High Internal Phase Emulsion As A Reaction Medium For Fabrication Of Brushite Crystal

This present work was aimed at fabrication of porous brushite crystals using oil-in-water high internal phase emulsion stabilized by synthesized palm-based nonionic surfactant as a reaction medium. This research work was divided into four categories. The first part of the work involved synthesizing palm-based nonionic surfactants. Palm oil derivatives, lauryl, palmityl and stearyl alcohols as renewable resources, were ethoxylated with an average of three, six (or eight or nine) and 100 moles of ethylene oxide. The critical micelle concentration of the synthesized surfactants was found to decrease with increasing ethylene oxide head groups due to intertwist amongst the head groups. This phenomenon enhances surfactant-surfactant interaction rather than surfactant-solvent interaction which increases the rate of micellization as proven by the Gibbs energy. The increase in the surfactant tail length had minimal effect on micellization. The second part of the work was to stabilize the high internal phase emulsion using the synthesized surfactants. The oil phase was vegetable oil, namely olive and olein oils. These UPLOAD emulsions, with dispersed phase of more than 75 wt%, were easily prepared by one-pot homogenization. Due to the high oil volume fraction, the oil droplets were no longer spherical but were squeezed to take the shape of polyhedral. Light scattering results showed that the droplet size increased with increasing ethylene oxide chain length. The rheology of the emulsions was governed by droplet size and oil volume fraction. The emulsions exhibited high stability as indicated by the rheological measurements even after storage at 40oC for three months. The third part of the work was on the fabrication of brushite crystals with high degree of porosity using the high internal phase emulsion as a reaction medium. The porosity of the crystals was manifested by precursor concentration, surfactant concentration, oil volume fraction, mixing method, mixing time, aging temperature, precursor type, mode of recovery and surfactant head group. Pore size of the brushite crystals was less than 5 μm. The mechanism for the formation of porous brushite crystals was postulated schematically based on the small angle x-ray scattering analysis. The fourth and final part of this work was related to the application of the porous brushite crystals as drug delivery devices. Prior to the controlled release study, the crystals were subjected to cytotoxicity test to ensure their compatibility with synoviocytes, which are cells that line the knee joints of rabbits. The crystals were found to enable cell growth for up to five days. Sodium ampicillin, a wide spectrum antibiotic, was successfully loaded into the pores of the crystals and subsequently released in vitro for 14 days. This work underlines the simplicity of using highly stable high internal phase emulsion as a reaction medium for the fabrication of porous brushite crystals, in which when loaded with drug, exhibited potential as localized bone treatment demonstrated by the promising controlled release rate.

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