Engineering the Cell Microenvironment Using Novel Photoresponsive Hydrogels.

In vivo, cells are located in a dynamic, three-dimensional (3D) cell microenvironment, and various biomaterials have been used to engineer 3D cell microenvironments in vitro to study the effects of the cell microenvironment on the regulation of cell fate. However, conventional hydrogels can only mimic the static cell microenvironment without any synchronous regulations. Therefore, novel hydrogels that are capable of responding to specific stimuli (e.g., light, temperature, pH, and magnetic and electrical stimulations) have emerged as versatile platforms to precisely mimic the dynamic native 3D cell microenvironment. Among these novel hydrogels, photoresponsive hydrogels (PRHs) that are capable of changing their physical and chemical properties after exposure to light irradiation enable the dynamic, native cell microenvironment to be mimicked and show great promise in deciphering the unknown mechanisms of the 3D cell microenvironment in regulating the cell fate. Several reviews have already summarized the advances of PRHs and have focused on specific photosensitive chemical groups and photoresponsive elements or on the reaction categories and mechanism of PRHs. However, a holistic view of novel PRHs, which highlights the multiple physical and chemical properties that can be tuned by remote light activation, as well as their applications in engineering a dynamic cell microenvironment for the regulation of cell behaviors in vitro is still missing and is the focus of this review.