Date of Award

Summer 8-16-2024

Level of Access Assigned by Author

Open-Access Thesis

Language

English

Degree Name

Master of Science (MS)

Department

Biological Engineering

Advisor

Michael Mason

Second Committee Member

Deborah Bouchard

Third Committee Member

Evan Wujcik

Additional Committee Members

Raymond Kennard

Abstract

The aquaculture industry faces significant economic losses due to disease, with global finfish production losses exceeding $6 billion annually. 1 Vaccination is a critical strategy for disease management. However, the current use of oil-based vaccines is linked to negative side effects, including internal adhesions and reduced growth rates in fish. 2 Recent advancements in biomaterial vaccines present a promising alternative to traditional oil-based adjuvants, offering the potential to enhance vaccine safety and efficacy.3 Injectable hydrogels are an established method of delivering nutrients and drugs.4 Biopolymers sourced from natural plant matter have been explored for various drug, nutrient, and cosmetic applications. The most abundant biopolymer, cellulose, is commonly sourced as softwood pulp. Through further mechanical fibrillation in a refiner, 90% of this pulp reaches a fiber size of hundreds of microns or smaller.5 This mechanically refined material is referred to as cellulose nanofibrils (CNF). Due to the presence of the surface hydroxyl groups, surface modifications to these fibers are commonly performed to tailor the material’s mechanical properties. One example of a CNF modification is (2,2,6,6-tetramethylpiperidine-1oxyl radical)- (TEMPO) mediated oxidation.6 The C6 hydroxyl group is replaced with a negatively charged carboxylic acid group. The fiber size decreases partially due to this change in fiber surface charge. 7 The final material (TCNF) is a clear gel when homogenously dispersed at low weight percentages in water. Like unmodified CNF, TCNF is hydrophilic, causing the matrix to degrade when introduced to an aqueous environment.6 Crosslinking between fibers ensures that the hydrogel matrix will stay intact after it is administered to the salmon. The bolus inside the fish's peritoneal cavity, including its vaccine payload, can interact with its immune system until the salmon reaches harvestable size. Salt-crosslinked TCNF hydrogels (NaCl, KCl, CaCl2, MgCl2, SrCl2), are novel to the aquaculture industry. Rheological testing with a cone and plate rheometer revealed a shear-thinning flow behavior beneficial for this injectable application.8 The hydrogel diffusion, and particle movement out of these hydrogels were analyzed using a custom UV-Vis spectrophotometer. Diffusion experiments showed that the diffusion behavior of various hydrogel payloads can be modeled, and diffusion coefficients can be extracted from experimental data. An in vivo Atlantic salmon trial was completed to examine salmon’s reaction to the sodium and calcium crosslinked material to test the hydrogel's efficacy as a vaccine adjuvant. Low internal adhesion scores, acceptable fish condition factors, and no mortalities were found across all salt crosslinked TCNF formulations examined. This research is funded by the USDA NIFA’s AFRI Foundational and Applied Science Program and is in collaboration with the University of Maine Cooperative Extension Diagnostic Research Laboratory.

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