Patternable protein resistant surfaces for multifunctional microfluidic devices via surface hydrophilization of porous polymer monoliths using photografting

Surface-modified macroporous polymer monoliths that resist the adsorption of proteins have been prepared using both single- and two-step photografting of hydrophilic monomers. The adsorption of protein was measured using a fluorescence assay based on bovine serum albumin labeled with fluorescein. Acrylamide, 2-hydroxyethyl methacrylate, vinyl pyrrolidinone, and poly(ethylene glycol) methacrylate (PEGMA) monomers were grafted and evaluated for their ability to prevent protein adsorption. Photografted layers of PEGMA reduced protein adsorption to less than 2% relative to unmodified surfaces. The sequential two-step photografting process consisted in (i) the formation of covalently bound surface photoinitiator sites followed by (ii) surface-localized graft polymerization. Monomer concentration and irradiation time during photografting were found to be the most important parameters for optimization of the two-step process. For simultaneous single-step photografting, the solvent and the presence of photoinitiator were the key variables. Initiator-free single-step photografting was less efficient than the two-step technique, yet resulted in similar prevention of protein adsorption after grafting for an extended period of time. The utility of photografting as a simple, patternable modification technique was demonstrated by first creating a hydrophilic surface within the monolith that was subsequently patterned with a layer of reactive 2-vinyl-4,4-dimethylazlactone polymer chains followed by the immobilization of green fluorescent protein.