Battery-Free, Wireless Three-Axial Sensor Array to Prevent Pressure Injury

Pressure injuries, also known as pressure ulcers, affect over 2.5 million patients annually in the United States alone, contributing to an estimated 9-11 billion USD in medical costs and resulting in approximately 60,000 deaths per year. These injuries often develop in hospitalized and bedridden patients due to prolonged exposure to mechanical loads, such as pressure and shear, especially over bony prominences. These factors lead to localized ischemia, tissue necrosis, and significant complications, including cellulitis and osteomyelitis. Prevention, rather than treatment, remains the most effective strategy, as the injuries are challenging to heal once developed. While existing preventive methods, such as repositioning patients and using pressure-relief mattresses, are widely employed, they are often insufficient to fully eliminate the risk of pressure injuries. Hence, there is an urgent need for advanced technologies that enable continuous, quantitative monitoring of pressure, shear, and temperature at the skin interface.
Wireless systems for monitoring pressure and temperature at skin interfaces have been developed to prevent pressure injuries. However, in the field of wearable sensor devices, there have been few solutions capable of simultaneously measuring both pressure and shear with a single sensor. While recent advancements have introduced sensor arrays for multi-parameter monitoring, research on three-axial sensors that can measure pressure and shear simultaneously within wearable platforms is still ongoing. To contribute to this growing area, we developed a battery-free, wireless three-axial sensor array for continuous monitoring of pressure, shear, and temperature at the skin interface. The sensor array incorporates a polyimide-based cantilever structure with two layers of metal strain gauges, forming a half-Wheatstone bridge for each cantilever. This design allows the sensor to function as a piezoresistive pressure sensor, ensuring reliable, long-term monitoring that remains unaffected by variations in skin or environmental temperature.
The three-axial sensor is designed with four cantilevers, each oriented axially, and positioned under a dome structure to uniformly distribute force across the sensor. This enables simultaneous measurement of pressure and shear, while an integrated temperature sensor monitors local skin temperature. The system automatically compensates for temperature effects via the half-Wheatstone bridge, enhancing measurement accuracy across varying environmental conditions.
By incorporating this sensor array, we can monitor pressure distribution over a broader surface area while also capturing critical shear and temperature data—factors that are directly implicated in pressure injury formation. The battery-free, wireless design eliminates patient discomfort associated with bulky wiring and enables seamless data acquisition via a Near Field Communication (NFC) platform. This allows medical staffs to continuously monitor clinical data in real time, facilitating early detection of risk factors and improving clinical decision-making for pressure injury prevention. In summary, this novel three-axial sensor array presents an advanced, non-invasive solution for continuous monitoring of pressure, shear, and temperature in patients, offering significant potential for reducing the incidence of pressure injuries and improving patient treatment.

Acknowledgment
This work was supported by (1) the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2021R1A2C3008742).(2) Alchemist Project grant funded by Korea Evaluation Institute of Industrial Technology (KEIT) & the Korea Government (MOTIE) (Project number: 1415179744, 20019169).