Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemistry

Supervisor

Tsun-Kong Sham

Abstract

Calcium silicate hydrate (CSH), a new type of bioceramics, has gained significant attention in hard tissue restoration because of their impressive role in the stimulation of osteoblast proliferation and differentiation in vitro. The further development of mesoporous bioceramics opens up new opportunities for drug delivery in hard tissue therapies. In this thesis, interaction mechanisms of drug molecules with CSH of different morphologies and CSH/polymer composites, imaging of drug distributions in CSH carriers in nanoscale, and the biomineralization mechanisms of CSH in vitro during drug release are extensively investigated using X-ray absorption near edge structure (XANES) and scanning transmission X-ray microscopy (STXM).

The interactions between different drug molecules and CSH with different morphologies are investigated using XANES. It is found that the morphology and the presence of hydrates of drug carriers influence the drug loading capacities (DLCs). CSH provides active linkage sites (Ca-OH and Si-OH groups) for the acidic functional groups of drug molecules via electrostatic interactions. Besides, it is also found that the stoichiometric ratio of Ca2+ ions of CSH carriers to the functional groups of drug molecules will significantly influence the DLCs.The mapping of an individual CSH microsphere, which was synthesized by a sonochemical method, before and after the loading of ibuprofen (IBU) is recorded by STXM. This STXM-XANES study illustrates the integrity and the homogenously distribution of drug molecules in these drug carriers.

The biomineralization of the drug carrier, CSH microspheres upon IBU release, are monitored with XANES and STXM. The biomineralization mechanisms for CSH microspheres loaded with IBU in the SBF solution, which were still controversial before, emerge via STXM mapping, spectral comparisons and fitting analysis.

Finally, CSH/polymer composites were synthesized using a controlled precipitation reaction between calcium salt and silicate salt, followed by the addition of various polymer solutions iv at room temperature. The interactions between different polymers and CSH, the interactions between drug molecule IBU and these polymer composites have been extensively studied by XANES. We find that the polymers alter the structure of CSH to various degrees, and that this behaviour further influences the DLCs and drug release kinetics.

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