Date of Award

Summer 2009

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical Engineering

First Advisor

Mark DeCoster

Abstract

The Layer-by-Layer (LbL) assembly technique was used to obtain a new type of protein/polyphenol microcapsule based on naturally occurring polyphenol (-)-epigallocatechin gallate (EGCG) and gelatin, type A. The dependence of permeability on the molecular weight of permeating substances was studied and compared with commonly used polyallylamine/polystyrene sulfonate capsules. A quartz crystal microbalance was used to monitor the regularities of EGCG adsorption in alternation with type A and B Gelatins and electrophoretic mobility measurements were used that indicated that the nature of assembly was dependent on Gelatin properties. It was shown that EGCG retains its antioxidant activity in the LbL assemblies.

Natural polyphenols, with previously demonstrated anti-cancer potential, EGCG, tannic acid, curcumin, and theaflavin, were encased in gelatin-based 200-nm nanoparticles consisting of a soft gel-like interior with or without a surrounding LbL-shell of polyelectrolytes (polystyrene sulfonate/polyallylamine hydrochloride, polyglutamic acid/poly-L-lysine, dextran sulfate/protamine sulfate, carboxymethyl cellulose/Gelatin, type A) assembled using the LbL technique. The characteristics of polyphenol loading and the factors affecting their release from the nanocapsules were investigated. Nanoparticle-encapsulated EGCG retained its biological activity and blocked hepatocyte growth factor (HGF) induced intracellular signaling in the breast cancer cell-line MBA-MD-231 as potently as free EGCG.

Since electrostatic LbL nano-assembly is proven to be a suitable method for surface modifications on charged templates, we also used this technique for nano-coating of the phototrophic purple sulfur bacterium Allochromatium Vinosum with different synthetic and biocompatible polyelectrolyte combinations in order to investigate its biomimetic applications as related to drug delivery. The contact mechanisms between the cell surface and the insoluble elemental sulfur was investigated and studied because this step is essential for elemental sulfur uptake. Furthermore, modified uptake of sulfide by the encapsulated cells was also investigated. Growth experiments, after coating of the cells, showed that the surface charge of the bacteria neither affected the uptake of sulfide nor the contact formation between the cells and elemental sulfur. However, an increasing number of layers assembled on the cells slowed or inhibited the uptake of sulfide and elemental sulfur depending on the polymer combination used for coating. This indicated that LbL self-assembly makes it a suitable method for investigation of cell-surface related aspects in microbiology.

After using LbL assembly successfully for coating microbes, we coated microbial spores in a sheath of functionalized nanofilms. Bacterial spores were encapsulated in organized ultrathin shells using LbL assembly in order to assess the biomaterial as a suitable core and determine the physiological effects of the coating. The coated spores were viable but the kinetics and extent of germination were changed from control spores in all instances. The results and insight gained from the experiments may be used to design various bioinspired systems. The spores can be made dormant for a desired amount of time using LbL encapsulation technique and can be made active when desired. In this work with LbL nanoassemly, we performed polyphenol based formulations and also modified the bacterial surface to study the effects of encapsulation on the uptake of various compounds. (Abstract shortened by UMI.)

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