Hydrogel Ink for 3D Printing with High and Widely Tunable Mechanical Properties via the Salting‐Out Effect

Due to the difficulty of simultaneously ensuring printability and controlling their mechanical properties, 3D printed hydrogels thus far have low modulus, far less than that of many biological tissues and organs. Therefore, their feasibility toward various biomimetic applications is currently limited. Herein, Direct‐Ink‐Writing (DIW) based 3D printable hydrogel ink with broadly adjustable mechanical properties is introduced. The salting‐out effect is utilized to effectively lower the gelation temperature of hydrogel inks with a wide range of modulus (0.193–1.072 MPa), making them all 3D printable. As a proof of concept, multi‐layered synthetic blood vessels that mimic the mechanical properties of biological blood vessels are printed, and their practicability toward surgical training is demonstrated. The versatility and simplicity of this technique make it highly promising for use in various 3D‐printed hydrogel biomaterials applications. The salts that exhibit a salting‐out effect control the behavior of Pluronic F‐127(PF127) micelles, thereby offsetting the decrease in viscosity(printability) caused by an increase in monomer content in the 3D printable hydrogel ink. Accordingly, the mechanical properties of PF127‐based hydrogel ink are greatly improved by the salting‐out effect and can also be adjusted as desired.