Patent Description:
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.

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. A syringe assembly having the features described within the preamble of claim <NUM> is known from <CIT>.

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).

A syringe assembly according to the invention is defined by the features of independent claim <NUM>. Preferred embodiment are defined by the features of the dependent claims.

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.

These and other features and characteristics of the present invention, as well as the methods of operation and functions of the related elements of structures and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. As used in the specification and the claims, the singular form of "a", "an", and "the" include plural referents unless the context clearly dictates otherwise.

For purposes of the description hereinafter, the terms "upper", "lower", "right", "left", "vertical", "horizontal", "up", "down", "lateral", "longitudinal", and derivatives thereof, shall relate to the invention as it is oriented in the drawing figures. It is also to be understood that the specific devices illustrated in the attached drawings, and described in the following specification, are simply exemplary aspects of the invention. Hence, specific dimensions and other physical characteristics related to the aspects disclosed herein are not to be considered as limiting.

With references to <FIG> and <FIG>, a first aspect of the stopper <NUM> includes a main body portion <NUM> defining an open rearward end <NUM> configured to receive a plunger rod and a closed front end <NUM> that forms a flexible roof. In one aspect, the stopper <NUM> is made of a thermal plastic elastomer. It is also contemplated that the stopper <NUM> is made of any alternative hard or soft plastic. The closed front end <NUM> of the main body portion <NUM> includes a substantially cylindrical portion <NUM>, a first angled portion <NUM> and a second angled portion <NUM>, which are both part of a single conical surface, that extend toward a tip <NUM>, thereby providing the closed front end <NUM> with 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 in <FIG>, at least dimple <NUM>, <NUM> extends from an outer surface of the first angled portion <NUM> and the second angled portion <NUM> of the closed front end <NUM>. Dimples <NUM>, <NUM> are designed to keep the stopper <NUM> from making contact with a front portion of the syringe barrel for preventing reflux flow at the end of an injection procedure. Although only one dimple <NUM>, <NUM> is shown extending from the first angled portion <NUM> and the second angled portion <NUM>, it is contemplated that additional features may be provided on these surfaces or no dimples may be provided on these surfaces.

As shown in <FIG>, the main body portion <NUM> of the stopper <NUM> is substantially hollow and designed to receive an attachment portion of a plunger rod, as described below. The main body portion <NUM> of the stopper <NUM> defines an inner cavity <NUM> that receives the attachment portion of the plunger rod. The inner cavity <NUM> is defined between the rearward end <NUM> and the closed front end <NUM> of the main body portion <NUM>. The inner cavity <NUM> defines an inner contour <NUM> in the main body portion <NUM>. The inner contour <NUM> defines a notch <NUM> configured to receive a portion of the attachment portion of the plunger rod to retain the attachment portion within the inner cavity <NUM>. The notch <NUM> is defined in the cylindrical portion <NUM> of the main body portion <NUM> and extends outwardly from the inner surface of the inner cavity <NUM> and around the circumferential surface of the inner contour <NUM>. The notch <NUM> defined in the inner contour <NUM> defines a reduced thickness of the main body portion <NUM> from the inner contour <NUM> to the outer surface of the main body portion <NUM> as compared to the thickness in the remaining portion of the main body portion <NUM>. The notch <NUM> is defined between a first contact surface 25a and a second contact surface 25b of the inner contour <NUM>. The reduction in thickness of the cylindrical portion <NUM> assists in reducing plunger rod misalignment loading forces transferring to the stopper rib contact surfaces.

The inner contour <NUM> of the inner cavity <NUM> also defines a first angled portion <NUM> and a second angled portion <NUM> in the front end <NUM> of the stopper <NUM> that correspond to the first angled portion <NUM> and the second angled portion <NUM> of the outer surface of the front end <NUM>. The first angled portion <NUM> and the second angled portion <NUM>, which are both part of a single conical surface, provide the inner surface of the closed front end <NUM> with a substantially conical appearance. Adjacent the first angled portion <NUM> and the second angled portion <NUM>, a pair of collapsible cut-outs <NUM>, <NUM> are defined in the inner contour <NUM>. The collapsible cut-outs <NUM>, <NUM> are notches or recesses defined in the inner contour <NUM> of the main body portion <NUM>. The collapsible cut-outs <NUM>, <NUM> are provided to allow the adjacent portions of the main body portion <NUM> to bend radially outward when the stopper is under fluid pressure, which causes the flexible roof of the front end <NUM> to bend axially inward in an aft direction. The portions of the main body portion <NUM> that are bent radially outward assist in keeping the outer surface of the main body portion <NUM> in contact with the inner surface of the syringe barrel in which the stopper <NUM> is moving to improve the interference fit between the stopper <NUM> and the syringe barrel so that the sealing contact pressure between the stopper <NUM> and the syringe barrel is proportional to the syringe fluid pressure acting on the stopper <NUM>.

With reference to <FIG> and <FIG>, the outer surface of the cylindrical portion <NUM> of the main body portion <NUM> includes a first rib <NUM> provided adjacent the rearward end <NUM> and a second rib <NUM> adjacent the front end <NUM> of the main body portion <NUM>. In one aspect, the ribs <NUM>, <NUM> extend around the entire circumferential outer surface of the cylindrical portion <NUM>. In another aspect, the ribs <NUM>, <NUM> are provided in segments around the circumferential outer surface of the cylindrical portion <NUM>. The ribs <NUM>, <NUM> extend outwardly from the outer surface of the cylindrical portion <NUM> to act as bearing points against the inner surface of the syringe barrel. The first rib <NUM> is spaced from the second rib <NUM> on the cylindrical portion <NUM>. As shown in <FIG>, a width of the first rib <NUM> is substantially equal to a width of the first contact surface 25a of the inner contour <NUM>. A width of the second rib <NUM> is substantially equal to a width of the second contact surface 25b of the inner contour <NUM>. Since the widths of the ribs <NUM>, <NUM> are substantially equal to the widths of the contact surfaces 25a, 25b of the inner contour <NUM>, a balanced support of the ribs <NUM>, <NUM> against the inner surface of the syringe barrel is achieved. This feature assists in reducing the stopper seal stress concentrations within the stopper <NUM>. 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 stopper <NUM>. The first rib <NUM> and the second rib <NUM> of the cylindrical portion <NUM> form a recess <NUM> on the outer surface of the main body portion <NUM>. The width of the recess <NUM> is substantially equal to the width of the notch <NUM> defined in the inner contour <NUM>. The surface of the recess <NUM> is not in contact with the inner surface of the syringe barrel.

With reference to <FIG>, the stopper <NUM> is shown in use with a plunger rod <NUM> and a syringe barrel <NUM> to form a syringe assembly <NUM>. The stopper <NUM> and the plunger rod <NUM> are adapted for use with the syringe barrel <NUM>. The syringe barrel <NUM> is made of medical-grade plastic or glass. The plunger rod <NUM> is made of a medical-grade plastic. The syringe barrel <NUM> is substantially cylindrical and extends from an open proximal end <NUM> to a distal dispensing end (not shown) from which fluid is ejected during use of the syringe assembly <NUM>. 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 end <NUM> is configured to receive the stopper <NUM> and the plunger rod <NUM>. A flange <NUM> is provided around the circumferential surface of the open end <NUM>. At least one protrusion <NUM> projects inwardly from an inner surface <NUM> of the syringe barrel <NUM>. In one aspect, the protrusion <NUM> extends around the entire circumferential surface of the inner surface <NUM> of the syringe barrel <NUM>. In another aspect, the protrusion <NUM> is provided as a plurality of segments that extend around the circumferential surface of the inner surface <NUM>. The protrusion <NUM> is provided adjacent the open end <NUM> of the syringe barrel <NUM>. It is also contemplated that additional protrusions may be provided on the syringe barrel <NUM> at a distal position from the protrusion <NUM>.

The plunger rod <NUM> is operatively connected to the stopper <NUM>, such that, upon depression of the plunger rod <NUM> in a distal direction, the stopper <NUM> is moved in a distal direction within the syringe barrel <NUM> to direct the fluid out of the dispensing end of the syringe barrel <NUM>. The plunger rod <NUM> includes a main body portion <NUM>, at least one support disk <NUM>, <NUM>, and an attachment member <NUM>. The main body portion <NUM> includes a proximal end having an actuator button or tab (not shown) for moving the plunger rod <NUM> in a distal or proximal direction, and a distal end upon which the support disks <NUM>, <NUM> are formed. The support disks <NUM>, <NUM> extend outwardly from the distal end of the main body portion <NUM> and are substantially circular in shape to correspond to the shape of the syringe barrel <NUM>. It is contemplated, however, that the support disks <NUM>, <NUM> can have alternative shapes that are accommodated in the syringe barrel <NUM>. The first support disk <NUM> is spaced proximally from the second support disk <NUM> on the distal end of the main body portion <NUM>. The support disks <NUM>, <NUM> have substantially the same diameter.

The attachment member <NUM> of the plunger rod <NUM> is provided on the distal end of the plunger rod <NUM> and is spaced distally from the support disks <NUM>, <NUM> on the plunger rod <NUM>. The attachment member <NUM> has a smaller diameter than the support disks <NUM>, <NUM>. The attachment member <NUM> also includes at least one gripping protrusion <NUM> that extends distally from the attachment member <NUM>. The gripping protrusions <NUM> are configured to assist in gripping the stopper <NUM> upon insertion of the attachment member <NUM> into the inner cavity <NUM> of the stopper <NUM>. During use, the plunger rod <NUM> is pushed in a distal direction into the open rearward end <NUM> of the stopper <NUM> so that the attachment member <NUM> is inserted into the inner cavity <NUM> of the stopper <NUM>. As the plunger rod <NUM> is moved in the distal direction, the attachment member <NUM> is moved into the notch <NUM> defined in the inner contour <NUM> of the stopper <NUM>. Using this interconnection between the attachment member <NUM> and the notch <NUM>, the plunger rod <NUM> is retained in the stopper <NUM> such that the stopper <NUM> and plunger rod <NUM> move in conjunction with one another in the syringe barrel <NUM>. It is also contemplated that the plunger rod <NUM> is molded integrally with the stopper <NUM> to form this arrangement. Since the diameter of the notch <NUM> is larger than the diameter of the attachment member <NUM>, the plunger rod <NUM> is permitted to rotate relative to the stopper <NUM>.

As shown in <FIG>, during use of the syringe assembly <NUM>, the plunger rod <NUM> may become misaligned relative to a longitudinal axis A of the syringe assembly <NUM> that extends through the syringe barrel <NUM>, the stopper <NUM>, and the plunger rod <NUM>. Misalignment of the plunger rod <NUM> can occur due to a clinician's thumb load misalignment on the plunger rod <NUM> with respect to the longitudinal axis A of the syringe assembly. Due to a side loading force B on the plunger rod <NUM>, the plunger rod <NUM> may be rotated at an angle α relative to the longitudinal axis A of the syringe assembly <NUM>. Based on this side loading force B, the attachment member <NUM> of the plunger rod <NUM> rotates within the stopper <NUM> causing stress concentrations in parts of the stopper <NUM>. Due to these stress concentrations, the seal between the stopper <NUM> and the syringe barrel <NUM> may be deteriorated or the material of the stopper <NUM> may be worn down under high temperatures. To reduce the effects of the misalignment of the plunger rod <NUM>, the support disks <NUM>, <NUM> are configured to bear against the protrusion <NUM> extending from the inner surface <NUM> of the syringe barrel <NUM>. Upon rotation of the plunger rod <NUM> relative to the longitudinal axis A, the proximal support disk <NUM> is configured to bear against a proximal side of the protrusion <NUM>, and the distal support disk <NUM> is configured to bear against a distal side of the protrusion <NUM>. The protrusion <NUM> acts as a bearing point for the support disks <NUM>, <NUM> to limit the amount of rotation of the plunger rod <NUM> and to reduce the bearing force exerted by the attachment member <NUM> within the stopper <NUM>. Using the protrusion <NUM> as a bearing point causes a significant portion of the side loading force B to be transferred directly from the plunger rod <NUM> to the syringe barrel <NUM> as a barrel reactive loading force C, which results in a reduced loading force that is transferred from the plunger rod <NUM> to the stopper <NUM>. The reduced loading force on the side of the stopper <NUM> reduces asymmetric stopper deflection-induced loading/leakage in the seal between the stopper <NUM> and the syringe barrel <NUM>.

With reference to <FIG>, another aspect of the syringe assembly <NUM> is shown. In this aspect, the syringe barrel <NUM> is the same as that described in the syringe assembly <NUM> of <FIG>. The stopper <NUM> and the plunger rod <NUM> of this aspect, however, are slightly different from the stopper <NUM> and the plunger rod <NUM> of the syringe assembly <NUM> shown in <FIG>. The stopper <NUM> has all of the same features as the stopper <NUM> of <FIG>, except the stopper <NUM> does not include a notch similar to the notch <NUM> in the stopper <NUM>. Instead, the stopper <NUM> defines a plurality of notches <NUM> in an inner contour <NUM> of the stopper <NUM>.

The plunger rod <NUM> includes a main body portion <NUM>, at least one support disk <NUM>, <NUM>, and an attachment member <NUM> configured to connect with the stopper <NUM>. The attachment member <NUM> is provided on a distal end of the plunger rod <NUM> and is distally spaced from the support disks <NUM>, <NUM>. The attachment member <NUM> has a diameter smaller than the support disks <NUM>, <NUM> and an inner cavity of the stopper <NUM>. A plurality of protrusions <NUM> are provided on the circumferential outer surface of the attachment member <NUM> and are configured to connect the attachment member <NUM> within the stopper <NUM>. The protrusions <NUM> are substantially triangular and correspond in shape to the notches <NUM> defined in the stopper <NUM>. Therefore, as the plunger rod <NUM> is moved distally towards the stopper <NUM>, the attachment member <NUM> is inserted into the inner cavity of the stopper <NUM>. As the attachment member <NUM> moves in a distal direction within the inner cavity of the stopper <NUM>, the protrusions <NUM> are moved from a first notch <NUM> to a second notch <NUM> within the stopper <NUM>. The notches <NUM> allow for distal movement of the attachment member <NUM> within the stopper <NUM>, but prevent proximal movement of the attachment member <NUM> out of the stopper <NUM>.

With continued reference to <FIG>, a recess <NUM> is defined in the main body portion <NUM> of the plunger rod <NUM>. The recess <NUM> is defined proximally from the first support disk <NUM>. The recess <NUM> is formed between the first support disk <NUM> and a protrusion <NUM> that extends from the main body portion <NUM>. The recess <NUM> assists in reducing the bearing load transferred to the stopper <NUM> upon misalignment of the plunger rod <NUM> within the syringe barrel <NUM>. Upon assembly of the plunger rod <NUM> in the syringe barrel <NUM>, the plunger rod <NUM> is moved distally within the syringe barrel <NUM> until the protrusion <NUM> on the syringe barrel <NUM> is positioned within the recess <NUM> of the plunger rod <NUM>. Upon misalignment of the plunger rod <NUM> within the syringe barrel <NUM> due to a side bearing load on the plunger rod <NUM>, the plunger rod <NUM> is rotated at an angle α from the longitudinal axis A of the syringe assembly <NUM>. Once the plunger rod <NUM> has been rotated, the distal end of the protrusion <NUM> bears against the proximal side of the protrusion <NUM> of the syringe barrel <NUM>, and a proximal side of the first support disk <NUM> bears against a distal side of the protrusion <NUM>. Further, the second support disk <NUM> may bear against the inner surface of the syringe barrel <NUM>. The protrusions <NUM> of the attachment member <NUM> also bear against the notches <NUM> defined in the stopper <NUM>.

The plunger rod <NUM> also includes a flexible region <NUM> between the first support disk <NUM> and the second support disk <NUM>. In one aspect, the flexible region <NUM> is more flexible than the remaining portions of the plunger rod <NUM>. Due to the flexibility of the flexible region <NUM>, upon misalignment of the plunger rod <NUM>, the angle of misalignment of the attachment member <NUM> within the stopper <NUM> is reduced. In particular, since the flexible region <NUM> is permitted to flex and rotate with the misalignment of the plunger rod <NUM>, the side bearing load is not fully transferred to the attachment portion <NUM>, which rotates a smaller angle than the main body portion <NUM> of the plunger rod <NUM>. In particular, the angle of rotation β of the attachment member <NUM> is less than the angle of rotation α of the main body portion <NUM>. Due to the smaller rotation of the attachment member <NUM> within the stopper <NUM>, the side loading force from the attachment member <NUM> applied to the stopper <NUM> is reduced. This reduction in side loading force on the stopper <NUM> reduces deflection-induced leakage on the sealing surface between the stopper <NUM> and the inner surface of the syringe barrel <NUM>.

With reference to <FIG>, another aspect of a syringe assembly <NUM> is shown. The syringe assembly <NUM> includes a stopper <NUM>, a syringe barrel <NUM>, and a plunger rod <NUM>. The stopper <NUM> is the same stopper <NUM> disclosed in <FIG>. The syringe barrel <NUM> is the same syringe barrel <NUM> disclosed in <FIG> and <FIG>. The plunger rod <NUM>, however, includes several features that are not provided in the plunger rod <NUM> of <FIG> and the plunger rod <NUM> of <FIG>. The plunger rod <NUM> includes at least one outer body member <NUM>, an inner body member <NUM>, at least one support disk <NUM>, <NUM>, and an attachment member <NUM> for connection of the plunger rod <NUM> to the stopper <NUM>. In one aspect, a plurality of outer body member <NUM> surround the inner body member <NUM>. The outer body members <NUM> are made of a rigid plastic material, and the inner body member <NUM> is made of a flexible plastic material. The inner body member <NUM> extends within the outer body member <NUM>. Upon misalignment of the plunger rod <NUM> due to a side bearing load on the plunger rod <NUM>, the inner body member <NUM> is configured to flex to reduce the angle of rotation α of the plunger rod <NUM> within the syringe barrel <NUM>. The outer body members <NUM> remain rigid during rotation of the plunger rod <NUM>. In one aspect, the attachment member <NUM> is formed on a distal end of the inner body member <NUM> so that, due to the flexion of the inner body member <NUM> during misalignment of the plunger rod <NUM>, the amount of side bearing load transferred from the attachment member <NUM> to the stopper <NUM> is reduced. During misalignment of the plunger rod <NUM>, the inner body member <NUM> experiences significant deflection, while the outer body member <NUM> remains rigid. The rigid outer body member <NUM> is designed to transfer a large portion of the side bearing load from the plunger rod <NUM> to the syringe barrel <NUM> through the support disks <NUM>, <NUM> bearing against the protrusion <NUM> on the syringe barrel <NUM>, as described hereinabove.

Claim 1:
A syringe assembly (<NUM>, <NUM>, <NUM>), comprising:
a) a substantially cylindrical syringe barrel (<NUM>) comprising a fluid dispensing end, an open end (<NUM>), and at least one protrusion (<NUM>) adjacent the open end (<NUM>), the at least one protrusion (<NUM>) projecting inwardly from an inner surface (<NUM>) of the syringe barrel (<NUM>);
b) a stopper (<NUM>, <NUM>) configured to be received within the open end (<NUM>) of the syringe barrel (<NUM>); and
c) a plunger rod (<NUM>, <NUM>, <NUM>) having a plunger rod body (<NUM>, <NUM>, <NUM>, <NUM>) extending along a longitudinal axis (A) from a proximal end to a distal end and at least one support disk (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) provided on the distal end thereof,
wherein the at least one support disk (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) on the plunger rod (<NUM>, <NUM>, <NUM>) is configured to bear against the protrusion (<NUM>) of the syringe barrel (<NUM>) upon misalignment of the plunger rod (<NUM>, <NUM>, <NUM>) in the syringe barrel (<NUM>),
characterized in that:
the at least one support disk (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) comprises a first support disk (<NUM>, <NUM>, <NUM>) and a second support disk (<NUM>, <NUM>, <NUM>) on the plunger rod (<NUM>, <NUM>, <NUM>) spaced from one another such that, when the plunger rod (<NUM>, <NUM>, <NUM>) is misaligned in the syringe barrel (<NUM>), the first support disk (<NUM>, <NUM>, <NUM>) bears against a proximal side of the protrusion (<NUM>) at a first load bearing point and the second support disk (<NUM>, <NUM>, <NUM>) bears against a distal side of the protrusion (<NUM>) at a second load bearing point.