Fabricating Tunable Polyacrylamide Hydrogels To Study Matrix Stiffness Effects On Stem Leydig Cells.

Extracellular matrix (ECM) stiffness critically regulates stem cell behavior. Previously, we demonstrated that pathological increases in matrix stiffness during aging disrupt stem Leydig cell (SLC) homeostasis, leading to a decline in testosterone. Building on this discovery, we here present a detailed protocol-originally developed in our laboratory-for fabricating polyacrylamide (PA) hydrogels with tunable stiffness to model the testicular microenvironment in vitro. This method enables reproducible casting of gels across a stiffness range of 1-100 kPa, covering physiological to pathological conditions. Key steps include precise mixing of acrylamide/bis-acrylamide, gel swelling equilibration, surface activation with Sulfo-SANPAH, and collagen coating to support SLC adhesion and culture. We provide optimized formulations for target stiffnesses and troubleshooting guidance for common issues such as incomplete polymerization and poor cell attachment. This system allows systematic investigation of how substrate stiffness modulates SLC proliferation, differentiation, and steroidogenic function under defined 2D conditions. Beyond reproductive biology, it also serves as a valuable platform for mechanobiological studies in other cell types and for screening therapeutics targeting stiffness-related dysfunction.