(9c) Geometric Control of Stem Cell Motility in 3D Synthetic Scaffolds

Currently, a large amount of effort is being put forth on combining marrow progenitor cells, or mesenchymal stem cells (MSCs) with 3D scaffolds to direct bone regeneration in critical size bone defects. Design of 3D scaffolds that can facilitate proper survival, proliferation, and differentiation of progenitor cells is a challenge for clinical applications involving large connective tissue defects, with cell migration within scaffolds a critical process governing tissue integration. Here, we examine effects of scaffold pore diameter, in concert with matrix stiffness and adhesivity, as independently tunable parameters, in governing marrow-derived stem cell motility. We adopted an ?inverse opal? processing technique to create synthetic scaffolds by crosslinking poly(ethylene glycol) at different densities (controlling matrix elasticity) and small doses of a heterobifunctional monomer (controlling matrix adhesivity) around templating beads of different radii. As pore diameter was varied from 7 to 17µm (i.e., from significantly smaller than the spherical cell diameter to approximately cell diameter), pores had a profound effect on migration ? including the degree to which motility was sensitive to changes in matrix stiffness and adhesivity. Surprisingly, the highest probability for substantive cell movement through pores was observed for an intermediate pore diameter rather than the largest pore diameter tested. The relationships between migration speed, displacement, and total path length were found to be strongly dependent on pore size, most likely resulting from the non-intuitive convolution of pore diameter and void chamber diameter yielding different geometric environments experienced by the cells within. Finally, we are currently using a simple, yet elegant, anomalous diffusion model to describe the provocative relationship between the scaffold biophysical cues and cell speed and displacement. Combined with existing data on MSC proliferation, survival, and differentiation in 3D scaffolds by our lab and others, this information on MSC motility could be very powerful for future intelligent scaffold design for MSC-directed bone regeneration in vivo.