GB2551729A

GB2551729A - Non-sputtering syringe

Info

Publication number: GB2551729A
Application number: GB1611187.4A
Authority: GB
Inventors: Dakin Iorwerth Wright David
Original assignee: Provensis Ltd
Current assignee: Provensis Ltd
Priority date: 2016-06-28
Filing date: 2016-06-28
Publication date: 2018-01-03
Also published as: GB201611187D0

Abstract

A syringe for dispensing foam comprising: a barrel 1 with a nozzle 6; a plunger 2 comprising a shaft disposed within the barrel 1 and comprising a front end 7 situated closest to the nozzle 6; and a flexible membrane 3 attached to plunger 2 and around an inner surface of the barrel 1 such as to define an injectate chamber 5 that is sealed except for a fluid communication with the nozzle 6, where the flexible membrane 3 is arranged so that it is displaced behind the front end 7 of the plunger as it is advanced toward the nozzle 6. The flexible membrane 3 may be attached to a lateral surface toward the distal end of the plunger 2. Preferably flexible membrane 3 is sufficiently long so that a portion of the flexible membrane 3 trails behind the front end 7 of the plunger 2 in its most withdrawn position. The flexible membrane 3 and/or the barrels inner surface may comprise an adhesive. The syringe may comprise a non sealing spacer 4 as a guide aligning the plunger 2 within the barrel 1. The syringe may comprise a stop that limits withdrawal of plunger 2 from barrel 1.

Description

(54) Title of the Invention: Non-sputtering syringe

Abstract Title: A syringe for administration of medical injectable foam with reduced friction.

(57) A syringe for dispensing foam comprising: a barrel 1 with a nozzle 6; a plunger 2 comprising a shaft disposed within the barrel 1 and comprising a front end 7 situated closest to the nozzle 6; and a flexible membrane 3 attached to plunger 2 and around an inner surface of the barrel 1 such as to define an injectate chamber 5 that is sealed except for a fluid communication with the nozzle 6, where the flexible membrane 3 is arranged so that it is displaced behind the front end 7 of the plunger as it is advanced toward the nozzle 6. The flexible membrane 3 may be attached to a lateral surface toward the distal end of the plunger 2. Preferably flexible membrane 3 is sufficiently long so that a portion of the flexible membrane 3 trails behind the front end 7 of the plunger 2 in its most withdrawn position. The flexible membrane 3 and/or the barrel’s inner surface may comprise an adhesive. The syringe may comprise a non sealing spacer 4 as a guide aligning the plunger 2 within the barrel 1. The syringe may comprise a stop that limits withdrawal of plunger 2 from barrel 1.

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Figure 2

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Figure 3

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Figure 6

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Non-Sputtering Syringe

The present invention relates to a near-frictionless syringe and particularly to a nearfrictionless syringe that is suitable for dispensing and administering foam to a patient, e.g. for receiving foam from a pressurized source and administering the foam intravenously to a patient. The invention is suitable in particular for dispensing medical foam, such as sterile, clinical grade sclerosing foam e.g. for the treatment of varicose veins.

Intravenous administration of sclerosing foam is widely used in the treatment of varicose veins. In the treatment of smaller veins particularly, where multiple, small volumes of foam are often administered, it is important to control rate of delivery of the sclerosing foam and the volume delivered.

Medical syringes typically comprise a barrel within which is disposed a plunger to form a chamber for receipt of a composition to be administered to a patient. The plunger forms a fluid-tight seal with the barrel so as to prevent leakage from the syringe and to allow the entire syringe contents to be forced out of the chamber when the plunger is depressed and thus ensure administration of the required dosage to the patient. However, the user must apply significant force to overcome the friction created by the interference fit between the plunger and the barrel. This reduces control over administration from the syringe, and can make it difficult to deliver small volumes accurately. The force applied by the user to overcome syringe friction to both initiate plunger movement (i.e. breakout force) and maintain plunger movement (i.e. glide force) causes compression (i.e. pressurization) of syringe contents, and injection of fluids under pressure can cause sputtering (i.e. uncontrolled or explosive release) of syringe contents, which makes controlled administration difficult. This can have consequences for the patient when treating smaller vessels, ranging from discomfort during injection to mechanical disruption of vessel walls that can lead to extravasation of syringe contents and damage to surrounding tissue. This problem is more pronounced for administration of foam than liquid because foam is compressible within the syringe whereas a liquid is not.

Syringes having various coatings on the inner surface of the barrel have been designed to provide smoother gliding of plungers within syringe barrels to avoid the problem of sputtering. However, such coatings tend to be silicone-based lubricants, which accelerate degradation of sclerosing foams and so are not suitable for use in foam sclerotherapy.

US 6,142,976 provides a syringe having a plastic film tube connected at one end to the syringe plunger and at the other end to a needle connecting member. The syringe requires an interference fit between plunger and barrel and requires application of significant force to express the syringe contents. This syringe doesn’t address or overcome the problem of syringe sputtering when administering syringe contents to a patient.

Accordingly, there remains a need for a syringe in which sputtering is reduced or even eliminated when the plunger is depressed so that foams can be delivered to a patient in a controlled manner, improving therapeutic efficacy and patient comfort.

The present invention enables improved foam administration to patients by providing a 10 syringe which reduces or even eliminates sputtering of the contents.

Accordingly, in a first aspect, the present invention provides a syringe for dispensing foam comprising:

a barrel comprising a nozzle;

a plunger comprising a shaft disposed within the barrel and comprising a front end 15 situated closest to the nozzle; and a flexible membrane attached to the plunger and around an inner surface of the barrel such as to define an injectate chamber that is sealed except for a fluid communication with the nozzle, characterised in that:

the flexible membrane is arranged such that it is displaced behind the front end of the plunger as it is advanced toward the nozzle.

A flexible membrane having a first end and a second end is provided within the barrel of the syringe. The first end is attached to the plunger and the second end is attached around an inner surface of the barrel. The attached flexible membrane defines an injectate chamber within the syringe barrel that is sealed except for fluid communication with the nozzle. The flexible membrane is displaced behind the front end of the plunger (i.e. it goes from being distal to the front end of the plunger to being proximal to it) as it is advanced within the barrel to reduce the volume of the injectate chamber and force the syringe contents through the nozzle. An interference fit to maintain a seal between the plunger and barrel, as seen in traditional syringes, is avoided. The absence of an interference fit ensures that depression of the plunger requires application of lower breakout force and lower glide force when compared with traditional plungers with interference fits. This reduces the amount of force required to administer syringe contents through the nozzle. Sputtering of the syringe contents is reduced as a consequence.

The syringe is very simple having a longitudinally coaxial barrel and plunger arrangement as is found in a traditional syringe. Additionally, the syringe is easy to use as it is operated in a manner substantially the same as a traditional syringe. It is suitable for receiving or withdrawing foam from any source, to which it can be attached in a similar manner to a traditional syringe, for example, by means of a Luer® lock or similar attachment. It can be filled from a foam generating device or by simple aspiration (i.e. withdrawal of the plunger). In particular, the syringe can be used to receive foam from a pressurized canister, for example as described in WO 2005/023678 or in WO 00/72821. The syringe can be connected directly to a pressurized canister, for example, by means of a Luer Lock® connector or similar attachment. In this arrangement, foam is dispensed directly into the syringe via the nozzle. The foam entering the syringe through the nozzle forces the plunger head backwards into a withdrawn position and fills the injectate chamber. The syringe is then disconnected from the foam generating device, and a suitable delivery conduit, for example, a hypodermic needle or catheter, is then attached so that foam can be administered from the syringe to a patient.

The syringe barrel is a traditional syringe barrel, comprising a substantially cylindrical bore that is closed at a forward (distal) end save for a nozzle providing fluid communication with the external environment, and open at a rearward (proximal) end to receive a plunger. The barrel walls have an inner surface that defines the diameter of the bore and an outer surface. The inner surface lacks a friction reducing coating, such as lubrication. Substantially cylindrical means that the bore has a circular cross-section that may be constant along its length (i.e. cylindrical) or that may vary along its length (e.g. tapered or frustoconical). The barrel is made of a rigid plastic that is biocompatible such that it is safe to use for administration of pharmaceutical compositions to a patient. Suitable plastics include, for example, polypropylene, polyethylene, cyclopolyolefin, polycarbonate, polymethyl-methacrylate, polystyrene, polyvinyl chloride and acrylonitrile-butadiene-styrene copolymer (ABS).

The nozzle is a traditional syringe nozzle, and it is provided at the closed end of the barrel to provide a fluid communication between the bore of the barrel and the external environment. Typically the nozzle comprises an adaptor, such as a Luer® fitting suitable for engaging a foam dispensing device, for example a pressurized canister, and suitable also for engaging a hypodermic needle or a catheter for administration of syringe contents to a patient.

The injectate chamber is provided within the syringe barrel by the flexible membrane. The flexible membrane is made of a polymer that is impermeable to the contents to be administered from the syringe. The injectate chamber has a cross-sectional shape that accommodates that of the plunger. This ensures that the flexible membrane can be displaced behind the front of the plunger as the plunger is advanced within the barrel. Optionally, the flexible membrane is tubular. This promotes formation of a smooth inner surface in the injectate chamber, and this reduces the likelihood of flexible membrane ruffling in front of the advancing plunger in the syringe barrel. Where the flexible membrane is tubular it has a diameter larger than that of the plunger. This facilitates displacement of the membrane behind the front end of the plunger as it moves forward within a substantially cylindrical barrel. It is capable of changing shape as necessary to expand or restrict the volume of the injectate chamber. The membrane may be stretchable at pressures encountered when administering foam to a patient. Pressures encountered when administering foam to a patient can be between 0 and 4 bar above ambient pressure, but more typically they are between 0 and 1 bar above ambient pressure. Stretching of the membrane prevents compression of foam within the injectate chamber that could cause unwanted sputtering during administration from the syringe. Suitable polymers include nylon, polyvinyl amide, polypropylene, polyethylene, polybutylene resin, thermoplastic elastomer and ethylene-vinyl acetate copolymer (EVA).

The flexible membrane has a first end attached to the plunger and a second end attached around an inner surface of the barrel such as to define the injectate chamber. The membrane is arranged about the inner surface of the barrel and attached to the plunger at the first end and to the inner surface of the barrel at the second end. In this manner the membrane forms an envelope, which is closed except for fluid communication with the external environment through the nozzle. This arrangement of the membrane provides an injectate chamber that retains the syringe contents and prevents them from contacting the inner surface of the barrel. Typically the envelope is cylindrical, having a first end attached to the plunger and a second end attached around the entire circumference of the inner surface of the barrel. At the plunger it is preferred that the first end of the membrane is attached around the entire lateral surface of the plunger. This arrangement makes it simpler for the membrane to be displaced behind the plunger as the plunger is displaced towards the nozzle.

The first end of the flexible membrane can be attached at any point on the plunger provided that foam can be delivered through the nozzle when the plunger is depressed. For example, the first end can be attached to an end of the plunger that faces the nozzle. Preferably the first end is attached around the lateral surface of the plunger, and such attachment can be provided at any point along the longitudinal length of the plunger that allows delivery of foam from the syringe. Preferably, the first end is attached towards the distal or front end of the plunger. This reduces the volume that the plunger occupies within the injectate chamber and allows larger volumes of foam to be received and administered to patients. In any case, it is preferred that the membrane is attached with free membrane trailing behind the front edge of the plunger. This predisposes the membrane to feed out behind the front end of the plunger as it advances, and it reduces the potential for the membrane to ruffle up. This reduces the amount of force required to begin the membrane displacement.

The second end of the flexible membrane can be attached around the inner surface of the barrel at any point that allows delivery of foam from the syringe, however it is preferred that the membrane is attached around the inner surface of the barrel wail toward the distal end. This causes the membrane to be forced against the inner wall of the barrel as the injectate chamber is filled with foam. This arrangement uses the force of foam filling the injectate chamber and the pressurisation of the injectate chamber during foam administration to ensure that the membrane does not become ruffled in front of the plunger as it advances in the barrel. This prevents any disturbances that can cause sputtering of syringe contents. Optionally, the membrane can be attached around the inner surface of the barrel wall that defines the diameter of the bore. This reduces the likelihood that the membrane might become trapped or ruffled in front of the plunger as it is advanced in the barrel. The membrane can be attached around the inner surface of the barrel wall at any position along its length, provided that the membrane is of sufficient length to permit movement of the plunger within the barrel to allow administration of foam through the nozzle. Optionally, the membrane is attached around the inner surface of the barrel wall toward the proximal end of the barrel. This advantageously reduces the length of membrane required to allow filling of the injectate chamber with foam.

The flexible membrane has dimensions sufficiently large to permit it to be displaced behind the plunger as it is depressed (i.e. moved forward) within the barrel. Optionally, the flexible membrane may be sufficiently long that a portion of it trails behind the front end of the plunger when the plunger is in its most withdrawn position, i.e. closest to the proximal end, within the barrel. This portion of membrane trailing behind the front end of the plunger provides a guide for the remaining membrane to become displaced in the desired manner as the plunger advances in the barrel. Optionally the length of the membrane is selected to prevent complete withdrawal of the plunger from the barrel. This prevents the plunger being mistakenly removed from the barrel as the syringe is filled.

The flexible membrane and/or the inner surface of the barrel may comprise an adhesive. This adhesive allows for the membrane to become attached to the inner surface of the barrel as the injectate chamber is filled with foam. This restrains the membrane against the inner wall of the barrel and prevents it from becoming ruffled (i.e. from gathering and puckering) in front of the plunger as it advances in the barrel. Optionally the adhesive is a low tack adhesive. This allows for reversible adhesion of the membrane to the barrel, and the membrane can be easily detached from the inner wall of the barrel as the plunger is depressed. Where the membrane is reversibly adhered to the barrel and can be detached the membrane becomes detached as the plunger is depressed. Consequently, it is possible to use a shorter length of membrane to form an injectate chamber that can be emptied completely.

The plunger comprises a shaft disposed within the barrel. The lateral surface of the shaft faces the inner surface of the barrel walls, and the front (distal) end of the plunger is located at the end of the plunger shaft nearest to the syringe nozzle. The shaft extends rearward from the front end of the plunger. Preferably, the shaft is substantially cylindrical. Substantially cylindrical means the shaft has a circular cross-section. A shaft with a circular cross-section provides reduced volume behind the front end of the plunger thereby reducing reflux of foam and formation of foam pockets that might hamper administration of syringe contents. The shaft may have a circular cross-section along a portion of its length or along its entire length. A circular cross-section along the entire length of the shaft is advantageous as it maintains the torsional rigidity of the plunger. A circular cross-section along only a portion of the shaft maintains the advantageous shape while permitting reduction of the amount of material used to manufacture the plunger. The circular cross-section may be of constant diameter (i.e. a cylinder) or of varied diameter (i.e. tapered or frustoconical). Optionally, the shaft comprises a cylinder. A cylinder has a constant diameter, and a shaft comprising a cylinder can improve foam administration to a patient by minimizing dead space within a syringe having a cylindrical bore. The skilled person will understand that plunger dimensions and shape may be adapted to optimize its use within a particular barrel. A varied diameter can advantageously provide different breakout forces or glide forces for movement of particular portions of the plunger within the barrel. This is particularly advantageous in allowing reduction of syringe breakout force by tapering the shaft, for example, such that it has a reduced diameter at the distal end of the plunger closest to the nozzle.

Optionally, the shaft may comprise a hollow portion or it may be hollow. The crosssectional properties of the shaft can vary as described above, but a shaft comprising a hollow portion or being below is advantageous because this reduces the amount of material required to make the syringe and thereby reduces its cost. Additionally, this reduces the weight of the syringe and eases its use by a physician while maintaining the torsional rigidity of the plunger in use. In a preferred embodiment the hollow portion of the shaft includes a waste chamber that can accept waste foam when filling it with foam from a pressurized canister, for example as described in WO 2005/053776.

In either case, the diameter of the plunger shaft is sufficiently less than that of the syringe barrel bore so that the bore is able to accommodate the flexible membrane that is displaced behind the front end of the plunger as it is advanced toward the nozzle. The difference in diameters can be between 4 and 20 times the thickness of the membrane, preferably it is between 6 and 12 times the thickness of the membrane. This is beneficial in reducing the space between the plunger and the inner surface of the syringe barrel thereby minimizing reflux and preventing formation of a pocket of foam behind the front end of the plunger.

The syringe can comprise a guide means for aligning the plunger with the syringe barrel. The guide means may be attached to the barrel and/or the plunger in order to align the movement of the plunger with the longitudinal axis of the syringe barrel. This maintains a constant gap between the barrel and plunger as the plunger is advanced to deliver foam. The guide means may be attached to the barrel and/or the plunger in order to prevent rotation of the plunger within the syringe barrel. This prevents the flexible membrane from becoming twisted and trapped ahead of the front end of the plunger as it moves forward within the barrel. In particular embodiments the guide means may comprise, for example, a constriction of the syringe barrel shaped to accommodate the plunger and to prevent it deviating from a straight pathway as it advances in the barrel or a protrusion on the shaft of the plunger that provides a cross sectional shape complimentary to the cross sectional shape of the barrel so that in use the plunger is not capable of rotating significantly as it travels coaxially within the barrel, or both.

Optionally, the guide means comprises a non-sealing spacer disposed between the plunger shaft and the inner surface of the barrel. The non-sealing spacer may provide slight resistance to movement of the plunger within the barrel such that it provides a sensory feedback to the user that confirms the application of force to the plunger. This reduces the possibility that a user will accidentally apply too much force and deliver too much foam when using the syringe, but it does not increase the breakout force or the glide force sufficiently to cause sputtering of the syringe contents. This improves the safety of foam delivery. In a preferred embodiment the non-sealing spacer is an O-ring. This is advantageous as it is a simple and low cost form of non-sealing spacer that is also capable of acting as a guide means.

The syringe can comprise a stop guard that limits withdrawal of the plunger from the barrel. This prevents the plunger from being withdrawn further than desired, and prevents the flexible membrane from being ruptured or torn. Preferably the stop guard comprises a projection from a surface of the plunger shaft and/or from the inner surface of the barrel.

Where the stop guard comprises a projection from the surface of the plunger shaft, that projection is arranged such that it cannot pass a guide means or a complementary projection arranged on the inner surface of the barrel. Where the stop guard comprises a projection from the inner surface of the barrel the projection is arranged such that it prevents the plunger from passing and being withdrawn. This reduces the risk of human error when receiving foam into the syringe from a pressurized canister.

Further features and advantages of the invention will be apparent from the following description of specific embodiments, which is made with reference to the accompanying drawings.

Figure 1 shows a schematic view of an embodiment of the invention in which the 25 plunger is in a withdrawn position within the barrel.

Figure 2 shows a schematic view of an embodiment of the invention in which the plunger is in an advanced position within the barrel.

Figure 3 shows a schematic view of an embodiment of the invention in which a closed flexible membrane is attached to the front end of the plunger.

Figure 4 shows a schematic view of an embodiment of the invention in which an open flexible membrane is attached to the front end of the plunger.

Figure 5 shows a schematic view of an embodiment of the invention in which an open flexible membrane is attached to the distal lateral surface of the plunger.

Figure 6 shows a schematic view of an embodiment of the invention in which an open flexible membrane is attached to the proximal lateral surface of the plunger.A syringe of the invention is shown in Figure 1, having a barrel 1 with a plunger 2 disposed coaxially in a withdrawn position, i.e. located rearward, within it. A flexible membrane 3 is attached to the inner surface of the barrel 1 and to the plunger 2 so as to provide an injectate chamber 5 within the syringe.

Connection to a pressurized source of foam (not shown) allows introduction of foam into the injectate chamber 5 through the syringe nozzle 6 causing increased pressure within the injectate chamber 5 that forces the plunger 2 backwards into a withdrawn position within the barrel 1. A sufficient length of flexible membrane 3 is provided so that that a portion of the membrane 3 remains displaced, i.e. inverted, behind the front end 7 of the plunger 2 when the injectate chamber 5 is filled with foam.

The syringe also includes a guide means consisting of two O-rings 4 that are attached to the inner surface of the barrel 1 and serve to position the plunger 2 centrally within the barrel 1 and maintain this position as the plunger 2 is moved within the barrel 1.

Depression of the plunger 2 within the barrel 1 leads to increased pressure within the injectate chamber 5 and expression of foam from the syringe through the nozzle 6. The distal end 7 of the plunger 2 does not make contact with the inner surface of the barrel because the flexible membrane 3 is forced against the inner wall of the barrel 1 by the increased pressure within the injectate chamber 5 caused by depression of the plunger 2. As can be seen in Figure 2, the flexible membrane 3 is displaced behind the front end 7 of the plunger 2 as it is depressed to express foam from the syringe. Because there is insufficient space behind the front end 7 of the plunger 2, the flexible membrane 3 does not form enlarged pockets of foam behind the front end 7 of the plunger 2 as it is depressed, and this allows the user to administer foam using the syringe without sputtering.

In Figure 3 a syringe is shown in which a flexible membrane 3 is provided as a closed bag that is attached to the front end 7 of the plunger 2 by a single attachment 8. This means of attachment secures the flexible membrane 3 in position with respect to the plunger 2 and the barrel 1 to define the injectate chamber 5. The syringe shown in Figure 4 includes an open flexible membrane 3 that is attached to the front end 7 of the plunger 2 by an annular attachment 9. Figure 5 shows a syringe in which an open flexible membrane 3 is attached to the lateral surface of the plunger 2 by an annular attachment 10 located toward the distal end of the plunger, i.e. the end of the plunger closest to the nozzle (not shown). Figure 6 shows a syringe in which an open flexible membrane 3 is attached to the lateral surface of the plunger

2 by an annular attachment 11 located toward the proximal end of the plunger, i.e. the end of the plunger further from the nozzle (not shown).

Claims

1. A syringe for dispensing foam comprising: a barrel comprising a nozzle;

5 a plunger comprising a shaft disposed within the barrel and comprising a front end situated closest to the nozzle; and a flexible membrane attached to the plunger and around an inner surface of the barrel such as to define an injectate chamber that is sealed except for a fluid communication with the nozzle,

10 characterised in that:

2. A syringe according to claim 1 wherein the plunger is substantially cylindrical.

3. A syringe according to claim 2 wherein the plunger comprises a cylinder.

4. A syringe according to any previous claim wherein the flexible membrane is attached to a lateral surface of the plunger.

5. A syringe according to claim 4 wherein the flexible membrane is attached to a lateral surface toward the distal end of the plunger.

6. A syringe according to any previous claim wherein the flexible membrane is attached 25 around an inner surface of the barrel toward the distal end of the barrel.

7. A syringe according to any previous claim wherein the flexible membrane is attached with free membrane trading behind the front edge of the plunger.

30

8. A syringe according to any previous claim wherein the flexible membrane is sufficiently long such that a portion of the flexible membrane trails behind the front end of the plunger in its most withdrawn position.

9. A syringe according to any previous claim wherein the flexible membrane and/or the inner surface of the barrel comprises an adhesive.

5

10. A syringe according to any previous claim which comprises a guide means arranged to align the plunger within the barrel.

11. A syringe according to claim 10 wherein the guide means comprises a non-sealing spacer.

12. A syringe according to any previous claim further comprising a stop guard that limits withdrawal of the plunger from the barrel.

Intellectual

Property

Office

Application No: Claims searched:

GB1611187.4

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