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AN IN VITRO AND IN VIVO STUDY OF THE EFFECT OF A PHOTOCHEMICALLY ETCHED TITANIUM SURFACE

The Centre for Biomedical Engineering, RNOHT, Brockley Hill, Stanmore, Middlesex, HA7 4LP

Introduction: The use of uncemented arthroplasty in joint replacement surgery requires osseointegration of the prosthesis to maximise function and longevity. It has been demonstrated that osteoblast-like cells will preferentially proliferate, differentiate and produce mineralised matrix in pits and grooves on non-biological surfaces, of similar dimensions to those of Howslip’s lacunae produced by osteoclasts in vitro. The hypotheses of this study were that a photochemically etched titanium alloy surface would 1) induce proliferation and differentiation in osteoblast-like cells; 2) induce osteoblastic differentiation of human mesenchymal stem cells and 3) induce greater bone to implant contact in a caprine model.

Methods: Three microgrooved titanium alloy surfaces (fine, medium & coarse) were created by photochemical etching, with dimensions of 200 to 515 microns. Human Mesenchymal stem cells (MSC) and Human Osteosarcoma (HOS) cells (TE-85) were seeded onto these surfaces and cultured in standard media; in the case of MSC, with and without the addition of osteogenic supplements. At intervals of time each surface and cell type were assessed for proliferation by Alamar blue assay and osteoblastic differentiation by Alkaline Phosphatase expression. A polished titanium surface was used as a control. A plate of each surface dimension was placed into a femoral condyle of ten adult male goats. The animals were euthanased at 6 and 12 weeks post-implantation. The specimens were histologically processed and examined under light and backscattered electron microscopy to establish the percentage of bone to implant contact and the presence of new bone within the grooves.

Results: In vitro, all cells showed an increase in proliferation with time, the greatest occurring on the coarse surface. Alkaline phosphatase expression showed a rise with time on all surfaces, the greatest being on the coarse surface seeded with HOS cells (p<0.05). MSC could not be induced to differentiate to an osteogenic lineage by these surface textures alone. On addition of osteogenic supplements their results followed the trends of HOS cells. In vivo, histomorphometric analysis showed significantly greater bone implant contact on the coarse surface at both 6 and 12 weeks (p<0.05). In a number of cases there were signs of osteogenesis occurring deep within the pits and grooves.

Discussion: This study confirms that a photochemically etched surface topography mimicking that created by osteoclasts will increase the proliferation and differentiation of osteoblastic cells in vitro. The rate of differentiation of these cells increased significantly in relation to the size of the grooves. When implanted in vivo these same surfaces were shown to support osseointegration. This surface has the potential to improve the function of uncemented arthroplasties in the future.

Correspondence should be addressed to Mr Carlos Wigderowitz, Honorary Secretary BORS, University Dept of Orthopaedic & Trauma Surgery, Ninewells Hospital & Medical School, Dundee DD1 9SY.