Abstract:
A dermal tissue transplantation system combining a tissue particle harvester, a tissue particle collector, and a chambered dressing. The system provides a harvester capable of harvesting tissue from a donor site on the order of about 100 microns. The integrated tissue particle collector provides a means for collecting the harvested tissue for in situ cultivation in a chambered dressing at the wound site.

Description:
CROSS-REFERENCE TO RELATED APPLICATION AND PRIORITY CLAIM  
       [0001]    The present application is based on and claims priority under 35 U.S.C. § 119(e)in U.S. Provisional Patent Application Serial No. 60/414,133; filed Sep. 28, 2003. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The invention relates to a dermal tissue transplantation system. More particularly, this invention relates to a system for obtaining, processing, collecting, and applying tissue samples for purposes of transplantation  
         BACKGROUND OF THE INVENTION  
         [0003]    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 bum 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, which function in many respects similar to a cheese slicer.  
           [0004]    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.  
           [0005]    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 are certainly possible, there is also a significant delay in epithelialization with such ratios.  
           [0006]    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.  
           [0007]    It is therefore an object of this invention to provide a simpler grafting procedure, improve micro-graft viability (“take”), reduce the bio-burden at the wound site by better preparation of the wound bed prior to grafting, improve the cosmetics of grafts as compared to meshed grafts, and reduce the size of the donor site.  
           [0008]    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.” 
           [0009]    It is still a further object of this invention to provide a grafting technique that does not extend the healing time as compared with traditional mesh-grafts, while also reducing the cost and time required to complete the procedure.  
         SUMMARY OF THE INVENTION  
         [0010]    In accordance with the foregoing objects, the present invention generally comprises a skin harvester for obtaining tissue from a donor site, a tissue particle collector for collecting tissue from the harvester, and a chambered dressing for propagating the collected tissue in situ at a wound site.  
           [0011]    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  
       [0012]    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:  
         [0013]    [0013]FIG. 1 is a block diagram generally illustrating the dermal tissue nano-grafting system of the present invention.  
         [0014]    [0014]FIG. 2 is a block diagram generally illustrating the tissue harvester assembly of the present invention.  
         [0015]    [0015]FIG. 3 is a cross-sectional side view of a harvester housing showing an interior space into which a tissue-cutting tool is received.  
         [0016]    [0016]FIGS. 4A and 4B are cross-sectional front views of a harvester housing illustrating the interface of the housing with the tissue source to be harvested.  
         [0017]    [0017]FIGS. 5A and 5B are a perspective view (A) and an end view (B) of a rotating shaft-type tissue cutter.  
         [0018]    [0018]FIG. 6 is an illustration of a “TI” type cutting features on a rotary drum-type cutting tool of the present invention.  
         [0019]    [0019]FIGS. 7A and 7B illustrate “scallop” type cutting features with hypo-tubes on a rotary drum type cutting tool of the present invention.  
         [0020]    [0020]FIG. 8 illustrates “square scallop” type cutting features useful for the cutting surface of a rotary drum-type cutting tool of the present invention.  
         [0021]    [0021]FIG. 9 illustrates “round scallop” type cutting features useful for the cutting surface of a rotary drum-type cutting tool of the present invention.  
         [0022]    [0022]FIGS. 10A and 10B illustrate a rotating shaft-type tissue cutter tool and harvester housing (A), and the rotating shaft-type tool installed in a type of tissue harvester assembly (B). The tool is a side cutting bit installed in a shear block type harvester housing of the present invention.  
         [0023]    [0023]FIG. 11 illustrates a fine scallop hypo-tube rotating shaft-type tissue cutter tool of the present invention.  
         [0024]    [0024]FIG. 12 illustrates a course scallop hypo-tube rotating shaft-type tissue cutter tool of the present invention.  
         [0025]    [0025]FIG. 13 illustrates a course scallop solid shaft-type tissue cutter tool of the present invention.  
         [0026]    [0026]FIG. 14 illustrates an alternative side cutting bit shaft-type tissue cutter tool of the present invention.  
         [0027]    [0027]FIG. 15 is a partial cross-sectional end view of the housing and tissue-cutter tool of an end-mill type tissue harvester assembly of the present invention of the present invention.  
         [0028]    [0028]FIG. 16 is a perspective view of a modified rough cutting end-mill cutter tool of the present invention.  
         [0029]    [0029]FIG. 17 is a perspective view of a razor cutter with serrations cutter tool of the present invention.  
         [0030]    [0030]FIGS. 18A and 18B are a top perspective (A) and a bottom perspective (B) view of a rotating drum cutter type tissue harvester assembly, with integral drive means of the present invention.  
         [0031]    [0031]FIG. 19 is a cross-sectional view of the cutter housing area of the harvester assembly of the present invention.  
         [0032]    [0032]FIGS. 20A, 20B, and  20 C are side angle views of the tissue particle harvester and collector in use.  
         [0033]    [0033]FIGS. 21A, 21B, and  21 C are cross-sectional views of a separate flushing container tissue particle collector of the present invention.  
         [0034]    [0034]FIG. 22 is a cross-sectional view of a bristled plunger tissue particle collector of the present invention.  
         [0035]    [0035]FIG. 23 is a cross-sectional view of a standard plunger tissue particle collector of the present invention.  
         [0036]    [0036]FIG. 24 is a cross-sectional view of an internal flushing channels embodiment of the tissue particle collector of the present invention.  
         [0037]    [0037]FIG. 25 is a cross-sectional view of a spring-loaded plunger tissue particle collector of the present invention.  
         [0038]    [0038]FIG. 26 is a cross-sectional view of a static internal screw tissue particle collector of the present invention. 
     
    
     DESCRIPTION OF THE INVENTION  
       [0039]    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.  
         [0040]    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.  
         [0041]    As illustrated in FIG. 1, the dermal tissue nano-grafting system  10  of the present invention comprises three main components: a tissue particle harvester assembly  20  for cutting tissue particles from dermal tissue; a tissue particle collector  30  for receiving, separating and collecting the tissue particles; and a chambered dressing  40  for receiving the collected tissue particles and culturing the growth of a dermal tissue graft. The ideal size of the tissue collected is about 50-300 microns; with the median particle size about 100 microns. The tissue particle harvester assembly  20  excises tissue particles of an appropriate size range from a dermal tissue source. The tissue particle collector  30  receives the harvested tissue particle, collects and holds them in a proper environment to maintain their viability prior to seeding the particles in a chambered dressing  40 . The chambered dressing  40  of the present invention is a type of tissue culture device for growing dermal graft tissue in situ on a skin graft site. Exemplary devices that may be used for the chambered dressing  40  are described in U.S. Pat. No. 5,152,757, issued on Oct. 6, 1992 to Eriksson, entitled “System For Diagnosis And Treatment Of Wounds” and U.S. Provisional patent application seral No. 10/361,341, entitled “Environmental Control Device For Tissue Treatment” filed on Feb. 11, 2002, by Johnson, et al., the disclosures of which are incorporated by reference herein as though fully set forth.  
         [0042]    As illustrated in FIG. 2, the tissue particle harvester assembly  20  comprises a harvester housing  50 , a tissue cutting tool  90  and a drive means  160 . As exemplified in FIG. 3, the harvester housing  50  has a tissue opening  54  accessing an interior space  56 , into which a tissue-cutting tool  90  is received. As further exemplified in FIGS. 4A and 4B, the harvester housing  50  interfaces with the dermal tissue source  14  from which tissue particles are to be harvested, and holds the tissue cutting tool  90  in a proper position relative to the dermal tissue  14 . The tissue opening  54  of harvester housing  50  serves as an orifice for pressing against and receiving a dermal tissue layer of the tissue source  14 .  
         [0043]    A proper position of the cutting tool  90  relative to the dermal tissue source  14  relates to the depth of penetration of the cutting tool  90  into the layers of the dermal tissue  14 . A proper positioning of the cutting tool  90  facilitates excising tissue particles of an appropriate size. The depth of penetration of the cutting tool  90  into the surface of the tissue  14  should range from about 0.01 mm to about 0.9 mm, and preferably should be about 0.1 mm+/−0.05 mm, depending on the type of cutting tool  90  being used. The depth of penetration can be modified by a number of means known to one of ordinary skill in the art, including adjusting the proximity of the cutting tool to the tissue opening  54  in the housing  50 , and by adjusting the cutting aspect  118  (see FIG. 5B) of the cutting features  114  of the cutting tool  90 . The cutting aspect  118  of a cutting feature  114  is the reach of a cutting feature  114  beyond the cutting surface  94  of the tool  90 . The harvester housing  50  can include a depth adjustment means for adjusting the proximity of the cutting tool to the tissue opening  54  in the housing  50 . Again, such adjustment means are known to and practicable in the present harvester assembly  20  by the ordinary skilled artisan. For example, as in FIG. 3, such adjustment means  58  can be made by moving an edge of the tissue opening  54  closer to, or farther away, from the cutting tool  90 .  
         [0044]    As exemplified in FIGS. 5A and 5B, a tissue cutting tool  90  has a cutting surface  94  and cutting features  114  which project from the cutting surface  94  and impinges on the tissue source  14  to cut or excise tissue particles of an appropriate size from the tissue  14  when the cutting tool  90  is rotated. A rotatable shaft  96  extends from the tool  90  along its axis of rotation  100 . The rotatable shaft  96  has a drive end  96   a  for engaging a drive means and a tool end  96   b  for mounting the cutting surface  94 . The cutting tool shaft drive end  96   a  is receivable by a drive means  160  (e.g., see FIGS. 10B and 16A &amp;  16 B) to impart rotation to the cutting tool  90 . The rotating drum type cutting tool  90   a  shown in FIGS. 5A and 5B has a tool end shaft  96   b  that extending from the tool  90  along the axis of rotation  100  opposite the drive end  96   a . In FIGS. 5A and 5B, the drum of the tool  90  has it axis disposed coaxially with the axis  100  of the rotatable shaft  96 .  
         [0045]    The cutting surface  94  of a rotating drum type cutting tool  90   a  can be practiced with any of a variety of different cutting features  114  selectable by the ordinary skilled artisan. In FIGS. 5A and 5B, the cutting features are a plurality of sharpened fingers  114   a , projecting from the cutting surface  94  spaced apart and in rows, forming a serrated blade  115 . Examples of other types of cutting features  114  practicable on the drum-type cutting tool  90   a  include: “TI” type cutting features  114   b  on a rotary drum type cutting tool (see FIG. 6); “scallop” type cutting features  114   c  with hypo-tubes on a rotary drum type cutting tool (see FIGS.  7 A and  7 B); and “square scallop” type cutting features  114   d  (see FIG. 8) and “round scallop” type cutting features  114   e  (see FIG. 9), both useful for the cutting surface of a rotary drum type cutting tool  90   a.    
         [0046]    Not all tissue-cutting tools  90  practicable in the present harvester assembly  20  are rotary drum type cutting tools  90   a . For example, rotating shaft cutting tools  90   b  (see FIGS. 10-14) may be used. As exemplified in FIG. 10A, a rotating shaft cutting tool  90   b  comprises a rotatable shaft  120  having a drive end  122  for engaging the drive means  50  and a tool end  124  for mounting the tissue cutting surface  126  and cutting features  128 . FIGS. 10A and 10B illustrate a rotating shaft-type tissue cutter tool  90   b  and harvester housing  130 , and the rotating shaft-type tool  90   b  installed in a type of tissue harvester assembly  20   b  and connected to a drive means  160 . The tool  90   b  has a side cutting bit feature  128   a  and is installable in a shear block type harvester housing 130 . Other configurations of rotating shaft-type tissue cutter tools  90   b  are practicable in the present harvester assembly  20   b . Examples include: a fine scallop hypo-tube rotating shaft-type tissue cutter tool (FIG. 11); a course scallop hypo-tube rotating shaft-type tissue cutter tool (FIG. 12); a course scallop solid shaft-type tissue cutter tool (FIG. 13); and alternative side cutting bit shaft-type tissue cutter tools (FIG. 14).  
         [0047]    Other types of cutting tools  90  such as an end mill type cutting tool  90   c  (see FIG. 15) are also practicable in the present invention. The rotating drum and shaft tissue cutting tools  90   a  &amp;  90   b  noted above can have both a drive end  96   a  and a tool end  96   b . However, an end mill type cutting tool  90   c  will have only a shaft drive end  96   a . A rotating end-mill cutting tool  90   c  comprises a rotatable shaft  132  having a drive end  96   a  for engaging the drive means  160  and a tool end  96   b  for mounting a cutting drum  136 . The cutting drum  136  is cylindrical and has an axis disposed coaxially with the drive and tool shaft ends  96   a  and  96   b . The tool end  96   b  is attached at one end of the cutting drum  136  and the other end of the cutting drum  136  mounts a tissue cutting surface  138 . The tissue-cutting surface can be constructed to have cutting features  114  similar to those practicable on the rotating drum type cutter  90   a  noted above. One of ordinary skill in the art is readily able to select from and adapt said cutting features  114  for incorporation onto the cutting surface  138  of a rotating end-mill cutting tool  90   c  of the present invention  10 . The drum  136  has an outer circumferential surface that is closely receivable in a width of the interior space of the end mill housing  140  associated depth alignment means  142 . The cutting drum  136  of the end mill tissue cutting tool  90   c  illustrated in FIG. 15 is a tapered cylinder proximate its tissue cutting surface  138 . The benefit of this taper is that centrifugal force can facilitate the migration of excised tissue particles passing through the cutting surface  138  into the interior of the drum (shown in phantom) and up the interior walls and away from the cutting surface  138 . This will help to prevent clogging certain of the cutting features  114  with excised tissue particles.  
         [0048]    Alternative cutting tools  90 , as shown in FIGS. 16 and 17, may be utilized include a modified rough-cutting end mill  148  and a razor cutter with serrations  150 . Such a modified end mill  148  exhibits cutting characteristics of a typical end mill cutting tool as shown in FIG. 15, however the modified end mill  148  exhibits a cylindrical shape and an axis  100  disposed coaxially with the drive and tool shaft ends  96   a  &amp;  96   b , similar to the rotating shaft cutter of FIG. 5A.  
         [0049]    The drive means  160  is typically a drive motor of some type (e.g., electric or pneumatic) for rotating the tissue-cutting tool in the harvester housing  50  &amp;  140 . The drive means  160  may be integral to (see FIGS. 18A and 18B) or separate from (see FIG. 10B) the harvester housing  50  &amp;  140 . A handle  162  may be connected or formed to the housing  50  in order for a user to more easily grasp and position the harvester assembly  20 .  
         [0050]    As is illustrated in FIG. 19, a port  170  may be provided within the cutter  90  to draw tissue that has been collected by the cutter  90  out of the housing  50 . While the port  170  has been shown in the center of the cutter  90  along its axis of rotation in this embodiment, it is to be understood that multiple mechanisms for removing tissue from the housing are envisioned and described further herein. A housing mounting  166  is provided for stability and support to the user during operation of the harvester  20 . Skid plates  164  are provided to ease in positioning of the cutter  90  at the tissue site, and to further aid in adjustment of the cutter  90  depth, especially when a shim stack  58 , or other adjustment means known in the art, are provided external of the cutter  90 .  
         [0051]    [0051]FIGS. 20A, 20B, and  20 C illustrate a tissue particle collector  30 , which may be comprised of a port  170  positioned within or near the drive means of the cutter  90 , and which may be accessible my a particle retriever  172 , such as a syringe. The particle retriever  172  may then be used to inject or otherwise instill the tissue collected into a nanograft cell  40 , as shown in FIG. 1. Various mediums may be utilized to suspend the tissue within the tissue particle collector  30 , and subsequently the nanograft cell  40 . Such mediums may include, but are not necessarily limited to, saline.  
         [0052]    Alternative embodiments of the tissue particle collector  30  for collecting tissue from the tissue particle harvester are illustrated in FIGS. 21-27. A separate flushing container  180 , as illustrated in FIG. 21A, may be utilized to retrieve tissue from the cutter  90 . The cutter  90  is removed from the harvester housing  50 , and placed into the flushing container  180 . A cap  182 , or other cover, is screwed or otherwise secured to the container  180 . A liquid medium, such as saline, is then flushed through a port  184  or luer, which may be integrated with the cap  182 , or otherwise introduced into the container  180 , and is directed towards the inner diameter and outer diameter of the cutter  90  by jets  184  or channels within the container  180 .  
         [0053]    An integral flushing container  190 , as illustrated in FIG. 21B, allows for collection of tissue without removal of the cutter  90  from its housing  50 . In this embodiment, the cutter  90  has a solid filled core. A gasketed cap  192  is fitted over the integral flushing container  190 , which may be the housing  50  having a receptor for the gasket cap  192 , after tissue is cut from the donor site. The housing  50 , with the cutter  90  in place, is removed from the tissue particle harvester  20  and fluid, which may be saline, is injected into the flushing container  190  through a luer fitting  194 , or port. The flushing container  190  is manually agitated, by hand or by a mechanical agitator known in the art. After agitation, the tissue that has been cut by the cutter  90  is now suspended in the fluid which has been injected, at which point it may be drawn out of the integral flushing container  190  through the luer fitting  194  by means of a syringe or similar device known in the art.  
         [0054]    An alternative embodiment of an integral flushing container  190  is illustrated in FIG. 21C. A core filled cutter  90  is utilized to remove tissue from the donor site. A cap  196 , which may be comprised of silicone or a material of similar physical characteristics is placed over the open-cutting face of the housing  50 . The housing may include a luer for injecting fluid, such as saline, which is then agitated by running the motor of the cutter  90 . The agitation results in suspension of the tissue cut by the cutter  90  in the fluid, which may then be drawn out by through the luer  194  by a syringe or similar device, for insertion into a chambered dressing  40 .  
         [0055]    Collection of tissue from the cutter  90  may also be accomplished by use of a bristled plunger  200 , as shown in FIG. 22. The bristled plunger  200  is insertable into the inner diameter of a cutter  90  having a hollow core. After collection of tissue by the cutter  90 , the plunger  200  is moved, manually or mechanically, into the inner diameter of the cutter  90 . Bristles  202  draw out the tissue that has been collected in the inner diameter of the cutter  90  as the plunger is retracted from the inner diameter of the cutter  90 . The plunger  200  may be retractable into an adjacent container (not shown) that may be filled with a fluid, such as saline, for suspension of the tissue collected from the cutter  90 . A luer (not shown) may be incorporated into the adjacent container for retrieval of the tissue suspended fluid by a syringe or similar device, and for injection of the fluid prior to tissue collection.  
         [0056]    In a further alternative embodiment as illustrated in FIG. 23, a standard plunger  210  rides over the shaft  212  of the cutter  90  assembly. The shaft  212 , plunger  210 , and cutter  90  all rotate together during operation of the harvester assembly  20 . After tissue has been removed from the donor site by the cutter  90 , the plunger  210  is moved across the inner diameter of the cutter  90  towards a removable end cap  214 . The end cap  214  is removed from the harvester assembly  20  so the tissue may be removed or flushed out by means of a syringe or other process well known to those skilled in the art.  
         [0057]    Still a further embodiment of the tissue particle collector  30  is the internal flushing channels  220  as illustrated in FIG. 24. An internal core  222  is positioned within the cutter  90 . The core  222 , which remains stationary during rotation of the cutter  90 , is toleranced tightly to the inner diameter of the cutter  90  while still allowing for free rotation of the cutter  90 . Tissue enters channels  222  through openings  224  in the cutter during operation of the cutter  90 . Fluid is flushed through the channels  222  during operation of the cutter into a collection chamber (not shown) for later removal to the wound site. It is to be understood that the fluid may also be flushed through the channels  222  when the cutter  90  is not being operated.  
         [0058]    [0058]FIG. 25 illustrates a spring-loaded plunger  230  that may be utilized to retrieve tissue particles from the cutter  90  after removal from the donor site. The spring-loaded plungers  230  are positioned within the recesses  232  of the cutting scoops  234  of a stationary core  236  of the cutter  90 . After collection of tissue from the donor site, the core  236  is moved radially, or alternatively axially, until the plungers  230  pop out and remove tissue particles from the recesses  232 . It is to be understood that the plungers  230  may be cam activated, or by similar mechanisms utilized by those skilled in the art, to extract tissue that has been collected within the recesses  232 .  
         [0059]    Tissue may be removed from the harvester  20  by means of a static internal screw  240 , as illustrated in FIG. 26. Such a screw  240 , which may be described by those skilled in the art as a reverse Archimedes screw, is positioned within the inner diameter of the cutter  90 . As the cutter  90  rotates and draws tissues into the cutter openings  242 , the static internal screw  240  moves particles to one end of the cutter for collection by wiping the inner diameter of the cutter  90 . It is envisioned that the screw  240  may be inserted after the tissue has been collected in order to wipe the inner diameter of the cutter  90 , and move the tissue to one end of the cutter  90  for collection.  
         [0060]    It is to be understood that manual agitation may also be utilized to remove tissue that has been collected by the cutter  90 . The cutter  90  is removed from the harvester  20  and placed in a container holding fluid, such as saline or a similar fluid. The cutter  90  is spun within the container to remove particles into the fluid. The container may then be centrifuged to separate the tissue particles from the fluid or alternatively, the fluid may be passed through a filter to remove the tissue from the fluid.  
         [0061]    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.