Innovative Device for Accurate Skin Temperature Measurement

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An ultrathin device for mapping changes in skin temperature is able to conform to complex changes in the shape of the skin surface. Photo by University of Illinois and Beckman Institute.

An ultrathin device for mapping changes in skin temperature is able to conform to complex changes in the shape of the skin surface. Photo by University of Illinois and Beckman Institute.

Could doctors laminate your skin with a thermometer to check your temperature? Researchers have developed new devices which can monitor the temperature of human skin with very high precision – they’re cheap to produce very thin – you can apply them directly onto the surface of the skin without causing discomfort. These ultra-thin thermometers can give valuable information about patients’ health, allowing a full monitoring outside the hospital, without clumsy devices.

Body Temperature Measurement Devices

Because of the importance of accurately measuring body temperature, researchers have developed several devices to measure skin temperature. The majority of these devices, however, despite being valid from technological point of view, are not very practical for patients.

Some of the measurement devices, for instance, are based on digital infrared cameras; they can read the temperature with a precision of millikelvin degrees and give high resolution spatial temperature mapping. They are, however, quite expensive and require the immobilization of the patients – and it’s difficult for patients to remain perfectly still. In other cases, point contact sensors are used; they do not require immobilization but, at the same time, they cannot provide spatial mapping.

Further to these problems, temperature-measurement devices should also be made of material(s) which do(es) not cause irritation to the skin; moreover the contact between the epidermis and the device should not constrain or alter the natural behavior of the skin itself. Quite a difficult proposition.

Innovative Solutions

To try to solve these problems, researchers investigated several compounds as possible temperature measurement devices. Researchers from University of Illinois (US); in cooperation with other research institutions in US (National Institute of Health – Maryland; University of Miami), China (Southwest Jiatong University; Zhejiang University) and Singapore (Institute of High Performance Computing) have made important progress in this area – publishing their results in Nature Materials on the 15th of September 2013.

The researchers developed two kinds of devices; the first one based on gold (Au), the second on silicon (Si).

Measuring the Temperature

Professor John Rogers, leading scientist in the project, explained how these devices were made to Decoded Science:

“The two devices we made use different materials and different physical principles to measure the temperature.

In the case of resistive measurements, we use a very thin gold serpentine (50 nm) wire and we determine its change in resistance. From this value we can calculate the temperature.

The second device relies on an array of PIN diodes made by a nanomembrane of doped silicon; we monitor any change in the turn-on voltage of the diode to determine the temperature.”

Lamination on Skin Surface

In both cases the devices are supported by a thin (50 micron) perforated elastomeric substrate, which can be placed directly on the surface of the skin. The perforation allows the skin perspiration; the elastomeric properties, on the other hand, allow complete and free movements of the skin (i.e. twisting) without causing discomfort to the patient.

An example of the device applied on the surface of the skin can be seen in the image above.

According to Professor Rogers:

“These devices showed performance comparable to the most sophisticated thermal cameras. The cost to make these devices, however, is much lower; roughly $1 – cost of the device – compared to $0.25 million  – cost of the camera.”

In this infrared image, active heating elements of an ultrathin device on the skin appear white due their increased temperature. Photo by University of Illinois and Beckman Institute.

In this infrared image, active heating elements of an ultrathin device on the skin appear white due their increased temperature. Photo by University of Illinois and Beckman Institute.

Different Thermal Properties and Functionalities

In addition to measuring skin temperature, these devices can give additional information and measure other properties, which include thermal conductivity. This is a very important information, as it correlates to the moisture level of the skin.

Moreover, these devices also allow local controlled heating, which can be essential in specific medical treatments. This is shown in the picture on the side.

Stick-on Thermal Monitors: The Future

“With a proper use of these devices, we can obtain rich, deep information about physiological status and health of patients. Blood perfusion, localized thermogenesis due to inflammations, changes in vascular flow, these are all examples of parameters which can be monitored.” Professor Rogers says,

“The systems may need optimization to be commercialized and effectively used outside of labs or hospital settings, but we are excited about their potential.”

As always, further study (and, as Professor Rogers says, optimization) is necessary for widespread use of this new technology, but a cheap and effective method of studying skin temperature in patients could result in a huge improvement for doctors and patients alike.

Sources

Webb, R.C. et al. Ultrathin conformal devices for precise and continuous thermal characterization of human skin. (2013). Nature Materials. Accessed September 17,  2013.

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