Poly(ethylene oxide) (PEO) polymer, in linear and star form, was covalently grafted to silicon surfaces, and the surfaces were tested for their ability to adsorb proteins. Linear PEG of molecular weight 3400, 10 000, and 20 000 g/mol and star PEO molecules were coupled via their terminal hydroxyl groups activated by tresyl chloride to aminosilane-treated silicon wafers. The amount of PEO coupled to the surface was varied by changing the concentration of the tresyl-PEO solution. The dry PEO thickness on the surface was measured using X-ray photoelectron spectroscopy (XPS) and ellipsometry, from which the grafting density was calculated. The PEO surfaces were exposed to solutions of each of three proteins: cytochrome-c, albumin, and fibronectin. The degree of adsorption of each protein was determined by XPS and ellipsometry and recorded as a function of PEO grafting density. All three proteins were found to reach zero adsorption at the highest grafting densities on all three PEG surfaces, which for all three PEG surfaces was a PEO content of 100 +/- 10 ng/cm2. On both star PEO surfaces, albumin and fibronectin decreased to zero adsorption at intermediate values of grafting density, whereas cytochrome-c continued to adsorb at all grafting densities, although with a decreasing trend. A physical model of the surface helped explain these protein adsorption results in terms of the spacing and degree of overlap of grafted PEO chains.

Silks are being reassessed as biomaterial scaffolds due to their unique mechanical properties, opportunities for genetic tailoring of structure and thus function, and recent studies clarifying biocompatibility. We report on the covalent decoration of silk films with integrin recognition sequences (RGD) as well as parathyroid hormone (PTH, 1-34 amino acids) and a modified PTH 1-34 (mPTH) involved in the induction of bone formation. Osteoblast-like cell (Saos-2) responses to the decorated silk films indicate that the proteins serve as suitable bone-inducing matrices. Osteoblast-like cell adhesion was significantly increased on RGD and PTH compared to plastic, mPTH, and the control peptide RAD. At 2 weeks of culture, message levels of alkaline phosphatase were similar on all substrates, but by 4 weeks, alkaline phosphatase mRNA was greatest on RGD. At 2 weeks of culture, alpha 1(I) procollagen mRNA was elevated on silk, RGD, RAD, and PTH, and hardly detectable on mPTH and plastic. However, by 4 weeks RGD demonstrated the highest level compared to the other substrates. Osteocalcin message levels detected by RT-PCR were greatest on RGD at both time points. Calcification was also significantly elevated on RGD compared to the other substrates with an increase in number and size of the mineralized nodules in culture. Thus, RGD covalently decorated silk appears to stimulate osteoblast-based mineralization in vitro.

A new method was developed for binding poly-(ethylene oxide) (PEO) to polymer surfaces that involves the use of electron beam irradiation in two steps. In the first, methacrylic acid was grafted and polymerized to a polymer surface, changing it from hydrophobic to hydrophilic. Exposure of this surface to aqueous PEO solutions resulted in strong hydrogen bonding of the PEO, which was covalently grafted in a second radiation step. The PEO grafts were stable; they could not be removed with extensive washing with water, soaking in basic solution, or gentle mechanical scraping. Both monolayers and multilayers of PEO were formed. The density of the monolayers were found to have little dependence on the molecular weight or concentration of the PEO solution; multilayers could be controlled by varying the viscosity of the PEO solution and the method of application. The PEO-grafted monolayers were tested for their ability to prevent protein adsorption of cytochrome-c, albumin, and fibronectin. Monolayers of star PEO were the most effective, at best showing a 60% decrease in adsorption from untreated controls. One million molecular wight linear PEO monolayers were almost as effective as star monolayers, and 35,000 g/mol linear PEO was bound too closely to the surface, owing to its small size, to have much impact in preventing protein adsorption. The reason for the continued protein adsorption was believed to be due to a close grafting of the PEO to the surface, as well as the grafted methacrylic acid chains being long enough to extend through the PEO monolayer, thus being accessible on the surface.

The formation of biodegradable hydrogels is reported based on enzymatic crosslinking reactions of modi®ed polyaspartic acid. Poly(aspartic acid) polymers functionalized with aromatic groups were crosslinked in aqueous solution via peroxidase with hydrogen peroxide to form hydrogels. The reaction products were characterized based on time to gel, swelling ratio, sol fraction, storage and loss modulus, and entrapped enzyme. Optimum reaction conditions for gel synthesis were determined. Poly(aspartic acid) hydrogels have signi®cant potential for use in biomedical applications such as in drug delivery due to the aqueous, nontoxic synthesis conditions as well as their inherent biodegradability by proteases.

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