A novel surface treatment for porous metallic implants that improves the rate of bony ongrowth.

Rapid implant fixation could prove beneficial in a host of clinical applications from total joint arthroplasty to trauma. We hypothesized that a novel self-assembled monolayer of phosphonate molecules (SAMP) covalently bonded to the oxide surface of titanium alloy would enhance bony integration. Beaded metallic rods were treated with one of three coatings: SAMP, SAMP + RGD peptide, or hydroxyapatite. Rods were inserted retrogradely into both distal femurs of 60 rabbits. Fifteen rabbits were sacrificed at 2, 4, 8, and 16 weeks. At each time, seven specimens for mechanical pull-out testing and three for histomorphometric analysis were available for each coating. At four weeks, both SAMP groups had significantly higher failure loads when compared to hydroxyapatite (p < 0.01). No significant differences were found among groups at other times, though the SAMP-alone group remained stronger at 16 weeks. Histology showed abundant new bone formation around all the three groups, though more enhanced formation was apparent in the two SAMP groups. With this novel treatment, with or without RGD, the failure load of implants doubled in half the time as compared with hydroxyapatite. Where early implant fixation is important, the SAMP treatment provides a simple, cost-effective enhancement to bony integration of orthopaedic implants.

Self-assembled monolayers of alpha,omega-diphosphonic acids on Ti enable complete or spatially controlled surface derivatization.

Alpha,omega-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.