Date of Award

8-2012

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor(s)

Jerry Goodisman

Keywords

Drug delivery, MCM-41, Mesoporous materials, SBA-15

Subject Categories

Chemistry

Abstract

The lower efficiency of the current common ways of delivering drugs to humans like oral administration and injection make it necessary to find more efficient delivery systems. In this regard, a class of nanostructured materials called mesoporous silicates such as MCM-41, SBA-15 has attracted the attention of many scientists as drug delivery vehicles for their outstanding features like high surface area, high porosity, well-ordered, tunable nanometer pores and "non-cytotoxic" properties.

In this dissertation, comparative investigations of the adsorption capacity and drug release properties of these materials whose surfaces were functionalized with judiciously chosen organic groups via either post-grafting or co-condensation synthesis were conducted. Furthermore, two model drugs of different hydrophobicity and hydrophilicity were used in the study. The hydrophobicity of the ordered mesoporous silica can also be altered by modification of the surface with organic groups and thus, the hydrophobic interaction with the drug molecules can be improved. Here a comparative study between the two material synthesis method, the use of different functional groups and the two model drug molecules, Rhodamine 6G and ibuprofen, were performed. The results indicated that functional groups really make an obvious difference on the adsorption capacity and release profile depending on the type of functional group and drug molecules. Furthermore, differences in adsorption capacity and drug release properties between the materials synthesized via co-condensation and those synthesized via post-grafting were also observed. The results of the study may give further insight into rational synthetic approaches to functionalized mesoporous materials with improved adsorption capacity and release properties for a variety of hydrophobic and hydrophilic drugs. In addition, pH responsive release study was conducted. Ibuprofen and R6G were used as model drug molecules. For the ibuprofen loading, amine functionalized MCM (NH2-MCM) was chosen as carrier while amine and thiol bi-functionalized MCM (NH2-MCM-SH) was chosen as carrier for the adsorption R6G. Poly (acrylic acid) PAA was encapsulated onto the silica matrix as pH stimuli because it is a well-know bioadhesive hydrogel and often used in drug formulation.

Among mesoporous materials, SBA-15 has large surface area, large pore size, and thick walls. It possesses a hexagonal array of mesopores 6.0-20 nm in diameter, which is much larger than the 3.0-nm pores characteristic of the MCM-41 and MCM-48. Their wall thickness is an important parameter for providing a high degree of hydrothermal stability and improved mechanical stability compared to mesoporous MCM-41 and related silicas, and thus a sufficiently long lifetime in biological environments. Therefore, SBA-15 mesoporous materials could be modified with various surface functional groups and still preserve the large pore channels and surface areas for drug adsorption and desorption after modification. So, drug adsorption and release study over SBA-15 and comparative study between SBA-15 and MCM-41 was also investigated. Results show that SBA-15 has larger release amount than MCM-41.

In this dissertation, the oxidation of epinephrine in the presence of SBA-15 and MCM-41 particles was also carried out. Dense silica particle was test as a control. It was reported that caffeine (1,3,7-trimethylxanthine) can work as a scavenger of the hydroxyl radical at millimolar concentrations. Here we investigated the epinephrine oxidation in the presence of caffeine. Antioxidant effects of caffeine and its metabolites were also evaluated by the epinephrine oxidation rate. Same experiment was also performed with its isomer, isocaffeine. It was found that influence of mesoporous silica (MCM-41 and SBA-15) nanoparticles and dense silica nanoparticles on epinephrine oxidation is pH-dependent. Aslo, in the presence of either caffeine or isocaffeine, the oxidation rate of epinephrine by MSN will be slowed down and with the increase of caffeine or isocaffeine concentration, the oxidation rate decrease accordingly.

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