Faculty Bibliography

Novel artificial extracellular matrices were synthesized in the form of semi-interpenetrating polymer networks containing copolymers of poly(ethylene glycol) and acrylic acid (PEG-co-AA) grafted with synthetic bioadhesive peptides onto exposed carboxylic acid moieties. These substrates were very resistant to cell adhesion, but when they were grafted with adhesive peptides they were highly biospecific in their ability to support cell adhesion. Extensive preadsorption of adhesive proteins or peptides did not render these materials cell adhesive; yet covalent grafting of adhesive peptides did render these materials highly cell adhesive even in the absence of serum proteins. Polymer networks containing immobilized PEG-co-AA were grafted with peptides at densities of 475 +/- 40 pmol/cm(2). Polymer networks containing immobilized PEG-co-AA N-terminally grafted with GRGDS supported cell adhesion efficiencies of 42 +/- 4% 4 h after seeding and became confluent after 12 h. These cells displayed cell spreading and cytoskeletal grafted with inactive control peptides (GRDGS, GRGES, or no peptide) supported cell adhesion efficiencies of 0 +/- 0%, even when challenged with high seeding densities (to 100,000 cell/cm(2)) over 14 days. These polymer networks are suitable substrates to investigate in vitro cell-surface interactions in the presence of serum proteins without nonspecific protein adsorption adhesion signals other than those immobilized for study.

OBJECTIVE:To assess the efficacy of a novel resorbable hydrogel barrier for preventing postoperative adhesions in animals. METHODS:A hydrogel barrier was formed in situ by photopolymerizing a solution of a macromolecular prepolymer in buffered saline using long-wavelength ultraviolet light. Two models in the rat were evaluated. In a primary adhesion model, devascularization and serosal injury were performed on the uterine horns using bipolar electrocautery. The prepolymer solution was applied to the horns and illuminated to form the barrier. On the seventh postoperative day, the fraction of the length of the horns involved in adhesions was scored, as was the quality of the adhesions. In a readhesion model, adhesions were formed as described and were surgically lysed on the seventh day, then were treated subsequently with the barrier and scored after 7 additional days. Each group in both models consisted of seven animals per treatment condition. Four prepolymer concentrations were examined in the primary adhesion model, and the optimal one was examined in the readhesion model. RESULTS:A conformal hydrogel barrier coating was formed upon in situ photopolymerization and adhered to the treated tissues. No residual hydrogel barrier was observed 7 days after application of the optimal gel concentrations. In the primary adhesion model, the mean fraction of the horns involved in adhesions was reduced significantly, from 76% in controls to 10% (P < .0001), and treatment with a 10% solution of prepolymer was determined to be optimal (P = .025). In the readhesion model, surgical lysis of adhesions alone did not reduce adhesions significantly (from 86% to 79%; P = .3), whereas lysis with barrier treatment did (79% to 28%; P = .002). CONCLUSIONS:In situ photopolymerization allowed the formation of adherent, conformal barriers, which demonstrated high efficacy in the prevention of adhesion formation and reformation in animals. This efficacy and ease of use warrant clinical evaluation.

Block copolyimides with varying amounts of polyethylene glycol (PEG) were synthesized and characterized by copolymerization of diaminodiphenyl ether (DDE), amino terminated PEG, and benzophenone tetracarboxylic acid dianhydride (BTDA). Strong materials were obtained, with enhanced flexibility as compared to the parent DDE-BTDA polyimide homopolymer. Incorporation of PEG led to an increase in water absorption by these copolymers, and hydrophilicity was increased as reflected by a decrease in air-water-polymer contact angle. These materials supported less cell adhesion in vitro than the parent polyimide homopolymer. Short term in vivo evaluation of these copolymers showed reduced fibrous encapsulation than was observed in the absence of PEG.

The biocompatibility of microcapsules made by the co-acervation of alginate and poly(l-lysine) (PLL) was enhanced by coating the surface of these microcapsules with a poly(ethylene glycol) (PEG)-based hydrogel. The hydrogel was formed by an interfacial photopolymerization technique using visible light from an argon ion laser. The light absorbing chromophore, eosin Y, was immobilized on the microcapsule surface. This restricted the formation of the PEG hydrogel to the surface of the microcapsule. The presence of the PEG gel on the surface was confirmed by fluorescent dextran entrapment, by direct visualization after dissolution of the underlying membrane and by electron spectroscopy for chemical analysis. The biological response of such microcapsules was evaluated by intraperitoneal implantation in mice. The PEG-coated microcapsules were found to be less inflammatory and were seen not to elicit a fibrotic response, as was the case with alginate-PLL microcapsules.

The laminin-based nonapeptide Cys-Asp-Pro-Gly-Tyr-Ile-Gly-Ser-Arg (CDPGYIGSR) and pentapeptide Tyr-Ile-Gly-Ser-Arg (YIGSR) have been previously demonstrated to support the attachment of several cell types and to competitively bind to the 67-kDa high affinity laminin receptor. Cell attachment, but not spreading, on substrates containing adsorbed CDPGYIGSR or YIGSR was observed. In this report we describe YIGSR-mediated attachment and spreading of a wide variety of cell types. GYIGSRY promoted cell spreading and stress fiber formation when it was covalently immobilized through the amino-terminal Gly residue, used as a spacer arm. Spreading was not observed when adsorbed YIGSR peptide was used. Functionally blocking antiserum directed against the 67-kDa and related laminin-binding proteins blocked human foreskin fibroblast (HFF) spreading, but not attachment, on covalently grafted GYIGSRY substrates. However, functionally blocking antisera directed against the vitronectin receptor, integrin alpha v beta 3, and the fibronectin receptor, integrin alpha 5 beta 1, did not affect HFF spreading on these substrates. When HFFs spread on these substrates, the 67-kDa laminin receptor co-localized with the cytoplasmic proteins alpha-actinin and vinculin into discrete structures. These results suggest that the adhesion ligand YIGSR is solely sufficient for cell spreading when it is conformationally constrained by covalent attachment to a solid substrate, at least when attached via its amino terminus. Furthermore, the role of the 67-kDa laminin receptor in recognition of this ligand and mediating cell attachment is confirmed in this study. This report also provides the first evidence for direct or indirect association of this receptor with vinculin and alpha-actinin when YIGSR-mediated cell spreading occurs.