WO2009053464A1

WO2009053464A1 - Jet injection unit with resilient liquid chamber

Info

Publication number: WO2009053464A1
Application number: PCT/EP2008/064442
Authority: WO
Inventors: Torben Strøm HANSEN; William Anthony Denne
Original assignee: Novo Nordisk A/S
Priority date: 2007-10-24
Filing date: 2008-10-24
Publication date: 2009-04-30

Abstract

A jet injection device comprising a base member (160), a load member (130), a resilient liquid chamber (143) being in fluid connection with an outlet orifice (142) in one end and an inlet channel (156) in the other end, an impulse transferring member (164), and a coil spring (127) suited for being rotationally pre-stressed by manipulation of the load member (130). When released the coil spring (127) will rotate and undergo a radial contraction which activates the impulse transferring member (164) to squeeze the resilient liquid chamber (143), thereby forcing the contents of the resilient liquid chamber (143) out through the outlet orifice (142).

Description

JET INJECTION UNIT WITH RESILIENT LIQUID CHAMBER

The invention relates to a jet injection unit integrating an actuating mechanism for a jet injector with a pressure chamber and nozzle part into one single compact unit.

BACKGROUND OF THE INVENTION

Subcutaneous and intramuscular delivery of liquid drugs by injection is common in the medical arts. As some medications such as insulin must be given frequently by injection to an individual, easy performance of the injections is desirable.

Many patients dislike needle injections due to pain or fear for needles. Further, blood-borne pathogens, such as HIV and hepatitis, can be transmitted to health care workers by accidental needle-sticks. Also, the disposal of used needles is a growing concern. This disposal presents a problem to individuals other than healthcare workers. Children, for example, may find used needles in the garbage, putting them at risk of contracting infection. Discarded needles likewise pose a risk to waste disposal workers. This is at the moment a huge worldwide problem, (though partly overlooked as it mainly hits countries of low development) causing deaths counted in millions.

In efforts to minimize the fears and risks associated with needle injections, several types of needle-free jet injectors have been developed. These devices penetrate the skin using a high velocity fluid jet and deliver medication into the tissue of a patient. In order to accomplish this, a force is exerted on the liquid medication. Jet injectors in general contain a fluid drug which has been transferred into a chamber having a small orifice at one end. A well known principle of jet injectors utilizes a piston to transfer the energy necessary to form a jet beam to the liquid. The piston can be a single or two pressure stage piston energized by a ram under the force of for instance a spring, pressurized gas or an explosive.

An alternative to a rigid liquid pressure chamber and a moving piston is a flexible liquid pressure chamber which can be influenced by an external ram. The flexible pressure chamber can have at least one or two liquid openings. Most important of course is the outlet which lets the liquid pass out through an orifice of a well defined dimension to form a liquid jet beam when sufficient pressure is exerted on the liquid. A second opening can be applied to the flexible liquid chamber to facilitate the connection to a liquid reservoir. In the latter case, the second opening can advantageously comprise counter flow restriction means, such as a check-valve to ensure correct flow direction out of the orifice when a jet injection is performed.

Piercing of the skin by means of a pressurized liquid beam requires a minimum critical pressure impulse. This impulse is for most known needle free jet injector concepts produced by release of an axially pre-stressed mechanical spring or a compressed gas. The mechanical spring based concepts often suffer from a release recoil and sound that gives the user an unintended bad perception of the given device. The recoil stems from the acceleration and deceleration of the mass of the mechanism used to propel the liquid. The compressed gas based concepts has got less accelerated mass and thereby recoil since the density of the compressed gas is much lower than that of the mechanical spring. However, the compressed gas needs a leak-safe compartment suitable for storage during the shelf life of the device and needs to be changed as an accessory imposing a significant cost and inconvenience on the user. It is therefore desirable to provide a jet injection device having a reduced recoil and release sound without the need for a leak-safe compartment.

PCT / GB 02 / 02633 describes a jet injector in which there is a rigid tube terminating at one end in a nozzle and at the other in a constriction which leads to the main drug supply. A portion of the rigid tube is formed as a flexible window. There is an over centre spring and an end thrust beam which may compress the window to cause a high speed flow through the nozzle. The device suffers a number of problems. Priming the pump is unstable, the spring acting in tension stores insufficient energy, the flexible window tears from its mount and causes inefficient energy transfer, the spring and beams carry insufficient momentum, the nozzle form tends to close the entrance to the track through the skin and energising by pressing against the skin of the patient is somewhat uncomfortable. The present specification details radical improvements to this device.

WO 2004/039438 discloses an injector comprising a rigid tube with an outlet at one end and a non-return valve at the other end, a hole in the tube wall, an elastomeric liner within the rigid tube and a piston arranged to impact the elastomeric liner through the hole in the tube to produce a high pressure transient. The injector includes a spring member arranged to act upon the piston to cause the piston to impact the liner. The piston is attached to a mass which is capable of being accelerated by the spring member. The spring member is bi- stable. It may be manually energised to a latched position and may then be triggered by pressure against the skin of a patient. Though compact and simple in nature this device still suffers from drawbacks especially regarding energy compactness and technical function of the actuating spring. The present invention aims to overcome these drawbacks.

WO 2005/070482 discloses a deformable impulse chamber which can be used for expelling an amount of fluid at a high pressure. The impulse chamber is collapsed by a radially moving piston which is activated upon release of a pre-stressed helical torsion spring. The piston activation mechanism comprises the spring and a number of other elements being arranged along an axle which is positioned on one side of the impulse chamber. This arrangement takes up a considerable amount of space and the unit consisting of the impulse chamber, the piston and the piston activation mechanism therefore appears rather bulky.

It is further desirable to provide a jet injection device which is more compact so that its size will not deter a user.

SUMMARY OF THE INVENTION

In the disclosure of the present invention, embodiments and aspects will be described which will address one or more of the above objectives or which will address objectives apparent from the below disclosure as well as from the description of exemplary embodiments.

The jet injection device of the present invention addresses the large recoil of a longitudinally pre-stressed coil spring and the inconvenience of a compressed gas accessory by changing the loading of a coil spring. The device comprises a coil spring which is suited for being rotationally pre-stressed and which is arranged so that upon triggering the spring will rotate and, due to a reduction of its radial dimension, impact a radially translating impulse transferring member, such as a piston, which will then compress a resilient liquid chamber containing a limited amount of liquid representing a sub-portion of the dose.

The rotational pre-stressing of a spring, particularly a rectangular cross section spring, allows for a dense storage of energy and thereby less accelerated mass. Furthermore, the accelerated mass rotates instead of moving longitudinally. This significantly reduces the recoil of the device. Additionally, by employing a resilient liquid chamber containing only a sub-portion of the dose, a reduced volume of liquid is actually accelerated to pierce the skin. This requires less pre-stress energy reducing both the device recoil and the force to be triggered by the user.

Thus, in an aspect of the invention a jet injection device is provided comprising a resilient liquid chamber, an outlet orifice in liquid communication with the resilient liquid chamber, an inlet for establishing a connection between the resilient liquid chamber and a source of liquid drug, a coil spring having a first end and a second end, the first end being essentially fixed and the second end being connected to a load member, spring release means, and an impulse transferring member, wherein the coil spring is suited for being rotationally pre- stressed by manipulation of the load member, and wherein at least a part of the coil spring and/or the load member encircles at least a part of the impulse transferring member so that upon activation of the spring release means the rotation of the coil spring will cause the impulse transferring member to move radially to compress the resilient liquid chamber.

A jet injection device of the above type provides for a very compact design which has a significantly reduced recoil and release sound due to the chamber deformation energy being transferred to the impulse transferring member by a rotating coil spring/load member arrangement.

When the coil spring is rotationally pre-stressed its radial dimension is increased compared to when it is in a relaxed or unstressed state, i.e. the majority of the coil spring is radially expanded. The pre-stressing may be carried out by turning the load member clockwise or anti-clockwise in relation to the part of the device which holds the first end of the coil spring in an essentially fixed position. The part of the device which holds the first end of the coil spring in an essentially fixed position may be a base part comprising the impulse transferring member, but any part of the device around which the load member revolves during pre- stressing could in principle be used to essentially fix the first end of the coil spring. The first end and the second end of the coil spring are thereby angularly displaced in relation to the helix axis and the unstressed state. A ratchet and pawl mechanism may be provided to ensure a firm and stable engagement between the load member and the part of the device holding the first end of the coil spring during the pre-stressing. When the load member has been rotated a number of turns it may reach a pre-defined stop and engage with a lock snap which then holds the coil spring in the pre-stressed position until a spring release means is activated. This indicates that the device is ready to be fired. Upon activation of the spring release means the second end of the coil spring will rotate with respect to the helix axis and with respect to the first end. This will cause a momentary reduction of the radial dimension of the coil spring, potentially as much as up to 30% compared to the unstressed state. In a concentric, or eccentric, arrangement of the coil spring and the impulse transferring member where at least a part of the coil spring encircles at least a part of the impulse transferring member the diameter reduction of the coil spring may, due to the coil spring being forced into engagement with the impulse transferring member, result in the impulse transferring member being moved radially to compress the resilient liquid chamber.

In an embodiment of the invention the reduction of the coil spring diameter causes the part of the coil spring which encircles the impulse transferring member to engage with the impulse transferring member and exert a radial force on it which moves a pair of jaws to compress the resilient liquid chamber.

In an embodiment of the invention, where the jet injection device may be made even more compact, the rotating coil spring may act directly on the resilient liquid chamber causing it to deform and thereby expel a liquid jet beam.

Thus, in an aspect of the invention a jet injection device is provided comprising a resilient liquid chamber, an outlet orifice in liquid communication with the resilient liquid chamber, an inlet for establishing a connection between the resilient liquid chamber and a source of liquid drug, a coil spring having a first end and a second end, the first end being essentially fixed and the second end being connected to a load member, and spring release means, wherein the coil spring is suited for being rotationally pre-stressed by manipulation of the load member, and wherein at least a part of the coil spring and/or the load member encircles at least a part of the resilient liquid chamber so that upon activation of the spring release means the coil spring will rotate to compress the resilient liquid chamber.

In an embodiment of the invention the load member may comprise a catch member, e.g. an annular catch member, which is used to guide the rotational movement of the coil spring in the device. In another embodiment of the invention the load member may comprise a load mass, e.g. an annular load mass, which is used to guide the rotational movement of the coil spring in the device and to increase the impulse transferred to the resilient liquid chamber, either directly from the rotating coil spring/load mass or via an impulse transferring member.

According to an embodiment of the invention, the jet injection device is adapted to be coupled to a source of liquid drug, such as a variable volume cartridge, which may supply the small volume of drug to the resilient liquid chamber for the initial skin penetrating jet beam as well as a bulk amount of drug for when the skin has been pierced by the liquid jet and the remaining part of the dose is to be administered. In such an arrangement the source of liquid drug may be comprised in a drug delivery device, such as a pen-type device, which drug delivery device may provide the means for transferring either the small volume of drug, the bulk amount of drug, or both, from the source of liquid drug to the jet injection device.

A drug feed tube may be provided to establish fluid connection between the resilient liquid chamber and the source of liquid drug and thereby serve as an inlet for filling or flushing the resilient liquid chamber. A non-return valve may be provided which may conveniently be a moulding on the drug feed tube. It may simply be a coaxial tube of elastomer, or slightly more complex as a flaps disposed either side of an elastomeric extension of the feed tube. On impact of the impulse transferring member, the hydraulic transient causes flow through the tube and a lowering of the pressure within it. The pressure profile across the length of the elastomeric tube also causes it to collapse, so very rapidly the tube is closed to flow.

Alternatively, the non-return valve may be provided as an inlet channel between a feed needle, adapted to establish fluid connection between the resilient liquid chamber and the source of liquid drug, and the resilient liquid chamber, said inlet channel having a radial dimension which is smaller than the radial dimension of the outlet orifice and/or an axial dimension which is longer than the axial dimension of the outlet orifice. By such an arrangement the pressure drops in the system caused by a compression of the resilient liquid chamber will cause the liquid to flow out of the outlet orifice, rather than in the reverse direction through the inlet channel, due to the significantly lower flow resistance at the outlet orifice.

In an embodiment of the present invention there is a jet injector incorporating a substantially helical metal spring as the power source. Rotation of the tip of the helical spring about the helix axis stores energy in the spring. The large displacement involved implies a very low finger pressure for a given energy storage. A rectangular cross section wire may be used to provide more efficient energy storage. The tip of the spring may latch in a fascia between the spring and skin of the patient. Pressure on the skin may then release the spring so that the stored energy is converted into kinetic energy. The helix may taper toward the stationary end of the spring or the injector body may expand, so collapse of the spring about the body is progressive from the stationary end to the free end. In addition, the taper may be such that the spring is pre-stressed in its unexcited state. Such pre-stress provides a more uniform excitation load throughout the excitation phase. It also effectively extends the permissible fractional spring over-wind. On de-excitation, the helical spring wraps securely around the body. At the moving point of contact, the moving spring is brought to a standstill with respect to the body. This deceleration force acting on the spring, causes it to precess about the body. The energy in the spring is thus conserved and concentrates in the free end of the spring. At the end of the collapse, there is an eccentric relief of the body. An annular load member or load mass connected to the tip of the spring, may wrap around this eccentric to linearly displace a radially disposed piston. In this manner, the rotatory motion of the spring may simply and efficiently be converted into a linear radial motion to generate the hydraulic transient.

A non return valve may be provided which may conveniently be a moulding on the drug feed tube. It may simply be a coaxial tube of elastomer, or slightly more complex as a flaps disposed either side of an elastomeric extension of the feed tube. On impact of the piston, the hydraulic transient causes flow through the tube and a lowering of the pressure within it. The pressure profile across the length of the elastomeric tube also causes it to collapse, so very rapidly the tube is closed to flow.

Most injector pens are cylindrical in format and generally the needle is in the form of a screw on cap. A helical steel spring is therefore a very compact means of storing energy around a screw-on cap. Conventionally, helical springs operate in extension or compression, the energy being stored as torsion in a circular cross section wire. Such an arrangement is not feasible in the present case as the maximum comfortable finger loading is around 10 N and an excitation energy of the order of 0.5 J is required for operation. Under these conditions an extension of 100 mm would be required which is clearly impracticable. However, the spring may be excited in bending by rotating the free end about the helical axis. A typical effective spring diameter might be 14 mm, in which case, 2.2 turns would provide the 100 mm translation required.

Compression and extension springs generally use circular cross section wire. As the wire is under rotational shear, the outer surface is uniformly under maximum stress. The arrangement is very efficient and energy storage is 50% of that possible if the material were uniformly stressed to its maximum permissible strain. In bending, a circular cross section is less efficient. The outer part of the circle is takes maximum stress, but there is very little volume of material to be stressed. The bulk of the material is consequently stressed at a very low level with correspondingly low energy storage. If a rectangular or flattened circular wire is used, the efficiency will rise to 66% of that in a circular wire under shear loading. A rectangular cross section is therefore very desirable.

The free tip of the spring may latch against a detente in a fascia placed between the spring and the skin of the patient. In this manner, pressure from the skin of the patient may unlatch the spring tip permitting the potential energy in the spring to convert to kinetic energy that may be used to drive the injection process. The fascia may also protect the skin of the patient from damage from the rapidly rotating spring tip.

The helical spring may be tapered toward the stationary end, or the injector body tapered with an increase in diameter toward the stationary end, so that the spring is progressively pre-stressed. This offers three advantages at the cost of slight loss in stored energy. It ensures that the spring collapses uniformly against the injector body from the stationary end to the free tip. This concentrates the kinetic energy in the free tip. The excitation force is proportional to the length of active spring as well as the stress within the spring. The pre- stressing therefore provides a much more uniform excitation force as the effective spring length increases with spring stress. The final advantage is additional protection against overwinding. If the spring is stressed to 75% of its plastic limit, a 25% overrun will cause permanent damage. If the spring is pre-stressed so that the excitation translation is reduced by a third, the maximum overrun will increase to 33% which gives a significant improvement is ruggedness.

On de-excitation, the helical spring wraps securely around the body. At the moving point of contact, the moving spring is brought to a standstill with respect to the body. This deceleration force acting on the spring, causes it to precess about the body. The energy in the spring is thus conserved and concentrates in the free end of the spring.

At the end of the collapse, the spring may wrap around a piston to convert the rotational energy into a linear thrust to generate a hydraulic transient in the axial drug filled tube.

In a further embodiment of the invention the impulse transferring member moves radially to compress the resilient liquid chamber due to a combined reduction of the radial dimension of the coil spring and precession of the coil spring about the impulse transferring member.

In an even further embodiment of the invention the impulse is transferred from the coil spring and/or the load member to the impulse transferring member via an eccentric arrangement. Such an eccentric arrangement could be realised by positioning the coil spring and/or the load member eccentrically to the impulse transferring member or in such a way that a contact face of the load member, suited to facilitate contact with a related contact face of the impulse transferring member, is positioned eccentrically to the impulse transferring member.

DESCRIPTION OF THE DRAWINGS

In the following the invention will be further described with references to the drawings, wherein

Figs. 1A - 1 C show contours of constant stress in wires under shear and tension, Figs. 2A and 2B show the helical spring according to an embodiment of the invention,

Figs. 3A and 3B show the load mass and its attachment to the spring according to an embodiment of the invention,

Figs. 4A - 4C show the injector body according to an embodiment of the invention,

Figs. 5A - 5C show the feed needle and non return valve according to an embodiment of the invention,

Fig. 6 illustrates the piston according to an embodiment of the invention,

Figure 7 shows the complete assembly according to an embodiment of the invention in cross section,

Figure 8 shows how the rotatory motion is converted to a linear piston stroke according to an embodiment of the invention, Figure 9 shows a cross-sectional perspective view of the jet injection device according to another embodiment of the invention,

Figure 10 shows a perspective view of the load member according to the embodiment of Figure 9, and Figure 11 shows a perspective view of the impulse transferring member according to the embodiment of Figure 9.

In the figures like structures are generally identified by like reference numerals.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

When in the following terms as "distal", "proximal" and "radial" or similar relative expressions are used, these only refer to the appended figures and not necessarily to an actual situation of use. The shown figures are schematic representations for which reason the configuration of the different structures as well as their relative dimensions are intended to serve illustrative purposes only.

Figure 1 shows contours of constant stress in wires and illustrates the reaction moment generated. Figure 1A shows a circular wire in torsion. The stress increases linearly with distance from the axis, 1 , as area of each element under stress and its associated moment arm. The moment of each element therefore increases as the cube of radius. The largest area is therefore under greatest stress and has the maximum moment arm. Energy storage is therefore very efficient.

Figure 1 B shows a circular cross section wire under bending stress. While the stress and moment arm also increase with distance from the neutral axis, 2, the element cross section decreases. Furthermore, as the outermost element determines the maximum permissible stress, most elements in this configuration are significantly understressed for efficient energy storage.

Figure 1C illustrates a rectangular wire cross section under bending. The element cross section is constant to the outer surface, and this represents a good compromise between practicality and efficiency of energy storage. Figure 2a shows the complete helical spring, 27, in axial projection and figure 2b in plan form. The wire, 20, is of rectangular cross section and the spring turns, 21 , are touching in the rest state. The spring tapers from the load mass end, 22, to the stationary end, 23. There is a slight inward return, 24, at the stationary end which engages with a hole, 47, in the injector body to provide a strong tether point.

There is a dog leg, 25, at the load mass end of the spring which separates the load mass tether turn from the bulk of the spring. A zig-zag termination, 26, provides a robust means of attachment to the load mass.

Figure 3a shows the load mass in axial elevation and figure 3b shows a plan form of the spring attached to the load mass. The load mass, 30, is essentially an annulus of stainless steel. There is an annular relief, 31 , which accepts the end of the spring and provides clearance between the spring, 27, and the injector body, 40.

There is a slot, 32, which accepts a peg, 33 which can engage with a slot in the fascia, 52, to retain the excited spring tip. The zig zag, 26, slides into a radial slot, 34, and an axial force is applied locally to upset the slot and rivet the zig zag securely in position.

Figure 4a shows the injector body, 40, in plan form. Figure 4b shows the latch actuator 50 in the displaced position. Figure 4c shows the fascia in axial projection, showing the nozzle, 42, and the latch actuator, 50. There is a coaxial tube, 41 , running the length of the body. It starts as a nozzle, 42, at one end, which widens conically to a tubular pumping chamber, 43. The continuation of this tube, 44, accepts the feed tube, 55, as an interference fit. The tubular section, 45, is bored out to provide clearance for the feed tube. The tubular section, 46, provides an internal thread for screw fitting to the injector pen.

Other features on the injector body are the rectangular hole, 47, which retains the stationary end of the spring, the radial cylindrical blind hole, 48, which accepts the piston, 60, the eccentric, 49, machined to facilitate the rotary to linear motion transformation, the fascia, 51 , which separates the spring from the skin of the patient, the notch, 52, which latches the excited spring and the latch actuator, 50. The latter is a low rate spring which accepts pressure from the skin of the patient and transmits it to the tip of the spring, eventually displacing it from the latch notch and initiating collapse of the excited spring. Figure 5a shows the drug delivery needle in plan form. Figure 5b and 5c show a close up section of the tubular elastomeric non return valve and illustrate how it is closed by hydraulic pressure.

The drug delivery needle, 55, has a significant diameter of between 1.5-2 mm typically. It has a capillary tube, 57, running its length, typically 0.3 mm diameter. A tubular elastomeric valve, 56, is moulded onto the internal end. The external end, 58, is machined down and sharpened to pierce the drug ampoule.

There is optionally a detente, 59, which facilitates removal on prototype devices for assessment of the pumping chamber, nozzle cleanliness and other matters.

Figure 5b shows the internal end of the drug delivery needle, 55, press fitting into the injector body, 43. The tubular elastomeric valve, 56 is moulded on to the internal tip of the drug delivery needle. There is clearance between the valve, 56, and the wall, 43. When the hydraulic pressure starts to build, it operates on the outer surface of the tubular valve. The pressure within the capillary steel drug delivery tube, 57, will remain close to zero. The pressure gradient across the elastomeric valve will cause it to collapse as in figure 5c, so sealing the pumping chamber.

Figure 6a and 6b shows the end and side elevations respectively of the simple cylindrical piston, 60.

Figure 7 shows the complete assembled injector in axial section. The spring, 27, is in its unexcited state. The load mass, 30, lies within the fascia, 51. The latch peg, 33, also can move freely within the fascia, 51. The piston, 60, is bonded within the piston channel, 48, with highly extensible, high strength elastomer, preferably addition cure silicone rubber. There is a retention ring, 70, which retains the first turn of the spring against over expansion.

Figure 8 illustrates the conversion of rotary motion to a linear impact. The load mass, 30, is rotating at full speed about the injector body axis when the dog leg, 25, of the last turn of the spring, tightens against the injector body and tethers the load mass. This causes the load mass to precess about the body and in so doing, depresses the piston. Correct matching is required for optimum effect, but pressures of the required magnitude and duration may be obtained. Figure 9 shows a cross-sectional perspective view of an assembled jet injection device according to another embodiment of the invention. A coil spring 127 is in its proximal end connected to a base member 160 and in its distal end connected to a load member 130 via a tail 128 which is accepted in a cavity (not visible) of the load member 130. The connections are arranged so that the coil spring 127 will not undergo any significant axial deformation during use of the device. The base member 160 comprises an outer circumferential part 161 and an inner elongated part 162 which is capable of acting as an impulse transferring member through a pair of radially displaceable jaws 164. In its unstressed state the coil spring 127 encircles and rests upon the inner elongated part 162. A radial clearance 180 between the outer circumferential part 161 and the inner elongated part 162 enables the coil spring 127 to expand radially during pre-stressing.

The base member 160 also comprises a circumferentially extending tooted rack 163 which is adapted to engage with a protruberance 138 on flexible arms 137 of the load member 130 to provide a ratchet and pawl mechanism that enables a one-way rotational movement between the base member 160 and the load member 130.

Centrally positioned in this arrangement is a tubular element 141 which comprises a resilient liquid chamber 143, an outlet orifice or nozzle 142, and an inlet channel 156 which also acts as a non-return valve. The resilient liquid chamber 143 extends axially from the outlet orifice 142 through openings in both the load member 130 and the base member 160 and is engaged in a proximal part of its axial extension by the pair of jaws 164. The proximal end of the tubular element 141 is adapted to receive a feed needle 155 for establishing fluid connection between a source of liquid drug (not shown) and the resilient liquid chamber 143.

Figure 10 shows the load member 130 comprising an axially extending annular body 136. A couple of partly circumferential tracks 139 have been cut in the body 136 to provide for the flexible arms 137. Each flexible arm 137 is provided with a radially inwards pointing protruberance 138.

Figure 11 shows the base member 160 comprising the outer circumferential part 161 and the inner elongated part 162. The base member 160 is formed in one piece, and the inner elongated part 162 provides for a radially flexible structure which when subjected to a compressive force will move the pair of jaws towards each other in a squeezing action. In operation of the device according to the embodiment illustrated in Figures 9-1 1 , upon attachment to a source of liquid drug (not shown), which is able to supply liquid drug to the resilient liquid chamber 143 through the feed needle 155 and the inlet channel 156, the load member 130 is rotated a number of turns relative to the base member 160. This will cause the protruberance 138 of each of the flexible arms 137 to ride over the toothed rack 163 until a pre-defined stop is reached. The relative rotation between the load member 130 and the base member 160 pre-stresses the coil spring 127 to a degree where it increases its radial dimension and lifts out of engagement with the inner elongated part 162. The radial clearance 180 allows the coil spring 127 to undergo this radial expansion.

The nozzle 142 is then placed against the skin of the user, and by exerting a force on the device to press it against the skin the base member 160 will move distally a short distance relative to the load member 130, traversing the axial clearance 190. This movement will slide the protruberances 138 out of engagement with the toothed rack 163, thereby releasing the coil spring 127 from its pre-stressed state. The distal end of the coil spring 127 will then rotate about the helix axis due to the conversion of its pre-stressed potential energy to kinetic energy. The elastic relief of the coil spring 127 will result in a decrease of its radial dimension and cause a momentary diameter reduction of up to 30% compared to the unstressed state. When the coil spring 127 reduces its diameter beyond the unstressed dimension it will engage with the inner elongated part 162 and exert a radially compressive force on it. Due to the construction of the base member 160, the inner elongated part constitutes a radially flexible structure which, under the compressive force from the coil spring 127, will cause the pair of jaws 164 to move radially inwards to thereby squeeze the resilient liquid chamber 143. The impulse thus transferred to the liquid in the resilient liquid chamber 143 generates a pressure variation along the tubular element 141 which due to the small dimension of the inlet channel 156 forces the liquid out of the device through the nozzle 142.

FEATURES OF EXEMPLARY EMBODIMENTS OF THE INVENTION:

1. A jet injection device comprising:

• a resilient liquid chamber,

• an outlet orifice in liquid communication with the resilient liquid chamber, • an inlet for establishing a connection between the resilient liquid chamber and a source of liquid drug,

• a coil spring having a first end and a second end, the first end being essentially fixed and the second end being connected to a load member, • spring release means, and

• an impulse transferring member, wherein the coil spring is suited for being rotationally pre-stressed by manipulation of the load member, and wherein at least a part of the coil spring encircles at least a part of the impulse transferring member so that upon activation of the spring release means the coil spring will rotate and thereby cause the impulse transferring member to move radially to compress the resilient liquid chamber.

2. A jet injection device comprising:

• a resilient liquid chamber, • an outlet orifice in liquid communication with the resilient liquid chamber,

• an inlet for establishing a connection between the resilient liquid chamber and a source of liquid drug,

• a coil spring having a first end and a second end, the first end being essentially fixed and the second end being connected to a load member, and • spring release means, wherein the coil spring is suited for being rotationally pre-stressed by manipulation of the load member, and wherein at least a part of the coil spring encircles at least a part of the resilient liquid chamber so that upon activation of the spring release means the coil spring will rotate to compress the resilient liquid chamber.

3. A jet injection device according to any of features 1 -2, wherein the jet injection device is suited for connection to a source of liquid drug.

4. A jet injection device according to feature 4, wherein the source of liquid drug is a cartridge having a variable volume.

5. A jet injection device according to any of features 1 -4, wherein the jet injection device is suited for connection to a medical drug delivery device. 6. A jet injection device according to feature 5, wherein the medical drug delivery device is a pen-type device comprising a drug containing cartridge.

7. A medical jet injector comprising; • a resilient liquid chamber in liquid communication with

• an orifice suited as outlet for a liquid jet

• an inlet designed to connect a drug chamber with the resilient chamber

• at least one reverse-flow restricting means securing that liquid displacement is substantially prevented from the resilient liquid chamber back into said inlet • a coil spring in connection with an impulse mass

• spring release means and

• an impulse transferring member, WHEREIN the coil spring is suited for being rotationally biased and when released by activation of the spring release means, said coil spring and the impulse mass is accelerated and rotates to engage with the impulse transferring member which upon engagement moves inwards towards the liquid chamber wall, thereby compressing the resilient liquid chamber causing liquid outflow through the orifice forming a liquid jet stream.

8. A medical jet injector according to feature 7, WHEREIN said coil spring has a substantially rectangular cross section.

9. A medical jet injector according to any of features 7-8, WHEREIN said impulse is transferred from the coil spring and the impulse mass to the impulse transferring member via an eccentric arrangement.

10. A medical jet injector according to feature 9, WHEREIN the impulse mass has a contact face suited to facilitate contact to a related contact face of the impulse transfer member, said contact face of the impulse mass is rotatably arranged eccentric relative to the impulse transfer member, whereby the impulse transfer member is moved substantially inwards upon rotation of the impulse member when the release member is activated.

11. A medical jet injector according to any of features 7-10, WHEREIN said coil spring tapers from one axial end to the other. 12. A medical jet injector according to any of features 7-1 1 , WHEREIN said medical jet injector is suited for connection to a drug reservoir.

13. A medical jet injector according to feature 12, WHEREIN said drug reservoir is a cartridge with variable liquid containing volume.

14. A medical jet injector according to any of features 7-1 1 , WHEREIN said medical jet injector is suited for connection to a medical drug expelling device.

15. A medical jet injector according to feature 14, WHEREIN said medical drug expelling device is a pen-type device comprising a drug containing cartridge.

16. A medical jet injector according to feature 14 or 15, WHEREIN said medical drug expelling device comprises manual or automatic actuating means for expelling a dose of liquid drug via the liquid passage of said medical jet injector and a passage in the skin of a subject provided by the impulse of the liquid jet stream exerted prior to expelling said dose.

17. A medical jet injector according to any of features 7-16, WHEREIN said medical jet injector comprises skin fixating means to ensure that the position of the orifice relative to a skin surface is maintained during a performing of an impulse jet injection and a following relatively low-pressure injection of a dose of liquid drug.

18. A medical jet injector according to feature 17, WHEREIN said skin fixation means comprise adhesive.

19. A medical jet injector according to any of features 7-18, WHEREIN the injected drug is insulin.

Claims

1. A jet injection device comprising:

• an impulse transferring member, wherein the coil spring is suited for being rotationally pre-stressed by manipulation of the load member, and wherein at least a part of the coil spring and/or the load member encircles at least a part of the impulse transferring member so that upon activation of the spring release means the rotation of the coil spring will cause the impulse transferring member to move radially to compress the resilient liquid chamber.

2. A jet injection device according to claim 1 , wherein the impulse transferring member moves radially to compress the resilient liquid chamber due to a reduction of the radial dimension of the coil spring.

3. A jet injection device according to claim 1 , wherein the impulse transferring member moves radially to compress the resilient liquid chamber due to a precession of the coil spring about the impulse transferring member.

4. A jet injection device according to claim 1 , wherein the impulse transferring member moves radially to compress the resilient liquid chamber due to a combined reduction of the radial dimension of the coil spring and precession of the coil spring about the impulse transferring member.

5. A jet injection device according to any of claims 1 -4, wherein an impulse is transferred from the coil spring and/or the load member to the impulse transferring member via an eccentric arrangement.

6. A jet injection device according to claim 5, wherein the load member has a contact face suited to facilitate contact with a related contact face of the impulse transferring member, the contact face of the load member being arranged eccentrically to the impulse transferring member, whereby the impulse transferring member is moved substantially inwards when the load member rotates following activation of the spring release means.

7. A jet injection device according to any of claims 1 -6, further comprising at least one reverse-flow restricting means securing that liquid displacement from the resilient liquid chamber back into the inlet is substantially prevented.

8. A jet injection device according to any of claims 1 -7, wherein the coil spring has a substantially rectangular cross section.

9. A jet injection device according to any of claims 1 -8, wherein the load member comprises a load mass.

10. A jet injection device according to any of claims 1-9, wherein the spring release means is activated when the jet injection device is pressed against the skin of the patient.

11. A jet injection device according to any of claims 1-10, wherein the jet injection device is suited for connection to a source of liquid drug.

12. A jet injection device according to claim 1 1 , wherein the source of liquid drug is a cartridge having a variable volume.

13. A jet injection device according to any of claims 1-12, wherein the jet injection device is suited for connection to a medical drug delivery device.

14. A jet injection device according to claim 13, wherein the medical drug delivery device is a pen-type device comprising a drug containing cartridge.

15. A jet injection device comprising:

• a resilient liquid chamber,

• a coil spring having a first end and a second end, the first end being essentially fixed and the second end being connected to a load member, and

• spring release means, wherein the coil spring is suited for being rotationally pre-stressed by manipulation of the load member, and wherein at least a part of the coil spring and/or the load member encircles at least a part of the resilient liquid chamber so that upon activation of the spring release means the coil spring will rotate to compress the resilient liquid chamber.