Material Processing of Aceal-Modified Cellulose for the Creation of Solubility Switching Fibers

Abstract

Absorbable sutures have become a popular modern solution to wound care. Sutures are generally categorized as being synthetic or natural, and absorbable or nonabsorbable. Natural absorbable sutures are degraded by hydrolytic enzyme activity mediated by the immune system. They have the potential to be more reactive in patients due to the immune system’s heightened recognition of non-native proteins. Synthetic absorbable sutures are made of polymers and have the advantage of having wide ranges of degradation time based on the applied material processing techniques used to create the fibers. These fibers are degraded via hydrolysis reactions with water present in and around wound areas. The hunt for new suture materials is a continuous area of advancement in biomedicine. Polysaccharides show promise to be used as suture material due to their non-protein natural origin and propensity for chemical modification. Cellulose is the most abundant biopolymer on earth and a polysaccharide that is especially promising for fiber applications due to its structural nature. The modification of interest includes solubility switching, which makes a polysaccharide, once modified, become insoluble until it interacts with a trigger, becoming soluble again. Acetal modification is promising due to its reversible nature. A polymer modified with an acetal will degrade in the presence of acid. The intention of this project was to modify cellulose with acetal groups and use modified cellulose to create fibers similar to what would be applicable in a suture. The modification of cellulose starts with its dissolution. Cellulose is not natural soluble in most solvents due to its inter and intra molecular hydrogen bonding and amphipathic nature. The process to dissolve cellulose requires soaking in a solvent exchange through water, methanol, and N, N-dimethylacetamide. One soaked, the cellulose is dissolvable in a lithium chloride and N, N-dimethylacetamide solution. The modification of the dissolved cellulose was conducted with 2-methoxypropene with a camphor sulphonic acid catalyst. The resulting acetal modified cellulose (Ac-Cell) was insoluble in water. The modification was confirmed with NMR spectroscopy. Other properties such as degradation in the presence of acid were also tested. The creation of a wet-spinning set up to elongate the Ac-Cell into fibers required inspiration from modern industrial fiber creation practices. Three different set ups for wet spinning were tested for ease of collection, consistency, and fiber properties such as thickness. Adjustments were made between iterations of the lab scale wet spinning procedure by taking inspiration from other fields such as plumbing and aeronautics to create more consistent fluid flow and less eddying. The fibers produced by wet spinning were evaluated under optical microscopes and a scanning electron microscope to evaluate uniformity, surface consistency, and size. Films of Ac-Cell were also produced and evaluated with scanning electron microscopy. The goals of this project were completed. A procedure for repeatable dissolving cellulose was optimized and the dissolved cellulose was successfully modified. The Ac-Cell was able to produce films, and more relevantly, fibers. The production of fibers, along with the proven degradation of the material, indicates a possible future use in biomedical applications such as absorbable sutures.