Poly(L-lysine)-grafted-poly(ethylene glycol)-based surface-chemical gradients.: Preparation, characterization, and first applications

A simple dipping process has been used to prepare PEGylated surface gradients from the polycationic polymer poly(L-lysine), grafted with poly(ethylene glycol) (PLL-g-PEG), on metal oxide substrates, such as TiO2 and Nb2O5. PLL-g-PEG coverage gradients were prepared during an initial, controlled immersion and characterized with variable angle spectroscopic ellipsometry and x-ray photoelectron spectroscopy. Gradients with a linear change in thickness and coverage were generated by the use of an immersion program based on an exponential function. These single-component gradients were used to study the adsorption of proteins of different sizes and shapes, namely, albumin, immunoglobulin G, and fibrinogen. The authors have shown that the density and size of defects in the PLL-g-PEG adlayer determine the amount of protein that is adsorbed at a certain adlayer thickness. In a second step, single-component gradients of functionalized PLL-g-PEG were backfilled with nonfunctionalized PLL-g-PEG to generate two-component gradients containing functional groups, such as biotin, in a protein-resistant background. Such gradients were combined with a patterning technique to generate individually addressable spots on a gradient surface. The surfaces generated in this way show promise as a useful and versatile biochemical screening tool and could readily be incorporated into a method for studying the behavior of cells on functionalized surfaces. (c) 2006 American Vacuum Society.