Watch a gel embedded with heart cells change color with every beat
Nature is full of organisms that iridesce in wild displays of structural color and some can even control it themselves. While dyes and pigments produce colour by selectively absorbing light, structural colors are produced when light interacts with the microscopic structure of a material. Inspired by an organism that uses structural color, the chameleon, researchers have created a biohybrid– a color-changing gel embedded with living heart cells that can display and control structural color on its own. Their method involves placing heart muscle cells, cardiomyocytes, onto biocompatible gels with structural color properties. The gels were made by arranging silica nanoparticles on a glass slide and covering them with a specialized gelatin. This gel was then peeled off, leaving imprints of tiny pores from the nanoparticles. Some wavelengths of light disappeared down into the pores, while others were reflected, creating vivid colors. When the heart cells swell and contract, the gel does the same, resulting in a shift in its structural color, in synchrony with the pulsing of the cells. By placing cells into tiny patterned grooves in the gel, the team was able to create a material that mimics a tiny butterfly flapping its wings. As the cells expand and contract, the wings move, displaying a changing structural color. The team also showed that the biohybrid gels could be combined with other materials to mimic the functions of the heart as a virtual “heart on a chip.” Such a device could be used for biomedical testing instead of using human or animal organs. They tested the heart-on-chip by adding various concentrations of a drug which is known to change the heart rate. Different concentrations of the drug made the heart cells beat at different frequencies and produce shifts in the structural colour of the gel. This platform could make it easier to monitor the effects of drugs in testing using only the naked eye.