Design and fabrication of dual-material honeycomb structures with enhanced magneto-responsive shape memory effect by 4D printing

Four-dimensional (4D) printing of magneto-responsive shape memory structures has triggered significant research enthusiasm in bone tissue engineering applications due to the possibility for minimally invasive surgery. Herein, magneto-responsive polylactic acid/thermoplastic polyurethane/Fe₃O₄ (P/T/F) composites with fillers were firstly developed. By adding thermal conductive fillers, the thermal conductivity was greatly improved and the shape recovery time shortened from 50 s to 38 s under external magnetic field. Subsequently, dual-material honeycomb structure using P/T and P/T/F/boron nitride (BN) fillers were designed and 4D-printed. A cold-programmed shape fixing under compression force and magneto-recovery cycle was established. Microstructural observation showed that alternative deposition based on the same polymeric matrix obtained a good interfacial adhesion. More importantly, the dual-material honeycomb achieved good shape recovery effect and comparable mechanical performance. The P/T/F/BN(4)-P/T(2) honeycomb completed the magnetic shape recovery time in 70 s with a shape recovery ratio above 93 %, while pure P/T honeycomb was unable to conduct shape response under magnetic field. Lastly, an interlocking design between dual-material layers was proposed to further accelerate the shape recovery process within 55 s, which indicated an effective strategy. Above all, the current research has highly attractive feature to design and fabricate intelligent composites for biomedical applications.