3D printed agar/ calcium alginate hydrogels with high shape fidelity and tailorable mechanical properties

In this study, calcium alginate/agar (CA/Ag) 3D structures were printed as strip assembles with high resolution and tailorable mechanical properties by a thermal-assisted 3D printing method. Specifically, alginate and agar were combined to minimize the Barus effect, and further improved the printing resolution. The introduction of agar altered the rheological properties of the ink, such as increasing its viscosity to obtain a 3D printing structure with higher precision. The alginate chains were crosslinked by calcium ions, which connected different layers together and had good interface adhesion among layers in 3D printing constructs. In addition, after printing, the crosslinking of calcium alginate affected the swelling behavior and mechanical properties of printing gels. The width of extrusion gel stripes was close to the diameter of needle, demonstrating that the printing resolution is well controlled by minimizing the Barus effect of concentrated solution. Furthermore, the printed gel structures showed low cytotoxicity, indicating that these biocompatible 3D printed structures are promising substitutes for tissue engineering. Most importantly, soft polyacrylamide (PAAm) network was introduced into 3D printed CA/Ag hydrogels to toughen interfacial surfaces between adjacent stripes by combination of rigid calcium alginate network and soft PAAm network. These 3D printed hydrogels with excellent mechanical properties, high compatibility and high shape fidelity can be regarded as a potential candidate in bio-medical field.