Wireless batteryless in vivo blood pressure sensing microsystem for small laboratory animal real-time monitoring

Genetically engineered small laboratory animals with in vivo real-time physiological signals monitoring are ultimately crucial for system biology research to identify genetic variation susceptibility to various diseases and to develop effective treatment methods for similar human diseases. Blood pressure is one of the most important vital signals used in such research. However, there is no adequate solution for its chronic blood pressure monitoring to date. By merging MEMS technology and low power CMOS integrated circuits design through a high level system integration together with a conventional molding-based packaging technique, miniature, light-weight, wireless, batteryless, less-invasive, and implantable blood pressure sensing microsystems have been demonstrated for untethered small laboratory animals real-time monitoring. These critical features of the microsystem greatly suppress stress and post-implant trauma-induced information distortion. The proposed microsystem employs a miniature instrumented elastic sensing cuff, wrapped around a blood vessel, for blood pressure monitoring. The blood pressure is coupled into the sensing cuff caused by the vessel expansion and contraction. The microsystem can detect the pressure signal and wirelessly transmit the information to a nearby receiver with an adaptive RF powering capability to ensure a stable system power supply. The sensing technique avoids vessel penetration and substantially minimizes vessel restriction due to the soft cuff elasticity, thus attractive for long-term implant. A MEMS capacitive pressure sensor is designed and fabricated for its low temperature dependence, time stability, and zero DC power consumption. The integrated electronics consisting of a low power low-noise correlated-double-sampling capacitance-to-voltage converter, an 11-bit cyclic ADC, an adaptive RF powering system, an oscillator-based transmitter, and digital control circuitry have been designed and fabricated in a 1.5μm CMOS process. The prototype system achieves a 10-bit system resolution with 300μW power consumption. The ASIC and the MEMS sensor are interfaced with a 5mm-diameter RF powering coil over a thin flexible substrate and packaged with the blood pressure sensing cuff. The microsystems designed for laboratory rats and mice monitoring exhibit a weight of 430mg and 130mg, respectively. Untethered laboratory animals implant study demonstrates the microsystem capability of capturing real-time high-fidelity blood pressure information under a wireless and batteryless condition. Other bio-sensing channels such as core body temperature and EKG can be integrated into the prototype system architecture.