Hydrogels as three-dimensional scaffold materials in tissue engineering and as organoid platforms

The field of tissue and organoid engineering is directly influenced by the advances made in biomaterial systems and depends fundamentally on the synthesis, composition, fabrication, and inherency of native tissues. Hydrogels are defined as water-based polymers with superior mechanical and biological properties and thus are an attractive choice as scaffolds and three-dimensional (3D) constructs for tissue engineering and organoid culture. Hydrogels mimic the natural matrix-like microenvironment and can promote in vitro and in vivo cell adhesion, migration, and proliferation, leading to de novo tissue growth. Hydrogels are easy to handle, undergo a relatively mild fabrication process, and have highly tunable chemical properties allowing their use in a wide range of applications. In this book chapter, we first briefly classify and characterize the hydrogels, and then discuss the different types of naturally and synthetically derived hydrogels used as 3D scaffolds, including 3D cultures.