High aspect ratio silicon nanowires control fibroblast adhesion and cytoskeleton organization

Abstract

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.

Curved microstructures promote osteogenesis of mesenchymal stem cells via the RhoA/ROCK pathway

“…However, our study had some limitations. Previous studies have confirmed that modifications of the actin cytoskeleton occur in response to change in substrate topography . Accordingly, additional in‐depth analyses of the actin polymerization dynamics in this curve‐dependent osteogenic process are needed.…”

High‐Aspect‐Ratio Nanostructured Surfaces as Biological Metamaterials

“…In the absence of clear trends, it is worth highlighting how experimental design should take into account changes in proliferation and viability, as they are often correlated to the measured experimental outcomes. Changes in proliferation may not occur until sufficient culture time has passed . Reduced proliferation rates have been linked to lower transfection efficiencies, hence will be linked to the efficacy of high‐aspect‐ratio nanostructures designed for delivery .…”

“…In a later report, they found that the stiffness of nanowire clusters correlated well between promoting osteogenic‐ or adipogenic‐fates, and that even subtle changes in stiffness resulted in differences in differentiation . Similarly, Andolfi et al concluded that their stochastically patterned sub‐100 nm diameter silicon nanowires were too flexible to facilitate actin‐stress fiber formation . Polymer micropillars, patterned with a gradient of stiffness have been used to guide cell migration (the process of durotaxis) .…”

“…Changes in proliferation may not occur until sufficient culture time has passed. [422] Reduced proliferation rates have been linked to lower transfection efficiencies, [279] hence will be linked to the efficacy of highaspect-ratio nanostructures designed for delivery. [27] Similarly, mechanotransduction, intracellular communication, and migration pathways are stimulated by the proportion of cell-to-cell contacts, [423] so studies on nanotopographies are likely to be influenced by proliferation-linked parameters, such as local cell density.…”

“…[166] Similarly, Andolfi et al concluded that their stochastically patterned sub-100 nm diameter silicon nanowires were too flexible to facilitate actin-stress fiber formation. [422] Polymer micropillars, patterned with a gradient of stiffness have been used to guide cell migration (the process of durotaxis). [425] Much remains unknown about the precise role of high-aspect-ratio nanostructure stiffness as biomechanical cue.…”