Dynamic bioabsorbable fastener for use in wound closure

A fastener for insertion into pierced openings of a tissue wound has a body formed of a generally bioabsorbable polymer defining an initial capture area internal to the body. The body includes a pair of arms, each with an inwardly projecting cleat operably joined at an elbow portion defining an internal elbow angle. The arms are operably joined to a backspan at a shoulder portion defining an internal shoulder angle. A durable tissue retention zone is defined between the cleat and the arm. The elbow portion and the internal elbow angle define an insertion width greater than a width of the pierced openings resulting in the pierced openings stretching over the cleat and being elastically retained within the durable tissue retention zone. The fastener initially captures wound tissue in the initial capture area and then dynamically reforms in response to lateral stresses applied by the wound tissue without a fracture failure of the fastener until a minimum degradation period.

FIELD OF THE INVENTION

The present invention relates generally to the field of surgical fasteners for use in wound closure. More particularly, the present invention relates to a design for a dynamic, bioabsorbable fastener designed for through-and-through insertion across a wound having a capacity to reform when exposed to wound stresses greater than the initial static strength of the fastener while continuously retaining and approximating opposing sides of a wound during the healing process.

BACKGROUND OF THE INVENTION

When an opening in tissue is created either through an intentional incision or an accidental wound or laceration, biological healing of the opening commences through the proximity of the opposed living tissue surfaces. If the opening is very large or if its location subjects the wound to continual movement, a physician will seek to forcibly hold the sides of the opening together so as to promote the healing process.

In the case of skin tissue, for example, healing occurs best when the opposing dermal layers of the skin tissue are held in tight, primary proximity with each other. Human skin tissue is comprised of three distinct layers of tissue. The epidermal layer, also known as the epidermis, is the outermost layer and includes non-living tissue cells. The dermal layer, or dermis, is the middle layer directly below the epidermal layer and comprises the living tissue of the skin that is the strongest of the three layers. The subcutaneous, or hypodermis layer, is the bottom layer of skin tissue and includes less connective tissue, making this the weakest layer of skin tissue.

The most prevalent method for forcibly closing a tissue opening is through the use of a suture or “stitches.” As early as the second century, the Greeks were using sutures to physically close skin openings. In its simplest form, a suture is simply a length of material that is attached to a tissue-piercing device, such as a needle, and looped through the opposing sides of a tissue opening. The suture is then pulled tight and the loop closes, causing the opposing sides of the tissue opening to come into close physical contact. The suture loop is held tight by the tying of a knot, or knots, or some other locking mechanism. The first sutures were made of animal gut. Eventually other natural suture materials including leather, horsehair, flax, cotton and silk came into use. As the sciences of medical and materials technology have advanced over the course of the past century, new bioabsorbable materials have been developed to further improve upon the basic suturing concept.

While traditional suturing remains a popular method of effectuating closure of skin openings, the use of fasteners, for example staples and staplers, as a skin closure technique has become increasingly popular, especially in surgical settings where the opening is created through a purposeful incision. In these settings, the incision tends to make a clean, straight cut with the opposing sides of the incision having consistent and non-jagged surfaces. Typically, stapling of a skin opening, for example, is accomplished by manually approximating the opposing sides of the skin opening and then positioning the stapler so that a staple will span the opening. The stapler is then manipulated such that the staple is driven into the skin with one leg being driven into each side of the skin opening and the cross-member of the staple traversing the skin opening. Generally, the staple is made of a deformable material such as surgical stainless steel and the legs of the staple are driven into an anvil causing the staple to deform so as to retain the skin tissue in a compressed manner within the staple. This process can be repeated along the length of the opening such that the entire incision is held closed during the healing process.

The earliest medical staple designs were manufactured of metal and designed to deform aroand the captured tissue. Examples of these staples include U.S. Pat. Nos. 2,684,070, 3,273,562 and 4,485,816. Although effective, metal staples suffer from the drawback of requiring post-operative removal. As the science of medical polymers developed, staple designs incorporating bioabsorbable materials became available. The use of these bioabsorbable materials eliminated the need for post-operative removal of the staples. Examples of these staples include U.S. Pat. Nos. 4,317,451, 4,741,337, 4,839,130 and 4,950,258. Due to the nature of bioabsorbable polymers; however, bioabsorbable staples could not be inserted with the same deformation approach used by metal staples. In fact, bioabsorbable staples were purposefully designed to avoid any deformation requirement, as deformation was seen as a potential failure mechanism. An example of such a design is illustrated by the inwardly biased skin fastener of U.S. Pat. No. 5,089,009. Thus, as the physical and chemical properties of bioabsorbable surgical staples evolved, the development of designs and insertion methods associated with bioabsorbable staples have focused on avoiding deformation of the bioabsorbable fastener.

One potential use for bioabsorbable fasteners is in the subcuticular application of such fasteners for use in closing skin wounds as shown, for example in a series of patents to Green et al. in U.S. Pat. Nos. 5,292,326, 5,389,102, 5,423,856, 5,489,287 and 5,573,541. These patents disclose the use of a bioabsorbable, rod-like fastener inserted in a subcuticular manner to assist the healing process. Another bioabsorbable fastener design contemplated for subcuticular wound closure is U.S. Pat. No. 5,618,311 to Gryskiewicz, in which a more traditional staple design is promoted.

If they could effectively retain tissue, the bioabsorbable staples of these designs would have many advantages over conventional metal staples, such as no visible scarring and no need for subsequent removal by a physician. Unfortunately, none of the designs for bioabsorbable staples to date has been incorporated into a medically or commercially efficacious fastener. It would be desirable to provide a bioabsorbable fastener for use in wound closure that could achieve the advantages of a bioabsorbable material and still provide for an efficacious wound closure.

SUMMARY OF THE INVENTION

The present invention is a bioabsorbable fastener for insertion into pierced openings on opposed sides of a tissue wound. A fastener body is formed of a generally bioabsorbable polymer material and defines an initial tissue capture zone internal to the fastener body. The fastener body includes a pair of fastener arms, a cleat operably joined to each fastener arm at an elbow portion and a backspan operably joined to each fastener arm at a shoulder portion. Each fastener arm is insertable into one of the pierced openings. Each cleat projects backward into the initial tissue capture zone with an internal elbow angle defined between the cleat and the fastener arm. A durable tissue retention zone of each fastener arm is defined between the cleat and the fastener arm. Each fastener arm has a maximum insertion width defined between outermost surfaces of the cleat and the fastener arm. Corresponding internal shoulder angles are defined between the backspan and each fastener arm and an internal midspan angle is defined between a midpoint of the backspan and the apex of each durable tissue retention zone.

The elbow portion and the internal elbow angle of each fastener arm are constructed with the maximum insertion width being greater than a width of the corresponding pierced opening such that at least a portion of the tissue surrounding the pierced opening is stretched over the cleat and elastically retained in the durable tissue retention zone for longer than a minimum degradation period of the bioabsorbable polymer material. The shoulder portions and the internal shoulder angles are constructed so as to capture wound tissue within the initial tissue capture zone during deployment of the fastener and then dynamically reform in response to lateral stresses applied by the wound tissue after deployment such that a sum of the internal elbow angles and the internal midspan angle remains less than 360 degrees without a fracture failure of the bioabsorbable polymer material until the minimum degradation period of the bioabsorbable polymer material.

While the use of bioabsorbable materials for a tissue fastener offers many advantages, the present invention is the first to recognize that the effective use of bioabsorbable materials in the design of a surgical fastener must both understand and overcome a number of issues related to the nature of bioabsorbable materials and human tissue, as well as the dynamic process of tissue healing.

First, the thermoplastic polymers used in typical bioabsorbable staples possess a viscoelastic quality or polymer creep when subjected to continuous stress loading due to the nature of their molecular level bonding and entanglements. Traditionally, bioabsorbable fastener designs have compensated for this creep by either thickening the backspans or staple legs to prevent or reduce the deformation of the staple, or adding retaining clips or latches to preclude such deformation. Instead of trying to counteract the viscoelastic qualities of the polymer, the present invention takes advantage of these properties to provide for a dynamic response to lateral tissue forces that can deform the fastener, but not so far that the cleats of the fastener would release the tissue in the durable tissue retention zone.

Second, if tissue is being retained as opposed to skewered, large amounts of subcuticular tissue must be retained by the fastener because subcuticular tissue tends to be elastic. Grabbing smaller volumes of tissue with a fastener might not ensure that the tissue will be approximated to achieve an efficacious closure. The fastener of the present invention accommodates this requirement without the need for an excessively large or excessively strong fastener. The fastener of the present invention utilizes two different types of tissue capture zones, a first larger initial tissue capture zone that can capture a sufficient amount of tissue when the fastener is deployed to counteract the initial elasticity of the tissue and still obtain an efficacious fastening. A second set of much smaller durable tissue retention zones within the cleats are then used to provide long term holding force while the main body of the fastener can dynamically reform in response to the lateral forces exerted by the tissue during the healing process.

Finally, when fastening opposing sides of a wound, the opposing sides must be physically approximated during placement of the fastener. Once the opposing sides have been retainably fastened, the opposing sides tend to return to a more relaxed disposition during the healing process, thereby increasing lateral pressure on the bioabsorbable fastener. In conventional practice, the bioabsorbable fastener ends up being over-designed in order to assist in the initial approximation of the tissue that can result in a design that is more susceptible to failure as a result of the longer term lateral pressures applied during the wound healing process. In contrast, the bioabsorbable fastener of the present invention is designed for use with an insertion apparatus that mechanically approximates the opposing sides of wound tissue to insure the creation of consistent and repeatable pierced openings into which the fastener is positioned in a through-and-through manner to take advantage of elastically securing the tissue within the durable issue retention zones created by the cleats of the fastener.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Depicted inFIGS. 1–3is a preferred embodiment of a dynamic, bioabsorbable fastener100of the present invention. Generally, fastener100comprises a pair of arms102,104being operably connected with a common backspan106at shoulder portions103and105, also depicted inFIG. 5, respectively. Arms102,104each preferably include a rounded tip108,110. Fastener100is further defined by an arcuate exterior, perimeter surface112and an arcuate interior surface114. The arcuate shape of interior surface114functions to even out and focus staple loading forces and reduces potential rocking of fastener100when in place within tissue. Most typically, fastener100has a generally circular cross-section taken through backspan106that gradually tapers to a more rectangular cross-section. In order to facilitate mold removal, fastener100can include a plurality of distinct segments and surfaces as shown for example inFIGS. 3 and 29.

Depending from each of tips108,110at an elbow region115,117is a rounded cleat116,118. As is more clearly depicted inFIG. 4, cleats116,118are defined by an outwardly facing cleat surface122, an inwardly facing cleat surface124and a rounded cleat tip126. Inwardly facing cleat surface124connects to interior surface114at a cleat base128defining a durable tissue retention zone129. In combination, interior surface114along arms102,104and backspan106along with the inwardly facing cleat surfaces124define an initial tissue capture zone130.

Design elements of fastener100are further depicted inFIG. 5. These design elements include an effective arm center line132, an effective backspan center line134, and an effective cleat center line136. With regard to effective arm center line132, effective backspan center line134and effective cleat center line136, the center lines generally refer to a line relatively equidistant between perimeter surface112and interior surface114or a line relatively equidistant between outwardly facing cleat surface122and inwardly facing cleat surface124. Due to the arcuate nature of fastener100, such center lines are only an approximation. The intersection of effective arm center line132and effective backspan center line134creates an internal shoulder angle138relative to fastener100. Shoulder regions103,105are defined as the areas proximate shoulder angles138. The intersection of effective arm center line132and effective cleat center line136creates an internal elbow angle142relative to fastener100. Elbow regions115,117are defined as the area proximate the elbow angles142. Other design elements include a backspan width146, an arm width147, an arm length148, a cleat length150, a cleat tip length152, a cleat tip126to cleat tip126distance154and a tip-to-tip distance156.

For purposes of a description of the present invention, fastener100is comprised of a generally bioabsorbable polymer selected to maintain effective retention strength for a period of at least 5 to 21 days within the body, and optimally at least 14 days before eventually being fully absorbed within the human body. Most preferably, bioabsorbable polymer comprises a blended bioabsorbable copolymer comprised of 63% polylactide and 37% polygycolide, commonly referred to as PLGA. While the PLGA copolymer is used in a preferred embodiment, other bioabsorbable polymers such as polylactide, polyglycolide and polycaprolactone, either individually, in blends or as copolymers, sharing similar traits including absorption traits, injection molding traits and polymer creep traits could be used as well. Similar to other polymers, the PLGA copolymer used in the preferred embodiment exhibits viscoelastic properties in which the entangled molecules under stress tend to slide past one another, creating a viscoelastic creep.

Due to the expense of bioresorbable polymer resins, it is preferable to avoid unncessary waste during the molding process. In order to reduce waste, fastener100is preferably formed using a micromolding injection molding process. Micromolding injection molding is typically used when the molding shot size is less than 1 gram. Using an appropriate micromolding injection system, for example a Battenfeld Microsystem M50, resin waste can be significantly reduced during production of a fastener100in accordance with the present invention. In addition, a micromolding injection system has other processing advantages such as allowing high injection speeds to promote dimensional stability, low residence times at elevated temperatures and integrated pan handling capabilities.

For purposes of maintaining wound closure during the healing process, fastener100is designed to supply a minimum dry initial closure strength of greater than 1.2 lbfper centimeter of wound length. In a preferred embodiment used in subcuticular wound closure, the dry initial closure strength correlates to a minimum fastener strength of 1.2 lbfper fastener100measured laterally between the durable tissue retention zones129. One way to achieve a dry initial closure strength of 1.2 lbfper centimeter of wound length is to increase the amount of bioabsorbable polymer present in fastener100as opposed to current fastener designs. In an embodiment of fastener100, the additional polymer is added proportionally to both the arms102,104and backspan106to optimize the strength of fastener100. In this embodiment, proportionally adding polymer eliminates weaknesses in fastener100, for instance along the backspan106, in the shoulder regions140, in arms102,104or in elbow regions144. Such weaknesses may ultimately lead to fastener100failure. In this embodiment of fastener100, the combination of the arcuate perimeter surface112and the arcuate interior surface114, distribute lateral forces supplied by the tissue along the shoulder regions103,105. By proportionally increasing backspan width146and arm width147, fastener100can accommodate the concentration of lateral forces without suffering a failure. Such a design optimizes the use of the expensive, bioabsorbable polymer thus eliminating unnecessary waste and expense in meeting the dry initial strength goals.

A preferred use of fastener100is in the subcuticular bilateral fastening of dermal tissue to close a skin wound158, depicted inFIGS. 6 and 7, as well as in U.S. patent application Ser. No. 10/179,628 entitled., “Mechanical Method And Apparatus For Bilateral Tissue Fastening,” and U.S. patent application Ser. No. 10/448,838, which is a divisional application also entitled “Mechanical Method And Apparatus For Bilateral Tissue Fastening,” both of which are commonly assigned to the assignee of the present invention and are hereby incorporates by reference in their entirety. Skin wound158generally comprises a pair of opposing skin surfaces160,162separated by a gap164. Gap164can be created through either purposeful means, such as a surgical incision, or accidental means such as an accidental cut. Opposing skin surfaces160,162each comprise three distinct layers: an epidermal layer, or epidermis166; a dermal layer, or dermis168; and a subcuticular layer170. The epidermis166comprises dead skin tissue that may hinder but does not assist in the biological healing process. The subcuticular layer170comprises a layer of fatty tissue typically lacking the strength necessary to anchor and hold skin closure fasteners throughout the biological healing process. Generally, a physician closes skin wound158by forcibly approximating the dermis168of opposing skin surfaces160,162. As the dermis168comprises living tissue, biological healing of skin wound158commences immediately upon approximation and limited healing occurs within the first 24 hours of approximation. In addition, the dermis168possesses enough strength and elasticity to anchor, hold and retain fastener100.

Generally as depicted inFIGS. 8,9,10and11, a delivery device172incorporating a pair of piercing members174,176is used to introduce fastener100into wound158. Most typically, delivery device172includes a handle177and trigger assembly178attached to an applicator head180for advancing and retracting the piercing members174,176. Piercing members174,176include a sharp tip182for piercing tissue as well as a semi-circular cross-section184defining a retaining space186that interfaces with and transports fastener100into wound158. Cross-section184defines a maximum piercing width188. Piercing members174,176are connected with a backspan member190. Applicator head180can also include a guide member192, a pair of capture zones194,196, a pair of compression members198,200and a pair of bores202,204.

In a preferred use of fastener100, subcuticular bilateral fastening of dermal tissue present in wound158is accomplished using a through-and-through bilateral tissue fastening technique described in the concurrently filed U.S. Patent Application entitled “Mechanical Method And Apparatus For Bilateral Tissue Fastening,” which is commonly assigned to the assignee of the present invention, a copy of which is attached and the disclosure of which is hereby incorporated by reference in its entirety, In this bilateral tissue fastening technique as shown, for example, inFIG. 8, fastener100is loaded between piercing members174,176and backspan member190. Cross-section184is designed to snugly accommodate exterior surface112such that only cleats116,118protrude inwardly from cross-section184. Once fastener100has been loaded, guide member192is positioned within skin wound158. Compression members198,200are used to approximate opposing skin surfaces160,162and force them within capture zones194,196. Compression members198,200force skin wound158into an everted disposition206shown inFIG. 12. As will be apparent, delivery device172is capable of a variety of alternative embodiments including varying orientations of guide member192, the incorporation of compression members198,200into delivery device172and designs in which delivery device172includes storage and loading means allowing for a multi-shot design.

Through precise dimensioning of capture zones194,196, a pair of target tissue zones208,210defined in the dermis168of opposing skin surfaces160,162are presented to tips182of piercing members174,176as depicted inFIG. 15. Using trigger assembly178, piercing members174,176are advanced forward into capture zones194,196and correspondingly through the target tissue zones208,210resulting in openings being pierced in dermal layer168. Tips182continue to advance out of the target tissue zones208,210and into the bores202,204present in guide member192as shown inFIG. 13. As piercing members174,176advance, fastener100is simultaneously advanced into target tissue zones208,210. As shown inFIG. 14, the outwardly facing cleat surface122of cleat116, and similarly cleat118, define a maximum insertion width212that is purposely designed and manufactured to be greater than the maximum piercing width188of piercing members174,176. Consequently, the openings pierced in the dermis168by tips182of piercing members174,176must stretch to accommodate maximum insertion width212. As cleats116,118are advanced into bores202,204, dermis168is forced to elastically stretch past the tips126of cleats116,118. Dermis168then rebounds and elastically snaps into position around cleat bases128and into durable tissue retention zone129.

Using trigger assembly178, piercing members174,176are sequentially withdrawn from bores202,204, target tissue zones208,210and capture zones194,196. However, fastener100remains within target tissue zones208,210as cleats116,118, durable tissue retention zone129and especially cleat bases128cooperate to retain the captured dermis168, preventing fastener100from being withdrawn. Backspan106traverses gap164, such that opposing skin surfaces160,162, and especially dermis168, are forcibly approximated to promote the biological healing process. The through-and-through insertion method is typically repeated along the length of skin wound158such that a plurality of fasteners100cooperate to forcibly close skin wound158as depicted inFIG. 16. Through the use of multiple fasteners100, the minimum dry initial closure strength can be increased beyond the typical 1.2 lbfper centimeter of wound length by reducing the distance between fasteners100along skin wound158. Correspondingly, the use of multiple fasteners100allows fastener100to be sized and designed for other wound closure applications or on differing locations of the body. In the preferred embodiment, fastener100is placed within skin wound158such that it resides generally parallel to the skin surface.

As depicted inFIG. 17, fastener100is shown following insertion into wound158via the through and through method. Prior to and immediately following wound closure, fastener100is present in a first disposition212having initial tissue capture zone130. When in first disposition212, shoulder angle138is slightly greater than 90°, while elbow angle142is substantially less than 90°, most preferably about 25°. First disposition212is representative of fastener100at time of insertion, herein referred to as T1. In a preferred embodiment, fastener100is symmetrical around a center axis214depicted inFIGS. 5 and 17. However, alternative embodiments can include asymmetrical designs, for example, varying arm lengths148, cleat lengths150, backspan widths146, differing shoulder angles138and elbow angles142. Preferably, fastener100is positioned such that equal amounts of first opposing side160and second opposing side162are retained within tissue capture zone130. Following through and through insertion of fastener100within wound158, fastener100is exposed to a series of lateral forces216as shown inFIG. 18. Lateral forces216act along interior surface114from cleat base128to shoulder regions103,105during a period of time after initial deployment of fastener100.

To prevent fastener100from failing when exposed to lateral forces216, fastener100is manufactured of a bioabsorbable polymer specifically selected to have polymeric creep during the healing period. If the sum of lateral forces216exceed the minimum dry initial closure strength of fastener100, fastener100will immediately begin to reform. Once fastener100is placed within wound158, the closure strength of fastener100begins to decrease as the combination of body temperature and body moisture begins to soften, then degrade the bioabsorbable polymer used in fastener100. Even if the sum of lateral forces216do not initially exceed the maximum dry initial closure strength of fastener100, degradation of bioabsorbable polymer will typically cause fastener100to reform at some time T2subsequent to wound closure.

Depicted inFIG. 19is fastener100in a semi-open disposition218following exposure to lateral forces216greater than the fastener closure strength. Preferably, fastener100does not reform to semi-open disposition218until a period of time T2of at least 24 hours from insertion, though depending upon placement and wound location, reformation may occur immediately upon insertion. As depicted, lateral forces216exceeding fastener closure strength induce polymer creep primarily in both shoulder regions103,105and to a lesser degree in elbow regions115,117. However, fastener100continues to retain and approximate the captured tissue due to the continuous retention of the elastic dermis around cleat bases128and within durable tissue retention zones129.

Depicted inFIGS. 20 and 21, is fastener100in a generally open disposition220following exposure to lateral forces216exceeding those required to reform to semi-open disposition218. Preferably, fastener100does not reform to generally open disposition220until a period of time T2of at least 1 to 14 days and optimally at least 7 days from insertion, though depending upon placement and wound location, reformation may occur immediately upon insertion. Fastener100is again reformed through polymer creep in shoulder regions103,105and elbow regions115,117. It should be noted that the closure strength of fastener100decreases over time due to the breakdown of the bioabsorbable polymer by the human body. As such, lateral forces216which may not initially be enough to induce reforming of fastener100, will likely induce at least some degree of fastener reforming at a time subsequent to placement of fastener100in wound158. In generally open disposition220, captured tissue remains approximated during the healing process as the elastic dermis continues to be retained within cleat bases128. In general cleat bases128will continue to retain the elastic dermis until the bioabsorbable polymer is absorbed to a point where failure, such as a fracture of arms102,104or backspan106occurs or polymeric creep in elbow regions115,177results in elbow angle142opening beyond 90° such that the elastic dermis168slides off of cleats128. In generally open disposition220, shoulder angles138are increasingly difficult to distinguish and instead, an internal midspan angle221defined by a midpoint of the backspan106and the apex of each durable tissue retention zone129, is created. In the preferred embodiment of subcuticular bilateral fastening of dermal tissue as depicted inFIG. 22, a pair of fasteners100that have reformed to generally open disposition220subsequent to insertion continue to approximate wound158. Due to the continuing capture of the dermis168within cleat bases128, wound158remains closed throughout the healing period, typically up to twenty-one (21) days. Throughout the reformation process, the sum of elbow angles142and the midspan angle remains less than 360° allowing fastener100to continually retain captured tissue beyond the minimum degradation period. Following minimum degradation period referred to as T3, fastener100is increasingly likely to suffer a fracture failure of the arms102,104, cleats116,118or backspan106.

While a preferred embodiment of fastener100and its method of use has been described, a variety of other staple configurations featuring the same dynamic reforming traits as well as through-and-through insertion method can be utilized. For example,FIGS. 23,24and25depict alternative fastener designs incorporating additional retaining elements to further assist in wound closure. Depicted inFIG. 23, a fastener222comprises a backspan224and arms226,228. Arms226,228include tips230,232having a hammerhead orientation234including an internal cleat236and an external recess238. Internal cleat236includes a cleat base240to similarly capture elastic tissue using the through-and-through insertion method. Depicted inFIG. 24, a fastener242comprises a backspan244and arms246,248. Arms246,248include tips250,252include an internal cleat254to similarly capture elastic tissue using the through-and-through method. In addition, arms246,248include a series of internal projections256to further assist in retaining captured tissue as fastener242reforms in response to lateral forces supplied by captured tissue. Depicted inFIG. 25, a fastener258comprises a backspan260and arms262,264. Arms262,264include tips266,268having an internal cleat270to similarly capture elastic tissue using the through-and-through method. In addition, backspan260includes a pair of opposed projections272,274to further assist in retaining captured tissue as fastener258reforms in response to lateral forces supplied by captured tissue. Although the fasteners of the present invention have been described with respect to an initial tissue capture zone that is defined by just two arms and within a single plane, it will be seen that a multiplicity of arms could be provided and that multiple planes could be accommodated for the tissue capture zone by, for example, making an angle in the backspan at the midpoint.

Depicted inFIG. 26is another embodiment of a fastener of the present invention. A fastener276can comprise any of the alternative fastener configurations but in a design using at least two distinct bioabsorbable layers. As depicted, fastener276includes a first bioabsorbable layer278, a second bioabsorbable layer280and a third bioabsorbable layer282. While this embodiment depicts a planar arrangement of different bioabsorbable materials, it will be recognized that multiple injection points along a mold could also be used to accomplish a similar construction with different polymer materials being present at the shoulder and elbow regions, for example. In practice, fastener276can be formed by adhesive, thermal or molding processes where the layers are bonded after being separately manufactured using the previously described micromolding process or alternatively, through an extrusion process284as shown inFIG. 27. In yet another alternative manufacturing process, fastener276can be stamped or cut from a sheet286comprising a plurality of bioabsorbable layers288as shown inFIG. 28. Fastener276having multiple bioabsorbable layers288has a number of design advantages including the ability to mix and match faster degrading bioabsorbable polymers with slower degrading bioabsorbable polymers. In addition, fastener276could be used as a delivery instrument by incorporating drugs or medicants, such as antibiotics, clotting agents, or even gene therapy between layers or zones to provide a time release as the layers are broken down within the body, or even onto the exterior surfaces of the fastener to facilitate the healing process.

Depicted inFIG. 29is another alternative embodiment of a fastener290. Fastener290comprises a backspan292and arms294,296. Fastener290included a thickness297that is generally consistent through backspan292and anus294,296. Arms294,296further include tips298,300, each tip298,300having an internal cleat302having a cleat base304. Arms294,296in combination with internal cleat302and cleat base304define a durable tissue retention zone306to capture elastic tissue using the through-and-through insertion method as previously described.

InFIGS. 30 and 31, there is shown an earlier embodiment of a fastener400of the present invention. Fastener400has body portion402, which comprises a cross-member408connecting a pair of fork members or legs406. The outer margins410of each leg406are dimensioned and shaped accommodatingly to the retaining space186of piercing members174,176, allowing fastener400to fit and slide between the piercing members174,176. Shoulders414preferably are provided to engage the solid cylindrical cross-section of the backspan member190, thus allowing fastener400to be advanced distally wit motion of the piercing members174,176. The distal end412of each leg406is incurvately shaped to allow easier passage through an opening in skin, referred to as a skive, that is created by piercing members174,176. Inwardly directed barbs404preferably are provided on each leg406to resist withdrawal of the fastener once emplaced.

Although an overall U-shape for the fastener400, as shown inFIGS. 30 and 31is preferred, other shapes having a capability for bilateral tissue engagement are also possible, and within the scope of the invention. Such other shapes include for example, but are not limited to, a square shape similar to an ordinary staple, a semi-circular or C-shape era V-shape or W-shape, in which the cross-member408has bends or other features. While the shape of fastener400is generally determined in a planar configuration, it will be recognized that other non-planar shapes and configurations can be used, such as a fastener having multiple projections for each leg406, with each projection oriented in a different plane, or a fastener having cross-member408arranged in a V-shape projecting out of the normal plane of the fastener400. Two leg members406are preferred, but it will be understood that additional leg members406could be aided in the same or a different plane of the fastener400such that the leg members of each side of the fastener form a dident or trident configuration, for example.

As shown inFIG. 32, an inner cross-sectional area409is defined by the fastener400for capturing the compressed dermal tissue. In a preferred embodiment, inner cross-sectional area409ranges from 1.5 sq. mm to 50 sq. mm and most preferably about 5 sq. mm to 10 sq. mm. This area is generally defined by an inner diameter length of between 1.5 mm and 9 mm and most preferably about 3.8 mm and an inner diameter width of between 1 mm and 5 mm and most preferably about 2 mm. It will be apparent that numerous shapes and configurations can be used for the shape and arrangement of cross-sectional area409. Preferably, inner cross-sectional area409is generally arrowhead shaped as a result of the positioning of the barbs412. As will be described, the barbs412or similar anti-reversing projections resist against the withdrawal of fastener400. While the barbs412are preferably oriented into the inner cross-sectional area409, it will be appreciated that barbs412may be omitted or may be oriented outwardly.

Although it is possible for fastener400to be deformed during delivery and application, preferably the majority of dermal tissue retained within cross-sectional area409is captured in a compressed state by a fastener400that is sufficiently rigid so as to retain the dimensional integrity of cross-sectional area409within +/−30% of its designed area for a period of preferably at least 10 days. Most preferably, structural integrity of fastener400is maintained for at least 21 days. In this way, the dermal tissue captured in fastener400is retained in a compressed state for a period sufficient to allow the biological healing process to occur without the dermal tissue being under tension during the healing process. Preferably, the dimensions of the fastener400and the operation of the applicator assembly100coordinate to create a compression ratio of dermal tissue within the inner cross-sectional area409that is greater than one. The compression ratio is defined either as a ratio of area or a ratio of width. In the case of width, the compression ratio is the ratio of the dimension defined by the position of the skive relative to the vertical interface51when the dermal tissue is at rest divided by the position of the skive relative to the vertical interface as held by the fastener400. In the case of area, the compression ratio is the ratio of the area of dermal tissue that will be retained by the fastener400when that dermal tissue is at rest divided by the actual cross-sectional area409.

Alternatively, it is possible to take advantage of the bilateral tissue fastening in the tissue target zone as taught by the present invention with a deformable fastener where the deforming of a bioresorbable or bioabsorbable fastener serves to provide at least some of the compression of the dermal tissue such that the need for a mechanical tissue manipulator is reduced or potentially eliminated. In this embodiment, a bioresorbable or bioabsorbable fastener would be deformed by the applicator apparatus in order to appropriately compress the dermal tissue. Deformation of a bioresorbable or bioabsorbable fastener could be accomplished in a number of ways, including prestressing the fastener into an open configuration such that it returns to a closed configuration, with or without mechanical assistance from the applicator, application of ultrasound, heat or light energy to alter the shape of, or reduce or relax stresses in, the fastener in situ, designing a polymer material with appropriate shapes and compositions that the material is deformable upon deployment without fracturing, or any combination of these techniques.

Fastener400is preferably formed from any suitable biodegradable material. The currently most preferred biodegradable material is a lactide/glycolide copolymer where the ratio is never less than at least 10% of one element and preferably in a range of 60%–70% lactide. Examples of other suitable materials include poly(dl-lactide), poly(l-lactide), polyglycolide, poly(dioxanone), poly(glycolide-co-trimethylene carbonate), poly(l-lactide-co-glycolide), poly(dl-lactide-co-glycolide), poly(l-lactide-co-dl-lactide) and poly(glycolide-co-trimethylene carbonate-co-dioxanone). In addition, other suitable materials could include compositions with naturally occurring biopolymers such as collagen and elastin, or stainless steel, metal, nylon or any other biocompatible materials in the case of a non-absorbable fastener, or even various combinations of such materials depending upon the desired application and performance of the fastener.

While a preferred embodiment of a dynamic, bioabsorbable fastener of the present invention has been described, it will be apparent to one skilled in the art that a fastener in accordance with the present invention is capable of numerous other embodiments without departing from the scope and spirit of the present invention.