Design and characterisation of polyhydroxyalkanoate bead-alginate hybrid materials : a dissertation presented in partial fulfilment of the requirements of the degree of Master of Science in Microbiology at Massey University, Manawatū, New Zealand

Abstract

Encapsulation is a technique to entrap a material of interest within a carrier material, and it has been used in a wide range of industries such as biopharmaceutical and biotechnological companies. Among biopolymers used for the carrier material, alginate has been widely used due to its attractive properties of biodegradability, biocompatibility and ease of gelation under mild conditions. In this study, a novel hybrid micro- or millisphere composed of functionalised polyhydroxyalkanoate (PHA) beads and alginate was fabricated through ionotropic gelation methods. The selected functional proteins displayed on PHA beads were the IgG binding domain (ZZ) of Protein A from Staphylococcus aureus, and organophosphate hydrolase (OpdA). The effect of alginate encapsulation on their functionality was assessed. In addition, alginate millispheres encapsulating PHA beads were assessed for their ability to remove lipophilic compounds from an aqueous solution. This utilised the hydrophobic polyester core of the PHA beads and was assessed by using the lipophilic dye, Nile red, as the reporter. The results of IgG binding assays using PHA beads encapsulated in alginate microspheres showed no significant difference compared with negative controls, and no elution of bound IgG was observed. However, the alginate encapsulation enhanced IgG binding to the PhaC derived proteins on PHA beads within alginate microspheres. In contrast, alginate encapsulation limited the activity of PHA beads displaying OpdA when compared to free PHA beads. The qualitative data obtained from phase contrast and fluorescence microscopy suggested that the enzyme displayed on PHA beads was active within alginate microspheres. The lipophilic dye removal by PHA beads encapsulated in alginate millispheres was influenced by different parameters used in the millisphere preparation. The adsorption kinetics aligned with a pseudo second-order kinetic model, and the equilibrium adsorption data was in agreement with the Freundlich isotherm model. This study has provided preliminary data for fabrication of a hybrid material of functionalised PHA beads with alginate. The development of combinations of highly functional PHA beads with other biomaterials is expected to expand the application field of PHA beads.