Analysis of Bone Cell Responses to Titanium Surface Roughness

Previous studies have suggested that titanium implant surfaces of differing roughness have marked effects on osseointegration in vivo and on bone cells in vitro. However, the molecular mechanisms underlying the surface-induced changes in bone cell function are poorly understood. Objectives: To examine the effects of different titanium surfaces on bone cell morphology, attachment, proliferation and, most importantly, gene expression in vitro. Methods: Primary cultures of alveolar bone cells were incubated for 3 and 24 h after attachment to a smooth polished (SMO) titanium surface and two rough surfaces - sandblasted and acid etched (SLA) and plasma-sprayed (TPS) titanium. SEM (scanning electron microscopy) was used to investigate morphology, 3[H]-thymidine labelling to measure attachment and proliferation and Atlas gene arrays to determine the relative expression of approximately 1150 genes. X-ray photoelectron spectrometry was used to characterize the surface chemistry. Results: Surfaces were found to vary in surface roughness, but not surface chemistry. Despite high attachment rates to all surfaces, cells on SLA exhibited initially poor spreading and growth rate relative to SMO, while cells on TPS were well spread and had a significantly higher growth rate than on SMO. Gene profiling showed that there were many more differences in gene expression on TPS than on SLA, compared with that on the smooth SMO surface. One of the genes most strongly affected by surface roughness was the axl receptor tyrosine kinase, involved in signal transduction. Conclusion: This study has shown that surface roughness has a number of effects on bone cells, including altered morphology, attachment, proliferation and fundamental changes in gene expression. Supported by grants from the ITI Foundation, Switzerland and the CRDC, UK.