The core temperature of the human body can reveal a number of things about a person’s health. The presence of a fever is the most obvious one, but changes in the core temperature can also indicate changes in metabolic function, fatigue, even insomnia and depression. No one walks around with a thermometer in their mouth all the time, though, so these changes in temperature go largely unmonitored – which means early warning signs of serious conditions can go unnoticed.
Wearable temperature sensors exist, but they measure skin temperature, which differs from core temperature as it’s influenced by other factors such as outside temperature. But a group of researchers from the University of California at Berkeley have developed a new kind of wearable – or, as they call it, an earable. The 3D printed device is designed to be worn in the ear and to take core temperature readings from the eardrum.
The design of the device is detailed in a paper entitled “3D Printed ‘Earable’ Smart Devices for Real-Time Detection of Core Body Temperature,” which you can access here. Earables use infrared sensors to measure core temperature and transmit the readings to a smartphone via Bluetooth. They look somewhat like wireless headphones; the sensor itself is inserted into the ear canal while the outer part of the device sits over the ear. If you’re wondering about how the device might affect hearing, the researchers have that taken care of, too – it also functions as a hearing aid. A microphone is embedded into the device to pick up sound, which is then transmitted to the inner ear via bone conduction with an actuator in contact with the temple.
Earables are not necessarily going to become the next Fitbit – it’s unlikely most people are going to want to walk around with a device covering their ear constantly just so they can know their core temperature all the time. The earable could be extremely helpful for some people, though, such as infants, the elderly, or people living with or at high risk for certain health conditions. The researchers are working on making the devices smaller, too, and as they’re 3D printed, each one can be fabricated to perfectly fit an individual’s ear, a benefit that has already made 3D printing near-ubiquitous in the hearing aid industry.
The 3D printing process used to fabricate the devices is an interesting one that involves embedding the electronics and sensors directly into the earable. Rather than traditional metal wiring, the team uses a liquid metal alloy called Galinstan. First, the personalized shape is 3D printed from flexible polyurethane, with microchannels for the liquid metal in addition to wells where IC chips can be inserted. The 3D printing was done on an M2 3D printer from MakerGear, using Filaflex filament from Recreus.
“After printing, Galinstan is injected into the microchannels and the thermopile sensor, conditioning circuit ICs, and Bluetooth module are inserted into the microchannel slots as the first device layer,” the researchers explain. “Poly(dimethylsiloxane) (PDMS) and epoxy resin are then used to securely set the IC chips in place. As the Bluetooth module is relatively thick (∼7 mm), it takes up space on both the first and second device layers. After curing of the PDMS and epoxy, the second layer containing the components of the bone conduction hearing aid including the microphone, potentiometer, and corresponding conditioning circuits are inserted into their respective microchannel pins. The actuator for the bone conduction is also inserted at this point through the side on the first device layer. Finally, the second layer of devices are also set into place using PDMS and epoxy and a 3D printed enclosure with holes for the microphone and potentiometer is put on to complete the packaging.”
The earables were tested on subjects who were placed in a room where the temperature was raised and lowered. While a skin sensor reflected the changing room temperature, the earable’s core temperature reading remained the same; likewise, after the subject exercised, the core temperature rose steadily.
Earables are an interesting, and promising, development that could help many people better monitor their health, and further work on the devices aims to not only make them smaller, but expand the range of sensors that can be embedded into them. Authors of the paper include Hiroki Ota, Minghan Chao, Yuji Gao, Eric Wu, Li-Chia Tai, Kevin Chen, Yasutomo Matsuoka, Kosuke Iwai, Hossain M. Fahad, Wei Gao, Hnin Yin Yin Nyein, Liwei Lin and Ali Javey. Discuss in the Earables forum at 3DPB.com.[All images: “3D Printed ‘Earable’ Smart Devices for Real-Time Detection of Core Body Temperature”]