Plunger rod for piston and plunger rod adapter

Abstract

Provided is a plunger rod and its adapter that are operable with the piston of a filled syringe, but are not removably connected to the piston and reduce or eliminate leakage. **Solution**: 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 the deformation force applied to the piston. The plunger rod and the plunger rod adapter include a distal end that abuts inside 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 smaller than the first diameter. When the plunger rod is slid inside the piston, the first portion contacts the proximal surface of the piston, and the second portion contacts inside the piston without being removably connected to the piston.

Description

Technical Field

[0001] (Cross - Reference to Related Applications) This application claims priority to U.S. Provisional Patent Application No. 63 / 330,200, filed on April 22, 2022, and 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 incorporated herein by reference.

[0002] (Field of the Invention) This application generally relates to plunger rods and plunger rod adapters, and more particularly to plunger rods and plunger rod adapters that include geometries that are complementary to the internal geometry of an associated piston but that do not removably connect to the associated piston.

Background Art

[0003] Auto - injectors can provide an intuitive and fear - free self - injection solution for patients or caregivers. Some auto - injectors can include a plunger rod that is compatible with an existing piston of a filled syringe, which can improve access to various drugs stored within such a filled syringe and can enable the filled syringe to be transported and / or stored without a plunger rod. However, unlike manually - driven plunger rods used with standard filled syringes, the plunger rods of some existing auto - injectors do not removably connect to the piston of the filled syringe. Connecting the plunger rod removably to the piston can complicate loading the filled syringe into the auto - injector, so the plunger rod of an auto - injector does not removably connect, at least in part, to the piston of the filled syringe. Some existing auto - injectors are operable with an existing piston of a filled syringe, but there can be an undesirable leakage of the drug.

[0004] Accordingly, there is a need for an improved plunger rod and plunger rod adapter that is operable with the piston of a filled syringe, but not removably connected to the piston and that reduces or eliminates leakage. SUMMARY OF THE INVENTION

[0005] 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 portion and a distal end portion. The distal end portion can include a first portion having a first diameter and a second portion distal to the first portion. The second portion has a second diameter that is smaller than the first diameter and has an outer geometry that is complementary to a distal portion within the piston. When the plunger rod is slid within the piston, the first portion is configured to contact a proximal face of the piston and the second portion is configured to contact within the piston without removably connecting to the piston.

[0006] The implementation form may include one or more of the following features. The plunger rod is configured such that its outer geometry is configured to engage with the piston so that the second portion can resist the deformation force applied to the piston during the axial movement of the piston within the syringe barrel. The plunger rod is configured to disengage from the piston without resistance from the piston by sliding proximally to move the plunger rod 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 inside the piston. The interior of the piston may include a snap fit portion, and the second portion does not engage with the snap fit portion when the plunger rod is slid within the interior of the piston. When the plunger rod is slid within the piston, the first portion contacts the proximal surface of the piston, and the second portion simultaneously contacts the interior of the piston without being removably connected to the piston. The second portion is conical and tapered in the distal direction. The distal end may further include a head configured to contact the distal portion inside the piston. The distal portion may further include a third portion between the second portion and the head. The third portion has a third diameter smaller than the second diameter. The third portion is cylindrical. The third portion is conical and tapered in the distal direction. 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.

[0007] Another general aspect includes a plunger rod adapter for adapting an end of a plunger rod to axially move a piston within a syringe barrel. The plunger rod adapter includes a proximal end and a distal end. The distal end can include a first portion having a first diameter and a second portion distal to the first portion. The second portion has a second diameter that is smaller than the first diameter and has an outer geometry that is complementary to a distal portion within the piston. When the plunger rod adapter is slid within the piston, the first portion is configured to contact a proximal face of the piston, and the second portion is configured to contact within the piston without removably connecting to the piston.

[0008] Implementations can include one or more of the following features. The plunger rod adapter is configured to engage the piston such that the outer geometry of the plunger rod adapter can resist, with the second portion, a deforming force applied to the piston during axial movement of the piston within the syringe barrel. The plunger rod adapter is configured to disengage from the piston without resistance from the piston by sliding proximally to move the plunger rod adapter away from the piston. The interior of the piston can include threads, and the second portion is configured to contact at least one crest of the threads within the piston. The interior of the piston can include a snap fit, and the second portion does not engage the snap fit when the plunger rod adapter is slid within the interior of the piston. When the plunger rod adapter is slid within the piston, the first portion contacts a proximal face of the piston, and the second portion simultaneously contacts within the piston without removably connecting to the piston. The distal end can further include a head configured to contact a distal portion within the piston.

[0009] Another general aspect includes a syringe for injecting a medicament. The syringe includes a barrel and a piston movably disposed within the barrel. The piston defines an interior that extends from a proximal face of the piston to a distal portion. The syringe also includes a plunger rod that may include a proximal end and a distal end configured to axially move the piston within the barrel in response to an applied force to the plunger rod. The distal end may include a first portion having a first diameter and a second portion distal to the first portion. The second portion has a second diameter that is smaller than the first diameter and has an outer geometry that is complementary to a distal portion of the interior of the piston. When the plunger rod is slid into the interior of the piston, the first portion is configured to contact the proximal face of the piston, and the second portion is configured to contact the interior of the piston without removably connecting to the piston.

[0010] Embodiments may include one or more of the following features. The syringe has a distal end that is integrally formed with the plunger rod. The distal end defines a plunger rod adapter removably connected to the plunger rod. The outer geometry is configured to engage the piston such that the second portion can resist a deformation force applied to the piston during axial movement of the piston within the barrel. The second portion is configured to disengage from the piston without resistance from the piston by sliding proximally to move the second portion 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 in the interior of the piston. The interior of the piston may include a snap fit, and the second portion does not engage the snap fit when the plunger rod is slid within the interior of the piston. The distal end may further include a head configured to contact a distal portion of the interior of the piston.

[0011] Various additional features and advantages of the present invention will become apparent to those of ordinary skill in the art upon consideration of the following detailed description of exemplary embodiments in conjunction with the accompanying drawings.

Brief Description of the Drawings

[0012] The following detailed description will be better understood when read in conjunction with the accompanying drawings. For purposes of illustration, embodiments are shown in the drawings, but the subject matter is not limited to the specific elements and means disclosed. The drawings are as follows.

Figure 1

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Figure 12

Modes for Carrying Out the Invention

[0013] The present disclosure is directed to a plunger rod and a plunger rod adapter that may be operable with a piston used with a filled syringe. The interior of the piston can include a connector such as a thread or a snap fit. The plunger rod and plunger rod adapter of the present disclosure include geometries that do not removably connect to an associated piston. This makes the plunger rod and plunger rod adapter suitable for use with a self-injector that does not removably connect the plunger rod and plunger rod adapter to the piston. The geometries of the plunger rod and plunger rod adapter are complementary to the interior geometry of the associated piston and substantially fill the interior portion without removably connecting to the piston. By substantially filling the interior of the piston, the plunger rod and plunger rod adapter can resist the deforming forces applied to the piston during injection, thereby reducing or eliminating drug leakage between the piston and the syringe barrel. These geometries can provide multiple target interaction points between the plunger rod or plunger rod adapter and the associated piston, removing free space within the associated piston to prevent distortion of the piston and resist compression. The multiple interaction points can balance piston-plunger extension and compression, which provides benefits in leakage performance and reduces uncontrolled deformation due to over-compression.

[0014] The plunger rod and plunger rod adapter of the present disclosure can self-align and can be used independently of the elastomeric composition of the piston. The plunger rod and plunger rod adapter of the present disclosure facilitate syringe operation with high force, high delivery speed, and / or high viscosity solutions. 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 enable the same rod to be used in both filled syringe systems and cartridge systems. These and other aspects of the present disclosure are described in more detail below with reference to FIGS. 1-12.

[0015] FIGS. 1-3 show views of a plunger rod 100 according to aspects of the present disclosure. FIG. 1 shows a perspective view of the plunger rod 100. FIG. 2 shows a partial view of the plunger rod 100 operably connected to a piston 200 and disposed within the barrel 202 of a filled syringe. FIG. 3 shows a cross-sectional view of the plunger rod 100, piston 200, and barrel 202 of FIG. 2.

[0016] The plunger rod 100 can axially move the piston 200 within the barrel 202. The plunger rod 100 can include a proximal end portion 102 and a distal end portion 104. The distal end portion 104 can include a first portion 106 having a first diameter 108. The distal end portion 104 can include a second portion 110 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 outer geometry that is complementary to the inner geometry of the interior 206 of the piston 200. The inner geometry of the piston can define a connector (e.g., threads, snap fit, etc.), and the outer geometry of the distal end portion 104 can be complementary to the geometry of the connector. For example, the outer geometry can be complementary to the distal portion 212 of the interior 206 and / or the peaks 220 of the threads 204 of the interior 206. As a result of this configuration, when the plunger rod 100 is slid into the interior 206 of the piston 200, the first portion 106 can contact the proximal face 218 of the piston 200, and the second portion 110 can contact (e.g., simultaneously) the connector (e.g., peak 220) of the piston 200 without removably connecting to the piston 200. For example, the plunger rod 100 can engage the piston 200 without removably connecting to the piston 200, such that the plunger rod 100 can 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 can be advantageous for use with a self-injector that does not removably connect to the piston of a syringe loaded in the self-injector. Since 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 and engage the piston 200, which can enable the distal end portion 104 to resist the deformation forces applied to the piston 200 during injection, thereby reducing or eliminating leakage.

[0017] In embodiments such as those shown in FIGS. 1-3, the plunger rod 100 can be operable with a piston 200 that includes a thread 204 within an interior 206 and a distal portion 212 that defines a recess extending distally beyond the thread 204. 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 that can be distal to the first portion 106. The second portion 110 can have a second diameter 112 that can be smaller than the first diameter 108. In an embodiment, the distal end 104 can include a third portion 114 distal to the second portion 110. The third portion 114 can have a third diameter 116 that can be smaller than the second diameter 112. The third portion 114 can define a head 118. In an embodiment, the head 118 can be substantially planar along a direction perpendicular to the longitudinal axis 120 of the plunger rod 100. Alternatively, the head 118 can define other shapes such as a conical shape, a dome shape, 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 the deformation forces applied to the piston 200 during injection, thereby reducing or eliminating leakage. For example, the second diameter 112 can be dimensioned such that the second portion 110 abuts at least one of the crests 220 of the thread 204 defined within the interior 206 of the piston 200 without contacting the flank 222 or the root 224 of the thread 204. In an embodiment, the second portion 110 abuts each of the crests 220 without contacting either the flank 222 or the root 224. By abutting at least one of the crests 220 of the thread 204 without contacting the flank 222 or the root 224 of the thread 204, the second portion 110 can engage with the piston 200 without being removably connected to the piston 200 and resist deformation of the piston 200 or crushing of the piston 200 into the interior 206.This variable resistor can serve to maintain contact between the circumferential rib 208 of the piston 200 and the inner wall 210 of the barrel 202, which can reduce and / or eliminate proximal-direction leakage of the agent between the piston 200 and the barrel 202.

[0018] In an embodiment, the third diameter 116 can be dimensioned such that the third portion 114 abuts against the distal portion 212 (e.g., the inner wall) of the piston 200. The distal portion 212 can be defined within the interior 206 of the piston 200 at a position distal to the thread 204. By abutting against the distal portion 212, the third portion 114 can resist deformation of the piston 200 or crushing of the piston 200 into the interior 206. This variable resistor can serve to maintain contact between the head 214 of the piston 200 and the inner wall 210, which can reduce and / or eliminate proximal-direction leakage of the agent between the piston 200 and the barrel 202. Additionally, the third portion 114 can transmit the displacement force applied to the plunger rod 100 to the distal portion 212 of the piston 200 to axially displace the piston 200 distally within the barrel 202.

[0019] In an embodiment, the first diameter 108 can be larger than the opening diameter 216 of the interior 206 of the piston 200. As a result of 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 crushing of the piston 200 into the interior 206. Additionally, the distal surface 122 can transmit the displacement force applied to the plunger rod 100 to the proximal surface 218 to axially displace the piston 200 distally within the barrel 202.

[0020] In an embodiment, the second portion 110 can include a distal surface 124. The distal surface 124 can abut against the distal portion 212 of the piston 200 and resist deformation of the piston 200 or crushing of the piston 200 into the interior 206. Additionally, the distal surface 124 can transmit the displacement force applied to the plunger rod 100 to the distal portion 212 of the piston 200 to axially displace the piston 200 distally within the barrel 202.

[0021] In an embodiment, the head 118 can abut against the distal portion 212 of the piston 200 and resist deformation of the piston 200 or crushing of the piston 200 into the interior 206. Additionally, the head 118 can transmit the displacement force applied to the plunger rod 100 to the distal portion 212 of the piston 200 to axially displace the piston 200 distally within the barrel 202.

[0022] The first portion 106, the second portion 110, and the third portion 114 can substantially fill the interior 206 of the piston 200 and can be dimensioned in several different ways to 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 as shown in FIGS. 1 and 3. In an alternative example, the second portion 110' can be conical with a distal taper as shown in FIG. 4. In an embodiment, the third portion 114 can be cylindrical as shown in FIGS. 1 and 3. In an alternative example, the third portion 114' can be conical with a distal taper as shown in FIG. 4. In an embodiment, the second portion 110 can be conical with a distal taper, the third portion 114 can be cylindrical, or the second portion 110 can be cylindrical and the third portion 114 can be conical with a distal taper. Other substitutions are possible.

[0023] In an embodiment, the second portion 110 can have a length along the longitudinal axis 120 that is greater than the length along the longitudinal axis 120 of the third portion 114. Due to this configuration, the second portion 110 can substantially fill the interior 206 of the piston 200 including the threads 204, and the third portion 114 can substantially fill the interior 206 of the piston 200 disposed distally with respect 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 of the second portion 110 along the longitudinal axis 120 can be greater than the length of the first portion 106 along the longitudinal axis 120. In an embodiment, the distal end 104 can be integral with the plunger rod 100.

[0024] The plunger rod 100 was tested using a filled syringe containing a fluid having a viscosity of 957 cP at various different speeds of the plunger 100 / piston 200 within the barrel 202. For each speed, the pressure and force applied to the piston 200 were calculated and the force was measured. Table 1 below shows an overview of the results of these tests, demonstrating that the plunger rod 100 of the present disclosure is suitable for leak - free use with a filled syringe under various different conditions.

[0025]

Table 1

[0026] Also, the plunger rod 100 was tested using a mechanical testing machine to measure the breakaway and push - output profiles for various different speeds of the plunger 100 / piston 200 within the barrel 202. The different speeds were taken to include speeds of 100 mm / min, 380 mm / min, and 450 mm / min. The plunger rod 100 was tested at each speed at least 10 times using different filled syringes containing different fluids at ambient temperature. The different fluids were taken to have viscosities of 1 cP, 20 cP, and 100 cP respectively. No leakage was detected during each test for all the fluids tested and all the speeds 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, namely plunger rod A and plunger rod B, having different distal - end geometries. Plunger rod A was taken to have a distal end smaller than the thread 204 so that it fits within the interior 206 but does not contact the crest 220 of the thread 204. Further, when plunger A moves the piston 200, no part of the distal end of plunger A contacts the proximal face 218 of the piston 200. Plunger rod B occupies less than half of the interior 206 of the piston 200 and has a distal end that does not contact either the top 220 of the thread 204 or the distal portion 212 of the interior 206 when plunger B moves the piston 200. Plunger B includes a distal face that contacts the proximal face 218 of the piston 200 when plunger A moves the piston 200. Table 2 shows that while each of plunger rods A and B exhibited leakage under at least some of the tested conditions, the plunger rod 100 had no leakage under any of the test conditions.

[0027]

Table 2

[0028] FIG. 5 shows exemplary break - loose glide profile data collected using a 100 cP fluid within plunger rod 100, piston 200, and barrel 202. The plunger rod 100 moved the piston 200 at a speed of 380 mm / min, and the compressive force for the movement in the glide force profile was collected. This data indicates that even at relatively high speeds (e.g., 380 mm / min) and fluid viscosities (e.g., 100 cP), when the fluid is extruded from the barrel 202, the plunger rod 100 can produce less strain and compression. This data shows that the plunger rod 100 can reduce or eliminate leakage.

[0029] FIG. 6 shows a partial view of another plunger rod 300 operably connected to another piston 400 and disposed within the barrel 202 of a filled syringe. FIG. 7 shows a cross - sectional view of the plunger rod 300, piston 400, and barrel 202 of FIG. 6. In an embodiment as shown in FIGS. 6 and 7, the plunger rod 300 can be operable with the piston 400, and the piston 400 includes a thread 404 within the interior 406 of the piston 400, and also defines a wall that can be perpendicular to the longitudinal axis of the piston 400 and includes a distal portion 412 that can be located at the distal end of the thread 404.

[0030] The plunger rod 300 and the piston 400 can include any of the respective features previously discussed with reference to the plunger rod 100 and the piston 200, and like parts correspond to like parts. The plunger rod 300 can differ from the plunger rod 100 in that the plunger rod 300 can have a distal end 304 having an outer geometry adapted to fit within the inner geometry of the piston 400. For example, the distal end 304 of the plunger rod 300 can include a first portion 306 having a first diameter 308. The distal end 304 can include a second portion 310 that can be distal to the first portion 306. The second portion 310 can have a second diameter 312 that can be smaller than the first diameter 308. The second portion 310 can define a head 318. In an embodiment, the head 318 can be substantially planar along a direction perpendicular to the longitudinal axis of the plunger rod 300. Alternatively, the head 318 can define other shapes such as a conical shape, a dome shape, and the like. The second portion 310 can define an outer geometry that can substantially fill the interior 406 of the piston 400. By substantially filling the interior 406 of the piston 400, the distal end 304 can resist the deformation forces applied to the piston 400 during injection, thereby reducing or eliminating leakage. For example, the second diameter 312 can be sized such that the second portion 310 abuts at least one of the peaks 420 of the threads 404 defined within the interior 406 of the piston 400 without contacting the flanks 422 or valleys 424 of the threads 404. In an embodiment, the second portion 310 abuts each of the peaks 420 without contacting either of the flanks 422 or valleys 424. By abutting at least one of the peaks 420 of the threads 404 without contacting the flanks 422 or valleys 424 of the threads 404, the second portion 310 can engage the piston 400 without being removably connected to the piston 400 and resist deformation of the piston 400 or crushing of the piston 400 into the interior 406.This variable resistor can help maintain contact between the circumferential rib 408 of the piston 400 and the inner wall 210 of the barrel 202, which can reduce and / or eliminate proximal-direction leakage of the agent between the piston 400 and the barrel 202.

[0031] In an embodiment, the head 318 abuts against the distal portion 412 (e.g., inner wall) of the piston 400. In an embodiment, the distal portion 412 can 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 crushing of the piston 400 into the interior 406. This variable resistor can help maintain contact between the head 414 of the piston 400 and the inner wall 210, which can reduce and / or eliminate proximal-direction leakage of the agent between the piston 400 and the barrel 202. Additionally, the head 318 can transmit the displacement force applied to the plunger rod 300 to the distal portion 412 of the piston 400 to axially displace the piston 400 distally within the barrel 202.

[0032] In an embodiment, the first diameter 308 can be larger than the opening diameter 416 of the interior 406 of the piston 400. As a result of 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 crushing of the piston 400 into the interior 406. Additionally, the distal surface 322 can transmit the displacement force applied to the plunger rod 300 to the proximal surface 418 to axially displace the piston 400 distally within the barrel 202.

[0033] FIG. 8 shows a partial view of another plunger rod 500 operably connected to another piston 600 and disposed within the barrel 202 of a filled syringe. FIG. 9 shows a cross-sectional view of the plunger rod 500, piston 600, and barrel 202 of FIG. 8. In an embodiment such as shown in FIGS. 8 and 9, the plunger rod 500 may be operable with the piston 600, including a snap fit portion 604 within the interior 606 of the piston 600.

[0034] The plunger rod 500 and the piston 600 can include any of the respective features previously discussed with reference to the plunger rod 100 and the piston 200, and like parts correspond to like parts. The plunger rod 500 can differ from the plunger rod 100 in that the plunger rod 500 can have a distal end 504 with an outer geometry adapted to fit within the inner geometry of the piston 600. For example, the distal end 504 of the plunger rod 500 can include a first portion 506 having a first diameter 508. The distal end 504 can include a second portion 510 that can be distal to the first portion 506. The second portion 510 can have a second diameter 512 that can be smaller than the first diameter 508. The second portion 510 can define a head 518. In an embodiment, the head 518 can be conical or domed so as to correspond to the shape of the distal portion 612 of the piston 600. The second portion 510 can extend radially beyond the opening diameter 616 of the piston 600 and can define an outer geometry that can substantially fill the interior 606 of the piston 600 except for the region 607 of the interior 606 that 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 region 607 that defines the snap fit 604, the distal end 504 can resist the deformation forces applied to the piston 600 during injection, thereby reducing or eliminating leakage without the need for a removable connection to the piston 600. For example, the second diameter 512 can be dimensioned such that the second portion 510 contacts the circumferential inner wall 626 of the piston 600 but does not contact the snap fit 604. That is, the second portion 510 does not engage the snap fit when the plunger rod 500 is slid within the interior 606 of the piston 600. In an embodiment, the second portion 510 contacts the entire circumferential inner wall 626.It abuts against the circumferential inner wall 626 but does not abut against the snap - fitting portion 604. As a result, the second portion 510 can engage with the piston 600 without being removably connected to the piston 600 and can resist deformation of the piston 600 or crushing of the piston 600 into the interior 606. This resistance to deformation can help maintain contact between the circumferential rib 608 of the piston 600 and the inner wall 210 of the barrel 202, which can reduce and / or eliminate proximal - direction drug leakage between the piston 600 and the barrel 202.

[0035] 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 crushing of the piston 600 into the interior 606. This resistance to deformation can help maintain contact between the head 614 of the piston 600 and the inner wall 210, which can reduce and / or eliminate proximal - direction drug leakage between the piston 600 and the barrel 202. Additionally, the head 518 can transmit the displacement force applied to the plunger rod 500 to the distal portion 612 of the piston 600 to axially displace the piston 600 distally within the barrel 202.

[0036] In an embodiment, the first diameter 508 can be larger than the opening diameter 616 of the interior 606 of the piston 600. As a result of 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 crushing of the piston 600 into the interior 606. Additionally, the distal surface 522 can transmit the displacement force applied to the plunger rod 500 to the proximal surface 618 to axially displace the piston 600 distally within the barrel 202.

[0037] In an embodiment as shown in FIG. 10, the distal end portion 704 of the plunger rod 700 can define both the distal stem end portion 726 and the plunger rod adapter 728. The plunger rod adapter 728 can be removably connected to the distal stem end portion 726. The distal end portion 704 can include any of the features discussed above with reference to the distal end portions 104, 304, and 504, except that the plunger rod adapter 728 is removably connected to the distal stem end portion 726 instead of being integrally formed with the distal stem end portion 726. For example, the plunger rod adapter 728 can include any of the geometries previously discussed with reference to the distal end portion 104. For example, the plunger rod adapter 728 can include a first portion 706, a second portion 710, and a third portion 714, each of which can include any of the features previously discussed with reference to the first portion 106, 306, 506, the second portion 110, 110', 310, 510, and / or the third portion 114 / 114'.

[0038] The plunger rod adapter 728 can be removably connected to the distal stem end 726 via any number of connection techniques, including, among other possibilities, adhesively bonding the plunger rod adapter 728 to the plunger rod 700 or fastening the plunger rod adapter 728 to the plunger rod 700 using fasteners. For example, in an embodiment, the distal stem 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 for threadedly connecting to the threads 730, or the plunger rod adapter 728 can be connected via other known connection techniques such as snap fits, adhesives, etc. Since the plunger rod adapter 728 can include a geometry for substantially filling the interior of the piston 200 without threadedly connecting to the piston 200, the plunger rod adapter 728 can be adapted for use with a syringe without needle having a threaded distal stem end 726, for example, to connect the plunger rod 700 to the piston 200 without threaded connection. That is, the plunger rod adapter 728 can be interposed between the threads 730 of the distal stem end 726 and the threads 204 of the piston 200 to connect the piston 200 to the plunger rod 700 without threadedly engaging the threads 204 of the piston 200.

[0039] Figures 11 and 12 show diagrams of a syringe without needle 800 for injecting a medicament. The syringe without needle 800 can include any one of the plunger rods and / or plunger rod adapters described herein. For example, the syringe without needle 800 can include a plunger rod 100. The syringe without needle 800 can include a base 802 that can receive a barrel 202 that houses a piston 200. The syringe without needle 800 can further include a handle 804 that can be integrally or removably connected to the plunger rod 100. Depressing the handle 804 moves the plunger rod 100 and axially displaces the piston 200 within the barrel 202 to inject the medicament into a patient.

[0040] The foregoing description will be understood to provide examples of the present disclosure. However, it is contemplated that other implementations of the present invention may differ in detail from the foregoing examples. All references to the present invention or its examples are intended to refer to the particular example being considered at that time and are not intended to imply any limitation with respect to the scope of the present invention more generally. All language indicating distinction and disparagement with respect to particular features is intended to indicate the lack of preference for those features, but is not intended to exclude such from the scope of the present invention entirely unless otherwise indicated. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims

1. A plunger rod for axially moving a piston within a syringe barrel, wherein the piston defines an interior that extends from a proximal face of the piston to a distal portion of the interior, and the plunger rod has a proximal end, a distal end, which has a first portion having a first diameter, a second portion distal to the first portion, the second portion having a second diameter smaller than the first diameter and having an outer geometry complementary to the distal portion of the interior of the piston, and when the plunger rod is slid into the interior of the piston, the first portion is configured to contact the proximal face of the piston, and the second portion is configured to contact the interior of the piston without removably connecting to the piston.

2. The plunger rod according to claim 1, wherein the outer geometry is configured to engage the piston such that the second portion can resist a deforming force applied to the piston during axial movement of the piston within the syringe barrel.

3. The plunger rod according to claim 1, wherein the plunger rod is configured to disengage from the piston without resistance from the piston by sliding proximally to move the plunger rod away from the piston.

4. The plunger rod according to claim 1, wherein the interior of the piston has a thread, and the second portion is configured to contact at least one crest of the thread in the interior of the piston.

5. The plunger rod according to claim 1, wherein the interior of the piston has a snap fit portion, and the second portion does not engage the snap fit portion when the plunger rod is slid within the interior of the piston.

6. The plunger rod according to claim 1, wherein when the plunger rod is slid within the piston, the first portion contacts the proximal face of the piston, and the second portion simultaneously contacts the interior of the piston without removably connecting to the piston.

7. The plunger rod according to claim 1, wherein the second portion is conical and tapered in the distal direction.

8. The plunger rod according to claim 1, further comprising a head configured such that the distal end portion contacts the distal portion inside the piston.

9. The plunger rod according to claim 8, wherein the distal portion further comprises a third portion between the second portion and the head, and the third portion has a third diameter smaller than the second diameter.

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

11. The plunger rod according to claim 9, wherein the third portion is conical and tapered in the distal direction.

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

13. The plunger rod according to claim 9, wherein 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.

14. A plunger rod adapter for axially moving a piston within a syringe barrel, the piston defining an interior extending from a proximal face of the piston to a distal portion of the interior, the plunger rod adapter comprising a proximal end portion, a distal end portion, a first portion having a first diameter, a second portion distal to the first portion, the second portion having a second diameter smaller than the first diameter and having an outer geometry complementary to the distal portion inside the piston, and a distal end portion comprising the second portion, When the plunger rod adapter is slid into the interior of the piston, the first portion is configured to contact the proximal face of the piston, and the second portion is configured to contact the interior of the piston without being removably connected to the piston. A plunger rod adapter.

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

16. The plunger rod adapter according to claim 14, wherein the plunger rod adapter is configured to disengage from the piston without resistance from the piston by sliding proximally to move the plunger rod adapter away from the piston.

17. The plunger rod adapter according to claim 14, wherein the interior of the piston is provided with a thread, and the second portion is configured to contact at least one crest of the thread in the interior of the piston.

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

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

20. The plunger rod adapter according to claim 14, further comprising a head configured such that the distal end contacts the distal portion within the piston.

21. A syringe for injecting a drug, a barrel, a piston movably disposed within the barrel, the piston defining an interior extending from a proximal surface to a distal portion of the piston, a plunger rod having a proximal end and a distal end, configured to axially move the piston within the barrel in response to an applied force to the plunger rod, the distal end a first portion having a first diameter, a second portion distal to the first portion, the second portion having a second diameter smaller than the first diameter and having an outer geometry complementary to the distal portion within the piston, a syringe, wherein when the plunger rod is slid into the interior of the piston, the first portion is configured to contact the proximal surface of the piston, and the second portion is configured to contact the interior of the piston without being removably connected to the piston.

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

23. The syringe according to claim 21, wherein the distal end portion defines a plunger rod adapter removably connected to the plunger rod.

24. The syringe according to claim 21, wherein the outer geometry is configured to engage the piston such that the second portion can resist a deforming force applied to the piston during axial movement of the piston within the barrel.

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

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

27. The syringe according to claim 21, wherein the interior of the piston comprises a snap fit portion and the second portion does not engage the snap fit portion when the plunger rod is slid within the interior of the piston.

28. The syringe according to claim 21, further comprising a head configured to contact the distal portion of the interior of the piston.

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