Heat shocks and metabolic syndrome are becoming more common – this is how photonics-based wearable health tech can help

The state of human health can be easily monitored even outside a hospital environment using wearable devices such as smartwatches. A key technology enabling this is photonics, based on the use of light, which allows versatile, accurate, and continuous monitoring of body tissues without harm to the user.

”Light can be manipulated on different wavelengths and powers so that it interacts with human tissue in a desirable manner. However, light itself requires plenty of other technology around it. The foundation for generating data is multimodal sensing based on several different technologies,” says Jussi Hiltunen, Research Professor at VTT.

Together with partners, VTT is currently developing wearable technology utilising multimodal sensing, for instance, to monitor dehydration and metabolic syndrome.

“Human dehydration will become a huge problem as heatwaves connected to global warming become more commonplace. Even people who are normally healthy may get heat shocks. In addition, senior citizens may become dehydrated without realising it. At the moment, commercial development of wearable monitoring devices is driven by companies manufacturing devices for athletes,” Hiltunen clarifies.

Multimodal sensors can measure, for instance, tissue moisture and the chemical composition of sweat. The amount of salt in sweat may indicate the level of dehydration. In addition, electric sensors can be used to measure conductivity of the body.

Wearable sensors can measure the accumulation of fat in internal organs and the development of metabolic syndrome risk factors by monitoring metabolic changes. Monitoring may help reveal latent inflammations.

“A person may feel slightly weak, but symptoms and reasons remain unclear. For instance, symptoms in the digestive tract may indicate that something is wrong in the body, and such signs could potentially be detected using wearable devices,” Hiltunen describes.

He estimates that wearable devices capable of monitoring dehydration and metabolism will be available in the market no sooner than 5 years from now. Field tests with VTT's partners are already on the roadmap, but large-scale adoption will take time.

Green or red light, familiar to many consumers from smart watches and smart rings, can indicate the presence of photonics. These colours are not sufficient for all measuring purposes.

“More complex physiological aspects require plenty of different colours and the use of infrared light. Therefore, we have now been developing wide-spectrum sensor technology,” tells Hiltunen.

As a new area, VTT is researching how laser technology could be used in wearable devices.

“Lasers have significant advantages compared to LED light. They are more efficient, capable of more accurate wavelength separation, and consume less energy. However, while LEDs cost a few cents, lasers cost at least a few euros per piece,” Hiltunen compares.

For a concrete measurement product, the problem lies in how light is generated, delivered to the skin, and transmitted through human tissue. Another challenge is the collection and processing of measurement data, as the volume is large. Much of the data must already be filtered on the device to ensure that storage space and the communications link are sufficient.

According to Hiltunen, the greatest challenge is connected to personalisation because similar data from different people doesn’t mean the same thing.

“We must bear in mind that people are individuals. The right conclusion requires both versatile, high-quality data from multiple sources and a personalised interpretation of that data. This may require, for instance, adaptive signal processing,” Jussi Hiltunen says.

The need for personalisation also applies to artificial intelligence used for processing sensor data. The system of AI algorithms must be capable of learning and adapting.

VTT can manufacture small batches following industrial production standards on its unique medical device pilot line in Oulu. In the batches, photonics-based sensors can be integrated in the devices, but also other technologies such as those for electric measuring and ultrasound.

“We go deep into multimodal data generation and move beyond the laboratory environment. We also have decades of experience in photonics and top expertise of data processing under the same roof. Our partner network includes end users, manufacturing industry and clinical partners,” tells Hiltunen.