EP1146917A1 - Medical adhesives - Google Patents

Abstract

Approaches have been developed to apply multicomponent medical adhesives that improve binding of the medical adhesive (106) to a substrate (104) having covalently bound adhesive components. Use of the multicomponent adhesive reduces the possibility of adverse effects due to the adhesive leaving the application site. In preferred approaches, the application of the adhesive leads to increased bond strengths. The medical adhesive (106) and/or the substrate (104) can be bioresorbable.

Description

MEDICAL ADHESIVES

BACKGROUND OF THE INVENTION The invention relates to adhesives suitable for use as medical/surgical/tissue adhesives and associated methods for attaching substrates to native tissue or other substrates.

Surgical glues/adhesives provide an alternative to sutures, staples and the like for closing wounds in soft tissue. Certain tissues, such as nerves and particular vital organs, are too delicate for suturing or stapling, so the use of surgical adhesives may be one of few viable repair options. Generally, the use of an adhesive to repair wounds in soft tissue is desirable due to its potential sealing properties and uniform stress distribution. In particular, surgical adhesives provide a means for closing a wound without introducing a risk of tearing tissue since adhesives tend to distribute the stress over the length of the wound . Generally, surgical adhesives can be classified according to whether they include synthetic polymers, natural (biological) polymers or both. A variety of synthetic urethane based polymers have been developed as surgical glues. The urethane based surgical adhesive compounds have been developed based on relatively low toxicity, strong binding and fast cure times. Natural surgical adhesives generally are based on proteins. For example, fibrin glues include the protein fibrinogen. Fibrinogen is used in natural wound healing mechanisms in humans and other mammals. Synthetic adhesives have the disadvantage of being potentially toxic. On the other hand, biological/ natural adhesives generally have relatively low binding (cohesive) strengths and rapid degradation times. Previous tissue adhesives have migrated from the point of application to locations where adverse consequences, such as thrombosis, can result. Medical adhesives can be used for other purposes including, for example, the production and/or implantation of medical devices.

SUMMARY OF THE INVENTION In a first aspect, the invention relates to a substrate/adhesive component composite comprising a first biocompatible substrate with a component of a medical adhesive covalently bonded to the biocompatible substrate .

In another aspect, the invention relates to a method of securing a first biocompatible substrate to a second biocompatible substrate. The method comprises contacting a substrate/adhesive component composite and a remaining component of a medical adhesive to a second substrate to form an adhesive bond. The substrate/adhesive component composite comprises a first biocompatible substrate with a component of a medical adhesive, which is covalently bonded to the first biocompatible substrate.

In a further aspect, the invention relates to a binding system comprising a first biocompatible substrate with a proteinaceous component of a medical adhesive forming a coating on the first biocompatible substrate, and a second medical adhesive component. The component coating forms following more than about one hour of contact between the proteinaceous component and the first biocompatible substrate. The application of the second medical adhesive component between the first substrate and a second substrate results in an adhesive bond after curing. Moreover, the invention relates to a method of securing a first biocompatible substrate to a second biocompatible substrate. The method includes the combining of the components of a binding system to form an adhesive bond. The binding system comprises the first biocompatible substrate with a proteinaceous component of a medical adhesive associated with the first substrate, and a second medical adhesive component. The application of the second medical adhesive component between the first substrate and the second substrate results in an adhesive bond after . curing, such that at least a portion of the second component of the medical adhesive is between the first substrate and the second substrate . In another aspect, the invention relates to a method of preparing a first biocompatible substrate for binding to a second biocompatible substrate. Both a component of a medical adhesive and a securing compound is applied to at least a portion of the first substrate. Securing compounds help to maintain the association between the first biocompatible substrate and the adhesive compound.

In an additional aspect, the invention relates to a biocompatible substrate comprising a medical adhesive component incorporated into the structure components of the substrate.

Furthermore, the invention relates to a method of forming a biocompatible substrate by incorporating a portion of a component of a medical adhesive with a component of the biocompatible substrate to form a blend and constructing the biocompatible substrate from the blend.

Moreover, the invention relates to a method of forming a prosthesis. The method includes securing a first substrate and a second substrate with a medical adhesive. The first substrate has an associated adhesive component, and remaining portions of the adhesive are placed between the first substrate and second substrate. The method can further include implanting the substrates within a patient . BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic perspective view of a substrate joined to native tissue with a medical adhesive.

Fig. 2 is a schematic perspective view of a substrate with a component or components of a multicomponent medical adhesive, associated with a portion of the substrate. Fig. 3 is a perspective view of a testing arrangement for measuring shear tear strength of an adhesive bond.

Fig. 4 is a histogram plot of average shear break strengths measured for five different types of substrates.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Improved methods for the application of multiple component medical/surgical/tissue adhesives and improved resultant medical devices have been discovered. In particular, a component of the medical adhesive is associated with a biocompatible substrate prior to the application of the remaining portion of the adhesive. The substrate with a component of the medical adhesive is secured to a natural tissue or other biocompatible substrate using another component of the medical adhesive. The substrate with an associated medical adhesive component (s) can form part or all of a medical device, such that the medical adhesive can be used to attach the medical device to a support substrate, which can be native tissue or a second biocompatible material to be incorporated into a medical device. While generally the adhesives described herein are useful for the attachment of a substrate to native tissue, the adhesives can be used also to attach two substrates to each other before or during implantation of the substrates into a patient . The adhesives can be used to reduce the number of sutures and staples that are required during surgery with a corresponding savings in time and surgical complexity. The adhesives can be particularly useful for the attachment of small components of a medical device that are difficult to secure with suture, staples and the like.

Generally, the use of an adhesive to repair wounds in soft tissue is desirable due to its potential sealing properties and uniform stress distribution. Initial association of a component (s) of the medical adhesive with a first substrate prior to attachment to a tissue or second substrate can result in improved tear strengths in the resulting adhesive bond. Also, association of a component of the medical adhesive with a substrate decreases the likelihood that portions of adhesive will separate from the adhesive bond and circulate within the patient. In certain preferred embodiments, a component of the medical adhesive is covalently attached to a substrate. In alternative embodiments, a component of the adhesive is incorporated within a substrate during the formation of the substrate . Referring to Fig. 1, the overall arrangement of the resulting structure 100 has native tissue 102 bound to a substrate 104 with a medical adhesive 106 between substrate 104 and native tissue 102. A portion of the tissue 102 forms a seal or adhesive bond with the substrate 104 or a portion of the substrate 104. As stated above, a substrate other than tissue could be used instead of tissue 102. Referring to Fig. 2, a component 108 of the medical adhesive is preferably applied first to substrate 104 either as a coating, by covalent binding or by incorporation into the matrix of the substrate.

The tissue adhesives described herein can be used for the formation and/or implantation of prostheses, such as a surgical patch. For example, a substrate, with a component of the adhesive, is secured over a wound site by the placement of the remaining portions of the adhesive either on the tissue where the substrate is to be placed, or on the substrate over the previously applied first component of the adhesive, such that the substrate adheres to the tissue upon contact and curing. The patch can include multiple layers. The multiple layers can be applied sequentially to the wound, or they can be adhered either completely or partially to each other prior to application to the wound. The layers may be pieced together. Generally, the top layer of the patch may be the same size or larger than the underlying layers. The medical adhesive can be used to fasten the layers together and/or to bind the patch to the wound site. The layers can be formed from tissue, such as pericardial tissue, or a synthetic material .

Alternatively, the medical adhesive can be used to attach a prosthetic device to the natural support tissue within a patient. Generally, a portion of the prosthetic device is formed from a substrate with an associated component (s) of the adhesive, although all of the device may be associated with the adhesive component (s) . The remaining portion of the adhesive can be added to the surface of the prosthesis with the first adhesive component or to the natural support tissue. After application of the remaining portions of the adhesive, the prosthesis is attached to the support tissue. For example, a cardiac prosthesis, such as a heart valve prosthesis or an annuloplasty ring, can be secured to the corresponding natural support tissue (i.e., annulus) within the patient using the medical adhesive of the invention. The adhesive preferably presents an interface between the first substrate and second substrate with suitable porosity and hydrophilicity . In particular, the adhesive interface should be sufficiently porous such that the adhesive can incorporate into or with the biocompatible material to achieve mechanical interlocking between the substrate and the adhesive. Similarly, an adhesive interface between a tissue and a biocompatible substrate should be sufficiently hydrophilic such that the adhesive will wet the substrate, allowing complete contact between substrate, adhesive and tissue and formation of a secure bond.

Suitable multiple component medical adhesives can include synthetic compounds, natural materials or a combination thereof. Suitable synthetic compound components of a medical adhesive include, for example, urethane based polymers . Suitable natural material components of a medical adhesive include, for example, a variety of proteinaceous materials and associated binding agents. In certain embodiments, one or more components of the medical adhesive are a natural material, such as a protein, while one or more components are synthetic compounds, such as a crosslinking agent. In certain embodiments, the medical adhesive is bioresorbable such that the adhesive is resorbed by the patient under natural physiological conditions after a suitable period of time. The period for resorption of the adhesive should be compatible with the time for the natural healing process. Generally, one or more components of the medical adhesive may be resorbable such that the adhesive is effectively absorbed by the patient over time. Thus, natural healing processes eventually provide association of the substrate with natural tissue by way of extracellular structures that take the place of the adhesive. Once the adhesive is resorbed, any potential alterations of the mechanical properties of the tissue caused by the adhesive are replaced by more natural mechanical properties of healed natural tissue.

The substrate with the associated component of the medical adhesive is prepared prior to the final application of the remaining portions of medical adhesive. Suitable timing for the application of the associated component of the medical adhesive to the substrate depends on the stability of the adhesive component once applied to the substrate. The remaining portions of the medical adhesive are generally applied shortly before forming the seal or adhesive bond between the substrate and a second substrate. Then, the adhesive bond is formed, and the adhesive bond is held together while the medical adhesive cures sufficiently to secure the adhesive bond. A. Prostheses And Patches

Prostheses for attachment with a medical adhesive generally include a tissue substrate or a synthetic substrate at least as a portion of the prosthesis. The substrate is suitable for attachment or association of a component of a medical adhesive. Generally, the prostheses are designed for implantation into or onto a patient for extended periods of time. Prostheses include, for example, prosthetic hearts, prosthetic heart valves, annuloplasty rings, vascular and structural stents, vascular grafts or conduits, pledgets, suture, leads, permanently in-dwelling percutaneous devices, vascular or cardiovascular shunts, dermal grafts for wound healing, surgical patches, neurological growth supports, and bone replacement grafts, such as joint replacement prostheses. A surgical patch, as well as other prostheses, may be fully bioresorbable such that the entire surgical patch is resorbed by the patient after a period of time. Biomedical devices that are designed to dwell for extended periods of time within a patient are also suitable for use with medical adhesives . These devices include, for example, Hickman catheters. B . Substrates Appropriate biocompatible substrates can be formed from natural materials, synthetic materials or combinations thereof. Natural, i.e., biological, material for use in the invention includes relatively intact living tissue, decellularized tissue and recellularized tissue. These tissues may be obtained from, for example, natural heart valves, portions of natural heart valves such as aortic roots, walls and leaflets, pericardial tissues, such as pericardial patches, connective tissues, bypass grafts, tendons, ligaments, skin patches, blood vessels, cartilage, dura mater, skin, bone, fascia, submucoεa, umbilical tissues, and the like.

Natural tissues are derived from a selected animal species, typically mammalian, such as human, bovine, porcine, seal, equine, canine or kangaroo. These natural tissues generally include collagen- containing material . Natural tissue is typically, but not necessarily, soft tissue. Tissue materials are particularly useful for the formation of tissue heart valve prostheses. The tissue can be living tissue, decellularized tissue or recellularized tissue. Decellularization approaches are described, for example, in U.S. Patent 5,855,620, incorporated herein by reference, and in published PCT Applications WO96/32905 and WO 96/03093, both incorporated herein by reference.

Tissues can be fixed by crosslinking.

Fixation provides mechanical stabilization, for example, by preventing enzymatic degradation of the tissue. Glutaraldehyde or formaldehyde is typically used for fixation, but other fixatives can be used, such as other difunctional aldehydes, epoxides, and genipin and derivatives thereof . Tissues can be used in either crosslinked or uncrosslinked form, depending on the type of tissue, the use and other factors. Generally, if xenograft tissue is used, the tissue is crosslinked and/or decellularized.

Relevant synthetic materials include, for example, polymers and ceramics. Appropriate ceramics include, without limitation, hydroxyapatite, alumina and pyrolytic carbon. Ceramics can be coated with a polymer, protein or other compound prior to use as a substrate, if desired. Appropriate synthetic materials include hydrogels and other synthetic materials that cannot withstand severe dehydration. Substrate materials can be fabricated from synthetic polymers as well as purified biological polymers.

Appropriate synthetic polymers include without limitation polyamides (e.g., nylon), polyesters, polystyrenes, polyacrylates, vinyl polymers (e.g., polyethylene, polytetrafluoroethylene, polypropylene and polyvinyl chloride) , polycarbonates, polyurethanes, poly dimethyl siloxanes, cellulose acetates, polymethyl methacrylates, ethylene vinyl acetates, polysulfones, nitrocelluloses and similar copolymers. These synthetic polymeric materials can be woven or knitted into a mesh to form a matrix or substrate. Alternatively, the synthetic polymer materials can be molded or cast into appropriate forms.

Biological polymers can be naturally occurring or produced in vitro by fermentation and the like. Purified biological polymers can be appropriately formed into a substrate by techniques such as weaving, knitting, casting, molding, extrusion, cellular alignment and magnetic alignment. For a description of magnetic alignments see, for example, R. T. Tranquillo et al . , Biomaterials 17:349-357 (1996). Suitable biological polymers include, without limitation, collagen, elastin, silk, keratin, gelatin, polyamino acids, cat gut sutures, polysaccharides (e.g., cellulose and starch) and copolymers thereof.

The particular substrate for association with an adhesive component can form the entire medical device or it can form portions of the medical device. Similarly, different substrates can be combined to form the medical device. For example, a fixed, heterologous tissue heart valve can be combined with a fabric sewing cuff to form a heart valve prosthesis. The fixed tissue and/or the sewing cuff can be associated with one or more adhesive components. The adhesive component can be associated with the substrate before or after the various portions are combined into the medical device. The selected approaches for association of the adhesive component with the substrate or substrates may influence the order of construction of the medical device. C. Medical Adhesives

Suitable medical/tissue/surgical adhesives preferably have multiple components. Generally, the adhesives have two components, although suitable adhesives can have more than two components. Besides adhesive components, the medical adhesives can include various additives described in more detail below. As noted above, the medical adhesives can include synthetic compounds, natural compositions/materials or a combination thereof.

The medical adhesive generally should be non- toxic. Approaches for application of the adhesive described herein are designed to reduce or eliminate circulation of the adhesive and/or one or more of the adhesive components. Furthermore, by reducing or eliminating circulation of the adhesive or adhesive components, risks associated with potential migration of the adhesive are correspondingly reduced or eliminated.

With respect to synthetic adhesives, preferred adhesives include, for example, urethane-based polymers , copolymers, and mixtures thereof. Polyurethanes are ester-amide derivatives of carboxylic acids. Urethane oligomers/prepolymers can be formed with terminal reactive functional groups. Because of the terminal functional groups, the prepolymers are particularly suitable for the formation of crosslinked mixed polymers exhibiting a range of desirable properties generally characteristic of polyurethanes and of the other components. With respect to the formation of an adhesive, in certain embodiments, the urethane prepolymer can be used as one component of the adhesive, with a crosslinking agent or agents being the other component or components of the adhesive.

Isocyanate (-NCO) - terminated urethane prepolymers are particularly suitable adhesive components. Polyurethanes including polyurethane prepolymers (urethane oligomers) can be formed either by the reaction of bischloroformates with diamines or the reaction of diisocyanates with polyhydroxy compounds. The approach to urethane polymerization involving diisocyanates with polyhydroxy compounds can be used to produce urethane prepolymers with isocyanate functional groups at their terminus . Suitable urethane prepolymers can be formed by the reaction of polyisocyanates with polyols . Suitable polyisocynates include, for example, aromatic polyisocyanates containing 6-20 carbon atoms excluding the -NCO groups, such as o-, m- and p- phenylene diisocyanates (PDI), 2,4- and 2,6-tolulene diisocyanates (TDI), diphenylmethane-2 , 4 ' and 4,4'- diisocyanates, diphenylmethane 2-4'- and 4,4'- diisocyanates (MDI), naphthalene-1 , 5-diisocyanate, triphenylmethane 4, 4' , 4"- triisocyanate, polymethylenepolyphenylenepolyisocyanates (PAPI ) obtained by phosgenation of aniline-formaldehyde condensation products, m- and p-isocyanato-phenyl sulfonyl isocyanate, and the like; aliphatic polyisocyanates containing 2-18 carbon atoms, such as ethylenediisocyanate, tetramethylenediisocyanate, hexamethylenediisocyanate , dodecamethylenediisocyanate , 1 , 6 , 11-undecanediisocyanate, 2 , 2 , 4- trimethylhexane diisocyanate, lysine diisocyanate, 2 , 6-diisocyanato methyl caproate, bis (2-isocyanato-ethyl fumarate, bis (2- iso-cyanato-ethyl) carbonate, 2-isocyanato-ethyl -2 , 6- diiso-cyanato-hexanoate, and the like; alicyclic polyisocyanates containing 4-15 carbon atoms, such as isophorone diisocyanate, dicyclohexylmethane diisocyanates, cyclohexylene diisocyanates, methylcyclohexylene diisocyanates, bis (2-isocyanato- ethyl) 4-cyclohexene-l , 2-dicarboxylate, and the like; araliphatic polyisocyanates containing 8-15 carbon atoms, such as xylylene diisocyanates, diethylbenzene diisocyantes, and the like; and modified polyisocyanates of these polyisocyanates, containing urethane, carbodiimide, allophanate, urea, biuret , urethdione, urethimine, isocyanurate and/or oxaolidong groups, such as urethane-modified TDI , carbodiimide-modified MDI , urethane modified MDI, and the like; as well as mixtures thereof . For surgical glues, preferred polyisocyanates from this group include aromatic polyisocyanates

(preferably diisocyanates) , particularly PDI , TDI (along with 2,4- and 2,6-isomers and mixtures of isomers with

TDI), MDI (along with 4,4'- and 2,4' -isomers and mixtures isomers with MDI or PAPI), and modified polyisocyanates containing urethane, carbodiimide, allophanate, urea, biuret and/or isocyanurate groups, derived from PDI, TDI and/or MDI.

Due to low toxicity, p-PDI (hereinafter PPDI) is particularly preferred. Alternative preferred embodiments include combinations of PPDI with a minor amount (usually up to about 50% by weight, preferably up to about 30% by weight) of one or more other polyisocyanates, such as aromatic polyisocyanates, particularly TDI, MDI, modified MDI and mixtures thereof. Preferably, the other polyisocyanates are reacted at early stages of prepolymer production so as to provide PPDI terminated prepolymers . Suitable polyols for the formation of the prepolymers include hydrophilic polyether polyols, other polyols and mixtures thereof. Representative suitable hydrophilic polyether polyols include adducts of ethylene oxide (hereinafter EO) or combinations of EO with other alkaline oxide (s) (hereinafter AO) formed with one or more compounds containing at least two active hydrogen atoms, such as polyhydric alcohols, polyhydric phenols, amines, polycarboxylic acids, phosphorous acids and the like. Suitable polyhydric alcohols include dihydric alcohols, such as ethylene glycol, propylene glycol, 1,3- and 1,4 -butane diols, 1,6-hexane diol, neopentyl glycol, diethylene glycol, bis (hydroxymethyl) cyclohexane, bis (hydroxyethyl) benzene, hydrogenated bisphenol A, hydrogenated bisphenol F, polytetramethylene glycols, polyester diols and silanol- terminated polysiloxanes ; trihydric alcohols, such as glycerol, trimethylol propane, trimethylol ethane, 1 , 2 , 3 , -butane triol, 1,2,6-hexane triol and polyester triols; and polyhydric alcohols having 4-8 or more hydroxyl groups, such as pentaerythritol, diglycerol, alphamethylglucoside, sorbitol, xylitol, mannitol, glucose, fructose, sucrose, and the like. Representative suitable polyhydric phenols include mono- and poly-nuclear phenols, such as hydroquinone, catechol, resorcin, pyrogallol, and bisphenols such as bisphenol F, bisphenol S and the like, as well as phenol-formaldehyde condensation products.

Suitable amines for the formation of polyether polyols include ammonia; alkanol amines, such as mono-, di- and tri-ethanol amines, isopropanol amines and the like; aliphatic, aromatic, araliphatic and alicyclic monoamines, such as C-,-C₂₀ alkyl amines (methyl, ethyl, isopropyl, butyl, octyl and lauryl amines, and the like) , aniline, toluidine, naphthyl amines, benzyl amine, cyclohexyl amine and the like, aliphatic, aromatic, araliphatic and alicylic polyamines, such as C₂-C₅ alkylene diamines (ethylene diamines) , diethylene triamine, toluene diamines, phenylenediamines, xy ly 1 ene d i amine s , methylene dianilines, diphenyletherdiamines , isophorone diamines cyclohexylenediamines, dicyclohexylmethane diamines and the like; and heterocyclic polyamines, such as piperazine, N-aminoethyl-piperazine, and other heterocyclic polyamines, disclosed in Japan Patent Publication No. 21044/1980.

Suitable AO, for use in combination with EO for producing polyether polyols, include, for example, propylene oxide [hereinafter PO] , 1,2-, 2,3-, 1,3- and 1,4-butylene oxides, styrene oxide, epichlorohydrin and the like, as well as combinations thereof. Preferred AO include PO .

For the formation of urethane prepolymers, addition of EO, or a combination of EO with an AO, to active hydrogen atom-containing compounds can be performed in conventional ways, with or without catalysts, such as alkaline catalysts, amine catalysts and acidic catalysts, under atmospheric pressure or at an elevated pressure, in a single step or in multiple steps. Addition of EO and AO may be performed by random-addition, block-addition or combination thereof, such as random-addition followed by block-addition. Random-addition is the preferred approach. Hydrophilic polyether polyols have an equivalent weight (molecular weight per hydroxl group) generally from about 100 to about 5,000, preferably from about 200 to about 3,000, and an oxyethylene content of generally at least about 30%, preferably from about 50% to about 90% by weight. Polyether polyols having an equivalent weight higher than 5,000 can be too viscous, while use of polyether polyols with an equivalent weight less than 100 can result in an adhesive with insufficient flexibility. Polyether polyols of oxyethylene content less than about 30% by weight, having insufficient hydrophilic nature, can have a slow cure rate and poor bonding power with water-rich tissue. Content of the primary hydroxyl groups of polyether polyols is preferably at least about 30%, more preferably at least about 50%, and most preferably at least about 70%.

Other polyols, optionally used in conjunction with hydrophilic polyether polyols, include low molecular weight polyols and/or hydrophobic polyols. Examples of such polyols are polyhydric alcohols described above as reactants for forming hydrophilic polyether polyols, AO adducts (such as PO adducts) of these polyhydric alcohols or other active hydrogen atom- containing compounds, and polyester polyols. Suitable polyester polyols include, for example, condensation products of dihydric and/or trihydric alcohols, such as ethylene glycol, propylene glycol, 1,3- and 1,4 -butane diols, 1,6-hexane diol, neopentyl glycol, diethylene glycol, glycerol, trimethylolpropane and the like, and/or polyether polyols, such as those described above, with dicarboxylic acids, such as aliphatic or aromatic dicarboxylic acids, including, for example, glutaric acid, adipic acid, sebacic acid, fumaric acid, maleic acid, phthalic acid and terephthalic acid, or ester- forming derivatives of dicarboxylic acids, such as anhydrides and lower alkyl esters, including, for example, maleic and phthalic anhydrides, dimethyl terephtharate, and the like, and ring-opening polymerization products of lactones, including, for example, epsilon-caprolactone .

Preferred polyols for producing NCO-terminated urethane prepolymers have an average equivalent weight from about 100 to about 5,000, more preferably from about 200 to about 3,000 and generally 2-8 hydroxyl groups, preferably 2-4 hydroxyl groups.

The polyisocyanate and polyol preferably are mixed with a ratio of NCO/OH of about 1.5 to about 5.0 and more preferably from about 1.7 to about 3.0. The resulting prepolymers preferably have an NCO-content from about 1% to about 10% by weight and preferably about 2% to about 8% by weight. Lower NCO-contents can result in a low binding strength and higher NCO-contents can lead to brittle bonds.

The polyisocyanates and polyols react to form urethane prepolymers. These prepolymers are moderate molecular weight oligomers. The size of the oligomers is controlled by the relative amounts of NCO functional groups and OH functional groups. Since the NCO functional groups are added in excess, the polymerization terminates when all of the OH groups have reacted. The unreacted NCO groups form the basis for further polymerization to form the final adhesive. Bioresorbable urethane based adhesives can be made from suitable hydrophilic urethane prepolymers. The urethane prepolymers are formed from an organic polyisocyanate and polyester polyol derived from a dicarboxylic acid with the formula HOOC - (A)_m - COOH where m is 0 or 1 and A is -CH₂- or an electron attracting group represented by the formula -R-CO- or

X

in which R is a divalent hydrocarbon group containing 1- 8 carbon atoms, R' is a divalent hydrocarbon group or halogen-substituted hydrocarbon group containing 1-20 carbon atoms, X is a halogen atom or nitro or cyano group, Y is a hydrogen atom, a halogen atom or nitro or cyano group, and n is 0, 1 or 2. Readily decomposable versions of the prepolymers result in adhesives that decompose within several weeks while other versions of the prepolymers result in decomposition over the course of several months or longer. Decomposition times can be evaluated empirically. Resorbable urethane adhesives are discussed further in U.S. Patent 5,173,301 to Itoh et al . , entitled "Surgical Adhesive," incorporated herein by reference.

Suitable compositions for the second component of the urethane based medical adhesives include polyols, such as the polyols used to form the prepolymer. The amount of polyols added can be based on the number of functional groups remaining unreacted in the urethane prepolymer. Alternatively, the second component of the urethane oligomer adhesive can be an unsaturated cyano compound containing a cyano group attached to a carbon atom involved in the polymerizable double bond, such as cyano acrylic acids and esters thereof. Examples of these unsaturated cyano compounds include, for example, cyanoacrylic acid, cyano methacrylic acid, methyl cyanoacrylic acid, methyl cyanomethacrylic acid, ethyl cyanoacrylic acid, ethyl cyanomethacrylic acid, isobutyl cyanoacrylic acid, isobutyl cyanomethacrylic acid, corresponding esters, a c r y 1 on i t r i 1 e s , methacrylonitriles, cyanoacrylonitriles, cyanomethacrylonitriles and mixtures thereof. Such adhesives are described in U.S. Patent 4,740,534 to Matsuda et al . , incorporated herein by reference. Mixtures of polyols and unsaturated cyano compounds can be used as the second or additional component (s) of the adhesive . The urethane based adhesive composition generally comprises about 20 to about 90 percent by weight urethane prepolymer and preferably about 30 to about 70 percent by weight urethane prepolymer. The ratio of urethane prepolymer to unsaturated cyano compound can be varied to achieve a desired hardness. The use of a higher percentage of urethane prepolymer results in an adhesive with greater flexibility. A catalyst can be added if desired.

Adhesives based on components that are natural compositions generally are based on inherent natural binding affinities and corresponding biological responses. Generally, one or more components of the adhesive is a protein or protein based compound. Protein is intended to be interpreted broadly in terms of any compound with a polypeptide (i.e., amino acid) component, and may include derivatives of natural proteins and polypeptides with additional covalently or non-covalently attached components, such as additional polypeptides, nucleotides, carbohydrates, and other organic or inorganic compounds. Protein components generally contain amino acids with side chains with functional groups useful for binding with the remaining adhesive components. Also, if the substrate is a crosslinked tissue, an adhesive component can replace functional groups that had been eliminated in the tissue substrate by reactions during the crosslinking process.

A type of biological adhesive is based on the protein fibrinogen. Fibrinogen, also known as factor I, is involved in natural blood clotting processes. The protein thrombin removes one or two peptides from fibrinogen to form fibrin. Thrombin is also involved in the blood clotting process. A variety of fibrin adhesives have been based on the crosslinking of fibrin. Fibrin glues generally involve combinations of fibrinogen, thrombin and Factor XIII. Factor XIII also is involved in the natural wound healing mechanism. Factor XIII, also known as fibrin stabilizing factor, is activated by thrombin, and converts soluble fibrin to an insoluble clot. Fibrin adhesives polymerize and also covalently crosslink with collagen and other tissue components to form a liquid tight bond. If fibrinogen, thrombin or factor XIII are associated with a substrate as a component of the adhesive, the additional portions of the adhesives can include additional amounts of these compounds. The final amounts of the fibrinogen, thrombin or factor XIII components in the complete adhesive can be adjusted, as desired, to yield selected adhesive proυerties, such as strenqth and/or cure times, or for convenient application.

U.S. Patent 4,818,291 to Iwatsuki et al . , incorporated herein by reference, described the inclusion of silk-fibroin protein into a fibrin glue to enhance its mechanical strength. Fibrin adhesives may also contain albumin, as described in U.S. Patent 4,414,976 to Schwarz et al . , incorporated herein by reference .

/Another type of adhesive includes a biological component and a synthetic component. Generally, the biological component includes a protein. For example, gelatin-resorcinol aldehyde adhesives involve a gelatin- resorcinol material that is formed by heating gelatin and resorcinol . Gelatin is formed by hydrolytic activity on collagen protein. Formaldehyde, glutaraldehyde or the like can be used to crosslink the gelatin-resorcinol material to complete the formation of the glue .

A similar adhesive is formed from water soluble proteinaceous material and di- or polyaldehydes . The proteinaceous materials may be purified proteins or mixtures of proteins. Preferred proteins include albumins, including ovalbumins . Particularly preferred proteins include serum albumins of human or animal origin. Suitable water soluble di- or polyaldehydes include glyoxal and glutaraldehyde . The adhesive cures within a minute or less after the application of the aldehyde by spraying a layer over a coating of the proteinaceous material . Such adhesives are described further in U.S. Patent 5,385,606 to Kowanko, incorporated herein by reference.

Similar adhesives based on proteinaceous material have been described in U.S. Patent 5,583,114 to Barrows et al . , incorporated herein by reference. Again, the proteinaceous material preferably includes serum albumin as a primary component . The second component includes bifunctional crosslinking agents, with preferred crosslinking agents including polyethylene glycol with a molecular weight ranging from about 1,000 to about 15,000. The polyethylene glycol can be modified to incorporate leaving groups to activate the crosslinking agent to bind at primary or secondary amines of the proteins . Suitable leaving groups include, for example, succinimidyl , maleimidyl, phthamimidyl , other imides, heterocyclic leaving groups such as imidazolyl, aromatic leaving groups such as nitrophenyl, and fluorinated alkylsulfone leaving groups such as tresyl (CF₃-CH₂S0₂-0- ) . A linking group can be bonded between the polyethylene glycol and the leaving group .

The adhesives can contain additives to modify the mechanical properties of the adhesive. Suitable additives include, for example, fillers, softening agents and stabilizers. Representative fillers include, for example, carbon black and metal oxides, silicates, acrylic resin powder, and various ceramic powders. Representative softening agents include, for example, dibutyl phosphate, dioctylphosphate, tricresylphosphate, tributoxyethyl phosphates and other esters. Representative stabilizers for the urethane based polymers include, for example, trimethyldihydroquinone, phenyl-β-naphthyl amine, p-isopropoxydiphenylamine , diphenyl-p-phenylene diamine, and the like. The protein based adhesives can also contain sugars such as glycine, glucose or sucrose to improve solubility, and stabilizers, including heparin. Fibrin glues can r-nntain additional components, such as an inhibitor of fibrinolysis (anti-fibrolytic agents), for example, aprotinin and/or transexamic acid, with calcium chloride .

D . Association of the Adhesive Component with the Substrate One or more components of the adhesive generally are associated with at least a section of the substrate. While the associated components can include more than one component, the associated components necessarily lack at least one necessary component in the formation of the adhesive. In other words, the associated component or components do not form an entire adhesive by themselves, in the sense that upon addition of other components, a strong adhesive bond is formed. The adhesive components associated with the substrate can be applied as a coating, bound covalently to the substrate, and/or incorporated into the substrate matrix or structure .

The additional portions of the adhesive include all adhesive components and additives that are not initially associated with the substrate. The additional portions of the adhesive can include additional quantities of the associated adhesive components. The additional portions of the adhesive can be added, for example, as a coating or by covalent binding, onto a native tissue surface or second substrate to be joined with the substrate, or applied over a section of the substrate associated with the adhesive components. Once all of the portions of the adhesives have been applied, the substrate is joined with native tissue to bind the substrate to the native tissue. The adhesive bond has an adhesive strength at least about three times greater than that exhibited by the one or more associated components adhered to the tissue without the additional portions. While the substrate generally is adhered to native tissue, the substrate can be bound to a second substrate before or during the process of implanting a medical device. Thus, the multiple substrates adhered to each other with the medical adhesive are implanted in a patient prior to, during or after complete curing of the adhesive. The attachment of the substrates to each other using the procedures herein has the same advantages with respect to localization of the adhesive and generally increased bonding strength.

The component or components associated with the substrate can be selected for the ability to associate with the substrate without losing the ability to bind with the remaining portions of the adhesive. In some cases, there may be several suitable components in the adhesive that can be associated with the substrate. For urethane adhesives, the urethane prepolymers generally can be associated with the substrate. For protein based adhesives, the protein generally can be associated with the substrate. If desired, one portion of the substrate can include associated components of one adhesive while other portions of the substrate can include associated components of another adhesive. The two portions with different associated components can overlap partially or completely, if desired.

Generally, the adhesive components are associated with the substrate such that large numbers of adhesive molecules are not easily dissociated from the substrate over the period of time required for curing of the adhesives. For some adhesive components, the direct application of the adhesive component (s) as a coating over the selected portion of the substrate is sufficient to provide sufficiently strong association. The strong association of an adhesive component coating can be due to natural attractions between the substrate material and the adhesive component, natural wetting effects of the adhesive component on a surface, the lack of solubility of the adhesive component in an aqueous solution and/or other similar effects.

The associated adhesive components can be associated with the substrate by covalent bonding or by application of a coating. Preferably, a component coating is stable for some period of time, preferably days or longer under proper storage. The component coating forms following at least an hour, and in some cases following two hours or more, of contact between the adhesive component (s) and the substrate, such that the adhesive component can fully associate with the surface of the substrate through various non-covalent interactions. As described further below, the substrate with the associated adhesive component (s) generally is prepared and stored prior to its intended use . To associate the adhesive component (s) with the substrate, the substrate can be placed in a solution containing the adhesive component. Alternatively, the adhesive components can be brushed onto the surface, administered from an applicator or sprayed on as an aerosol or the like. In alternative embodiments, the associated adhesive components can be incorporated into the matrix of the substrate.

To form a coating with the medical adhesive components, the method can be selected to be suitable for the substrate material and the adhesive components. For example, if the adhesive components and the substrate are not sensitive to drying, the adhesive component can be added to the substrate and dried to remove the solvent. Alternatively, the adhesive components can be applied as a concentrated solution, with the resulting composite being kept moist to prevent the substrate/adhesive component composite from drying out . A suitable container for the storage of moisture sensitive substrate/adhesive component composites is described in PCT/US98/03519 , entitled "Storage Container," incorporated herein by reference.

In some preferred embodiments, a component of the medical adhesive is covalently linked with the substrate. If the covalently linked adhesive component is a protein, a variety of approaches can be used for the covalent binding, depending on the nature of the substrate. For tissue based substrates, standard tissue crosslinking agents can be used for the covalent binding, such as difunctional aldehydes, including glutaraldehyde. Crosslinking agents bind to the protein in the adhesive component and to proteins in the tissue substrate . For synthetic substrates and proteinaceous or nonproteinaceous adhesive components, suitable crosslinking agents can be used for the covalent binding. Molecules of the crosslinking agent have one or more functional groups active to bind with the adhesive component and one or more functional groups to bind with the substrate. Suitable substrates have functional groups capable of chemical crosslinking. Based on the nature of the material in a synthetic substrate, a suitable functional group in the crosslinking agent can be selected. The functional group of the crosslinking agent would be identifiable as a functional group that can chemically crosslink with the synthetic polymer.

For example, chlorosulfonated polyethylene, as a substrate material, can react with crosslinking compounds having alcohol or amine groups. Thus, a compound having both an aldehyde functional group and an alcohol or amine functional group can crosslink between a protein adhesive component and a chlorosulfonated polyethylene substrate. Similarly, a polystyrene substrate can react with halogenated hydrocarbons. Thus, a suitable crosslinking agent to bind a protein to a polystyrene substrate would have an aldehyde functional group and a halogenated methyl group. If an adhesive component is covalently bonded to the substrate, the bonding conditions can be adjusted to covalently bond a desired amount of the adhesive component without inactivating the adhesive ability of the component. To accomplish this goal, the concentrations of the binding agent and the adhesive component can be adjusted. A protein adhesive component generally has a concentration in a bonding solution from about lng protein/ml to about 50μg protein/ml and preferably from about 25ng/ml to about lOOμg/ml. The selection of suitable concentrations can be evaluated empirically.

For the bonding of a protein adhesive component to a tissue substrate, bonding with a crosslinking agent can be performed under carefully controlled conditions to avoid inactivating the adhesive properties of the adhesive component. In particular, the crosslinking is preferably performed with a dilute solution of crosslinking agent, such as glutaraldehyde. Crosslinking preferably is performed with a concentration of crosslinking agent less than about 0.1% crosslinking agent, more preferably less than about 0.05% crosslinking agent and even more preferably from about 0.005% to about 0.02% crosslinking agent. According to conventional use in the field, percent values are based on a volume per volume dilution of a concentrated volume percent glutaraldehyde stock solution, generally a fifty percent (50%) by volume stock solution. The crosslinking of a protein adhesive component to a tissue substrate can be performed for at least about 5 minutes and generally is performed for about 15 minutes to about 24 hours or longer. For the glutaraldehyde crosslinking of certain proteins to tissue substrates, it has been observed that the extent of binding levels off relatively quickly with respect to crosslinking time, see copending and commonly assigned U.S. Patent application, serial number 09/186,810, entitled "Prostheses With Associated Growth Factors," incorporated herein by reference. Preferred crosslinking times can be evaluated empirically based on the disclosure herein. Under the preferred mild conditions described herein, a tissue substrate generally is not significantly fixed by the crosslinking agent .

For tissue based substrates, the solution containing the adhesive component preferably is buffered at a near physiological pH ranging from about 6.0 to about 8.5, and more preferably ranging from about 6.9 to about 7.5. Suitable buffers can be based on, for example, the following compounds: phosphate, borate, bicarbonate, carbonate, cacodylate, citrate, and other organic buffers such as tris (hydroxymethyl) aminomethane (TRIS), N- (2-hydroxyethyl) piperazine-N' - ( 2 - ethanesulfonic acid) (HEPES) , and morpholine propanesulphonic acid (MOPS) .

In an alternative embodiment, photochemical coupling can be used to induce covalent coupling of an adhesive component to the substrate. Photochemical coupling is based on the use of high energy light, e.g., ultraviolet light, to form reactive intermediates of certain functional groups. These reactive intermediates can form carbon-carbon bonds between two compositions. Aryl ketone functional groups are particularly useful in this respect. When photochemical coupling is used, a crosslinking agent may not be needed to covalently bond the adhesive component to the substrate.

Photochemical coupling can be used for attachment of protein adhesive components to a tissue substrate. See, for example, Dunkirk et al . , J. Biomaterials Applications 6 : 131-156 (1991), incorporated herein by reference. The tissue may or may not be separately crosslinked since the photochemical coupling generally also crosslinks the tissue, i.e., photofixation. Alternatively, photochemical coupling can be used to attach a linker to the tissue either before, after, or during binding of the linker to a protein adhesive component.

Ultraviolet light can also be used to crosslink various synthetic polymers to a substrate. Specifically, vinyl polymers crosslink when exposed to radiation due to a free radical mechanism. A crosslinking agent can be used with a group known to photoactivate . In addition, a variety of polymer side groups are known to be photoactive including, for example, alkyne, anthracene, benzothiophene dioxide, chalcone, cinnamate, coumarin, dibenzazepine, diphenylcyclopropene carboxylate, episulfide, maleimide, stilbazole, stilbene, styrene, 1 , 2 , 3-thiadiazole, and thymine . Thus, the substrate polymer and/or the adhesive component can include these groups that may undergo photoactivation. In alternative preferred embodiments, the medical adhesive component can be incorporated into the structure/matrix of a biocompatible substrate when the substrate is formed. In particular, at an appropriate time in the preparation of the substrate, an amount of the medical adhesive component can be mixed with the components of the substrate to form a blend. When the substrate is formed, the substrate includes within its structure the molecules of the medical adhesive component. Thus, a portion or all of the resulting substrate includes the medical adhesive component distributed through the matrix of the substrate. The biocompatible substrate can include several portions and/or layers such that the medical adhesive component is only distributed within a subset of the portions and/or layers of material that form the biocompatible substrate.

Polymer substrates can be formed by conventional polymer processes. The polymer can be synthetic polymers or natural polymers, such as purified collagen. The substrate materials can be selected such that the surgical glue component is not decomposed by the processing. For example, if the adhesive component is sensitive to heat, a substrate formation process can be selected that does not require the addition of the adhesive component to a hot substrate material. In this type of case, a solvent casting process or the like can be used instead of a thermal molding process. The concentration of the adhesive component can be selected empirically to provide sufficient adhesion upon addition of the remaining portions of the adhesive and completion of the adhesive bond with the native tissue or other substrate . E . Formation of the Adhesive Bond The additional portions of the adhesive can be added in a variety of ways. For example, the additional portions of the adhesive can be applied directly to the portion of native tissue or second substrate to which the first substrate is applied. The second substrate may or may not include an associated adhesive component (s) . Alternatively, the additional portions of the adhesive can be applied over the substrate with the associated adhesive components prior to contacting the substrate with the native tissue or second substrate for attachment. The additional portions of the medical adhesive can be brushed onto the surface, administered from an applicator, applied by dipping the appropriate substrate into a solution comprising the additional portions, or sprayed on as an aerosol or the like. The consistency of the additional portions of the medical adhesive may indicate which approaches for its application are particularly suitable.

The additional portions of the adhesive generally include one or more additional adhesive components that are not included in the adhesive components associated with the substrate. The additional portions of the adhesive can include additional quantities of the adhesive component or components that are associated with the substrate. The additional portions of the adhesive can include additives .

If the additional portions of the adhesive are applied to the natural tissue or second substrate prior to the formation of the adhesive bond, the formation of the adhesive bond involves the joining of the different components of the adhesive. If the additional portions of the adhesive are applied over the substrate at the location of the associated component (s) of the adhesive, the resulting structure is distinguishable from the application of a coating of the adhesive since the adhesive forms layers of components with the components in the undermost layer incapable of forming an adhesive alone. Thus, in either approach for the application of the additional portions of the adhesive, the resulting structure of the substrate and adhesive is distinct from the addition of a coating of a fully blended adhesive, including all components within the blended adhesive.

Generally, the additional portions of the adhesive are added just prior to the forming of the interface, although the precise timing can be adjusted based on a variety of factors. Relevant timing factors include cure rate, the timing of the surgical procedure, and the stability of the separate components under the environmental conditions, such as humidity, to which they are applied. Preferred adhesives have cure times ranging from about 1 minute to about 5 hours, more preferably from about 5 minute to about 1 hour, and even more preferably from about 5 minutes to about 30 minutes. After the application of the remaining portions of the medical adhesive, the substrate is contacted with native tissue or a second substrate at the desired point of attachment . A variety of approaches can be used to hold the substrate to the native tissue or second substrate while the adhesive cures sufficiently. The adhesive has cured sufficiently when the adhesive bond can hold against standard stresses applied to the adhesive bond without the need for additional support. Standard stresses can vary over significant ranges. For example, the stresses can be relatively low for adhesives holding a surgical patch or higher for adhesives securing a heart valve prosthesis. When fully cured, the adhesive reaches levels of strength for the adhesive bond to meet expected durability requirements.

With respect to initial curing of the adhesive, a health care professional can hold or maintain the substrate in place long enough to reach sufficient curing. Alternatively, clamps, clips or the like can be used to hold the substrate in place. These approaches can be used with adhesives having reasonably rapid cure rates. Alternatively, or in addition, a few suture stitches or staples can be applied to hold the substrate in place. A suitable degree of suturing or stapling generally would be considerably less using the medical adhesive than the degree of suturing or stapling required if the suture or staples were providing the primary support for the attachment of the substrate. The limited use of suture and/or staples are intended to provide stabilization to the adhesive bond at the early stages of curing to prevent tearing of the adhesive bond. Properties of the Adhesive Bond

After the application of the additional portions of the adhesive, a junction, seal or adhesive bond is formed between the substrate and the native tissue or other substrate with at least a portion of the surgical glue between the substrate and the native tissue or other substrate. The presence of an adhesive bond does not imply anything about the characteristics of the connection at the point of attachment between the native tissue/second substrate and first substrate. The junction can involve a "seamless joining" of the native tissue/second substrate to the first substrate in the sense of a smooth connection between the two materials.

The adhesive bond includes the overlapping region with the adhesive between the first substrate and the tissue or other substrate. The adhesive bond preferably has a bond strength of at least about 75 g/cm² and more preferably at least about 100 g/cm². Since it is not possible to measure the bond strength of an actual adhesive bond in a patient, the bond strength refers to a comparable adhesive bond formed between an equivalent section of substrate and a piece of tissue that corresponds to and is roughly equivalent to the native tissue in the actual adhesive bond. Referring to Fig. 3, the bond strength is measured by forming an adhesive bond 150 at overlapping edges of a portion of substrate 152 and a section of fresh tissue 154, i.e., nondegraded tissue without fixation, such that substrate 152 and tissue 154 extend in opposite directions from the adhesive bond 150. A different substrate can be used instead of the tissue, as appropriate. The edges extending away from the adhesive bond are held between clamps 160, 162, 164, 166.

Adhered substrates 152, 154, positioned between clamps 160, 162, 164, 166, are pulled, as shown in Fig. 3, in the respective direction in which they extend from the adhesive bond 150 until the adhesive bond ruptures under the shear forces . The value of the shear force (tear strength) applied when the adhesive bond breaks divided by the area of the adhesive bond is a measure of the bond strength. While actual adhesive bonds may not be planar, i.e., flat, the bond strengths are evaluated as planar adhesive bonds for consistency. The bond strengths of nonplanar adhesive bonds generally should be roughly equal to the area of the adhesive bond multiplied by the planar bond strength per area if a good hemostatic or liquid tight seal is formed around the adhesive bond.

With bioresorbable adhesives, the adhesive is resorbed preferably over a time period during which the substrate and tissue are joined together during natural healing processes. Thus, the adhesive is replaced by natural tissue without compromising the integrity of the adhesive bond. Variations in the resorption rate can be adjusted empirically to ensure that the adhesive remains at least for sufficient periods of time so that the strength of the adhesive bond is not compromised. The length of time for the wound to heal can depend significantly on the size of the wound and on the stresses to which the wounded tissue is subjected. For example, tissue subjected to little stress may heal sufficiently after a few days, while tissue subjected to considerable stress may require a considerably longer period of time. G. Biologically Active Additives

The adhesive can contain biological response modifiers. Inclusion of the biological response modifiers within the adhesive can result in the gradual release of the biological response modifier, especially if the adhesive is bioresorbable . Suitable biological response modifiers include, for example, antimicrobial agents, anticalcification agents and growth factors. Generally, the additives are combined with the additional portions of the adhesive that are applied topically, although protein additives can be combined with the adhesive components that are associated with the substrate if the association process would also associate the protein additives with the substrate. Antimicrobial agents include, for example, antibiotic organic chemical agents and antimicrobial metal ions. Organic antibiotic agents include, for example, penicillin and the like. Antimicrobial metal ions include, for example, ions of Ag, Au, Pt, Pd, Ir, Cu, Sn, Sb, Pb, Bi, Zn and combinations thereof. To associate the antimicrobial metal ions with the prosthesis, the prosthesis or a portion of the prosthesis can be soaked in a solution of the antimicrobial metal ions, such as a silver nitrate solution. Alternatively, the solution can be sprayed, brushed or similarly applied to the substrate.

Alternatively, antimicrobial metal ions can be applied in the form of an antimicrobial metal salt with a relatively low solubility in aqueous solutions. Silver compounds are particularly preferred. Suitable silver compounds include, for example, silver chloride, silver bromide, silver iodide, silver carbonate and silver phosphate. Suitable copper compounds include, for example, cupric stearate and cupric phosphate. Suitable zinc compounds include, for example, zinc stearate and zinc phosphate. Similarly, suitable palladium compounds include, for example, palladium acetate . The use of antimicrobial metal ions to reduce the risk of infection is described further in copending and commonly assigned U.S. Patent Application serial number 08/974,992 to Ogle, entitled "Medical Article with Adhered Antimicrobial Metal," incorporated herein by reference. Antimicrobial metal ions can be delivered using exogenous storage structures, as described in copending and commonly assigned U.S. Patent application 08/787,139 to Tweden et al . , entitled "Silver Delivery System," incorporated herein by reference. Certain polyvalent metal ions are effective at reducing calcification of prostheses. Preferred anticalcific metal ions include, for example, aluminum ions (AIM and ferric ions (Fe⁺³) . Other suitable metal ions include, for example, manganese ions, zinc ions, gallium ions, lanthanum ions and beryllium ions. To introduce the polyvalent anticalcific metal ions into the prosthesis, the prosthesis or a portion of the prosthesis can be soaked in a solution of the anticalcific ions. For example, an aluminum nitrate or ferric nitrate can be used. Alternatively, the anticalcific metal ions can be deposited as a relatively insoluble salt by the addition of a selected anion to a solution of soluble salt of an anticalcific cation in contact with a prosthesis or a portion of a prosthesis. For example, aluminum palmitate can be precipitated from a solution of aluminum chloride by the addition of palmitic acid, and ferric phosphate can be precipitated from a solution of ferric chloride. In addition, exogenous storage structures have been shown to be useful in delivering these polyvalent cations. See, commonly assigned and copending U.S. Patent application 08/690,661 to Schroeder et al . , entitled Calcification-Resistant Biomaterials , " incorporated herein by reference. These exogenous storage structures with stored anticalcific ions can be combined with the deposits of antimicrobial elemental metal . The biological response modifier can be a growth factor. A particularly preferred growth factor includes, for example, vascular endothelial growth factor (VEGF) . VEGF encourages the proliferation of endothelial cells which line vascular tissue. VEGF is a protein that can be included with the adhesive components associated with the substrate or with the additional portions of adhesive. The association of VEGF with prostheses is described further in copending and commonly assigned U.S. Patent Applications serial numbers 09/014,087 and 09/186,810 to Carlyle et al . , both entitled "Prostheses With Associated Growth Factors," both of which are incorporated herein by reference . H . Storage, Packaging, Distribution and Use Following binding of the adhesive component onto the substrate, the modified substrate can be stored. Preferred storage techniques minimize the risk of microbial contamination. For example, modified substrates that are not moisture sensitive can be stored in a dry air tight container. Alternatively, the modified substrate can be stored in a sterile sealed container with an antiseptic solution. The nature of the antiseptic solution should be compatible with the substrate and maintain the activity of the adhesive component . For example, a crosslinked tissue substrate with a protein adhesive component can be stored in a dilute aqueous glutaraldehyde solution. Due consideration should be given to possible loss over time of the bonded adhesive component or the efficiency of the bonded adhesive component. Additives, including antioxidants, such as ascorbic acid, can be added to the storage solution to reduce the loss of efficiency of the adhesive component during storage. For distribution, the modified substrate can be placed in sealed and sterile containers. The containers are generally dated such that the date reflects the maximum advisable storage time considering possible degradation of the adhesive component as well as other factors. The containers are packaged along with instructions for the proper use of the substrate and along with appropriate and/or required labeling. The containers are distributed to health care professionals for use in appropriate medical procedures. If the medical articles are stored in a solution, a health care professional may rinse the substrate after removing it from the storage container just before its use. The remaining components of the adhesive may or may not be distributed along with the modified substrate. If the remaining components are not distributed with the modified substrate, the remaining components, in some circumstances, may be purchased as a separate adhesive product.

Alternatively, the substrate can be modified at the hospital or another site remote from the production facilities. In this case, the modified substrate may only be stored a short period of time prior to use. In this case, the substrate and adhesive components needed to modify the substrate can be distributed separately or together. Appropriate instructions can be distributed with either the substrate, one or more of the adhesive components/portions, or combinations thereof. For short term storage, the modified substrate can be kept in the solution used for modifying the substrate. Alternatively, the modified substrate can be used immediately after completing the modification of the substrate . EXAMPLE

This example demonstrates increased binding strengths resulting from covalently attaching a component of a fibrin adhesive to components of a tissue bond. The samples were prepared from porcine aortic walls. Two pieces of aorta approximately 2 cm x 6 cm were cut from the same vessel removed from a valve. The length dimension of each piece corresponded to the radial direction of the vessel prior to cutting the sample. Twelve aorta pieces (six pairs) were crosslinked and stored for about 3 weeks in 0.5 percent glutaraldehyde in 0.9% saline (saline, Baxter Health Care Corp., Deerfield, IL) . The glutaraldehyde solution was prepared as a volume per volume dilution of a fifty percent (50%) by volume glutaraldehyde stock solution.

Eighteen uncrosslinked aorta pieces (nine pairs from nine sections of aorta) were prepared. Six pieces (three pairs) were placed overnight in 50 ml of 0.9% saline. Six additional aorta pieces (three pairs) were placed overnight in solutions containing fibrin, and six other aorta pieces (three pairs) were placed overnight in a solution of fibrinogen (80% activated, i.e., clottable) . The concentrated fibrin solution was prepared by dissolving 5. Og of fibrin (fibrin from bovine blood, Sigma Chemical Company, lot 110H9304) in 100 ml 0.9% saline. Similarly, the fibrinogen solution was formed by dissolving 5. Og fibrinogen (Sigma Chemical, lot 64H9300) in 100ml of 0.9% saline. Then, the aorta pieces stored overnight in fibrin or fibrinogen were placed separately in a 0.5 volume percent phosphate buffered glutaraldehyde solution for two hours. After two hours in the glutaraldehyde solution, the samples were removed and incubated for one hour in 0.1 molar tris buffer (Tris Ultra Pure, tris (hydroxymethyl) aminomethane, Gibco BRL, Life Technologies, Inc., Grand Island, NY).

The corresponding crosslinked or uncrosslinked pieces from the same vessel were then glued together with an adhesive. About 2 square centimeters of adhesive was applied to the surface at the end of one piece of tissue. The adhesive was a fibrin glue

(CryoSeal™ from Thermo Genesis Corp, Rancho Cordova,

CA, produced using 5,000 units/5ml fibrin from Park Davis, Morris Plains, NJ) , except for three pairs of pieces of crosslinked aorta (labeled CY/x-linked) that were attached with a cyanoacrylate glue, Duro^® (Super Glue, Hartford, CT) . The fibrin glue samples are labeled FG along with a label indicating tissue treatment - crosslinked as "x-linked", untreated as "fresh", fibrinogen treated as "fibrinogen" and fibrin treated as "fibrin". The fibrin glue was applied using a two orifice nozzle that combines the components through a single tube upon application. The samples were overlaid, and the adhesive was allowed to cure for about 20 minutes.

The strength of the bond was tested on an Instron 50 lb Load Cell, Model Sintech l/S from the Sintech Division of MTS Systems Corporation (Research Triangle Park, NC) . The full width of the two joined tissue pieces were gripped in the load cell to apply an even force across the adhesive bond. The load that results in sufficient shear force to tear the adhesive bond was measured in a configuration approximately as shown in Fig. 3.

The results are presented in Table 1, and the aver.age results are plotted in Fig. 4.

TABLE 1

The synthetic cyanoacrylate provided the strongest bonding. Crosslinking fibrinogen to the pieces prior to the application of the application of the fibrin glue resulted in an increase of almost a factor of four in the tear strength. The covalent attachment of fibrin resulted in an increase, but the magnitude of the increase may not be statistically significant. Thus, the covalent attachment of a component of the glue can result in a significant increase in the strength of the bond . The embodiments described above are intended to be illustrative and not limiting. Additional embodiments are within the claims below. Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

Claims

WHAT IS CLAIMED IS:

1. A substrate/adhesive component composite comprising a first substrate with a component of a medical adhesive covalently bonded to the substrate.

2. The composite of claim 1 wherein the adhesive component comprises a protein.

3. The composite of claim 2 wherein the protein comprises fibrinogen.

4. The composite of claim 2 wherein the protein comprises albumin.

5. The composite of claim 1 wherein the medical adhesive component comprises a urethane prepolymer.

6. The composite of claim 1 wherein the first substrate comprises tissue.

7. The composite of claim 6 wherein the tissue comprises crosslinked tissue.

8. The composite of claim 1 wherein the first substrate comprises a synthetic matrix.

9. A method of securing a first substrate to a second substrate, the method comprising contacting the composite of claim 1 and a remaining component of a medical adhesive to the second substrate to form an adhesive bond.

10. The method of claim 9 wherein the second substrate comprises tissue.

11. The method of claim 9 wherein the first substrate comprises a plurality of layers.

12. A binding system comprising a first substrate with a proteinaceous component of a medical adhesive forming a component coating on the first substrate following more than about one hour of contact between the proteinaceous component and the first substrate, and a second medical adhesive component, wherein the application of the second surgical glue component between the first substrate and a second substrate results in an adhesive bond after curing.

13. The binding system of claim 12 wherein the medical adhesive comprises a resorbable composition.

14. The binding system of claim 12 wherein the first surgical glue component is covalently bound to the first substrate.

15. The binding system of claim 12 wherein at least a portion of the first substrate has a coating comprising a resorbable polymer, the resorbable polymer having the first surgical glue component incorporated therein, to associate the first surgical glue component to the substrate .

16. The binding system of claim 12 wherein the first substrate comprises a crosslinked tissue.

17. The binding system of claim 12 wherein the first substrate comprises a synthetic matrix.

18. The binding system of claim 12 wherein the second substrate comprises native tissue.

19. A method of securing a first substrate to a second substrate, the method comprising combining the components of the system of claim 11 to form an adhesive bond such that at least a portion of the second component of the surgical glue is between the first substrate and the second substrate.

20. The method of claim 19 wherein the first substrate with the coating of adhesive component is stored in a closed, sterile container prior to formation of the adhesive bond.

21. A method of preparing a first substrate for binding to a second substrate, the method comprising applying both a component of a medical adhesive and a securing compound to at least a portion of the first substrate .

22. The method of claim 21 wherein the securing compound is a crosslinking agent.

23. The method of claim 21 wherein the securing compound induces a covalent bonding of the component of the surgical glue to the first substrate .

24. The method of claim 21 wherein the securing compound is a resorbable polymer.

25. A substrate comprising a medical adhesive component incorporated into the matrix components of the substrate .

26. The substrate of claim 25 wherein the matrix components of the substrate comprise synthetic polymers.

27. The substrate of claim 25 wherein the matrix components of the substrate comprises natural polymers.

28. A method of forming a substrate comprising incorporating a portion of a component of a medical adhesive with a component of the substrate to form a blend and constructing the substrate from the blend.

29. A method of forming a prosthesis, the method comprising: securing a first substrate and a second substrate with a medical adhesive wherein the first substrate has an associated adhesive component and wherein a remaining portion of the adhesive are placed between the first substrate and second substrate.

30. The method of claim 29 further comprising implanting the substrates within a patient, wherein the implantation is performed prior to the complete curing of the adhesive.

31. The method of claim 29 further comprising implanting the substrates within a patient, wherein the implantation is performed following complete curing of the adhesive.