Plunger rod and plunger rod adapter for piston

Abstract

A plunger rod and a plunger rod adapter are described. The plunger rod and the plunger rod adapter axially move the piston within the syringe barrel without being removably connected to the piston and resist a deformation force applied to the piston. The plunger rod and plunger rod adapter include a distal end that abuts the interior of the piston. The distal end defines: a first portion having a first diameter; and a second portion distal to the first portion. The second portion has a second diameter less than the first diameter. When the plunger rod slides into the interior of the piston, the first portion contacts the proximal side of the piston and the second portion contacts the interior of the piston without being removably connected to the piston.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 352,637 filed on June 16, 2022 and U.S. Provisional Patent Application No. 63 / 376,611 filed on September 22, 2022, the disclosures of which are hereby incorporated by reference into this document. Technical Field

[0003] The present application relates generally to plunger rods and plunger rod adapters, and in particular to plunger rods and plunger rod adapters that include a geometry that is complementary to the geometry of the interior of an associated piston but that is not removably connected to the associated piston. Background Art

[0004] Automatic syringe can provide intuitive, non-daunting self-injection solution for patients or caregivers.Some automatic syringes may include plunger rods compatible with the existing pistons of prefilled syringes, which can improve the acquisition of various medicines stored in such prefilled syringes, and can allow the transport and / or storage of prefilled syringes without plunger rods.But unlike the manually driven plunger rods used with standard prefilled syringes, the plunger rods of some existing automatic syringes are not removably connected with the pistons of prefilled syringes.At least in part, the plunger rods of automatic syringes are not removably connected with the pistons of prefilled syringes because the prefilled syringes are loaded into the automatic syringes and are complicated, so the plunger rods of automatic syringes are not removably connected with the pistons of prefilled syringes.Although some existing automatic syringes can operate with the existing pistons of prefilled syringes, undesirable drug leakage may occur.

[0005] Therefore, a need exists for an improved plunger rod and plunger rod adapter that are operable with the piston of a prefilled syringe but are not removably connectable to the piston and that reduces or eliminates leakage. Summary of the invention

[0006] These needs are largely met by a plunger rod for axially moving a piston within a syringe barrel. The plunger rod includes a proximal end and a distal end. The distal end may include: a first portion having a first diameter; and a second portion, the second portion being distal to the first portion. The second portion has a second diameter less than the first diameter and an external geometry complementary to the distal portion of the interior of the piston. When the plunger rod slides into the interior of the piston, without being removably connected to the piston, the first portion is configured to contact the proximal side of the piston, and the second portion is configured to contact the interior of the piston.

[0007] Specific implementations may include one or more of the following features. Wherein the external geometry is configured to engage with the piston plunger rod so that the second portion can resist the deformation force applied to the piston during the axial movement of the piston in the syringe barrel. The plunger rod is configured to disengage from the piston without resistance from the piston by sliding the plunger rod proximally away from the piston. The interior of the piston may include a thread, and the second portion is configured to contact at least one crest of the thread of the interior of the piston. The interior of the piston may include a snap fit, and when the plunger rod slides in the interior of the piston, the second portion does not engage with the snap fit. When the plunger rod slides in the piston, the first portion contacts the proximal side of the piston without being removably connected to the piston, and the second portion simultaneously contacts the interior of the piston. The second portion is conical and tapers distally. The distal end may also include a head, which is configured to contact the distal portion of the interior of the piston. The distal portion may also include a third portion located between the second portion and the head. The third portion has a third diameter less than the second diameter. The third portion is cylindrical. The third portion is conical and tapers distally. The first portion, the second portion and the third portion are arranged concentrically along the longitudinal axis of the plunger rod. The length of the second portion along the longitudinal axis of the plunger rod is at least twice the length of the third portion along the longitudinal axis.

[0008] Another general aspect includes a plunger rod adapter for axially moving a piston at the end of a plunger rod within a syringe barrel. The plunger rod adapter includes a proximal end and a distal end. The distal end may include: a first portion having a first diameter; and a second portion, the second portion being distal to the first portion. The second portion has a second diameter that is smaller than the first diameter and has an external geometry that is complementary to the distal portion of the interior of the piston. When the plunger rod adapter slides into the interior of the piston, without being removably connected to the piston, the first portion is configured to contact the proximal side of the piston and the second portion is configured to contact the interior of the piston.

[0009] Specific implementations may include one or more of the following features. A plunger rod adapter in which the external geometry is configured to engage with the piston enables the second portion to resist deformation forces applied to the piston during axial movement of the piston in the syringe barrel. The plunger rod adapter is configured to disengage from the piston without resistance from the piston by sliding the plunger rod adapter proximally away from the piston. The interior of the piston may include threads, and the second portion is configured to contact at least one crest of the threads of the interior of the piston. The interior of the piston may include a snap fit, and when the plunger rod adapter slides in the interior of the piston, the second portion does not engage with the snap fit. When the plunger rod adapter slides in the piston, the first portion contacts the proximal side of the piston, and the second portion simultaneously contacts the interior of the piston without being removably connected to the piston. The distal end may also include a head configured to contact the distal portion of the interior of the piston.

[0010] Yet another general aspect includes a syringe for injecting a drug. The syringe includes: a barrel; and a piston, which is movably disposed within the barrel. The piston defines an interior extending from a proximal side of the piston to a distal portion. The syringe also includes a plunger rod, which may include a proximal end and a distal end, and the plunger rod is configured to axially move the piston within the barrel in response to a force applied to the plunger rod. The distal end may include: a first portion having a first diameter; and a second portion, which is distal to the first portion. The second portion has a second diameter less than the first diameter and has an external geometry complementary to the distal portion of the interior of the piston. When the plunger rod slides into the interior of the piston, the first portion is configured to contact the proximal side of the piston and the second portion is configured to contact the interior of the piston without being removably connected to the piston.

[0011] Specific implementations may include one or more of the following features. A syringe wherein the distal end is integrally formed with the plunger rod. The distal end defines a plunger rod adapter that is removably connected to the plunger rod. The external geometry is configured to engage with the piston so that the second portion is able to resist deformation forces applied to the piston during axial movement of the piston in the barrel. The second portion is configured to disengage from the piston without resistance from the piston by sliding the second portion proximally away from the piston. The interior of the piston may include threads, and the second portion is configured to contact at least one crest of the threads of the interior of the piston. The interior of the piston may include a snap fit, and the second portion does not engage with the snap fit when the plunger rod slides within the interior of the piston. The distal end may also include a head configured to contact the distal portion of the interior of the piston.

[0012] Various additional features and advantages of the present invention will become apparent to those skilled in the art upon reading the following detailed description of illustrative embodiments in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The following detailed description is better understood when read in conjunction with the accompanying drawings.For purposes of illustration, various examples are shown in the drawings; however, the subject matter is not limited to the specific elements and instrumentalities disclosed.

[0014] In the attached picture:

[0015] Figure 1 A plunger rod according to aspects of the present disclosure is shown;

[0016] Figure 2 A plunger rod is shown disposed within a syringe barrel and operatively connected to a piston;

[0017] Figure 3 Shows Figure 2 A cross-sectional view of a plunger rod, piston and syringe barrel;

[0018] Figure 4 shows alternative geometries of plunger rods or plunger rod adapters according to aspects of the present disclosure;

[0019] Figure 5 Shows the use of Figure 1 Example loose glide distribution data for a plunger;

[0020] Figure 6 Another plunger rod is shown disposed within the syringe barrel and operatively connected to the piston;

[0021] Figure 7 Shows Figure 6 A cross-sectional view of a plunger rod, piston and syringe barrel;

[0022] Figure 8 Another plunger rod is shown disposed within the syringe barrel and operatively connected to the piston;

[0023] Fig. 9 Shows Figure 8 A cross-sectional view of a plunger rod, piston and syringe barrel;

[0024] Fig.10 Plunger rods and plunger rod adapters according to aspects of the present disclosure are shown;

[0025] Fig.11 An autoinjector including a plunger rod according to aspects of the present disclosure is shown; and

[0026] Fig.12 Shows Fig.11 Exploded view of the auto-injector. DETAILED DESCRIPTION

[0027] The present disclosure relates to a plunger rod and a plunger rod adapter that can be operated with a piston used in a prefilled syringe. The interior of the piston may include a connector, such as a threaded or snap-fit ​​portion. The plunger rod and plunger rod adapter of the present disclosure include a geometry that cannot be removably connected to an associated piston. This makes the plunger rod and plunger rod adapter suitable for use with an automatic syringe that cannot be removably connected to a piston. In the case of not being removably connected to the piston, the geometry of the plunger rod and the plunger rod adapter complements the geometry of the interior of the associated piston to substantially fill the various parts of the interior. By substantially filling the interior of the piston, the plunger rod and the plunger rod adapter can resist the deformation force applied to the piston during injection, and thereby reduce or eliminate drug leakage between the piston and the barrel of the syringe. These geometries can provide multiple target interaction points between the plunger rod or plunger rod adapter and the associated piston, and the free space in the associated piston can be removed to prevent deformation of the piston and resist compression of the piston. Multiple interaction points can balance piston-plunger stretching and compression, which is beneficial to leakage performance and reduces uncontrolled deformation caused by excessive compression.

[0028] The plunger rod and plunger rod adapter of the present disclosure can be self-aligning and can be used independently of the elastomeric composition of the piston. The plunger rod and plunger rod adapter of the present disclosure facilitate the operation of the syringe with high delivery speed and / or high viscosity solution under high force. Additionally, the plunger rod and plunger rod adapter of the present disclosure can provide a universal connection for different applications. For example, the plunger rod and plunger rod adapter of the present disclosure can allow the same rod to be used in both prefilled syringe systems and syringe systems. Figures 1 to 12 These and other aspects of the disclosure are described in further detail.

[0029] Figures 1 to 3 Shown are views of a plunger rod 100 in accordance with aspects of the present disclosure. Figure 1 A perspective view of the plunger rod 100 is shown. Figure 2 A partial view of the plunger rod 100 operatively connected to the piston 200 and disposed within the barrel 202 of the prefilled syringe is shown. Figure 3 Shows Figure 2 1. A cross-sectional view of the plunger rod 100, the piston 200 and the cylinder 202.

[0030] The plunger rod 100 can axially move the piston 200 within the barrel 202. The plunger rod 100 can include a proximal end 102 and a distal end 104. The distal end 104 can include a first portion 106 having a first diameter 108. The distal end 104 can include a second portion 110, which is distal to the first portion 106. The second portion 110 can have a second diameter 112 that is smaller than the first diameter 108. The second portion 110 can have an external geometry that is complementary to the internal geometry of the interior 206 of the piston 200. The internal geometry of the piston can define a connector (e.g., a thread, a snap fit, etc.), and the external geometry of the distal end 104 can be complementary to the geometry of the connector. For example, the external geometry can be complementary to the distal portion 212 of the interior 206 and / or can be complementary to the crest 220 of the thread 204 of the interior 206. Due to this configuration, when the plunger rod 100 is slid into the interior 206 of the piston 200, the first portion 106 may contact the proximal side 218 of the piston 200 without being removably connected to the piston 200, and the second portion 110 may (e.g., simultaneously) contact a connector (e.g., crest 220) of the piston 200. For example, the plunger rod 100 may be engaged with the piston 200 without being removably connected to the piston 200, so that the plunger rod 100 may be disengaged from the piston 200 without resistance from the piston 200 by sliding the plunger rod 100 proximally away from the piston 200. This may be advantageous for use with an auto-injector that is not removably connected to the piston of the syringe loaded in the auto-injector. Because the outer geometry of the second portion 110 is complementary to the inner geometry of the interior 206 of the piston 200, the second portion 110 can substantially fill the interior 206 of the piston 200 to engage with the piston 200, which can allow the distal end 104 to resist deformation forces applied to the piston 200 during injection and thereby reduce or eliminate leakage.

[0031] In such Figures 1 to 3In the illustrated embodiment, the plunger rod 100 may be configured to operate with a piston 200 that includes threads 204 within an interior 206 and includes a distal portion 212 that defines a concave surface that extends distally beyond the threads 204. The distal end 104 may include a first portion 106 having a first diameter 108. The distal end 104 may include a second portion 110 that may be distal to the first portion 106. The second portion 110 may have a second diameter 112 that may be smaller than the first diameter 108. In an embodiment, the distal end 104 may include a third portion 114 that is distal to the second portion 110. The third portion 114 may have a third diameter 116 that may be smaller than the second diameter 112. The third portion 114 may define a head 118. In an embodiment, the head 118 may be substantially planar along a direction perpendicular to the longitudinal axis 120 of the plunger rod 100. Alternatively, the head 118 may define other shapes, such as a cone, a dome, etc. The second portion 110 and the third portion 114 can together define an outer geometry that can substantially fill the interior 206 of the piston 200. By substantially filling the interior 206 of the piston 200, the distal end 104 can resist deformation forces applied to the piston 200 during injection and thereby reduce or eliminate leakage. For example, the second diameter 112 can be sized such that the second portion 110 abuts against at least one of the crests 220 of the threads 204 defined within the interior 206 of the piston 200 without contacting the flanks 222 or roots 224 of the threads 204. In an embodiment, the second portion 110 abuts against each of the crests 220 without contacting either the flanks 222 or roots 224. The second portion 110 can engage with the piston 200 to resist deformation of the piston 200 or collapse of the piston 200 toward the interior 206 without being removably connected to the piston 200 by abutting against at least one of the crests 220 of the threads 204 without contacting the flanks 222 or roots 224 of the threads 204. This resistance to deformation can help maintain contact between the circumferential ribs 208 of the piston 200 and the interior wall 210 of the barrel 202, which can reduce and / or eliminate proximal drug leakage between the piston 200 and the barrel 202.

[0032] In an embodiment, the third diameter 116 can be sized so that the third portion 114 abuts against a distal portion 212 (e.g., an inner wall) of the piston 200. The distal portion 212 can be defined within the interior 206 of the piston 200 at a location distal to the threads 204. By abutting against the distal portion 212, the third portion 114 can resist deformation of the piston 200 or collapse of the piston 200 toward the interior 206. This deformation resistance can help maintain contact between the head 214 of the piston 200 and the inner wall 210, which can reduce and / or eliminate drug leakage to the proximal side between the piston 200 and the barrel 202. Additionally, the third portion 114 can transfer the displacement force applied to the plunger rod 100 to the distal portion 212 of the piston 200 to move the piston 200 axially distally in the barrel 202.

[0033] In an embodiment, the first diameter 108 can be larger than the opening diameter 216 of the interior 206 of the piston 200. Due to this configuration, the distal surface 122 of the first portion 106 can abut against the proximal surface 218 of the piston 200. By abutting against the proximal surface 218, the distal surface 122 can resist deformation of the piston 200 or collapse of the piston 200 into the interior 206. Additionally, the distal surface 122 can transfer the displacement force applied to the plunger rod 100 to the proximal surface 218 to cause the piston 200 to move axially distally in the barrel 202.

[0034] In an embodiment, the second portion 110 may include a distal surface 124. The distal surface 124 may abut against the distal portion 212 of the piston 200 to resist deformation of the piston 200 or collapse of the piston 200 into the interior 206. Additionally, the distal surface 124 may transfer the displacement force applied to the plunger rod 100 to the distal portion 212 of the piston 200 to cause the piston 200 to move axially distally in the barrel 202.

[0035] In an embodiment, the head 118 can abut against the distal portion 212 of the piston 200 to resist deformation of the piston 200 or collapse of the piston 200 into the interior 206. Additionally, the head 118 can transfer the displacement force applied to the plunger rod 100 to the distal portion 212 of the piston 200 to cause the piston 200 to move axially distally in the barrel 202.

[0036] The first portion 106, the second portion 110, and the third portion 114 can be sized in a variety of different ways to substantially fill the interior 206 of the piston 200 and thereby resist deformation of the piston 200. The first portion 106, the second portion 110, and the third portion 114 can be arranged concentrically along the longitudinal axis 120. In an embodiment, the first portion 106 can be cylindrical. In an embodiment, the second portion 110 can be cylindrical, such as Figure 1 and Figure 3In another example, the second portion 110' may be a conical shape that tapers toward the distal side, such as Figure 4 In an embodiment, the third portion 114 may be cylindrical, such as Figure 1 and Figure 3 In another example, the third portion 114' may be a conical shape that tapers toward the distal side, such as Figure 4 In an embodiment, the second portion 110 may be conical and the third portion 114 may be cylindrical, or the second portion 110 may be cylindrical and the third portion 114 may be conical and the third portion 114 may be conical. Other arrangements are also possible.

[0037] In an embodiment, the second portion 110 can have a length along the longitudinal axis 120 that is greater than the length of the third portion 114 along the longitudinal axis 120. Due to this configuration, the second portion 110 can substantially fill the interior 206 of the piston 200, the interior of which includes the threads 204, while the third portion 114 can substantially fill the interior 206 of the piston 200, the interior of which is disposed distally relative to the threads 204. In an embodiment, the length of the second portion 110 can be at least twice the length of the third portion 114. Additionally or alternatively, the length along the longitudinal axis 120 of the second portion 110 can be greater than the length along the longitudinal axis 120 of the first portion 106. In an embodiment, the distal end 104 can be integrally formed with the plunger rod 100.

[0038] The plunger rod 100 was tested at various speeds of the plunger 100 / piston 200 within the barrel 202 using a prefilled syringe containing a fluid having a viscosity of 957 cP. For each speed, the pressure and force applied to the piston 200 were calculated and force measurements were made. Table 1 below shows a summary of the results of these tests and demonstrates that the plunger rod 100 of the present disclosure is suitable for use with prefilled syringes without leaks under a variety of different conditions.

[0039] Table 1

[0040]

[0041] The plunger rod 100 was also tested using a mechanical test machine to measure the loosening and extrusion force distribution under various different speeds of the plunger 100 / piston 200 in the barrel 202. The different speeds included speeds of 100 mm / min, 380 mm / min, and 450 mm / min. The plunger rod 100 was tested at least 10 times at each speed with different prefilled syringes containing different fluids at ambient temperature. The different fluids had corresponding viscosities of 1 cP, 20 cP, and 100 cP. During each test for all fluids and all test speeds, no leakage was detected when the plunger rod 100 was used with the piston 200. Table 2 below shows the test results of the plunger rod 100 under some of these test conditions compared to two known plunger rods (plunger rod A and plunger rod B) with different distal end geometries. The plunger rod A has a distal end that fits in the interior 206, but the distal end is smaller than the thread 204 so as not to contact the crest 220 of the thread 204. In addition, when plunger A moves piston 200, no portion of the distal end of plunger A contacts the proximal side 218 of piston 200. Plunger rod B has a distal end that occupies less than half of interior 206 of piston 200 and does not contact any crest of crest 220 of thread 204 or distal portion 212 of interior 206 when plunger B moves piston 200. Plunger B includes a distal side that contacts the proximal side 218 of piston 200 when plunger A moves piston 200. Table 2 shows that each of plunger rods A and B exhibits leakage under at least some of the test conditions, while plunger rod 100 does not leak under any of the test conditions.

[0042] Table 2

[0043]

[0044] Figure 5 The example loose glide distribution data collected with the plunger rod 100, piston 200 and 100 cP fluid in the barrel 202 is shown. The plunger rod 100 moves the piston 200 at a speed of 380 mm / min, and the compression force used for movement during the collection of the glide force distribution. The data shows that when the fluid is discharged from the barrel 202, the plunger rod 100 can produce less deformation and compression, even at relatively high speeds (e.g., 380 mm / min) and fluid viscosities (e.g., 100 cP). The data shows that the plunger rod 100 can reduce or eliminate leakage.

[0045] Figure 6 A partial view of another plunger rod 300 operatively connected to another piston 400 and disposed within the barrel 202 of the prefilled syringe is shown. Figure 7 Shows Figure 6A cross-sectional view of the plunger rod 300, the piston 400 and the cylinder 202. Figure 6 and Figure 7 In the illustrated embodiment, the plunger rod 300 may be capable of operating with a piston 400 that includes threads 404 located within an interior 406 of the piston 400 and includes a distal portion 412 that defines a wall that may be perpendicular to the longitudinal axis of the piston 400 and may be located at a terminal distal end of the threads 404.

[0046] The plunger rod 300 and the piston 400 may include any of the corresponding features discussed previously with reference to the plunger rod 100 and the piston 200, where like parts correspond to like parts. The plunger rod 300 may differ from the plunger rod 100 in that the plunger rod 300 may have a distal end 304 having an outer geometry adapted to fit the inner geometry of the piston 400. For example, the distal end 304 of the plunger rod 300 may include a first portion 306 having a first diameter 308. The distal end 304 may include a second portion 310, which may be distal to the first portion 306. The second portion 310 may have a second diameter 312 that may be smaller than the first diameter 308. The second portion 310 may define a head 318. In an embodiment, the head 318 may be substantially planar along a direction perpendicular to the longitudinal axis of the plunger rod 300. Alternatively, the head 318 may define other shapes, such as a cone, a dome, etc. The second portion 310 may define an outer geometry that may substantially fill the interior 406 of the piston 400. By substantially filling the interior 406 of the piston 400, the distal end 304 may be able to resist deformation forces applied to the piston 400 during injection, and thereby reduce or eliminate leakage. For example, the second diameter 312 may be sized such that the second portion 310 abuts against at least one of the crests 420 of the threads 404 defined within the interior 406 of the piston 400 without contacting the flanks 422 or the roots 424 of the threads 404. In an embodiment, the second portion 310 abuts against each of the crests 420 without contacting either the flanks 422 or the roots 424. By abutting against at least one of the crests 420 of the threads 404 without contacting the flanks 422 or the roots 424 of the threads 404, the second portion 310 may engage with the piston 400 without being removably connected to the piston 400 to resist deformation of the piston 400 or collapse of the piston 400 into the interior 406. This resistance to deformation may help maintain contact between the circumferential ribs 408 of the piston 400 and the interior wall 210 of the barrel 202 , which may reduce and / or eliminate proximal drug leakage between the piston 400 and the barrel 202 .

[0047] In an embodiment, the head 318 abuts against a distal portion 412 (e.g., an inner wall) of the piston 400. In an embodiment, the distal portion 412 may be defined within the interior 406 of the piston 400 at the distal end of the thread 404. By abutting against the distal portion 412, the head 318 can resist deformation of the piston 400 or collapse of the piston 400 into the interior 406. This deformation resistance can help maintain contact between the head 414 of the piston 400 and the inner wall 210, which can reduce and / or eliminate drug leakage to the proximal side between the piston 400 and the barrel 202. Additionally, the head 318 can transfer the displacement force applied to the plunger rod 300 to the distal portion 412 of the piston 400 to move the piston 400 axially distally in the barrel 202.

[0048] In an embodiment, the first diameter 308 can be larger than the opening diameter 416 of the interior 406 of the piston 400. Due to this configuration, the distal surface 322 of the first portion 306 can abut against the proximal surface 418 of the piston 400. By abutting against the proximal surface 418, the distal surface 322 can resist deformation of the piston 400 or collapse of the piston 400 into the interior 406. Additionally, the distal surface 322 can transfer the displacement force applied to the plunger rod 300 to the proximal surface 418 to cause the piston 400 to move axially distally in the barrel 202.

[0049] Figure 8 A partial view of another plunger rod 500 operatively connected to another piston 600 and disposed within the barrel 202 of the prefilled syringe is shown. Fig. 9 Shows Figure 8 500, piston 600 and cylinder 202. Figure 8 and Fig. 9 In the illustrated embodiment, the plunger rod 500 may be operable with a piston 600 that includes a snap fit 604 within an interior 606 of the piston 600 .

[0050] The plunger rod 500 and the piston 600 may include any of the corresponding features previously discussed with reference to the plunger rod 100 and the piston 200, where like parts correspond to like parts. The plunger rod 500 may differ from the plunger rod 100 in that the plunger rod 500 may have a distal end 504 having an outer geometry adapted to match the inner geometry of the piston 600. For example, the distal end 504 of the plunger rod 500 may include a first portion 506 having a first diameter 508. The distal end 504 may include a second portion 510, which may be distal to the first portion 506. The second portion 510 may have a second diameter 512 that may be smaller than the first diameter 508. The second portion 510 may define a head 518. In an embodiment, the head 518 may be conical or dome-shaped to correspond to the shape of the distal portion 612 of the piston 600. The second portion 510 can define an outer geometry that can substantially fill the interior 606 of the piston 600, except for an area 607 of the interior 606 that radially extends beyond the opening diameter 616 of the piston 600 and defines the snap fit 604. For example, in an embodiment, the diameter of the second portion 510 is smaller than the opening diameter 616 of the piston, such that the second portion 510 does not connect with the snap fit 604. By substantially filling the interior 606 of the piston 600 (except for the area 607 that defines the snap fit 604), the distal end 504 can resist deformation forces applied to the piston 600 during injection, and thereby reduce or eliminate leakage without being removably connected to the piston 600. For example, the second diameter 512 can be sized such that the second portion 510 abuts against the circumferential inner wall 626 of the piston 600 but not against the snap fit 604. That is, when the plunger rod 500 slides within the interior 606 of the piston 600, the second portion 510 does not engage with the snap fit. In an embodiment, the second portion 510 abuts the entire circumferential inner wall 626. By abutting the circumferential inner wall 626 but not abutting the snap fit 604, the second portion 510 can engage with the piston 600 to resist deformation of the piston 600 or collapse of the piston 600 toward the interior 606 without being removably connected to the piston 600. This resistance to deformation can help maintain contact between the circumferential ribs 608 of the piston 600 and the interior wall 210 of the barrel 202, which can reduce and / or eliminate proximal drug leakage between the piston 600 and the barrel 202.

[0051] In an embodiment, the head 518 abuts against the distal portion 612 (e.g., the inner wall) of the piston 600. By abutting against the distal portion 612, the head 518 can resist deformation of the piston 600 or collapse of the piston 600 into the interior 606. This deformation resistance can help maintain contact between the head 614 of the piston 600 and the inner wall 210, which can reduce and / or eliminate drug leakage proximally between the piston 600 and the barrel 202. Additionally, the head 518 can transfer the displacement force applied to the plunger rod 500 to the distal portion 612 of the piston 600 to cause the piston 600 to move axially distally in the barrel 202.

[0052] In an embodiment, the first diameter 508 can be larger than the opening diameter 616 of the interior 606 of the piston 600. Due to this configuration, the distal surface 522 of the first portion 506 can abut against the proximal surface 618 of the piston 600. By abutting against the proximal surface 618, the distal surface 522 can resist deformation of the piston 600 or collapse of the piston 600 into the interior 606. Additionally, the distal surface 522 can transfer the displacement force applied to the plunger rod 500 to the proximal surface 618 to cause the piston 600 to move axially distally in the barrel 202.

[0053] In such Fig.10 In the illustrated embodiment, the distal end 704 of the plunger rod 700 can define both a distal rod end 726 and a plunger rod adapter 728. The plunger rod adapter 728 can be removably connected to the distal rod end 726. The distal end 704 can include any of the features discussed above with reference to the distal ends 104, 304, and 504, except that the plunger rod adapter 728 is removably connected to the distal rod end 726 rather than being integrally formed therewith. For example, the plunger rod adapter 728 can include any of the geometries previously discussed with reference to the distal end 104. For example, the plunger rod adapter 728 can include a first portion 706, a second portion 710, and a third portion 714, which can include any of the features previously discussed with respect to the first portion 106, 306, 506, the second portion 110, 110', 310, 510, and / or the third portion 114 / 114', respectively.

[0054] The plunger rod adapter 728 can be removably connected to the distal rod end 726 via any number of connection techniques, including adhering the plunger rod adapter 728 to the plunger rod 700 with an adhesive, fastening the plunger rod adapter 728 to the plunger rod 700 with a fastener, and other possibilities. For example, in an embodiment, the distal rod end 726 can include threads 730, and the plunger rod adapter 728 can be removably connected to the threads 730. The plunger rod adapter 728 can include internal threads that are threadedly connected to the threads 730, or the plunger rod adapter 728 can be connected via other known connection techniques (such as snap fit, adhesion, etc.). Because the plunger rod adapter 728 can include a geometry for substantially filling the interior of the piston 200 rather than being threaded to the piston 200, the plunger rod adapter 728 can make the plunger rod 700 with a threaded distal rod end 726 suitable for use with, for example, an automatic injector that is not threadedly connected to the piston 200. That is, the plunger rod adapter 728 may be interposed between the threads 730 of the distal rod end 726 and the threads 204 of the piston 200 to connect the piston 200 to the plunger rod 700 without threadingly engaging the threads 204 of the piston 200 .

[0055] Fig.11 and Fig.12 A view of an automatic injector 800 for injecting a drug is shown. The automatic injector 800 may include any of the plunger rods and / or plunger rod adapters described herein. For example, the automatic injector 800 may include a plunger rod 100. The automatic injector 800 may include a base 802 that may accommodate a barrel 202 containing a piston 200. The automatic injector 800 may also include a handle 804 that may be integrally or removably connected to the plunger rod 100. Depressing the handle 804 may move the plunger rod 100 and cause the piston 200 to axially displace within the barrel 202 to inject the drug into the patient.

[0056] It should be understood that the foregoing description provides each example of the present disclosure. However, it is contemplated that other specific implementations of the present invention may differ from the foregoing examples in detail. All references to the present invention or its examples are intended to reference the specific examples being discussed at this time, and are not intended to more generally imply any limitation on the scope of the present invention. All language of distinction and disparagement of certain features is intended to indicate that those features are non-preferred, but are not completely excluded from the scope of the present invention, unless otherwise indicated. All methods described herein can be performed in any suitable order, unless otherwise indicated herein or clearly contradictory to the context.

Claims

1. A plunger rod for axially moving a piston within a syringe barrel, the piston defining an interior extending from a proximal side of the piston to a distal portion of the interior, the plunger rod comprising: proximal end; and A distal end portion, the distal end portion comprising: a first portion having a first diameter; and a second portion distal to the first portion, the second portion having a second diameter less than the first diameter and having an exterior geometry complementary to the distal portion of the interior of the piston, Wherein when the plunger rod slides into the interior of the piston, without being removably connected to the piston, the first portion is configured to contact the proximal side of the piston and the second portion is configured to contact the interior of the piston.

2. The plunger rod of claim 1, wherein the outer geometry is configured to engage the piston such that the second portion is able to resist deformation forces applied to the piston during axial movement of the piston within the syringe barrel.

3. The plunger rod of claim 1, wherein the plunger rod is configured to be disengaged from the piston without resistance from the piston by sliding the plunger rod proximally away from the piston.

4. The plunger rod of claim 1, wherein the interior of the piston includes threads, and wherein the second portion is configured to contact at least one crest of the threads of the interior of the piston.

5. The plunger rod of claim 1, wherein the interior of the piston includes a snap fit, and wherein the second portion does not engage the snap fit when the plunger rod slides within the interior of the piston.

6. The plunger rod of claim 1, wherein when the plunger rod slides within the piston, without being removably connected to the piston, the first portion contacts the proximal side of the piston and the second portion simultaneously contacts the interior of the piston.

7. The plunger rod of claim 1, wherein the second portion is conical and tapers distally.

8. The plunger rod of claim 1, wherein the distal end further comprises a head configured to contact the distal portion of the interior of the piston.

9. The plunger rod of claim 8, wherein the distal portion further comprises a third portion located between the second portion and the head, the third portion having a third diameter that is smaller than the second diameter.

10. The plunger rod of claim 9, wherein the third portion is cylindrical.

11. The plunger rod of claim 9, wherein the third portion is conical and tapers distally.

12. The plunger rod of claim 9, wherein the first portion, the second portion, and the third portion are concentrically arranged along a longitudinal axis of the plunger rod.

13. The plunger rod of claim 9, wherein a length of the second portion along a longitudinal axis of the plunger rod is at least twice a length of the third portion along the longitudinal axis.

14. A plunger rod adapter for enabling a plunger rod to axially move a piston within a syringe barrel, the piston defining an interior extending from a proximal side of the piston to a distal portion of the interior, the plunger rod adapter comprising: proximal end; and A distal end portion, the distal end portion comprising: a first portion having a first diameter; and a second portion distal to the first portion, the second portion having a second diameter less than the first diameter and having an exterior geometry complementary to the distal portion of the interior of the piston, Wherein when the plunger rod adapter is slid into the interior of the piston, without being removably connected to the piston, the first portion is configured to contact the proximal side of the piston and the second portion is configured to contact the interior of the piston.

15. The plunger rod adapter of claim 14, wherein the outer geometry is configured to engage the piston such that the second portion is able to resist deformation forces applied to the piston during axial movement of the piston within the syringe barrel.

16. The plunger rod adapter of claim 14, wherein the plunger rod adapter is configured to be disengaged from the piston without resistance from the piston by sliding the plunger rod adapter proximally away from the piston.

17. The plunger rod adapter of claim 14, wherein the interior of the piston includes threads, and wherein the second portion is configured to contact at least one crest of the threads of the interior of the piston.

18. The plunger rod adapter of claim 14, wherein the interior of the piston includes a snap fit, and wherein the second portion does not engage the snap fit when the plunger rod adapter is slid within the interior of the piston.

19. The plunger rod adapter of claim 14, wherein when the plunger rod adapter slides within the piston, without being removably connected to the piston, the first portion contacts the proximal side of the piston and the second portion simultaneously contacts the interior of the piston.

20. The plunger rod adapter of claim 14, wherein the distal end further comprises a head configured to contact the distal portion of the interior of the piston.

21. A syringe for injecting a drug, the syringe comprising: Cylinder; a piston movably disposed within the barrel, the piston defining an interior extending from a proximal side of the piston to a distal portion; A plunger rod comprising a proximal end and a distal end, the plunger rod being configured to axially move the piston within the barrel in response to a force applied to the plunger rod, the distal end comprising: a first portion having a first diameter; and a second portion distal to the first portion, the second portion having a second diameter less than the first diameter and having an exterior geometry complementary to the distal portion of the interior of the piston, Wherein when the plunger rod slides into the interior of the piston, without being removably connected to the piston, the first portion is configured to contact the proximal side of the piston and the second portion is configured to contact the interior of the piston.

22. The syringe of claim 21, wherein the distal end is integrally formed with the plunger rod.

23. The syringe of claim 21, wherein the distal end defines a plunger rod adapter that is removably connected to the plunger rod.

24. The syringe of claim 21, wherein the outer geometry is configured to engage the piston such that the second portion is able to resist deformation forces applied to the piston during axial movement of the piston within the barrel.

25. The syringe of claim 21, wherein the second portion is configured to be disengaged from the piston without resistance from the piston by sliding the second portion proximally away from the piston.

26. The syringe of claim 21, wherein the interior of the piston includes threads, and wherein the second portion is configured to contact at least one crest of the threads of the interior of the piston.

27. The syringe of claim 21, wherein the interior of the piston includes a snap fit, and wherein the second portion does not engage the snap fit when the plunger rod slides within the interior of the piston.

28. The syringe of claim 21, wherein the distal end further comprises a head configured to contact the distal portion of the interior of the piston.

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