The physiochemical properties and biocompatibility of poly-3-hydroxyalkanoates

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The physiochemical properties and biocompatibility of poly-3-hydroxyalkanoates


Author: Cheng, Yin-chung
Title: The physiochemical properties and biocompatibility of poly-3-hydroxyalkanoates
Degree: M.Phil.
Year: 2006
Subject: Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Applied Biology and Chemical Technology
Pages: xxv, 129 leaves : ill. (some col.) ; 30 cm
Language: English
InnoPac Record:
Abstract: Poly-3-hydroxybutrate (PHB) and its copolymers have been considered a class of biomaterial suitable for tissue engineering due to its biodegradability, biocompatibility, non-toxicity and thermoplasticity. PHB is biocompatible. It means it is a metabolite normally present in blood. They have been used to support cell growth in vitro, guide tissue growth inside the body, and found to be fully biocompatible to several cell lines, including articular cartilage chondrocytes, osteoblasts and epithelial cell. The physical and chemical properties of the biomaterials are also found to be important factors in affecting the growth of tissue like the surface morphology, hydrophilicity, crystallinity and chemical composition of the materials. The biocompatibility of Poly-3-hydroxyalkanoates (PHA) with different molar ratio of hydroxyvalerate produced by different strain of bacteria was investigated. Poly(3-hydroxybutyrate-co-valerate) (PHBV) containing 23 mol% and 37 mol% of hydroxyvalerate were used in Part I. Two sets of poly(3-hydroxybutyrate-co-valerate) (PHBV) containing 23% and 37% by mole of hydroxyvalerate were selected in this study. One set of PHBV was biosynthesized by Bacillus cereus and the other set by a recombinant Escherichia coli XL-1 Blue harboring plasmid pKS/CAB. The four types of PHBV differed in surface properties such as surface roughness and hydrophilicity. These properties are considered to be important parameters in clinical applications such as scaffold implantation. PHBV was cast into thin films by using solvent casting method and seeded with Chinese Hamster Ovary cells (CHO-K1) to evaluate their biocompatibilities. The results of 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxy phenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay showed that CHO-K1 cells proliferated better on P(HB-co-23%-HV) film produced by recombinant Escherichia coli XL-1 Blue harboring plasmid pKS/CAB, than on the other types of PHBV. The growth of CHO-K1 cells was correlated to the surface roughness. Also, the leachables of extract from the PHBV films were investigated whether there were some toxic things inside the polymer or not. Only the extracts of P(HB-co-23%-HV) of B. cereus had some negative effects of growth inhibition and reduction of protein content. It is difficult to control the even surfaces in solvent casting film. One type of PHBV film was perforated by laser to have even pores. The hydrophilicity and the cell proliferation were improved after perforation. In Part II of this research, PHB and PHBV fibers were experimentally produced. The mechanical properties of the fibers were also investigated. Moreover, PHB fibers were banded together to become fiber-plate and fiber-plate scaffold. The cells were proliferated on L929 fibroblasts on PHB fiber-plate, fiber-plate scaffold and PHB salt-leaching scaffold and PHB film. Salt-leaching scaffolds were commonly used to investigate the biocompatibilities of the biomaterials. However, the surface topography of salt-leaching scaffold is difficult to measure. Woven fibers could be used to band together as a fiber-plate, such that the surface properties could be easily measured and controlled. Apart from the scaffolds application, the other application of PHB is drug delivery and this was tested in Part III. The formation of PHB-PEG-PHB nanoparticles were found useful for delivery drugs in the body. PEG is hydrophilic and PHB is hydrophobic. When PHB-PEG-PHB is dissolved into aqueous, PHB forms a core shell and the outermost shell is PEG. For future research, the cytotoxicity and blood compatibility of the nanoparticles is an interesting for investigation because whether they are non-toxic to animals' cells and blood are to be examined.

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