Tailoring Cell Behavior with Functional Biomaterials Composed of Natural Building Blocks

This dissertation describes the synthesis and applications of functional polymeric biomaterials from natural monomeric building blocks. In Chapter 1, background information on the field of tissue-mimic extracellular matrices (ECMs) will be introduced, including the various criteria important in the design of a functional synthetic ECM. For the rest of my dissertation chapters, I will focus on understanding the fundamental in cell-substrate interactions in 2D and 3D. First in chapter 2, the synthesis and characterization of a novel extracellular matrix will be introduced. The polymers were synthesized from natural building blocks such as saccharides and amino acids, namely, galactaric acid and lysine on the backbone, with tyrosine grafted onto the side chain as a handle for enzyme-catalyzed hydrogelation. Mesenchymal stem cells (MSCs) were first utilized for optimization of the material in 2D. Later, two cells lines, PC-12 neuronal cells and fibroblasts, with very different native cellular environment were evaluated on these matrices. As a demonstration of the versatility of the system, the mechanical properties of the gels can be independently controlled without changing the polymer chemical composition. Using an identical copolymer solution, by simply allowing different lengths of cross-linking time, a series of hydrogels was obtained with different mechanical moduli at constant chemical structure. Depending on the substrate mechanical modulus, the cell morphology changed and proliferation rate differed by an order of magnitude for different cell lines.;In chapter 3, hydrogels from Michael-type conjugated addition were utilized as a system to encapsulate MSCs in 3D. Upon the addition of two different polymer solutions, Michael-type addition reaction between vinyl sulfone (VS) and cysteine (Cys) would enable crosslinking of the polymers in the presence of cells. Changes to hydrogel properties, such as the mechanical modulus, equilibrium swollen ratio, and degradation could be varied independently by changing the ratio of VS:Cys or the gelation pH. In Chapter 4 and 5, the functionalization aspect of the saccharide-peptide hydrogels was explored in PC-12 cells and smooth muscle cells. Various functional groups, such as hydrophobicity and aromatics, could be introduced into our hydrogel system. Accordingly, tyrosine or valine standing for aromatic and hydrophobic functionality was coupled to saccharide-peptide copolymer along with the regular Cys coupling. Cys copolymers with tyrosine/valine were capable of crosslinking with VS polymer to afford more hydrophobic hydrogels compared to Cys:VS hydrogels. It is worth noting that this controlled functionality was achieved without varying crosslinking density and structure, which could lead to changes the surface charge and degradation behavior. In addition, given the diversity and versatility of substrates to Michael addition, proteins and peptides containing Cys thiol group could be brought into hydrogel to give specific function. Therefore, cell adhesion to the hydrogels can be fine-tuning through incorporation of RGD-containing peptides. Similarly, controlled degradation to the cell periphery could be modulated through incorporation of matrix metalloproteinase (MMP)-sensitive peptide. Subsequent cell behavior and ECM production for the aforementioned parameters could be assessed. Specifically, the effects of fine-tuning hydrogel parameters on cell viability, cell proliferation, PC-12 cell neurite formation and matrix production were determined in 3D.