By drawing inspiration from the structures and functionalities of squid skin cells, a team of researchers designed and engineered human cells that contain stimuli-responsive photonic architectures and, as a consequence, possess the ability to change their appearance and transmission of light.
Left: squid reflectin protein nanostructures in human cells (dark regions, with some indicated by white arrows). Right: associated pathlength for light traveling through a given area (red corresponds to longer pathlengths and blue corresponds to shorter pathlengths). Image credit: Atouli Chatterjee / University of California, Irvine.
“Our project — which is decidedly in the realm of science — centers on designing and engineering cellular systems and tissues with controllable properties for transmitting, reflecting and absorbing light,” said first author Atrouli Chatterjee, a doctoral student in the Department of Chemical and Biomolecular Engineering at the University of California, Irvine.
For the study, Chatterjee and colleagues drew inspiration from the way females of a squid species called Doryteuthis opalescens can evade predators by dynamically switching a stripe on their mantle from nearly transparent to opaque white.
The researchers then borrowed some of the intercellular protein-based particles involved in this biological cloaking technique and found a way to introduce them into human cells to test whether the light-scattering powers are transferable to other animals.
Doryteuthis opalescens have light-scattering cells called leucophores.
Within these cells are leucosomes, membrane-bound particles which are composed of proteins known as reflectins, which can produce iridescent camouflage.
In their experiments, the scientists cultured human embryonic kidney cells and genetically engineered them to express reflectin.
They found that the protein would assemble into particles in the cells’ cytoplasm in a disordered arrangement.
They also saw through optical microscopy and spectroscopy that the introduced reflectin-based structures caused the cells to change their scattering of light.
“We were amazed to find that the cells not only expressed reflectin but also packaged the protein in spheroidal nanostructures and distributed them throughout the cells’ bodies,” said senior author Dr. Alon Gorodetsky, a researcher in the Department of Chemical and Biomolecular Engineering, the Department of Materials Science and Engineering, and the Department of Chemistry at the University of California, Irvine.
“Through quantitative phase microscopy, we were able to determine that the protein structures had different optical characteristics when compared to the cytoplasm inside the cells.”
“In other words, they optically behaved almost as they do in their native cephalopod leucophores.”
The team also tested whether the reflectance could potentially be toggled on and off through external stimuli.
The authors sandwiched cells in between coated glass plates and applied different concentrations of sodium chloride.
Measuring the amount of light that was transmitted by the cells, they found that the ones exposed to higher sodium levels scattered more light and stood out more from the surroundings.
“Our experiments showed that these effects appeared in the engineered cells but not in cells that lacked the reflectin particles, demonstrating a potential valuable method for tuning light-scattering properties in human cells,” Chatterjee said.
The results are published in the journal Nature Communications.
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A. Chatterjee et al. 2020. Cephalopod-inspired optical engineering of human cells. Nat Commun 11, 2708; doi: 10.1038/s41467-020-16151-6
