Advanced stretchable electronic sensors with a complex structure place higher requirements on the mechanical properties and manufacturing process of the stretchable substrate materials. Herein, three kinds of polyurethane acrylate oligomers were synthesized successfully and mixed with a commercial acrylate monomer (isobornyl acrylate) to prepare photocurable resins with a low viscosity for a digital light processing three-dimensional (3D) printer without custom equipment. Results showed that the resin containing poly­(tetrahydrofuran) units (PPTMGA-40) exhibited optimal mechanical properties and shape recoverability. The tensile strength and elongation at break of PPTMGA-40 were 15.7 MPa and 414.3%, respectively. The unprecedented fatigue resistance of PPTMGA-40 allowed it to withstand 100 compression cycles at 80% strain without fracture. The transmittance of PPTMGA-40 reached 89.4% at 550 nm, showing high transparency. An ionic hydrogel was coated on the surface of 3D-printed structures to fabricate stretchable sensors, and their conductivity, transparency, and mechanical performance were characterized. A robust piezoresistive strain sensor with a high strength (∼6 MPa) and a wearable finger guard sensor were fabricated, demonstrating that this hydrogel-elastomer system can meet the requirements of applications for advanced stretchable electronic sensors and expand the usage scope.

Shape memory polymer (SMP)-based 4D printing combines the advantages of SMP and 3D printing to form active materials with delicate structure. Nowadays, studies of SMP-based 4D printing materials mainly focus on cross-linked (meth)­acrylate of which the permanent shape cannot be changed for their covalent linkage, limiting the usage of 4D printing materials. In this paper, a novel (meth)­acrylate monomer with an aldehyde group (2-(methacryloyloxy)­ethyl 4-formylbenzoate, MEFB) and hyperbranched cross-linker (HPASi) are synthesized to build (meth)­acrylate systems (IEMSis) with dynamic imine bonds for 4D printing. The flexible chain structure of HPASi significantly enhances the toughness of IEMSis, which is 33–97-fold higher than that of the one without HPASi (IEM). The addition of HPASi also endows IEMSis good shape memory properties, and the shape fixity and shape recovery ratios of them are 97.5–97.6 and 91.4–93.7%, respectively. At the same time, IEMSis can undergo a stress relaxation process by dynamic exchanges of imine bonds under relatively mild conditions without a catalyst to acquire an ability of permanent shape reconfiguration. The shape retention ratio of IEMSi3 is 84.3%. In addition, the 4D-printed structures displayed here indicate that these 4D printing systems have a myriad of potential applications including aerospace structures, soft robotic grippers, smart electron switches, and intelligent packaging, while the reconfigurability shown by IEMSi3 will expand the scope of application fields of 4D printing materials.

Taking advantage of unlimited geometry design, 3D printed sacrificial mold cast with highly conductive polymer composites is used to prepare a sensor with designed structures. However, the disposal of the mold in a mild condition while the refined structures can be maintained is still a challenge. Herein, a bifunctional monomer hydrolyzable hindered urea acrylate is synthesized to create a cross‐linked polymer network, preventing the dissolution of printed parts in the uncured resin. 3D printed scaffolds can be hydrolyzed in hot water, which provides an attractive option for sacrificial molds. Also, a porous flexible strain sensor (PFSS) is fabricated by casting polyurethane/carbon nanotubes composites into the sacrificial molds, which demonstrates a high stretchability (≈510%) and an excellent recoverability. Meantime, the pressure sensitivity (0.111 kPa−1) and a long‐term electrical resistance of PFSS is characterized. The resistance response signal remains nearly unchanged after 100 compressive loading cycles at a large strain of 60%. Benefiting from the design freedom of 3D printing, a practical application of the PFSS with a complex and customized structure to monitor human motion is demonstrated. These results prove that the sacrificial molding process has great potential for user‐specific stretchable wearable devices.

Fabricating biobased heat-resistant photoactive acrylates from aliphatic biomass for three-dimensional (3D) printing is a great challenge with enormous implications for energy saving and sustainable development of polymers. Herein, two fully biobased acrylate monomers with di-or tri-functionality (BHMP2 and BHMP3) are synthesized from renewable glycidyl methacrylate and succinic acid or itaconic acid through a one-step method under solvent-free condition. These monomers are then cured by digital light processing 3D printing without diluters. The influences of structure on the curing behavior and performances are systematically studied. The BHMP3 resin shows excellent thermal and mechanical properties. Specifically, its glass transition temperature and heat deflection temperature under 0.455 MPa reach up to 183 and over 250 °C, respectively, while its tensile strength, modulus, and hardness are as high as 45.2 MPa, 4480 MPa, and 0.49 GPa, respectively. The outstanding performances of BHMP3 resin result from its compact cross-linking structures. This work pioneers a sustainable way to produce heat-resistant photoactive acrylates from renewable low-cost aliphatic biomass for photocurable 3D printing.

As the 3D printing technology is getting more and more popular and useful, demands for materials for 3D printing have increased significantly. Cyanate ester (CE) resin possesses the characteristics of high heat distortion temperature and high glass transition temperature, outstanding mechanical properties, low dielectric constant, and excellent water uptake. However, CE resin has not been widely used in 3D printing of UV curing because it is difficult for photopolymerizable groups to graft onto the chains of CE resin. On the other hand, the glass transition temperature (T g) of the homopolymer of the tris­(2-hydroxyethyl)­isocyanurate triacrylate (THEICTA) outclasses that of other acrylates. Although THEICTA is particularly advantageous to prepare a UV-curing prepolymer with high glass transition temperature, it also cannot be directly used for fabricating heat-resistant 3D-printed parts because it is solid and adding diluents will reduce the thermal stability of printed objects. This study is unique in producing 3D-printed materials, in which the THEICTA tactfully dissolves in low viscosity (about 100 mPa·s under 25 °C) bisphenol E cyanate (BECy) without sacrificing two kinds of bulk material properties. In the process of 3D printing, the carbon–carbon double bonds from THEICTA are cured by radical polymerization. Postprinting thermal treatment transforms three cyanate groups to a triazine ring structure. Additionally, the two kinds of structures are interpenetrating. The high-performance 3D-printing material has potential in fields ranging from space flight and aviation to the automotive and electronic industry.