Abstract:
A skin pricking apparatus including a casing  1 , a lancet  15  located within the casing, a firing button  9  arranged to transfer a user applied force to the lancet  15  to drive the lancet through the casing  1 , and lancet retaining element  12, 13, 23   a,b  arranged to substantially prevent movement of the lancet  15  through the casing  1  until the user applied force exceeds a predefined threshold force.

Description:
FIELD OF THE INVENTION 
     The present invention relates to skin pricking apparatus and in particular, though not necessarily, to a skin pricking apparatus for use in providing a sample of blood. 
     BACKGROUND 
     In the medical and related diagnostic and testing fields, it is often required to take small samples of blood from a subject for the purpose of testing or analysing the blood. A common way of achieving this is by using a small needle to pierce the skin at a location where blood vessels are close to the surface. The combination of a needle and its holder is commonly known as a lancet. In order to avoid infection and contamination, lancets are preferably intended for single use and are disposable. They must therefore be compact to allow users to carry multiple lancets on their person, and cheap to manufacture. 
     A number of disposable lancet devices are currently on the market. These include the Unistik™ manufactured and marketed by Owen Mumford Ltd (Woodstock, UK). The current designs comprise a moulded plastics casing within which is mounted a short, spring-loaded needle. A trigger is formed in the casing which, when depressed, releases the lancet causing the tip to be fired out through an opening in the casing. Some of the current designs require a user to preload or cock the spring prior to firing. In other designs, the lancet devices are supplied already cocked. It is also generally necessary for users to remove a cap from the front of the device or the needle tip prior to firing. Users must therefore perform at least two steps, and sometimes three, in order to perform the blood sampling procedure. 
     There exists a desire for a lancet device or apparatus which is simpler to operate than current designs. Of course, any improved design must meet high standards with regard to manufacturing costs. It must also be reliable, ensuring that lancet devices are provided to users in an operable condition. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention there is provided a skin pricking apparatus comprising a casing, a lancet located within the casing, a firing button arranged to transfer a user applied force to the lancet to drive the lancet through the casing, and lancet retaining means arranged to substantially prevent movement of the lancet through the casing until the user applied force exceeds a predefined threshold force. 
     Embodiments of the present invention provide a lancet device which can be fired in an essentially one-step process. Nonetheless, accidental firing is unlikely, and the delivery of operable devices to users is ensured. Moreover, lancet devices embodying the invention are of relatively simple construction and have may have a lower component count than conventional designs. 
     In a preferred embodiment of the invention, said lancet retaining means comprises cooperating components on the casing and lancet. More preferably, these components comprise a first surface in which is formed a protrusion or recess and a second surface on which is formed a protrusion. The first and second surfaces may be provided on the inside of the casing and on the lancet respectively, or vice versa. The surfaces may be provided with a plurality of interengaging structural features. 
     In a preferred embodiment of the invention, said firing button is provided with an abutment surface arranged in use to contact a surface of the lancet in order to transfer said user applied force. More preferably, said surfaces are oriented obliquely with respect to the direction of travel of the lancet through the casing. This angle between the surfaces and this direction may be in the range 25-65 degrees, more preferably, 40-50 degrees, and more preferably still 45 degrees. 
     In a preferred embodiment of the invention, said firing button is moveable upon the application of a user force in a direction substantially perpendicular to the direction of travel of the lancet through the casing. Preferably, the firing button is formed integrally with the casing. 
     In a preferred embodiment of the invention, the apparatus comprises biasing means coupled between the lancet and the casing for biasing the lancet to a withdrawn position within the casing, the spring being extended by the application of said driving force to the lancet. Said biasing means may be a platform spring, moulded integrally with the casing and firing button. 
     Preferably, the lancet comprises a plastics body and a lancet needle embedded at one end within the body. More preferably, the lancet body is molded integrally with the casing. More preferably, the lancet body is molded integrally with the platform spring. 
     In a preferred embodiment, the lancet needle is shielded by a protective cover. More preferably, this cover is a moulded flexible plastics sheath, e.g. of thermoplastic elastomer. 
     In a preferred embodiment, the firing button comprises means for latching the button into a depressed position following depression and firing of the button, in order to prevent reuse of the apparatus and to provide a visual indication that the device has been used. More preferably, the latching means is a latch arranged to engage a lip formed in an opening in the casing. 
     According to a second aspect of the present invention there is provided a skin pricking apparatus comprising a casing, a lancet located within the casing and comprising a lancet driver plate, and a firing button resiliently coupled to the casing and comprising a lancet driver member, whereby depression of the firing button brings the lancet driver member into contact with the lancet driver plate and transfers a user applied force from the firing button to the lancet, the apparatus further comprising cooperating features on the casing and the lancet which substantially prevent movement of the lancet through the casing until the user applied force exceeds a predefined threshold force. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present invention and in order to show how the same may be carried into effect reference will now be made by way of example to the accompanying drawings in which: 
         FIG. 1  is a perspective view of a single use lancet device; 
         FIG. 2  is a perspective view of a moulded component used to form a casing of the lancet device of  FIG. 1 ; 
         FIG. 3  is a perspective cross-sectional view of the lancet device of  FIG. 1 ; 
         FIGS. 4 to 6  show vertical cross-sectional views of the device of  FIG. 1  in various operational configurations. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     There is illustrated in  FIG. 1  an assembled single use lancet device designed for pricking a users skin to provide a small blood sample. Typically a user pricks the pad of his or her finger, leaving a small spot of blood on the finger. This spot can then be collected, e.g. using a test strip, for use in performing some measurement or test. The lancet device of  FIG. 1  is formed from a single molded plastics component  1  illustrated in  FIG. 2 . 
     With reference to  FIG. 2 , the molded component  1  comprises a lower casing section  2  and an upper casing section  3  which are secured together by a pair of flexible hinges  4   a,   4   b.  A molded platform spring  5  is formed integrally with the casing components, and is attached to the lower casing component  2  by a flexible hinge  6 . A lancet body  7  is also formed integrally with the casing components, and is fixed to the end of the platform spring  5  remote from the casing. As will be readily apparent from  FIG. 3 , which shows a vertical cross-section through the device of  FIG. 1 , the device is assembled by folding the spring and lancet into the lower casing section  2 , about the hinge  6 . The upper and lower casing sections are then folded together about the hinges  4   a,   4   b.  The upper and lower casing sections are provided with semi-circular recesses in one end wall which, when the device is folded together, combine to provide a circular opening  8 . 
     Considering first the upper casing section  3 , this comprises a trigger button  9  which is free on three sides but which is integral with the body of the casing on a fourth side, i.e. the side closest to the rear of the device. The trigger button  9  is able to flex at the point of attachment to the casing body so that it can be pressed downward (as viewed in  FIG. 1 ) by finger pressure. Depending from the lower surface of the trigger button (again as viewed in  FIG. 1 ) are a lancet driver  10  and a latch  11 . In front of the trigger button  9 , towards the opening  8 , a blocking rib  12  depends from the inner surface of the upper casing section. A corresponding blocking rib  13  depends from the inner surface of the lower casing section. A pair of lancet guide rails  14   a,   14   b  are formed on the inner surface of the lower casing section. 
     A lancet  15  is provided by the lancet body  7  and a lancet needle  16  which is embedded at one end in the body  7 . An angled drive plate  17  of the lancet body  7  provides a surface for engaging the lancet driver  10  as will be described below. A sharpened tip  18  projects outwardly from the lancet body  7  and, when the device is assembled, is aligned with the opening  8  formed in the end of the casing. The exposed portion of the needle  16  including the tip  18  is overmolded with a flexible and elastic plastics cover  19 , e.g. of thermoplastic elastomer (TPE) such as SANTOPRENE or EVOPRENE (alternatively, the material may be polyurethane or polyurethane foam, silicon rubber, or liquid silicon rubber). The cover  19  has an enlarged, generally frustoconical shaped, head  20 , which covers the tip of the needle (this feature is preferred, but not essential). The overmolding narrows in a stepwise manner to provide a narrow sleeve  21  which covers the remainder of the needle  16 . The overmolding also covers the end surface of the body  7 . The overmolding ensures sterility of the needle prior to use. Flexible fingers  22   a,   22   b  extend outwardly from the upper and lower surfaces of the lancet body, partially overlapping the lancet needle  16 . Ribs  23   a,   23   b  are formed on the outwardly facing surfaces of respective fingers. 
     The casing comprises a number of components which mate together once the casing is folded, and which allow the various components of the lancet to be secured in place. These are apparent from the Figures, but will not be explained in any further detail as their construction and function will be readily apparent to the person of skill in the art. 
     When the device is folded together, the ribs  23   a,   23   b  on the lancet body  7  locate directly behind the blocking ribs  12  and  13  formed on the upper and lower casing sections, and the lancet body locates between the guide rails  14   a,   14   b.  In this state, the platform spring  5  is not subject to any compression or expansion force. In the assembled configuration, the lancet driver  10  sits above and out of contact with the angled drive plate  17  of the lancet body  7 . This configuration is illustrated in the vertical cross-sectional view of  FIG. 4 . 
     Operation of the lancet device will now be described with reference to  FIGS. 4 to 6 . In the pre-use configuration illustrated in  FIG. 4 , the trigger button  9  is in its resting position, with the lancet driver  10  sitting above, but not in contact with, the drive plate  17  of the lancet body  7 . In order to operate the lancet, a user holds the lancet device in one hand, with his or her thumb placed over the firing button  9 . The end of the device at which the opening  8  is located is then brought into contact with the area of skin to be pricked, e.g. the pad of a finger on the user&#39;s other hand. The user then depresses the trigger button  9 , bringing the lancet driver  10  into contact with the drive plate  17  of the lancet body  7 , tending to drive the lancet  15  towards the opening  8  in the casing. However, after a possibly short travel of the lancet  15  towards the opening, the ribs  23   a,   23   b  on the lancet body  7  engage the respective ribs  12 , 13  on the upper and lower casing sections, blocking further motion. The user will sense this resistance, and will increase the pressure applied to the trigger button  9 . 
     When some predefined pressure is reached, e.g. say 5 to 10N, the fingers  22   a,   22   b  on which the ribs are formed will have flexed inwardly sufficient to release the lancet  15  for further travel. At this point, the user applied force remains high, and the lancet  15  will snap quickly past the ribs whilst experiencing a relatively “explosive” propelling force. This force is significantly greater than the resistance provided by the now expanding platform spring  5 . 
     The lancet  15  travels through the casing until the head  20  of the overmolded section on the needle  16  contacts the inner surface of the opening  8  in the casing, surrounding the opening. This prevents further progress of the head. However, a force is still being exerted on the back of the lancet by the lancet driver  10 , causing the needle tip  18  to be driven through the head  20 . The sleeve  21  tends to concertina around the needle  16 . The needle tip  18  is driven out through the opening  8  in the casing, and pierces the skin of the user. This is the configuration illustrated in  FIG. 5 . (In an alternative arrangement, the opening  14  may be large enough to allow passage of the head  29 , in which case the user&#39;s skin provides the stop surface for the head.) 
     The dimensions of the lancet device are such that, at some point in the travel of the lancet  15  prior to the needle tip  18  exiting the opening  8 , the drive plate  17  of the lancet body  7  has moved sufficiently to separate from the lancet driver  10 . However, the momentum of the lancet  15  is sufficient to propel the needle tip out of the opening into contact with the user&#39;s skin. Once this kinetic energy has been spent, the platform spring  5  will begin to contract, pulling the lancet  15  and with it the needle tip  18  back inside the casing. It is noted that the overmolded cover  19  on the lancet needle tends to remain in a partially compressed state, and does not expand to recover the needle tip  18 . This used configuration is illustrated in  FIG. 6 . 
     The purpose of the latch  11  formed on the inner surface of the trigger button  9  is to prevent reuse of the lancet device. As is seen in  FIG. 6 , the latch  11  slides across the opposed surface  24  of the upper casing section  3 , before snapping behind the lower lip  25  of that surface. The resistance presented between the latch and the wall surface is easily overcome by the force which the user applies to release the lancet  15  from within the casing. 
     It will be appreciated by the person of skill in the art that various modifications may be made to the above described embodiments without departing from the scope of the present invention. In one such modification, the lancet body may be molded as a separate component with the needle embedded in the body to form the lancet, the lancet being placed inside the casing during assembly. The platform spring  5  may also be a separate component, or could be molded integrally with the lancet body or the casing.