This paper presents the fabrication of controlled release devices for anticancer drug paclitaxel using supercritical antisolvent method. The thermodynamic and hydrodynamic effects during supercritical antisolvent process on the particle properties obtained were investigated. Scanning electron microscopy was employed to study particle sizes and morphologies achieved. It was observed that increasing supercritical pressure improves the surface morphology of particles obtained, and increasing the flow rate of the organic solution jet reduces the particle sizes obtained. A modified Supercritical Antisolvent with Enhanced Mass transfer setup was developed to produce monodispersed nanoparticles with high recovery yield. High performance liquid chromatography was used to determine the encapsulation efficiency and in vitro release profiles of paclitaxel loaded particles obtained. The encapsulation efficiencies of particles obtained using the modified SASEM process were high and up to 83.5%, and sustained release of paclitaxel from the polymer matrix was observed over 36 days release. The thermogram properties of the particles were also analyzed using differential scanning calorimetry to determine the crystalline state of polymer and drug. / Singapore-MIT Alliance (SMA)

Molecular recognition is an important tool for developing tunable controlled release systems and fabricating biosensors with increased selectivity and sensitivity. The development of polymer-based materials that exploit molecular recognition events such as host-guest complexation, enzyme-substrate and enzyme-inhibitor interactions and nucleic acid hybridization was pursued in this thesis. Using polymers as an anchor for molecular recognition can enhance the affinity, selectivity, and the capacity for immobilization of recognition units, enabling the practical use of affinity-based systems in real applications. To introduce the potential for immobilization while preserving or enhancing the affinity of small molecule recognition units, the affinity of derivatized cyclodextrins for the hydrophobic drug, dexamethasone, was investigated. Cyclodextrins (CDs) are molecules that possess a hydrophilic exterior and a hydrophobic cavity capable of accommodating a wide range of small molecule guests. Analysis of the solubilization capacities, thermodynamic parameters and aggregative potentials of carboxymethyl and hydrazide derivatives of CDs established the dextran-conjugated βCD derivative as an ideal carrier of hydrophobic drugs and the hydrazide βCD derivative as an optimal solubilizer of lipophilic pharmaceuticals, both alone and when incorporated in a polymer-based drug delivery vehicle. To enable non-covalent immobilization and stabilization of biomacromolecular recognition units, a printed layer hydrogel was investigated as a selective diffusion barrier for analyte sensing and enzyme inhibitor recognition. A printable hydrogel platform was developed from an established injectable system composed of aldehyde- and hydrazide-functionalized poly(oligoethylene glycol methacrylate) polymers. The printed layer hydrogel effectively immobilized a wide range of enzymes and protected enzyme activity against time-dependent and protease-induced denaturation, while facilitating the diffusion of small molecules. Furthermore, to demonstrate the potential of the printed film hydrogel immobilization layer to enhance the selectivity of the target, the printable hydrogel platform was used to develop a microarray-based assay for the screening of inhibitors of the model enzyme, β-lactamase. The assay was able to accurately quantify dose-response relationships of a series of established inhibitors, while reducing the required reagent volumes in traditional drug screening campaigns by 95%. Most significantly, the assay demonstrated an ability to discriminate true inhibitors of β-lactamase from a class of non-specific inhibitors called promiscuous aggregating inhibitors. Finally, to enable non-covalent immobilization of DNA recognition units, the printable hydrogel-based microarray was tested for its ability to immobilize DNA recognition sites and promote the detection of DNA hybridization events. A long, concatameric DNA molecule was generated through rolling circle amplification and was used as a sensing material for the detection of a small, fluorophore labeled oligonucleotide. The printable hydrogel was able to effectively entrap the rolling circle amplification product. Properties of the printable hydrogel were investigated for their ability to support the detection of DNA hybridization events. / Thesis / Doctor of Philosophy (PhD) / This thesis describes the development of polymer-based materials that exploit molecular recognition events for drug delivery and biosensing applications. First, cyclodextrins (CDs) are molecules that are capable of binding a wide range of small molecules. A comprehensive analysis of the complexation properties of CD derivatives revealed critical insight regarding their application in polymer-based drug delivery vehicles. Second, a printable hydrogel platform was developed to support the immobilization and activity of biomolecules and establish a biosensing interface that facilitates the diffusion of small molecules but not molecular aggregates. A microarray-based assay was developed by employing the printed hydrogel interface for the screening of inhibitors of the model enzyme, β-lactamase, and the detection of DNA hybridization events.