Simple Preparation of Injectable Hydrogels with Phase-Separated Structures That Can Encapsulate Live Cells

Injectable hydrogels are biomaterials that can be administered minimally invasively in liquid form and are considered promising artificial extracellular matrix (ECM) materials. However, ordinary injectable hydrogels are synthesized from water-soluble molecules to ensure injectability, resulting in non phase-separated structures, making them structurally different from natural ECMs with phase-separated insoluble structural proteins, such as collagen and elastin. Here, we propose a simple material design approach to impart phase-separated structures to injectable hydrogels by adding inorganic salts. Injecting a gelling solution of mutually cross-linkable tetra-arm poly(ethylene glycol)s with potassium sulfate at optimal concentrations results in the formation of a hydrogel with phase-separated structures in situ. These phase-separated structures provide up to an 8-fold increase in fracture toughness while allowing the encapsulation of live mouse chondrogenic cells without compromising their proliferative activity. Our findings highlight that the concentration of inorganic salts is an important design parameter in injectable hydrogels for artificial ECMs.

Automated summary

Injectable hydrogels are promising artificial extracellular matrix materials that can be administered minimally invasively in liquid form. This study proposes a simple material design approach to introduce phase-separated structures to injectable hydrogels by adding inorganic salts. These phase-separated structures enhance the fracture toughness of the hydrogel and do not compromise the proliferative activity of encapsulated cells.