Differential regulation of osteoblasts by substrate microstructural features.

Microtextured titanium implant surfaces enhance bone formation in vivo and osteoblast phenotypic expression in vitro, but the mechanisms are not understood. To determine the roles of specific microarchitectural features in modulating osteoblast behavior, we used Ti surfaces prepared by electrochemical micromachining as substrates for MG63 osteoblast-like cell culture. Cell response was compared to tissue culture plastic, a sand-blasted with large grit and acid-etched surface with defined mixed microtopography (SLA), polished Ti surfaces, and polished surfaces electrochemically machined through a photoresist pattern to produce cavities with 100, 30 and 10 microm diameters arranged so that the ratio of the microscopic-scale area of the cavities versus the microscopic-scale area of the flat region between the cavities was equal to 1 or 6. Microstructured disks were acid-etched, producing overall sub-micron-scale roughness (Ra=0.7 microm). Cell number, differentiation (alkaline phosphatase; osteocalcin) and local factor levels (TGF-beta1; PGE(2)) varied with microarchitecture. 100 microm cavities favored osteoblast attachment and growth, the sub-micron-scale etch enhanced differentiation and TGF-beta1 production, whereas PGE(2) depended on cavity dimensions but not the sub-micron-scale roughness.

Time-dependent morphology and adhesion of osteoblastic cells on titanium model surfaces featuring scale-resolved topography.

The role of micrometer and submicrometer surface roughness on the interaction of cells with titanium model surfaces of well-defined topography was investigated using human bone-derived cells (MG63 cells). The early phase of interactions was studied using a kinetic morphological analysis of adhesion, spreading and proliferation of the cells. By SEM and double immunofluorescent labeling of vinculin and actin, it was found that the cells responded to nanoscale roughness by a higher cell thickness and a delayed apparition of the focal contacts. A singular behavior was observed on nanoporous oxide surfaces, where the cells were more spread and displayed longer and more numerous filopods. On electrochemically microstructured surfaces with hemispherical cavities, arranged in a hexagonal pattern, the MG63 cells were able to go inside, adhere and proliferate in cavities of 30 or 100 microm in diameter, whereas they did not recognize the 10 microm diameter cavities. Cells adopted a 3D shape when attaching inside the 30 microm diameter cavities. Condensation of actin cytoskeleton correlated with vinculin-positive focal contacts on cavity edges were observed on all microstructured surfaces. Nanotopography on surfaces with 30 microm diameter cavities had little effect on cell morphology compared to flat surfaces with same nanostructure, but cell proliferation exhibited a marked synergistic effect of microscale and nanoscale topography.

XPS and AES analysis of passive films on Fe-25Cr-X (X = Mo, V, Si and Nb) model alloys.

Corrosion resistance of stainless steel is due to the presence of a thin passive film of typically 1-2 nm thickness. The influence of ternary alloying elements on the composition of passive films on Fe-Cr alloys and their pitting corrosion resistance has been investigated. Iron-chromium alloys were analyzed by XPS and AES with model alloys (Fe-25Cr-X with X = at % Mo, Si, V and Nb) formed in sulphate solution in the presence and absence of chloride ions. All ternary alloying elements increase the pitting potential compared to the corresponding binary alloy. Films formed in chloride containing sulphate solution contain both electrolyte anions. Scanning Auger microscopy reveals that for a two phase system such as Fe-25Cr-11Nb, the dendritic phase is enriched with chromium, while essentially all of the niobium is located in the interdendritic eutectic.