Engineering Functionality in Hydrogels

Hydrogels are soft polymer networks whose mechanical and functional properties can be tuned by chemical design. The objective of this thesis was to introduce specific functionalities into different hydrogel systems and to evaluate their effect on network mechanics. To this end, Polyethylene glycol – Peptide nucleic acid (PEG-PNA), Polyethylene glycol – Dopamine methacrylate (PEG-DMA) and polyhydroxyethyl methacrylate - Rose Bengal octyl ester (pHEMA - RB) hydrogels were synthesised and characterised using rubber elasticity theory and the Mooney-Rivlin model, enabling quantitative analysis of crosslink density and molecular weight between crosslinks. The results indicate that functionalisation alters network homogeneity and elasticity. In PEG-PNA gels, base-pairing interactions reduced elasticity but may provide a route towards self-healing at higher concentrations. PEG-DMA gels displayed catechol-driven self-adhesiveness with increased network heterogeneity, and pHEMA-RB enabled immobilisation of photoactive molecules within the network while maintaining a large accessible surface area. In addition, this work presents a PEG-Chitosan double-network hydrogel crosslinked with sodium hexametaphosphate (SHMP), which showed pronounced Mullins-type energy dissipation and results were compared to a well-known PEG-Alginate system.
These findings demonstrate that functionalisation introduces both desired properties and changes in network architecture. The thesis provides design principles for tailoring functional hydrogels with potential applications ranging from self-adhesive and catalytic active systems to tough and energy-dissipating materials and thus offering design principles for future functional and application-oriented hydrogels.