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A gelatin nanofiber film that shows a failure tensile stress of 35 MPa, much stronger than conventional polyacrylamide hydrogels (<0.2 MPa), tough double network hydrogels (0.2–1.0 MPa), some engineering plastics such as polyethylene films (16 MPa) and polysulfones (1–10 MPa), is prepared by electrospinning. It is processed into a graphene oxide film, which exhibits high conductivity, via a high‐temperature treatment. A simple approach to prepare graphene oxide films using gelatin is provided. A highly sensitive and responsive wearable sensor is fabricated using the graphene oxide film, which is capable of sound recognition, apexcardiogram recording, and pulse spectrum measurement. The apexcardiogram is strongly associated with hemodynamic cardiac health, which reflects the cardiac process of ventricular contraction, blood ejection, diastole, semilunar valve open/close, atrioventricular valve valve open/close, etc. The developed cardiac sensor could be used to measure arterial stiffness index, a derivative of pulse spectrum, useful to evaluate artery walls stiffness and health status. Using the developed sensor, the detection result can be wirelessly relayed to mobile devices for personal cardiac health monitoring.

Key indicatorsSingle-crystal X-ray study T = 298 K Mean '(C±C) = 0.006 A Ê R factor = 0.041 wR factor = 0.113 Data-to-parameter ratio = 14.0For details of how these key indicators were automatically derived from the article, see

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