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To address the need for bioactive materials toward clinical applications in wound healing and tissue regeneration, an artificial protein was created by recombinant DNA methods and modified by grafting of poly(ethylene glycol) diacrylate. Subsequent photopolymerization of the acrylate-containing precursors yielded protein-graft-poly(ethylene glycol) hydrogels. The artificial protein contained repeating amino acid sequences based on fibrinogen and anti-thrombin III, comprising an RGD integrin-binding motif, two plasmin degradation sites, and a heparin-binding site. Two-dimensional adhesion studies showed that the artificial protein had specific integrin-binding capability based on the RGD motif contained in its fibrinogen-based sequence. Furthermore, heparin bound strongly to the protein's anti-thrombin III-based region. Protein-graft-poly(ethylene glycol) hydrogels were plasmin degradable, had Young's moduli up to 3.5 kPa, and supported three-dimensional outgrowth of human fibroblasts. Cell attachment in three dimensions resulted from specific cell-surface integrin binding to the material's RGD sequence. Hydrogel penetration by cells involved serine-protease mediated matrix degradation in temporal and spatial synchrony with cellular outgrowth. Protein-graft-poly(ethylene glycol) hydrogels represent a new and versatile class of biomimetic hybrid materials that hold clinical promise in serving as implants to promote wound healing and tissue regeneration.

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Synthetic polymers have attained a dominant position in materials science and technology largely on the basis of their excellent physical and mechanical properties. The more subtle chemical and biological properties of natural polymers, especially of the proteins and nucleic acids, have been difficult to capture in synthetic macromolecular materials, in part because these properties arise from microstructural features that cannot be controlled in statistical polymerization processes. We describe herein the use of artificial genes to direct the synthesis of polymers of precisely controlled architecture, 1 in which biological functionsspecifically, the capacity to support attachment of vascular endothelial cellssis the primary object of the design. A long-term objective of this work is the development of improved materials for the regeneration, replacement or repair of vascular tissue.Surgical reconstruction of small-and medium-diameter blood vessels is exceedingly difficult. The material of choice for vascular reconstruction in the lower leg is autologous saphenous vein if it is available and healthy; unfortunately, the success rates for such reconstructive procedures are generally only about 70% after 5 years. 2 Poly(tetrafluoroethylene) and poly(ethylene terephthalate) have also been used for small-and medium-caliber grafts; however, patency rates for these materials are even lower than those for saphenous vein. 2b,3 Failure most often occurs through thrombosis and occlusion of the graft or through neointimal hyperplasia at the junction between the graft and the surrounding tissue. New materials are needed for the construction of improved vascular prosthetics.In an attempt to address this need, we report herein the preparation of artificial extracellular matrix proteins 4 comprising two kinds of elements: (i) a repeating unit structure (GVPGI) x 5 related to mammalian elastin and (ii) a cell-binding domain (designated CS5) derived from the natural extracellular matrix protein fibronectin. 6 Our choice of the elastin-like repeating unit was based on the extensive work of Urry and co-workers 7 on the family of polypentapeptides represented as -(GVPGZ) x -, where Z can be any of a wide variety of amino acid residues; the specific choice of Z ) I was dictated by the anticipated thermal transition behavior of the polymer (vide infra). Urry has suggested the use of elastinlike polypeptides in a vascular graft design in which the intimal layer bears peptide signals for endothelial cell attachment. 8 The results reported here relate directly to this proposal, in that the CS5 region of fibronectin contains the REDV sequence previously shown to support attachment and spreading of endothelial cells, but not smooth muscle cells or platelets, on artificial surfaces. 9 We describe here the microbial expression of artificial extracellular matrix proteins carrying CS5 domains, and we demonstrate that such proteins do in fact support attachment and spreading of vascular endothelial cells.The target polymers can be represented b...

Activation of cyclic nucleotide dependent signaling pathways leads to relaxation of smooth muscle, alterations in the cytoskeleton of cultured cells, and increases in the phosphorylation of HSP20. To determine the effects of phosphorylated HSP20 on the actin cytoskeleton, phosphopeptide analogs of HSP20 were synthesized. These peptides contained 1) the amino acid sequence surrounding the phosphorylation site of HSP20, 2) a phosphoserine, and 3) a protein transduction domain. Treatment of Swiss 3T3 cells with phosphopeptide analogs of HSP20 led to loss of actin stress fibers and focal adhesion complexes as demonstrated by immunocytochemistry, interference reflection microscopy, and biochemical quantitation of globular-actin. Treatment with phosphopeptide analogs of HSP20 also led to dephosphorylation of the actin depolymerizing protein cofilin. Pull-down assays demonstrated that 14-3-3 proteins associated with phosphopeptide analogs of HSP20 (but not peptide analogs in which the serine was not phosphorylated). The binding of 14-3-3 protein to phosphopeptide analogs of HSP20 prevented the association of cofilin with 14-3-3. These data suggest that HSP20 may modulate actin cytoskeletal dynamics by competing with the actin depolymerizing protein cofilin for binding to the scaffolding protein 14-3-3. Interestingly, the entire protein was not needed for this effect, suggesting that the association is modulated by phosphopeptide motifs of HSP20. These data also suggest the possibility that cyclic nucleotide dependent relaxation of smooth muscle may be mediated by a thin filament (actin) regulatory process. Finally, these data suggest that protein transduction can be used as a tool to elucidate the specific function of peptide motifs of proteins.

A rapidly forming polymer matrix with affinity-based controlled release properties was developed based upon interactions between heparin-binding peptides and heparin. Dynamic mechanical testing of 10% (w/v) compositions consisting of a 3:1 molar ratio of poly(ethylene glycol)-co-peptide (approximately 18,000 g/mol) to heparin (approximately 18,000 g/mol) revealed a viscoelastic profile similar to that of concentrated, large molecular weight polymer solutions and melts. In addition, the biopolymer mixtures recovered quickly following thermal denaturation and mechanical insult. These gel-like materials were able to sequester exogenous heparin-binding peptides and could release these peptides over several days at rates dependent on relative heparin affinity. The initial release rates ranged from 3.3% per hour for a peptide with low heparin affinity to 0.025% per hour for a peptide with strong heparin affinity. By altering the affinity of peptides to heparin, a series of peptides can be developed to yield a range of release profiles useful for controlled in vivo delivery of therapeutics.

The ability to alter collagen organization could lead to more physiologically relevant scaffolds for tissue engineering. This study examined collagen organization in the presence of polysaccharide and the resulting effects on viscoelastic properties. Fibrillogenesis in the presence of chondroitin sulfate (CS) resulted in changes in the collagen network organization with an increase in void space present. The increased void space caused by CS addition correlated with a decreased stiffness of the collagen gel. These changes occurred with physiologically relevant ratios of collagen to CS, at physiological pH and ionic strength, and without a decrease in the amount of collagen incorporated into fibrils. The addition of dextran, an uncharged polysaccharide, yielded no change in network void space or mechanical properties. Changes in fibril diameter caused by CS or dextran were not correlated with mechanical properties. The results of this study demonstrate that collagen organization can be modified by the addition of GAG, leading to altered matrix mechanical properties.

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