Engineering Lubricious, Biopassive Polymer Brushes by Surface-Initiated, Controlled Radical Polymerization

Surface-initiated controlled radical polymerization enables the fabrication of biopassive polymer brushes with interfacial, physicochemical properties that can be independently varied across a single substrate. Poly[(oligoethylene glycol) methacrylate] (POEGMA) brushes were synthesized by surface initiated atom transfer radical polymerization (SI-ATRP), locally varying the exposure of initiator-functionalized surfaces to the polymerization solution to yield POEGMA brush thickness gradients. A combination of variable-angle spectroscopic ellipsometry (VASE) and atomic force microscopy (AFM) demonstrated that brush swelling, grafting density, nano mechanical properties, and biopassivity towards protein adsorption all remained constant within a thickness range between 20 and 90 nm. However, the nanotribological properties of POEGMA brushes, investigated by lateral force microscopy (LFM), were found to vary progressively along the gradient, thinner brushes showing significantly lower friction than thicker and more viscoelastic grafts. The independent variation of lubricity across a biopassive brush gradient shows how SI-ATRP can be used to tailor surfaces destined for applications involving both contact with biological media and exposure to shear stresses, as is the case for tissue-replacement implants and scaffolds for tissue engineering.