# Thiol‐Methylsulfone Crosslinked Hydrogels for Cell Encapsulation: Molecular Scale Modulation of Physiochemical Properties

## TL;DR

This paper introduces a new hydrogel system for cell encapsulation with improved gelation speed and cell distribution.

## Contribution

A new TzMS hydrogel variant with electron-withdrawing substituent enables faster and more controllable cell encapsulation.

## Key findings

- The new PEG4-CONH-TzMS hydrogel variant shows faster gelation and easier mixing of precursors.
- The hydrogel provides homogeneous cell distribution and high enzymatic stability.
- The electron-withdrawing substituent improves synthesis and reaction rate control.

## Abstract

Hydrogels mimicking the mechanical and biochemical features of the cellular microenvironment allow cell encapsulation and facilitate in vitro 3D culture. In addition to biocompatibility and reactivity in physiological conditions, a key criterion for crosslinking chemistry is appropriate gelation kinetics to allow mixing and homogeneous distribution of cells with the hydrogel precursors. We have previously presented aryl methylsulfone/thiol (MS/SH) reaction as a thiol‐reactive cross‐linking system for cell encapsulation in star polyethylene glycol (PEG4) hydrogels with a gelation kinetics in minutes time scale. Remaining experimental challenges for this system are a finer modulation of gelation kinetics and streamlining the synthesis of the prepolymer. Here we present the possibility to tune the gelation kinetics by introducing an electron‐withdrawing substituent at p‐position of the aryl MS ring. This variant also presents synthetic advantages. We study the influence of the p‐substituent on the physicochemical properties of MS/SH crosslinked hydrogels, and their performance for cell encapsulation. We compare these properties with the PEG‐MS variant containing an electron‐donating linker. The new star poly(ethylene glycol)‐4‐(5‐(methylsulfonyl)‐1H‐tetrazol‐1‐yl)benzamide (PEG4‐CONH‐TzMS) shows superior properties as cell encapsulating hydrogel in terms of ease of mixing polymer precursors, faster gelation, homogenous cell distribution and high enzymatic stability.

We have synthesized a new variant of tetrazole methylsulfone (TzMS) precursor as a thiol‐reactive cross‐linking system for homogenous cell encapsulation in star poly(ethylene glycol) with gelation kinetics in minutes time scale. Our strategy entailed introduction of an electron‐withdrawing substituent at p‐position of the TzMS ring to fine tune the reaction rates and streamline the synthesis of the prepolymer.