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Whole heart decellularization combined with patient-specific cells may prove to be an extremely valuable approach to engineer new hearts. Mild detergents are commonly used in the decellularization process, but are known to denature and solubilize key proteins and growth factors and can therefore be destructive to the extracellular matrix (ECM) during the decellularization process. In this study, the decellularization of porcine hearts was accomplished in 24 h with only 6 h of sodium dodecyl sulfate exposure and 98% DNA removal. Automatically controlling the pressure during decellularization reduced the detergent exposure time while still completely removing immunogenic cell debris. Stimulation of macrophages was greatly reduced when comparing native tissue samples to the processed ECM. Complete cell removal was confirmed by analysis of DNA content. General collagen and elastin preservation was demonstrated. Glycosaminoglycans and collagen quantification both showed no significant differences in content after decellularization. The compression elastic modulus of the ECM after decellularization was lower than native at low strains, but there was no significant difference at high strains. Polyurethane casts of the vasculature of native and decellularized hearts demonstrated that the microvasculature network was preserved after decellularization. A static blood thrombosis assay using bovine blood was also developed. Finally, the recellularization potential of the ECM samples was demonstrated by reseeding cardiac fibroblasts and endothelial cells on the myocardium and endocardium samples.

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Developing patient-specific transplantable organs is a promising response to the increasing need of more effective therapies for patients with organ failure. Advances in tissue engineering strategies have demonstrated favorable results, including the use of decellularized hearts as scaffolds for cardiac engineering; however, there is a need to establish methods to characterize the cytotoxicity and blood compatibility of cardiac extracellular matrix (cECM) scaffolds created by decellularization. In this study, porcine hearts were decellularized in an automated perfusion apparatus utilizing sodium dodecyl sulfate (SDS) detergent. Residual SDS was measured by a colorimetric assay. Phosphate-buffered saline, distilled water (DW), and Triton X-100 washes were used to remove SDS. The efficiency of detergent removal was measured as a function of time. It was observed that using Triton-X 100 can nearly double the rate of SDS removal. An assay based on human blood hemolysis was developed to measure the remaining cytotoxicity of the cECM. The results from the hemolysis cytotoxicity assay were consistent with a standard live/dead assay using MS1 endothelial cells incubated with the cECM. This study demonstrated an effective, reliable, and relatively inexpensive method for determining the cytotoxicity and blood compatibility of decellularized cECM scaffolds.

The limited treatment options available for heart disease patients has lead to increased interest in the development of embryonic stem cell (ESC) therapies to replace heart muscle. The challenges of developing usable ESC therapeutic strategies are associated with the limited ability to obtain a pure, defined population of differentiated cardiomyocytes, and the design of in vivo cell delivery platforms to minimize cardiomyocyte loss. These challenges were addressed in Chapter 2 by designing a cardiomyocyte selectable progenitor cell line that permitted evaluation of a collagen- iii and function. Notably, no significant differences in cell survival, cardiac phenotype, and cardiomyocyte function were detected with the addition of the RGD domain to the collagen scaffold. Thus, in summary, these three studies have resulted in the identification of a potential cell surface marker for ESC-derived cardiomyocyte purification, and prove that collagen-based scaffolds can sustain ES-cardiomyocyte growth and function. This has set the framework for further studies that will move the field closer to obtaining a safe and effective delivery strategy for transplanting ESCs onto human hearts.