Laser-Induced Functionalization of Flexible Polyimide-Carbon Fiber for Real-Time Multimodal Physiological Monitoring...

Translating laser‑induced graphene (LIG) from rigid planar films to wearable textiles has been limited by substrate transfer steps that fracture the porous carbon architecture. Here, we report laser‑induced functionalized fibers (LIFF), a transfer‑free strategy that directly writes graphitic carbon onto polyimide (PI) fiber substrates via laser irradiation, forming an in situ 3D conductive network. By optimizing defocus distance (z = -0.5 mm) and pulse density (PPI/DPI), we achieve subsurface graphitization and continuously program surface wettability without chemical or plasma treatment. This allows tuning from hydrophobic (>120°, 650 PPI/DPI) to superhydrophilic (<5°, 1500 PPI/DPI), the first demonstration on fibrous PI. Hydrophobic LIFF in configuration (knitted) serves as a strain sensor (gauge factor GF = 25), while in a non‑stretchable configuration (woven), it provides a temperature sensor (0.181% °C^{- 1}). Hydrophilic LIFF (woven) enables a humidity sensor (0.585% RH^{- 1}) and a pH sensor (-68 mV pH^{- 1}). All sensors are integrated into a wound dressing with Bluetooth low energy (BLE) micro-device, validated in artificial wound fluid. An in vitro cytotoxicity assessment (L929 fibroblasts, CCK‑8, 24-72 h) confirms >90% viability. This LIFF platform establishes a design principle in which laser parameters simultaneously govern graphitization, surface energy, and cross-sensitivity, eliminating fabrication trade-offs that constrain current LIG-based wound sensors.