Microfluidic fabrication of dual-functional hydrogel optical fibers with controlled swelling for simultaneous light transmission and ionic conductivity

Abstract

Multifunctional hydrogel fibers with integrated optical and electrical properties are essential for bioelectronics and soft robotics. Herein, we report on conductive hydrogel optical fibers (CHOFs) that combine light transmission, ionic conductivity, and mechanical flexibility via microfluidic coaxial extrusion. The fibers feature core-cladding structures composed of double-network hydrogels made of acrylamide and alginate. The strategic incorporation of sodium acrylate (SA) into the cladding enabled controlled differential swelling and maintained refractive index contrast for optical waveguiding under ionic conditions. Systematic SA variation (0–5 mol%) demonstrated precise property control, achieving a numerical aperture of 0.339, an optical attenuation of 0.088 dB cm⁻¹, an ionic conductivity of 26.6 mS cm⁻¹ in 1.0 M NaCl, and a stretchability of up to 321% strain. These CHOFs can function as strain sensors (gauge factor = 1.21) while maintaining optical transmission. Real-time human motion detection validated the dual functionality in wearable applications, demonstrating superior performance under mechanical deformation compared to conventional optical fibers. These CHOFs provide a platform for applications that require integrated optical transmission, electrical conduction, and mechanical sensing.