Self-Supporting Nanoclay as Internal Scaffold Material for Direct Printing of Soft Hydrogel Composite Structures in Air

Three dimensional (3D) bioprinting technology enables the freeform fabrication of complex constructs from various hydrogels and is receiving increasing attention in tissue engineering. The objective of this study is to develop a novel selfsupporting direct hydrogel printing approach to extrude complex 3D hydrogel composite structures in air without the help of a support bath. Laponite, a member of the smectite mineral family, is investigated to serve as an internal scaffold material for the direct printing of hydrogel composite structures in air. In the proposed printing approach, due to its yield-stress property, Laponite nanoclay can be easily extruded through a nozzle as a liquid and self-supported after extrusion as a solid. Its unique crystal structure with positive and negative charges enables it to be mixed with many chemically and physically cross-linked hydrogels, which makes it an ideal internal scaffold material for the fabrication of various hydrogel structures. By mixing Laponite nanoclay with various hydrogel precursors, the hydrogel composites retain their self-supporting capacity and can be printed into 3D structures directly in air and retain their shapes before cross linking. Then, the whole structures are solidified in situ by applying suitable cross-linking stimuli. The addition of Laponite nanoclay can effectively improve the mechanical and biological properties of hydrogel composites. Specifically, the addition of Laponite nanoclay results in a significant increase in the Young's modulus of each hydrogel Laponite composite: 1.9 -fold increase for the poly(ethylene glycol) diacrylate (PEGDA) Laponite composite,7.4-fold increase for the alginate Laponite composite, and 3.3-fold increase for the gelatin Laponite composite.