Ultrathin poly(ethylene glycol) films for silicon-based microdevices

Development of poly(ethylene glycol) (PEG) films that are ultrathin, uniform, conformal and stable in vivo-like environments is extremely desirable for biocompatible silicon-based microdevices. To this end, we have characterized PEG thin films, created by chemical coupling, at different PEG concentrations for various immobilization times, using the techniques of X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), ellipsometry and contact angle measurement. A continuous increase in film thickness and contact angle was measured with increase in PEG concentration and immobilization time (30–120 min). The surface roughness had a minimum value for 1.0% PEG (immobilization time=60 min). The biocompatibility of ultrathin PEG films was also tested using fluorescein isothiocyanate (FITC)-labeled bovine serum albumin (BSA). Results indicated PEG-modified silicon surfaces to be more resistant to protein adsorption. The stability of ultrathin PEG films over time in dry and aqueous in vivo-like environments was also examined. While ultrathin PEG films were extremely stable in dry conditions, their stability was compromised in aqueous in vivo-like environments (PBS, 37 °C, pH 7.4, 5% CO2). Nevertheless, ultrathin PEG films retained their efficacy to control protein fouling for the period investigated.