Study On The Application Of Poly(3-hydroxybutyrate-co-hydroxyhex-anoate) In Vascular-Related Tissue Engineering

Polyhydroxyalkanoates (PHAs) are a family of biodegradable polyesters, which have attracted commercial interest as substitutes in tissue engineering grafts as they are generally biodegradable, with good biocompatibility and possess various plastic and elastomeric material properties depending on their monomer constituents. One novel PHA, copolyesters of 3-hydroxybutyrate and 3-hydroxyhexanoate (PHBHHx) improved the mechanical properties significantly in comparison to that of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) because the 3-hydroxyhexanoate unit is not incorporated into the crystal-lattice. The biocompatibility of PHBHHx was evaluated comprehensively by examining its interaction with blood, cells and tissues to drop a new hint for the applications of PHBHHx in vascular-related tissue engineering. In order to extend the potential of PHBHHx in vascular-related tissue engineering, surface modifications of PHBHHx were made by either fibronectin (Fn) coating with NH2-plasma treatment (PFn-PHBHHx) or blending with PEG. Following results were obtained:1. In vitro blood contact experiments revealed that the hemolysis of PHBHHx was only 3% while that of PHB and PHBV was 5% and 8% respectively. Few platelets, in normal morphology, adhered on the 12% 3HHx-containing PHBHHx in comparison with other test films. These results suggest that PHBHHx has improved hemocompatibiliy compared to PHBV and PHB.2. Human umbilical vein endothelial cells (HUVECs), human umbilical artery smooth muscle cells (HuSMCs) and rabbit aorta smooth muscle cells (RaSMCs) on PHBHHx containing 20%,12%,20% 3HHx respectively had similar MTT value to the control cells on tissue culture plates (TCPs). In addition, the MTT value tended to increase in a 3HHx-content dependent manner.3. The highest expression level and typical spindle-like distribution of a-actin on 20%HHx-containing PHBHHx were characterized as the contractile-like phenotype, suggesting that RaSMCs tended to differentiate rather than proliferate when compared to the cells grown on other tested polymer. These results suggested that 20%HHx-containing PHBHHx was suitable for RaSMCs proliferation and resulted in its change to contractile phenotype. This study confirmed the interesting functions of PHBHHx in restricting the overgrowth of SMCs, which further extends the potential applications of PHBHHx in SMCs related graft scaffold fabrication for tissue engineering.4. Ammonia plasma-treated PHBHHx coated with fibronectin was found to benefit endotheliazation rather than RaSMCs proliferation, while PHBHHx blending with PEG in ratio of 1:1 prefered RaSMCs'proliferation than HUVECs'. These results suggest that these two modified PHBHHx are promising materials as a luminal or middle-layer candidates for constructing complex multilayer vascular grafts.5. Compared with PHB and PLA, PHBHHx was very inert in vivo, as indicated by the thinnest surrounding capsule consisting of fibers, fibroblasts and no inflammatory cells. It was also demonstrated that a high degradation rate occurred in an amorphous region rather than in a crystalline region within PHBHHx, while the hydrolysis of PHB was found to begin with a random chain scission both in amorphous and crystalline regions of the polymer matrix. These results give new clues in improving the degradation of PHBHHx by decreasing the crystallization. The first try of PHBHHx implantation also confirmed the promising applications in tissue engineering.