Date of Award

Spring 5-2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Molecular Science and Nanotechnology

First Advisor

David Keith Mills

Abstract

Polymer composites have witnessed increased research interest in the last decades, and the applications of these materials include drug delivery, tissue engineering, and wound bandages and dressings. Numerous polymers have been studied to fabricate the ideal wound dressing. Making these polymer composites biocompatible, porous, and bioactive with high absorption capabilities is critical to guide cell growth and differentiation and limit their detrimental effects on incorporated therapeutic molecules. This research work aims to address shortcomings of available wound dressings by fabricating a biocompatible, porous, bioactive, and antimicrobial dressing using chitosan (CTS) and carboxymethyl cellulose (CMC) polymers incorporated with zinc-doped halloysites (ZnHNT). In line with the points mentioned earlier, three distinct objectives are proposed in this research that involve using natural biopolymers and nanomaterials. The first objective involves the fabrication and characterization of chitosan/carboxymethylcellulose composite incorporated with zinc-coated halloysites (HNTs) via the solution-gel method, without the use of chemical crosslinkers. Here, the individual biomaterial components used in this research were tested for their inherent antibacterial properties while determining the minimum inhibitory concentration of each constituent biomaterial. A modified physical crosslinking method was used to fabricate a hydrogel biocomposite comprising CTS, CMC, and zinc-coated HNT. The physical characteristics of the hydrogel were assessed via rheological studies. SEM and digital microscopy were used to observe zinc-coated halloysites and the character of the hydrogel produced. Additional characterization tests carried out in this study include Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis, x-ray fluorescence, and x-ray diffraction (XRD). The results showed that zinc doped HNTs, when loaded with a low dose of gentamicin sulfate, stagnated the growth of gram-positive and gram-negative bacteria for extended hours, suggesting the possibility of less dependence on the use of antibiotics. The results also demonstrate the feasibility of fabricating a CTS/CMC polymer conjugate via a simple physical crosslinking method devoid of harsh crosslinking chemical agents.

The second project involved in vitro assessment of the effect of the fabricated chitosan-based composite on wound closure and cell migration. These properties were evaluated via in vitro assays, including proliferation and live/dead assays for cytotoxicity assessment, antimicrobial tests, alizarin red staining and scratch assay. The results suggested that the chitosan polymer conjugate had improved functionalities of biocompatibility, non-toxicity, and antimicrobial properties against gram-positive and gram-negative bacteria. In addition, the fabricated chitosan/CMC composite also showed an improved cell migration effect on human skin dermal fibroblast. This result suggests that the chitosan-based fabricated conjugate could serve as a new promising candidate for wound healing applications.

In a closely related third study, the use of solvent casting method to fabricate CTS/CMC film membranes bearing added functionality for biomedical applications is reported. Material characterization tests were carried out to confirm the presence of the constituted biomaterials. The tests include microscopy imaging and SEM analysis to determine the physical and surface topography of the fabricated biomaterial. Additional tests carried out include, thermogravimetric analysis (TGA), tensile strength, cell proliferation, cytotoxicity (live/dead), and antibacterial studies. The results of this project showed that the prepared biomaterial was relatively hydrophobic and non-toxic with improved thermal stability. Additional tests will be performed in future studies to obtain the ideal film membrane.

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