Date of Award

Spring 1-1-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical & Biochemical Engineering

First Advisor

Kristi S. Anseth

Second Advisor

Jefferey W. Stansbury

Third Advisor

Stephanie J. Bryant

Fourth Advisor

Joel L. Kaar

Fifth Advisor

Virginia L. Ferguson

Abstract

Poly(ethylene glycol) (PEG)-based hydrogels have emerged as important class of biomaterials for use as cell and drug delivery vehicles for tissue engineering and also as two- and three-dimensional cell culture substrates. PEG is commonly used due to its hydrophilic and bio-inert properties. The versatility of PEG chemistry allows for independent tailoring of biophysical properties and biochemical functionalization of the microenvironment experienced by cells allowing researchers to conduct systematic studies, in vitro, to study and understand the role of physiological cues experienced by cells in a biologically relevant fashion. The main goal of this thesis is to design appropriate hydrogel substrates to design biomaterials platforms to study and understand the role of extracellular matrix (ECM) cues on osteogenic differentiation of human mesenchymal stem cells. First, the role of phosphate functional groups, found abundantly in the mineral phase of bone, on osteogenic differentiation of hMSCs in the absence of osteogenic supplements was studied. Role of sequestered serum proteins in mediating the adhesion and interaction of hMSCs with the phosphate functional groups was characterized. The role of focal adhesion kinase (FAK) mediated integrin signaling on inducing osteogenic differentiation in hMSCs cultured on phosphate functionalized hydrogels was assessed. Second, thiol-ene photopolymerization chemistry was exploited to synthesize α5 integrin priming hydrogels and the role of substrate elasticity on osteogenic differentiation of hMSCs induced by α5β1 signaling was studied. cyl(RRETAWA) peptide that specifically binds to α5 integrin was synthesized and the effect on soluble delivery to hMSCs was assessed by measuring ALP activity. Hydrogel formulations were identified to independently control their peptide functionalization and elasticity. The interplay of substrate elasticity and peptide functionalization on hMSC adhesion and focal adhesions formation was quantified. Towards understanding the role of substrate elasticity on osteogenic differentiation of hMSCs induced by α5β1 integrin signaling, the ALP activity of the cultures as a function of substrate elasticity and peptide concentration was measured. Last, towards development of chemical strategies that allow dynamic tunablity of biochemical environment experienced by cells, we have designed and synthesized addition-fragmentation-chain transfer capable allyl sulfide functionalized PEG hydrogel networks. Biochemical patterning via photo-initiated thiol-ene reactions on ally sulfide was studied and characterized with fibronectin based CRGDS motif as a model thiol containing bioactive compound. The ability to reversibly exchange any thiol containing biochemical cues in these hydrogels was demonstrated and the kinetics of exchange reactions was characterized.

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