Ultrafast Piezoresistive Pulse Sensors Based on Laser-Induced Graphene on PCL-b-PDMS-b-PCL Crosslinked Polymers

The rapid growth of sensors for monitoring physiological parameters has created a need for high-performance materials with properties appropriate for biomedical applications. However, most existing materials either lack environmental compatibility or fail to provide the flexibility and durability required for continuous monitoring. To address this gap, we present flexible piezoresistive pulse sensors that integrate laser-induced graphene (LIG) with newly synthesized PCL-b-PDMS-b-PCL polyurethane (PU) networks. These PUs provide tunable elasticity, and are composed of soft segments (ss.) (PCL and PDMS) that are reported in the literature to exhibit biodegradability and biocompatibility, making them attractive candidates for pulse sensing. Sensors were fabricated by first producing porous LIG patterns on polyimide, followed by transfer onto PU films prepared with varying soft-segment contents (40-70 wt.%). Comprehensive physicochemical characterization (Raman, XRD, FTIR, SEM-EDS, TEM, WCA, and tensile testing) revealed that 40 wt.% ss. substrates offered the most favorable balance of flexibility and mechanical stability. Pulse sensors based on this formulation achieved signal-to-noise ratios of 27.5-51.8 dB, a fast response time of 24 ms, a gauge factor of 22.2, hysteresis errors in the range of 7-10%, and a limit of detection (LOD) of 0.2% at 85 Pa. The sensors exhibited consistent performance over five remove-and-reapply cycles. This work advances the field by introducing tunable synthetic PUs as LIG substrates and establishes clear links between polymer composition, integration method, and device performance, thereby providing design rules for next-generation wearable health monitors.