Bioactivation of metal oxide surfaces. 1. Surface characterization and cell response

Silicon and titanium oxide surfaces (SiO2/Si and TiO2/Ti) were covalently m odified with bioactive molecules (e.g., peptides) in a simple three-step pr ocedure. Bioactive surfaces were synthesized by first immobilizing N-(2-ami noethyl)-3-aminopropyl-trimethoxysilane (EDS) to either polished quartz dis ks, polished silicon wafers, or sputter-deposited titanium films. Subsequen tly, a maleimide-activated surface amenable to tethering molecules with a f ree thiol (e.g., cysteine) was created by coupling sulfosuccinimidyl 4-(N-m aleimidomethyl) cyclohexane-1-carboxylate (sulfo-SMCC) to the terminal amin e on EDS. In particular, Cys-Gly-Gly-Asn-Gly-Glu-Pro-Arg-Gly-Asp-Thr-Tyr-Ar g-Ala-Tyr (-RGD-) and Cys-Gly-Gly-Phe-His-Arg-Arg-Ile-Lys-Ala (-FHRRIKA-) p eptides with terminal cysteine residues were immobilized on maleimide-activ ated oxides. X-ray photoelectron spectroscopy (XPS) and spectroscopic ellip sometry were used to assess the chemistry, thickness, and surface density o f the grafted layers. EDS deposited from anhydrous methanol produced reacti on site-limited monolayers (similar to 0.28 nmol/cm(2)). Coupling of the su lfo-SMCC crosslinker (similar to 0.03 nmol/cm(2)) and peptides (similar to 0.004 nmol/cm(2)) resulted in an order of magnitude drop in surface density for each stage of the reaction scheme. Peptide-modified surfaces with dens ities varying over 2 orders (0.01-4 pmol/cm(2)) of magnitude were synthesiz ed to study the effect of the peptides on mammalian cell function. The adhe sion and spreading of cells derived from mammalian bone, in contact with th e peptide-modified surfaces, was dependent on the specific peptide sequence grafted in a concentration-dependent manner. The grafting scheme presented has generality in coupling thiol-specific molecules to silicon or titanium surfaces.