(499a) Fabrication of Lignin-Based Hydrogels with Enhanced Material Properties

Given its biodegradability, antimicrobial properties, chemical activity, and economic appeal, lignin has garnered attention for use in the fabrication of sustainable materials. However, the heterogenous nature of lignin poses a barrier to our understanding of how the introduction of lignin alters the network structure, obfuscating our ability to intelligently tune mechanical and transport properties of these soft composites to a specific application. In response, we have fabricated a collection of lignin–poly(vinyl alcohol) (PVA) hydrogel composites were synthesized using Kraft lignin (raw, unfractionated lignin), as well as lignin that was cleaned and fractionated into lignin of prescribed molecular weights. While the molecular weight (MW) of the PVA was held constant at 133,000 g/mol, both the lignin content and lignin MW were varied. Specifically, the lignin content was varied between 0 mass % and 60 mass %, while the lignin MW was varied between approximately 6,000 g/mol and 160,000 g/mol. Further, these soft composites were synthesized using two fabrication routes: (1) the “Freeze-Thaw” method, whereby physical crosslinks between PVA chains are created and (2) chemical crosslinking, whereby permanent, covalent bonds between PVA and lignin are created.

To elucidate the impact of the lignin in the network structure and material properties, both the transport and mechanical properties of the soft composites were investigated. Specifically, the transport properties were explored via performing equilibrium water uptake, methylene blue permeability, and poroelastic relaxation indentation experiments. Furthermore, the hydrated Young’s modulus of each soft composite was characterized via mechanical indentation. Results from this portion of the study highlighted the improved transport properties achieved without compromising the mechanical robustness of the soft composites.

Finally, the prospect for the use of these materials in biomedical applications such as tissue engineering and cartilage repair, biocompatibility was tested. Specifically, the antimicrobial and antioxidant properties, as well as the cytotoxicity were examined. For the antimicrobial studies, the inhibitory effects of lignin on the growth of E.coli were explored. Preliminary data suggested that the growth of bacterial colonies was hindered as the lignin concentration was increased. To examine the cytotoxicity of the soft composites, neuroblastoma cells were seeded on the surface of the lignin hydrogels and the growth was monitored over the course of a few days. However, to date, the results of these cytotoxicity studies are inconclusive.