Patent Description:
When a user of a medical syringe administers a substance, it is common, in particular within certain areas of treatment, to distribute the total volume carried by the syringe over an area. Some examples of such areas of treatment are dermatology, plastic surgery, cosmetic surgery, and odontology. The distribution is for instance done by inserting the needle of the syringe just beneath and approximately in parallel with the skin surface and then administering the substance while withdrawing the needle. Another way is to administer the substance at several anatomic locations within a limited area, i.e. to administer a fraction of the total volume at each location. In both these, and other, methods of distributing the substance it is an advantage if the syringe is provided with some kind of dosing aid, which aids the user in knowing how large fraction of the total volume of the substance is administered at each location or per time unit. Conventionally, the syringe barrel is provided with a gradation scale, and the user observes the position of the plunger along the scale. However, the scale is difficult to see and might sometimes be partly or fully covered by a sticker, or the like, and the syringe is at times held at an angle where the scale is hidden. Another practical problem with gradation scales provided on the syringe barrel is that sometimes very small amounts of a substance shall be provided which requires correspondingly small movements of the plunger in the barrel which movements can be hard to detect by a user. Further, a main problem with the use of a gradation scale as such is the fact that a user has to observe it during injection which means that a distraction of attention arises when the user has to look at the gradation scale every now and then instead of focusing on the course of events at the treatment area. Mechanic or electronic injectors providing an accurate dosing have been used, but they are more expensive and heavier than syringes and many users prefer to hold the injection device in the way that a conventional syringe is held. Further, most injectors do not allow a user to perform needle aspiration prior to injection of the medicament. This is a serious drawback since it does not allow a user to realize that injection has been done in a blood vessel. Also, this prevents the use of substances that need to be drawn up into the barrel of the syringe from a reservoir containing the substance prior to injection.

An effort to provide a syringe with a dosing aid is disclosed in <CIT>, where an engagement member is provided on the finger grip and engages with a structure of the plunger rod. Other examples of syringes are described in the following documents: <CIT> relates to a syringe with alternative selectable graduations. <CIT> relates to a syringe with actinic ray blocking stripe. <CIT> relates to hypodermic syringes. <CIT> relates to a syringe for injection of hypodermic or intravenous injections.

It would be advantageous to provide a syringe with user friendly means that informs and provides feedback to a user about the injected amount or an injection rate and which also has a simple construction.

To better address at least some of these concerns, the invention comprises a syringe as defined in claim <NUM>. Additional features of preferred embodiments of the invention are specified in the dependent claims. In a first aspect of the invention it is presented a syringe comprising a barrel and a plunger which is moveably arranged within the barrel. The syringe further comprises a plunger rod intended for driving the plunger in a direction parallel to a longitudinal direction of the plunger rod for expelling or drawing up of a substance. Further, an engagement member is arranged at the barrel to engage with a grooved surface provided on the plunger rod such that feedback is given to a user as the plunger is moved relative to the barrel for driving the plunger. The barrel and the engagement member are arranged relative to each other such that the engagement member, due to the engagement and interaction with the grooved surface of the plunger rod, will move solely in a direction generally perpendicular to a longitudinal direction of the plunger rod as the plunger rod is moved relative to the barrel for driving the plunger. The engagement member comprises a main part and a protruding element protruding from the main part for engaging a grooved surface of the plunger rod. The extension of the protruding element in a direction parallel to a longitudinal direction of the plunger rod is larger than the thickness of the engagement member perpendicularly to the longitudinal direction and an end portion of the protruding element is provided with a tapering in the longitudinal direction. This construction will provide for an improved dosing accuracy. With the solution presented in <CIT> the engagement member consists of a flat member lying on top of the finger grip, see e.g. <FIG> and <FIG> in that prior art document. A major drawback with that prior art solution has been identified where a user intends to administer e.g. botulinum toxin. Typically, botulinum toxin has to be drawn up into the barrel of an empty syringe from a reservoir prior to injection. When this is done with a syringe as described in <CIT>, at the end of the draw up operation, there is a high likelihood that the flat engagement member will be situated in a position where it is slightly bent upwards resting on a ridge of the grooved surface of the plunger rod. The engagement member of the prior art will thus be biased in the wrong direction. Normally, one click from the engagement member represents a certain dose of the substance in the barrel corresponding to the distance between two adjacent ridges of the grooved surface of the plunger rod. However, the fact that the starting position of the engagement member of <CIT> will be one where it is bent slightly upwards, the plunger rod will have to travel much farther than what was initially intended before the first click-sound is generated by the engagement member. The engagement member will in this case have to move first from its position bent slightly upwards towards a position where it is horizontal and thereafter towards a position where it is bent slightly downwards before the first click-sound will be generated. Continued movement will of course cause repeated click-sounds caused by the interaction between the engagement member and the grooved surface of the plunger rod having an intended dose. However, tests have proven that a first dose with such prior art constructions can be up to three time larger than actually intended and such overdosing can in certain situations be catastrophic for patients causing e.g. unintended muscle paralysis. It should also be noted, that these continued click-sounds are generated with the engagement member of that prior art solution positioned in a position where it at all times is more or less bent downwardly. This means that during injection when the engagement member passes over a ridge of the grooved surface of the moving plunger rod and hits an adjacent ridge, thus creating the click-sound, it will most likely never assume a horizontal position. Therefore, another situation where a too large dosis can be expelled by a syringe according to that prior art solution is when the click function is switched-off during e.g. aspiration or draw-up of a substance or if it for some reason is switched-off during treatment. If the click function thereafter is resumed again, the engagement member will be introduced to the grooved surface in a neutral position perpendicular to the longitudinal direction of the plunger rod and will therefore require the plunger rod to travel farther the initially intended before a first click sound will be generated. The same applies to a situation where a pre-filled syringe having an engagement member as described in that prior art is used. In this case the engagement member will be positioned in a position perpendicular to the longitudinal direction of the plunger rod and will also require the plunger rod to travel farther the initially intended before a first click sound will be generated. With the solution of the present invention, where the engagement member is arranged to only travel in a direction perpendicular to the longitudinal direction of the plunger rod, this drawback is avoided. Similar to <CIT>, in the present invention the distance between two ridges of the grooved surface of the plunger rod corresponds to a certain dose and is represented by one click during use. In contrast to that prior art solution, with a syringe according to the present invention the first click after the substance has been drawn up represents no more than one dose. This since the engagement member of the present invention will never require any initial travel to relieve a bias in the wrong direction such as it is required by the prior art solutions. This since the engagement member of the present invention will never, as in the prior art solution, merely travel with the grooved surface of the pluinger rod towards a position where the click-sound generating movement of the engagement member is even initiated. Instead, the engagement member of the present invention always reciprocates between an outer and an inner end position irrespective of the direction in which the plunger rod is moved or has previously been moved, e.g. after draw up of a substance. Hence, an overdosing as it is risked by the prior art solutions is not possible with the present invention.

In accordance with an embodiment of the syringe, the engagement member is arranged within the barrel.

In accordance with an embodiment of the syringe, the engagement member is arranged at the barrel immovable in a direction parallel to the longitudinal direction of the plunger rod. By avoiding any play or similar between the barrel and the engagement member the dosing accuracy is improved.

In accordance with an embodiment of the syringe, the immovable arrangement of the engagement member at the barrel is achieved by a tight fit. A tight fit between the two parts is a simple yet reliable way of arranging them immovably to each other since no separate attaching members or means are required.

In accordance with an embodiment of the syringe, the immovable arrangement of the engagement member at the barrel is achieved by a snap locking. A snap-lock is another simple and reliable solution which is easy to manufacture and provides for simple assembly of the syringe.

In accordance with an embodiment of the syringe, the immovable arrangement of the engagement member at the barrel is achieved by a cap arranged at the barrel. A separate cap can also be provided to secure the engagement member to the barrel.

In accordance with an embodiment of the syringe, the engagement member comprises a main part having a circular or semi-circular shape and a protruding element protruding from the main part for engaging the grooved surface of the plunger rod. A circular or semi-circular engagement member encircling the plunger rod at least partly and having an inwardly protruding element that engages the grooved surface of the plunger rod is simple to arranged within a barrel which is typically circular in cross-section and it also easy to provide such engagement member with a suitable prestress in a direction perpendicular to the longitudinal direction of the plunger rod such that the protruding element will at all time abut the grooved surface of the plunger rod.

In accordance with an embodiment of the syringe, the engagement member comprises a main part being generally plate shaped and a protruding element protruding from the main part for engaging the grooved surface of the plunger rod. A plate shaped main part having a protrusion thereon provides for a very simple manufacturing and assembly.

In accordance with an embodiment of the syringe, the protruding element is connected to the main part along an edge of the protruding element. This edge extends generally in parallel with the longitudinal direction of the plunger rod. This arrangement will provide a high degree of rigidity such that any deflection of the protruding element in a direction parallel to the longitudinal direction of the plunger rod can be avoided completely or at least to a large extent.

In accordance with an embodiment of the syringe, the protruding element is folded from the main part of the engagement member along the edge. By folding the protruding element from the main part, a strong and reliable construction is obtained.

In accordance with an embodiment of the syringe, the protruding element is punched out from the main part of the engagement member.

In accordance with an embodiment of the syringe, the engagement member comprises a main part having a semi-circular shape and a protruding element, wherein the protruding element is arranged as an extension of the main part and having a narrower bending radius than said main part such that an end of the protruding element engages the grooved surface of the plunger rod. By curving the protruding element with a radius that is sufficiently narrow, the protruding member will be directed towards and engaging with the grooved surface of the plunger rod.

In accordance with an embodiment of the syringe, the engagement member comprises a main part having a semi-circular shape and a protruding element for engaging the grooved surface of the plunger rod, wherein the protruding element is arranged as an extension of the main part by folding along an edge generally parallel to the longitudinal direction of the plunger rod.

In accordance with an embodiment of the syringe, the engagement member is arranged in a compartment of the barrel being generally shaped as an annulus, wherein the plunger rod extends through the inner circle of the annulus and wherein the engagement member can engage the grooved surface of the plunger rod through an opening in the compartment.

In accordance with an embodiment of the syringe, the plate shaped main part of the engagement member is attached to the barrel along two edges of the plate shaped main part. By attaching the plate shaped member along two, possibly opposed, edges the main part can bias the protruding member towards the grooved surface of the plunger rod. Further, this will allow the plate shaped main part to act as an acoustic membrane enhancing the click sound of the syringe.

In accordance with an embodiment of the syringe, an end portion of the engagement member engaging with the grooved surface of the plunger rod has a tapering such that feedback is given to a user irrespective of the moving direction of the plunger rod. This is an important aspect since it is often desirable to have the click sound also during aspiration and draw up of substances. Also, this provides the possibility of providing a syringe that always assumes a given start position. For example, when a substance has been drawn up into the barrel of the syringe and the user releases the grip on the plunger rod, the tapered end portion can cause the plunger rod to move slightly until the tapered end reaches a bottom of the of the grooved surface of the plunger rod. This of course also requires that a sufficient preload is placed on the protruding member from e.g. the main part of the engagement member. This action can be further alleviated by choosing a suitable geometry and surface material of the grooved surface of the plunger rod.

These and other aspects and advantages of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

The invention will now be described in more detail and with reference to the appended drawings in which:.

An embodiment of the syringe <NUM>, as most schematically illustrated in <FIG>, comprises a barrel <NUM>, a plunger <NUM> and a plunger rod <NUM> arranged to drive the plunger <NUM> during use of the syringe <NUM> and is provided with a thumb plate <NUM> for activation of the plunger rod <NUM>. The plunger rod <NUM> can be attached to the plunger <NUM> by any suitable means as would be obvious to the skilled person. A threaded connection would for example be suitable since it allows for the plunger <NUM> to be moved in both directions, i.e. pushed and pulled through the barrel <NUM>, which is not always possible with other connecting means. The syringe <NUM> further comprises a needle <NUM> and the barrel <NUM> can be provided with a finger grip <NUM>. The plunger rod <NUM> is provided with a grooved outer surface <NUM> having a plurality of ridges and valleys provided in an alternating manner along a length of the plunger rod <NUM>. This can be achieved by providing the plunger rod <NUM> with a large number of narrow grooves, defined by narrow flanges. Different shapes of the flanges can be imagined and chosen depending on the requirements. For example, they can protrude from the plunger rod perpendicularly to a longitudinal axis of the plunger rod. Another possibility is to provide such flanges having a wedge shape that is symmetrical about a plane that extends perpendicularly to a longitudinal axis of the plunger rod through the outer tip of the flange. Another possibility is a non-symmetrical wedge shape. Yet another possible shape is best disclosed in <FIG> and can be described to correspond to a plurality of frustums stacked on top of each other. The pitch of the flanges, i.e. the centre distance between two adjacent flanges, is typically between <NUM>,<NUM> and <NUM>. The pitch is typically chosen depending on the substance to be injected and the size, i.e. the diameter, of the barrel <NUM> of the syringe <NUM>. A narrow barrel <NUM> means that a smaller amount is expelled from the syringe <NUM> for a given travel of the plunger <NUM> and accordingly a larger pitch of the flanges has to be used to represent a certain amount of injected substance. Further, the plunger rod <NUM> could be carried out as a hollow rod. The plunger rod <NUM> could be manufactured by injection moulding and if the plunger rod <NUM> is made solid, cooling of the product would be rather time consuming in order to avoid problems with shrinkage which in turn would cause tolerance problems of the flanges, i.e. varying distances between flanges and varying protrusion of the flanges. Such tolerance variations are of course unwanted and often not tolerable. Therefore, the plunger rod <NUM> could be made hollow which saves material and remedies the cooling and tolerance problems. The syringe <NUM> further comprises a compartment <NUM> generally defined by an outer cylindrical element <NUM> and an inner cylindrical element <NUM> and an engagement member <NUM> arranged within said compartment <NUM>. Of course, other shapes of the compartment <NUM> are imaginable, e.g. square, elliptic etc. In the embodiment shown in <FIG>, the engagement member <NUM> comprises a semi-circular element <NUM>, a protruding element <NUM> and an adjusting member <NUM>. The engagement member <NUM> is arranged within the compartment <NUM> in such manner that the protruding element <NUM> reaches through an opening <NUM> in the inner cylindrical element <NUM> and engages with the grooved surface <NUM> of the plunger rod <NUM>. Typically, the engagement member <NUM> is retained within compartment <NUM> such that it can move to a certain degree in a direction perpendicular to the longitudinal direction of the plunger rod <NUM> but is prevented from any movement in a direction parallel to the longitudinal direction of the plunger rod <NUM>. This retention can be provided in a number of ways. For example a cap <NUM>, as is shown in <FIG>, can be provided such that the engagement member <NUM> is free to move within compartment <NUM> in a direction perpendicular to the longitudinal direction of the plunger rod <NUM> but is prevented from any movement in a direction parallel to the longitudinal direction of the plunger rod <NUM>. Other suitable means are slots into which the engagement member <NUM> can be inserted with a tight or press fit or snap-lock means that will lock the engagement member <NUM> in place. When the user is administering the medical substance, and thus pushes the plunger rod <NUM> further into the barrel <NUM>, a sound is generated by the flanges passing the engagement member <NUM>, causing the engagement member <NUM> to move in a direction perpendicular to the longitudinal direction of the plunger rod <NUM> which gives feedback to the user in the form of a click-sound and possibly also in the form of a tactile feedback. It is easy for the user to learn to associate the click-sound with the amount of medical substance that is administered, and also to associate the sound with a certain injection rate, thereby allowing the user to accurately dose the substance and distribute it as desired. The motion pattern of the engagement member <NUM> of the present invention has a major advantage in that one click-sound always represents the initially intended dose corresponding to one click. In some of the prior art solutions, there is a problem with engagement members that during aspiration or draw up of a substance will be biased in an opposite direction and will during injection of a first dose require the plunger rod to travel much farther than initially intended for one click before the first click-sound is generated. It has been shown in tests that the first dose in such prior art syringes can be up to three times larger than intended. Such overdosing is of course highly unwanted and can in certain cases have devastating effects. With the solution of the present invention, common to all embodiments of this patent application, the engagement member <NUM> always reciprocates back and forth between two given turning points irrespective of the direction in which the plunger rod <NUM> is driving the plunger <NUM> and no biasing in a wrong direction of the engagement member <NUM> is done, instead the protruding element <NUM> of the engagement member <NUM> always slides over the grooved surface <NUM> of the plunger rod <NUM> as the plunger rod <NUM> moves. This is probably best shown in <FIG>. This stands in sharp contrast to the mentioned prior art solution where the engagement member during a first part of a first dose merely rests on the grooved surface of the plunger rod and travels with it until it eventually reaches a position where the sliding movement of the engagement member and the actual click-function is initiated. In the embodiment shown in <FIG>, the protruding element <NUM> of the engagement member <NUM> is folded from the main part <NUM>. The engagement member <NUM> is typically made from metal having a thickness of ~<NUM>,<NUM>-<NUM>,<NUM>. The height of the protruding element <NUM>, i.e. the extension in a direction parallel to the longitudinal direction of the plunger rod <NUM>, is chosen to be large enough to avoid that the protruding element <NUM> is bent in a direction parallel to the longitudinal axis of plunger rod <NUM>, during use. Instead the moving of plunger rod <NUM> and the interaction between the grooved surface <NUM> and the protruding element <NUM> should only bring about a movement of the protruding element <NUM>, and thus the whole engagement member <NUM>, in a direction perpendicular to the longitudinal axis of plunger rod <NUM>. Typically, the height of the protruding element <NUM> would lie between <NUM>-<NUM>. To this end, it could also be suitable to provide the end portion <NUM> with a tapering. A tapering of the end portion <NUM> can, in combination with a suitable preload of the main part <NUM> acting as a spring forcing the protruding element <NUM> against the grooved surface <NUM>, also have the effect that when a user releases the force exerted on the plunger rod <NUM>, during for example draw up of a substance, the plunger rod <NUM> will assume a position in which the tapered end portion <NUM> rests at the bottom between two ridges of the grooved surface <NUM>. This could be especially interesting after draw up of a substance into barrel <NUM> since the dose of the first click in such case will be neither larger, nor smaller than initially intended. In any case, the pre-stress of main part <NUM> shall be large enough to make sure that the protruding element <NUM> always rests against the grooved surface <NUM> such that a click-sound is always generated when the plunger rod is moved. In the embodiment shown in <FIG>, the click-function can be switched off by pressing adjusting member <NUM> in either direction, thus causing engagement member <NUM> to rotate within compartment <NUM>. This will have the effect that protruding element <NUM> leaves the opening <NUM> and will thus no longer be in contact with the grooved surface <NUM>.

In the embodiment shown in <FIG>, the engagement member <NUM> is provided in the form of a plate shaped member having a main part <NUM> and a protruding element <NUM> folded out from the main part <NUM>. Regarding the thickness of the engagement member <NUM> and the height of protruding element <NUM>, the same applies as described in connection with <FIG>. Of course, there are other suitable ways in which the protruding element <NUM> can be achieved. For example attaching it by welding or gluing; providing a welding spark on the surface of the main part <NUM>; attaching a sufficiently stiff dowel or pin to the main part <NUM> etc. The engagement member <NUM> of <FIG> can be attached within the compartment <NUM> by means of slots arranged within the compartment <NUM> (shown in <FIG> but without reference numerals) that are either narrow enough to provide a tight or press fit with two opposing edges of the plate shaped engagement member <NUM> or the slots may be provided with snap-locks locking the engagement member <NUM> in place. A tight or press fit or snap-lock both have the advantage of being simple and allowing for cheap manufacture. Other means such as gluing, heat welding or the use of separate attachment means are of course also imaginable. The main thing is that the engagement member <NUM> is prevented from moving in a direction parallel with the longitudinal direction of the plunger rod <NUM>. This of course applies for all embodiments of the present invention.

In the embodiment shown in <FIG>, the engagement member <NUM> is provided in the form of a continuous semi-circular element. Instead of being folded out from the main part <NUM>, the protruding element <NUM> in this embodiment is created as a continuation of the main part <NUM> but having a narrower bending radius such that end portion <NUM> will abut the grooved surface <NUM> of the plunger rod <NUM>. It should be noted that the protruding element <NUM> does not have to be bent as far as pointing in a direction of a radius of the plunger rod <NUM>; it is enough that the end portion <NUM> of protruding element <NUM> is directed in a direction of a chord of a cross-section of the plunger rod <NUM>. As in <FIG>, the dimensions and materials mentioned in connection with <FIG> apply here as well.

<FIG> disclose cross-sectional side views of the embodiment from <FIG> where the reciprocal movement of the engagement member <NUM> due to a movement of plunger rod <NUM> is illustrated. As can easily be understood from these figures, the drawback with a bias in a wrong direction of the engagement member known from prior art solutions is avoided with the solution of the present invention. Further, in <FIG> one imaginable shape of the flanges of the grooved surface <NUM> is described. This is, however, only an example as many other shapes are also conceivable within the scope of the appended claims.

<FIG> shows a perspective view of a syringe according to an embodiment of the present invention. Here, the retention of the engagement member <NUM> (not shown) is achieved by means of a cap <NUM>. As described earlier, this retention can be done in many other manners as well.

The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope of the claims.

Claim 1:
Syringe (<NUM>) comprising a barrel (<NUM>), a plunger (<NUM>) moveably arranged within said barrel (<NUM>) and a plunger rod (<NUM>) for driving said plunger (<NUM>), and an engagement member (<NUM>) arranged at the barrel (<NUM>) to engage with a grooved surface (<NUM>) on the plunger rod (<NUM>) such that feedback is given to a user as the plunger rod (<NUM>) is moved relative to the barrel (<NUM>) for driving said plunger (<NUM>);
wherein the engagement member (<NUM>) comprises a main part (<NUM>) having a circular or semi-circular shape, or being generally plate shaped, and a protruding element (<NUM>) protruding from said main part (<NUM>) for engaging the grooved surface (<NUM>) of the plunger rod (<NUM>), wherein the extension of the protruding element (<NUM>) in a direction parallel to said longitudinal direction of the plunger rod, is larger than the thickness of the engagement member perpendicularly to said longitudinal direction, and wherein an end portion (<NUM>) of the protruding element is provided with a tapering in said longitudinal direction, and
characterized in that,
said barrel (<NUM>) and said engagement member (<NUM>) are arranged relative to each other such that the engagement member (<NUM>), due to engagement with the grooved surface (<NUM>) of the plunger rod (<NUM>), is arranged to move solely in a direction generally perpendicular to a longitudinal direction of said plunger rod (<NUM>) as the plunger rod (<NUM>) moves relative to the barrel (<NUM>);
wherein the engagement member (<NUM>) is configured to reciprocate between two given turning points irrespective of a direction of movement of the plunger rod (<NUM>), and the protruding element (<NUM>) is configured to slide over the grooved surface (<NUM>) as the plunger rod (<NUM>) moves, and wherein the extension of the protruding element (<NUM>) in a direction parallel to the longitudinal direction of the plunger rod (<NUM>) is large enough to avoid that the protruding element (<NUM>) is bent in a direction parallel to the longitudinal axis of the plunger rod (<NUM>).