Battery-Free, Wireless, Wearable Ionic Liquid Sensor Array
A research team from Changwon National University and KAIST has developed an ‘ionic liquid sensor array’ to prevent pressure ulcers in patients with limited mobility.
According to Changwon National University on the 5th, a collaborative research team led by Professor Oh Yong-seok of the Department of Mechanical Engineering, Smart Manufacturing Convergence major at Changwon National University, and Professor Park In-gyu of the Department of Mechanical Engineering at KAIST created a ‘battery-free, wireless, wearable ionic liquid sensor array for continuous measurement of pressure and temperature distribution on patient skin.’
This research was conducted with support from the Ministry of Trade, Industry and Energy and the Ministry of Science and ICT through the Korea Evaluation Institute of Industrial Technology’s ‘K-Sensor Technology Development Project Led by Korea for Market Leadership’ and the National Research Foundation of Korea’s ‘Creative Challenge Research Base Support Project.’
According to Professor Oh, continuous pressure applied to bony prominences such as the sacrum and heels of a patient’s body causes circulatory disorders in capillaries that supply oxygen and nutrients to skin tissue, leading to ischemic tissue necrosis.
Damage to the skin or underlying tissues, known as pressure ulcers, can worsen when skin temperature rises and frequently occurs in patients with impaired movement, sensation, or cognitive abilities.
The incidence and prevalence of pressure ulcers are increasing alongside the aging society and the rise of chronic diseases.
Professor Oh emphasized that early diagnosis and prevention are very important because pressure ulcers increase hospitalization duration and medical expenses for inpatients and cause significant physical and mental suffering to patients and caregivers.
He explained that pressure ulcers in patients are mainly prevented by periodically changing the position of bedridden patients to redistribute pressure on the skin, following the method proposed by the National Pressure Injury Advisory Panel (NPIAP) in the United States.
Professor Oh pointed out that elderly people who have difficulty moving on their own or paralyzed patients require medical staff to consistently change their whole-body position for pressure ulcer management, but this is realistically difficult due to a shortage of personnel.
Changing the whole-body position of patients can also lead to musculoskeletal injuries for patients, medical staff, and caregivers.
Research team collaboration between Changwon National University and KAIST: Hyunseok Han, KAIST PhD candidate (from left), Yongseok Oh, Professor at Changwon National University, Inkyu Park, Professor at KAIST. [Photo by Changwon National University]
To address these limitations, the research team developed the ionic liquid sensor array and applied it to patients at risk of pressure ulcers, verifying the system’s effectiveness and stability.
Using the developed ionic liquid sensor array integrated with antennas in beds and wheelchairs, they continuously monitored the pressure and temperature distribution around the bony prominences of paralyzed patients.
Based on the acquired data, the team inserted memory foam or water cushions between the skin and mattress interface to redistribute and reduce skin pressure and temperature with minimal position changes.
The study concluded that preventing pressure ulcers based on quantitative pressure and temperature data is efficient in terms of labor and time costs and that minimal position changes, rather than whole-body repositioning, can effectively prevent secondary musculoskeletal injuries to caregivers and patients.
According to the research team, the ionic liquid sensor was fabricated by injecting ionic liquid into microfluidic microchannels within an elastomer.
The sensor accurately measures pressure based on the principle that the volume and resistance inside the microchannel change according to the applied pressure.
As a conductive liquid-based sensor, the team developed and applied a pre-compression process of the microchannels to achieve high sensitivity (0.68 /kPa).
The sensor also possesses key characteristics required, including low drift, low hysteresis, high linearity, and insensitivity to shear and bending.
Considering the ionic liquid’s conductivity changes with temperature, the sensor was designed with a temperature sensor to enable skin temperature measurement and temperature compensation.
The fabricated ionic liquid sensor is the size of a 500-won coin, with a diameter of 25 mm, and shows low sensor-to-sensor variation and uniformity.
The electromagnetic field generated by the transmitting coil antenna induces current in the sensor’s receiving coil antenna, and based on the generated power, the sensor measures temperature and pressure and stores the data on a chip.
The data stored on the chip is transmitted to the transmitting coil antenna based on the near-field communication (NFC) protocol.
The research team configured an integrated system by combining multiple transmitting coil antennas?two for the bed and four for the wheelchair?using a reader and multiplexer.
The integrated system, used alongside the ionic liquid sensor array, was applied for clinical evaluation of patients at risk of pressure ulcers, such as paralyzed patients.
The research team plans to reduce pressure and temperature by continuously monitoring the pressure and temperature distribution around bony prominences and applying minimal position changes using memory foam or water cushions.
Professor Oh said, “Medical staff participating in the research can obtain meaningful quantitative pressure and temperature distribution data using this system, which can be utilized for effective pressure ulcer prevention.”
This research was conducted jointly by first author Han Hyun-seok, a doctoral student in the Department of Mechanical Engineering at KAIST, and Professor Oh Yong-seok of Changwon National University, with Professor Park In-gyu of KAIST serving as the corresponding author.
The clinical study was supported by Professor Lee Byung-joo of the Department of Rehabilitation Medicine at Pusan National University Hospital, and Manager Lee Je-sang and Director Min Won-ki of Gimhae Hansol Rehabilitation and Nursing Hospital.
The research results were published online in March 2023 in the prestigious international journal Small (impact factor 15.153).
The paper is titled ‘Battery-Free, Wireless, Ionic Liquid Sensor Arrays to Monitor Pressure and Temperature of Patients in Bed and Wheelchair.’
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