Abstract:
An embodiment of the invention includes a method of fastening together two tissue portions. The method may include positioning a medical device adjacent a region of tissue having two tissue portions. The medical device may include a male member and a female member having a first bioabsorbable material overlying one of a non-bioabsorbable material and a second bioabsorbable material. The first bioabsorbable material may have a first degradation rate, and the second bioabsorbable material may have a second degradation rate slower than the first degradation rate. The method may also include inserting the male member inside the female member so as to inhibit withdrawal of the male member from the female member with the two tissue portions between the male member and the female member.

Description:
This is a continuation application of U.S. patent application Ser. No. 10/712,966, filed Nov. 12, 2003 now U.S. Pat. No. 7,442,201, which is a continuation application of U.S. patent application Ser. No. 09/935,950, filed Aug. 23, 2001 now U.S. Pat. No. 6,692,507, the entirety of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to biocompatible fasteners and more particularly to impermanent biocompatible fasteners. 
     Biocompatible fasteners have long been used to fasten together two or more biological materials on or within a patient. Examples of biocompatible fasteners include sutures, staples, surgical glues, tissue clips and orthopedic fixation devices, such as bone plates, screws and the like. For certain applications, such as where the biocompatible fastener is implanted within a patient and is needed therewithin for only a limited period of time, it is highly desirable that the biocompatible fastener be impermanent or capable of degrading over time so that an additional medical procedure not be required to remove the fastener from the patient. For this reason, many biocompatible fasteners now in use are made entirely out of materials that, over time, become chemically degraded within a patient and, ultimately, are fully metabolized and excreted by the patient. (Other biocompatible fasteners are made out of materials that the body needs and are not excreted.) Such impermanent biocompatible fasteners are typically referred to in the art as bioabsorbable fasteners and are made out of materials including, but not limited to, homopolymers and copolymers of glycolide, lactide, ε-caprolactone and p-dioxanone, copolymers of glycolide and trimethylene carbonate, as well as polyanhydrides and polyorthoesters. See Middleton et al., “Synthetic Biodegradable Polymers as Medical Devices,”  Medical Plastics and Biomaterials  (March 1998), the disclosure of which is incorporated herein by reference. 
     Gastroesphageal reflux disease (GERD) is a disorder in which the lower esophageal sphincter, which is located in a distal portion of the esophagus adjacent to the junction between the esophagus and the stomach, allows contents of the stomach, including gastric acid and bile, to reverse flow into the distal portion of the esophagus during digestion. Complications associated with GERD include heartburn, pulmonary disorders, chest pain, esophageal ulcers, esophagitis, Barrett&#39;s esophagus, and esophageal carcinoma. 
     Although weight loss and/or prescription acid blockers are typically preferred treatment options for GERD, various surgical procedures have been devised to treat GERD where weight loss and/or prescription drugs are ineffective or impractical. In one surgical procedure, known as Nissen fundoplication, a portion of the gastric fundus of the stomach is wrapped around the esophagus and is secured thereto using one or more biocompatible fasteners, typically in the form of sutures, surgical staples or surgical two-part fasteners. The wrapped gastric fundus applies pressure to the esophagus in such a way as to eliminate the reverse flow of stomach contents into the esophagus. 
     One of the more commonly used fundoplication procedures requires abdominal or thoracic incisions through which the fundus wrapping and securing can be performed. Due to the highly invasive nature of such surgery, complications and morbidity occur in a significant percentage of cases. In addition, these procedures are time-consuming, often taking a number of hours to perform, and may leave disfiguring scars where the incisions were made. 
     More recently developed fundoplication procedures limit somewhat the necessity of making large surgical incisions by utilizing laproscopic ports or percutaneous endoscopic gastrostomy. Although these procedures are less invasive than those involving large abdominal and thoracic incisions, they are still invasive and have certain risks associated therewith. For example, general anaesthesia, which entails well-known risks, is typically used during these procedures. 
     An even more recently developed fundoplication procedure is endoluminal fundoplication. In endoluminal fundoplication, a flexible endoscope is passed first through a patient&#39;s mouth and then through the esophagus to locate an attachment site at the gastroesophageal junction. A tissue grasping device is then positioned at the distal end of the endoscope and is attached to the located attachment site. Next, a tissue displacement device is positioned at the distal end of the endoscope and is used to displace the fundus of the stomach in such a way as to create an intussusception of the esophagus into the gastric lumen. A fastener delivery device is then used to secure the gastric fundus to the esophagus at a first location. The fastener delivery device is then used to place additional fasteners at a plurality of additional desired fastener locations, thus securing the gastric fundus entirely around the esophagus. 
     Examples of endoluminal fundoplication procedures are disclosed in U.S. Pat. No. 6,086,600, inventor Kortenbach, which issued Jul. 11, 2000, and in U.S. Pat. No. 6,113,609, inventor Adams, which issued Sep. 5, 2000, both of which are incorporated herein by reference. 
     In the aforementioned U.S. Pat. No. 6,113,609, there is disclosed a fundoplication fastener that is made entirely out of a bioabsorbable material. One problem that has been noted by the present inventors is that, whereas a fundoplication fastener need only be capable of securing the gastric fundus to the esophagus for the approximately three- to six-month period of time necessary for the gastric fundus and the esophagus to become fused to one another, a bioabsorbable fundoplication fastener typically will remain in place for approximately two years before chemical degradation results in its structural decay. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a novel biocompatible fastener. 
     Therefore, according to one aspect of the invention, there is provided a biocompatible fastener, said biocompatible fastener having a first portion and a second portion, said first portion being made out of a first bioabsorbable material, said first bioabsorbable material having a first degradation rate, said second portion being made out of a material selected from the group consisting of a non-bioabsorbable material and a second bioabsorbable material, said second bioabsorbable material having a second degradation rate, said second degradation rate being slower than said first degradation rate. 
     It is another object of the present invention to provide a novel impermanent biocompatible fastener. 
     Therefore, according to another aspect of the invention, there is provided a biocompatible fastener as described above wherein said first portion is positioned within said biocompatible fastener so that degradation of said first portion results in fragmentation of the biocompatible fastener. 
     It is still another object of the present invention to provide an impermanent biocompatible fastener that overcomes at least some of the shortcomings discussed above in connection with existing impermanent biocompatible fasteners. 
     Therefore, according to still another aspect of the invention, there is provided a biocompatible fastener that comprises, in a preferred embodiment, a male portion and a female portion. The male portion includes a first base member, the first base member being generally flat and oval. A pair of male members are mounted on the bottom surface of the first base member, each male member comprising a cylindrical post extending downwardly from the bottom surface of the first base member and a conical head disposed at the bottom end of the post. The female portion includes a second base member, the second base member being generally flat and oval. A pair of sleeves are mounted on the top surface of the second base member and extend upwardly therefrom. Each sleeve defines a bore adapted to receive a head from a corresponding male member and is provided with a pair of longitudinal slots that endow the sleeve with some radial flexibility to facilitate insertion of a head into the bore. In addition, each sleeve is provided with a sharp tip at its top end to facilitate insertion of the sleeve through biological tissue. A substantially circumferential flange is formed on the inside of each sleeve. The flange extends radially into the bore and is engageable with the head once the head has been inserted therepast so as to inhibit premature withdrawal of the head from the bore. Except for an outer coating on each of the two heads, the fastener is made entirely of a non-bioabsorbable material. By contrast, the outer coating of the heads is made of a bioabsorbable material having a desired degradation rate. The thickness of the outer coating is appropriately selected so that degradation of the outer coating after a desired period of time permits each head to be withdrawn past its flange. 
     Because the heads of the aforementioned fastener are not made entirely of a bioabsorbable material, but rather, are made of an inner core of a non-bioabsorbable material and an outer coating of a bioabsorbable material, the thickness of the bioabsorbable material is less than it would otherwise be in a corresponding head made entirely out of the bioabsorbable material. Consequently, because of its reduced thickness, the bioabsorbable material becomes fully hydrated more rapidly and, therefore, degrades more quickly in the present fastener than in a corresponding fastener made entirely out of bioabsorbable material. As a result, by selecting an appropriate bioabsorbable material and by dimensioning the fastener appropriately, the life-span of the fastener can be tailored to the healing time for the fastened biological material, e.g., three to six months for tissue subjected to a fundoplication procedure. 
     As can readily be appreciated, instead of or in addition to making the heads out of an inner core of non-bioabsorbable material and an outer coating of bioabsorbable material, the flanges can be made out of an inner core of non-bioabsorbable material and an outer coating of bioabsorbable material. A variety of other modifications to the aforementioned fasteners are also possible. 
     The above-described fasteners are amenable to being mass-produced by conventional molding techniques. 
     For purposes of the present specification and claims, it is to be understood that certain directional terms used herein, such as “top,” “bottom,” “upwardly,” “downwardly,” and the like, when used to describe the fastener of the present invention, are relative terms dependent upon the fastener being situated in a particular orientation vis-à-vis the viewer at a particular-point in time. As can readily be appreciated, if the orientation of the fastener is altered, such directional terms may also need to be altered correspondingly. 
     Additional objects, features, aspects and advantages of the present invention will be set forth, in part, in the description which follows and, in part, will be obvious from the description or may be learned by practice of the invention. In the description, reference is made to the accompanying drawings which form a part thereof and in which is shown by way of illustration specific embodiments for practicing the invention. These embodiments will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is best defined by the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are hereby incorporated into and constitute a part of this specification, illustrate preferred embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings wherein like reference numerals represent like parts: 
         FIG. 1  is a front view of a first embodiment of a biocompatible fastener constructed according to the teachings of the present invention, the biocompatible fastener being shown in an assembled state; 
         FIG. 2  is a perspective view of the biocompatible fastener of  FIG. 1 , the biocompatible fastener being shown in an unassembled state; 
         FIG. 3  is a fragmentary section view of the biocompatible fastener of  FIG. 1 ; 
         FIG. 4  is a fragmentary section view of a second embodiment of a biocompatible fastener constructed according to the teachings of the present invention, the biocompatible fastener being shown in an assembled state; 
         FIG. 5  is a fragmentary section view of a third embodiment of a biocompatible fastener constructed according to the teachings of the present invention, the biocompatible fastener being shown in an assembled state; 
         FIG. 6  is a front view of a fourth embodiment of a biocompatible fastener constructed according to the teachings of the present invention, the biocompatible fastener being shown in an assembled state; 
         FIG. 7  is a fragmentary section view of the biocompatible fastener of  FIG. 6 ; 
         FIG. 8  is a perspective view of a fifth embodiment of a biocompatible fastener constructed according to the teachings of the present invention, the biocompatible fastener being shown in an unassembled state; and 
         FIGS. 9(   a ) through  9 ( d ) are top views of alternative embodiments of the female portion of the biocompatible fastener of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to  FIGS. 1 through 3 , there are shown various views of a first embodiment of a biocompatible fastener constructed according to the teachings of the present invention, said biocompatible fastener being represented generally by reference numeral  11 . 
     Fastener  11 , which is particularly well-suited for, but is not limited to, temporarily securing the gastric fundus to the esophagus as part of a fundoplication procedure, is a two-piece, mating-type fastener comprising a male portion  13  and a female portion  15 . 
     Male portion  13 , which may be made by molding, is a generally rigid structure comprising a base  17 . Base  17 , which is generally flat and oval, has a top surface  17 - 1  and a bottom surface  17 - 2 . A pair of parallel male members  19 - 1  and  19 - 2  are disposed on opposite sides of the transverse centerline of base  17  and extend downwardly a short distance from bottom surface  17 - 2  of base  17 . Male members  19 - 1  and  19 - 2  are substantially identical to one another, each male member  19  comprising a generally cylindrical post  21  terminating at its bottom end in a generally conical head  23 . 
     Female portion  15 , which may be made by molding, is a generally rigid structure comprising a base  31 . Base  31 , which is generally flat and oval, has a top surface  31 - 1  and a bottom surface  31 - 2 . A pair of generally cylindrical, parallel sleeves  33 - 1  and  33 - 2  extend upwardly a short distance from top surface  31 - 1  of base  31 , sleeves  33 - 1  and  33 - 2  being spaced apart appropriately for alignment with male members  19 - 1  and  19 - 2 , respectively. Sleeves  33 - 1  and  33 - 2  are substantially mirror images of one another taken along the transverse centerline of base  33 , and it is to be understood that the description below of sleeve  33 - 1  is correspondingly applicable to sleeve  33 - 2 . 
     Sleeve  33 - 1  terminates at its top end in a relatively sharp tip  35 - 1 , tip  35 - 1  being so shaped to facilitate insertion of sleeve  33 - 1  through biological tissue or the like. Sleeve  33 - 1  is additionally shaped to include a longitudinally-extending bore  37 - 1  adapted to receive male member  19 - 1 . A pair of longitudinally-extending slots  39 - 1  and  39 - 2  that are in fluid communication with bore  37 - 1  are provided in sleeve  33 - 1  to endow sleeve  33 - 1  with a certain degree of radial flexibility to facilitate insertion of member  19 - 1  into bore  37 - 1 . However, it should be understood that, depending upon the applicable flexibility requirements of sleeve  33 - 1 , one or both of slots  39 - 1  and  39 - 2  could be changed in size or eliminated entirely and that one or more additional slots could be provided in sleeve  33 - 1 . 
     Sleeve  33 - 1  is further shaped to include a substantially circumferential flange  41 - 1 , flange  41 - 1  extending radially inwardly a short distance into bore  37 - 1 . Flange  41 - 1  is appropriately sized so that, once head  23  is inserted into bore  37 - 1  and past flange  41 - 1 , head  23  cannot easily be withdrawn from bore  37 - 1  back past flange  41 - 1 , except under the conditions described below. 
     Referring now to  FIG. 3 , head  23  can be seen to comprise a core  23 - 1  and a coating  23 - 2 . Core  23 - 1  is made out of a non-bioabsorbable material, and coating  23 - 2  is made out of a bioabsorbable material having a desired degradation rate. Said non-bioabsorbable material used to make core  23 - 1  may be conventional in nature and may comprise one or more non-bioabsorbable compounds. Said bioabsorbable material used to make coating  23 - 2  may also be conventional in nature and may comprise one or more bioabsorbable compounds. 
     The remainder of male portion  13  (and the entirety of female portion  15 ) is preferably made entirely out of the same non-bioabsorbable material as core  23 - 1 . Head  23  may be formed by insert molding coating  23 - 2  onto core  23 - 1 . Core  23 - 1  and coating  23 - 2  are appropriately sized relative to flange  41 - 1  so that, when coating  23 - 2  becomes sufficiently degraded after having been implanted within a patient for a particular period of time, head  23  shrinks in size until head  23  is no longer retained in bore  37 - 1  by flange  41 - 1 . (In other words, top surface  24  of head  23  is no longer engaged by flange  41 - 1 .) 
     As can readily be appreciated, fastener  11  has a shorter life-span (i.e., will fragment sooner) than a corresponding fastener made entirely out of a bioabsorbable material for the reason that the thickness of the bioabsorbable material in fastener  11  is considerably less than that in a corresponding “all-bioabsorbable” fastener. Consequently, because of its reduced thickness, the bioabsorbable material of fastener  11  takes less time to become fully hydrated and, therefore, degrades more rapidly than a corresponding “all-bioabsorbable” fastener. 
     It should be understood that one can alter the life-span of fastener  11  by, among other things, modifying the type of bioabsorbable material used in coating  23 - 2 , modifying the thickness of coating  23 - 2 , and modifying the relative dimensions of core  23 - 1 , coating  23 - 2  and flange  41 - 1 . It should also be understood that the non-bioabsorbable material used to make all of fastener  11 , except for coating  23 - 2 , could be replaced with one or more bioabsorbable materials having a slower degradation rate than the bioabsorbable material used to make coating  23 - 2 . 
     In addition, it should be understood that the number of sets of male members  19  and sleeves  33  in fastener  11  is illustrative only and that, in other embodiments, there could be as few as one male member  19  and one sleeve  33  or as many as three or more sets of male members  19  and sleeves  33 . 
     Referring now to  FIG. 4 , there is shown a fragmentary section view of a second embodiment of a biocompatible fastener constructed according to the teachings of the present invention, the biocompatible fastener being shown represented generally by reference numeral  61 . 
     Fastener  61  is similar in many respects to fastener  11 , fastener  61  comprising a male portion  63  and a female portion  65 , male portion  63  being identical in overall size and shape to male portion  13  of fastener  11 , female portion  65  being identical in all respects to female portion  15  of fastener  11 . 
     The principal difference between fastener  61  and fastener  11  is that male portion  63  of fastener  61  is constructed to comprise, instead of a pair of posts  21  each terminating at its bottom end in a generally conical head  23 , a pair of posts  67  each terminating at its bottom end in a generally conical head  69  (only one such post  67  and head  69  being shown and described herein although it is to be understood that the two post/head combinations are identical). 
     Post  67 , which is cylindrical in shape, comprises a core  67 - 1  and a coating  67 - 2 . Core  67 - 1  is made out of a non-bioabsorbable material, and coating  67 - 2  is made out of a bioabsorbable material having a desired degradation rate. Said non-bioabsorbable material used to make core  67 - 1  may be conventional in nature and may comprise one or more non-bioabsorbable compounds. Said bioabsorbable material used to make coating  67 - 2  may also be conventional in nature and may comprise one or more bioabsorbable compounds. 
     Head  69 , which is conical in shape, comprises a core  69 - 1  and a coating  69 - 2 . Core  69 - 1  is made out of a non-bioabsorbable material, and coating  69 - 2  is made out of a bioabsorbable material having a desired degradation rate. Said non-bioabsorbable material used to make core  69 - 1  may be conventional in nature and may comprise one or more non-bioabsorbable compounds. Said bioabsorbable material used to make coating  69 - 2  may also be conventional in nature and may comprise one or more bioabsorbable compounds. 
     Coating  67 - 2  is appropriately sized relative to flange  41 - 1  so that, when coating  67 - 2  becomes sufficiently degraded after having been implanted within a patient for a particular period of time, head  69  shrinks in size until head  69  is no longer retained in bore  37 - 1  by flange  41 - 1 . As can be seen, as contrasted with head  23  of fastener  11 , the entirety of the top surface  72  of head  69  of fastener  61  is made of bioabsorbable material. This may be advantageous as it may prevent tissue or other matter disposed on top surface  72  from being snagged by top surface  72  and, in so doing, hindering the desired breaking apart of fastener  61 . 
     Cores  67 - 1  and  69 - 1  are preferably molded as a unitary structure with base  70 , with coatings  67 - 2  and  69 - 2  being simultaneously insert molded thereover as a unitary coating. 
     It should be understood that one can alter the life-span of fastener  61  by, among other things, modifying the type of bioabsorbable material used in coatings  67 - 2  and  69 - 2 , modifying the thicknesses of coatings  67 - 2  and  69 - 2 , and modifying the relative dimensions of core  69 - 1 , coating  69 - 2  and flange  41 - 1 . It should also be understood that the non-bioabsorbable material used to make all of fastener  61 , except for coatings  67 - 2  and  69 - 2 , could be replaced with one or more bioabsorbable materials having a slower degradation rate than the bioabsorbable material used to make coatings  67 - 2  and  69 - 2 . 
     Referring now to  FIG. 5 , there is shown a fragmentary section view of a third embodiment of a biocompatible fastener constructed according to the teachings of the present invention, the biocompatible fastener being shown represented generally by reference numeral  81 . 
     Fastener  81  is similar in many respects to fastener  61 , fastener  81  comprising a male portion  83  and a female portion  85 , male portion  83  being identical in overall size and shape to male portion  63  of fastener  61 , female portion  85  being identical in all respects to female portion  65  of fastener  11 . 
     The principal difference between fastener  81  and fastener  61  is that the bottom portion of post  87  and the entirety of head  89  are made only of bioabsorbable material whereas the remainder of post  87  comprises a core  87 - 1  made out of a non-bioabsorbable material and a coating  87 - 2  made out of a bioabsorbable material having a desired degradation rate. As can readily be appreciated, the relative lengths of core  87 - 1  and post  87  can be modified as desired. It is to be noted that, because head  89  is made entirely out of bioabsorbable material, as opposed to comprising a coating of bioabsorbable material formed on a non-bioabsorbable core, head  89  may take comparatively longer to become fully hydrated. 
     Referring now to  FIGS. 6 and 7 , there are shown front and fragmentary section views, respectively, of a fourth embodiment of a biocompatible fastener constructed according to the teachings of the present invention, said biocompatible fastener being represented generally by reference numeral  101 . 
     Fastener  101  is similar in many respects to fastener  11 , the principal differences between the two fasteners being that fastener  101  comprises a head  103  made entirely out of a non-bioabsorbable material and that fastener  101  comprises a flange  105  comprising a core  105 - 1  and a coating  105 - 2 , core  105 - 1  being made out of a non-bioabsorbable material and coating  105 - 2  being made out of a bioabsorbable materials  105 - 2  having a desired degradation rate. (It should be understood that the non-bioabsorbable material used to make all of fastener  101 , except for coating  105 - 2 , could be replaced with a bioabsorbable material having a slower degradation rate than coating  105 - 2 .) 
     As can readily be appreciated, fastener  101  could be modified by replacing head  103  with head  23  of fastener  11 , head  69  of fastener  61 , head  89  of fastener  81  or the like. Alternatively, fastener  101  could be modified by replacing flange  105  with a flange made entirely out of the bioabsorbable material of coating  105 - 2  and/or by replacing head  103  with a head made entirely out of the bioabsorbable material of coating  105 - 2 . 
     Referring now to  FIG. 8 , there is shown a perspective view of a fifth embodiment of a biocompatible fastener constructed according to the teachings of the present invention, the biocompatible fastener being represented generally by reference numeral  201 . 
     Fastener  201  is similar in many respects to fastener  101 , fastener  201  comprising a male portion  203  and a female portion  205 . Male portion  203  is identical to the male portion of fastener  101 . 
     Female portion  205  comprises a base  207 , which in the present embodiment is generally rectangular in shape. Base  207  is made out of a non-bioabsorbable material and is shaped to include a pair of transverse bores  209 , each bore  209  being adapted to receive a head  103 . A pair of flanges  211 - 1  and  211 - 2  made of a bioabsorbable material are disposed within each bore  209 , flanges  211 - 1  and  211 - 2  being sized and shaped so that, once head  103  is inserted therepast, head  103  cannot easily be withdrawn from bore  209  back past flanges  211 - 1  and  211 - 2 , unless flanges  211 - 1  and  211 - 2  have degraded sufficiently. Flanges  211 - 1  and  211 - 2  are preferably formed by insert-molding. Alternatively, in another embodiment, bore  209  and flanges  211 - 1  and  211 - 2  could be separately constructed as an insert that is press-fit into a larger bore (not shown) previously formed in base  207 . 
     As can readily be appreciated, the number of heads  103  and bores  209  in fastener  201  is illustrative only, and it is to be understood that, in other embodiments, there could be as few as one head  103  and one bore  209  or as many as three or more sets of heads  103  and bores  209 . Also, it can readily be appreciated that head  103  could be replaced with any of heads  23 ,  69  or  89 . 
     Referring now to  FIGS. 9(   a ) through  9 ( d ), there are shown various alternative embodiments of female portion  205  of fastener  201 . In  FIG. 9(   a ), a female portion  301  is shown that is adapted for use with a one-headed male portion, female portion  301  additionally differing from female portion  205  only in that it includes a generally disc-shaped base  303 . 
     In  FIG. 9(   b ), there is shown another female portion  351  that is adapted for use with a one-headed male portion, female portion  351  additionally differing from female portion  205  only in that it includes three flanges  353 - 1  through  353 - 3 , instead of two flanges. 
     In  FIG. 9(   c ), there is shown still another female portion  371  that is adapted for use with a one-headed male portion, female portion  371  differing from female portion  351  only in that it includes five flanges  373 - 1  through  373 - 5 , instead of three flanges. 
     In  FIG. 9(   d ), there is shown still yet another female portion  391  that is adapted for use with a one-headed male portion, female portion  391  differing from female portion  371  only in that it includes four flanges  393 - 1  through  393 - 4 , instead of five flanges. 
     It can readily be appreciated that the number of flanges in female portions  205 ,  301 ,  351 ,  371  and  391  are illustrative only and that other numbers of flanges could be substituted. It can also readily be appreciated that female portions  351 ,  371  and  391  could be modified to include bases having a shape other than rectangular. 
     The biocompatible fastener of the present invention is not limited to a two-piece, mating-type fastener and could also be, for example, a bone screw, a surgical staple, or the like, wherein an intermediate portion along the length thereof is made out of a bioabsorbable material having a desired degradation rate and wherein the ends thereof are made out of a non-bioabsorbable material or a bioabsorbable material having a slower degradation rate than the bioabsorbable material of the intermediate portion. In this manner, a biocompatible fastener can be designed that fragments within the intermediate portion in a controllable and predictable manner after a desired period of time. 
     The embodiments of the present invention recited herein are intended to be merely exemplary and those skilled in the art will be able to make numerous variations and modifications to it without departing from the spirit of the present invention. All such variations and modifications are intended to be within the scope of the present invention as defined by the claims appended hereto.