Watch a gel embedded with heart cells change color with every beat

Some of the most brilliant displays of color in the natural world, such as a peacock’s iridescent tail and the shimmering wings of the Morpho butterfly, are created not by pigments, but by the microscopic structure of feathers, scales, and skin. Now, inspired by the structural colors produced by chameleons, scientists have created a “living” gel that uses beating heart cells to change its own color.

A chameleon’s skin contains tiny crystals that reflect some wavelengths of light but absorb others; it alters the distance between these crystals to change which wavelengths are reflected. To mimic this system, researchers created tightly packed arrays of nanoparticles, and then they poured on a special gel which they hardened and peeled away, leaving a network of tiny pores. Some wavelengths of light disappeared down these holes, while others were reflected, producing vivid colors. The researchers then cultured heart muscle cells from rats onto the gel. These cells beat in synchrony, causing the gel to bend and altering its microscopic structure. This produced a changing color in rhythm with the contraction of the cells, they report today in Science Robotics.

The scientists used this biohybrid gel to create a 3D, color-changing butterfly. As the heart cells beat, the butterfly bent its wings back and forth, producing shimmering colors. They also created a “heart-on-a-chip” system to look at the effects of drugs on the gel. When they added isoproterenol, a medication that increases heart rate, the frequency of beating increased—and the color of the gel shifted more. This could be a useful tool to screen new medications, they say, allowing researchers to see drug effects using only the naked eye.