Date of Award

5-2009

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Bioengineering

Advisor

Simionescu, Dan T

Committee Member

Nagatomi , Jiro

Committee Member

Simionescu , Agneta

Committee Member

Webb , Ken

Abstract

Tissue engineered constructs with autologous adult stem cells capable of self-repair and growth are highly desired replacements for diseased heart valves. However, the current approaches have inadequate mechanical properties to withstand in vivo implantation. Therefore, our group hypothesized that an in vitro environment of physiological intra-cardiac pressures and flow will stimulate stem cells to differentiate and remodel valvular scaffold constructs before implantation.
The group developed a pneumatic-driven conditioning system (Aim I) consisting of a three-chambered heart valve bioreactor, a pressurized compliance tank, a reservoir tank, one-way valves, pressure-retaining valves, and pressure transducers. The system can be sterilized using conventional autoclaving and ethylene oxide gas. The most novel feature is its ability to accommodate all clinically relevant sizes of stented or stentless biological, mechanical, or tissue engineered substitutes. A tissue derived heart valve substitute was used to test the bioreactor's functional capabilities (Aim II) at 60 beats per minute. The tests resulted in excellent opening and closing of the valve, pulsatile flows reaching 1400 mL per minute, and aortic pressures reaching 100 mmHg. The bioreactor then tested tissue engineered heart valves (Aim III) made from decellularized and lightly cross-linked tissues. Two stentless porcine aortic heart valves were conditioned in the bioreactor for 21 days. The first was seeded with adipose-derived stem cells (valve 1) and the second with aortic endothelial cells (valve 2). The third valve was made of valve-shaped fibrous sheets encasing a spongy collagen scaffold. It was seeded with human bone marrow-derived stem cells (valve 3) and conditioned in the bioreactor for 8 days. After progressive adaptation, valves were tested at 60 beats per minute and 10 mL per stroke. Each experiment also included a static control.
The bioreactor created proper closing and opening of the heart valves and allowed for multiple mounting methods. Results indicated successful cell seeding and attachment in valves 1, 2, and 3; noticeable intercellular alignment in valves 2 and 3; and stem cell differentiation in valve 3. Overall, the conditioning system provides a dynamic three-dimensional cell culture setting designed to provide optimal physiological conditions for tissue engineered heart valve development over extended time periods. The group will continue to develop this approach to study multiple aspects of tissue engineered heart valve development and heart valve pathology.

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