A nanoporous titanium surface promotes the maturation of focal adhesions and the formation of filopodia with distinctive nanoscale protrusions by osteogenic cells

Publication date: Available online 17 July 2017
Source:Acta Biomaterialia
Author(s): Dainelys Guadarrama Bello, Aurélien Fouillen, Antonella Badia, Antonio Nanci
While topography is a key determinant of the cellular response to biomaterials the mechanisms implicated in the cell-surface interactions are complex and still not fully elucidated. In this context, we have examined the effect of nanoscale topography on the formation of filopodia, focal adhesions, and on gene expression of proteins associated with cell adhesion and sensing. Commercially pure titanium discs were treated for oxidative nanopatterning with a solution of H2SO4/H2O2 50:50 (v/v). Scanning electron microscopy and atomic force microscopy characterizations showed that this facile chemical treatment efficiently creates a unique nanoporous surface with a root-mean-square roughness of 11.5 nm and pore diameter of 20 ± 5 nm. Osteogenic cells were cultured on polished (control) and nanotextured discs for periods of 6, 24, and 72 h. Immunofluorescence analysis revealed an increase in adhesion formation per cell area and in the focal adhesion length, and maturity on the nanoporous surface. Gene expression for various focal adhesion markers, including paxillin and talin, and different integrins (e.g. α1, β1, and α5) was also significantly increased. Interestingly, scanning electron microscopy imaging revealed the presence of more filopodia on cells grown on the nanoporous surface. These cell extensions displayed abundant and distinctive nanoscale lateral protrusions in the range of 10-15 nm diameter that molded the nanopore walls. Together the increase in focal adhesions, the abundance of filopodia and associated protrusions could contribute to strengthening the adhesive interaction of cells with the surface and thereby alter the nanoscale biomechanical relationships that trigger cellular cascades regulating cell behavior.Statement of SignificanceOxidative patterning was applied to nanosculpture a unique three-dimensional network of nanopores on titanium surfaces. Our study illustrates how such facile treatment can be advantageously used to modulate cellular behavior. The nanoscale lateral protrusions on filopodia elicited by this surface are novel adhesive structures illustrating their membrane fluidity. Altogether, the increase in focal adhesions length and maturity and infilopodiawith distinctive lateral protrusions could substantially increase contact area and the adhesion strength of cells, thereby promoting the activation of cellular signaling cascadesthat may explain the positive osteogenic outcomes previously achieved with this surface. Such physicochemical cueing offers an advantageous alternative to the use of bioactive agents for guiding tissue repair/regeneration around implantable metals, thereby improving their tissue integration.

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