly and is either empty or filled with air or other gas. It is preferably disposable, but may also be reusable. The inside diameter of the front opening 14 is 0.1-0.6 mm, preferably of the order of 0.15 mm. As mentioned, the opening may be adapted for either needleless injection as shown schematically in the figures or for needle injection in which case the front opening 14 may be provided with a needle connecting member. It is clear that a short needle in the range of 1 to 3 mm in length may be used to penetrate the outermost layer of the skin and thus reduce the jet velocity necessary to reach the target depth in the tissue.

The storage chamber 6 for storing the liquid or liquid precursor ingredients comprises a storage sleeve 16 with at least one section of substantially constant cross-section defining the axis 18 of the storage sleeve 16 which is intended to receive at least one piston 20, 22. bypass section (not shown in the figure). The storage sleeve 16 has an open front end and a preferably open rear end. Most preferably, the storage chamber 6 has a substantially constant cross section from the leading end to the rear end so as to give it the generally cylindrical shape shown. The internal cross-sectional area of ​​the storage sleeve 16 is adapted to the area

The internal cross section of the pressure sleeve 10, so as to allow the front piston 22 to pass from the storage sleeve 16 to the pressure sleeve 10, for example by the fact that the storage sleeve 16 is smaller and preferably equal to the pressure sleeve 10, and preferably the cross-sectional area transverse and shapes are basically the same. The front piston 22 is at the front open end and the second piston 20 is at the rear end of the storage sleeve 16.

Between the pressure chamber 4 and the storage chamber 6 there is a fluid connection allowing liquid to flow from the storage chamber 6 to the pressure chamber 4. Fig. 2 shows this fluid connection as a conventional bypass section 24 in the pressure chamber 4. Fig. 2 shows a view in a cross-section along the line AA of Fig. 3 (which schematically shows the pressure chamber), illustrating a preferred embodiment of the bypass section.

The bypass section illustrated includes one or more bypass channels located on the inner surface of the bypass section 24 of the pressure chamber 4. The bypass channels may be parallel to the longitudinal direction of the feed chamber, and may also be angled with respect to the longitudinal direction. The number of channels is selected depending on the amount of liquid to be charged and is preferably from 1 to 15. The bypass section 24 can be arranged in many different ways. It may be located on the inner surface of the upper part of the storage chamber 6 with an equivalent bypass function. Many other methods of arranging a volume section are known in the art.

It is important not to place too many channels because of the volume of liquid that remains in the channels as the liquid passes through. It is also advantageous to reduce the dead volume between the edges of the pistons by keeping a slight difference between the diameter at the edges and that of the main body of the piston.

According to an alternative embodiment of the device, the shape of the inner surface of the bypass section is such that the piston is deformed as it passes, and thus allows liquid to pass from the storage chamber 6 to the pressure chamber 4.

The storage chamber 6 is independent of the pressure chamber 4 and is preferably made of a different material. According to a preferred embodiment, the storage chamber 6 is made of glass, for example Type I glass, and the pressure chamber 4 is made of plastic, for example polycarbonate. These chambers are put together by placing the storage chamber 6 in the pressure chamber 4. Between these chambers there is an annular gasket 30 to seal the connection with the pressure sleeve 10 in order to avoid backflow and maintain sterility. Also, the front opening may have a temporary seal to close the pressure chamber 4 and keep it sterile, for example a seal in the form of a closure or rupture or removable diaphragm. The assembly of the chambers is performed in a sterile environment, for example as an additional step on a production line where the storage chamber 6 is filled with a liquid drug. After collapsing, the axes of the pressure chamber 4 and the storage chamber 6 are co-rotating.

This assembly is then placed in a housing 2 provided with a compression mechanism 8 when an injection is to be made. This operation does not have to be performed in a sterile environment. The assembly of the pressure chamber 4 and the storage chamber 6 is preferably thrown away when worn, but the cover 2 and the compression mechanism 8 can be used repeatedly.

The pressure sleeve 10 and the storage sleeve 16 have internal diameters similar enough to allow the resilient piston to pass from the storage sleeve 16 to the pressure sleeve 10 in a sealed manner, except when it is in an optional bypass section or fluid engagement section. The compression mechanism 8 for applying pressure (indicated by the arrow in the figures) directly or indirectly to the piston via the plunger 28 when it is in the pressure sleeve 10 to generate the liquid pressure necessary for the injection is only schematically depicted in figures and may be, for example, a spring mechanism. The pressure inside the pressure chamber 4 during the injection is of the order of 28 MPa.

The pistons of the storage chamber 6 are used not only to seal the storage chamber 6, but also when the liquid passes into the pressure chamber 4.

The various steps during the injection procedure will now be described with reference to Figs. 1a-1e.

This is generally a three step procedure including a charging step in which the liquid passes from the storage chamber 6 to the pressure chamber 4, the step of removing air from the chamber c and 6.

Tube 4 and the injection step. The liquid passage steps and the deaeration step are performed relatively slowly and at low pressure so as not to break the glass, over-regulate the bypass, foam the liquid, or splash liquid through the opening. Only the injection step is to be performed under high pressure. The simple structure of the device according to the invention allows all steps to be performed by forward movement of the prop 28 as illustrated in the figures, although speed and force requirements may vary. As will be explained below, it is also possible to use different mechanisms for the different steps, each adapted to its task.

During the loading step, the rear piston of the storage chamber 6 is pushed upward by the compression mechanism 8 (Fig. 1a). Under the pressure of the rear piston 20, the liquid moves the front piston 22 to the bypass section, where the liquid, bypassing the front piston 22, flows into the pressure chamber 4 (Fig. 1b). This first stage is complete when all the liquid has been introduced into the pressure chamber 4, i.e. the pistons 20, 22 are in contact with each other. The surfaces of the pistons facing each other are preferably shaped such that when they are in contact with each other, no liquid remains between the pistons. They preferably have flat surfaces in communication with each other so that they are not resilient under pressure. This can be achieved by using a slightly convex shape under non-pressure conditions, which shape becomes flat under radial pressure, as described in US 5,743,890.

The pressure on the rear piston during the loading step is illustrated in the figure by the force exerted by the compression mechanism 8. It only illustrates the relative pressure / displacement between the plunger 28 and the piston. Instead, according to another preferred embodiment, the pressure in the charging step is obtained by moving the pressure chamber and storage chamber assembly on one side and the plunger 28 and the compression mechanism 8 on the other side towards each other, while keeping the plunger 28 and the compression mechanism 8 stationary on each other. This can be done by arranging respective units in different parts of the cover 2 that are movable relative to each other, for example by mutual screw rotation of the two parts of the cover, which ensures a smooth and moderate flow of the liquid. The liquid is forced into the pressure chamber 4 from the storage chamber 6 and no non-return valves are needed. Preferably, de-aeration is also performed during such relative movement between the parts. Such an assembly also has the advantage of being able to reduce the demands on the compression mechanism 8, which can now be designed only for the injection step and can include, for example, a strong gas or mechanical spring and a trigger mechanism for releasing it. Such mechanisms are well known in the art of jet injection as exemplified in the cited references in the art.

During the air removal step, both pistons are moved to the bypass section and further into the pressure chamber 4 (Fig. 1c). The distance the pistons enter the pressure chamber 4 depends on the volume of liquid introduced into the chamber. It is important that there is no air in the pressure chamber 4 during the injection. The pistons provide a good seal in the pressure chamber 4. In Fig. 1d shows the situation when the air removal step has been completed, i.e. when there is no more air in the pressure chamber 4. The displacement of the pistons during this step can be achieved either by displacing the skirt 2 or parts thereof with respect to the plunger 28, i.e. in the same way as in the loading step or by activating the compression mechanism 8.

During both the charging stage and the air purging stage, the device is preferably held in a slightly upright position, i.e. with the pressure chamber front end opening above the horizontal, obliquely or fully upwards, to prevent liquid from spilling out.

The injection device is now ready for injection (Figure 1d). A compression mechanism 8 connected to the pistons via the plunger 28 is actuated and the pistons are exerted with the necessary pressure to force the liquid jet 30 out of the front opening 14 of the pressure chamber 4 (Fig. 1e). During injection, the upper end of the pressure chamber 4 is held in close contact with the skin of the patient.

The distal end of the front piston 22 is preferably adapted to fill the front end of the pressure chamber 4 when the plunger 28 has reached this end. This is important in order to expel as much liquid as possible from the pressure chamber 4 during injection.

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According to an alternative embodiment, the storage chamber 6 is divided into two separate compartments by the third piston and provided with a bypass section, while the proximal compartment contains a liquid, e.g. water, and a further compartment contains a solid component, e.g. a lyophilized powder. Via the bypass section, the liquid is forced into the distal compartment where it dissolves the solid component. This is a procedure well known in the art for dual chamber syringes. The thus mixed liquid in the further compartment then passes into the pressure chamber in exactly the same way as described above.

Figures 4a-4d show a schematic illustration of an injection procedure using an injection device according to an alternative embodiment of the invention.

Figures 4a-4d only show the pressure chamber 4 and the storage chamber 6, and the pistons and seal inside these chambers. The assembly of the pressure chamber 4 and the storage chamber 6 is, of course, inside an enclosure 2 having all the necessary injection properties according to the embodiments disclosed above.

The pressure chamber 4 comprises a pressure sleeve 10 with a substantially constant cross section for receiving at least one piston therein and having a front opening 14 for the discharge of liquid. The pressure chamber 4 is strong enough to withstand the pressure of the liquid during the injection procedure. The pressure sleeve 10 has an open rear end 26 (in Fig. 3).

The pressure chamber 4 is sterilized before use and filled with air or other gas. It is preferably disposable, but may also be reusable.

The inside diameter of the front opening is 0.1-0.6 mm, preferably of the order of 0.15 mm.

The storage chamber 6, intended to contain the liquid or liquid precursor ingredients, comprises a storage sleeve 16 with at least one section of substantially constant cross-section for receiving a rear piston 20, a front piston 22 and an intermediate piston 23 therein. bypass section 25.

Between the pressure chamber 4 and the storage chamber 6 there is a bypass section 24 allowing liquid to flow from the storage chamber 6 to the pressure chamber 4. This connection may be a conventional bypass section in the pressure chamber 4.

The chambers are folded together by placing the storage chamber 6 in the pressure chamber 4. Between these chambers there is a gasket 30, preferably of the O-ring type, in order to obtain a tight connection with the pressure sleeve 10. The chambers are folded in a sterile environment, for example as an additional step on the production line, where the storage chamber 6 is filled with a liquid and a solid component.

Referring to Figs. 4a-4d, the various steps of the injection procedure will now be described.

These steps are similar to the three-step procedure described with reference to Figs. 1a-1e, i.e. including a loading step where liquid is introduced from the storage chamber 6 into the pressure chamber 4, the step of removing air from the pressure chamber 4, and the injection step. In this embodiment, a preparatory step is added before the loading step.

The storage chamber S comprises two compartments, separated by an intermediate piston 23. The lower compartment 31 contains a liquid, e.g. water, adapted to dissolve a solid material 35, e.g. a lyophilized powder, in the upper compartment 33.

During the preparatory stage (Figs. 4a, 4b), the first piston 20 is pushed upwards (e.g. by a compression mechanism 8 or as described alternatively above) and, via the liquid in the lower compartment 31, pushes the third piston into the bypass section 25. As the liquid enters into the upper compartment 33 via the bypass section, this dissolves the solid material. When all the liquid has passed into the upper compartment 33 and the solid material has dissolved, the first and third pistons together continue to push the second piston 22 upward into the bypass section 24 of the pressure chamber via the liquid. In this position, the liquid enters the pressure chamber 4 (Fig. 4c).

Figure 4d shows the injection device ready for injection when the second piston 22 is pushed out of the bypass section and seals tightly against the inner surface of the distal part of the pressure chamber 4. The exact position of the piston inside the pressure chamber 4 when the device is ready for injection depends on from the volume of liquid entering the pressure chamber 4. In this position, substantially all of the air is removed from the pressure chamber 4 through the front opening 14.

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In the embodiment of Figs. 4a to 4d, the inside diameter of the pressure sleeve 10 is slightly larger than the inside diameter of the storage sleeve 16, and the second piston 22 has a larger diameter upper or front portion to match the diameter of the pressure chamber 4, and a smaller lower or rear diameter. a part that is matched to the diameter of the storage sleeve 16, which allows it to be sealed to both chambers. The smaller first piston 20 and the third piston 23 can continue to move into the pressure sleeve 10 while the second piston seals.

The high-pressure stream of liquid generated by the device penetrates the skin of the patient. However, the main idea of ​​the invention is equally applicable to needle injection of high viscosity liquid drugs, for example gels. Nowadays, when it is necessary to inject the gel with a needle syringe, a needle with a relatively large inside diameter must be used, which can be very painful. In fig. 5 is a schematic illustration of an alternative embodiment of the pressure chamber 4. In this embodiment, a hypodermic needle 41 is attached to the front opening of the injection device, including a connection 43 made in a solid manner to withstand the pressure inside the pressure chamber during injection. The needle is preferably attached to the pressure chamber 4 during the manufacture of the chamber, for example during a molding process. The injection procedure is the same as for needle-free injection as described above. By using a pressure chamber provided with a needle with a similar inner diameter to the front opening of the pressure chamber, the high viscosity liquid can be injected using a needle thinner than before. This is very beneficial as it is less painful for the patient.

The pressure required to perform a needle injection with the device according to an alternative embodiment is dependent, inter alia, on the inner diameter of the needle and the viscosity of the liquid gel.

Typical pressures in pressure chamber 4 are generally greater than 25 atm. (2.5 MPa), often above 50 atm. (5 MPa) or above 100 atm. (10 MPa). Usually these pressures are less than 1000 atm. (100 MPa), often less than 800 atm. (80 MPa) or below 500 atm. (50 MPa).

Figures 6a-6b show schematically an illustration of an alternative embodiment in which the pressure chamber and storage chamber assembly is movably arranged with respect to a housing containing the injection mechanism. As with other embodiments, the pressure chamber 4 and the storage chamber 6 form a chamber assembly in which the storage chamber 6 is coaxially and stationarily positioned at the rear end of the pressure chamber 4. In this embodiment, the rear end of the pressure chamber 4 has an external thread 61. The skirt 62 houses a compression mechanism 8 to push the plunger 28 forward and may, for example, include a biased spring and a trigger assembly (not shown). The skirt 62 has an internal thread which corresponds to the external thread 61 on the pressure chamber 4. In Fig. 6a shows the device under conditions prior to the liquid transit process, for example pre-filled and delivered to the end user. The user activates the device by twisting the pressure chamber 4 and the skirt 62 together while the plunger 28 is idle and stationary with respect to the skirt. This will move the rear piston 22 forward to carry out the same preparatory phases as described for the other embodiments, i.e. to move the front piston into a bypass section 24 allowing liquid to flow into the pressure chamber 4 and vent the pressure chamber. The device will then be in the condition illustrated in Fig. 6b, with the compression mechanism 8 and plunger 28 taking their initial positions, and ready for the injection. The injection can occur by releasing the energy stored in the compression mechanism 8 and moving the plunger 28 forward as the liquid expels from the pressure chamber 4.

Figures 7a and 7b schematically illustrate a modification of the plunger assembly to reduce the resultant elasticity in the system during the injection step. Fig. 7a is similar to Fig. 1a, i.e. it comprises a pressure chamber 4 and a storage chamber 6 with a bypass section 24 allowing fluid to pass therebetween, and a front piston 22 and a rear piston 20 adapted to move in the chambers. In fig. 7a the internal diameters of the pressure chamber 4 and the storage chamber 6 are substantially the same, which means that the pistons, when they are in the storage chamber 6 or the pressure chamber 4, are subjected to approximately the same radial pressure, which should be sufficient to obtain a seal between the inside walls of the chamber .

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Accordingly, the pistons fill the cross-sectional areas of the chambers as illustrated in the cross-sections to the right. The upper cross-section passes through the pressure sleeve 10 of the pressure chamber 4 and the front piston 22 when it is completely inside the sleeve and fills the cross-section, possibly with the exception of the plunger portion 23 between the sealing edges of the plunger. The lower cross-section extends across the pressure chamber 4 at the bypass section 24, and the rear piston 20 when adjacent to this bypass section 24, with the piston 20 filling the cross-section except for the channels of the bypass section 24. The pistons are in this position. once all the liquid had passed from the storage chamber 6 to the pressure chamber 4 and both plungers were moved slightly forward, for example to vent and prepare for injection. When the compression mechanism 8 exerts pressure on the rear piston 20, both pistons tend to deform as the friction of the front piston surface against the wall resists movement. This deformation can be considerable as the axial force in turn tends to radially expand the pistons. This effect can be intensified by the size and number of pistons, for example in the case of a dual storage chamber as illustrated in Fig. 4. The flexibility may contribute to squashing and vibration in the pressure profile during injection with arbitrary and less reliable effects. Fig. 7b shows some modifications to overcome these problems. The inside diameter of the storage chamber 6 is here somewhat smaller than the inside diameter of the pressure chamber 4, at least in its front part, which means that for each piston passing from the storage chamber 6 to the pressure chamber 4, the radial pressure is reduced. Moreover, the front piston 22 is designed to seal when it is in the storage chamber 6 but not to seal in the pressure chamber 4, while the rear piston is designed to seal both in the storage chamber 6 and in the pressure chamber. 4. This is illustrated in the cross sections on the right. As in fig. 7a, the upper cross section extends across the pressure sleeve 10 of the pressure chamber 4 and the front piston 22 when the piston is completely in the sleeve, it can be seen that the piston is somewhat triangular in shape so as to form a 4 point with the pressure chamber inner wall contact 71 and left spaces 72 allowing the liquid to pass through. In the lower cross section through the pressure chamber 4 and the rear piston 20 it can be seen that this piston fills the cross section and forms a seal with the inner wall of the pressure chamber 4. In the embodiment shown, there is no need for a fluid connection in the form of a bypass cutout in the walls of the chamber, since the spaces 72 allow liquid to flow from the storage chamber 6 to the pressure chamber 4 after the forward plunger 28 has passed into the pressure chamber 4, and will therefore function. as a connection allowing the fluid to pass through. The eliminated or reduced friction on the front plunger 28 will reduce the deformation of the plunger 28 during injection and accordingly, reduce the overall flexibility of the system. The fact that the pressure in the pressure chamber 4 is made available to all sides of the front piston reduces the deformation of the piston.

Embodiments other than those shown in Fig. 7b may be used to fulfill the indicated tasks. As a minimum requirement, the friction of the face against the wall of the front piston surface necessary for a full and secure seal in the pressure sleeve 10, for example by light contact with the wall or the presence of a small clearance, is reduced, in which case a bypass section may again be needed in the pressure sleeve 10. sleeve wall.

Advantageously, this design allows for pressure equalization around at least the sides of the front piston, which may require more space than just reducing friction. Most preferably, the piston can leave a larger circumferential gap relative to the wall sufficient for the passage of the liquid and acting as a connection allowing the fluid to flow, although it is preferable to maintain point contact with the wall under some pressure, for example by point spacers or axial line contact with the wall. for example through axial or helical edges to avoid tumbling or accidental displacement towards the front of the sleeve, for example due to the non-circular cross-section or, conversely, the displacement of the circular piston in the non-circular sleeve or sleeve with the edges of the inner wall. The front piston may have conventional annular edges, although it is also possible to reduce or eliminate such edges to take advantage of the non-sealing properties of the piston after expansion. Each contact surface is less detrimental the smaller its axial extension and the further it is located to the rear. For example, it would be permissible to even use a trailing edge

An annular or apron. In contrast, the piston which is intended to form seals also after expansion may have better properties in this respect, for example by being large enough, deformable or grooved to fill the pressure sleeve also after expansion. Neither of these adaptations need to be extreme, however, as the subsequent pressure on the plunger 28 will cause the piston to expand to some extent, resulting in enhanced sealing contact. However, the only requirement is that the piston seals the pressure chamber. The sealing of the storage chamber can also be achieved without expansion. For example, in embodiments with equal cross sections of pressure chamber 4 and storage chamber 6, the front of the storage chamber 6 and / or the back of pressure chamber 4 may be constructed to be sealed by the smaller front piston, with the only requirement that the rear piston is passable. by a constriction and then to expand again, which is facilitated when the constriction is continuous or smooth at least on the entrance side.

Any means or designs can be used to achieve the intended reduction in piston deformation. As already mentioned, the internal cross-section of the pressure chamber 4 can be larger than the corresponding area in the storage chamber 6, either with a step change as illustrated, or with a continuous increment at least in the rear section of the pressure chamber sleeve 4 or the front of the storage chamber 6. If the piston has an enlarged portion outside the storage chamber 6, as illustrated in FIG. 4, then the surface must be adapted to this enlarged portion. Optionally or in addition to this surface change, a change in the cross-section of the sleeve may be used to change the shape of the piston from a high degree of fit in the storage chamber 6 to a less degree of fit in the pressure chamber 4.

In order to achieve the stated objectives, the principles for reducing deformation above should be applied to at least one piston, but may be applied to more than one piston, for example the front and intermediate pistons of the embodiment of Fig. 4. In general, it is possible to have more than one sealing piston in the pressure sleeve 10, although often one sealing piston is sufficient and a second piston is used to reduce dead volumes. Typically, the pistons are made of an elastically deformable material such as rubber to form a reliable and durable seal. For the purposes outlined, it is preferable that the material present in the pistons is additionally deformable but not compressible, for example by avoiding air bubbles or foam. It is also advantageous to reduce the dead space between the common sealing edges of the pistons or to replace them with another adapter, such as a soft or compressible skin.