3D printing of high-strength chitosan hydrogel scaffolds without any organic solvents.

3D printing of chitosan hydrogels has attracted wide interest because of their excellent biocompatibility, antibacterial activities, biodegradability, zero toxicity and low cost. However, chitosan inks are often involved in toxic and organic solvents. Moreover, the recently reported 3D-printed chitosan scaffolds lack enough strength, thus limiting their use in tissue engineering. Here, we reported a chitosan ink obtained by dissolving chitosan into an alkali aqueous solution. This chitosan ink is a stable solution at low temperature (5 °C), but once heated, the chitosan chains self-assemble to lead to gelation. Based on this principle, a corresponding direct ink writing (DIW) method was developed to print high-strength chitosan hydrogels. Specifically, the chitosan ink was extruded into heated deionized water to complete the in situ gelation. The temperature of the nozzle and hot water was well controlled to keep the printing process stable. The rheological behavior of the chitosan ink was investigated and the printing parameters were systematically studied to print chitosan hydrogel scaffolds with high quality and high strength. Based on these, high-strength (2.31 MPa for compressive strength) and complex chitosan hydrogel structures can be directly printed. The cell culture and the wound healing results further show that the printed chitosan scaffolds with this method have great potential in tissue engineering.