Date of Award

Summer 8-24-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical Engineering

First Advisor

Yuri Lvov

Abstract

In this study, we have generalized an assembly of 50 nm diameter clay nanotubes on larger 20-50 μm diameter biological microfibers such as human hair (protein), cotton (cellulose) and synthetic polyethylene terephthalate- PET. We developed a common set of parameters and nanoclay coating techniques on these naturally different microfibers. We exploited and optimized the electrostatic interaction of the components through strategic adjustments in the solvent pH, employing polycation treatment, as well as selectively modifying the halloysite nanotubes with silanes. For 5 mins, a 5 wt% aqueous dispersion of halloysite nanotubes were applied to get approximately 1-2 μm thick fiber coating after a pretreatment with 0.1 wt % of cationic polyethyleneimine – PEI to allow for a more stable coating. In our first study, we reported the optimized properties of a polycation treatment PEI for hair surface nanoclay coating, where the ideal molecular weight to use for PEI was found to be at 1300 at pH 11. At the optimized conditions, halloysite coverage was over 70 % and the color retention lasted for up to 6 shampoo washes. As an extension of this project, we also further investigated magnetite nanoparticles coating on human hair by stabilizing them with polyelectrolytes such as polystyrene sulfonate - PSS. The findings from this study showed that magnetite nanoparticles of 200 nm diameter could be deposited on human hair in dense arrays and may be used as effective carriers for drug loading and delivery. Similarly, we also investigated enhanced flame retardancy and antibacterial protection on cotton through the application of a halloysite nanoclay coating. Unbleached, unprocessed cotton was treated with multiple PEI/HNT bilayers and was burned to determine the extent of fire protection. Through our experiments we found out that simply adding two bilayers of PEI/HNT coating reduced cotton flammability. The two bilayers accounted for a total of 7 wt% of the tissue. Surprisingly, we also found out that adding increased nanoclay layers improved flame retardancy by only 6%. We were also able to load the clay nanotubes with color-enhancing dyes and antimicrobial chloramphenicol showing that we can construct an architectural coating with complex functionality. Finally, we attempted to study assembly of enzyme loaded HNTs on plastic microfibers for their biocatalytic degradation. We obtained preliminary data for National Science Foundation (NSF) proposal by loading enzymes into halloysite nanotubes and applying such HNT colloids for 5-10 μm diameter polyethylene terephthalate – PET microfibers from used COVID medical masks. We found excellent coating that could be exploited for enzyme delivery to microplastic and to initiate biocatalytic degradation. This may be done in future work if the project will be supported by NSF.

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