Biophysics of recellularized porcine cardiac extracellular matrix for myocardial tissue engineering
Au-Yeung, Chi Ting
Date of Issue2015
School of Materials Science and Engineering
Myocardial Infarction (MI) causes severe damage to cardiac muscles and remains the leading cause for congestive heart failure. Donations’ shortage for heart transplantations and limited benefits from conventional medications and surgeries have motivated researchers to find alternative ways to restore heart function post-MI, where a large scale of myocardium is scarred and no longer contractile. Myocardial Tissue Engineering (MTE) using scaffolds with or without cell seeding offers potential for in-vitro engineering of a myocardium-substitute construct for transplantation. Yet, many potential scaffold materials studied fail to give a physiological relevant thickness as compared to native myocardium in their intact form (10-15mm). Most of them also fail to provide matched modulus and flexibility that may hinder the proper mechanical functioning of the construct. Moreover, they are mostly lacking the optimal infrastructure resembling that of native myocardium to support desired cell engraftment. Our lab has developed and patented the decellularization of porcine left ventricle wall, yielding acellular porcine cardiac extracellular matrices (ECM), which are of surgical applicable transplant dimensions. These acellular cardiac matrices retained major ECM proteins and preserved inherent vasculature to address the above-mentioned limitations of existing biomaterials. In this PhD research, the ECM’s potential as a scaffold for cardiac restoration therapy was further investigated from the material engineering point of view. We aim to experimentally show that improved biophysical functionality of reseeded ECM-based cardio-mimetic constructs can be achieved through optimized culturing methods; and to rationalize the results with computational modeling and material biophysical properties correlations. Characterization on mechanical, thermal, surface conformational, protein adsorption kinetic, and electrical properties was performed. Strong focus was put on the biomechanical properties as it crucially determines a scaffold’s functional compatibility with the host tissue upon implantation. Sample mounting, experimental methods (in both uniaxial and biaxial tensile settings) and computational viscoelastic analytic tool were particularly developed for this purpose to test our unique thick and soft ECM. To provide a basis for evaluation, native adult porcine myocardium, which possesses the closest-to-human anatomy, was thoroughly characterized in the same fashion. This allowed us to identify the similarities and discrepancies between ECM and native myocardium. The effect of recellularization towards a more native-mimicking construct was then evaluated in terms of cell proliferation and the recovery of the native-like biophysical properties. Four different seeding methods and three different culturing regimes in static and dynamic conditions were employed. The results from this research thesis supports our hypothesis that the acellular ECM scaffold alone, and more so when reseeded with human bone-marrow derived mesenchymal stem cells (MSC), possesses biophysical properties that are close to those of the native myocardium. Its potential to be a suitable cardio-mimetic construct for myocardial tissue engineering was reaffirmed, supporting our vision to step forward in putting the ECM scaffold as an off-the-shelf biomedical product for diseased myocardium replacement and cardiac regeneration therapy.