Date of Award

12-2014

Document Type

Thesis

Degree Name

Master of Science (MS)

Program

Biomedical Engineering

Research Advisor

Tao L. Lowe, Ph.D.

Committee

Joel D. Bumgardner, Ph.D. George T.J. Huang, D.D.S., M.S.D., D.Sc. Richard A. Smith, Ph.D.

Abstract

Polymers have revolutionized the field of tissue engineering due to the countless possibilities of scaffolds that can be constructed from such a material. Through conjugation of other functional groups onto a polymer backbone, the mechanical properties of polymers can be controlled and has the ability to span a wide range of strengths, allowing for application in multiple tissue environments. One such polymer, hyaluronic acid (HA), is a natural polysaccharide found most abundantly in the extracellular matrix (ECM) of connective tissues with structural, lubricating, and wound healing functions in the human body; for this reason, HA has great potential for utilization in tissue engineering application. To strengthen the mechanical properties of HA, we conjugated 2-aminoethyl methacrylate (AEMA) to the carboxyl group of HA polymer in various degrees of substitution. In addition, different molecular weights of HA were used during synthesis to analyze molecular weight as a factor for tunable mechanical properties. The final product HA-AEMA, with use of photoinitiator Irgacure 2959, forms a hydrogel via UV polymerization following dissolution of macromer into photoinitiator solution. Both the rheological and mechanical properties of various macromer/photoinitiator solutions and hydrogels were measured, respectively, in regards to viscosity, solubility, shear modulus, and compression strength. To test HA-AEMA potential for use of tissue engineering applications involving stem cells, human dental pulp stem cells (DPSCs) were exposed to both HA-AEMA macromer and hydrogels for cytotoxicity and encapsulation studies by MTT using mitochondrial based assays and fluorescent viable cell staining respectively. Results of our experiments indicate successful synthesis of HA-AEMA macromer of various molecular weights of HA as well as degree of substitution of AEMA. As the molecular weight of HA and/or the degree of substitution of AEMA increased, the viscosity, swelling ratio, shear storage modulus, and compressive strength increased; specifically for storage modulus, more significant increases were observed as MW of HA was increased from 16 kDa to 66 kDa compared to increases from 66 kDa to 270 kDa. As the hydrogels swelled over time in phosphate buffer solution (PBS), the compressive strength of hydrogels diminished by a factor of 3 after 24 hours of swelling time and a factor of 2 from 1 day to 3 days swelling time, most likely due to hydrolysis of the ester bond along the HA chain. Results of the cytotoxicity studies indicate DPSCs survive exposure to HA-AEMA macromer as well as encapsulation inside hydrogels formed following the standard UV polymerization protocol. Based on these results, we have concluded that HA-based hydrogels have the potential to be used in various tissue engineering applications due to its tunable properties and biocompatibility to DPSCs

DOI

10.21007/etd.cghs.2014.0056

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