Patent Publication Number: US-2018028103-A1

Title: A blood lancet unitarily-moulded with an elastic member

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates generally to blood lancet used for capillary blood sampling. More particularly, the present invention relates to the design, the fabrication method and the use of a blood lancet unitarily moulded with an elastic member for capillary blood sampling. 
     Background of the Invention 
     Blood extraction is required for carrying out various in-vitro diagnostic tests. There are in general two types of blood extractions: (1) the first type is the venous blood extraction (venepuncture) in which a cannula is inserted into a superficial vein to draw venous blood directly from the vein, the blood volume is normally in terms of millilitres; (2) the second type is capillary blood sampling in which a blood lancet is normally used for making an incision on a fingertip for extracting capillary whole blood from the capillary network right below the skin. The blood volume obtained is normally in the range of 0.3 ul-100 ul, which is suitable for point-of-care diagnostic applications, for instance, blood glucose monitoring, rapid lateral-flow assay tests, and other point-of-care tests. Normally, venous blood is collected at the hospital when a large blood volume is required for multiple blood tests to be carried out at the central laboratories. On the other hand, capillary blood is collected from fingertips or other skin sites with rich capillary network at home or a point-of-care for rapid blood screening tests or other specific point-of-care blood tests. 
     The present invention relates to the capillary blood sampling for in-vitro diagnostic blood tests. For capillary blood sampling via a finger prick, the current practice is to actuate a blood lancet with a metal spring for rapidly and linearly incising the skin to minimize the pain. The incision involves linearly inserting and retracting a needle at high speed, and the incision depth ranges from 0.5 mm to 2 mm deep. The incision (penetration and retraction) speed provided by the spring is in the range of 1 m/s-6 m/s. Therefore, for a penetration of 0.5 mm at the speed of 1 m/s, the time of penetration is 0.5 msec and the time of retraction is also 0.5 msec, giving a total of 1 msec. In addition to great reduction of the incision time, the linear and rapid incision stroke also reduces much pain by minimally disrupting the nerve ending. Hence, it is essential that a metal spring is used together with a blood lancet for effective capillary blood sampling. 
     Blood lancets are used in two groups of users, the first group consists of the home users who regularly sample their blood for blood tests, for instance the diabetic patients who are required to monitor their blood glucose levels daily and regularly; the second group consists of medical personnel who sample blood for patients, for instance the nurses in the hospitals. 
     For the home users, the blood lancets are loaded in a re-usable spring-operated lancing device so that the disposable components are minimized to save costs. For the hospital users, the spring and the blood lancet are housed in a casing (this device is called safety lancet hereinafter) so that the needle is not exposed to prevent finger-stick and that the entire device can be disposed of to prevent cross infection between patients. As a result, the safety lancet is much more expensive compared to the home-use blood lancets in long term, mainly due to the spring, which is almost universally made of metal such as stainless steel (of course there are other components such as the casing which adds on to the costs, but their contribution will be minor). 
     It is apparent that for the benefit of re-using the spring, the home users are required to handle the needles every time they load the blood lancet into the lancing device, for which they are exposed to finger-stick hazard. On the other hand, the hospital users throw away the spring after each use, this makes the blood sampling cost very expensive. If a home user were to use safety lancets, the costs may be doubled in the long term. 
     Hence, the present invention&#39;s primary objective is to reduce the cost of the metal spring by unitarily moulding an elastic member onto a blood lancet, wherein the elastic member acts to provide the required actuation force for skin incision when charged and discharged (i.e. compressed to store potential energy, then released to actuate the blood lancet). 
     Closest Prior Art 
     U.S. Pat. No. 8,652,158 B2 to Owen Mumford Limited reported a blood lancet which is integrally moulded with a pair of undulating plastic webs (springs) at the forward end of the blood lancet. The undulating plastic webs were incorporated for returning the blood lancet after actuation. The springs in this patent do not provide any actuation that is needed for skin penetration, so a metal spring is still needed in the device. 
     U.S. Pat. Nos. 5,628,765 B2 and 5,755,733 B2 to APLS Co. Ltd. reported a safety lancet comprising a plastic spring member coupled to a blood lancet. Although the plastic spring member is injection moulded, it is not unitarily moulded to the blood lancet, therefore requiring two separate injection moulding processes. 
     SUMMARY OF THE INVENTION 
     The present invention provides a blood lancet unitarily moulded with an elastic member for capillary blood sampling. In the preferred embodiment, a blood lancet  100  comprises a needle component  120  having a forward end  122  and a rearward end  124 , the forward end  122  is disposed with a detachable safety cap  160  for protecting the needle tip, the rearward end  124  is disposed with an elastic member  140  for providing actuation force to the needle component  120  for skin penetration, wherein the detachable safety cap  160  and the elastic member  140  are unitarily moulded to the needle component  120 . In the second preferred embodiment, a two-part safety lancet  1000  is provided. The two-part safety lancet  1000  comprises a holder  1200  and a blood lancet  1100 , the blood lancet  1100  comprises a needle component  1120  having a forward end and a rearward end, a detachable safety cap  1160  disposed at the forward end, an elastic member  1140  disposed at the rearward end, wherein the detachable safety cap  1160  and the elastic member  1140  are unitarily moulded to the needle component  1120 . In operation, the blood lancet  1100  is inserted into the holder  1200  which provides the necessary latching mechanism for charging and discharging the elastic member  1140  for providing actuation force to the needle component  1120 . 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  illustrates a perspective view of a blood lancet unitarily moulded with an elastic member 
         FIG. 2  illustrates an exploded view of a blood lancet unitarily moulded with an elastic member 
         FIG. 3  illustrates a perspective view of two other possible designs of blood lancet unitarily moulded with an elastic member 
         FIG. 4  illustrates a perspective view of a safety lancet configuration which comprises a blood lancet unitarily moulded with an elastic member 
         FIG. 5  illustrates an exploded view of a safety lancet configuration which comprises a blood lancet unitarily moulded with an elastic member 
         FIGS. 6( a ) and ( b )  illustrate the assembly process of the safety lancet comprising a blood lancet unitarily moulded with an elastic member 
         FIG. 7( a ) to ( e )  illustrate the operation of the safety lancet comprising a blood lancet unitarily moulded with an elastic member 
     
    
    
     DESCRIPTION OF THE INVENTION 
     Detailed Description of the Invention 
     The present invention is provided to reduce the device cost of capillary blood sampling by integrating the function of the metal spring into the blood lancet. This integration can be achieved by over-moulding an elastic member behind the needle to provide the required actuation force. A typical capillary blood sampling device can be seen in the closest prior arts &#39;765 and &#39;733 of APLS Co., Ltd, where a safety lancet with a plastic spring is provided. In this device, a blood lancet with which its tip is over-moulded with a detachable safety cap was incorporated to improve a previous design by Danish Design Patent MR 0933 which used a bare blade. It is non-obvious that the elastic member can be unitarily moulded to the blood lancet for providing the actuation force, as shown by the present invention. 
     It is a vital aspect of current capillary blood sampling that the use of a metal spring or any other spring provides a rapid and linear incision to minimize pain. As mentioned previously, the total incision time by a spring-assisted blood sampling is in the range of 1 millisecond. These characteristics greatly reduce the pain incurred if compared by a hand prick without using a metal spring. Currently, the metal spring is incorporated into a spring-operated lancing device for home use so as to minimize the blood sampling costs. This is a common practice for diabetes patients where they need to perform a few finger pricks daily to monitor their glucose levels. However, this approach subject the users to finger-stick hazard since they will need to handle the needles when loading and unloading of the lancets on/from the lancing device. There is a long-felt need to eliminate the finger-stick hazard by providing low-cost disposable safety lancets to make capillary blood sampling more viable. 
     The present invention provides a blood lancet unitarily moulded with an elastic member for providing the required actuation force. In the preferred embodiment  100 , which is shown in  FIG. 1  and  FIG. 2 , the present invention involves a needle component  120 , which further comprising a forward end  122  and a rearward end  124 , an elastic member  140 , and a detachable safety cap  160 . The needle component  120  can be made of several materials such as polymers, metals and ceramics. In the preferred embodiment, polymer poly-etherimide is used for making the needle component  120  by injection moulding. The elastic member  140  is unitarily moulded on the rearward end  122  of the needle  120 . Similarly, the detachable safety cap  160  is unitarily moulded on the forward end  124  of the needle component  120 . 
     If the needle component  120  is made of metals or ceramics, the unitary moulding process involved is insert moulding, in which the needle component  120  is inserted into a mould and a polymer resin is injected over the needle component  120  to form the elastic member  140  and the detachable safety cap  160 . 
     If the needle component  120  is made of polymer resin, such as poly-etherimide, the unitary moulding process involved is twin-shot injection moulding, or more commonly known as ‘two-colour’ moulding. The preferred embodiment blood lancet  100  is preferably made by twin-shot injection moulding wherein the needle component  120  is first moulded with a first material, namely poly-etherimide, and subsequently the elastic member  140  and the detachable safety cap  160  is over-moulded with a second material, namely polyacetal (POM), polyethylene, polypropylene, and so on, onto the rearward end  122  and the forward end  124  of the needle component  120  respectively. The detachable safety cap  160  protects the needle tip and will be pulled off to expose the needle at the point of use. The elastic member  140  will provide the required spring force or actuation force when it is charged and then dis-charged, as described in  FIG. 7 . 
     A preferred method for manufacturing the blood lancet  100  is by twin-shot injection moulding. Materials used for injection moulding the blood lancet  100  should be bio-compatible and gamma-irradiation stable. In addition, the polymer for moulding the needle component  120  should have sufficient impact and flexural strength. Particularly important is that the glass transition temperature (the temperature that a polymer starts to soften) should be higher than the melting temperature of the second plastic resin to prevent distortion or deformation of the plastic tip. One identified material that has all the characteristics is polyether-imide (PEI), which has a glass transition temperature of 220° C. 
     On the other hand, the second polymer for moulding the elastic member  140  and the detachable safety cap  160  does not require high impact and flexural strength but has to have a low melting temperature so that the heat will not affect the shape of the needle tip during the second moulding process. Another important condition is that there should be no chemical or covalent bonding present between the first material PEI and the second material, otherwise the detachable safety cap  160  cannot be removed to expose the needle tip. One identified polymer is high density polyethylene (HDPE), which has a melting temperature of 130° C. and does not have covalent bonding after the over-moulding process. The low melting temperature is good for a stable moulding process because under normal circumstances the polymer melt is normally raised to higher temperature to enhance flowability of the polymer melt. The wide gap between the melt temperature of HDPE and the glass transition temperature of PEI provides a good range of process window under which the over-moulding can be operated. 
       FIG. 3  shows two other designs that the elastic member  140  can take. The geometry and the shape of the elastic member  140  are not crucial so long as it provides the required actuation force when it is charged and dis-charged. 
       FIGS. 4 and 5  show the second preferred embodiment which is a safety lancet  1000 , which comprises a blood lancet  1100  and a holder  1200 .  FIG. 4  shows a perspective view of the safety lancet  1000  in which the blood lancet  1100  is assembled in the holder  1200 .  FIG. 5  shows the exploded view of the safety lancet  1000  which comprises a blood lancet  1100  and a holder  1200 . The blood lancet  1100  further comprises a needle component  1120  having a forward end and a rearward end, an elastic member  1140  and a detachable safety cap  1160 . 
     Assembly of the Second Preferred Embodiment 
       FIG. 6  shows the section view of the safety lancet  1000  during its assembly process. For the assembly of the safety lancet  1000 , the blood lancet  1100  and the holder  1200  are provided. The blood lancet  1100  comprises a needle component  1120  having a forward end and a rearward end, an elastic member  1140  disposed at the rearward end, a detachable safety cap  1160  disposed at the forward end, a pair of latch hooks  1170   a  attached to the needle component  1120 , a U-shape button  1180  having a pair of arms, each arm further comprises a hammer  1210   a  and a reverse hook  1190   a  at the end of the arm, wherein all the components, i.e. the elastic member  1140 , the detachable safety cap  1160 , the pair of latch hooks  1170   a , the U-shape button  1180 , the pair of hammers  1210   a  and the pair of reverse hooks  1190   a , are unitarily moulded on the needle component  1120 . 
     On the other hand, the holder  1200  is a substantially longitudinal hollow body which is designed to receive the blood lancet  1100 . For example, the holder&#39;s  1200  inner surface is moulded with a pair of latch stoppers  1170   b  for engaging the latch hooks  1170   a  and a pair of reverse stoppers  1190   b  for engaging the reverse hooks  1190   a,  wherein the latch hooks  1170   a  and reverse hooks  1190   a  are unitarily moulded on the blood lancet  1100 . The holder  1200  also comprises a proximal opening  1240  and a distal opening  1260 . 
     During the assembly process, a blood lancet  1100  is inserted into the holder  1200  via its proximal opening  1240  by applying compression force  1220  on the U-shape button  1180 . The insertion will be first resisted by the pair of hammers  1210   a  at the end of the arms of the U-shape button  1180 , after which the hammers  1210   a  will be overcome by the compression force  1220  and are pushed inward so that the blood lancet  1100  can go into the holder  1200 . The blood lancet  1100  will continue to be pushed forward until the latch hooks  1170   a  are stopped by the latch stoppers  1170   b  on the holder  1200 . At this moment, the elastic member  1140  is slightly compressed (or charged). Finally, the compression force  1220  is removed and the U-shape button  1180  will retract slightly due to the relaxation of the elastic member  1140  and the blood lancet  1100  is now locked by the latch stoppers  1170   b  and the reverse stoppers  1190   b.  In this final configuration, the blood lancet  1100  is firmly held in the holder  1200  but the elastic member  1140  is not charged. Pre-charging the elastic member  1140  will subject the elastic member  1140  to material creeping (a common phenomenon for plastic material), which sees the elastic member  1140  lengthening over time and losing the elasticity for providing actuation force. 
     Operations of the Second Preferred Embodiment 
       FIGS. 7( a )-( e )  show the operation of the safety lancet  1000 . Firstly, the detachable safety cap  1160  is removed as shown in  FIG. 7( a ) . At this stage, the blood lancet  1100  is firmly held in the holder  1200  and the elastic member  1140  is only slightly charged (or compressed). To use the safety lancet  1000 , a user holds the device in between his index and middle fingers and points the device at a skin site  1300 . 
     Next, as shown in  FIG. 7( b ) , the user uses his thumb to exert a compression force  1220  onto the U-shape button  1180  which pushes the U-shape button  1180  forward and charges (or compresses) the elastic member  1140 . The compression or charging of the elastic member  1140  is achieved because the blood lancet  1100  is prevented from moving forward due to the engagement of the latch hooks  1170   a  and the latch stoppers  1170   b.    
     Subsequently, as shown in  FIG. 7( c ) , the hammers  1210  on the arms of the U-shape button  1180  make contact with the latch hooks  1170   a  and push them inward, thereby releasing the latch which is formed by the latch hooks  1170   a  and the latch stopper  1170   b.    
     As a result, as shown in  FIGS. 7( d ) and 7( e ) , the charged elastic member  1140  releases its stored potential energy and actuates the needle component  1120  forward. The needle component  1120  travels linearly at 1 m/s-6 m/s and penetrates the skin site  1300 , making an incision on the skin, then quickly retracts back to the holder  1200  at a retraction speed similar to the penetration speed.