Compression therapy is a standard form of treatment for varicose ulcers and other venous blood flow disorders, such as the use of pressure socks and bandages to help stimulate blood flow. But there is no clear way to test whether these products can exert the best pressure under certain conditions.

Recently, engineers at the Massachusetts Institute of Technology have developed a kind of pressure – sensing photonic fiber and weave it into a typical compression bandage. When the bandage is stretched, the fiber changes color. The nursing staff can check the pressure according to the discoloration of the bandage to determine whether the bandage needs relaxation or tightening. The research results were published on Advanced Healthcare Materials.

Inspiration from Nature  

Researchers were inspired by a kind of tropical berry called Margaritaria nobilis that can produce very bright blue(the epidermis of this berry is made up of periodic cellulose structure cells, which can be reflected through these cells and make the fruit have a marked metallic blue), and they have found the method of constructing this special structure in the synthetic material. The multi layer fiber is made from tensile material so that it can change the thickness of the single layer at the time of drawing, so that the color of the fiber can be adjusted.

Researchers say that the color of this photon fiber is not derived from any inherent pigments, but rather from well-designed structures: Each fiber is about 10 times the diameter of a man’s hair. It is made by coating the thin transparent rubber layer evenly on the elastic core wire by spin coating. Each layer of the transparent rubber layer is only a few hundred nanometers thick, and the thickness can be determined by the speed of rotation.

In this structure, light can be reflected by every interface between layers. When a fiber layer with uniform thickness is sufficient, the interface is reflected to interact to enhance the brightness of some colors in the visible spectrum, such as red, while reducing the brightness of other colors. This gives the fiber a certain color, and the thickness of the fiber varies with different layers. Researchers say that the color of this structure can be brighter and stronger than that of ink or dye, and these colors will persist as long as the structure remains unchanged.

Reflecting pressure changes  

The research team further used optical fiber standard optical modeling method to adjust the thickness of the optical fiber layer and made any photonic fibers that could achieve with any desired color. By using the relationship between the tension and pressure of the bandage and the relationship between the fiber color and the strain, they drew a color chart to match the different colors of the fiber during stretching with the pressure generated by the bandage.

To test the effect of bandages, the researchers compared ordinary bandages, photon fiber bandages and commercially available rectangular bandages with rectangular patterns. Among them, the bandage that prints rectangular pattern extends to square at the best pressure. The bandage of the fiber knitted fabric gives the clearest pressure feedback, which is most likely to exert the most ideal pressure on the affected limb.