Synthesis of novel hybrid polymer functionalized hollow silica as stable smart systems

• Main Author: Lay, Chee Leng.
• Other Authors: Lu Xuehong
• Format: Theses and Dissertations
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Materials::Nanostructured materials
• Online Access: http://hdl.handle.net/10356/51866
• Institution: Nanyang Technological University

Current controlled release systems lack good integrity and fluidity for secure encapsulation and targeted delivery of active ingredients. This project aims to improve the performance of these systems by developing stable and smart vesicles for encapsulation and delivery via polymer functionalized hollow silica nanoparticles. Polymer functionalized hollow silica vesicles comprise of silica shells which contribute to mechanical stability while grafted polymers render solubility and controlled release/uptake properties with stimuli response. For this purpose, the following work was carried out: • pH sensitive poly(methacrylic acid) (PMAA) brushes were successfully grafted from surface of hollow silica spheres by atom transfer radical polymerization (ATRP). It was observed that an increase in solution pH induced ionisation of the carboxylate groups on PMAA, and hence increased the hydrophilicity of the poly(methacrylic acid) grafted hollow silica (PMAA-g-hollow silica) systems. Thereby affording pH-triggered encapsulation and release properties. At pH 2.0, fluorescence probes could be entrapped within interior cavities of PMAA-g-hollow silica nanoparticles and were released at pH 7.4. • The effect of different durations of ultrasonic irradiation on the integrity of poly(ethylene glycol) (PEG) chains grafted on hollow silica vesicles (PEG-g-hollow silica) was investigated. Gel permeation chromatography (GPC) and thermogravimetric analysis (TGA) was used to evaluate the maximum time the particles could be sonicated without deteriorating the PEG stealth layers and the results suggest no chain fragmentation but rather, a reduction in PEG content of PEG-g-hollow silica instead. From dynamic light scattering (DLS) results and transmission electron microscopy (TEM) images, ultrasonication had negligible effect on particle size and distribution of PEG-g-hollow silica and its silica shell integrity. Therefore it was postulated that the detachment of PEG from the hybrids occurred selectively at weak bond sites of linkers incorporating silica vesicles and PEG chains. Therefore it is recommended that dispersion of PEG-g-hollow silica in aqueous solutions aided by ultrasound should not be more than 3 h during sample preparation to preserve PEG content on silica surfaces. • A layer of interpolymer complex was generated on silica sphere by incorporating PMAA chains with PEGylated hollow silica (PMAA/PEG-g-hollow silica) vesicles via cooperative hydrogen bonding (H-bonding). The influence of medium pH on stability of intermolecular association between PMAA chains and PEG stealth layers on hollow silica surfaces was scrutinized. pH induced dissociation of PMAA/PEG-g-hollow silica vesicles was examined via determination of hybrids’ solubility in different pH media and studies on release profiles of entrapped fluorescence dyes. It was concluded that PMAA/PEG-g-hollow silica vesicles could precisely control encapsulation and release of cargo ingredients with respect to pH variation. Although PMAA/PEG-g-hollow silica vesicles had better protection efficiency than PMAA-g-hollow silica vesicles at pH below 7.0, the efficiency could not be enhanced with increasing PMAA molecular weight at pH 7.0. Due to their stability and pH response, both PMAA-g-hollow silica and PMAA/PEG-g-hollow silica systems are promising for pharmaceutical (e.g. drugs, proteins, enzymes, contrast agents, etc) and nonmedical (e.g. fragrance, adsorbents, pesticides, etc) applications. The morphology and composition of polymer functionalized hollow silica vesicles was determined by TEM, TGA, proton nuclear magnetic resonance spectroscopy (1H NMR) and Fourier transform infrared spectroscopy (FT-IR). Dependence of conformation transition of PMAA chains or PMAA/PEG interpolymer complex on hollow silica surfaces upon influence of medium pH was investigated by 1H NMR, ξ potential and fluorescence spectrometry. Molecular weight and weight distribution of PEG were studied by GPC.