Generation of contact-printing based poly(ethylene glycol) gradient surfaces with micrometer-sized steps

A surface with a density gradient of poly(ethylene glycol) (PEG) is an attractive substrate for combinatorial studies of biological phenomena. In this study, the generation of discrete step-wise density gradients of PEG utilizing a contact-printing approach is reported. The step-wise gradient template is achieved by contact-printing n-octadecyltrichlorosilane (OTS) to a glass from a hemispherical elastomeric stamp when the stamp is brought into contact with the substrate, and then step-wisely increasing the contact area as the corresponding contact-printing time for the step decreases. A PEG-silane is then used to backfill the unoccupied spaces of the contact printed OTS gradient to generate the OTS-PEG density gradient. Various characterizations, including water contact angle measurement, lateral force microscopy, and X-ray photoelectron spectroscopy, are conducted and confirmed that the surface coverage of OTS increases (or the coverage of PEG decreases) with the increase of contact-printing time of OTS. The step-wise gradient is illustrated by adsorption of a bovine serum albumin labeled with fluorescein isothiocyanate and subsequent attachment of fibroblasts. The amounts of protein adsorption and cellular attachment increase with the decrease of the surface coverage of PEG.