Dissolution and mineralization of sintered and thermally sprayed hydroxy-fluoroapatites

Sol-Gel Synthesis and Characterization of Lanthanide-Substituted Nanostructured Calcium Hydroxyapatite

In this study, nanostructured Ce- and Sm-substituted Ca10(PO4)6(OH)2 samples have been synthesized using an aqueous sol-gel chemistry route. For the characterization of obtained specimens, the XRD, SEM, UV-visible reflection and IR spectroscopy and luminescence measurements were recorded. It was shown that phase purity of the end products highly depends on the amount of lanthanide element. The reflectance of lanthanide-substituted calcium hydroxyapatite samples is wavelength independent in the wavelength range of 450-800 nm and equal almost 100%. The cerium-substituted samples show a significant decrease of transmission at ~300 nm. The characteristic samarium absorption line (~430 nm) is evident in the UV-vis reflection spectra of samarium-substituted hydroxyapatites.

Osteoclast resorption of thermal spray hydoxyapatite coatings is influenced by surface topography

Coating characteristics such as composition, crystallite features and topography collectively impact the cell response. The influence from splats has not yet been assessed for hydroxyapatite (HAp) thermal spray coatings. The objective of this work is to (a) survey the topography on commercial implants, (b) ascertain topography formation from single splats, and (c) determine the osteoclast resorption pattern on a topographically refined coating compared to dentine. Coatings on dental implants, an orthopedic screw, a femoral stem and a knee implant were studied for reference. The effects of substrate pre-heat, roughness, spray distance and particle size on the coating roughness and topography were studied. Human-derived osteoclasts were placed on a coating with refined topography and compared to dentine, a polished coating and polished sintered HAp. A pre-heat of at least 200°C on titanium was required to form rounded splats. The greatest influence on coating roughness and topography arose from particle size. A 2-fold increase in the mean particle size from 30 to 72 μm produced a significant difference (P<0.001) in roughness from 4.8 and 9.7 μm. A model is shown to illustrate topography formation, nanostructure evolution on single splats, and the topography as seen in commercial implants. Osteoclasts showed a clear preference for activity on coatings with refined topography. A one-way ANOVA test revealed a significantly greater pit depth (P=0.022) for dentine (14 μm) compared to the as-sprayed and polished coating (5 μm). Coatings with topography display a similar number of resorption pits with dentine, but a 10-fold greater number than polished coatings, emphasizing the importance of flattened droplet topography on implant surfaces.

The effect of novel fluorapatite surfaces on osteoblast-like cell adhesion, growth, and mineralization

There is increasing demand for biomedical implants to correct skeletal defects caused by trauma, disease, or genetic disorder. In this study, the MG-63 cells were grown on metals coated with ordered and disordered fluorapatite (FA) crystal surfaces to study the biocompatibility, initial cellular response, and the underlying mechanisms during this process. The long-term growth and mineralization of the cells were also investigated. After 3 days, the cell numbers on etched metal surface are significantly higher than those on the ordered and disordered FA surfaces, but the initial adherence of a greater number of cells did not lead to earlier mineral formation at the cell-implant interface. Of the 84 cell adhesion and matrix-focused pathway genes, an up- or down-regulation of a total of 15 genes such as integrin molecules, integrin alpha M and integrin alpha 7 and 8 was noted, suggesting a modulating effect on these adhesion molecules by the ordered FA surface compared with the disordered. Osteocalcin expression and the mineral nodule formation are most evident on the FA surfaces after osteogenic induction (OI) for 7 weeks. The binding of the ordered FA surfaces to the metal, with and without OI, was significantly higher than that of the disordered FA surfaces with OI. Most significantly, even without the OI supplement, the MG-63 cells grown on FA crystal surfaces start to differentiate and mineralize, suggesting that the FA crystal could be a simple and bioactive implant coating material.