Researchers at MIT developed a compression bandage with pressure-sensing photonic fibres, which change colour when stretched.

Compression bandages and stockings are use for conditions in which veins struggle to return blood from the lower extremities. When wrapped tightly around the affected limb, the bandage can stimulate blood flow. However, there was no clear way to measure whether the bandage was applying an optimal pressure for a given condition, until now.

Engineers at MIT developed pressure-sensing, photonic fibres, which they wave in a typical compression bandage. As the bandage is stretched, the fibres change colour. Using a colour chart, the caregiver can stretch the bandage until it matches the colour for a desire pressure.

The photonic fibres can also serve as a continuous pressure sensor. If the colour changes, the colour chart can be used to determine to which degree the bandage has to be loosened or tightened.

The colours of the fibres come from their carefully designed structural configuration, rather than intrinsic pigmentation. The fibres are made from ultrathin layers of transparent, commonly available rubber materials, which are rolled up. Each layer is only a few nanometres thick.

The fibres’ design relies upon a phenomenon called optical interference, in which light is reflected from a periodic stack of thin, transparent layers and produces an array of colours, depending on the stack’s geometric parameters and material composition. The same phenomenon can be spotted in oil puddles, soap bubbles, peacock feathers and butterfly wings. With enough layers of consistent thickness, the light reflections interact to strengthen come colours in the visible spectrum, while diminishing the brightness of other colours. This causes the fibre to appear a certain colour.

The team can tune the thickness of the fibres’ layers to produce any desired colour tuning, using standard optical modelling approaches customised for their fibre design.

Images: MIT