Self-assembly of amphiphiles and polyphenols for drug delivery and environmental remediation
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Description
This dissertation encompasses the adaptation of concepts on self-assembly of amphiphiles and polyphenols to develop materials for applications in fields such as drug delivery and harmful algal bloom mitigation. The first part of the dissertation focuses on elucidating the structural transitions in a lipid/nonionic surfactant mixture. The phospholipid lecithin (L) and the nonionic surfactant Tween 80 (T) are used together in various contexts, including in drug delivery and oil spill remediation. There is hence a need to elucidate the nanostructures in LT mixtures, which is the focus of this section. We study these mixtures using cryogenic transmission electron microscopy (cryo-TEM), coupled with dynamic light scattering (DLS) and small angle neutron scattering (SANS). As the concentration of Tween 80 is increased, the self-assembled phospholipid vesicles formed by lecithin are transformed into spherical micelles. We identify bicelles (i.e., disc-like micelles) as well as cylindrical micelles as the key stable nanostructures formed at intermediate L/T ratios. We are able to directly visualize the microstructure of the aggregates formed by lecithin-Tween 80 mixtures, thereby enhancing the understanding of morphological changes in the lecithin-Tween 80 system. The second part of the dissertation establishes the ability to place a high concentration of self-assembled phospholipid vesicles (liposomes) in a confined volume as a multicompartment cluster that mimics biological cells and allows for the modulation of release of encapsulated species. The formation of these coated multicompartmental structures is achieved by first binding liposomes into clusters before encapsulating them within a two-dimensional metal organic framework composed of tannic acid coordinated with a metal ion (Metal phenolic network (MPN)). The binding of lipid vesicles will be achieved using tannic acid, where we exploit the fact that polyphenolics exhibit properties of adhesion to surfaces in water. We further show the possibility of communication between the adjacent nano-compartments in the cluster by demonstrating enhanced energy transfer using Fluorescence Resonance Energy Transfer (FRET) experiments where a lipophilic donor dye incorporated within one liposomal compartment transfers energy upon excitation to the lipophilic acceptor dye in a neighboring liposomal compartment due to their close proximity within the multicompartmental cluster. These observations have significance in adapting these multicompartmental structures that mimic biological cells for cascade reactions and as new depot drug delivery systems. The third part of the dissertation is focused on developing effective methods for the mitigation of harmful algal blooms (HABs). The use of MPNs to cluster phospholipid vesicles (liposomes), which we thoroughly explored in the second part of the dissertation, serves as an inspiration to test the use of MPNs for HABs mitigation since lipid vesicles are the biomimetic equivalent to cells. We demonstrate the flocculation and sinking of the harmful dinoflagellate Karenia brevis using MPNs and small amounts of chitosan to form a thin shroud over K. brevis cells and clay particles. Anchoring of the shroud is through the bioadhesion mimetics of polyphenol hydrogen bonding to surfaces. We also establish an approach for the targeted delivery of an algaecide to flocculated Karenia brevis cells, through the targeted release of algacidal hydrogen peroxide within flocs. The HABs mitigation methods developed in this work are easily scalable and effective.