Abstract:
A felt for repairing soft tissue defects comprising a membranous collagen substrate and a bioresorbable fiber felted onto the collagen substrate. Methods of preparing a felt and methods of repairing soft tissue damage with a felt are also provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/010,836 filed on Dec. 13, 2004 (now U.S. Pat. No. 7,252,832 issued Aug. 7, 2007). The disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD 
     The present teachings relate to composite collagen materials. More particularly, the present teachings relate to a composite collagen felt used for soft tissue repair. 
     BACKGROUND 
     Collagen is useful in various pharmaceutical applications and as an implant material for soft tissue defects. The collagen useful for implant materials may be broadly categorized into xenograft collagen and allograft collagen. Selecting the appropriate collagen materials may present challenges as there is a need to balance strength and durability of the implant with reducing immunogenicity and promoting soft tissue ingrowth. 
     It may be desirable to provide an implant which promotes soft tissue ingrowth, minimizes the amount of the implant used, and is not prone to an immunogenic response. 
     SUMMARY 
     Embodiments of the present invention relate to felts for repairing soft tissue defects comprising a collagen substrate and a bioresorbable material felted onto the collagen substrate. The collagen substrate may be selected from a xenograft source, an allograft source, or a synthetic source. The collagen substrate may be from a porcine source. The collagen substrate may be uncrosslinked, partially crosslinked, or fully crosslinked. Chemical crosslinking may be introduced in an amount sufficient to make the collagen substantially non-bioactive. Bioresorbable materials may be selected from synthetic polymers, natural polymers, polysaccharides, and mixtures thereof. Synthetic polymers may include polymers and copolymers of glycolic acid, L-lactic acid, D-lactic acid, urethane urea, trimethylene carbonate, dioxanone, caprolactone, hydroxybutyrate, orthoesters, orthocarbonates, aminocarbonates, and physical combinations thereof. Natural polymers may include collagen, elastin, silk, fibrin, fibrinogen, or other naturally occurring tissue-derived proteins. Natural polysaccharides may include hyaluronic acid, chitin, chitosan, alginate, carboxymethylcellulose, or other polysaccharides. The felt may be substantially planar. The felt may also have nutrient factors, growth factors, antimicrobials, anti-inflammatory agents, blood products, autologous or allogeneic differentiated cells, autologous or allogeneic undifferentiated or stem cells, and mixtures thereof incorporated into the felt. Cartilage implants, ligament implants, or tendon implants are examples of what may be made with the felt. 
     Various embodiments of the present teachings relate to methods of augmenting a cartilage defect in need of soft tissue repair. A bioresorbable polymer in the form of a batting, web, or thread is felted onto a membranous collagen substrate to pass the bioresorbable polymer through the membranous collagen substrate. The felt is shaped to a predetermined shape to accommodate the cartilage defect and then implanted at the cartilage defect. 
     Still other various embodiments of the present teachings provide methods of augmenting a soft tissue defect. A felt is provided which includes a membranous collagen substrate and a bioresorbable polymer felted onto the substrate. The felt is shaped to provide at least a first attachment point and a second attachment point. The felt is then disposed at the soft tissue defect to encircle at least a region of a surrounding tissue at the soft tissue defect. The felt is affixed about the surrounding tissue at the soft tissue defect. 
     Further areas of applicability of the present teachings will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the teachings, are intended for purposes of illustration only and are not intended to limit the scope of the teachings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present teachings will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  depicts a felt according to embodiments of the present teachings; 
         FIG. 2  depicts a cut away view of a felt according to embodiments of the present teachings; 
         FIG. 3  depicts a bifurcated felt according to embodiments of the present teachings; 
         FIGS. 4A-4B  depict a torn coracoclavicular ligament repaired with a felt according to embodiments of the present teachings; 
         FIGS. 5A-5B  depict a torn ulnar collateral ligament repaired with a felt according to embodiments of the present teachings; and 
         FIGS. 6A-6B  depict a torn biceps tendon repaired with a felt according to embodiments of the present teachings. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the teachings, their application, or uses. Although various embodiments may be illustrated in conjunction with a shoulder, elbow, or finger, it is understood that the felt and methods of the teachings may be of any appropriate shape and may be used with any appropriate procedure and not solely those illustrated. 
     As depicted in  FIGS. 1 and 2 , a felt  10  comprises a membranous collagen substrate  12  and a bioresorbable polymer  14  felted onto the substrate  12 . The membranous collagen may be naturally derived from tissue such as submucosal intestine, or may be fabricated by casting a collagen solution into a membrane. The collagen substrate  12  may be from a xenograft source, an allograft source, or a synthetic source. For example, a porcine collagen may be used for the collagen substrate  12 . Porcine collagen is readily available, provides flexibility of the collagen substrate  12 , and is durable. Depending on the end use of the felt, the collagen substrate  12  may be from any collagen source (e.g. human, porcine, or bovine) which provides the desired durability, flexibility and permanence. 
     The collagen substrate  12  may uncrosslinked (0% linkages), partially crosslinked (greater than 0% and less than 100% linkages), or fully crosslinked (100% linkages). The collagen substrate  12  may be sufficiently crosslinked to be substantially non-resorbable and non-bioactive. One skilled in the art appreciates that the non-resorbtion or permanency of the collagen substrate  12  increases with the amount of crosslinked bonds. For example, in a highly crosslinked collagen substrate  12  having 85% crosslinked bonds, the collagen substrate  12  may remain implanted and substantially intact inside of a recipient for months, decades, or a lifetime. Furthermore, the high percentage of crosslinked bonds may ensure that the substantial majority of the collagen substrate  12  does not degrade, deform, or otherwise lose strength over the life of the implanted felt  10 . In contrast, a lesser crosslinked collagen substrate  12  having about 10% linkage, may be for temporary use and designed to retain the majority of its structural integrity for only a few weeks or months. This may be useful in less load bearing areas of the body or in situations where the repair is minor and may be replaced with regenerated tissue in a short time period. 
     The bioresorbable polymer  14  may be a synthetic polymer, a natural polymer, polysaccharides, and mixtures thereof. Synthetic bioresorbable materials may include, but are not limited to, polymers and copolymers of glycolic acid, L-lactic acid, D-lactic acid, urethane urea, trimethylene carbonate, dioxanone, caprolactone, hydroxybutyrate, orthoesters, orthocarbonates, aminocarbonates, and physical combinations thereof. Other polymerizable hydroxy acids may also be employed. Synthetic resorbable materials may provide control in the amount of the material used as the benefits and delivery rates of the resorbable material  14  may be calculated based on known dissolution rates of the polymer. The bioresorbable polymer  14  may also be a natural polymer such as collagen, elastin, silk, fibrin, fibrinogen, other naturally occurring tissue-derived proteins, and mixtures thereof. Natural polysaccharides may include, without limitation, hyaluronic acid, chitin, chitosan, alginate, carboxymethylcellulose, other polysaccharides, and mixtures thereof. The bioresorbable polymer  14  collagen may be of the same or a different type or strength as the collagen substrate  12 . 
     The bioresorbable polymer  14  may be a fluffy batting or web of threads of the linked monomers or the collagen. The fluffy batting forms a felt or dense cover over at least one of a top surface  16  and/or a bottom surface  18  of the collagen substrate  12 . The dense cover may be of a random orientation or in a patterned form. The felt  10  may also include combinations of random and patterned orientations. The bioresorbable polymer  14  may be tightly felted to the surface of the collagen substrate  12  such that the fibers are touching or there is minimal space between each of the intertwined fibers. The tightness of the felt  10  may also be modified by having the bioresorbable polymer  14  fibers abut the top surface  16  and bottom surface  18  of the collagen substrate  12 . The close fit between the bioresorbable polymer  14  and the collagen substrate  12  makes the felt  10  appear substantially planar when viewed from the side, as depicted in  FIG. 2 . The tightness of the felt  10  may be adjusted to incorporate additional elements into the substrate  12  or into the substrate  12  and the web of the bioresorbable polymer  14  such as autologous or allogeneic differentiated cells, autologous or allogeneic undifferentiated or stem cells and other biological agents, such as nutrient factors, growth factors, antimicrobials, anti-inflammatory agents, blood products, and mixtures thereof. 
     The bioresorbable polymer  14  resorbs faster than the collagen substrate  12  and elicits a positive tissue response to make newly generated tissues develop into the collagen substrate  12 . The selection of bioresorbable polymers  14  may enhance the healing process. For example, it may be desirable to incorporate 65% of a slowly resorbing polymer  14  and 35% of rapidly resorbing polymer  14 . The presence of the slowly resorbing polymer  14  may be used to enhance the strength of the felt  10  because the rapidly resorbing polymer  14  would initially elicit a tissue ingrowth response until it completely dissolved at which time the slowly resorbing polymer  14  would continue to promote ingrowth. The slowly resorbing polymer  14  may also provide enhanced strength to the felt  10  for a longer duration than a felt  10  containing a single bioresorbable polymer  14  or multiple bioresorbable polymers  14  having the same resorbtion rates. 
     Embodiments of the present teachings also provide methods of preparing the felt  10 . A membranous collagen substrate  12  is provided. The collagen may be uncrosslinked or partially or fully crosslinked using, for example, chemical crosslinking, UV radiation, dehydrothermal crosslinking, and combinations of these treatments. Chemical crosslinking may be performed using a chemical crosslinking agent, including, but not limited to, carbodiimide, glutaraldehyde, formaldehyde, diisocyanates, and mixtures thereof. The crosslinking is carried out for a time and under conditions sufficient to provide a non-immunogenic collagen substrate  12 . In embodiments where a greater degree of crosslinking is desired, the duration of the crosslinking treatment may increase or a successive series of crosslinking treatments (UV radiation followed by carbodiimide treatment, for example) may be used. 
     The felting process consists of using a barbed needle to pass the bioresorbable polymer  14  through a portion the collagen substrate  12 . The barbs in the needle catch nearby bioresorbable polymer  14  fibers and mix, interlock, or weave them with other fibers to form the dense cover felt. The bioresorbable polymer  14  may be placed on the top surface  16 , bottom surface  18 , or both surfaces of the collagen substrate  12  to facilitate the felting process. The needle punches the bioresorbable polymer  14  through the top surface  16 , into the collagen substrate l 2 , through the bottom surface  18 , and back through the collagen substrate  12 , or vice versa. The needle may also punch the resorbable polymer  14  through only a single surface of the collage substrate  12  without engaging the opposing surface. Repeating the felting punch or stitch provides a felt  10  with bioresorbable polymer  14  covering a single surface or both surfaces of the collagen substrate  12 . 
     Selection of the felting needle may influence the final porosity of the collagen substrate  12 . Needles may be selected for shaft type (conical, square, star, or triangular), gauge, and the number of barbs on the needle. For example, a felt  10  created with a 20-gauge needle has a greater pore size after the bioresorbable polymer  14  resorbs, as compared to the pore size created by a 32-gauge needle. The pores and indentations created by the shaft shape and barbs may be exploited to maximize tissue ingrowth and thereby increase the strength of the implant in the body. The needle barb number, needle gauge size, the placement of the bioresorbable polymer  14  on the collagen substrate  12 , and the extent of the punching process may be altered to provide a tight felt  10  with closely felted fibers. 
     After the felting process, the felt  10  may be treated to increase compatibility in the body. The felt  10  may be sterilized using radiation, for example. Agents to increase ingrowth of tissues into the collagen substrate  12  may also be applied to the felt  10 , such as nutrient factors, growth factors, antimicrobials, anti-inflammatory agents, blood products, autologous or allogeneic differentiated cells, autologous or allogeneic undifferentiated or stem cells, and mixtures thereof. 
     Various embodiments of the present teachings may be used to augment a site in need of soft tissue repair  20 . The felts  10  of embodiments of the teachings are placed at a site in need of soft tissue repair  20 . If needed, the felts  10  may be shaped prior to use. For example, the felt  10  may be shaped into a bifurcated strip having a base  22  and prongs  24 , as depicted in  FIG. 3 . The bifurcated shape (or trifurcated, etc.) may be useful in augmenting sites by attaching the base  22  to one area in need of repair  20  and the prongs  24  to another area in need of repair  20  or by looping at least one of the prongs  24  around the site in need of repair  20 . As depicted in  FIG. 4A , an injury to the acromioclavicular ligament, coracoclavicular ligament, or the coracoacromial ligaments in the shoulder may cause displacement of the clavicle. A bifurcated felt  10  of the present teachings may be used to reduce the clavicle to the appropriate level by attaching the base  22  to the coracoid process and attaching the prongs  24  to the coracoclavicular ligament. The prongs  24  may also be looped around the clavicle or in the case of the clavicle having a drill hole therein (not depicted), looped through the clavicle to reduce it to the appropriate level. The felt  10  may be attached using any suitable attachment means such as sutures, screws, staples, etc. 
     The methods may also be used in other regions of the body. Referring to  FIGS. 5A and 5B , the site in need of repair  20  is a torn ulnar collateral ligament of the thumb. In such an embodiment a small felt  10  may be used to create a bridge between the torn tissues. As depicted in  FIGS. 6A and 6B , the site in need of repair  20  is a torn biceps tendon which may also be repaired with the felt  10  bridging the two torn pieces of the biceps tendon. It is understood that the methods of the present teachings may be employed in various areas of the body, including knees, wrists, ankles, etc. 
     The description of the teachings is merely exemplary in nature and, thus, variations that do not depart from the gist of the teachings are intended to be within the scope of the teachings. Such variations are not to be regarded as a departure from the spirit and scope of the teachings.