Multimaterial 3D Printing of Soft and Stretchable Electronics

The development of soft and stretchable microelectronics is critical for next-generation flexible devices, biointerfaces, and microscale energy systems due to their unique electrical and mechanical properties. However, current 3D printing methods, particularly two-photon polymerization (2PP), remain limited by low electrical conductivity, filler aggregation, and loss of optical transparency. Here, we present a multimaterial 2PP-compatible resin that integrates the conducting polymer PEDOT:PSS and multi-walled carbon nanotubes within a hydrogel PEGDA matrix to overcome these challenges. The optimized composite achieves a conductivity of 1.4 × 10⁵ S m^-1 (≈10⁴-fold improvement over pristine PEGDA), > 80% optical transmittance, and stable high-resolution patterning. Directly printed microresistors and microcapacitors exhibit a specific capacitance of ≈667 F g^-1, combining electric-double-layer and pseudocapacitive charge storage. The printed structures maintain ≈65% of their conductivity under 50% tensile strain and remain conductive after 3000 stretching cycles at 10% strain, with no delamination from PDMS. The composite also preserves geometry and adhesion across pH 3-10, confirming chemical robustness. This sequential multimaterial 2PP approach enables monolithic integration of conductive, insulating, and electroactive domains for flexible, stretchable, and chemically stable soft microelectronics, advancing scalable fabrication of biointerfaces, wearable devices, and microscale energy-storage systems.