Methods were developed to perform precipitation photopolymerization of PEG-diacrylate. Previously, co-monomers have been added to PEG when precipitation polymerization was desired. In the present method, the LCST of the PEG itself was lowered by addition of the kosmotropic salt sodium sulfate to an aqueous solution. Typical of a precipitation polymerization, small microparticles or microspheres (1–5 micron) resulted with relatively low polydispersity. However, aggregate formation was often severe, presumably due to a lack of stabilization of the phase-separated colloids. Microparticles were also produced by copoymerization of PEG-diacrylate with acrylic acid or aminoethylmethacrylate. The co-monomers affected the zeta potential of the formed microparticles, but not the size. The carboxyl groups of acrylic acid-containing PEG microparticles were activated and scaffolds were formed by mixing with amine-containing PEG microparticles. Although the scaffolds were relatively weak, human hepatoma cells showed excellent viability when present during microparticle crosslinking.

Conformational changes in adsorbed fibrinogen may enhance the exposure of platelet adhesive sites that are inaccessible in solution. To test this hypothesis, mass spectrometric methods were developed to quantify chemical modification of lysine residues following adsorption of fibrinogen to biomaterials. The quantitative method used an internal standard consisting of isotope-labeled fibrinogen secreted by human HepG2 cells in culture. Lysine residues in the internal standard were partially reacted with NHS-biotin. For the experimental samples, normal human fibrinogen was adsorbed to polyethylene terephthalate (PET) particles. The adsorbed fibrinogen was reacted with NHS-biotin and then eluted from the particles. Constant amounts of internal standard were added to sample fibrinogen and analyzed by liquid chromatography/tandem mass spectrometry. Biotinylation of the lysine residue in the platelet-adhesive gamma chain dodecapeptide (GCDP) was quantified by comparison to the internal standard. Approximately 80% of the GCDP peptides were biotinylated when fibrinogen was reacted with NHS-biotin in solution, or adsorbed onto PET. These results are generally consistent with previous antibody binding studies and suggest that other regions of fibrinogen may be crucial in promoting platelet adhesion to materials. The results do not directly address but are consistent with the hypothesis that only activated platelets adhere to adsorbed fibrinogen.