Surface Modification of SU-8 for Enhanced Biofunctionality and Nonfouling Properties

Abstract

SU-8 is a chemically amplified, epoxy-based negative photoresist typically used for producing ultrathick resist layers during device manufacturing in the semiconductor industry. As a simple resist, SU-8 has garnered attention as a possible material for a variety of biomedical applications, including tissue engineering, drug delivery, as well as cell-based screening and sensing. However, as a hydrophobic material, the use of SU-8 is limited due to a high degree of nonspecific adsorption of biomolecules, as well as limited cell attachment. In this work, surface chemistry is utilized to modify the SU-8 surface by covalently attaching poly(ethylene glycol) (PEG) to increase biofunctionality and improve its nonfouling properties. Different molecular weights and concentrations of PEG were used to form films of various grafting densities on SU-8 surfaces. X-ray photoelectron spectroscopy (XPS) was used to verify the presence of PEG moieties on the SU-8 surface. High-resolution C1s spectra show that, with an increase in concentration and immobilization time, the grafting density of PEG also increases. Further, a standard overlayer model was used to calculate the thickness of the PEG films formed. The effect of PEG-modified SU-8 was examined in terms of protein adsorption on the surface and fibroblast-surface interactions.