Transparent and Low-Voltage-Driven Conductive Nanocomposite Hydrogels for Tunable Optical Lenses

Electrically tunable soft lenses are essential for emerging applications in soft robotics, adaptive optics, and minimally invasive biomedical imaging. Among various materials, electroactive hydrogels have emerged as ideal candidates for constructing such lenses due to their tissue-like softness and intrinsic electrical actuation capabilities. However, current hydrogel-based actuators often face a fundamental trade-off between high optical transparency and low-voltage responsiveness due to the uncontrolled aggregation of conductive fillers. Herein, we report a transparent, low-voltage-driven electroactive hydrogel lens based on a polyacrylamide (PAM) matrix incorporated with sodium-functionalized multiwalled carbon nanotubes (Na-MWCNTs). By engineering the interfacial chemistry of the nanotubes with surface carboxylate groups (-COONa), uniform dispersion of nanotubes in PAM via electrostatic repulsion at a low loading (≤0.1 mg mL^-1) was achieved. Consequently, this well-dispersed state preserves high visible-light transmittance, while the incorporation of Na-functionalized MWCNTs modulates the overall charge transport behavior within the hydrogel matrix, facilitating rapid charge redistribution. Under a 30 V stimulus, the focal length of the hydrogel lens can be tuned from 73.6 mm to 53.7 mm, achieving a 27% tunability. Mechanistically, this focal tuning is realized through the asymmetric modulation of surface curvature, driven by an electric-field-induced osmotic pressure gradient. Ultimately, this PAM/Na-MWCNT hydrogel platform offers a versatile solution for next-generation adaptive biomimetic optical devices, endoscopic probes, and soft robotic vision.