Polyurethane (PU) elastomers have great potential to work as flexible substrates in electronic materials. In this work, hyperbranched PU elastomers are designed and prepared utilizing dipentaerythritol, isophorone diisocyanate, and polytetrahydrofuran as the monomers. The mechanical properties and transparency of the PU elastomers are regulated by the molar ratio of hydroxyl group to isocyanate group (-OH/-NCO). High tensile strength (26 MPa) and elongation at break (>600%) are achieved. Furthermore, PU elastomer composites are developed by introducing graphene into the surface of PU elastomers. PU elastomer composites are further utilized in assembling flexible strain sensors, which achieve a gauge factor (GF) of 170 in the strain range of 0-75% and a GF of 549 in the strain range of 75-225%. The response time is as low as 140 ms and at least 1000 reversible sensing cycles are successfully conducted. Utilizing such flexible sensors, monitoring of various human motions, including biceps motion, finger bending, knee joint bending, elbow bending, and vocal cord vibration, are demonstrated. Overall, this work not only develops a new kind of PU elastomer with hyperbranched structure but also provides candidate materials for flexible sensors and other flexible electronic devices.

Traditional synthetic hydrogels for flexible electronic devices are mostly derived from nonsustainable polymers, resulting in environmental pollution. Herein, scalable, moldable, and stretchable ionic hydrogels are synthesized utilizing two model biopolymers, κ-carrageenan (κ-CG) and amylopectin (Amy). In such hydrogels, physically cross-linked κ-CG networks work as a relatively rigid component to maintain the shape of hydrogels, Amy networks cross-linked by borate/cis-diol dynamic covalent bonds help to improve the stretchability, and ZnSO4 is introduced as an ionic conductive component. The hydrogels, denoted as κ-CG/Amy/Zn2+ hydrogels, exhibit acceptable stretchability (>100%) because of the special cross-linking structure and ionic conductivity (2.9 S·m–1) due to the existence of various ions. Flexible mechanosensors (resistive strain sensors and capacitive pressure sensors) are demonstrated utilizing κ-CG/Amy/Zn2+ hydrogels, and high gauge factors (0.76 for strain sensors and 0.77 kPa–1 for pressure sensors) are achieved. Interestingly, κ-CG/Amy/Zn2+ hydrogels also work as quasi-solid-state electrolytes in zinc-ion hybrid supercapacitors, which exhibit an initial specific capacity of 47.4 mAh·g–1 at a current density of 3 A·g–1 and stable charge/discharge ability in more than 42,000 cycles. The sustainable biopolymer hydrogels may provide promising eco-friendly materials for future wearable devices and energy storage systems.

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