Cell-based therapies require removal of cells from their optimal in vivotissue context and propagation in vitroto attain suitable number. However, bereft of their optimal tissue niche, cells lose their phenotype and with it their function and therapeutic potential. Biophysical signals, such as surface topography and substrate stiffness, and biochemical signals, such as collagen I, have been shown to maintain permanently differentiated cell phenotype and to precisely regulate stem cell lineage commitment (1, 2). Herein, we developed and characterised substrates of variable rigidity and constant nanotopographical features to offer control over cellular functions during ex vivoexpansion.

PDMS substrates with varying ratios of monomer to curing agent (0:1, 1:1, 5:1) were fabricated based on established protocols. Grooved substrates were created using a silinated wafer with groove dimensions of 2µm × 2µm × 2µm; planar control groups were created using flat glass. The aforementioned PDMS solutions were poured onto the wafer/glass, cured at 200 ºC and treated with oxygen plasma. Substrates were then investigated with/without collagen I coating. (0.1, 0.5, and 1 mg/ml). Atomic force microscopy (AFM) and optical profilometry were used to assess the topographical features of the substrates. Dynamic mechanical analysis (DMA) was used to determine the mechanical properties of the substrates. The simultaneous effect of surface topography / substrate rigidity on cell phenotype and function was assessed using human permanently differentiated cells (dermal fibroblasts, tenocytes) and stem cells (human bone marrow stem cells) and various morphometric and gene / protein assays.

PDMS substrates of varying stiffness (1000 kPa, 130 kPa, 50 kPa) can be made by varying the Sylgard ratio, while maintaining topographical features. Human adult dermal fibroblasts, tenocytes, and tenocytes attach, align, elongate and deposit aligned extracellular matrix on the grooved PDMS substrate surface of all 3 stiffnesses.

Preliminary in vitrodata indicate that surface topography and substrate stiffness play crucial role in maintaining cell phenotype and the prevention of phenotypic drift in vitro.