Prof. Yongjun Zhang's research focuses on some long-existing fundamental problems associated with hydrogel biomaterials, i.e., the slow response of hydrogel sensors, how to achieve zero-order drug release, and the difficulty in multicellular spheroid production. To solve these problems, we proposed new optical sensing methods based on miniature gels, instead of macroscopic gels. Novel glucose optical sensors with fast response were fabricated. We developed dynamic layer-by-layer assembled films as platform for zero-order drug release. Zero-order release of many drugs, including anticancer and peptide drugs, was achieved. We also designed new hydrogel materials for the fabrication of multicellular spheroids. Monodisperse multicellular spheroids were produced in a massive and controllable way.