Battery-free, wireless, crack-activated pressure sensor and movable system for pressure injury prevention

Abstract

Pressure injury refers to localized damage to the skin or underlying tissues caused by the continuous or repetitive pressure, elevated temperature at a specific part of the body. hemiplegia patients with Wheelchair are one of the highest risk populations for developing sitting acquired pressure injury. The current pressure injury prevention protocol is repositioning the posture of wheelchair users at regular intervals to prevent repetitive pressure and elevated temperature. However, it is insufficient to completely prevent pressure injury due to a lack of quantitative medical information on the pressure and temperature of patients. Therefore, to effectively prevent pressure injury, there is a need for a wireless wearable pressure sensor that enables real-time monitoring that can provide quantitative pressure and time information and does not cause discomfort of movement even when attached to various parts of the body. Recently, several types of research about skin-mountable wireless pressure sensors have been proposed that can non-invasively monitor the human body. However, real-time tracking and monitoring about pressure/temperature distribution studies with stability and reliability for clinic testing are in the early stages. In addition, despite studies on the structure of various nanomaterials and pressure sensors, there are no medical wearable pressure sensors that simultaneously satisfy low-pressure measurement, high sensitivity, high signal to noise ratio(SNR), linearity, low hysteresis, and mechanical stability to measure high pressure at skin interfaces in wheelchair patients. Here this paper proposes a battery-free, wireless, skin-mountable, crack-activated pressure sensor and movable system for real-time monitoring of the pressure of major skin area. The pressure sensor includes a cracked-metal trace encapsulated with a nanoscale, thin film for excellent sensitivity ($\Delta R/R_o$ ~ 3 %, 100kPa), low hysteresis (0.1 %), high linearity ($R^2$ ~ 0.99) and stability, required for use in this application. Also, the battery-free, wireless mode of operation is capable of continuously measuring at critical locations across the whole body of subject sitting in wheelchair during stationary or in motion. Such devices yield continuous, simultaneous readings of pressure and temperature in a sequential readout scheme from four multiplexed antennas integrated under back rest, seat and two footrests, respectively, and connected to a wireless reader, potable batteries and a multiplexer located over back rest of wheelchair. Experimental evaluation of the performance of the wireless sensing platform includes benchtop measurements and temperature compensation through combination with temperature sensor. In addition, experimental evaluation includes measuring the maximum operating distance on the movable system and evaluating the stability in various environments to show the functionality of the overall system. Finally, the clinical trials with paraplegia patients (e.g. hospitalized patient and outpatients) including the diverse weight shift behaviors to demonstrate the potential of the system for pressure injury prevention.