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Cell-cell and cell-matrix interactions are essential to the survival and proliferation of most cells, and are responsible for triggering a wide range of biochemical pathways. More recently, the biomechanical role of those interactions was highlighted, showing, for instance, that adhesion forces are essential for cytoskeleton organization. Silicon nanowires (Si NWs) with their small size, high aspect ratio and anisotropic mechanical response represent a useful model to investigate the forces involved in the adhesion processes and their role in cellular development. In this work we explored and quantified, by single cell force spectroscopy (SCFS), the interaction of mouse embryonic fibroblasts with a flexible forest of Si NWs. We observed that the cell adhesion forces are comparable to those found on collagen and bare glass coverslip, analogously the membrane tether extraction forces are similar to that on collagen but stronger than that on bare flat glass. Cell survival did not depend significantly on the substrate, although a reduced proliferation after 36 h was observed. On the contrary both cell morphology and cytoskeleton organization revealed striking differences. The cell morphology on Si-NW was characterized by a large number of filopodia and a significant decrease of the cell mobility. The cytoskeleton organization was characterized by the absence of actin fibers, which were instead dominant on collagen and flat glass support. Such findings suggest that the mechanical properties of disordered Si NWs, and in particular their strong asymmetry, play a major role in the adhesion, morphology and cytoskeleton organization processes. Indeed, while adhesion measurements by SCFS provide out-of-plane forces values consistent with those measured on conventional substrates, weaker in-plane forces hinder proper cytoskeleton organization and migration processes.

Understanding nanostructured materials - cell interactions is essential for the development of innovative substrates for cell culture, differentiation and precise electrical stimulation. In this framework, silicon nanowires (SiNWs), characterized by high aspect ratio and a broad range of mechanical, optical and electrical properties, are interesting nanomaterials for innovative cellular engineering. We investigated and quantified, using single cell force spectroscopy (SCFS), the interaction of murine embryonic fibroblast with two mechanically different SiNW substrates, and two reference substrates, collagen gel which is generally used for cell culture, and flat glass which has the same chemical reactivity of SiNWs. We observed comparable adhesion values on SiNWs substrates and on gel substrate, while flat glass generate a 10-times weaker interaction. A closer analysis of the adhesion curves revealed significant differences between soft and hard SiNW, suggesting that a different cell membrane organization is developed depending on the mechanical and geometrical properties of the substrate. In conclusion SiNW substrates are compatible with cell engineering and thanks to their high range of mechanical and geometric properties, a fine tuning of cellular response can be achieved.Figure 1: representative SCFS curves for rigid NWs, flexible NWs and collagen-coated coverslips.View Large Image | View Hi-Res Image | Download PowerPoint Slide