Flexible, wearable biomedical sensors based on laser-induced graphene (LIG) have garnered significant attention due to a straightforward fabrication process and exceptional electrical and mechanical properties. However, most relevant studies rely on commercial polyimide precursors, which suffer from inadequate biocompatibility and weak adhesion between the precursor material and the LIG layer. To address these challenges, we synthesized cross-linked polyurethanes (PUs) with good biocompatibility and used them as substrates for LIG-based wearable pulse sensors. During fabrication, we employed two methods of LIG transfer to achieve optimal transfer yield. We adjusted the thickness of PU films and tailored their mechanical and physicochemical properties by varying the soft segment content to achieve optimal sensor performance. Our findings demonstrate that the success of LIG transfer is strongly influenced by the structure and composition of the polymeric substrate. Tensile testing revealed that increasing the soft segment content in PU films significantly improved their tensile strength, elongation at break, and flexibility, with PU based on 50 wt.% soft segment content (PU-50) showing the best mechanical properties. LIG exhibited minimal sensitivity to humidity, while PU films maintained high transparency (>80% at 500 nm), and PU-50 was non-toxic, with less than 5% lactate dehydrogenase (LDH) release in endothelial cell cultures, confirming its biocompatibility. Adhesion tests demonstrated that LIG transferred onto PU-50 exhibited significantly stronger adhesion compared to other tested substrates, with only a 30% increase in electrical resistance after the Scotch tape test, ensuring stability for wearable sensors. The optimal substrate, a semicrystalline PU-50, yielded superior transfer efficiency. Among all tested sensors, the LIG/PU-50, featuring a 77 μm thick substrate with good mechanical properties and improved adhesion, exhibited the highest signal-to-noise ratio (SNR). This study showcases a skin-safe LIG/PU-based pulse sensor that has significant potential for applications as a wearable patch in medical and sports monitoring.

This review summarizes the recent developments in titanium suboxide (TSO) doping and the application of doped materials in pollutant degradation and electrochemistry. Doping is mainly limited to transition and rare-earth metals, with some exceptions, of similar ionic radii and charge, that can replace Ti ions in TSO without too much disturbance to the lattice. Consequently, doping is limited to below 10 at%, which predominantly induces oxygen vacancy formation. Doping mechanisms are weighted, and their effect on conductivity, stability, and catalytic activity is overviewed. High-temperature H₂ reduction of TiO₂ is still the dominant preparation method, with carbothermal reduction and Ti reduction gaining ground due to safety and energy concerns. Doping predominantly increases the conductivity 2–5 times, while the stability can be both improved or worsened, depending on the size and charge of the doping ion. Electrochemical oxidation, at positive overpotentials, of per- and polyfluoroalkyl substances (PFAS), antibiotics, and other water pollutants, is the main avenue of application. Doping almost exclusively leads to complete selected pollutant degradation and improvement of the pristine TSO, which is summarized in detail. New niche applications of peroxide, hydrogen, and chlorine production are also viable on doped TSO and are touched upon. Complementing experimental results are theoretical calculations, and we give an overview of density functional theory (DFT) results of transition metal-doped TSOs, identifying active centers, degradation trends, and potential new doping candidates.

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 poly( ϵ -caprolactone)-b-polydimethylsiloxane-b-poly( ϵ -caprolactone) (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, x-ray diffraction, FTIR, scanning electron microscopy-EDS, transmission electron microscopy, 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 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.