Cardiac tissue engineering: how the physical properties of the scaffold affect the phenotype of naïve cardiomyocytes

Abstract

Human induced pluripotent stem cell derived cardiomyocytes (iPSC-CMs) are widely suggested as a suitable in vitro model for cardiac drug toxicity screening and for in vivo cardiac repair of damaged myocardium. However, the current immature phenotype of the iPSC-CMs limits their use in both these situations. Tissue engineering can promote in vitro maturation of iPSC-CMs towards a phenotype that is more representative of the human adult myocardium by using bioengineered matrices to provide elements associated with in vivo structure and function of native cardiac tissue, e.g. conductive or elastic polymers. However, the response of immature cardiomyocytes to some of these bioengineered constructs, serum albumin (SA) hydrogels, conductive polyaniline (PANI) scaffolds and biodegradable elastic polyhydroxyalkanoate (PHA) scaffolds, is unknown and hence investigated in this study. The bovine SA hydrogels are biocompatible and can be used to significantly increase the gene expression and significantly decrease the Ca2+ transient decay time of the neonatal rat ventricular myocytes (NRVMs), in comparison to NRVMs cultured on glass. The culture of NRVMs and fibroblasts on the SA hydrogels resulted in significantly slower Ca2+ cycling, but prolonged culture time in comparison to NRVMs alone. The bovine and human SA hydrogels can support the culture of iPSC-CMs for at least 28 days and the gene expression of the cells significantly increases with time in culture. The Ca2+ cycling is significantly faster in comparison to glass too. Conductive and non-conductive PANI scaffolds, coated with FBS proteins, are biocompatible with high NRVM and fibroblast adhesion and viability, which remain unchanged in comparison to glass. The NRVMs on the conductive PANI scaffolds have significantly faster Ca2+ transients and action potentials than those on the non-conductive PANI scaffolds, which suggest that the cells interact with the PANI scaffolds but the mechanism behind these changes is unknown and requires further investigation. PHA film scaffolds are biocompatible with iPSC-CMs and their blends may be used to manipulate cell properties to obtain tissue-engineered patches with significantly faster beating rate and Ca2+ influx. Sarcomere length remains unchanged, but comparable to adult myocardium. PHA aligned fibre scaffolds promote significantly increased cell alignment and significantly faster Ca2+ handling in iPSC-CMs, in comparison to randomly orientated PHA fibres, however further work is required to further optimise this and promote enhanced iPSC-CMs alignment to create a more biomimetic model. This thesis demonstrates the ability of different bioengineered constructs to manipulate the properties of immature cardiomyocytes with varying outcomes. Further work is required to produce functionally mature iPSC-CMs that are representative of native adult human myocardium.