Harnessing cell response to substrate rigidity for tissue engineering applications using novel substrates with patterned elasticity

Cell response to substrate rigidity is an emerging field with implications in processes ranging from embryological development to the pathogenesis of disease states such as cancer or fibrosis, in which changes in tissue mechanical properties may inform cellular behavior. It may also serve as a valuable tool in tissue engineering, where materials must be chosen to best influence desired cell phenotype. This thesis describes novel substrates with patterned mechanical properties and their effects on mesenchymal stem cell (MSC) and macrophage behavior. Though substrate rigidity has previously been shown to guide MSC differentiation in two dimensions on unpatterned substrates, differentiation in response to substrates with patterned mechanical properties and in three dimensions has never been demonstrated. Unfortunately, all systems currently used to study these phenomena are limited in their ability to combine spatial patterning of rigidity with cell encapsulation and 3D culture. By altering polymer molecular weight and concentration and using defined mixing and photolithographic patterning techniques, I have developed poly(ethylene glycol) diacrylate hydrogels with tunable rigidity patterned in distinct patterns and gradients. These hydrogels are highly biocompatible and may be crosslinked and patterned under conditions that allow cellular encapsulation and 3D culture. Using these hydrogels, I have shown spatial control over cellular behavior including patterned MSC differentiation in three dimensions in response to substrate rigidity. The potential to drive differentiation in 3D using the mechanical properties of the substrate is particularly exciting, as it bypasses the difficulties of spatially restricting the growth factors currently used to guide progenitor cell differentiation in vitro. In the future, these substrates may be used to engineer tissues with complex architecture in three dimensions