Abstract:
A test strip is provided for use in the determination of the concentration of an a chemical in blood. The test strip comprises a plurality of microneedles and a test area. Each microneedle is adapted to puncture skin and to draw blood. The test area is in fluid communication with the microneedles. The test area contains a reagent adapted to produce a reaction indicative of the concentration of the chemical in blood.

Description:
This application claims benefit of Provisional Application Ser. No. 60/217,424 filed Jul. 11, 2000. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to blood monitoring devices, and, more particularly, to a test patch for painlessly obtaining a sample of blood. 
     BACKGROUND OF THE INVENTION 
     It is often necessary to quickly and painlessly obtain a sample of blood and perform a quick analysis of the blood. One example of a need for painlessly obtaining a sample of blood is in connection with a blood glucose monitoring system where a user must frequently use the system to monitor the user&#39;s blood glucose level. 
     Those who have irregular blood glucose concentration levels are medically required to regularly self-monitor their blood glucose concentration level. An irregular blood glucose level can be brought on by a variety of reasons including illness such as diabetes. The purpose of monitoring the blood glucose concentration level is to determine the blood glucose concentration level and then to take corrective action, based upon whether the level is too high or too low, to bring the level back within a normal range. The failure to take corrective action can have serious implications. When blood glucose levels drop too low—a condition known as hypoglycemia—a person can become nervous, shaky, and confused. That person&#39;s judgment may become impaired and that person may eventually pass out. A person can also become very ill if their blood glucose level becomes too high—a condition known as hyperglycemia. Both conditions, hypoglycemia and hyperglycemia, are both potentially life-threatening emergencies. 
     One method of monitoring a person&#39;s blood glucose level is with a portable, hand-held blood glucose testing device. A prior art blood glucose testing device  100  is illustrated in FIG.  1 . The portable nature of these devices  100  enables the users to conveniently test their blood glucose levels wherever the user may be. The glucose testing device contains a test sensor  102  to harvest the blood for analysis. The device  100  contains a switch  104  to activate the device  100  and a display  106  to display the blood glucose analysis results. In order to check the blood glucose level, a drop of blood is obtained from the fingertip using a lancing device. A prior art lancing device  120  is illustrated in FIG.  2 . The lancing device  120  contains a needle lance  122  to puncture the skin. Some lancing devices implement a vacuum to facilitate the drawing of blood. Once the requisite amount of blood is produced on the fingertip, the blood is harvested using the test sensor  102 . The test sensor  102 , which is inserted into a testing unit  100 , is brought into contact with the blood drop. The test sensor  102  draws the blood to the inside of the test unit  100  which then determines the concentration of glucose in the blood. Once the results of the test are displayed on the display  106  of the test unit  100 , the test sensor  102  is discarded. Each new test requires a new test sensor  102 . 
     One problem associated with some conventional lancing devices is that there is a certain amount of pain associated with the lancing of a finger tip. Diabetics must regularly self-test themselves several time per day. Each test requires a separate lancing, each of which involves an instance of pain for the user. 
     Another problem associated with some conventional lancing devices is that the lacerations produced by the lances are larger than necessary and consequently take a greater time to heal. The greater the amount of time for the wound to heal translates into a longer period of time in which the wound is susceptible to infection. 
     Another problem associated with some conventional blood glucose monitoring devices is that the user&#39;s blood physically contacts the elements within the testing unit. Cross-contamination can be a problem if the monitoring device is used by more than one user such as a clinical setting. 
     SUMMARY OF THE INVENTION 
     According to one embodiment of the present invention, a test strip is provided for use in the determination of the concentration of a chemical in blood. The test strip comprises an array of microneedles and a test area. Each microneedle is adapted to puncture skin and to draw blood. The test area is in fluid communication with the microneedles. The test area contains a reagent adapted to produce a reaction indicative of the concentration of the chemical in blood. 
     The above summary of the present invention is not intended to represent each embodiment, or every aspect, of the present invention. Additional features and benefits of the present invention will become apparent from the detailed description, figures, and claims set forth below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the invention will become apparent upon reading the following detailed description in conjunction with the drawings in which: 
     FIG. 1 is a top view of a prior art blood glucose testing device; 
     FIG. 2 is a perspective view of a prior art lance; 
     FIG. 3 is a perspective view of a microneedle patch according to one embodiment of the present invention; 
     FIG. 4 is a cross-sectional view of the embodiment of the microneedle patch illustrated in FIG. 3; 
     FIG. 5 is another cross-sectional view of the embodiment of the microneedle patch illustrated in FIG. 3; 
     FIG. 6 is a collection point of a microneedle according to a second alternative embodiment of the present invention; 
     FIG. 7 is a collection point of a microneedle according to a third alternative embodiment of the present invention; 
     FIG. 8 is a collection point of a microneedle according to a forth alternative embodiment of the present invention; 
     FIG. 9 is an embodiment of a blood glucose monitoring device for use in conjunction with a microneedle patch according to a sixth alternative embodiment of the present invention; 
     FIG. 10 is an embodiment of a blood glucose monitoring device for use in conjunction with a microneedle patch according to a seventh alternative embodiment of the present invention; 
     FIG. 11 is an embodiment of a blood glucose monitoring system according to an eighth alternative embodiment of the present invention; and 
     FIG. 12 is an embodiment of a blood glucose monitoring system according to a ninth alternative embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIG. 3, a hollow microneedle patch  200  according to one embodiment of the present invention is illustrated. The microneedle patch  200  comprises a plurality of hollow microneedles  202  coupled to a test chamber  204 . Blood is moved through each of the plurality of microneedles  202  by capillary action to the test chamber  204 . In the illustrated embodiment of the present invention, the plurality of hollow microneedles  202  are arranged in a twenty by twenty array so that the microneedle patch  200  includes four hundred hollow microneedles  202 . The microneedle patch  200  is used to lance a user&#39;s skin and to harvest a sample of blood. Essentially, the microneedle patch  200  integrates the prior art test sensor  102  and the lance  120  (discussed in conjunction with FIGS. 1 and 2) into a single unit. 
     Each microneedle penetrates the skin to a depth of about two-hundredths of an inch (0.005 inch). The microneedles  202  extend below the surface of the skin a distance sufficient to collect a sample of blood from the outermost layer of capillaries. The skin&#39;s outer layer, called the stratum corneum, does not contain any nerve endings. The first extensive nerve layer is disposed below the outermost layer of capillaries. Because each of the microneedles  202  do not contact any nerves, the lancing of the skin and the collection of blood is essentially painless. Further, because the lacerations created in the skin are much smaller that those created by a conventional lance, the risk of infection is lessened and the healing of the lacerations is expedited. The precise dimensions of the microneedles  202  and the microneedle  200  patch are a function of several variables including the amount of blood to be harvested and the type of blood glucose analysis to be used in conjunction with the microneedle patch  200 . 
     Referring now to FIGS. 4 and 5, the microneedle patch  200  is illustrated pressed onto a user&#39;s skin  206  causing each of the microneedles  202  to penetrate the skin  206 . Each of the microneedles  202  are hollow and have a collection point  208  and an outlet  210 . The outlet  210  of each microneedle  202  is coupled to the test chamber  204 . After penetrating the skin  206 , blood  212  is collected though the collection point  208  of each of the microneedles  202 . The blood  212  is moved though an interior  214  of the hollow microneedles  202  by capillary action to the test chamber  204 . The requisite volume of blood  212  necessary for accurate testing is dependent on the type of glucose analysis employed. For example, the applicant has found that at least approximately one micro-liter of blood  212  is necessary to employ electrochemical analysis to determine the blood glucose concentration. Each of the plurality of microneedles  202  draws a portion of the requisite volume of blood  212  into the test chamber  204  where the analysis occurs. 
     A reagent  215  is incorporated in the test chamber  204  of the microneedle patch  200 . Once blood is moved into the test chamber  204 , the glucose in the blood  212  reacts with the reagent  215  in the test chamber  204  to produce a detectable signal. That signal is then measured by a sensor which can measure the concentration of the glucose in the blood  212  based on the signal. The specific reagent  215  incorporated into the test chamber  204  is a function of the type of sensing employed to determine the concentration of glucose in the blood  212 . 
     In operation, a user can measure the concentration of the user&#39;s blood by pressing the microneedle patch  200  onto the user&#39;s skin. Each of the microneedles  202  lances the skin  206 . A quantity of blood  212  is moved by capillary action from the collection point  208  of each microneedle  202  to the test chamber  204 . The glucose in the blood  212  reacts with a reagent  215  incorporated into the test chamber  204  producing a signal indicative of the blood glucose concentration. That signal is then measured with an appropriate sensor in a blood glucose analyzer to determine the concentration of glucose in the user&#39;s blood. Once the blood glucose analyzer measures the signal produced by the reaction, the microneedle patch  200  can be discarded. 
     An advantage to the use of the microneedle patch  200  is that blood never comes into contact with the blood glucose analyzer. Therefore, in addition to self-testing, the microneedle patch  200  may be used at a clinical level because cross-contamination is not an issue. For example, a doctor may use a single blood glucose analyzer to test the blood glucose concentration for that doctor&#39;s patients. One microneedle patch  200  would be used for each patient. The microneedle patch is pressed onto the patient&#39;s skin and the signal produced by the reaction within the microneedle patch  200  is read by a blood glucose analyzer which never contacts the patient&#39;s blood. The blood glucose analyzer can be used again while the used microneedle patch  200 , containing the sample of blood, is discarded. 
     Referring to FIGS. 6,  7  and  8 , three alternative embodiments of the collection point of each microneedle  202  is illustrated. Each microneedle  202  of the present invention is generally shaped as a hollow cylinder having cylindrical walls  230 . In FIG. 6, the collection point of the microneedle  202  is an angled collection point  232 . A plane parallel to the angled collection point  232  is disposed at an angle relative to the longitudinal axis of the microneedle  202 . 
     In another alternative embodiment, the microneedle  202  has a generally concave collection point  234  as illustrated in FIG.  7 . The generally cylindrical walls  230  of the microneedle  202  are formed upwardly sloping radially away from the longitudinal axis of the microneedle  202  at the collection point  234 . 
     In still another alternative embodiment, the microneedle  202  has a generally convex collection point  236  is illustrated in FIG.  8 . In the embodiment illustrated in FIG. 8, the generally cylindrical walls  230  of the microneedles  202  are formed downwardly sloping radially away from the longitudinal axis of the microneedle  202  at the collection point  236 . The shape of the alternative embodiments of the collections points illustrated in FIGS. 6-8 reduces surface tension at the collection point of the microneedle  202  thus facilitating the movement of blood from the collection point through the hollow microneedle  202  to the test chamber  104 . 
     Colorimetric analysis is one type of analysis that can be utilized with the microneedle patch  200  of the present invention. The reaction of the glucose and a specific reagent produces a change in color, or a colorimetric reaction, which is indicative of the amount of glucose in the blood. That color change can be compared to a color chart, wherein the colors on the color chart were obtained using blood having a known glucose concentration, to determine the blood glucose concentration. The color change in the test chamber  204  caused by the reaction of the glucose and the reagent  215  can be read with a spectrophotometric instrument incorporated into a glucose monitoring device for use with the patch  200 . In such an embodiment where colorimertic sensing is employed, a back side  218  (FIG. 4) of the test sensor  204  may be transparent allowing the glucose monitoring device to optically detect the color change. 
     Alternatively, electrochemical analysis is another type of analysis which may be utilized in conjunction with the microneedle patch  200  of present invention to determine the concentration of glucose in a user&#39;s blood. In such an embodiment, the test chamber  104  includes a pair of electrodes. In electrochemical analysis, the change in current across the electrodes caused by the reaction of the glucose and the reagent is indicative of the concentration of the glucose in the blood. The reaction of the glucose and the reagent creates an oxidation current at the electrode which is directly proportional to the user&#39;s blood glucose concentration. This current can be measured by an appropriate sensor implemented in an glucose monitoring device for use with the patch  200 . The glucose monitoring device can then communicate to the user the blood glucose concentration. Both calorimetric and electrochemical testing systems are described in detail by commonly-owned U.S. Pat. No. 5,723,284 entitled “Control Solution and Method for Testing the Performance of an Electrochemical Device for Determining the Concentration of an Analyte in Blood” which is incorporated herein by reference in its entirety. 
     Referring now to FIG. 9, a glucose monitoring device  300  having a calorimetric sensor (a spectrophotometric instrument)  302  which may used in conjunction with the microneedle array patch  200  is illustrated. The test chamber  204  of the microneedle array patch  200  contains appropriate reagents designed to react with glucose in a manner to produce a change in color indicative of the glucose concentration in the user&#39;s blood. The glucose monitoring device  300  having a colorimetric sensor  302  determines the glucose concentration and informs the user of the result. The monitoring device  300  is activated with a switch  304 . After the microneedle array patch  200  is pressed onto the user&#39;s skin and the requisite amount of time has past for the reaction to occur, the monitoring device  300  is brought into close proximity to the microneedle array patch  200  to read the colorimetric signal produced by the reaction. The test chamber  204  has a transparent back cover  218  allowing the calorimetric sensor  302  in the monitoring device  300  to optically read the signal. The monitoring then determines the blood glucose concentration and communicates those results to the user via a display  306 . The microneedle patch  200  can then be removed and discarded. 
     Alternatively, electrochemical sensing can be employed in conjunction with the microneedle array path of the present invention. FIG. 10 illustrates a suitable monitoring device  320  which can be used in conjunction with an embodiment of the microneedle patch  200  designed for electrochemical sensing. The embodiment of the microneedle patch  200  designed for electrochemical sensing contains a pair of electrodes  353 . The blood glucose monitoring device  320  contains a pair of corresponding electrodes  352  (shown in FIG.  10 ). The blood glucose monitoring device  350  is activated with a switch  354 . Once the microneedle patch  200  is pressed onto a users skin and a requisite amount of time has passed for the electrochemical reaction to occur, the electrodes  352  of the monitoring device are bought into contact with the corresponding electrodes  353  on the microneedle patch  200 . The results of the blood glucose analysis are communicated to the user via a display  356 . 
     Referring now to FIG. 11, another application of the microneedle patch  200  of the present invention is in an integrated blood glucose monitoring system  350  which integrates the microneedle array patch  200  and a blood glucose analyzer into a single instrument. The integrated blood glucose monitoring system contains a plurality of microneedle patches  200  and when activated moves a new microneedle patch  200  to the test end  352  of the system  350 . In operation, a user would activate the system  350  with a switch  354 . A new microneedle patch  200  is advanced to the test end  352  of the system  350 . The user would then press the test end  352  of the system against the user&#39;s skin causing each of the microneedles  202  in the array of microneedles  202  to lance the user&#39;s skin and to harvest the blood sample. Once the requisite blood sample has been obtained and the requisite time has elapsed for the reaction in the test chamber  204  of the microneedle patch  200  to occur, the blood glucose monitoring system  350  determines the blood glucose concentration and communicates the result to the user via a display  356 . The used microneedle array patch is then ejected from the system  350 . Both electrochemical sensing and colorimetric sensing as well as other types of blood glucose analysis may be implemented within the blood glucose monitoring system  350  of the present invention. 
     Referring now to FIG. 12, another alternative embodiment of the present invention is illustrated wherein the microneedle patch  200  has an adhesive  360  disposed on an upper surface  362  of the microneedle patch  200  in an another alternative embodiment of the present invention. The adhesive  360  holds the microneedle patch  200  against a user&#39;s skin  206 . The adhesive  360  is useful in an embodiment of the microneedle patch  200  wherein a longer period of time is required for the harvesting of the blood sample and then the occurrence of the reaction between the glucose in the blood and the reagent disposed in the test chamber  204 . Also illustrated in FIG. 12 are the pair of electrodes  353  disposed in the test chamber  203 . 
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that it is not intended to limit the invention to the particular forms disclosed, but, to the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the appended claims.