Development of cardiac patches using medium chain length polyhydroxyalkanoates for cardiac tissue engineering

Medium chain length-PHAs (MCL-PHAs) have properties that make them exceptional for applications in cardiac tissue engineering. Cardiovascular diseases (CVD) are a major cause of death worldwide. Cardiac patches aim to facilitate the normal functioning of the heart muscle by providing repair and support to the infarcted tissue post myocardial infarction. In this project, two MCL-PHAs, poly(3-hydroxyoctanoate) (P(3HO) homopolymer and poly(3-hydroxynonanoate-co-3-hydroxyheptanoate) P(3HN-co-3HHP) were produced from Pseudomonas mendocina CH50 using sodium octanoate and sodium nonanoate respectively as the carbon source and the growth profiles were monitored for 48 h. The polymers were characterised to confirm the chemical structure of the polymers. Different types of scaffolds were fabricated like plain films, random fibres and aligned fibres, using different ratios of P(3HO) and P(3HN-co-3HHP) which were 100:0 (P(3HO)), 20:80 (P(3HO):P(3HN-co-3HHP), 50:50 (P(3HO):P(3HN-co-3HHP), 80:20 (P(3HO):P(3HN-co-3HHP) and 0:100 P(3HN-co-3HHP). The mechanical and thermal properties of the films were analysed along with the wettability of all the scaffolds. In vitro cytocompatibility studies were also conducted on all the different scaffolds (films, random and aligned fibres) by growing human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CM) on them. The cells were found to be viable and healthy with comparable beating rates and calcium transients to that measured on gelatin which was used as the positive control. The cell alignment quantification on the aligned fibres indicated around 50% of the cells were aligned in one direction. Porous 5 wt% 2D scaffolds and porous 20 wt% 3D structure were fabricated using P(3HO) and different concentrations of the porogen, sucrose and NaCl respectively, to obtain pores in the size range of 250-300 μm which exhibited decreased hydrophobicity compared to the neat scaffolds. In vitro cell culture with C2C12 exhibited higher cell proliferation rate on the porous P(3HO) structures as compared to the neat P(3HO) film. The P(3HO) and PANI (polyaniline) blend scaffolds were fabricated to introduce electrical conductivity and they were analysed for their material characteristics. The effect of the addition of PANI on cardiomyocyte proliferation was studied using neonatal ventricular rat myocardial cells (NVRM). A one step method involving the use of poly(ethylene oxide-stat-propylene oxide) with isocyanate end groups (NCO-sP(EO-stat-PO) was used for the incorporation of RGD, YIGSR peptides and the vascular endothelial growth factor (VEGF) on the surface of P(3HO)/P(3HN-co-3HHP) (80:20) electrospun fibres and enhanced cell viability was studied using NVRMs.