3D Printing Mechanically Robust and Transparent Polyurethane Elastomers for Stretchable Electronic Sensors.

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, IBOA) to prepared resins with a low viscosity for a digital light processing (DLP) 3D printer without custom equipment. Results showed that the photocurable 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 cycles extreme deformations of 80%compression cycles of 80% at high 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 (approximately 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 scope of application.