Syringe stopper and plunger rod arrangement for a syringe assembly

A syringe assembly includes a substantially cylindrical syringe barrel including a fluid dispensing end, an open end, and at least one protrusion adjacent the open end, the at least one protrusion projecting inwardly from an inner surface of the syringe barrel, a stopper configured to be received within the open end of the syringe barrel, and a plunger rod having a plunger rod body extending along a longitudinal axis from a proximal end to a distal end and at least one support disk provided on the distal end thereof. The support disk on the plunger rod is configured to bear against the protrusion of the syringe barrel upon misalignment of the plunger rod in the syringe barrel.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates, in general, to a stopper assembly for use with a syringe and, more particularly, a stopper and plunger rod arrangement for use with a syringe.

Description of Related Art

Current syringe designs can typically be categorized as two-piece syringes or three-piece syringes. A typical three-piece syringe includes a tubular barrel having an access opening formed at one end, and a smaller discharge opening formed at the opposing end. The lead end of an elongated plunger is received within the access opening of the barrel so as to be slidable within the barrel. Attached to the lead end of the plunger is a flexible sealing member or stopper that snugly seals against the interior surface of the barrel. A needle, a threaded member, or a non-threaded member is usually attached to the discharge opening on the barrel. The needle can be used to penetrate a surface while the threaded member can be used to attach the syringe to another medical device, such as a catheter. The flexible stopper is usually manufactured from an elastomeric material, such as a rubber or a cross-linked or thermal plastic elastomer.

A two-piece syringe, on the other hand, includes a “stopper” that is in the form of a rigid sealing disc, also known as a plunger rod head. It is typically made of the same rigid plastic as the rest of the plunger rod. The sealing force in a two-piece syringe comes from a thin elastic barrel that deforms around the rigid plunger rod head.

During use, the discharge end of the syringe is initially placed in contact with a fluid. For example, the needle on the syringe can be inserted into a liquid medication. As the plunger is retracted within the barrel, a process known as aspiration, a negative pressure is formed within the end of the barrel so as to cause the fluid to be drawn into the barrel. The syringe can then be moved to a second location where advancing the plunger within the barrel causes the fluid to be pushed or expressed out of the discharge end of the barrel.

Current two-piece and three-piece syringe designs suffer from various deficiencies. In some instances, a syringe may be used during a high temperature autoclave sterilization process. An autoclave is typically used to sterilize surgical equipment, laboratory instruments, pharmaceutical items, and other materials. It can sterilize solids, liquids, hollows, and instruments of various shapes and sizes. An autoclave chamber sterilizes medical or laboratory instruments by heating them above boiling point. Steam is the autoclave's sterilization agent, which is typically produced at relatively high temperatures and pressures.

Typically, syringe designs that are subjected to high temperatures and pressures during an autoclave sterilization cycle use a vulcanized rubber for the stopper base material. There are, however, several significant disadvantages associated with using vulcanized rubber in syringe stopper applications that are used with an autoclave sterilization process. The bulk material cost of vulcanized rubber is significantly higher than alternative materials, such as thermal plastic elastomers. Further, the vulcanized rubber is more costly to manufacture in both capital equipment costs and production labor when compared to injectable moldable thermal plastic elastomers. The vulcanized rubber also has relatively higher chemical leachable characteristics that can negatively impact the medication stored in the syringe in comparison to thermal plastic elastomers.

Due to these disadvantageous characteristics, medical device manufacturer have begun using thermal plastic elastomer in prefilled autoclaved syringes. The thermal plastic elastomeric material, however, has a significantly lower resistance to high temperature compression set characteristics in comparison to the vulcanized rubber syringes. Therefore, the syringe stoppers made of the thermal plastic elastomeric material are designed with relatively low contact stress concentrations in order to have low yielding at high autoclave temperatures, which translates to acceptable fluid sealing robustness capabilities.

Some manufacturers have also accomplished the use of thermal plastic elastomeric material in the stoppers in part by using more complicated, multipart plunger rod designs in order to reduce plunger rod side loading transfer to the stopper. This effectively reduces stopper stress induced yielding and leakage. The multi-part syringe designs, however, tend to increase manufacturing and assembly costs. In addition, the multi-part plunger rod designs have a higher amount of mechanical backlash or play in both the axial and angular directions. This backlash has a less than optimal infusion positional control (feel) for the end user (clinician).

SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved syringe stopper and plunger rod arrangement for use with thermal plastic elastomers. This improved arrangement is configured to better tolerate the high temperatures experienced by the arrangement during an autoclave sterilization process for increased syringe sealing performance robustness. The new arrangement makes it possible to use lower compression set performance materials such as thermal plastic elastomer resins for the syringe stopper, while still satisfying sterility, leakage, and other performance requirements necessary for a syringe. Utilizing thermal plastic elastomer resins for the syringe stopper significantly decreases bulk material costs, manufacturing costs, and leachable toxins to the syringe medication, as compared to traditional vulcanized rubber syringe stoppers.

To incorporate thermal plastic elastomers into syringe stoppers for use with autoclave syringes, the stopper stress concentrations can be reduced in order to reduce material yielding and increase sealing pressure. Further, the plunger rod side loading can be transferred directly from the plunger rod to the syringe barrel, thereby reducing asymmetric stopper deflection induced loading/leakage.

The stopper seal stress concentrations in the stopper ribs can be reduced to minimize localized stopper rib yielding during high temperature autoclave sterilization processing. This stress concentration reduction can be accomplished by balancing the stopper rib contact area with the internal structural features of the stopper and the overall barrel interference fit. The fluid sealing robustness can be increased by using fluid pressure during infusion with stopper cone internal support features. These support features allow the stopper cone to marginally collapse or slightly bend when the syringe fluid is under pressure. The cone bending causes the stopper cone base to apply radial loading on the stopper ribs, which increases the sealing contact pressure proportional to the syringe fluid pressure.

Angular misalignment of the stopper when the plunger rod is subjected to side loading can also be reduced by incorporating design features to limit the angular misalignment between the plunger rod and the barrel. The angular misalignment of the plunger rod can be further reduced by incorporating angular flex plunger rod design features between the plunger rod and the stopper. The angular flex features allow the plunger rod to barrel angular misalignment loading to be decoupled or significantly reduced at the plunger rod to stopper interface.

According to one aspect of the invention, the syringe assembly includes a substantially cylindrical syringe barrel including a fluid dispensing end, an open end, and at least one protrusion adjacent the open end, the at least one protrusion projecting inwardly from an inner surface of the syringe barrel, a stopper configured to be received within the open end of the syringe barrel, and a plunger rod having a plunger rod body extending along a longitudinal axis from a proximal end to a distal end and at least one support disk provided on the distal end thereof. The support disk on the plunger rod is configured to bear against the protrusion of the syringe barrel upon misalignment of the plunger rod in the syringe barrel. The at least one protrusion of the syringe barrel is a continuous rib that extends around an inner circumferential surface of the syringe barrel. The at least one support disk includes two support disks on the plunger rod spaced from one another such that, when the plunger rod is misaligned in the syringe barrel, a first support disk bears against a proximal side of the protrusion at a first load bearing point and a second support disk bears against a distal side of the protrusion at a second load bearing point. The plunger rod further includes a recess defined in the plunger rod body adjacent the support disk, the recess being defined by two protrusion members extending from an outer surface of the plunger rod body. Upon misalignment of the plunger rod in the syringe barrel, a first protrusion member bears against a proximal side of the protrusion at a first load bearing point, a second protrusion member bears against a distal side of the protrusion at a second load bearing point, and the support disk bears against the inner surface of the syringe barrel at a third load bearing point. The plunger rod further includes an attachment member provided on the distal end and configured for connection to the stopper. The support disk is spaced proximally from the attachment member. The plunger rod body further includes a rigid outer body member and a flexible inner body member provided within the rigid outer body member. The flexible inner body member is configured to flex upon misalignment of the plunger rod in the syringe barrel. The plunger rod body further includes an attachment member configured for connection with the stopper. The attachment member is provided on a distal end of the flexible inner body member. The at least one support disk includes two support disks on the plunger rod spaced from one another. Provided between the support disks, the plunger rod further includes a flexible region configured to flex upon misalignment of the plunger rod in the syringe barrel. The stopper includes a main body portion defining an open rearward end, a closed front end, and an inner cavity to receive the distal end of the plunger rod. An inner surface of the inner cavity defines a recess configured to act as a load bearing point for the plunger rod upon misalignment of the plunger rod within the syringe barrel. The stopper includes a main body portion defining an open rearward end, a closed front end, and an inner cavity to receive the distal end of the plunger rod. A portion of an inner surface of the inner cavity defines a plurality of notches configured to receive a plurality of projections extending from the distal end of the plunger rod body. Upon misalignment of the plunger rod in the syringe barrel, at least one projection on the plunger rod body bears against a corresponding notch in the inner cavity of the stopper at a load bearing point. The stopper is made of a thermal plastic elastomer.

In another aspect of the invention, the stopper adapted for attachment with a plunger rod for use within a syringe barrel includes a main body portion defining an open rearward end, a closed front end, and an inner cavity defined between the rearward end and the front end, the inner cavity defining an inner contour including a notch extending outwardly from an inner surface of the inner cavity, the notch separating a first contact surface of the inner contour from a second contact surface of the inner contour, a first rib extending from an outer surface of the main body portion and around an outer circumference of the main body portion, and a second rib spaced from the first rib, the second rib extending from an outer surface of the main body portion and around an outer circumference of the main body portion. A width of the first contact surface is substantially equal to a width of the first rib, and a width of the second contact surface is substantially equal to a width of the second rib. The notch defined in the inner contour provides a reduced thickness of the main body portion from the inner contour to an outer surface of the main body portion. The closed front end of the main body portion has a conical shape with a tip. A recess is formed on the outer surface of the main body portion between the first rib and the second rib. A width of the recess is substantially equal to a width of the notch. At least one collapsible cut-out is defined in the inner contour of the inner cavity. The collapsible cut-out permits the stopper to collapse or bend when under pressure. The stopper is made of a thermal plastic elastomer.

In another aspect of the invention, the plunger rod for use in a syringe assembly includes a plunger rod body extending along a longitudinal axis from a proximal end to a distal end, and at least two support disks provided on a distal end thereof. The support disks on the plunger rod are configured to bear against a protrusion on a syringe barrel upon misalignment of the plunger rod in the syringe barrel. An attachment member is provided on the distal end and configured for attachment to a stopper. The support disks are spaced proximally from the attachment member. The plunger rod further includes a recess defined in the plunger rod body adjacent the support disks. The recess is defined by two protrusion members extending from an outer surface of the plunger rod body. The plunger rod body further includes a rigid outer body member and a flexible inner body member provided within the rigid outer body member. The flexible inner body member is configured to flex upon misalignment of the plunger rod in the syringe barrel. The plunger rod body further includes an attachment member configured for connection with the stopper. The attachment member is provided on a distal end of the flexible inner body member. Provided between the support disks, the plunger rod further includes a flexible region configured to flex upon misalignment of the plunger rod in the syringe barrel.

DESCRIPTION OF THE INVENTION

With references toFIGS.1and2, a first aspect of the stopper2includes a main body portion4defining an open rearward end6configured to receive a plunger rod and a closed front end8that forms a flexible roof. In one aspect, the stopper2is made of a thermal plastic elastomer. It is also contemplated that the stopper2is made of any alternative hard or soft plastic. The closed front end8of the main body portion4includes a substantially cylindrical portion9, a first angled portion10and a second angled portion12, which are both part of a single conical surface, that extend toward a tip14, thereby providing the closed front end8with a substantially conical appearance. However, this shape of the flexible roof is not to be considered as limiting the present invention as the roof may be flat. Such a roof would not provide flexing roof action in which a flexible roof of the stopper flexes inward and expands sideways in a radial direction. As shown inFIG.1, at least dimple16,18extends from an outer surface of the first angled portion10and the second angled portion12of the closed front end8. Dimples16,18are designed to keep the stopper2from making contact with a front portion of the syringe barrel for preventing reflux flow at the end of an injection procedure. Although only one dimple16,18is shown extending from the first angled portion10and the second angled portion12, it is contemplated that additional features may be provided on these surfaces or no dimples may be provided on these surfaces.

As shown inFIG.2, the main body portion4of the stopper2is substantially hollow and designed to receive an attachment portion of a plunger rod, as described below. The main body portion4of the stopper2defines an inner cavity20that receives the attachment portion of the plunger rod. The inner cavity20is defined between the rearward end6and the closed front end8of the main body portion4. The inner cavity20defines an inner contour22in the main body portion4. The inner contour22defines a notch24configured to receive a portion of the attachment portion of the plunger rod to retain the attachment portion within the inner cavity20. The notch24is defined in the cylindrical portion9of the main body portion4and extends outwardly from the inner surface of the inner cavity20and around the circumferential surface of the inner contour22. The notch24defined in the inner contour22defines a reduced thickness of the main body portion4from the inner contour22to the outer surface of the main body portion4as compared to the thickness in the remaining portion of the main body portion4. The notch24is defined between a first contact surface25aand a second contact surface25bof the inner contour22. The reduction in thickness of the cylindrical portion9assists in reducing plunger rod misalignment loading forces transferring to the stopper rib contact surfaces.

The inner contour22of the inner cavity20also defines a first angled portion26and a second angled portion28in the front end8of the stopper2that correspond to the first angled portion10and the second angled portion12of the outer surface of the front end8. The first angled portion26and the second angled portion28, which are both part of a single conical surface, provide the inner surface of the closed front end8with a substantially conical appearance. Adjacent the first angled portion26and the second angled portion28, a pair of collapsible cut-outs30,32are defined in the inner contour22. The collapsible cut-outs30,32are notches or recesses defined in the inner contour22of the main body portion4. The collapsible cut-outs30,32are provided to allow the adjacent portions of the main body portion4to bend radially outward when the stopper is under fluid pressure, which causes the flexible roof of the front end8to bend axially inward in an aft direction. The portions of the main body portion4that are bent radially outward assist in keeping the outer surface of the main body portion4in contact with the inner surface of the syringe barrel in which the stopper2is moving to improve the interference fit between the stopper2and the syringe barrel so that the sealing contact pressure between the stopper2and the syringe barrel is proportional to the syringe fluid pressure acting on the stopper2.

With reference toFIGS.1and2, the outer surface of the cylindrical portion9of the main body portion4includes a first rib34provided adjacent the rearward end6and a second rib36adjacent the front end8of the main body portion4. In one aspect, the ribs34,36extend around the entire circumferential outer surface of the cylindrical portion9. In another aspect, the ribs34,36are provided in segments around the circumferential outer surface of the cylindrical portion9. The ribs34,36extend outwardly from the outer surface of the cylindrical portion9to act as bearing points against the inner surface of the syringe barrel. The first rib34is spaced from the second rib36on the cylindrical portion9. As shown inFIG.2, a width of the first rib34is substantially equal to a width of the first contact surface25aof the inner contour22. A width of the second rib36is substantially equal to a width of the second contact surface25bof the inner contour22. Since the widths of the ribs34,36are substantially equal to the widths of the contact surfaces25a,25bof the inner contour22, a balanced support of the ribs34,36against the inner surface of the syringe barrel is achieved. This feature assists in reducing the stopper seal stress concentrations within the stopper2. This stress concentration reduction thereby reduces the localized stopper rib yielding during high temperature autoclave sterilization processing. The reduction in material yielding translates to increased passive sealing robustness capabilities for the stopper2. The first rib34and the second rib36of the cylindrical portion9form a recess38on the outer surface of the main body portion4. The width of the recess38is substantially equal to the width of the notch24defined in the inner contour22. The surface of the recess38is not in contact with the inner surface of the syringe barrel.

With reference toFIG.3, the stopper2is shown in use with a plunger rod40and a syringe barrel42to form a syringe assembly44. The stopper2and the plunger rod40are adapted for use with the syringe barrel42. The syringe barrel42is made of medical-grade plastic or glass. The plunger rod40is made of a medical-grade plastic. The syringe barrel42is substantially cylindrical and extends from an open proximal end46to a distal dispensing end (not shown) from which fluid is ejected during use of the syringe assembly44. The distal dispensing end includes an outlet opening and/or a mechanism (such as a luer fitting) for attachment to a separate medical device (such as a catheter). The open end46is configured to receive the stopper2and the plunger rod40. A flange48is provided around the circumferential surface of the open end46. At least one protrusion50projects inwardly from an inner surface52of the syringe barrel42. In one aspect, the protrusion50extends around the entire circumferential surface of the inner surface52of the syringe barrel42. In another aspect, the protrusion50is provided as a plurality of segments that extend around the circumferential surface of the inner surface52. The protrusion50is provided adjacent the open end46of the syringe barrel42. It is also contemplated that additional protrusions may be provided on the syringe barrel42at a distal position from the protrusion50.

The plunger rod40is operatively connected to the stopper2, such that, upon depression of the plunger rod40in a distal direction, the stopper2is moved in a distal direction within the syringe barrel42to direct the fluid out of the dispensing end of the syringe barrel42. The plunger rod40includes a main body portion54, at least one support disk56,58, and an attachment member60. The main body portion54includes a proximal end having an actuator button or tab (not shown) for moving the plunger rod40in a distal or proximal direction, and a distal end upon which the support disks56,58are formed. The support disks56,58extend outwardly from the distal end of the main body portion54and are substantially circular in shape to correspond to the shape of the syringe barrel42. It is contemplated, however, that the support disks56,58can have alternative shapes that are accommodated in the syringe barrel42. The first support disk56is spaced proximally from the second support disk58on the distal end of the main body portion54. The support disks56,58have substantially the same diameter.

The attachment member60of the plunger rod40is provided on the distal end of the plunger rod40and is spaced distally from the support disks56,58on the plunger rod40. The attachment member60has a smaller diameter than the support disks56,58. The attachment member60also includes at least one gripping protrusion62that extends distally from the attachment member60. The gripping protrusions62are configured to assist in gripping the stopper2upon insertion of the attachment member60into the inner cavity20of the stopper2. During use, the plunger rod40is pushed in a distal direction into the open rearward end6of the stopper2so that the attachment member60is inserted into the inner cavity20of the stopper2. As the plunger rod40is moved in the distal direction, the attachment member60is moved into the notch24defined in the inner contour22of the stopper2. Using this interconnection between the attachment member60and the notch24, the plunger rod40is retained in the stopper2such that the stopper2and plunger rod40move in conjunction with one another in the syringe barrel42. It is also contemplated that the plunger rod40is molded integrally with the stopper2to form this arrangement. Since the diameter of the notch24is larger than the diameter of the attachment member60, the plunger rod40is permitted to rotate relative to the stopper2.

As shown inFIG.3, during use of the syringe assembly44, the plunger rod40may become misaligned relative to a longitudinal axis A of the syringe assembly44that extends through the syringe barrel42, the stopper2, and the plunger rod40. Misalignment of the plunger rod40can occur due to a clinician's thumb load misalignment on the plunger rod40with respect to the longitudinal axis A of the syringe assembly. Due to a side loading force B on the plunger rod40, the plunger rod40may be rotated at an angle α relative to the longitudinal axis A of the syringe assembly44. Based on this side loading force B, the attachment member60of the plunger rod40rotates within the stopper2causing stress concentrations in parts of the stopper2. Due to these stress concentrations, the seal between the stopper2and the syringe barrel42may be deteriorated or the material of the stopper2may be worn down under high temperatures. To reduce the effects of the misalignment of the plunger rod40, the support disks56,58are configured to bear against the protrusion50extending from the inner surface52of the syringe barrel42. Upon rotation of the plunger rod40relative to the longitudinal axis A, the proximal support disk56is configured to bear against a proximal side of the protrusion50, and the distal support disk58is configured to bear against a distal side of the protrusion50. The protrusion50acts as a bearing point for the support disks56,58to limit the amount of rotation of the plunger rod40and to reduce the bearing force exerted by the attachment member60within the stopper2. Using the protrusion50as a bearing point causes a significant portion of the side loading force B to be transferred directly from the plunger rod40to the syringe barrel42as a barrel reactive loading force C, which results in a reduced loading force that is transferred from the plunger rod40to the stopper2. The reduced loading force on the side of the stopper2reduces asymmetric stopper deflection-induced loading/leakage in the seal between the stopper2and the syringe barrel42.

With reference toFIG.4, another aspect of the syringe assembly64is shown. In this aspect, the syringe barrel42is the same as that described in the syringe assembly44ofFIG.3. The stopper66and the plunger rod68of this aspect, however, are slightly different from the stopper2and the plunger rod40of the syringe assembly44shown inFIG.3. The stopper66has all of the same features as the stopper2ofFIG.3, except the stopper66does not include a notch similar to the notch24in the stopper2. Instead, the stopper66defines a plurality of notches70in an inner contour72of the stopper66.

The plunger rod68includes a main body portion74, at least one support disk76,78, and an attachment member80configured to connect with the stopper66. The attachment member80is provided on a distal end of the plunger rod68and is distally spaced from the support disks76,78. The attachment member80has a diameter smaller than the support disks76,78and an inner cavity of the stopper66. A plurality of protrusions82are provided on the circumferential outer surface of the attachment member80and are configured to connect the attachment member80within the stopper66. The protrusions82are substantially triangular and correspond in shape to the notches70defined in the stopper66. Therefore, as the plunger rod68is moved distally towards the stopper66, the attachment member80is inserted into the inner cavity of the stopper66. As the attachment member80moves in a distal direction within the inner cavity of the stopper66, the protrusions82are moved from a first notch70to a second notch70within the stopper66. The notches70allow for distal movement of the attachment member80within the stopper66, but prevent proximal movement of the attachment member80out of the stopper66.

With continued reference toFIG.4, a recess84is defined in the main body portion74of the plunger rod68. The recess84is defined proximally from the first support disk76. The recess84is formed between the first support disk76and a protrusion86that extends from the main body portion74. The recess84assists in reducing the bearing load transferred to the stopper66upon misalignment of the plunger rod68within the syringe barrel42. Upon assembly of the plunger rod68in the syringe barrel42, the plunger rod68is moved distally within the syringe barrel42until the protrusion50on the syringe barrel42is positioned within the recess84of the plunger rod68. Upon misalignment of the plunger rod68within the syringe barrel42due to a side bearing load on the plunger rod68, the plunger rod68is rotated at an angle α from the longitudinal axis A of the syringe assembly64. Once the plunger rod68has been rotated, the distal end of the protrusion86bears against the proximal side of the protrusion50of the syringe barrel42, and a proximal side of the first support disk76bears against a distal side of the protrusion50. Further, the second support disk78may bear against the inner surface of the syringe barrel42. The protrusions82of the attachment member80also bear against the notches70defined in the stopper66.

The plunger rod68also includes a flexible region88between the first support disk76and the second support disk78. In one aspect, the flexible region88is more flexible than the remaining portions of the plunger rod68. Due to the flexibility of the flexible region88, upon misalignment of the plunger rod68, the angle of misalignment of the attachment member80within the stopper66is reduced. In particular, since the flexible region88is permitted to flex and rotate with the misalignment of the plunger rod68, the side bearing load is not fully transferred to the attachment portion80, which rotates a smaller angle than the main body portion74of the plunger rod68. In particular, the angle of rotation R of the attachment member80is less than the angle of rotation a of the main body portion74. Due to the smaller rotation of the attachment member80within the stopper66, the side loading force from the attachment member80applied to the stopper66is reduced. This reduction in side loading force on the stopper66reduces deflection-induced leakage on the sealing surface between the stopper66and the inner surface of the syringe barrel42.

With reference toFIG.5, another aspect of a syringe assembly90is shown. The syringe assembly90includes a stopper66, a syringe barrel42, and a plunger rod92. The stopper66is the same stopper66disclosed inFIG.4. The syringe barrel42is the same syringe barrel42disclosed inFIGS.3and4. The plunger rod92, however, includes several features that are not provided in the plunger rod40ofFIG.3and the plunger rod68ofFIG.4. The plunger rod92includes at least one outer body member94, an inner body member %, at least one support disk98,100, and an attachment member102for connection of the plunger rod92to the stopper66. In one aspect, a plurality of outer body member94surround the inner body member96. The outer body members94are made of a rigid plastic material, and the inner body member96is made of a flexible plastic material. The inner body member96extends within the outer body member94. Upon misalignment of the plunger rod92due to a side bearing load on the plunger rod92, the inner body member % is configured to flex to reduce the angle of rotation a of the plunger rod92within the syringe barrel42. The outer body members94remain rigid during rotation of the plunger rod92. In one aspect, the attachment member102is formed on a distal end of the inner body member % so that, due to the flexion of the inner body member96during misalignment of the plunger rod92, the amount of side bearing load transferred from the attachment member102to the stopper66is reduced. During misalignment of the plunger rod92, the inner body member % experiences significant deflection, while the outer body member94remains rigid. The rigid outer body member94is designed to transfer a large portion of the side bearing load from the plunger rod92to the syringe barrel42through the support disks98,100bearing against the protrusion50on the syringe barrel42, as described hereinabove.