Abstract:
A lancet assembly having a lancet holder and a triggler enclosing a lancet structure. The triggler is partially inserted into a lancet holder from the distal end. The holder is provided with a rigid internal spring holder to receive the spring-loaded lancet structure. The lancet structure is provided with a body coupled to a spring which extend from the proximal end of the body. The spring has a linear axis of compression which coincide with the longitudinal axis of the lancet assembly. A lancet is attached to the body with the sharp tip pointing towards the distal end. The triggler interacts with the lancet holder via a triggering element to maintain the spring in a compressed state such that the lancet structure is in a stable standby position which is not easily triggered by accidental bumps on the assembly.

Description:
FIELD OF THE INVENTION 
     The present invention is related to finger-pricking devices. In particular, the present invention is related to lancets for medical use. 
     BACKGROUND OF THE INVENTION 
     Lancets or finger-pricking devices is widely used in the medical field for applications such as skin incisions and blood drawing. In some lancet assemblies, the blade or needle is kept in a standby position until it is triggered by the user, who is typically a medical personnel in charge of drawing the blood from a patient. In other lancet assemblies, the user has to manually set the assembly to an armed position before firing can be triggered. Upon triggering, the blade fires onto the skin of the patient, for example on the finger, and makes an incision. 
     Such lancet assemblies must be sterilized before use, and the lancet maintained under sterile conditions until use. Furthermore, the lancet assembly should be disposable to eliminate the chances of disease transmission due to the blade being used on more than one person. In this regard, the lancet should ideally be designed for only one firing, and have safety features to prevent reuse. Other features which are desirable include safety features to reduce the chance of the lancet accidentally misfiring and pricking someone. 
     It is therefore an object of the present invention to provide a safe and reliable lancet assembly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the triggler in FIG. 1 with the side walls cut away to expose the internal features. 
     FIG. 2 is the bottom view of the triggler according to the present invention. 
     FIG. 3A is an exploded perspective view of the lancet assembly according to the present invention. 
     FIG. 3B is an exploded cross-sectional view of the lancet assembly along line A—A according to the present invention. 
     FIGS. 4A and B are longitudinal cross-sectional views along line A—A of the lancet assembly in the after use and firing positions respectively according to the present invention. 
     FIGS. 4C and D are longitudinal cross-sectional views along line A—A of the lancet assembly in the standby position with (FIG.4C) or without (FIG.4D) the protective cap according to the present invention. 
    
    
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides in one aspect a lancet assembly having a distal end, a proximal end and a longitudinal axis running therebetween. The triggler is partially inserted into a lancet holder from the distal end. The lancet holder is provided with a rigid internal spring holder to receive a spring-loaded lancet structure. The lancet structure is provided with a body coupled to a spring which extend from the proximal end of the body. A lancet is attached to the body with the sharp tip pointing towards the distal end. The triggler interacts with the lancet holder via a triggering element to maintain the spring in a compressed state such that the lancet structure is in a stable standby position which is not easily triggered by accidental bumps on the assembly. The standby position is automatically maintained, and an additional arming step is eliminated. In another aspect, the assembly is provided with a safety feature to prevent: tampering of the lancet assembly. In yet another aspect, the spring is secured to the end wall of lancet holder such that dislocation caused by the sudden expansion force of the firing process is prevented. Furthermore, the spring is chosen to over-extend upon firing, such that the sharp tip of the lancet can jab a patient&#39;s skin held outside the lancet holder upon firing, but the sharp tip is withdrawn safely back into the lancet assembly when the spring is recoiled into the resting position. 
     In another aspect, a method is provided for finger pricking using a lancet assembly with a distal end and a proximal end. This lancet assembly contains a lancet with a sharp tip that fires outwards from the distal end when the assembly is compressed inwards from the same distal end. The method involves placing the distal end of the lancet assembly onto a finger to be pricked, and pressing the assembly into the finger from the proximal end. This compresses the assembly and causes firing of the lancet whereby the finger is pricked. 
     In the preferred embodiment, the lancet holder is provided with an open distal end and a closed proximal end defined by an end wall. Side walls extend from the end walls to form a box-like exterior casing. A mating element, preferably disposed on the interior surface of the side walls, is provided to interact with the triggler. The lancet holder also contains an elongated spring holder having an open first end and a second end attached to and extending from the end wall of the lancet holder. The supporting structures between the first end and the second end define an interior space wherein the lancet structure is received. A receiving element is provided on the spring holder for mating with a guiding element on the lancet structure such that the lancet can move along the longitudinal axis. A securing element is provided near the proximal end of the lancet holder for securing the proximal end of the spring from dislocation during firing. 
     The triggler contains an end wall for closing the open distal end of the lancet holder. This triggler end wall contains an aperture wherethrough the sharp tip of the lancet fires when triggered. A stabilizing element, extending from the triggler end wall, is inserted between the side walls of the lancet holder and the supporting structures of the spring holder, allowing sliding movement of the triggler relative to the lancet holder along the longitudinal axis. This sliding movement is limited by a safety catch on the triggler which is designed to engage the mating element of the lancet holder such that the triggler is maintained between a standby position and a firing position. A triggering element is also provided in the triggler for engagement with the guiding element of the lancet structure. When the triggler and the triggering element are in the standby position, the guiding element is forced towards the proximal end of the lancet holder, such that the spring is maintained in the standby position of a compressed high potential energy state. When a compression force is applied to the triggler end wall in the direction of the proximal end, the triggering element may be moved into a firing position in which it is disengaged from the guiding element. Once the guiding element is no longer held in the standby position, the potential energy stored in the compressed spring is released and the spring extends, forcing the sharp tip of the lancet structure to fire through the aperture of the triggler end wall. 
     DESCRIPTION OF THE INVENTION 
     The lancet assembly according to the present invention has a longitudinal axis defined by the axis of compression of the spring. The triggler (or triggering device) and the lancet holder interact by keeping the spring of the lancet structure in a standby compressed state. Upon compression of the assembly along the longitudinal axis by the user pressing the end wall of the triggler onto the skin of a patient, the lancet will be fired to pierce the skin. 
     The following detailed description describes the preferred embodiment for implementing the underlying principles of the present invention. One skilled in the art should understand, however, that the following description is meant to be illustrative of the present invention, and should not be construed as limiting the principles discussed herein. In the following discussion, and in the claims the terms “including”, “having” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including but not limited to.” 
     FIG. 1 shows an embodiment of the lancet holder  26  with the side walls cut away to reveal the spring holder  36 . A spring  45   a  is shown in dotted line. In this embodiment, the spring holder  36  is generally shaped into a cylinder with an open first end  102 , and a second end  104  attached to the end wall  30  of the lancet holder. Two slits  106 , running from the open first end towards the proximal end are provided on the side wall of the spring holder. In this embodiment, a wider slot  108  is further cut into the side wall of the spring holder. To strengthen the side walls of the spring holder, two ridges  112  are provided to connect the side walls of the spring holder and the lancet holder. This improves the rigidity of the spring holder, and hence the reliability and accuracy of the firing procedure. An additional pair of lugs  114  is provided at the proximal end of the spring holder juxtaposing the two sides of slot  108 . These lugs can interact with a unshaped extension  47  in the spring. The lancet holder is preferably made from a rigid plastic material with good mechanical strength such as polycarbonate material in order to withstand the high energy firing process of the metal spring. 
     FIG. 2 shows detailed features of the triggler  50 . In this embodiment, the triggler is of a rectangular shape having an end wall  52  with aperture  54 . Side walls  58  extending from the four corners of end wall  52  to form a stabilizing element. The triggering element, in the form of actuating ribs  56  extends from two opposing sides of end wall  52 . A small protrusion, in the form of wedge  60 , is provided at the end of each actuating rib  56 . Wedge  60  protrudes into the interior of the triggler. Two L-shaped clips  62  further extend from opposing sides of end wall  52 . The triggler is preferably made from a slightly flexible plastic, such as Acrylonitrile Butadiene Styrene (ABS) material to allow the actuating ribs to bend with the right resistance. 
     FIGS. 3A,  3 B and  4 A-D show how the lancet assembly, having a longitudinal axis  38 , a distal end  22  and a proximal end  23 , is assembled to provide the desired features. The lancet structure includes a lancet body  40 , a lancet  44  with a sharp tip  46 , and a spring  45  with a linear axis of compression. In this embodiment, spring  45  is a helical metal coil, and has a U-shaped extension  47  at the proximal end. Lancet body  40  is provided with channel  42  for receiving and securing the lancet such that the sharp tip  46  of the lancet is at the distal end. Guiding pins  48  are provided on opposing sides of body  40 . Securing pins  49  extend from the proximal end of body  40  for securing spring  45  onto the body. 
     The assembled lancet structure is received within spring holder  36  with spring  45  pressed onto end wall  30  of lancet holder  26 . Guiding pins  42  are slotted into slits  106  such that lateral movement and rotational movement around the longitudinal axis is prevented. The spring  45  is fitted onto the lancet body  40  such that the U-shaped extension  47  extends through slot  108  and wraps around either one of lug  114 . This arrangement prevents the spring from being easily dislocated from the spring holder during the firing process. 
     The side walls  58  of triggler  50  are slidably inserted into the space between the spring holder  36  and the side walls  32  of the lancet holder such that the small wedges  60  of actuating ribs  56  slide through slits  106  and press the guiding pins towards the proximal end of the lancet holder. The L-shaped clip  62  on the triggler is adapted to engage the elongated recess  34  on the lancet holder to limit the longitudinal movement of the triggler relative to the lancet holder. 
     During assembly, the triggler is pressed down toward the lancet holder in the direction shown by arrow  120 , and in the process, the guiding pins, are forced down concomitantly by the small wedges on the actuating ribs. This compression force compresses the spring. As the triggler is pressed lower, the resistance of the spring to further compression becomes greater. When the resistance of the spring exceeds the mechanical strength of the actuating ribs to push on the guiding pins, the actuating ribs are bent outwards relative to the longitudinal axis of the lancet holder, releasing the compression of the lancet structure and resulting in firing of the lancet. 
     In the preferred embodiment, a cap  66  is provided to interact with the side walls  32  of the lancet holder to maintain sterility and to protect users in cases of accidental firing. The cap is preferably an air-seal or sterile cap. 
     In the standby position, the resistance of the spring to compression forces clip  62  towards the distal end of recess  34 . In the most preferred embodiment, the length of actuating ribs  56  is designed to allow the end wall of the triggler to extend a short distance  41  from the side walls  32  of the lancet holder when the assembly is in the standby position, for example,  12  mm from the distal end. This short distance means that the triggler is well protected from firing due to accidental bumping. Furthermore, due to the lack of lateral movement, the direction of the external pressure has to be very close to the longitudinal axis of the assembly in order for the triggler to be compressed sufficiently for firing to occur. The mechanical strength of the actuating rib may be designed such that deformation (i.e. firing) only occurs when sufficient pressure is provided on the triggler end wall. In addition, the spring may be chosen such that triggering only occurs when the triggler is flush against the edge of the proximal end of the lancet holder, or even pushed slightly inside. All these parameters may be varied to reduce the chance of accidental firing without undue experimentation. When the user wants to prick the finger of the patient, he presses the end wall  52  of the triggler against the skin of the finger. This compression force pushes clip  62  towards the proximal end of the recess and the triggler towards the proximal end of the lancet holder, increasing the compression of the spring. This causes the spring to generate an opposing extension force, which pushes against wedges  60  of the actuating ribs  56 . Ribs  56  are designed to bend outwards into the firing position with this additional pressure, in which wedges  60  disengages from guiding pin  48 , causing the spring to fire into a fully extended position and the lancet to jab the skin of the patient. It is clear that from the above description, the triggering mechanism is from the interaction with the patient&#39;s skin. As a result, if the patient pulls back his hand just when the user is about to press down the triggler, triggering would not occur. 
     The slot  108  and lug  114  at the proximal end of spring holder acts as the securing element of the spring such that after firing, the distal end of the spring recoils towards the proximal end. In this way, the sharp tip of the lancet is retracted completely back into the lancet holder after firing. This is a highly desirable safety feature. 
     While the present invention has been described particularly with references to the aforementioned figures, it should be understood that the figures are for illustration only and should not be taken as limitation on the invention. It is contemplated that many changes and modifications may be made by one of ordinary skill in the art without departing from the function, spirit and the scope of the invention described, examples of which are described below. 
     The stabilizing element in the present invention, described as side walls  68  at the four corners of the triggler  50  in above embodiment, serves not only as a structure to allow interaction between the triggler and the lancet holder, but also a structure to prevent lateral movements therebetween. As a result, only firm compressional pressure almost directly along the longitudinal axis is required for firing to occur, and accidentally knocking the triggler in any other direction is not likely to cause firing. Besides having side walls on all four corners, other embodiments may be possible, such as rigid structures symmetrically extending from the end walls of the triggler. The tight association between the triggler and the lancet holder also means that the lancet structure is completely protected and enclosed, and it is extremely difficult to dismantle the assembly without breaking some parts. 
     The securing element may be other structures in the molded plastic spring holder that allows interaction of the proximal end of the spring with the proximal end of the lancet holder. This securing element allows a metallic helical spring with superior springback properties to be used instead of plastic springs that may be fabricated as an integral part of the spring holder. 
     Besides a recess on the interior side wall of the lancet holder, other structures, such as an elongated aperture or a bracket in the side wall may also serve as the mating element. A structure which is only accessible from the interior is, however, preferred as it prevents external tampering.