Enzyme-Activated RGD Ligands on Functionalized Poly(ethylene glycol) Monolayers: Surface Analysis and Cellular Response

We report on the design, stepwise synthesis, and surface analysis of enzyme-responsive surfaces that present cell adhesive RGD sequences on-demand, that is, by enzymatic hydrolysis of inactive RGD containing precursors that carry cleavable steric blocking groups. These surfaces, incorporating poly(ethylene glycol) (PEG) monolayers coupled via epoxy silanes to glass, are functionalized via stepwise solid phase synthesis, presenting a versatile and straightforward approach to preparation of peptide surfaces. Successive amino acid coupling and deprotection steps using fluorenylmethoxycarbonyl (Fmoc) chemistry are verified using surface analysis with time-of-flight secondary-ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS). Exposure of surfaces to elastase results in activation of cell binding ligands as demonstrated using osteoblast cells. These surfaces may have applications in spatiotemporally controlled attachment of cells as relevant for three-dimensional tissue engineering scaffolds and cell-based biosensors.