Tetrakis (hydroxymethyl) phosphonium sulfate is a protein crosslinker and hydrogel modifier. Tetrakis (hydroxymethyl) phosphonium sulfate covalently binds to primary and secondary amines of amino acids or proteins via a Mannich-type reaction, thereby constructing stable crosslinking bonds between protein molecules. Tetrakis (hydroxymethyl) phosphonium sulfate not only regulates the gelation time and storage modulus of recombinant elastin-like protein hydrogels, but also exhibits excellent cytocompatibility, and supports the differentiation and growth of embryonic stem cells and neural cells in a three-dimensional encapsulation environment. Tetrakis (hydroxymethyl) phosphonium sulfate is suitable for protein-based hydrogel systems, especially for applications related to cell encapsulation[1].