Engineers design colour-changing compression bandage
01 June 2018
Engineers at MIT have developed pressure-sensing photonic fibres that they have woven into a typical compression bandage designed to help carers at home.
As the bandage is stretched, the fibres change colour. Using a colour chart, a caregiver can stretch a bandage until it matches the colour for a desired pressure, before, say, wrapping it around a patient’s leg.
The photonic fibres can then serve as a continuous pressure sensor — if their colour changes, caregivers or patients can use the colour chart to determine whether and to what degree the bandage needs loosening or tightening.
“Getting the pressure right is critical in treating many medical conditions including venous ulcers, which affect several hundred thousand patients in the U.S. each year,” says Mathias Kolle, assistant professor of mechanical engineering at MIT. “These fibres can provide information about the pressure that the bandage exerts. We can design them so that for a specific desired pressure, the fibres reflect an easily distinguished colour.”
The colour of the photonic fibres arises not from any intrinsic pigmentation, but from their carefully designed structural configuration. Each fibre is about 10 times the diameter of a human hair. The researchers fabricated the fibre from ultrathin layers of transparent rubber materials, which they rolled up to create a jelly-roll-type structure. Each layer within the roll is only a few hundred nanometres thick.
In this rolled-up configuration, light reflects off each interface between individual layers. With enough layers of consistent thickness, these reflections interact to strengthen some colours in the visible spectrum, for instance red, while diminishing the brightness of other colours. This makes the fibre appear a certain colour, depending on the thickness of the layers within the fibre.
“Structural colour is really neat, because you can get brighter, stronger colours than with inks or dyes just by using particular arrangements of transparent materials,” Sandt says. “These colours persist as long as the structure is maintained.”
The researchers are now looking for ways to scale up the fibre fabrication process. Currently, they are able to make fibres that are several inches long. Ideally, they would like to produce metres or even kilometres of such fibres at a time.
“Currently, the fibres are costly, mostly because of the labour that goes into making them,” Kolle says. “The materials themselves are not worth much. If we could reel out kilometres of these fibres with relatively little work, then they would be dirt cheap.”
Then, such fibres could be threaded into bandages, along with textiles such as athletic apparel and shoes as colour indicators for, say, muscle strain during workouts. Kolle envisions that they may also be used as remotely readable strain gauges for infrastructure and machinery.
“Of course, they could also be a scientific tool that could be used in a broader context, which we want to explore,” Kolle says.