Biopolymer-Based Hydrogel Systems: Towards Advanced Wound Healing Materials from Marine Waste-Derived Resources

Collagen is a structural protein that forms a triple-helical fibrillar network that provides integrity and mechanical strength to various tissues, including skin, tendons, and bones. Type I collagen is the most abundant and widely used in biomedical applications due to its biocompatibility, biomimeticity, and recognition by cells as a key component of the extracellular matrix (ECM) [1]. Although collagen has been exploited in hydrogels, fibers, and composite biomaterials, large-scale applications are limited by high costs, ethical and religious concerns related to bovine and porcine sources, and challenges in recombinant production. Expanding the use of collagen-based devices requires identifying abundant, low-cost sources and developing suitable processing strategies for their valorization. This work focuses on extracting collagen from marine waste, such as swim bladders, due to their high premium-grade collagen content. Although previous studies have shown that collagen can be extracted from fish sources, the reported yields are generally relatively lower (from 6 to 68 % of the dry mass of the swim bladder) [2, 3]. Instead, the present work achieved a high yield of soluble collagen relative to the sturgeon swim bladder's dry weight, approximately 97 %. This method offers dual benefits: it provides access to a collagen-rich source and adds value to a by-product of the fish industry, creating a high-value biomedical device. This extracted collagen was then engineered to create two functional materials for biomedical applications. In Chapter 2, collagen was mixed with fish-skin-derived gelatin to create hydrogels for burn wound treatment. Gelatin was selected for its low cost, ready availability, and biodegradability, while retaining biomimetic properties similar to those of collagen [4]. However, unlike collagen, it exhibits low mechanical strength [5]. Therefore, the two proteins were combined to harness their advantages. The limitation that both proteins are liquid at 37 °C is overcome by crosslinking them with microbial transglutaminase, a biocompatible enzyme that forms covalent bonds between them. The swelling degree and mechanical properties of the hydrogels were optimized by adjusting the degree of crosslinking. This allowed the creation of materials with a wide range of swelling values (250 - 27071 %) and elastic modulus values (0.07 kPa - 10.56 kPa) that mimic those of various soft tissues in the human body. Rutin, a natural antioxidant flavonoid, was incorporated as a model drug to evaluate the system’s drug delivery potential and to target oxidative stress in burns. In vitro tests showed a burst release of antioxidants within 24 h, and consequent protection of HaCaT cells against oxidative stress. These hydrogels are proposed as potential wound dressings, and to that end, biocompatibility tests using red blood cells, HaCaT, and HFF-1 cells indicated no adverse effects. A model study of UV-B-induced mouse skin burns was used to evaluate wound-healing ability. Visual examination of the skin, combined with histological analysis and ELISA quantification of pro-inflammatory cytokines involved in the burn-healing process (TNF-α, IL-6, and IL-1β), clearly demonstrated the effectiveness of the tested samples in accelerating healing and reducing inflammation in damaged skin. Ex vivo studies were conducted using human skin models to further assess the wound-healing potential of the developed hydrogels; the results were discussed in Chapter 3. Specifically, cell viability was evaluated through LDH assays, inflammatory activity was analyzed by cytokine quantification (IL-6, IL-8, and IL-1α), and re-epithelialization capacity was assessed by immunostaining for keratin 17 and CD31. Overall, these outcomes suggest that the developed collagen and gelatin-based hydrogels are promising candidates for use as active wound dressings. In Chapter 4, collagen was mixed with carboxymethylcellulose (CMC) to create superabsorbent polymer (SAP) hydrogels, which are crosslinked, three-dimensional networks capable of absorbing water amounts far exceeding their own weight [6], making them highly relevant for applications ranging from hygiene products to biomedicine. The aim was to develop a fully bio-based SAP. Although synthetic, petroleum-based SAPs represent 90% of the SAP market due to their excellent swelling properties and cost-effectiveness, their persistence in the environment and their contribution to microplastic generation raise sustainability concerns. In this study, the highly hydrophilic CMC was combined with marine-derived collagen to develop fully biodegradable, polyacrylate-free SAPs. Carbodiimide (EDC) crosslinking was employed to stabilize the CMC-collagen matrix, thereby enhancing its structural integrity and water retention. The resulting hydrogels were characterized by FTIR, XRD, and SEM, confirming successful crosslinking and network formation. Swelling kinetics were assessed in various fluids, demonstrating high water uptake, reswelling capacity, and stability in simulated body fluids. Biodegradation in soil confirmed environmental safety, while biocompatibility tests on fibroblasts demonstrated suitability for biomedical applications. These results highlight the potential of marine waste valorization to produce eco-friendly SAPs that combine strong absorption capacity, biocompatibility, and biodegradability, aligning with the United Nations Sustainable Development Goals (UN SDGs).