Alon A. Gorodetsky of the University of California, Irvine, and coworkers have given some of that camouflage ability to human cells. The researchers engineered human embryonic kidney cells to make a protein called reflectin that gives somecephalopod skin cells and organs their optical properties (Nat. Commun. 2020, DOI: 10.1038/s41467-020-16151-6).
Tests show that the reflectin protein changed the refractive index of the human cells. Regions of the cells with reflectin nanoparticles had refractive indices that approximated those of cephalopod skin cells, whereas regions without the nanoparticles had refractive indices like those of the cytoplasm of mammalian cells. The researchers then tuned the optical properties of cells containing reflectin nanostructures by adjusting the ionic strength of the solution in which they were grown.
The work is “a revolutionary accomplishment,” says Daniel E. Morse, who studies biophotonics in cephalopods at the University of California, Santa Barbara. Gorodetsky and colleagues have “opened the door to the exciting and long-envisioned opportunities for genetic and cellular engineering of tunable biophotonics,” Morse says.
A self-described “sci-fi nerd,” Gorodetsky has a long-term vision of engineering human camouflage a-la H. G. Wells’s Invisible Man, but he also sees more immediate applications for the reflectin-producing human cells. Cephalopod cells are difficult to grow in labs. Engineered human cells could provide a way to study reflectins. In addition, reflectin nanostructures could be used as biomolecular tags for phase microscopy, he says.
“These exciting first steps illustrate the ability to program living cellular systems with non-natural, photonic properties that are reminiscent of how cephalopod dermal organs perform,” says Leila F. Deravi, who designs cephalopod-mimicking materials at Northeastern University. “Will we be seeing humans on the street with color-changing skin any time soon? Probably not. But these early proof-of-concept studies definitely ignite the imagination as we begin to envision a path towards such futuristic concepts.”