Continuous Stereolithography 3D Printing of Multi-Network Hydrogels in Triply Periodic Minimal Structures (TPMS) With Tunable Mechanical Strength for Energy Absorption

A fast additive manufacturing (AM) protocol to fabricate multi-network hydrogels is reported in this work. The gas-permeable PDMS film creates a polymerization-inhibition zone, facilitating the continuous stereolithography (SLA) 3D printing of hydrogels. The fabricated multi-bonding network integrates the rigid covalent bonding and the tough ionic bonding. The elastic modulus and strength could be effectively tuned by varying the ratio between the covalent and ionic bonding networks to fulfill various loading conditions. The printed triply periodic minimal structures (TPMS) hydrogels demonstrated high compressibility for up to 80% recoverable strain. Moreover, the dried TPMS hydrogels show novel energy absorption properties. We fabricated uniform and gradient hydrogels and compared their energy absorption capability. The anisotropy and quasi-isotropy behavior of TPMS structures were analyzed using simulation studies, providing insights into designing and controlling the TPMS structures for energy absorption. The results showed that the gradient TPMS hydrogels are preferable energy absorbers and have potential applications in impact resistance and absorption.