Rapid Volumetric Additive Manufacturing in Solid State: A Demonstration to Produce Water-Content-Dependent Cooling/Heating/Water-Responsive Shape Memory Hydrogels

Cryopolymerized Polyampholyte Gel with Antidehydration, Self-Healing, and Shape-Memory Properties for Sustainable and Tunable Sensing Electronics

Hydrogel-based wearable flexible electronics are attracting tremendous interest for use in human healthcare. However, many of the existing hydrogel electronics are often susceptible to dehydration, leading to weakened stretchability and inaccurate signal extraction. Besides, hydrogels are desired to be much smarter for self-repairing physical damage and enabling performance manipulation. Herein, we develop a kind of cryopolymerized polyampholyte gels with the multifunctionality of antidehydration, self-healing, and shape-memory for wearable sensing electronics. The antidehydration property is enabled by the incorporation of glycerol, endowing the sensing electronics with excellent stretchability and strain-sensing performance in long-term monitoring. The ionic bonds in the polyampholyte gel possess a dynamic feature regulated by alternant NaCl(aq) and H₂O treatments, laying the foundation for self-healing and shape-memory. As a result, the sensing electronics can automatically repair physical damages without any sacrifice in sensing performance, after healing both conductivity and strain-sensing performance could return to the initial levels. The shape-memory function enables the temporal adjustment of the initial state of the sensing electronics; both the conductivity and sensing performance, for instance, signal intensity, can be manually manipulated. In all, the cryopolymerized polyampholyte gels with antidehydration, self-healing, and shape-memory properties can be an inspiration to develop sustainable and tunable gel-based electronics for human motion monitoring.

Room-Temperature Solid-State UV Cross-Linkable Vitrimer-like Polymers for Additive Manufacturing

In this paper, a UV cross-linkable vitrimer-like polymer, ureidopyrimidinone functionalized telechelic polybutadiene, is reported. It is synthesized in two steps. First, 2(6-isocyanatohexylaminocarbonylamino)-6-methyl-4[1H]-pyrimidinone (UPy-NCO) reacts with hydroxy-functionalized polybutadiene (HTPB) to obtain UPy-HTPB-UPy, and then the resulted UPy-HTPB-UPy is cross-linked under 365 nm UV light (photo-initiator: bimethoxy-2-phenylacetophenone, DMPA). Further investigation reveals that the density of cross-linking and mechanical properties of the resulting polymers can be tailored via varying the amount of photo-initiator and UV exposure time. Before UV cross-linking, UPy-HTPB-UPy is found to be vitrimer-like due to the quadruple hydrogen-bonding interactions. The UPy groups at the end of the chain also enable for rapid solidification upon the evaporation of the solvent. The unsaturated double bonds in the HTPB chains enable UPy-HTPB-UPy to be UV cross-linkable in the solid state at room temperature. After cross-linking, the polymers have good shape memory effect (SME). Here, we demonstrate that this type of polymer can have many potential applications in additive manufacturing. In the cases of fused deposition modelling (FDM) and direct ink writing (DIW), not only the strength of the interlayer bonding but also the strength of the polymer itself can be enhanced via UV exposure (from thermoplastic to thermoset) either during printing or after printing. The SME after cross-linking further helps to achieve rapid volumetric additive manufacturing anytime and anywhere.