Cell-based therapies have exciting clinical promise. In particular, bone marrow derived mesenchymal stem cells (MSC) can be easily isolated and have the potential to repair a variety of tissues. However, key challenges, including substantial loss of viability, impair cell therapy efforts. Biomaterials may augment cell therapies by providing a substrate that improves cell survival, while simultaneously locally manipulating cell fate. The hypothesis driving this work is that physical cues from these materials, including elasticity and the formation and distribution of micron-scale pores, can be manipulated to influence MSC.
MSC responses to integrin-binding peptides were first studied with cell-encapsulating, RGD-modified alginate hydrogels. In these studies, a high density of RGD peptides, in concert with soluble factors, promoted osteogenic (bone) differentiation in vitro. Next, the potential that MSC fate can be controlled by manipulating the elasticity of 3D hydrogels was studied. In these studies, osteogenesis was predominant in materials with elastic modulus near 20 kPa. However, cell shape, previously identified as a putative "mechanosensor" from 2D studies, did not correlate with fate. It was hypothesized instead that nanoscale changes in the cell-matrix interface might underlie these fate changes. Using techniques based on Förster Resonance Energy Transfer (FRET) or newly developed biochemical methods, it was discovered that matrix rigidity controlled cells' ability to bind RGD peptides grafted to the hydrogel, and the range of elasticity which was optimal for osteogenesis was also optimal for αV and α5-integrin-RGD bond formation.
Finally, a means to create macroscale pores within hydrogel materials, independent of the elasticity of the hydrogel surrounding pores, was developed. The composite materials formed using this technique were injectable, and pore formation appeared to be relatively independent of the hydrogel material surrounding micro-beads which eventually degraded in situ to form pores. Porogen degradation could be tuned to manipulate the kinetics of MSC deployment from these materials, and cell fate could further be altered by modulating hydrogel elasticity and RGD density.
These studies, and the techniques developed and refined to perform them, should improve our basic understanding of design parameters for fabricating materials to influence cell fate.
|Advisor:||Mooney, David J.|
|School Location:||United States -- Massachusetts|
|Source:||DAI-B 72/01, Dissertation Abstracts International|
|Subjects:||Cellular biology, Biomedical engineering, Biophysics|
|Keywords:||Adhesion ligand bonds, Cell cultures, Integrin, Mechanosensors, Mesenchymal stem cells|
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