Thermoreversible ABC Polypeptoid Hydrogels The ABC copolypeptoids [i.e., poly(N-allylglycine)-b-poly(N-methylglycine)-b-poly(N-decylglycine) (AMD)] exhibit rapid and fully reversible sol-gel transition with a narrow transition window. The gelation temperature (Tgel) and mechanical stiffness of the hydrogels are highly tunable: Tgel in the 27.2-60.0 C range, the storage modulus (G’) and Young’s modulus (E) in the 0.2-734 Pa and 0.6-2207 Pa range respectively at the physiological temperature (37 C) can be readily accessed by controlling the block copolypeptoid composition and the polymer solution concentration. Preliminary study showed that the hydrogels exhibit minimal cytotoxicity towards human adipose derived stem cells (hASCs) and revealed biological activity in inducing chondrogenesis of hASCs. The enzymatic activity of horseradish peroxidase (HRP) remain unperturbed after encapsulation in the hydrogel at 37 C for up to 7 d. All the results render our hydrogel a highly promising synthetic platform for tissue engineering or protein storage applications. Cryo-SEM image of hydrogel Sunting Xuan