Choline-based hydrogels and deep eutectic solvent systems for next-generation biomedical platforms: a review

Quaternary ammonium containing hydrogels have been widely investigated for antimicrobial and drug delivery applications, yet concerns related to cytotoxicity, limited biodegradability, and environmental persistence remain unresolved. This review examines the development of choline (Cho)-based hydrogels and deep eutectic solvent (DES) systems from a polymer design perspective. Cho, an endogenous quaternary ammonium compound, has recently emerged as a viable alternative ionic component in polymer networks. The main emphasis is on the Cho/its salt derivatives for enhancing network formation, mechanical behavior along with swelling, and transport characteristics of hydrogel. Cho-derived DES are discussed as functional media capable of enhancing the solubility and stability of poorly water-soluble drugs while modifying polymer microstructure. Several recent studies on injectable, self-healing, and stimuli-responsive eutectogels are evaluated in relation to their structure & property relationships. Various applications in controlled drug delivery and wound repair are also considered to demonstrate the influence of ionic network design on antimicrobial activity, moisture regulation, and diffusion-controlled release. Different challenges, such as hygroscopicity, leaching risk, and mechanical reinforcement, are also addressed.