Plunger for reducing the dead volume of a syringe

Abstract

The invention relates to a syringe (1) having a longitudinal section (5) in which a plunger (10) is movably guided that closes the syringe barrel (5) at one and and can be moved by means of a plunger rod (9). A connection (4) for placing an injection needle (11) is provided distally at the other end of the syringe barrel (5), and the plunger (10) can be moved out past the distal end of the connection (4) in order to reduce the dead volume.

Description

PISTON TO REDUCE THE DEAD VOLUME OF A SYRINGE Description

[0001] The invention relates to an application vessel, in particular a syringe, with a longitudinal section in which a piston is movably guided, closing the application vessel at one end and movable by means of a piston rod. The application vessel has a connection for attaching an injection needle at the other end and can be a pre-inserted application vessel or a vessel that can be filled prior to application, as is common with syringes.

[0002] With the increasing development of sensitive, highly effective, expensive or even limitedly available active ingredients for injection, which generally become effective even at low dosages in the microliter range, there is a need for application vessels, in particular syringes, which on the one hand can dose small quantities very precisely even with manual injection and on the other hand in which as little active ingredient as possible remains unused in the application vessel and the connected injection needle, which are no longer used and must be disposed of together with the vessel.

[0003] For the injection of small volumes, it is known to use disposable syringes with a small inner diameter of, for example, 4.5 mm, a fine scale, and intended for injecting, for example, 1 ml. To reduce the dead volume, it is state of the art to equip these syringes with a so-called displacement plug, which protrudes into the Luer cone, i.e., the connection of the application vessel, especially the syringe, and which displaces the liquid contained therein. liquid is displaced and expelled through the needle. However, a cannula must be attached for injection, and the dead volume of the cannula socket and the needle always remains. Further optimization of the dead volume is difficult when using the globally adopted Luer standard. However, a deviation from this standard would result in the syringe losing its compatibility with available cannulas and thus ultimately its general usability.

[0004] Alternative syringes with an integrated needle, where the needle does not need to be attached but is formed integrally with the syringe, can be designed with a smaller dead volume, but the needle is not replaceable. Furthermore, the finest needles available today are very difficult to connect to the syringe due to manufacturing technology. The needle should also be changed after the medication has been drawn up to prevent damage to the needle tip, medication sticking, unsterility, and the like. Lift-off needles are often unsuitable for injections.

[0005] If, however, prefilled syringe systems are used, the aforementioned problems can be largely avoided. However, for precise dosing, the smallest possible syringe diameter is required, which should be constant over the length of the syringe, whereby the syringe must not exceed a manageable length to hold the required volume. The minimum filling volume commonly used today for glass syringes is 0.5 ml, whose glass tube has a minimum inner diameter of 4.5 mm and which are available with a Luer or Luer-Lock connection, as well as with an integrated needle. However, glass syringes have manufacturing-related disadvantages compared to plastic syringes with regard to dead volume and dosing accuracy, since the latter are less accurate in terms of The inner diameter and the contour of the syringe cap can be manufactured more precisely. However, due to established industry standards, plastic syringes are also based on the dimensions commonly used for glass syringes.

[0006] For prefilled syringes with an integrated needle, the needle tip must be sealed tightly and sterilely, which is usually achieved with a needle cap. Especially with very thin needles, such as those required for intraocular injections, there is a risk that the needle could become kinked or damaged, rendering the entire syringe and its contents unusable.

[0007] In addition, glass or plastic cartridges are state-of-the-art. These are integrated into a motor-driven feed system for precise control, allowing for very accurate and reproducible dosing. However, the ability to empty the cartridges is rather unfavorable, especially if they are sealed with a septum, which may be pierced several times by the needle of the syringe being filled.

[0008] Against this background, the invention is based on the object of designing an application vessel, in particular a syringe of the type mentioned at the outset, in such a way that the aforementioned problems are overcome, in particular the dead volume during injection is reduced.

[0009] This object is achieved according to the invention by an application vessel having the features specified in claim 1. Advantageous embodiments of the invention emerge from the subclaims, the following description, and the drawings.

[0010] The application vessel according to the invention, in particular the syringe according to the invention, has a longitudinal section in which a piston is movably guided, which closes the application vessel at one end and is movable by means of a piston rod. The application vessel has a connection for attaching an injection needle at the other end of the application vessel. According to the invention, the piston can be displaced beyond the distal end of the connection to reduce the dead volume. It should be noted at this point that the terms "distal" and "proximal" refer to the user of the application vessel and not to the patient to whom the contents of the application vessel are administered.

[0011] The basic idea of ​​the solution according to the invention is to design an application vessel with a connection for attaching an injection needle and a piston movably guided therein in such a way that the piston can be displaced beyond the distal end of the connection and thus the dead volume otherwise present in the area of ​​the counter-connection piece with the injection needle is at least partially filled by the piston in order to dispense the agent in the application vessel as completely as possible through the injection needle.

[0012] An application vessel in the sense of the invention is typically a syringe barrel, but can also be another vessel for storing and dispensing a medication or other medical agent. The cross-sectional shape of the longitudinal section, in which a piston is movably guided, is preferably but not necessarily circular; it can also be oval or triangular or polygonal and preferably with rounded corners. The piston, which does not necessarily have the same cross-sectional shape, but at least has a shape adapted thereto, is arranged displaceably but sealingly within the longitudinal section, so that the vessel, in particular the syringe barrel, is closed at one end by the piston and at the The other end has a connection for attaching an injection needle with a mating connector or another line mating connector. After passing over the distal end of the vessel-side connector, the piston can at least dip into the mating connector with the injection needle or into the other line mating connector to at least partially displace the dead volume located there. The arrangement is advantageously such that the piston completely displaces the dead volume in the mating connector up to the needle.

[0013] In terms of design, this is advantageously achieved by the inner cross-section of the longitudinal section, in which the piston is movably guided, continuing into the inner cross-section of the connection or being smaller than it. Preferably, the inner wall of the longitudinal section merges flush, preferably seamlessly, into the inner wall of the connection. It is understood that in plastic containers, particularly in plastic syringes produced by injection molding, a certain conicity of this inner wall is always present, which is necessary for shaping the workpiece. This conicity is negligible as far as the aforementioned constant cross-section, which is essential for the invention, is concerned.

[0014] The design of the connection, in particular the syringe connection, as a Luer or Luer-Lock connection is particularly advantageous, since, as already mentioned above, this ensures high compatibility of the application vessel according to the invention with existing cannulas or line connections. When using a Luer or Luer-Lock connection, it is expedient to design the piston and the surrounding longitudinal section of the application vessel with a circular cross-section and to make the inner diameter of the cylinder smaller than the outer diameter of the (male) Luer cone, so that the piston can displace the dead volume formed in the (female) mating connector on the Luer cone as completely as possible.

[0015] When the inner wall of the longitudinal section of the application vessel merges into the inner wall of the Luer cone of the Luer or Luer-Lock connector, a high displacement volume results within the attached Luer or Luer-Lock mating connector.

[0016] According to an advantageous development of the invention, this displacement volume can be further increased if at least one section at the distal end of the piston is designed to be flexible, at least transversely to its displacement direction, such that it expands radially beyond the distal end of the connection after the distal end of the piston is displaced. With such a design, practically the entire volume of the mating connection piece can be filled up to the needle or the narrow recess leading to the needle. Then, practically only the internal volume of the needle and the channel leading thereto in the mating connection piece remains as dead volume.

[0017] For the purposes of the invention, "soft elastic" refers to soft or flexible materials (elastomers) with a modulus of elasticity <700 MPa. Hard elastic, on the other hand, refers to rigid and semi-rigid materials as defined in ISO 80369. Rigid materials have a flexural or tensile modulus of elasticity >3,433 MPa, and semi-rigid materials have a modulus of elasticity between 700 and 3,433 MPa.

[0018] However, apart from the conicity that may be required for demolding the syringe, it is advantageous to design the longitudinal section in which the piston is movable with a consistent internal cross-section that continues into the connection. This longitudinal section is preferably cylindrical and has a circular cross-section.

[0019] Optionally, when the injection needle is placed on the connector, a dead space with an axial dead space length and a radial dead space internal cross-section can extend distally from the distal end of the connector, with the piston being movable into the dead space. This dead space can result from the standardized design of the injection needle's mating connector with a female Luer or Luer-Lock connector when it is placed on the male Luer or Luer-Lock connector of the application vessel.

[0020] Optionally, the piston can have an axial length that exceeds the axial dead space length. This has the advantage that a proximal part of the piston remains sealed in the connection, thus preventing backflow into the longitudinal section.

[0021] Optionally, the piston rod can be sufficiently long so that the piston axially impacts a mating connector of the injection needle in the dead space, causing it to be plastically and / or elastically compressed axially in the dead space and expand radially to the internal cross-section of the dead space. The dead space is then almost completely filled by manually compressing the piston, so that the only remaining dead volume is practically the internal volume of the needle and the channel leading to it in the mating connector. The axial compression of the piston can push a proximal trailing edge of the piston beyond the distal end of the connector, so that the proximal trailing edge of the piston engages behind an axial end face of the connector during radial expansion in the dead space.

[0022] Optionally, the dead space internal cross-section can be larger, at least at the proximal end of the dead space, than an internal cross-section of the longitudinal section which continues into the connection, wherein at least a part of the piston, for example an external sealing lip of the piston, is designed to be so soft and elastic at least transversely to its direction of displacement that it expands radially to the inner cross-section of the dead space in the dead space. The dead space is then almost completely filled by the piston in that it is radially compressed in the inner cross-section of the longitudinal section and independently expands elastically and radially in the dead space, so that practically the only remaining dead volume is the inner volume of the needle and the channel leading to it in the mating connection piece. The axial length of the piston can correspond approximately to the length of the dead space. This allows a proximal trailing edge of the piston to be pushed beyond the distal end of the connection so that the proximal trailing edge of the piston engages behind an axial end face of the connection when it expands radially in the dead space.

[0023] To prevent the piston from exerting excessive axial force on the mating connector in the extended position, it is advantageous to limit the axial extension of the piston in the distal direction. This limitation is preferably achieved in such a way that the flexible part of the piston, upon retraction into the mating connector, practically completely fills the dead volume therein, without, however, exerting an unacceptably high axial force distally, which could endanger the connection between the connector and the mating connector.

[0024] Such a limitation can advantageously be formed by a locking arrangement, preferably formed between the piston and the inner wall of the application vessel or between the piston rod and the application vessel. Instead of a locking position, a stop can also be provided that limits the distal extension path of the piston.

[0025] In addition to limiting the extension path, it may be advantageous to provide one or more locking arrangements, for example with a A locking position in which the piston closes the application vessel but has not yet moved to dispense the vessel contents in a measured manner and / or a locking position in which the distal end of the piston has reached the distal end of the Luer connector.

[0026] It is particularly advantageous if the application container, if designed as a syringe, has a finger rest at the proximal end, which forms a stop for a thumb rest located at the end of the plunger rod. This makes it particularly easy to handle for manual dispensing, and operating errors are virtually eliminated.

[0027] The inventive design is particularly suitable, but not only, for syringes with a small dispensing volume of, for example, 0.3 ml. It is also ideally suited as a prefilled application vessel, with the Luer or Luer-Lock connector tightly sealed by a cap, which is removed immediately before use and replaced with an injection needle equipped with a Luer or Luer-Lock counter-connector.

[0028] It is particularly advantageous if the cap covering the application vessel is designed in such a way that it simultaneously blocks the retraction of the piston, e.g., by covering the thumb rest, or if a separate protective cap is provided, which is placed on the proximal side of the application vessel and shields the piston rod, in particular the thumb rest of the piston rod, from actuation. This cap must be removed before use.

[0029] In principle, the design according to the invention can be implemented in a variety of suitable application vessels, and it is particularly advantageous for syringes, regardless of whether the syringe body is made of glass or plastic. However, the invention can be implemented with a syringe body made of plastic. The inventive design is advantageously used with a prefilled syringe.

[0030] The invention is explained in more detail below with reference to exemplary embodiments illustrated in the drawings. They show: Figure 1 a syringe with Luer-Lock connector in longitudinal section, Figure 2 a syringe with Luer connector and attached counter connector with needle in longitudinal section, Figure 3 shows an alternative embodiment in the representation according to Figure 2, Figure 4 shows a vessel-side Luer-Lock connection with an inner cone in a greatly enlarged longitudinal section, Figure 5 shows a schematic representation of a syringe with a piston in five different positions, Figure 6 a syringe with attached injection needle and proximal protective cap, and Figure 7 shows the syringe according to Figure 6 with the distal protective cap attached.

[0031] The syringe 1 shown in Figure 1 is a prefilled syringe with a distal Luer-Lock connector, which, through a protective cap 3 seated thereon, seals the distal end of the syringe 1, in particular the Luer cone 4. The syringe has a syringe barrel 5, the cylindrical inner wall 6 of which extends into the Luer cone 4 continues, forming a continuous cylindrical inner wall that extends through the entire syringe 1. A finger rest 7 is formed on the proximal end of the syringe barrel 5, which, in conjunction with a thumb rest 8 on the proximal end of a piston rod 9, is provided for manually dispensing the agent contained in the syringe barrel. At the end of the piston rod 9 is the actual piston 10, which is arranged axially movable within the syringe barrel 5 and seals it on the proximal side. The syringe barrel 5 and piston rod 9 are made of hard, elastic plastic, whereas the piston 10 is made of soft, elastic plastic, as is the interior of the protective cap 3, which seals the Luer cone 4.The elasticity of the material is such that the piston 10 expands radially when passing over the distal end of the Luer cone 4 in order to fill the dead volume existing there in the female mating connector of the Luer cone.

[0032] The axial dimensioning of piston rod 9 with piston 10 and the syringe cylinder 5 with Luer cone 4 is not to scale in Figure 1 and is such that the piston 10 can be pushed distally by means of the piston rod 9 after removal of the protective cap 3 until it protrudes distally of the Luer cone 4 in order to fill the dead space formed in this area when the mating connection piece is attached, as is the case with the illustration of the syringe according to Figure 2. In the syringe according to Figure 2, a Luer cone 4 is formed at the end of the syringe cylinder 5, onto which an injection needle 11 is placed, which is fastened to the Luer cone 4 with its mating connection piece 12. There, the piston rod 9 with the piston 10 attached to it on the distal side is pushed beyond the distal end of the cone 4 into the mating connection piece 12, namely up to a shoulder in which the mating connection piece 12 tapers to accommodate the needle 13.In this position, the syringe contents are completely dispensed and only a tiny remaining cavity formed by the needle 13 is still filled.

[0033] In the embodiment shown in Figure 3, the counter-connector 12 is tapered in the area 14 projecting beyond the Luer cone 4, so that the soft-elastic piston 10 can practically completely fill the dead volume there.

[0034] The sectional view according to Figure 4 shows a syringe-side design of the Luer-Lock connector 2, in which the cylindrical inner wall 6 in the area of ​​the Luer cone 4 transitions into a conically tapered distally tapered area 14. In this area 14, the soft-elastic piston 10 is radially compressed upon advancement, increasing the sliding resistance so that the user feels that the piston 10 has now reached the end of the Luer cone 4 and then only needs to travel the short distance to remove the dead volume in the mating connector 12. At the same time, the radial compression leads to the piston 10 expanding radially more effectively beyond the Luer cone 4.

[0035] The handling of such a syringe 1 can be simplified by suitable locking arrangements, as shown in Figure 5. The syringe shown in Figure 5a has a circumferential locking lug 15 on the cylindrical inner wall 6 near the proximal end, which is arranged such that the piston rod 9 with the piston 10 cannot be completely removed from the syringe, but only until the maximum possible volume has been drawn up. In the illustration according to Figure 5b, in addition to the circumferential locking lug 15, a cooperating circumferential locking lug 16 is provided on the piston 10, which marks a specific position of the piston 10, for example a predetermined filling volume.

[0036] The design of the locking lugs 15 and 16 is expediently such that they can be traversed by elastic deformation after overcoming a resistance. In the embodiment shown in Figure 5c In the syringe, such a locking position is provided when the piston 10 is approximately half-retracted. The locking arrangement shown in Figure 5d indicates the position in which the piston 10 has reached the distal end of the Luer cone 4, thus representing a resistance that signals to the practitioner that, after overcoming this resistance, only the dead volume in the mating connector 12 remains to be filled.

[0037] Finally, Figure 5e shows an arrangement which can be designed as a locking arrangement or as a stop, depending on the radial extent of the circumferential locking lugs 15 and 16. In the position illustrated in Figure 5e, it is advantageous to provide a stop instead of the locking arrangement, since this is the end position in which the piston 10 has been moved distally beyond the Luer cone 4 into the mating connector 12. There, it rests against the shoulder in the mating connector 12. The stop can effectively prevent the axial force exerted by the piston 10 on the mating connector 12 from becoming unacceptably high and jeopardizing the secure fit of the mating connector on the Luer cone 4.

[0038] In the syringe shown in Figure 6, in which the piston 10 is in its distal end position, in which the piston 10 is located in the mating connection piece 12, the stop is formed by the thumb rest 8, which rests against the finger rest 7 attached there as a separate component. This illustrates that, depending on the design of the piston-cylinder arrangement, the stop does not necessarily have to be provided between the piston rod and the cylinder, but can also be formed, for example, by the thumb rest 8 at the end of the piston rod 9 in conjunction with the finger rest 7. The finger rest 7 is further extended proximally by a cylindrical projection 17, which is provided for the attachment of a proximal protective cap 18, which protects the proximal end of the piston rod 9 with the thumb rest 8 from actuation. This The proximal protective cap 8 is particularly advantageous in the case of a prefilled syringe, as shown in Figure 7, in which the piston rod 9 is extended proximally and the volume 19 is formed between the cylindrical inner wall 6, the piston 10 and the end of the Luer cone 4, which is firmly and tightly closed by the protective cap 3.

[0039] As the above explanations make clear, individual features of the present invention can be used advantageously on their own, but also in combination. List of reference symbols 1 syringe 2 Luer-Lock connector 3 protective cap 4 Luer cone 5 syringe barrels 6 cylindrical inner wall 7 Finger rest 8 Thumb rest 9 Piston rod 10 pistons 1 1 injection needle 12 Counter connection piece 13 needle 14 tapered area 15 locking lug 16 locking lug 17 cylindrical attachment 18 proximal protective cap 19 volumes

Claims

AMENDED CLAIMS received by the International Bureau on 25 March 2024 (25.03.2024)

1. Application vessel, in particular syringe (1), with a longitudinal section (5) in which a piston (10) is movably guided, which closes the application vessel at one end and which is movable by means of a piston rod (9), with a connection (4) for attaching an injection needle (11) at the other end of the application vessel, characterized in that the piston (10) is displaceable beyond the distal end of the connection (4) to reduce a dead space, characterized in that the connection is designed as a Luer (4) or Luer-Lock (2) connection, wherein the dead space extends distally from the distal end of the connection (4) with an axial dead space length and a radial dead space inner cross section, wherein the piston (10) is displaceable into the dead space, wherein the dead space inner cross section is larger than an inner cross section of the longitudinal section (5),which continues distally into the connection (4), wherein at least a part of the piston (10) is designed to be soft-elastic at least transversely to its direction of displacement in such a way that it expands radially in the dead space to the dead space inner cross-section.

2. Application vessel according to one of the preceding claims, characterized in that the longitudinal section (5) has a constant, in particular cylindrical, internal cross-section (6) which continues into the connection (4).

3. Application vessel according to one of the preceding claims, characterized in that the piston (10) has an axial length which is greater than the axial dead space length.

4. Application vessel according to one of the preceding claims, characterized in that the piston rod (9) is sufficiently long so that the piston (10) axially abuts a counter-connecting piece (12) of the injection needle (11) in the dead space and is thereby axially compressed in the dead space.

5. Application vessel according to one of the preceding claims, characterized in that the axial extension path of the piston (10) is limited in the distal direction.

6. Application vessel according to one of the preceding claims, characterized in that at least one locking arrangement (15, 16) is provided between the piston (10) and the inner wall (11) of the application vessel or between the piston rod (9) and the application vessel.

7. Application vessel according to claim 6, characterized in that a Ra- AMENDED SHEET (ARTICLE 19) st arrangement (15, 16) is provided with a locking position in which the piston (10) has reached the distal end of the Luer (4) or Luer-Lock (2) connection.

8. Application vessel according to claim 6 or 7, characterized in that a locking arrangement (15, 16) is provided with a locking position in which the piston (10) closes the application vessel but has not yet moved to the metered dispensing of the vessel contents.

9. Application vessel according to one of the preceding claims, characterized in that a stop (15) is provided for the piston (10) or the piston rod (9), which stops the travel path of the piston (10) distally.

10. Application vessel according to claim 9, characterized in that the stop (15) is arranged such that it limits the travel path of the piston (10) before or until reaching a shoulder of the cannula base (12) of a cannula (11) placed on the Luer (4) or Luer-Lock (2) connection.

11. Application vessel according to one of the preceding claims, characterized in that a stop support (7) is arranged at the proximal end of the application vessel, which forms a stop for a thumb rest (8) arranged at the end of the piston rod (9).

12. Application vessel according to one of the preceding claims, characterized in that the application vessel is pre-filled and provided with a cap (3) closing the Luer (4) or Luer-Lock (2) connection.

13. Application vessel according to one of the preceding claims, characterized in that a protective cap (18) is provided which is placed on the proximal side of the application vessel and which shields the thumb rest (8) of the piston rod (9) against actuation.

14. Application vessel according to one of the preceding claims, characterized in that it is made of plastic and is designed as a plastic injection-molded part.

15. Application vessel according to one of the preceding claims, characterized in that the inner diameter of the syringe cylinder (5) is smaller than the outer diameter of the Luer cone (4). AMENDED SHEET (ARTICLE 19)

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