Wireless battery-free ultrathin lithium-niobate resonator as wearable and implantable electronics for continuous monitoring of mechanical vital signs

Continuous monitoring of physiological parameters associated with dynamic biomechanics, such as intracranial pressure (ICP) and vital signs, is important for clinical diagnosis of brain diseases and timely medical intervention. Current skin-interfaced and implant technologies face challenges in terms of bulky tethers and/or percutaneous wires with high infection risks. Here, we report the wireless, battery-free, and lightweight devices for both wearable and fully implantable applications. The devices incorporate an ultrathin piezoelectric resonator with suspended lithium niobate thin film (LNTF, 3 μm thick), enabling the wireless tracking of mechanophysiological signals by detecting variations in resonance frequency. We experimentally and computationally establish the operational principles of the resonator sensor and assess the device performance as wearables for dynamically monitoring artery pulse and apnea events during respiration. Implantable wireless pressure sensors adapted from this scheme allow for untethered, minimally invasive ICP sensing with a low detection limit of 0.15 mmHg over a wide range up to 240 mmHg. In vivo experiments performed on rat models validate the device capabilities of accurately capturing clinically relevant ICP variations and elevated levels of ICP under pathophysiological conditions of hydrocephalus, with excellent biocompatibility after long-term implantation periods. These findings create the clinical significance of such battery-less and wireless devices for precise characterization of dynamic biomechanics of living tissues.