Pressure-monitoring stockings help prevent diabetic health problems
In total, 40 dielectric elastomer sensors measure compression load and distribution for diabetes patients – taking over the job usually performed by the nerves in their feet.
Diabetes patients often suffer from nerve and circulation problems in the feet, which reduce their perception of pain. They literally don’t know when it’s time to take the load off their feet. In healthy individuals, the nerve pathways ensure that weight is automatically transferred from one foot to the other during prolonged standing. Diabetics, however, don’t notice that their toes, heels or the balls of their feet are too heavily loaded – the foot receives no relief, and pressure sores may develop unnoticed. Even small uneven areas or shoe pressure can lead to open wounds or damaged tissue on the foot.
“Existing systems on the market measure the pressure distribution only on the bottom of the foot using shoe inserts. Our sensors are attached to the stocking’s sole, at the heel, the top of the foot and the ankle, so they can take readings in three dimensions. This is a totally new approach,” explained Fraunhofer ISC research scientist Dr. Bernhard Brunner. A pair should cost no more than 250 euros because the measuring system can be cost-effectively manufactured in series.
The sensors are made from a soft and stretchy elastomer silicone film that is easy to integrate into textiles. The film is coated on both sides with flexible electrodes of graphite or carbon black. When the film deforms as a result of compression or stretching, its thickness decreases and its surface area simultaneously increases. The capacitance rises with pressure – an effect the ISC researchers can measure. For example, if a patient stands for an extended period in one spot, pressure will build. The sensors can recognize this, and transmit the measurement signal via a conductive thread to a wireless electronics unit developed by researchers at Fraunhofer IIS and consisting of an application-specific integrated circuit (ASIC) chip and a controller.
“The unit is designed to record high-resolution readings from up to 40 capacitive sensors across an extremely wide value range,” explained Johann Hauer, the Fraunhofer IIS project manager responsible for the project. The ASIC collects the measurement data and the controller transmits it wirelessly to a smartphone or tablet, which then informs the diabetes patient that it is time to change foot position or weight distribution.
“With the current prototype, the electronics are attached to the end of the stocking. We’re planning to relocate them to a small, button-sized housing that can be detached with a hook-and-loop fastening strip. There’s no way around this until a reliable method for cleaning the electronics is developed,” said Brunner. The sensors have to be resistant to water and detergent.
The sensors are either stitched or glued between two layers of fabric, which makes the stockings more comfortable to put on or take off. The stockings themselves are made from a blend of cotton and synthetic fibers. Brunner points out that the fabric is by necessity breathable, moisture wicking and comfortable to wear. “This is important, since the wearer will need to wear them daily.”
The researchers have already filed a patent application for the pressure-monitoring stockings, and will be presenting their prototype from May 19-21 at the SENSOR+TEST 2015 Measurement Fair in Nuremberg (Hall 12, Booth 537).
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