Patent Publication Number: US-8109187-B2

Title: Tissue harvesting device and method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a division of co-pending application Ser. No. 10/442,488 entitled “Tissue Harvesting Device and Method,” filed May 21, 2003, which is a continuation-in-part of co-pending application Ser. No. 10/379,342 entitled, “Tissue Processing System,” filed Feb. 3, 2003; the prior applications are herewith incorporated by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a device and method for harvesting dermal tissue. More particularly, this invention relates to a device and method for extracting small particles of dermal tissue for transplantation to a recipient site. 
     BACKGROUND OF THE INVENTION 
     Traditional skin grafting is accomplished by taking a thin slice of dermal tissue from a donor site in order to cover a wound site, such as a burn area. In some instances, the slice of dermal tissue is meshed to expand its size, creating a meshed graft. Traditional devices used to harvest the tissue from the donor site include dermatomes for removing a thin slice of the upper layers of skin from a donor site. The slice is then meshed using traditional techniques to create and expand the sheet of skin tissue that gives the slice a weave-like appearance. The purpose of expanding the skin from the donor site is to increase the amount of area on a recipient site that can be covered by the donor site. Some of the most desirable expansion ratios currently available are 6:1. That is, under the most ideal conditions, skin taken from a donor site would be able to cover a recipient site that is six times larger than the donor site. 
     Traditional meshed grafting techniques have been shown to yield 90% viability at the donor site. A slightly lower viability rate occurs for non-meshed sheet grafts, mostly due to fluid accumulation under the sheet graft. Factors that lead to graft failure include poor circulation, unclean wounds, patient interference with the graft dressing, obesity, and smoking. Additionally, in at least approximately 10% of cases, infection at the donor site occurs. Although such donor site infections are not likely related to graft failure at the wound site, they still pose problems for both the patient and caregiver. 
     As mentioned, traditional meshing techniques yield a most favorable expansion ratio of 6:1. For example, a 1 cm 2  donor site can cover a 6 cm 2  wound site. While greater ratios of 9:1 and 12:1 may be possible using meshing techniques, there is also a significant delay in epithelialization with such ratios. 
     Micro grafting techniques, in which the donor tissue is actually minced in order to achieve a greater than 10:1 expansion ratio, are known in the art. Such techniques allow for a much greater coverage area from a small donor site. However, traditional techniques are cumbersome, and often the viability of the cells is compromised to such an extent that sometimes less than 50% of the cells are viable when applied to the wound site. Additionally, traditional techniques have thus far been inadequate in producing viable cells in the range of 500-1500 microns. 
     Traditional micrograft techniques, dating back to 1963, utilized minced skin that is between ⅛ th  inch (approximately 3 mm, or 3000 microns) or 1/16 th  inch (approximately 1.5 mm, or 1500 microns) in size. However, disadvantages of using pieces larger than 1500 microns have been noted. Among the disadvantages are that many of the cells are trapped within the pieces of skin, and are thus unable to proliferate or produce new cells required to form new skin. Furthermore, if such large pieces of skin are to be transplanted, the epidermis side of each piece has to be oriented upwards, and the dermis side oriented downwards. This makes the procedure tedious and impractical. Also, the appearance of the new skin that is produced using particles of this size is poor, often having a cobblestone appearance. 
     Other micrografting techniques have utilized minced skin that is 200 to 500 microns in size. While sometimes producing cosmetically better grafts over the larger micrografts, many of the cells contained in the particles are rendered non-viable by the process of producing cells of such a small size. 
     It is therefore an object of this invention to provide a system for obtaining and processing tissue samples from a donor site on the order of 50-1500 microns in size, such that the vast majority of tissue processed at this size is viable when transplanted to a recipient site. It is a further object of the present invention to strike the ideal balance between cell viability and cell proliferation between the size range of 500-1500 microns, and most preferably 600 microns, which has heretofore not been achieved. 
     Additional objects of the present invention include a significant reduction in the size of the donor site as compared to traditional mesh-graft procedures; minimizing scarring of the graft site as compared to traditional mesh-graft procedures; improvement of the pliability of tissue in the graft site; improvement of the cosmetic appearance of the graft site as compared to current methods; and improvement of graft “take.” 
     SUMMARY OF THE INVENTION 
     In accordance with the foregoing objects, the present invention generally comprises a device for harvesting tissue from a donor site into particles in the size range of 50-1500 microns, and most preferably about 600 microns, such that the particles may produce an expansion ratio, or cell proliferation, of at least 6:1 and up to or over 20:1. 
     The present invention includes a method for cutting and removing tissue from a donor site. The typical donor site may be equivalent to a split—thickness—skin graft (“STSG”). A traditional dermatome may be utilized to obtain the donor sample, or STSG, which is then processed into smaller micrografts between 50-1500 microns in size. More preferably, the micrografts are processed into sizes between 500 microns and 1500 microns, and most preferably to about 600 microns, which has been shown to yield the greatest viability and proliferation. A cutter is utilized to process the tissue into the desired size. Alternatively, the donor tissue may be processed into the desired size directly on the donor site, and thereafter removed from the donor site. 
     The present invention also includes a cutter for processing the tissue into the desired size range. Several alternative cutters may be utilized in accordance with the present invention, including roller cutters. In one embodiment, a roller have having a square-shaped grid pattern of raised edges is used to achieve tissue particles of the desired size. Alternatively, dual rollers may be utilized, in which each roller has a series of evenly spaced parallel raised cutting edges, which are oriented perpendicular to the raised edges on the opposing roller. The donor tissue or STSG may be passed between the rollers, or the rollers may be pressed against a single surface of the donor tissue. 
     Other alternative cutters include die-cast rigid sheets, which may be flat or concave. The rigid sheet is pressed to the donor tissue manually or by means of a reciprocating roller. The cutting edges of the rigid sheet include a raised, square-shaped grid pattern, or alternatively, a series of opposing facing, raised concave cutting edges. 
     Cutters that may be utilized to process the donor tissue directly at the donor site include bundled capillary tubes, having a sharpened edge. Other cutters for processing donor tissue that has already been excised from the donor site include a cylindrical press cutter. 
     Removing the tissue from the cutters, after it has been processed into the desired size, is accomplished by positioning an elastomer, such as rubber or other flexible material, between the cutting surfaces of the cutters. As the cutter is pushed into the donor tissue, the elastomer retreats from the cutting edge to allow the tissue to be cut. As pressure is relieved from the cutter, the elastomer returns to its original position, thereby pushing the cut tissue out from the cutting edges. 
     The foregoing has outlined some of the more pertinent objects of the present invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or by modifying the invention as will be described. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the following Detailed Description of the Invention, which includes the preferred embodiment 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features and advantages of the invention will now be described with reference to the drawings of certain preferred embodiments, which are intended to illustrate and not to limit the invention, and wherein like reference numbers refer to like components, and in which: 
         FIG. 1  is a perspective view of a donor tissue excised from a donor site using traditional methods; 
         FIG. 2  is a perspective view of a cylindrical roller cutter of the present invention; 
         FIG. 3  is a perspective view of donor tissue processed into the desired size directly at the donor site in accordance with the present invention; 
         FIGS. 4A ,  4 B, and  4 C are perspective views of a rigid sheet cutter of the present invention; 
         FIG. 5  is a perspective view of a circular blade cutter of the present invention; 
         FIGS. 6A and 6B  are perspective views of dual roller cutters of the present invention; 
         FIG. 7  is a perspective view of a stacked microtome cutter of the present invention; 
         FIG. 8  is a perspective view of a bundled capillary tubes cutter of the present invention; 
         FIG. 9  is a cross-sectional view of a cylindrical press cutter of the present invention; 
         FIG. 10  is a perspective view of a stacked disc cutter of the present invention; and 
         FIG. 11  is cross-sectional view of a tissue extraction means of the present invention. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     Although those of ordinary skill in the art will readily recognize many alternative embodiments, especially in light of the illustrations provided herein, this detailed description is exemplary of the preferred embodiment of the present invention as well as alternate embodiments, the scope of which is limited only by the claims that may be drawn hereto. 
     Referring now to the drawings, the details of preferred embodiments of the present invention are graphically and schematically illustrated. Like elements in the drawings are represented by like numbers, and any similar elements are represented by like numbers with a different lower case letter suffix. 
     As illustrated in  FIG. 1 , a donor tissue sample  10 , such as a split-thickness-skin graft (“STSG”) may be removed from a healthy region of skin tissue  12  using traditional techniques, such as by running a dermatome  14  across the surface of the donor site  12 . The donor tissue  10  is positioned on a flat surface  18 , so that the cutter  16  of the present invention may be applied to it, as is shown in  FIG. 2 , in order to process the tissue into the desired size. In the preferred embodiment, the donor tissue  10  is processed into the desired size range of between 50-1500 microns 2 , more preferably between 500-1000 microns 2 , and most preferably 600 microns 2 . Alternatively, the donor tissue  10  may be processed into the desired size or size range directly at the wound site  12 , as depicted in  FIG. 3 . A dermatome  14 , or similar traditional device, may be used to excise the processed tissue particles  10  from the donor site  12 . 
     After the donor tissue is removed from the donor site, the tissue is processed by the tissue processor  16 , as illustrated in  FIGS. 2A and 2B . In an alternative embodiment, the tissue processor  16  cuts the donor tissue at the donor site  10  directly. The tissue processor is comprised of a series of sharpened blades  18  arranged in parallel to one another and fixed along an axis  20 . The distance  22  between the blades  18  may be adjusted according to the desired size of the tissue sample to be obtained. The preferred distance  22  between each blade  18  is in the range of about 250 microns to 1000 microns. The most preferable distance  22  is one of about 16 of the present invention for processing donor tissue  10  into particles  20  of the desired size. The cutter  16  consists of a cylindrical roller  22  in which the cutting surface  24  consists of a square-shaped grid pattern of raised edges  26 , that form blades for cutting the donor tissue  10  into particles  20  of the desired size. The roller  22  is pressed onto the donor tissue  10  manually, such as by handles  30  attached along the longitudinal axis  28  of the roller  22 , or by an electromechanical actuator (not shown), such as an electric motor and axle along the longitudinal axis  28 , similar to that used in traditional dermatomes known in the art. 
     An alternative embodiment of the cutter  16 , as illustrated in  FIGS. 4A ,  4 B, and  4 C, includes a rigid sheet  34  having a plurality of raised cutting edges  32 . The rigid sheet  34  may be a die as shown in  FIGS. 4A and 4B , in which the cutting edges  32  form a square-shaped grid pattern, in which each grid is the size of the desired particle to be cut from the donor tissue  10 . Alternatively, the cutting edges  32  may consist of a series of oppositely facing, raised concave cutters  36 , as shown in  FIG. 4C . The rigid sheet  34  may be flat, as shown in  FIG. 4A , or concave to aid in manual pressing of the cutter  16  to the donor tissue  10 , as shown in  FIG. 4B . In such an embodiment, the cutting edges are positioned on the outer curve  38  of the rigid sheet  34 . 
     The particles may be extracted from the donor tissue after application of the rigid sheet  34  cutter  16  by oscillating the sheet  34 , such as by a piezo-electric driver, along a vertical axis  40 , as illustrated in  FIG. 4C . Alternatively, the rigid sheet  34  may be pressed onto the donor tissue  10  manually. Other alternative pressing means include use of an arbor (not shown), such as an axle press known in the art, or by means of a roller actuator  42 , that presses the sheet  34  against the donor tissue  10  as the roller  44  of the actuator  42  is passed across the surface of the rigid sheet  34 , as shown in  FIG. 4A . 
     Turning now to  FIG. 5 , there is illustrated a further embodiment of the cutter  16 . The cutter is comprised of a series of sharpened circular blades  50  arranged in parallel to one another and fixed along an axis  52 . A handle  60  may be positioned along an opposing axis  62 . The distance  54  between the blades  50  may be adjusted according to the desired size of the tissue sample to be obtained. The preferred distance  54  between each blade  50  is in the range of about 50 microns to 1500 microns. The more preferable distance  54  is between about 500 microns and 1000 microns, and most preferably 600 microns. In the preferred embodiment, the space  54  between blades  50  may be adjusted to within the preferred distances mentioned, or alternatively, fixed to a distance within the preferred distances mentioned. The distance  54  between the blades  50  allows for uniform tissue particles to be produced at the ideal range of 50 square microns to 1500 square microns. As mentioned, tissue particles within the desired range have been shown to yield the highest expansion ratio while retaining the greatest viability. 
       FIGS. 6A and 6B  illustrate a further embodiment of the cutter  16 , which consists of a pair of cylindrical rollers  70   a ,  70   b . The first cylindrical roller  70   a  has a first set of raised, parallel cutting edges  72 . The second cylindrical roller  70   b  has a second set of raised, parallel cutting edges  74  that are oriented approximately perpendicular to the first set of raised cutting edges  72 . The cutting edges  72 ,  74  are separated by between about 50-1500 microns, and most preferably 600 microns. In the embodiment depicted in  FIG. 6A , the donor tissue  10  is passed between the first and second rollers  70   a ,  70   b , which are rotating in opposite directions around their respective axes of rotation  76   a ,  76   b . Alternatively, and as depicted in  FIG. 6B , the rollers  70   a ,  70   b  rotate in the same direction as they are pressed along the surface  80  of the donor tissue  10 . 
     Still another embodiment, as illustrated in  FIG. 7 , of the cutter  16  of the present invention consists of multiple microtomes  82  stacked and separated by a space  84  within the range of about 50-1500 microns, and most preferably 600 microns. The microtomes  82  are pressed against the donor tissue to achieve particles of the size desired. 
     A further embodiment, shown in  FIG. 8 , of the cutter  16  of the present invention, consists of a bundle  84  of capillary tubes  86  having sharpened edges  88 . The edges  88  are pressed into the donor tissue to extract particles of a size equivalent to the inner diameter 90 of the capillary tube  86 , which is in the range of about 50-1500 microns, and most preferably 600 microns. An elastomer (not shown), such as soft rubber, may be positioned within each capillary tube  86  to aid in extraction of the particles after they have been cut from the donor tissue  10 . As the capillary tube  86  is pushed into the tissue, the elastomer retreats from the edges  88  of the tube  86 , allowing the tissue to be cut. As pressure is relieved, the elastomer returns to its original position within the tube, pushing the cut tissue particles out of the tubes  86 . 
     A cylindrical press  100 , as shown in  FIG. 9 , may be utilized to cut tissue into a desired size within the range of 50-1500 microns, or preferably 600 microns, after the donor tissue  10  has been removed from the donor site  12 . The press  100  is housed within a housing  102  having an open proximal end  104  and a closed distal end  106 , which is closed by the press  100  itself. An elastomer  108 , such as rubber, is fixed to the press within the housing, and a removable cap  110  is positioned along the open proximal end  104  for catching the tissue particles after they have been cut. Multiple blades  112  are fixed within the housing  102  between the elastomer  108  of the press  100 , and the open proximal end  104 . The donor tissue  10  is placed within the housing  102  between the press  100 , which is removable, and the blades  104 . As the press  100  passes through the housing  102 , the elastomer  108  contacts the tissue  10  and forces it into and through the blades  112 . The particles, having been cut to the desired size, are trapped within the cap  104 . 
     Still a further embodiment of the cutter  16  is illustrated in  FIG. 10 . The cutter may consist of multiple serrated discs  120 . Slots  122  are formed within the discs  120 , which are positioned along an axis  124 . The discs  120  are fixed along the axis  124  such that a space of between 50-1500 microns, or preferably 600 microns, exists between each disc  120 . A ring  126  of longitudinal blades  128  envelops the discs  120 , and configured to pass between the serrations of the discs  120 . Previously excised donor tissue  10  is placed between the discs  120 , cutting them into the desired particle size as the ring  126  is passed over the discs  120 . 
     Extraction of the particles from the blades or edges  130  of the cutter  16  is illustrated in  FIG. 11 . An elastomer  132  is positioned within the space  134  between the blades or edges  130 . As pressure is exerted by the cutter  16  against the donor tissue  10 , the elastomer  132  retracts. The cut tissue trapped in the space  134  between the blades  130  is forced out from the space  134  as pressure is relieved from the cutter  16  and the elastomer  132  returns to its original position. 
     The present invention includes a method of processing harvested donor tissue into micrograft particles within the size range of 50-1500 microns, and most preferably 600 microns. A further embodiment includes processing donor tissue to micrograft particles between 50-1500 microns, and most preferably 600 microns, directly at the donor site, and thereafter excising the particles from their contact points at the donor site using traditional means, such as a dermatome. 
     While the above description contains many specifics, these should not be construed as limitations on the scope of the invention, but rather as exemplifications of one or another preferred embodiment thereof. Many other variations are possible, which would be obvious to one skilled in the art. Accordingly, the scope of the invention should be determined by the scope of the appended claims and their equivalents, and not just by the embodiments. 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in a Tissue Harvesting Device and Method, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.