Self-assembled Monolayers of α,ω-Diphosphonic Acids on Ti Enable Complete or Spatially Controlled Surface Derivatization

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Abstract
α,ω-Diphosphonic acids self-assemble on the native oxide surfaces of Ti or Ti-6Al-4V. Heating gives strongly bonded phosphonate monolayers. Infrared and X-ray spectroscopic and water contact angle data show that the films are bonded to the surface by one phosphonate unit; the other remains a phosphonic acid. Surface loadings were measured by quartz crystal microbalance procedures. Mechanical shear strengths for the films were also measured; these do not correlate simply with surface loadings. Films formed from 1,12-diphosphonododecane were treated with zirconium tetra(tert-butoxide) to give surface Zr complex species; derivatives of these surface complexes are stable to hydrolysis under physiological conditions and are mechanically strong. The complexation reaction can be accomplished over the entire surface; alternatively, dropwise application of the alkoxide to the surface enables spatial control of deposition. The cell attractive peptide derivative RGDC can be bound to these surface Zr alkoxide complexes through (maleimido)alkylcarboxylate intermediates. Surfaces modified with RGDC were shown to be effective for osteoblast binding and proliferation.