Hydrogel Biosensor Detects and Differentiates Blood Circulation Complications

However, designing sensors that adhere securely during monitoring while avoiding tissue damage when removed remains a major challenge, particularly for fragile or healing tissues. Researchers have now developed a flexible biosensor featuring a printable hydrogel interface that can monitor blood circulation in reconstructed tissues while allowing safe removal after use.

The soft biosensor system with a thermoresponsive hydrogel interface, developed by researchers at Huazhong University of Science and Technology (HUST, Wuhan, China), is designed for precise physiological monitoring. The hydrogel layer provides strong adhesion to the skin during measurement but reduces adhesion after monitoring, enabling painless removal and minimizing damage to delicate tissues. The system is designed specifically for postoperative monitoring of free flaps, a surgical technique commonly used in reconstructive procedures where transplanted tissue requires careful monitoring of blood circulation to ensure survival.

Free flap procedures can face complications such as venous congestion, arterial spasm, and arterial occlusion, all of which can threaten the viability of the transplanted tissue. Early detection of these problems is critical for timely intervention. The researchers developed a printable hydrogel ink that allows precise fabrication of the biosensor interface with line widths below 720 micrometers. The patterned hydrogel layer can be printed within 30 seconds, enabling efficient manufacturing and customization.

The hydrogel includes thermoresponsive monomers and adhesive functional groups that provide an initial adhesion strength of 27.8 kPa and allow a wide 10.8-fold adhesion adjustment range. During monitoring, the biosensor maintains strong contact with the skin to capture physiological signals, including reflective infrared photoplethysmography (PPG) signals and temperature measurements.

In pilot clinical studies, the biosensor successfully monitored blood circulation in postoperative free flaps. Researchers introduced a new analytical metric called the balance index, derived from morphological analysis of PPG signals, which allows clinicians to distinguish between venous and arterial complications. Compared with traditional monitoring approaches and commercial microcirculation systems, the hydrogel biosensor offers several advantages, including lower cost, wireless data communication and reduced risk of mechanical tissue damage.

The thermoresponsive printable hydrogel interface could serve as a universal platform for flexible medical electronics requiring reliable skin contact and gentle removal. Beyond reconstructive surgery monitoring, the technology may also support a wide range of healthcare applications that depend on continuous physiological signal monitoring through wearable sensors.

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