Restriction lift date: 2024-09-30
The design, synthesis and characterisation of selected chitosan-based thin films and studies of their use as materials for antimicrobial, heavy metal adsorption, and wound dressing applications
Loading...
Files
Date
2022-09
Authors
Pemble, Oliver James
Journal Title
Journal ISSN
Volume Title
Publisher
University College Cork
Published Version
Abstract
Chitosan is a naturally-derived polymer, sourced from the chitin present in crustacean shells and insect exoskeletons. It is a highly diverse molecule, with heavy metal adsorption, antibacterial and pH-based swelling properties. However, these properties may be hindered by the lack of strength of a singular polymer structure. Chitosan has the ability to cross-link with other polymers or reagents to create interpenetrating polymer networks (IPNs) and blends to improve the mechanical strength or application mechanisms. These composites can be cast into films which have superior properties for the applications listed above.
The first half of this PhD thesis sets out to describe the process of synthesising thin films made from combining chitosan with cross-linking reagents and other polymer networks. These materials comprise two siloxane networks Tetraethyl-orthosilicate (TEOS) and 3-aminopropyltriethoxysilane (APTES), glutaraldehyde (GA), and the polymer polyacrylamide (PAM). Aqueous acidic solutions of low molecular weight chitosan were made and combined with one of the four materials at different ratios to produce hydrogels that could then be cast into thin films. These chitosan-based films were characterised as to their molecular structures via FT-IR spectroscopy and their mechanical elasticity/plasticity via tensile strength tests.
The method of casting the films was primarily drop-casting in a Petri dish and drying for 24 hours, but an alternative procedure that utilises a doctor blade slot-die head was also developed. This novel method was studied in-depth, and the findings were published. For this reason, the results of the slot-die casting studies are presented in their published form. Briefly, the slot-die casting technique produced high quality thin films of chitosan-based composites in under 2 hours. Further, there was no influence of the direction of travel of the films during deposition on their mechanical properties. This study served as a proof-of-concept that high volumes of chitosan-based films could be made quickly, cheaply, and reproducibly.
The second half of this thesis explores the applications of the composite chitosan-based films, by use of their adsorption, antimicrobial, and swelling abilities.
The adsorption of radioactive technetium pertechnetate 99mTcO4- ions via chelation from solution was evaluated and correlated based on the Langmuir and Freundlich isotherms. It was found that the chitosan-glutaraldehyde films showed the best ability to adsorb 99mTcO4- ions and that a Langmuir-type, monolayer-based adsorption process was most likely in operation.
A preliminary study of the antimicrobial properties of the chitosan-based films was undertaken via Gram-negative and Gram-positive bacterial growth and attachment assays. The intent of the study was to test the antibacterial abilities of the films while also speculating as to the mechanism of said abilities. The chitosan-tetraethyl-orthosilicate films were found to be the most effective against both types of bacterial growth and attachment. However, the chitosan-glutaraldehyde films showed little-to-no antibacterial ability, suggesting the antibacterial mechanism may be affected by the cross-linking reagent.
Finally, a prototype for a smart wound dressing device that incorporates a pH sensitive sensor for chronic wounds was designed and developed using the chitosan-based films. The device utilised chitosan’s natural swelling ability and colloidal photonic crystal technology to create an indicator that produced a visual colour change in response to fluctuating pH levels, which may occur in chronic wounds. The mechanism was based on the distortion of photonic crystal layers by the swelling of the chitosan-based films to give a distinct red to green colour change. This preliminary study shows the potential of chitosan /photonic crystal-based sensors for use in medical devices that do not require an external power source to operate.
Description
Keywords
Chemistry , Polymers , IPN , Chitosan , Sorption , Antibacterial , Swelling , Tensile , Synthesis , Wound , Casting
Citation
Pemble, O. J. 2022. The design, synthesis and characterisation of selected chitosan-based thin films and studies of their use as materials for antimicrobial, heavy metal adsorption, and wound dressing applications. PhD Thesis, University College Cork.