Hydrogels as an emerging engineering platform for immobilizing cells or enzymes

Possessing superior water retention capacity, exceptional biocompatibility, and versatile design flexibility, hydrogels have emerged as a prominent engineering platform for cell and enzyme immobilization. The core advantage of hydrogels lies in the structure-activity relationship between their physicochemical properties-governed by crosslinking mechanisms and fabrication techniques-and the biological performance of the immobilized biocatalysts. This relationship is central to constructing microenvironments that either promote cell proliferation or stabilize enzymatic reactions. This paper systematically reviews this structure-activity paradigm, emphasizing how raw material selection and manufacturing technologies determine hydrogel functionality. We further analyze the critical design criteria for immobilization-oriented hydrogels, which must balance physical performance, support biological activities, and exhibit environmental adaptability. Distinct design requirements for the immobilization of living cells versus enzymes are explicitly compared. Building upon this foundation, the review elaborates on the unique application value of this technology in medical diagnostics, therapeutics, biosensors, industrial biotransformation, and environmental remediation. Finally, we identify core challenges and propose a concrete development roadmap to provide more efficient and stable engineering solutions for related fields.