Date of Award

Spring 1-1-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical & Biochemical Engineering

First Advisor

Stephanie J. Bryant

Second Advisor

Amy Palmer

Third Advisor

Theodore Randolph

Fourth Advisor

Kristi Anseth

Fifth Advisor

John Kisiday

Abstract

Osteoarthritis is a degenerative joint disease for which there is no cure, but therapies such as tissue engineering offer hope. One of the challenges is that clinical therapies utilizing autologous chondrocytes require tissue engineering strategies that are suitable for adult chondrocytes, however additional questions remain as to whether cells isolated from donors of different ages affects how cells sense and respond to their external cues and regenerate new tissue. The overall goal of this thesis is to improve current strategies for cartilage tissue engineering by gaining a fundamental understanding of how chondrocytes respond to their external environment and the role of cell age in this response. First, we aim to improve strategies for the encapsulation of chondrocytes in photopolymerizable hydrogels, thus enhancing their survival and ECM synthesis. Second we aim to investigate the fundamental mechanisms by which environmental cues, specifically physiological and injurious loading, impact anabolic and catabolic activities in chondrocytes and the role of age in this response. Third we aim to investigate the role of a charged environment in regulating tissue production through intracellular calcium signaling with dynamic loading. The results of this thesis have concluded that a physiological osmolarity and the presence of a PCM does increase viability and ECM synthesis for adult chondrocytes photoencapsulated in PEG gels and protects cells from oxidative damage incurred during photoencapsulation. Physiological and injurious loading conditions differentially regulate tissue production with respect to cell age, due to age-related changes in mechanotransduction pathways. Finally, the addition of negative charges into PEG hydrogels regulated tissue production with dynamic loading and may be mediated by intracellular calcium signaling. This thesis has shown that chondrocyte age is a major factor in cellular response to physiological cues and that tissue engineering strategies utilizing PEG hydrogels will require specific cues based on the age of the patient. The presence of a charged environment has proved to be a potentially useful tool in guiding cartilage tissue production, however specific mechanisms of tissue regulation through calcium signaling remain to be elucidated. This thesis has provided a greater understanding age-associated changes in how chondrocytes sense their environment and has laid the ground work for future studies to investigate the differential regulation of calcium signaling and tissue production by ionic and osmotic effects, such that the specific cues responsible for regulation of tissue production can be isolated towards developing better tissue engineering strategies. Investigations into the mechanisms by which chondrocytes respond to physiological cues will provide a tool set for tissue engineering strategies to better engineer cartilage with specific mechanical properties and will also further current knowledge of chondrocyte biology, which may provide insights into development and treatments for joint disease, such as osteoarthritis.

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