Regulating myoblast phenotype through biomimetically designed hydrogels

The loss or failure of human tissues or organs is a frequent and costly problem in terms of life and economic loss. The limitations of currently available therapies have spurred the creation of a research field entitled Tissue Engineering. Development of advanced biomaterials will play a key role in the success of tissue engineering. This thesis research focuses on designing material scaffolds presenting bioactive molecules with controllable degradation, and understanding how the signaling molecules regulate cellular function.; In the first series of experiments, alginate material platforms were developed that incorporated RGD peptides as adhesion ligands while varying the ligand density, ligand affinity, and nanoscale distribution. Increasing ligand density or binding affinity led to a similar enhancement in proliferation of C2C12 cells and human primary myoblasts. The nanoscale distribution of clustered RGD influenced C2C12 cells and human primary myoblasts but proliferation was effected in an opposing manner. To understand how the RGD presentations modulate cellular function, rheological measurements and a FRET technique were further utilized to quantify the extent of receptor-ligand interactions. Higher relative numbers of bonds formed when RGD density and affinity were increased, as assessed by both approaches, and this finding correlated with cell growth rates. This suggested that varying peptide density and affinity may regulate cellular function by altering the number of bonds formed. However, the influence of nanoscale distribution could not be explained by the number of bonds.; Secondly, the hypothesis that alginate gel degradation could regulate the function of myoblasts encapsulated in 3-D microenvironment was tested. Development of degradable alginate gels with tunable rates was established by a combination of partial oxidation and bimodal molecular weight distribution. Myoblasts were encapsulated in gels varying in degradation rate. C2C12 cells in degradable gels exhibited lower proliferation, due to exiting the cell cycle to differentiate, as compared to those in non-degradable gels. Mouse primary myoblasts illustrated significantly higher proliferation in degradable gels, while cells in non-degradable gels showed limited proliferation. Subsequent reduction of mechanical properties also influenced myoblast adhesion, proliferation, and differentiation in a 2-D cell culture model. Cells on stiffer gels illustrated higher spreading, proliferation, and differentiation.; Altogether, the material developments in this study elucidate how one can acquire specific bioactivity from biomaterials to control desirable cellular functions and to understand these processes. The degradability of scaffolding materials might also be crucial for long-term success of tissue engineering. The principles delineated in these studies may be useful to tailor smart biomaterials that can be applied to many other polymeric systems and tissue types.