Date of Award

12-2010

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Bioengineering

Advisor

Simionesu, Dan

Committee Member

Isenburg , Jake

Committee Member

LaBerge , Martine

Committee Member

Nagatomi , Jiro

Committee Member

Williams , Timothy

Abstract

Tissue engineering holds great promise for treatment of valvular diseases. Scaffolds for engineered heart valves must function immediately after implantation, but must also permit repopulation with autologous host cells and facilitate gradual remodeling.
Native aortic heart valves are composed of three layers, i.e. two strong external fibrous layers (ventricularis and fibrosa) separated by a central, highly hydrated spongiosa. The fibrous layers provide strength and resilience while the spongiosa layer facilitates shearing of the external layers. Our working hypothesis is that partially cross-linked collagen scaffolds that closely mimic the layered histo-architecture of the native valve would fulfill these requirements. To test this hypothesis we have developed heart valve-shaped tri-layered constructs based on collagen, the major structural component in natural heart valves. We describe here the development and characterization of two types of scaffolds, namely the fibrous scaffolds prepared from decellularized porcine pericardium and spongiosa scaffolds from elastase-treated decellularized pulmonary arteries. Fibrous scaffolds were cross-linked with penta galloyl glucose (PGG) to control remodeling. In order to assemble the scaffolds into a 3D valve structure and form the tri-layered leaflets, we developed a bio-adhesive consisting of mixtures of bovine serum albumin and glutaraldehyde (BTglue) and an efficient method to reduce aldehyde toxicity. Glued fibrous scaffolds were tested in vitro for biocompatibility (cell culture) and degradation (collagenase and proteinase K digestion). Tri-layered constructs were also tested for in vivo biocompatibility, cell repopulation and calcification.
In current studies, we have confirmed that scaffolds glued with BTglue were non-cytotoxic, with living cells spread across the entire surface of the BT-glue test area and cells growing directly on to the glued surfaces. With the long term aim of our studies being to create anatomically correct scaffolds to be used as personalized constructs for heart valve tissue engineering, we created silicone molds from porcine aortic heart valves and then modeled decellularized porcine pericardium into anatomically correct scaffolds. After drying them in their molds, the scaffolds have acquired the shape of the aortic valve which could then be preserved by exposure to PGG. After inserting decellularized pulmonary artery between the fibrous scaffolds to mimic the spongiosa layer, functionality testing of the heart valve-shaped scaffolds in a custom-made bioreactor showed good leaflet coaptation upon closure and good opening characteristics. Stem cell-seeded scaffolds also showed cellular differentiation into valvular interstitial-like cells (VICs) in similar bioreactor studies.
Future studies are needed to perfect the assembly process of the tri-layered construct. Additionally, further evaluation of stem cell differentiation is needed to confirm the presence of VICs in the aortic valve. If successful, there is potential that this approach of layering collagenous scaffolds into tri-layered constructs that mimic the native structure of the native aortic heart valve holds promise for the future of heart valve tissue engineering.

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