Spatially Controlled Multi-Phenotypic Differentiation of Stem Cells in 3D Via an Engineered Mechanical Gradient

The goal of this research was to engineer a scaffold composed of a mechanical gradient and understand the effects of dynamic stimulation on the morphogenesis of the interfacial tissue via spatially controlled differentiation of a single stem cell source. Osteoarthritis is a degenerative joint disease affecting articular cartilage and the underlying subchondral bone resulting in severe pain and disability of the joints. While current clinical treatments provide limited efficacy in long-term success, tissue engineering strategies prove to be a viable option to address regeneration of the osteochondral gradient interface. To address this challenge spatial patterning of mechanical factors are essential for the development of a gradient tissue structure in three dimensions. Here, the overarching goal of this work was to examine (1) the preferential differentiation capacity of MSCs towards multi-phenotypic lineages when subjected to variations in compressive strain, (2) the control of micro- and macro-scale scaffold mechanics through utilizing a core-shell microfiber electrospinning technique, and finally (3) the engineering of a dynamic mechanical gradient that can spatially control the local strain that MSCs will sense and differentiate into multi-phenotypic lineages. My findings demonstrate that MSCs differentiate in a magnitude-dependent and phenotype-specific manner in response to different magnitudes of dynamic compressive strain suggesting that MSCs are mechano-responsive and their multi-phenotypic differentiation can be controlled by varying the strain regimens. Furthermore, it was demonstrated that the mechanical properties of core-shell electrospun fibers can be modulated by controlling the composition and the dimension of core, decoupled from the cell-interfacing surface chemistry. More importantly, it was shown that mechanical properties of such fibers/scaffolds at the micro- and macroscale can be independently regulated by modulating micro- and macro-structure. Finally, spatial control of the mechanical properties of individual core-shell fibers in a monolithic scaffold was able to modulate the preferential multi-phenotypic differentiation of MSCs when subjected to dynamic compressive strain. Thus, these findings provide an additional avenue for directing stem cell differentiation in lieu of biochemical cues commonly used for osteochondral tissue regeneration. Addressing the influence of mechanical stimulation on spatially controlled multi-phenotypic MSC differentiation is the basis behind the work presented in the following dissertation