Adaptively radio frequency powered implantable multi-channel bio-sensing microsystem for untethered laboratory animal real-time monitoring.

摘要

Genetic engineering of mice DNA sequences with real-time physiological monitoring has become the most critical research tool for identifying genetic variation susceptibility to diseases. Genetically engineered mice have been widely used as research vehicles with their physiological data being highly important for advanced biological research. Animal-based research results are expected to make a significant impact in treating similar human diseases. Due to the small size of a laboratory mouse, a miniature, light-weight, wireless, batteryless, and implantable multi-channel bio-sensing microsystem is developed to capture real-time accurate biological signals from an untethered animal in its natural habitat, thus eliminating stress and post-implant trauma-induced information distortion. A reliable radio frequency (RF) powering technique based on inductive coupling allows the batteryless microsystem to be achieved with a small form factor. The RF powering technique widely employed in biomedical applications typically relies on a set of external coil and an implantable coil with a relatively fixed position to inductively couple an external RF energy to an implanted microsystem. However, the proposed microsystem is implanted in a freely roaming mouse; hence resulting in a drastically changing magnetic coupling as the mouse moves and tilts its position with respect to the external stationary coil. Therefore, an optimized remote RF powering system with an adaptive control capability is designed and implemented. The prototype sensing microsystem can detect two vital signals, electrocardiogram (EKG) and core body temperature, and wirelessly transmit the information to a nearby receiver by employing a low power CMOS integrated circuits design with a minimal number of off-chip components for a high-level system integration. The overall implant unit exhibits a dimension of 9 mm x 7 mm x 3 mm and a weight of 400 mg including a pair of stainless steel EKG electrodes. A low power 2 mm x 2 mm integrated circuit, consisting of an EKG amplifier, a proportional-to-absolute-temperature (PTAT) circuit, an RF power-level sensing circuit, an RF-to-DC power converter, an 8-bit analog-to-digital converter, a digital control unit, and a wireless transmitter, is designed and fabricated in a 1.5microm CMOS process. An adaptively controlled external RF energy at 4 MHz is employed to ensure an on-chip stable 2V supply with a 156 microA current driving capability for the overall microsystem. This technique limits the on-chip voltage variation to ensure a proper electronic operation and reliable implant power, and also minimizes the external power dissipation; hence the environment temperature rise. Untethered laboratory mice implant study demonstrates the microsystem capability of capturing real-time EKG and core body temperature information under a wireless and batteryless condition. Other biological sensing channels such as blood pressure and activity signals can be potentially integrated with the system architecture.