Laser-induced functionalization of flexible polyimide-carbon fiber for real-time multimodal physiological monitoring of chronic wounds

Translating laser-induced graphene (LIG) from rigid planar films to wearable textile substrates has been constrained by substrate transfer steps that fracture the three-dimensional porous carbon architecture and destroy surface wettability control. Here we report laser-induced functionalized fibers (LIFF), a transfer-free strategy that directly writes graphitic carbon onto polyimide (PI) fiber substrates via direct laser irradiation. This approach forms an in?situ 3D conductive network on fibrous surfaces. By co-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 (contact angle >120°, 650?PPI/DPI) to super?hydrophilic (contact angle <5°, 1500?PPI/DPI), the first demonstration on fibrous PI. Raman spectroscopy (ID/IG < 0.5, La ≈ 40 nm), XPS (sp² carbon ~80%), and HR-TEM (d-spacing 3.47 Å) confirm well-ordered graphitic domains. The wettability programmability is exploited as a materials-level cross-sensitivity management strategy: Hydrophobic LIFF in a stretchable configuration (knitted) serves as a strain sensor (gauge factor GF = 25, 0–120%, 2700-cycle stability), while in a non?stretchable configuration (woven), it provides a temperature sensor (0.181% °C?¹). Hydrophilic woven LIFF enables humidity sensing (0.585% RH?¹) and, after PANI-PU functionalization, potentiometric pH sensing (−68 mV pH?¹, super-Nernstian, n=5). To enable real-time wound monitoring, all four sensors are integrated into a wound dressing with a BLE -enabled micro-device developed for wireless data acquisition and validated in artificial wound fluid. In vitro CCK-8 assay (L929 fibroblasts, 24–72?h) confirms >90% viability. This wettability-programmable, transfer-free LIFF platform establishes a design principle in which laser parameters simultaneously govern graphitization quality, surface energy, and cross-sensitivity, eliminating the fabrication trade-offs that constrain current LIG-based wearable sensor platforms.

Tahir Raza is a final-year PhD candidate at Fudan University, Shanghai, China, specializing in electronic science and technology. He received his master’s degree in Textile Engineering from Qingdao University, China. His research focuses on development of wearable and flexible smart sensing systems and integrated energy storage platforms using laser-induced functionalization and advanced printing techniques for applications in sports analytics, healthcare monitoring, and humanoid robotic electronic skin. He has published several research articles in high-impact journals and actively participates in international conferences related to advanced materials and biomedical engineering.