Thiol-methylsulfone-based Hydrogels for Cell Encapsulation: Reactivity Optimization of Aryl-methylsulfone Substrate for Fine-tunable Gelation Rate and Improved Stability

Abstract

Hydrogelsare widely used as hydrated matrices for cell encapsulation in a number of applications, spanning from advanced 3D cultures and tissue models to cell-based therapeutics and tissue engineering.Hydrogel formation in the presence of living cells requires crosslinking reactions that proceedefficiently underclose to physiological conditions.Recently, the nucleophilic aromatic substitution ofphenyl-oxadiazole(Ox)methylsulfones (MS)by thiolswas introduced as a new crosslinking reaction for cell encapsulation. Reportedpoly(ethylene glycol) (PEG)-based hydrogels featuredtunable gelation times within secondsto a fewminuteswithin pH 8.0to 6.6and allowedreasonably goodmixing with cells. However, their rapiddegradation prevented cell cultures to be maintained beyond 1 week.In this article, we presentthereactivityoptimizationof the heteroaromatic ring of the MS partnerto slow down the crosslinking kineticsand the degradability of derived hydrogels.NewMS substrates based on phenyl-tetrazole(Tz) and benzothiazole (Bt) rings,withlowerelectrophilicity than Ox,were synthesized by simple pathways. When mixed with PEG-thiol, the novel PEG-MSextended the working time of precursor mixtures and allowed longer term cell culture.Tz-based MS substratewas identified as the best candidate as it is accessible by simple chemical reactions from cost-effective reactants, hydrogel precursorsshow >3 monthsstability in aqueous solution, and the derived Tz gelssupport cell culturesfor> 2 weeks. The Tzsystem also shows tunable gelation kinetics within seconds to hoursand allowscomfortable manipulation and cell encapsulation. Our findings expand the toolkit of thiol-mediated chemistryfor the synthesisofhydrogelswith improvedproperties for laboratory handling and future automatization.