Cell architecture–cell function dependencies on titanium arrays with regular geometry

Atomic force microscopy studies of the influence of convex and concave nanostructures on the adsorption of fibronectin

Atomic force microscopy (AFM)-based force spectroscopy was used to analyze the adsorption of bovine plasma fibronectin on periodically grooved nanostructures (groove/summit width: 90 nm; depth: 120 nm). We present a simple procedure that allowed us to directly compare the local protein density and conformation for the convex summits, the concave grooves and planar reference regions of the substrate. At a bulk fibronectin concentration of 5 μg/ml, the amount of adsorbed protein per surface area was significantly higher in all regions of the nanostructure than on the planar reference, and fibronectin tended to adsorb preferentially in the concave grooves. The increased surface concentration resulted in an additional stabilization of the molecules by protein-protein interactions and a lower degree of denaturized fibronectin in the nanostructured regions. The stabilization was less pronounced in concave regions, indicating that the increased contact area in the grooves counteracted the stabilization by increased protein-substrate interactions and must be compensated for by additional protein-protein interactions. Less favorable sites were occupied at higher bulk fibronectin concentrations (25 μg/ml, 100 μg/ml), and a high degree of native folded fibronectin was observed in both the nanostructured and planar regions. Our results demonstrate that the amount of adsorbed fibronectin per surface area can be increased if a substrate is provided with a topographic nanostructure. Our results also show that the local conformational state of fibronectin is determined by the locally different interplay of protein-protein and protein-substrate interactions.

Existence of a typical threshold in the response of human mesenchymal stem cells to a peak and valley topography

Our objective in this study was to determine whether a threshold in sensitivity of human mesenchymal stem cells (hMSC) to isotropic roughness exists. Using electrical discharge machining a very wide range of roughnesses (1.2μm<R(a)<21μm) with a perfectly isotropic, fractal and self-affine topography can be produced on titanium, with a range of roughness overlapping the hMSC length dimensions. The curve of the number of adherent hMSC after 2days culture as a function of roughness showed a U-shape with a minimum number of attached cells for a roughness amplitude R(a)=4.5μm and a distance between surface features (width of peaks and valleys) S(m)=110μm. The maximum cell number was observed at the lowest and highest roughnesses. Due to this very wide range of roughness it was possible to demonstrate that the response of hMSC to roughness varies with the dimensions of the surface features relative to the cell size. Above or below their own size hMSC essentially adhere to the nano and submicron features. When the surface displays features about the same size as hMSC the curvature of these surface features will decrease the number of attached cells by a factor of two. A modelling approach is proposed to help the interpretation of these results. It is hypothesized that this minimal adhesion is a consequence of an unfavourable stress imposed on the cell cytoskeleton.

Adhesion of osteoblasts to a nanorough titanium implant surface

This work considers the adhesion of cells to a nanorough titanium implant surface with sharp edges. The basic assumption was that the attraction between the negatively charged titanium surface and a negatively charged osteoblast is mediated by charged proteins with a distinctive quadrupolar internal charge distribution. Similarly, cation-mediated attraction between fibronectin molecules and the titanium surface is expected to be more efficient for a high surface charge density, resulting in facilitated integrin mediated osteoblast adhesion. We suggest that osteoblasts are most strongly bound along the sharp convex edges or spikes of nanorough titanium surfaces where the magnitude of the negative surface charge density is the highest. It is therefore plausible that nanorough regions of titanium surfaces with sharp edges and spikes promote the adhesion of osteoblasts.

Restoration of motor control and dopaminergic activity in rats with unilateral 6-hydroxy-dopamine lesions - Retracted

This article was retracted on 16/01/2014