Abstract:
The skin preparation device and sensor of the present invention include an array of rigid tines. The tines serve to “self-prepare” the skin at each electrode site. These tines, when pressed against the skin, penetrate the stratum corneum, thereby reducing skin impedance and improving signal quality. A self-prepping device of the present invention is an optimized array of short non-conductive rigid tines in which the individual tines are created in a geometry that allows for a sharp point at the tip when molding, machining or etching is used as a method of fabrication. This non-conductive array with rigid penetrating structures may, therefore, be used in combination with a conductive medium, preferably an ionic conductive gel. In penetrating the stratum corneum, micro-conduits are created in the layers of the skin enabling the conductive medium to reach the low impedance layers and to transmit bioelectrical signals from the skin to the electrode surface. Such a self-prepping device can be readily mass produced using molding methods or possibly other manufacturing methods, thereby providing for a low cost means of achieving improved performance of the biopotential sensor. Additionally this invention includes the integration of this self-prepping device into a biopotential sensor comprising an array of one or more electrodes.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims benefit of Provisional Application Ser. No. 61/126,849, filed on May 2, 2008. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates to a skin preparation device that can be used to penetrate the outermost layer of skin to allow for the penetration and/or displacement of the stratum corneum. A typical use of such invention is in the non-invasive monitoring of electrophysiological signals. This skin preparation device may be integrated into the electrodes of a biopotential sensor. 
         [0003]    The human skin tissue is composed primarily of connective tissue, the dermis, covered by a protective layer, the epidermis. The outermost layer of the epidermis is the stratum corneum. In the study of electrophysiological monitoring using surface electrodes, the stratum corneum is significant, due to its function as a protective barrier. The stratum corneum is on average approximately 20 μm thick, and is composed primarily of denucleated, dead skin cells that are inherently a source of high electrical impedance. Very low amplitude signals are associated with some electrophysiological recordings, particularly electroencephalography (EEG); therefore, it is important to optimize the signal acquisition and minimize noise artifact. Thus, impedance measured at the interface between a patient&#39;s skin and the electrode used for acquiring the electrophysiological signals is an important consideration in biopotential monitoring. Additionally, variance in impedance between electrode sites can result in unwanted noise in the signal. Good electrical conduction between the patient&#39;s skin and the electrode can be better achieved by removing or penetrating the stratum corneum layer of the epidermis. 
         [0004]    The most common electrodes that are applied to the surface of the skin often require that the skin be prepared before the electrode is applied. Preparation of the skin typically begins with cleaning off the surface with alcohol to remove dirt and oils, followed by abrasion of the skin&#39;s surface with an abrasive material or a grit-impregnated gel to remove the stratum corneum layer. To simplify the skin preparation process that is required prior to application of an electrode, several forms of self-prepping electrodes have been developed. Such electrodes, which have an integrated mechanism for achieving this preparation of the skin, provide numerous advantages over standard EEG or electrocardiogram (ECG) electrodes because they eliminate the need for the additional step of skin preparation as well as the need to have the abrasive material available in a clinical setting. 
         [0005]    In many of these developments, the means by which the skin preparation occurs is by employing a textured component in conjunction with the electrode, which when pushed against the skin attempts to abrade or penetrate the outermost layer. This textured component may be a part of the electrode surface itself or an independent part affixed to the electrode surface. International Patent Application WO 02/00096A2 describes a means of collecting EEG using a “volcano tip” tine structure, in which tines formed from perforations in the electrode material are used to abrade the outer layers of skin and improve electrical contact. This application does not describe the design or manufacturing procedures for the volcano tip tine structure. 
         [0006]    U.S. Pat. No. 5,305,746 issued to Fendrock et al. describes an electrode which provides a textured component by way of an integrated array of non-conductive flexile tines. The flexile tines are of length 0.025″-0.110″ and of thickness 0.002″-0.015″, and are embedded in a wet conductive gel. The flexile tines part the stratum corneum layer to expose the low impedance layers without scratching or abrading deeper layers of the skin. Although this device does generally reduce the measured impedance at the skin to electrode (skin to gel) interface, the mechanism by which flexile tines part the skin varies from person to person and skin type to skin type. Long flexile tines lack uniformity of orientation and insertion angle into the skin. Rigid tines may provide better control over the tine orientation and the mechanism by which they bypass the stratum corneum. Due to their size, macro-sized tines, as described in U.S. Pat. No. 5,305,746, limit the potential density of the tines in the array thereby also limiting the ability to reduce the overall electrode size and overall area of skin that is affected while maintaining equivalent signal quality. In addition, long tines facilitate being pressed too deeply into the skin causing unnecessary penetration beyond the stratum corneum while a shorter tine limits the deformation of the skin. Consequently, the advantage of an array of shorter and more rigid tines is that they can produce more repeatable low impedance signals with potentially less irritation of the skin. 
         [0007]    U.S. Pat. No. 5,309,909 issued to Gadsby discloses a skin preparation and monitoring electrode that penetrates a patient&#39;s skin prior to acquiring biopotentials. The electrode has tines, mounted on the concave surface of a dome, that penetrate first the conductive layer of the electrode and then the skin when force is applied to the dome causing it to deflect towards the skin. Upon cessation of the application of force, the tines retract with the movement of the dome. The complexity of this design does not support the cost effectiveness and ease of manufacturing required for a disposable electrode and skin preparation device. 
         [0008]    The concept of using an array of shorter rigid tine structures for skin penetration is commonly associated with the applications of biopotential signal acquisition and transdermal drug delivery mechanisms. Among rigid tine array designs presented in journal and patent literature, there is a variety of tine array structures, materials, and dimensions, all optimized for their particular application. 
         [0009]    International Patent Applications WO 2004009172A1, WO 2007075614A1, WO 2007081430A2 describe microneedle devices for delivering a drug to a patient via the skin. These needles typically have a channel through the middle allowing fluid to pass through the microneedle array or they are coated with a drug, or active component that is intended to dissolve in the skin beneath the stratum corneum. These needles for transdermal drug delivery have no conductive requirement because they do not serve to transmit any electrical signal away from the skin. These microneedles utilize lithographic processes on silicon in order to be created at such small scale. 
         [0010]    An example of an additional application of an array of spikes used to achieve electrical contact with a series of very closely located electrode sites is described in U.S. Pat. No. 7,103,398 B2, issued to Sieburg. In this patent Sieburg describes a device for sensing electrical signals on the surface of human or animal skin. The device is comprised of a substrate containing a plurality of electrodes with each of those electrodes having one pointed contact end facing away from the substrate. In this design, each pointed contact, or “tine” is coupled electrically to an independent electrode site, rather than having multiple tines together penetrate an area of skin from which the signal will be conducted to the electrode surface. 
         [0011]    U.S. Pat. No. 6,622,035, issued to Merilainen et al. also aims to effectively acquire biopotential signals with an electrode comprising an array of cylindrical or tapered “spikes” to make the skin more permeable. Each electrode is described as having 100-10,000 (ideally 400-2000) spikes per electrode, with the length of the spikes ranging from 50-250 μm (≦0.010″) from the carrier or electrode surface. A subsequent patent, U.S. Pat. No. 6,961,603, also issued to Merilainen describes the same spike geometry and spike density; however such patent also teaches injection molding the “spikes” using a non-conductive material which will then be coated with a conductive layer such as silver-silver chloride. Such “spike” arrays, in addition to being conductive, are very small in size, fine in geometric characteristics and high in number spikes per array. These factors result in a non-cost effective design for molding, particularly for a disposable device. 
         [0012]    U.S. Pat. No. 6,690,959, issued to Thompson also teaches the use of “nano-spikes” to penetrate the epidermis of the skin for collecting electrical biopotentials. The spikes are formed using a Microelectromechanical System (MEMs) construction technique and are subsequently coated with a conductive metal. Besides an indication that the nano-spikes are 10 μm in length and have an angularly disposed end shaped to assist in penetration of the cornified layer of the skin, no further detail regarding the geometry of the spikes is offered. 
         [0013]    Similar biopotential signal acquiring devices have been created using carbon nanotubes. This approach is a highly effective means of creating very small, conductive tines in an array, however the cost and time associated with the growth of these arrays is currently prohibitive for integration into a high volume disposable product. The same drawbacks apply to microneedles formed using dry-etching of silicon, as it is a multi-step manufacturing process with high development costs. 
         [0014]    One object of the proposed invention is the transduction of low impedance electrophysiological signals using a device that employs an array of sharp, rigid structures that can be integrated into a set of one of more electrodes to conduct the signals to a monitoring system. A further object is to provide a device that can be mass produced, for this application, at a cost appropriate for a disposable use product. 
       SUMMARY OF INVENTION 
       [0015]    The device of the present invention includes an array of rigid tines. The tines serve to “self-prepare” the skin at each electrode site, providing for sufficiently low impedances required to collect high quality electrophysiological signals. These structures, when pressed against the skin (i.e. “prepping the skin”), penetrate the stratum corneum, thereby reducing skin impedance and improving signal quality. The function of this invention is to acquire repeatable bioelectrical signals with impedance less than 20 kΩ per electrode. These bioelectrical signals can then be transmitted from the electrode surface via the sensor conductors (leads) to the monitoring system. A self-prepping device of the present invention is an optimized array of short non-conductive rigid tines in which the individual tines are created in a geometry that allows for a sharp point at the tip when molding, machining or etching is used as a method of fabrication. This non-conductive array with rigid penetrating structures may, therefore, be used in combination with a conductive medium, preferably an ionic conductive gel. In penetrating the stratum corneum, micro-conduits are created in the layers of the skin enabling the conductive medium to reach the low impedance layers and to transmit bioelectrical signals from the skin to the electrode surface. Such a self-prepping device can be readily mass produced using molding methods or possibly other manufacturing methods, thereby providing for a low cost means of achieving improved performance of the biopotential sensor. Additionally this invention includes the integration of this self-prepping device into a biopotential sensor comprising an array of one or more electrodes. 
         [0016]    The specific invention described herein of tines within a tine array, which can be integrated into the electrodes of a biopotential sensor, is optimized for performance in a specific application and additionally is optimized for successful and cost effective manufacturing by injection molding methods. An alternative method of manufacturing may include micromachining and resin casting from a mold. Post processes may include a vacuum depositioning of precious metals or conductive ink layering if a conductive part is desired. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1A  is a schematic illustration of an embodiment of the sensor system in use. 
           [0018]      FIG. 1B  is a top plan view of an embodiment of the sensor system 
           [0019]      FIG. 1C  is an enlarged perspective view of a skin preparation device incorporated in a sensor system. 
           [0020]      FIG. 2  is a perspective view of one embodiment of a skin preparation device. 
           [0021]      FIG. 3A  is a perspective view of a second embodiment of a skin preparation device. 
           [0022]      FIG. 3B  is a top plan view of the second embodiment of the skin preparation device. 
           [0023]      FIG. 3C  is a front cross-sectional view of the embodiment of  FIG. 3A . 
           [0024]      FIG. 3D  is a side cross-sectional view of the embodiment of  FIG. 3A . 
           [0025]      FIG. 4A  is a perspective view of a third embodiment of the skin preparation device. 
           [0026]      FIG. 4B  is a top plan view of the embodiment of  FIG. 4A . 
           [0027]      FIG. 4C  is a side view of the embodiment of  FIG. 4A . 
           [0028]      FIG. 5A  is an enlarged perspective view of an embodiment of the tines of a skin preparation device. 
           [0029]      FIG. 5B  is a side view of the tines shown in  FIG. 5A . 
           [0030]      FIG. 5C  is a front view of the tines shown in  FIG. 5A . 
           [0031]      FIG. 6  is a perspective view of an embodiment of a skin preparation device including a separate gel chamber. 
           [0032]      FIG. 7A  is a perspective view of an embodiment of a skin preparation device. 
           [0033]      FIG. 7B  is an enlarged perspective view of a tine of the embodiment shown in  FIG. 7A . 
           [0034]      FIG. 7C  is an alternate embodiment of the skin preparation device shown in  FIG. 7A . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0035]    A biopotential sensor  12  shown in  FIGS. 1A and 1B  is a device that contains an array of one or more electrodes  14  and a set of conductors that provide an electrical conduction path for the acquired signals from the electrodes  14  to a single terminating connector  16  which in turn connects to the mating receptacle  18  of the biopotential monitoring system  20 . The sensor device  12  may be coupled to the monitoring system via a terminating connector  16  inserted into a mating receptacle  18  on the monitoring system  20 . Once electrical connection is achieved, the monitoring system  20  may perform analysis of the acquired biopotential signals. 
         [0036]    The biopotential sensor  12  includes one or more electrodes  14 . In the embodiment of the biopotential sensor  12  shown in  FIG. 11B , the sensor  12  is comprised of four electrodes  14 . In this embodiment, the sensor  12  includes a flexible substrate  22  with an adhesive layer on at least portions of the substrate  22  to enable secure placement on the skin. Not shown in the figure are the conductors which may be printed on the substrate  22  with conductive material or alternately be a set of conductive wires mounted on the substrate  22 , and the terminating connector which enables connection of the conductors to the monitoring system. The electrodes  14  that comprise the sensor  12  may be formed with a layer of conductive material, preferably silver/silver chloride, which may be printed. Alternately the electrodes may incorporate a silver/silver chloride coated surface in contact with a post or stud on the opposite (non-patient contacting) surface. The post or stud makes electrical contact via a common EEG snap or a pre-attached wire, between the electrode surface and the conductors to the connector. The conductive surface of the electrode may also be formed of conductive carbon. 
         [0037]    The surface of the electrode  14  may be coated with a conductive medium, preferably an ionic conductive wet gel, comparable to those commercially available for the application of signal acquisition. Alternately, a solid conductive gel may be used to coat the surface of the electrode  14 . In another embodiment, the conductive gel may be both a conductive medium as well as an adhesive. The conductive gel provides continuous contact between the electrode surface and the surface of the skin even if the electrode substrate does not conform precisely to the curvature of the electrode site on the skin. In yet another embodiment the electrode  14  area may contain a sponge to keep the electrolytic gel in suspension. 
         [0038]    Referring to  FIG. 1C , included as part of the electrode  14  of this biopotential sensor  12  is a prepping device which is an array  26  of rigid tines  24 . In one embodiment, the tine array  26 , or multiple tine arrays, may be affixed to the electrode(s)  14  with an adhesive either on the bottom surface of the tine array  26  base or around its perimeter. The tine array  26  may be positioned such that a portion of the length of the tines  24  in a tine array  26  extends above the adhesive layer which may be on the flexible sensor substrate  22 . In an alternate embodiment, the tine array  26  is not part of an array of electrodes  14 , but instead is a separate component that is utilized to prepare the skin. 
         [0039]    The rigid tines  24  may remain in contact with the skin and still remain affixed to the electrode surface once the electrode  14  with the prepping device on the sensor  12  has been pressed firmly against the skin. The tines  24  may retract from the skin once pressure is no longer being applied. In either arrangement pressing the electrode  14  toward the skin allows the tine structure to displace or penetrate the stratum corneum and allows the bioelectrical signal to be conducted from the skin to the electrode surface by way of the conductive gel in which the tines are embedded. In one embodiment, the conductive gel may be applied to the top surface of the tine array  26  or alternately it may be contained in a sponge which may overlay the tines. A preferred tine height is 0.020″-0.040″, however the tine height may range from 0.010″-0.080″, ensuring that the tine will efficiently create micro-conduits through the depth of the stratum corneum, while at the same time limiting the amount of deformation of the skin. The decreased height of the tine  24  in combination with small tine size minimizes sensation on the skin during the process of prepping the sensor  12 . An adhesive layer, which could be adhesive backed foam, on the perimeter of the electrode  14  may be employed to create a central cavity in which the tine disk is secured. The small size of the tines  24  and the reduced number of times allow the electrode  14  to be worn comfortably for long periods of time. The application procedure does not require specialized training and thus can be performed by any person, including self preparation by the subject of the biopotential recording. Furthermore, it eliminates the need for initial skin preparation by separate abrasive materials or gels prior to electrode application. 
         [0040]    In some embodiments, the rigid tine array  26  is formed from a non-conductive material. This same nonconductive material is used to form both the base of the tine array and the tine structures  24  themselves. In an alternate embodiment the tine array material is deposited with conductive particles, such as gold, silver or carbon, to make the part conductive and allow for direct electrode conduction through the structure. Each rigid tine array  26  may have multiple identical or unique tine structures ranging in quantity from 20-60 tines per array. The spacing between the tines  24  is such that the tine array  26  can be adequately machined or molded. For manufacturability, the tines  24  may be aligned in rows or a circular pattern and the orientation of the individual tines  24  may vary. Alternate embodiments may contain tines numbering anywhere between 10 and 100 per array. In addition, the use of tines of various heights may be advantageous to reducing “bed of nails” effect when trying to obtain low skin impedances in certain parts of the body. The differing tine heights may avoid the disadvantage of distributing the applied pressure evenly between identical length tines and thus being unable to pierce the stratum corneum. 
         [0041]    The base of the tine array  26  may be flat, convex, or any geometry such that the base conforms to the shape of the skin at the electrode application site. Alternately, the base may be formed in multiple stepped levels  28  as shown in  FIG. 2  to allow better displacement or penetration of the stratum corneum at more pliable areas of the skin. 
         [0042]    In another embodiment shown in  FIG. 3A , the tines  24  are formed on the top surface of the array base. In one embodiment the base  30  of the array  26  is a round disk with a diameter in the range of 0.25″-0.50″, however it may range in size from 0.10″-1.0″. The shape of the base  30  of the array  26  may also be created in any size and geometry such that the tine array  26  fits within the area of the electrode  14 . The base  30  of the tine array  26  may be solid or may contain one or more holes or channels  32 . The holes or channels will allow the passage of conductive gel from the surface of the skin to the surface of the electrode. 
         [0043]    An alternate embodiment of the arrangement of the tine array shown in  FIG. 4A to 4C  is a solid annular ring  36  which contains the tines  24  and which includes a central opening  38  to permit gel flow and electrical contact between the conductive medium and the electrode surface ( FIG. 4A ). Yet another alternate embodiment has a small round tine array that leaves an outer ring of the electrode surface exposed. Alternate embodiments may contain electrode surfaces up to 1.5″ in diameter. In yet another embodiment, the gel may be contained in a separate cavity during storage and gets displaced to the skin site during application or during the prepping action ( FIG. 6 ). 
         [0044]    The tine structure is preferably created from a plastic such as polycarbonate (PC), acrylonitrile butadiene styrene (ABS), nylon, etc., through the process of injection molding. In the preferred embodiment the tine structure is created from liquid crystal polymer (LCP), such as Vectra E130i manufactured by Ticona Engineering Polymers, Florence, Ky. The material may alternatively be any nonconductive plastic which is rigid, such that the tips do not bend upon contact with the skin; however, this material, as applied to the structure, must not be brittle, in order to prevent breakage of the tips in the skin. The entire tine array structure may be created through injection molding using the same material in a single piece for both the base  30  and individual tines  24 . Alternately, the tine array may be assembled from multiple molded pieces. The use of nonconductive material ensures that offset voltages are not created by contact between metal and skin. The preferred manufacturing method is injection molding due to repeatability and low cost of mass production and the preferred array shape of a disk is optimal for efficiency of injection molding techniques. However, the tine array  26  may be formed by machining, etching or printing methods. An alternate embodiment may include the impregnation of the molded material with carbon nanotubes in order to increase the hardness of the tines  24 . The carbon nanotubes may also make the electrode surface partly conductive, which aids in signal acquisition. 
         [0045]    As shown in  FIGS. 5A to 5C , each individual tine  24  is generally tapered from base to tip and protrudes in a perpendicular direction from the base. Thus, the tip of each tine  24  penetrates approximately at a 90 degree angle to the skin upon pressing of the electrode against the surface of the skin. Rigid, perpendicular penetration effectively creates repeatable micro-conduits in the stratum corneum with the least force required. The geometry, including the aspect ratio of the tine, is determined to optimize the sharpness of the tip, the effectiveness of skin penetration and the manufacturability of the device. The sharpness of the tip of the tine  24  can be quantified as a radius of curvature. The tines  24  in the arrays  26  have a radius of curvature less than 0.02″. Additionally, the height of an individual tine may be in the range of 0.010″-0.080″ though the preferred height is in the range of 0.020″-0.040″. The preferred geometry of the tine  24  is that of a triangular pyramid with an isosceles triangle shaped base. The base of the triangular pyramid may also be an equilateral or scalene triangle. The geometry of the tine  24  may be various other shapes which allow for a taper from base to tip such as a rectangular pyramid, a half cone with a semicircular base or a full cone with a full circle or an elliptical base, or the tine  24  can be in the shape of an obelisk where the taper does not necessarily begin at the base of the tine. In a preferred embodiment, one face of the pyramid, preferably the face corresponding to the longest side of the triangle may extend at a 90 degree angle from the base. 
         [0046]    As shown in  FIG. 5B , the cross section of such a tine would be a right-angled triangle having one side as vertical, that is, perpendicular to the base. 
         [0047]    Impedance measurements at the skin interface were obtained with a biopotential sensor consisting of an array of four (4) electrodes (in an arrangement as shown in  FIG. 1B ) each including an embodiment of the rigid tine device. This embodiment of the tine device consisted of an array of twenty four (24) pyramidal tines at 0.030″ in height, and with a sharp point having a radius of curvature less than 0.01″. The measurements averaged 7 kΩ with less than 2.6 kΩ standard deviation across subjects. 
         [0048]    Referring to  FIG. 1B , an implementation of the skin prepping device is shown in a sensor array. Each electrode area  14  contains multiple tine arrays  26  which are arranged over a layer of conductive material. The prepping structures or tine arrays  26  are arranged on the individual electrodes  14  such that a substructure is created with independent prepping areas. When the individual electrodes  14  with the created substructure of tine arrays  26  are pressed upon, in order to prep the skin, the tine arrays  26  approach the skin at different angles. The angulations of the individual tine arrays  26  accommodate skin irregularities in certain areas of the body or in the softer tissue areas. 
         [0049]    In an alternate embodiment, shown in  FIG. 6 , an exemplary gel storage container or chamber  50  is shown coupled to a prepping device  60 . In certain embodiments, the gel storage container may be a burst container. The burst container is designed to open upon the application of force. The gel storage container  50  will hold the conductive gel separate from the electrode and prepping mechanism until the sensor is applied to a patient&#39;s skin. This will aid in a longer shelf life for the sensor since any dryout by the conductive gel will be avoided during storage. The gel storage container  50  is shown with a ring prepping mechanism, however, the gel storage container may be used in combination with any of the skin preparation mechanisms shown. In the illustrated embodiment of  FIG. 6 , the prepping mechanism includes a base member  62  that is contiguous with a plurality of generally pyramidal tines  64 . Each tine  64  may have a concave side that is aligned with a curved sidewall of an aperture or hole  66  formed in the base member  62  of the prepping device  60 . In some embodiments, the gel storage container is designed such that applying pressure on the skin prepping device causes the gel to flow from the gel storage device through the aperture into the area between the prepping device and the skin. This serves to precisely place the gel at the site of the micro conduits created by the time arrays. 
         [0050]    Turning now to  FIG. 7A , an alternate prepping mechanism or device  70  is shown. The prepping device  70  may include a plurality of holes or apertures  72  formed in a base member  74 . The base member  74  is shown as rectangular in shape, but other shapes may be used. The base member  74  may also include a plurality of tines  76 . Each tine  76  is generally pyramidal in shape having a concave side wall. In the preferred embodiment, the concave sidewall is perpendicular to the base of the pyramid as shown in  FIG. 7B . This tine construction of a pyramid with a perpendicular concave wall creates a much sharper edge than a pyramid alone, as is evident by the smaller radius of the tip of the preferred construction in comparison to an equivalently-sized pyramid without a concave wall. The concave sidewall of the tine  76  is aligned with a sidewall of one of the apertures  72  in the base member  74 . Although, the illustrated embodiment of  FIG. 7A  shows four tines  76  for each aperture  72 , any number of tines  76  may be provided for each aperture  72 . 
         [0051]    In  FIG. 7B , an enlarged drawing of a generally pyramidal tine  76  is shown. The concave sidewall  78  is shown as extending from the apex of the pyramid through the base of the pyramid. This curved sidewall  78  may be aligned with an aperture formed in the base member  74 . 
         [0052]    In  FIG. 7C , an alternate embodiment of a prepping device or mechanism  70  including the generally pyramidal tines  76  is shown. In this embodiment, an exemplary tine pattern is shown. The tines  76  in combination with the apertures  72  is shown in a cross pattern. Any pattern using the combination of tines  76  and apertures  72  formed in the base member  74  may be used to form a prepping device or mechanism. The pattern shown here is one example of a pattern that is contemplated. 
         [0053]    While the foregoing invention has been described with reference to its preferred embodiments, various alterations and modifications may occur to these skilled in the art. All such alterations and modifications are intended to fall within the scope of the appended claims.