Protocol to culture cells on genipin-mixed collagen gels with different stiffnesses

The stiffness of extracellular matrices is critical for cellular functions such as growth and differentiation. Here, we present a protocol for culturing cells on stiffness-modulated collagen gels by adding genipin, an amine crosslinker with low cytotoxicity. We describe the steps for preparing collagen gels with genipin, culturing the cells, and immunofluorescent staining of the cells on the gels. This protocol has potential applications in the analysis of function or protein/gene expression in cultured cells on extracellular matrices of different stiffnesses. For complete details on the use and execution of this protocol, please refer to Ishihara et al.¹.