Patent Publication Number: US-2018043110-A1

Title: Syringe plunger and pressure indicator

Description:
TECHNICAL FIELD 
     The invention relates to syringes and syringe plungers. More specifically, the invention relates to, but is not limited to, syringes and syringe plungers for monitoring a pressure at which a substance is expelled from a syringe. 
     BACKGROUND 
     The pressure at which a fluid is expelled from a syringe may have significant consequences on the efficacy of the fluid to undertake the task it was designed for. For example, where a medicament is expelled from a syringe into a human or animal subject, if too high a pressure is used then this may damage the medicament such that it is less effective or non-effective. In addition, if a fluid is expelled from a syringe into a human or animal subject at too high a pressure then this may cause significant discomfort for the subject. The acceptable pressure for a given fluid may alter. The acceptable pressure for a given fluid may be dependent on the viscosity of the fluid. 
     Apparatus exist that use a power source and an indicator source that come into contact and emit a beep or colour change, such as U.S. Pat. No. 5,270,685. 
     SUMMARY 
     According to the invention in a first aspect, there is provided a syringe plunger for insertion within a barrel of a syringe for expelling the contents of the barrel from an open end thereof, the syringe plunger comprising: a first portion; a second portion moveable with respect to the first portion if a relative force between the first portion and the second portion exceeds a threshold; and an indicator, wherein translation of movement of the first portion relative to the second portion causes mechanical movement of the indicator. 
     Optionally, the first portion comprises a plunger head and the second portion comprises a plunger shaft. 
     Optionally, the syringe plunger further comprises a resiliently deformable member coupled to the first and second portions. 
     Optionally, the resiliently deformable member is configured to bias the first portion away from the second portion and/or bias the second portion away from the first portion. 
     Optionally, the resiliently deformable member is positioned between the first portion and the second portion and is configured to compress if the relative force between the first portion and the second portion exceeds the threshold. 
     Optionally, the resiliently deformable member is configured to bias the first portion towards the second portion and/or bias the second portion towards the first portion. 
     Optionally, the resiliently deformable member is positioned between the first portion and the second portion and is configured to expand if the relative force between the first portion and the second portion exceeds the threshold. 
     Optionally, the resiliently deformable member comprises one or more arms extending between the first portion and the second portion. 
     Optionally, the one or more arms are configured to flex with respect to the syringe plunger on movement of the first portion with respect to the second portion. 
     Optionally, the indicator is configured to provide a haptic indication to a user of a syringe. 
     Optionally, the indicator comprises an indicator rod configured to contact the user&#39;s skin after movement of the first portion with respect to the second portion. 
     Optionally, the indicator rod is fixed with respect to the second portion. 
     Optionally, the first portion comprises an aperture in a force application surface, and wherein the indicator rod is configured to pass through the aperture after movement of the first portion towards the second portion. 
     According to the invention in a second aspect, there is provided a pressure indicator for coupling to a syringe plunger, the pressure indicator comprising: a first portion; a second portion moveable with respect to the first portion if a relative force between the first portion and the second portion exceeds a threshold; and an indicator, wherein translation of movement of the first portion relative to the second portion causes mechanical movement of the indicator. 
     Optionally, the first portion comprises a plunger head and the second portion is configured to be directly coupled to a syringe plunger. 
     Optionally, the pressure indicator further comprises a resiliently deformable member coupled to the first and second portions. 
     Optionally, the resiliently deformable member is configured to bias the first portion away from the second portion and/or bias the second portion away from the first portion. 
     Optionally, the resiliently deformable member is positioned between the first portion and the second portion and is configured to compress if the relative force between the first portion and the second portion exceeds the threshold. 
     Optionally, the resiliently deformable member is configured to bias the first portion towards the second portion and/or bias the second portion towards the first portion. 
     Optionally, the resiliently deformable member is positioned between the first portion and the second portion and is configured to expand if the relative force between the first portion and the second portion exceeds the threshold. 
     Optionally, the resiliently deformable member comprises one or more arms extending between the first portion and the second portion. 
     Optionally, the one or more arms are configured to flex with respect to the syringe plunger on movement of the first portion with respect to the second portion. 
     Optionally, the indicator is configured to provide a haptic indication to a user of a syringe. 
     Optionally, the indicator comprises an indicator rod configured to contact the user&#39;s skin after movement of the first portion with respect to the second portion. 
     Optionally, the indicator rod is fixed with respect to the second portion. 
     Optionally, the first portion comprises an aperture in a force application surface, and wherein the indicator rod is configured to pass through the aperture after movement of the first portion with respect to the second portion. 
     According to the invention in a third aspect, there is provided a syringe plunger comprising a pressure indicator described above. 
     According to the invention in a fourth aspect, there is provided a syringe comprising a barrel and a syringe plunger as described above. 
     According to the invention in a fifth aspect, there is provided a kit of parts comprising: a first portion of a syringe plunger; a second portion of a syringe plunger; and an indicator, wherein the first portion is configured to be coupled to the second portion such that it is moveable with respect to the second portion if a relative force between the first portion and the second portion exceeds a threshold, and wherein translation of movement of the first portion relative to the second portion causes mechanical movement of the indicator. 
     Optionally, the indicator forms part of one of the first portion and the second portion. 
     Optionally, the kit of parts further comprises a resiliently deformable member coupled to the first and second portions. 
     Optionally, the resiliently deformable member forms part of the first portion and/or the second portion. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIGS. 1 a - b    show perspective views of a syringe plunger; 
         FIG. 2 a    shows a side elevation of a syringe plunger in an extended state; 
         FIG. 2 b    shows a section through a syringe plunger in an extended state; 
         FIG. 3 a    shows a side elevation of a syringe plunger in a compressed state; 
         FIG. 3 b    shows a section through a syringe plunger in a compressed state; 
         FIGS. 4 a - b    show perspective views of a pressure monitor for fitting to a syringe plunger; 
         FIG. 5 a    shows a side elevation of a pressure monitor in an extended state; 
         FIG. 5 b    shows a section through a pressure monitor in an extended state; 
         FIG. 6 a    shows a side elevation of a pressure monitor in a compressed state; 
         FIG. 6 b    shows a section through a pressure monitor in a compressed state; 
         FIGS. 7 a - b    show perspective views of a pressure monitor for fitting to a syringe plunger; 
         FIG. 8 a    shows a side elevation of a pressure monitor in an extended state; 
         FIG. 8 b    shows a section through a pressure monitor in an extended state; 
         FIG. 9 a    shows a side elevation of a pressure monitor in a compressed state; 
         FIG. 9 b    shows a section through a pressure monitor in a compressed state; and 
         FIG. 10 a - b    show perspective views of a syringe comprising a syringe plunger. 
     
    
    
     DETAILED DESCRIPTION 
     Generally disclosed herein are methods and apparatus for monitoring pressure within a barrel of a syringe. The pressure within the barrel typically increases as a user depresses a syringe plunger. The methods and apparatus disclosed comprise means to indicate to the user if the pressure within the barrel exceeds a threshold value. 
     Referring to  FIGS. 1 a    and  1   b,  a syringe plunger  100  is shown. The syringe plunger  100  comprises a first portion  102 , which may be a plunger head, and a second portion  104 , which may be a plunger shaft. The terms plunger head and plunger shaft are used throughout this document, but it should be understood that the first and second portions  102 ,  104  of the syringe plunger  100  may comprise other features. For example, the separation between the first and second portions  102 ,  104  may be at a point along the plunger shaft. 
     The plunger head  102  is moveable with respect to the plunger shaft  104  if a relative force between the plunger head  12  and the plunger shaft  104  exceeds a threshold value. That is, if a first force is applied to the plunger head  102 , say from a user&#39;s finger or thumb while operating a syringe, and a second force is applied to the plunger shaft, say due to an increase in pressure inside a barrel of the syringe, if the resultant force exceeds a threshold value then the plunger head  102  will move with respect to the plunger shaft  104 . In exemplary syringe plungers  100 , the plunger head  102  moves towards the plunger shaft  104 . 
     The plunger shaft  104  in  FIGS. 1-3  has a substantially circular cross section, although other cross sections are possible. For example, the plunger shaft  104  may have a cross shaped cross section. In addition, the plunger shaft may comprise a bung connector  105  for connection to a bung that travels in the barrel of the syringe to expel the contents of the syringe from an open end of the barrel. In exemplary syringe plungers, the bung connector  105  may comprise a threaded portion for securing the bung to the syringe plunger  100 . In other arrangements, the bung may be connected to the syringe plunger as part of the manufacturing process, or the plunger shaft  104  may butt up against the bung without any connection of the plunger shaft  104  to the bung. 
     In the exemplary syringe plunger of  FIGS. 1-3 , at least one resiliently deformable member is positioned between the plunger head  102  and the plunger shaft  104 . However, the resiliently deformable member is optional, as other means may be employed to provide a coupling between the plunger head  102  and the plunger shaft  104  allowing movement of the plunger head  102  towards the plunger shaft  104  if the relative force between them exceeds a threshold. For example, there may be a friction engagement between the plunger head  102  and the plunger shaft  104  that is configured to be overcome if the relative force exceeds a threshold. Alternatively, a ratchet and pawl arrangement may be used. Other options are available that are not elaborated on here. 
     In the exemplary syringe plunger of  FIGS. 1-3 , the resiliently deformable member comprises a plurality of arms  106   a - b.  The arms  106   a - b  are positioned between the plunger head  102  and the plunger shaft  104 . In exemplary syringe plungers  100 , the arms  106   a - b  are connected to the plunger head  102  and/or the plunger shaft  104 . In other exemplary syringe plungers  100 , the arms  106   a - b  may form part of the plunger head  102  and/or the plunger shaft  104 . The plunger shaft  104  comprises a lip  108  at a head end thereof. The lip provides a top surface of the plunger shaft  104  that the resilient member may interact with and/or be connected to. 
     The arms  106   a - b  are configured to bow or flex outwardly with respect to a longitudinal axis of the syringe plunger  100  on movement of the plunger head  102  towards the plunger shaft  104 . In the exemplary syringe plunger  100  of  FIGS. 1-3 , the arms  106   a - b  comprise first and second portions with a bend in between to form a basic spring. The arms  106   a - d  have the bend at a halfway point along the entire length of the arm, although this is not essential. In other exemplary syringe plungers, the arms may comprise one continuous portion that is bowed perpendicular to the longitudinal axis between the plunger head  102  and the plunger shaft  104  so as to form a basic spring. The arms are manufactured from a suitable material such that they have sufficient elasticity to return towards their original shape if a relative force between the plunger head  102  and the plunger shaft  104  is reduced below a threshold. 
     It is noted that the resiliently deformable member may be provided by any other suitable means, such as a helical spring. 
     The syringe plunger  100  also comprises an indicator  110 . In the exemplary syringe plunger  100  of  FIGS. 1-3 , the indicator comprises an indicator rod  112  and an aperture  114  in the plunger head  102 . The indicator rod  112  is configured to pass through the aperture  114  to protrude from an upper (or force application) surface  116  of the plunger head  102  after the plunger head  102  moves towards the plunger shaft  104 . That is, the movement of the plunger head  102  causes the aperture  114  to pass down over the indicator rod  112 . In this way, the movement of the plunger head  102  is translated into a mechanical actuation or movement of the indicator  110 . The indicator rod  114  may be connected to the plunger shaft  104  and, in specific exemplary syringe plungers, may be formed as part of the plunger shaft  104 . 
     In the case of the indicator  110 , the movement of the plunger head  102  is mechanically translated into mechanical operation of the indicator  110  and this may also be the case with other exemplary arrangements. The indicator may comprise other features that are operational based on direct or indirect mechanical translation to provide an indication to a user. The indicator  110  provides a haptic response in that the indicator rod is configured to contact a user&#39;s skin, probably on the thumb or finger. However, other indicators may provide an audible indication, such as the clicking of a ratchet and pawl, or a visual indication, such as a colour change or the like. 
       FIGS. 2 a  and 2 b    show a side elevation of the syringe plunger  100  and a longitudinal section through the syringe plunger  100 , respectively. In  FIGS. 2 a  and 2 b   , the syringe plunger  100  is in an extended state, in that the plunger head  102  is biased away from the plunger shaft  104  as no force is applied to either. 
     As a force F 1  is applied, most likely by a user&#39;s thumb, to the plunger head  102 , the syringe plunger  100  will travel within the barrel of a syringe (not shown) to expel the contents of the barrel from the opposite and open end. The open end of the barrel typically has an aperture that has a smaller diameter than the internal diameter of the barrel and the pressure within the barrel therefore increases with the force F 1  that is applied to the plunger head  102 . This results in a force F 2  opposing the force F 1 . If the resultant force (i.e. the addition of F 1  and F 2 ) is greater than a threshold value then the plunger head  102  begins to move towards the plunger shaft  104 , as shown in  FIGS. 3 a  and 3 b   , which show a side elevation of the syringe plunger  100  and a longitudinal section through the syringe plunger  100 , respectively. In  FIGS. 3 a  and 3 b   , the syringe plunger  100  is shown in a compressed state, in that the resultant force has exceeded the threshold value. The threshold value may be determined by the resilient member (e.g. the arms  106   a - b ) or the other coupling of the plunger head  102  and the plunger shaft  104 . 
     As shown in  FIGS. 3 a  and 3 b   , the plunger head  102  has moved towards the plunger shaft  104 . The arms  106   a - b  have flexed or bowed outwardly with respect to the syringe plunger  100 . The indicator rod  112  has passed through the aperture  114  and protrudes from a surface  116  of the plunger head  102 . As such, the indicator rod  114  contacts the skin of the user and thereby produces a haptic indication. As stated previously, other indications, such as audible or visual indications are possible. 
     In exemplary syringe plungers, the indicator rod  112  may be tapered towards the plunger head  102  such that the haptic indication is more obvious to the user. That is, by reducing the cross sectional area of the indicator rod  112  at the plunger head end, the amount of pressure applied to the user&#39;s skin is increased. 
     If a user increases the force F 1  too much, i.e. they press too hard on the plunger head  102 , then the indicator rod  112  will contact the skin of the user and indicate that they should reduce the force F 1 . As the force F 1  is reduced, the resiliently deformable member expands towards its resting state and the plunger head  102  moves away from the plunger shaft  104  and the indicator rod  112  recedes back within the aperture  114  and no longer protrudes from the surface  116 . This indicates to the user that the force F 1  is now below the required force. It is noted that the return of the indicator is not essential for the operation of the syringe plunger. 
     The haptic response provided by the indicator advantageously provides a steady indication that is not sudden and is not likely to shock the user. This is advantageous as shocks to users of syringes may be dangerous for any subject on which the syringe is being used. In addition, the mechanical translation of the movement of the plunger head  102  with respect to the plunger shaft  104  means that a simple apparatus may be formed. Indeed, in exemplary embodiments, the syringe plunger may be formed of a single piece and may be moulded plastics material. The inventor has appreciated that the mechanical movement of the plunger head may provide the power to operate the indicator. A further advantage is that the indicator may provide an indication to the user that the syringe plunger has completed its travel within the barrel of the syringe and, therefore that all of the fluid contained in the barrel has been expelled from the open end. As the syringe plunger (or the bung) contacts the end of the barrel, the plunger head will begin to move towards the plunger shaft and the indicator will indicate to the user that the syringe plunger has reached the limit of its travel. 
       FIGS. 4-9  show exemplary pressure indicators  400 ,  700  for coupling to a syringe plunger. The pressure indicators  400 ,  700  comprise the same or similar features as the syringe plunger  100 . These have been given corresponding reference numerals and are not explained in detail again here. It is noted that any corresponding features between the syringe plunger  100  and the pressure indicators  400 ,  700  that are described as optional in respect of the syringe plunger are also optional in respect of the pressure indicators. In addition, the description of the pressure indicators  400 ,  700  is given in detail with respect to the exemplary pressure indicators  400 ,  700  shown in  FIGS. 4-9 , however, the features of the pressure indicators  400 ,  700  that correspond to the features of the syringe plunger  100  may also be broadly defined as in the description above. For the avoidance of doubt, the description of the syringe plunger  100  above relates equally to the corresponding features of the pressure indicators  400 ,  700 . 
     The pressure indicators  400 ,  700  comprise a first portion  402 ,  702  and a second portion  404 ,  704 . The first portion  402 ,  702  may be the plunger head and the second portion  404 ,  704  may be a coupling means that is defined in more detail below. A resiliently deformable member (e.g. arms  406   a - b  and  706   a - b ) is positioned between the plunger head  402 ,  702  and the coupling means  404 ,  704 . An indicator rod  412 ,  712  is configured to pass through an aperture  414 ,  714 . 
     The second portion may comprise a coupling means  404 ,  704  for coupling the pressure indicator  400 ,  700  to a known syringe plunger. In this way, the pressure indicator may be retro-fitted to an existing syringe plunger. 
     The coupling means  404  comprises a slot  418  in a retaining wall  420 . Syringe plungers typically comprise a shaft and a head, wherein the head has a greater diameter than the shaft such that a lip is formed all around the circumference of the top of the shaft. In the coupling means  404 , the shaft of the syringe plunger passes through the slot  418  and the lip formed by the head is held behind the retaining wall  420 . There may additionally be a locking means to hold the syringe plunger in a coupled configuration with the coupling means. 
     The coupling means  704  comprises one or more resiliently deformable members  718  comprises lugs  720 . The deformable members  718  are configured to deform outwards as they pass over a head of a syringe plunger and then to snap back to engage the lugs  720  under the lip formed by the head of the syringe plunger. The exemplary pressure indicator of  FIGS. 7-9  shows two resiliently deformable members, but there may be more than two, for example three, resiliently deformable members. 
     It is noted that the coupling means may take any of numerous forms and should not be limited to the examples shown in  FIGS. 7-9  and described above. 
       FIGS. 5, 6, 8 and 9  show operation of the pressure indicators  400 ,  700 . This is explained above in respect of the syringe plunger  100  and is not discussed again here. 
     The syringe plunger may be moulded from a single piece of plastics material. Alternatively, the syringe plunger may be provided as a kit of a number of separate parts. The kit may comprise the first portion, the second portion and the indicator. In exemplary kits, the indicator may be formed as part of the first portion or the second portion. The kit may also comprise the resiliently deformable member, which may be formed as part of the first portion and/or the second portion. 
       FIGS. 10 a  and 10 b    show perspective views of a syringe  1000  comprising a syringe plunger that is extended ( FIG. 10 a   ) and at least partially inserted ( FIG. 10 b   ) into a barrel of the syringe. The syringe comprises a syringe plunger as described herein. The syringe plunger may comprise a pressure indicator as a built in feature or may have a pressure indicator retro-fitted. 
     The skilled person will be able to envisage other embodiments of the invention without departing from the scope of the appended claims.