A biomimetic engineering strategy was applied to tissue generation through the creation of precisely controlled, cell-instructive synthetic hydrogels. Thermoresponsive sol-gels were synthesized from high molecular weight, comb-like copolymers of Nisopropyl acrylamide (NIPAAm) and methoxy poly(ethylene glycol) methacrylate (mPEGMA), P(NIPAAm-co-mPEGMA), with varying PEG graft density and molecular weight, as the structural component of an associative hydrogel system. The swelling and mechanical characteristics of these materials were characterized in order to engineer hydrogels with desired handling properties and targeted elastic moduli. Particular formulations with physiologically useful gelation temperatures were identified that retained their swelling ratios upon phase transition. They were used to encapsulate cells and could be injected through a syringe and needle. In order to impart specific bioactivity, peptide and protein conjugates of hyaluronic acid were synthesized and incorporated to create biomimetic hydrogels. A novel characterization method was developed by combining size-exclusion chromatography multi-angle laser light scattering with refractive index detection and ultra-violet spectroscopy (SEC-MALS-RI-UV) to determine conjugate molecular weight, degree of substitution, valency, and to optimize the chemical conjugation reaction.

Combinatorial admixtures of particular concentrations and combinations of conjugates were created in the solution state to produce hydrogels with controlled ligand density. A computational study of temporal gene expression profiles during in vivo tissue regeneration was performed in order to identify potential targets for biomimetic elements, including enzymatically degradable linkages. The biomimetic hydrogels developed were applied to rat mesenchymal stem cell differentiation, human embryonic stem cell selfrenewal, and mammary epithelial cell culture. The materials were found to preserve cell viability and induce specific cellular differentiation and behavior. In this way, they also served as three-dimensional organotypic cell culture models.