Date of Award

8-2020

Degree Name

MS in Polymers and Coatings

Department

Chemistry & Biochemistry

College

College of Science and Mathematics

Advisor

Sandra Ward, Ph.D.

Advisor Department

Chemistry & Biochemistry

Advisor College

College of Science and Mathematics

Abstract

In order for a drug, or any material used for the purpose of eliciting a change in an organisms’ physical or chemical state, to be effective it must reach the intended target intact and for a sustained rate over time. Drug delivery systems encapsulate a drug to protect it from degradation, prevent side reactions, increase solubility, improve accumulation rates at target sites, and release drugs at a controlled rate. Controlled and sustained release of drugs is achieved by degradation of the carrier triggered by breaking dynamic chemical bonds caused by changes in the chemical environment such as pH or redox conditions. Slow, first order kinetic release of drugs increase therapeutic efficacy while also reducing side effects and other cytotoxicity issues.

Up and coming drug delivery systems include hydrogels and nanocarriers such as vesicles. Hydrogel drug delivery systems are unique three-dimensional networks of crosslinked hydrophilic polymers that contain anywhere from 50-90 wt% of water. Drugs can be loaded via encapsulation during the gelation process or may be covalently bound to the polymer backbone before gelation. Amphiphilic molecules or polymers that self-assemble in aqueous solutions to form supramolecular nanostructures, such as vesicles, can encapsulate hydrophilic drugs in the aqueous interior or hydrophobic drugs in the lipophilic bilayer membrane.

This study seeks to embed vesicles into a hydrogel to create a hybrid drug delivery system which may be applied as a coating to medical devices to prevent bacterial adhesion and growth, injected directly to a target site, or as an additive for wound dressings. This hybrid system mitigates burst release from the hydrogel, as well as stabilizes the vesicles to afford a longer shelf life.

Vesicles are prepared from a novel supramolecular amphiphile composed of thio-alkyl modified��-cyclodextrin as a macrocyclic host, and an adamantyl-dithiopropionic acid modified poly(ethylene glycol) as a linear guest. This host-guest system forms inclusion complexes that self-assemble to bilayered vesicles, which may encapsulate a payload, in aqueous solutions. These vesicles serve as three-dimensional multivalent junctions to form a hydrogel, which may encapsulate a second payload, through a dynamic disulfide exchange crosslinking reaction. This novel drug delivery system will be capable of dual and selective release of two different encapsulated payloads. A pH sensitive acid labile bond embedded in the crosslinker will cleave under acidic conditions to release the payload enclosed in the hydrogel matrix, while a disulfide bond embedded in the supramolecular amphiphile of the free vesicle can be cleaved in the presence of naturally occurring antioxidant glutathione, GSH, to release the second payload.

It has been discovered that vesicles efficaciously form, can encapsulate a payload, and are stable for several weeks, up to a month. Vesicle stability is examined in the presence of both intracellular and extracellular concentrations of GSH, and it is found that vesicles are more stable in extracellular concentrations of GSH. Crosslinking of vesicles is attempted at several molecular weights of linear thiol terminated poly(ethylene glycol) crosslinker, concentrations ratios of crosslinker: vesicle, pHs, and temperatures. It can be concluded that the crosslinking density with the linear crosslinker is not high enough to form a hydrogel. Future studies will include 4-arm crosslinkers which are predicted to increase the number of crosslinking points and hence the crosslinking density.

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