Revisiting the biophysical aspects of extracellular-matrix-mimicking hydrogels: what cells see what cells feel.

The extracellular matrix (ECM) is critical in regulating cell behavior and tissue function. This recognition has driven the development of ECM surrogates to better understand cell-ECM interactions and advance biomedical applications. Hydrogels are promising candidates for this purpose due to their biocompatibility, tunability, and ability to embed cells in 3D environments. While early efforts in the design of ECM-mimicking hydrogels focused on macromolecular type, it is now clear that their biophysical parameters, such as polymer molecular weight, fibrous non-fibrous structures, pore size, and mechanical properties, significantly influence cell behavior. Understanding the interplay of these factors is crucial for the rational design of biomaterials, but remains challenging given the complexity of hydrogel systems and the rapid pace of new findings. This review critically evaluates hydrogels as ECM mimics for 3D cell cultures. We revisit key ECM properties to replicate, examine how hydrogel design can meet these needs, and summarize the impact of biochemical, structural, and mechanical features on cell behavior. We also explore how structural and mechanical properties-what cells "see" and "feel"-are interrelated and jointly affect cell function. Our analysis concludes that strategic combinations of polymeric materials will play an important role for next-generation hydrogels to replicate physiological conditions and independently enable precise control over key parameters. These advancements will enhance our understanding of cell-ECM interactions and support the development of innovative biomaterials for tissue engineering and regenerative medicine.