SummaryThe differentiation of stem cells can be modulated by physical factors such as the micro-and nano-topography of the extracellular matrix. One important goal in stem cell research is to understand the concept that directs differentiation into a specific cell lineage in the nanoscale environment. Here, we demonstrate that such paths exist by controlling only the micro-and nano-topography of polymer surfaces. Altering the depth (on a nanometric scale) of micro-patterned surface structures allowed increased adhesion of human mesenchymal stem cells (hMSCs) with specific differentiation into osteoblasts, in the absence of osteogenic medium. Small (10 nm) depth patterns promoted cell adhesion without noticeable differentiation, whereas larger depth patterns (100 nm) elicited a collective cell organization, which induced selective differentiation into osteoblast-like cells. This latter response was dictated by stress through focal-adhesion-induced reorganization of F-actin filaments. The results have significant implications for understanding the architectural effects of the in vivo microenvironment and also for the therapeutic use of stem cells.

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Hygrothermal ageing has been investigated on glass fibre reinforced polyethylene terephthalate (PET) composites using complementary techniques and a multiscale approach in order to identify the different steps of the material's degradation. For early ageing times (t ! 6 h), DMTA tests give evidence of the plasticisation of the PET matrix. GPC measurements and acid end group titration show that the chemical degradation step of the composites occurs immediately and that the main degradation mechanism is random chain scission. The changes in morphology resulting from hydrolysis, investigated through DSC and SAXS experiments, reveal a decrease in the long period that may result from the diffusion of oligomers out of the spherulites. The water uptake for long ageing times is attributed to an interfacial debonding which induces an osmotic pressure in this area. Photomechanical measurements highlight the development of microcracks within the aged material that induced an increase in the variation of material volume.