Nanoparticle-Coated Poly(3-Hydroxybutyrate) Granules For Biomedical Applications

Abstract

Poly(3-hydroxybutyrate) (PHB) is a biodegradable and biocompatible polymer produced by many bacteria as a stored carbon source. Recent reviews have recently recognized PHB granules as a biomaterial that can be functionalized for use in various biomedical applications. The studies in this dissertation describe a novel means of producing nanoparticle-coated PHB granules that expands the capabilities of functionalized PHB granules through harnessing versatile properties of inorganic nanoparticles. PHA synthase was conjugated to gold nanoparticles (AuNP) and superparamagnetic iron oxide nanoparticles (SPION) and upon the addition of 3hydroxybutyrate-CoA (3HB-CoA), these nanoparticle-PHA synthase conjugates produce poly(3-hydroxybutyrate) (PHB) which aggregate to form nano- to micronsized nanoparticle-coated PHB granules. The resulting nanoparticle-polymer hybridmaterials are shown to exhibit unique properties to those of PHB and the nanoparticles alone and are a result of the rearrangement of the nanoparticles on the PHB granule surface. SPION-coated PHB granules are potential enhanced MRI contrast agents exhibiting ~2-fold improvement in spin-spin (T2) relaxivity (168 s-1 mmol-1 Fe) when compared to free SPION conjugated to PHA synthase (87.5 s-1 mmol-1 Fe). Control of the SPION-coated PHB granule size is also demonstrated via the addition of the surfactant Tween 20 that allows for producing PHB granules as small as 100 nm in diameter offering the possibility of controlling their biodistribution. Furthermore, SPION-PHA synthase is shown to also allow for controlled retention of SPION within porous matrices via PHB polymerization where in situ polymerization of PHB from SPION-PHA synthase within agarose gel was shown retain up to 4.2-times greater amount of SPION when compared to SPION-PHA synthase samples that did not undergo polymerization. Similarly, gold nanoparticle-coated PHB granules also exhibit unique properties that may be suitable in biomedical applications. AuNP-coated PHB granules are potential theranostic agents that have enhanced imaging capabilities, including surface-enhanced Raman scattering (SERS) and enhanced fluorescence, and can generate localized heating upon near-infrared (NIR) laser irradiation. The AuNPcoated PHB exhibited 11-fold enhancement in SERS over AuNP-PHA synthase particles prior polymerization. In addition, AuNP-coated PHB stained with the fluorophore Nile red exhibited a 6-fold enhancement in fluorescence intensity as well as a 1.3-fold decrease in photobleaching rate when compared to PHB granules alone. The granules were also shown to emit heat when illuminated at 808 nm with a 3.9-fold increase in heating rate when compared to AuNP-PHA synthase alone. In addition, NIR laser illumination of fluorescent doxorubicin (Dox)-loaded AuNP-PHB granules resulted in loss of fluorescence due to destruction of the PHB granule structure, providing a potential means of laser-triggered drug delivery from AuNP-PHB granules.