Cephalopod-inspired optical engineering of human cells

Abstract

Although many animals have evolved intrinsic transparency for the purpose of concealment, the development of dynamic, that is, controllable and reversible, transparency for living human cells and tissues has remained elusive to date. Here, by drawing inspiration from the structures and functionalities of adaptive cephalopod skin cells, we design and engineer human cells that contain reconfigurable protein-based photonic architectures and, as a result, possess tunable transparency-changing and light-scattering capabilities. Our findings may lead to the development of unique biophotonic tools for applications in materials science and bioengineering and may also facilitate an improved understanding of a wide range of biological systems.

Structure, self-assembly, and properties of a truncated reflectin variant

“…For concentrations of ≤∼5 mg/mL, the measurements again revealed small radii of <∼1.5 nm, but for concentrations of ≥∼7.5 mg/mL, the measurements revealed large radii of >∼14 nm. Based on the DLS experiments, RfA1TV achieved its smallest R H at pH values of ≤∼4 and for concentrations of ≤∼5 mg/mL, in agreement with our and others’ findings for RfA1 ( 32 , 35 – 37 , 40 ). As such, we studied presumably monomeric RfA1TV solubilized in pH = 3.2, 20 mM ammonium formate buffer at concentrations of ≤∼5 mg/mL, as shown in Fig.…”

“…The UV-Vis absorption spectra revealed a main peak at ∼280 nm, corresponding to absorption by the aromatic amino acids, as well as little tailing at higher wavelengths, confirming negligible aggregation into larger particles ( Fig. 3 C ) ( 32 , 40 ). The fluorescence emission spectra exhibited a peak at ∼350 nm associated with RfA1TV’s tryptophan residues, as expected from prior observations for RfA1 ( Fig.…”

“…As the parent protein for our truncated variant, we specifically chose D. pealeii reflectin A1 (RfA1), for which the sequence is shown in Fig. 1 G , because this isoform contains prototypical RMN and RMI motifs separated by variable linker regions, features a >60% homology with most of the reported reflectins, exhibits reasonable aqueous solubility, possesses well-studied self-assembly characteristics, demonstrates valuable optical functionality, and is found in multiple types of squid skin cells ( 15 , 18 , 22 , 27 , 32 , 33 , 35 – 37 , 39 , 40 ). From full-length RfA1’s amino acid sequence, we selected a prototypical truncated reflectin variant (RfA1TV) consisting of the first RMI motif and its preceding linker region, as shown in Fig.…”

“…Within this context, unique structural proteins known as reflectins have recently attracted substantial attention because of their key roles in the fascinating color-changing capabilities of cephalopods, such as the squid shown in Fig. 1 A , and have furthermore demonstrated their utility for unconventional biophotonic and bioelectronic technologies ( 11 – 40 ). For example, in vivo, Bragg stack-like ultrastructures from reflectin-based high refractive index lamellae (membrane-enclosed platelets) are responsible for the angle-dependent narrowband reflectance (iridescence) of squid iridophores, as shown in Fig.…”

Phylogenetic comparison of egg transparency in ascidians by hyperspectral imaging

“…The mechanism of ascidian transparency may also be elucidated by focusing on these factors in the future. The study of transparency is quite attractive because it contributes to various fields not only in ecological evolutionary developmental biology (eco-evo-devo) but also imaging systems and materials science 43 . Figure 6.…”