Abstract

Polyhydroxyalkanoates (PHAs) are biopolyesters of 3-, 4-, 5- and 6-hydroxyalkanoic acids. They are produced in a wide range of bacteria, normally under nutrient limiting conditions. Depending on the carbon chain length they can be divided into two main types, short chain length PHAs (SCL-PHAs) and medium chain length PHAs (MCL-PHAs). SCL-PHAs are partially crystalline, thermoplastic in nature whereas MCL-PHAs are elastomeric with low crystallinity, low tensile strength, low melting point and high elongation at break. Cardiovascular diseases (CVD) are a major cause of death worldwide. Myocardial infarction (MI) and congestive heart failure (CHF) are the main cardiovascular diseases which account for 40% of mortality in industrial and developing nations. Cardiac patches aim to facilitate the normal functioning of the heart muscle by providing repair and support to the infarcted tissue post MI. MCL-PHAs are ideally suited for the production of cardiac patches due to their elastomeric properties and high biocompatibility. The main objective of this study was to fabricate cardiac patches using Poly(3-hydroxyoctanoic acid), P(3HO), which would be able to mimic the structure and functionality of the cardiac muscle. The P(3HO) polymer as produced from Pseudomonas mendocina using sodium octanoate as the carbon source. Neat and porous 2D films were prepared using the polymer and characterizations were carried out including GC-MS, FTIR and NMR, DMA, DSC and water contact angle. Random and aligned fibres were also electro-spun using P(3HO) to mimic the structure of the extracellular cell matrix. In vitro cell culture was carried out by seeding C2C12 myoblast cells and the cell proliferation was measured using the MTT assay. Human induced pluripotent stem cells derived cardiomyocytes (hiPSC-CM) were also seeded on the scaffolds and their proliferation measured using the live vs dead assay. The beating rate of the cells was also measured. The confirmation of the P(3HO) polymer structure was carried out using FTIR, GC-MS and NMR. The porous P(3HO) 2D film scaffolds were found to have a lower Young’s modulus value (0.467 MPa), similar to that of cardiac muscle, as compared to the neat P(3HO) scaffolds (3.32 MPa). The in vitro culture of C2C12 cells showed a 100% increase in proliferation when porous films were used, exhibiting a 44.42% of cell proliferation rate compared to Tissue Culture Plastic. A live vs dead assay conducted on the human iPS cells-derived cardiomyocytes (hiPS-CM) grown on the P(3HO) constructs showed that the cardiomyocytes grew as a monolayer on the constructs and were found to be very healthy and beating. This observation concluded that the material is biocompatible with the cardiomyocytes. The results obtained confirmed that P(3HO) is a promising novel material for myocardial tissue engineering applications.