The colors of plants and animals can be achieved by different interactions of light with matter. [10][11][12][13][14][15][16][17] Animals or plants use the biological system colors as warning, for camouflage, or for signaling. Coloration can be generated by the selective absorption of light from the visible range of the spectrum by using pigments (pigmentary colors), which are absorbing subsets of the visible spectrum and transmitting and reflecting the other parts of the visible light. Therefore, the tissue occurs in the color of the wavelength of the reflected radiation. This is used for example by flowers of plants as a signal, because they have to stand out against the background of the vegetation in order to attract pollinating insects. Therefore, they appear in bright colors by reflecting certain wavelengths of visible light, which are then perceivable for the pollinating insects as well as for humans. [10][11][12][13] However, light-matter interaction with respect to absorption is of general importance, but will not be further discussed in this review. On the other hand, coloration can be created by coherent or incoherent scattering of light on highly structured and unstructured tissues (structural colors) in the range of the wavelength of incident light. Here, different wavelengths of light are selectively reflected from a structure and the remaining wavelengths can then be transmitted or absorbed. [10][11][12][13][14][15] These biological photonic sub-micrometer structures yield a distinct coloration through the creation of a refractive index contrast between the used materials. This is an interesting fact, because natural systems cannot be built on high-refractive index inorganic materials, which are commonly used in contemporary technology. Instead, nature makes use of biopolymers such as keratin, chitin, collagen, and cellulose. However, all of these biopolymers exhibit a refractive index around ≈1.5. In order to be able to create bright structural colors, a high refractive index contrast is required. Therefore, nature is using air voids to create the necessary refractive index contrast (Δn ≈ 0.5). Alternatively, nature can also use melanin with a refractive index of about 2 and keratin in mixed composites or by using anhydrous guanine with a refractive index of 1.83, whose crystal arrangements are responsible for the metallic luster of many fish. [15,16] Pigmentary color as well as structural color can also occur in combination (combined colors). All of these aspects can also be separated in iridescent or noniridescent colors. [10,15] Birds, like the Panama Amazon parrot (Amazona ochrocephala panamensis) or the kingfisher (Alcedo atthis) are using different combinations of pigments and sub-micrometer structured components.Cellulose is one of the most abundant biopolymers on earth. It is a sustainable and renewable raw material with many beneficial properties. Due to its availability, nontoxicity, environmental friendliness, biocompatibility, and biodegradability, cellulose is one of the world's most ...

Currently, almost all polymer optical materials are derived from fossil resources with known consequences for the environment. In this work, a processing route to obtain cellulose-based biopolymer optical fibers is presented. For this purpose, the optical properties such as the transmission and the refractive index dispersion of regenerated cellulose, cellulose diacetate, cellulose acetate propionate, and cellulose acetate butyrate were determined from planar films. Cellulose fibers were produced using a simple wet-spinning setup. They were examined pure and also coated with the cellulose derivatives to obtain core–cladding-structured optical fibers. The cellulose-based optical fibers exhibit minimum attenuations between 56 and 82 dB m–1 at around 860 nm. The ultimate transmission loss limit of the cellulose-based optical fibers was simulated to characterize the attenuation progression. By reducing extrinsic losses, cellulose-based biopolymer optical fibers could attain theoretical attenuation minima of 84.6 × 10–3 dB m–1 (507 nm), 320 × 10–3 dB m–1 (674 nm), and 745.2 × 10–3 dB m–1 (837 nm) and might substitute fossil-based polymer optical fibers in the future.

Nanoprecipitation is one of the most popular methods for producing polymer nanoparticles. However, the reported results show a large variability. In order to provide a first-hand comparative study, we prepared cellulose-based nanoparticles via different nanoprecipitation methods. Here, the influence of the coagulating solvents acetone, N,N-dimethylacetamide and tetrahydrofuran on the size and shape of the particles via precipitation using dialysis was investigated. The influence of temperature and concentration was determined by dropwise addition of the coagulation medium. Then, via rapid solvent shifting, particles were prepared from cellulose acetates with different molecular masses and the cellulose acetate propionate and cellulose acetate butyrate derivatives in the concentration range of 1–20 mg mL− 1. Thereby, it was possible to prepare spherical particles in the range from 43 to 158 nm. Furthermore, the impact of the molecular weight of these derivatives on the obtained particle size distributions was determined. It is possible to obtain pure regenerated cellulose particles in the nanometer range by a deacetylation of the derivatives. In addition, the findings were used to directly convert cellulose from a DMAc/LiCl solvent system into regenerated cellulose nanoparticles with a size of 10 ± 3 nm. Graphical abstract

Bacterial cellulose (BC) represents a renewable biomaterial with unique properties promising for biotechnology and biomedicine. Komagataeibacter hansenii ATCC 53,582 is a well-characterized high-yield producer of BC used in the industry. Its genome encodes three distinct cellulose synthases (CS), bcsAB1, bcsAB2, and bcsAB3, which together with genes for accessory proteins are organized in operons of different complexity. The genetic foundation of its high cellulose-producing phenotype was investigated by constructing chromosomal in-frame deletions of the CSs and of two predicted regulatory diguanylate cyclases (DGC), dgcA and dgcB. Proteomic characterization suggested that BcsAB1 was the decisive CS because of its high expression and its exclusive contribution to the formation of microcrystalline cellulose. BcsAB2 showed a lower expression level but contributes significantly to the tensile strength of BC and alters fiber diameter significantly as judged by scanning electron microscopy. Nevertheless, no distinct extracellular polymeric substance (EPS) from this operon was identified after static cultivation. Although transcription of bcsAB3 was observed, expression of the protein was below the detection limit of proteome analysis. Alike BcsAB2, deletion of BcsAB3 resulted in a visible reduction of the cellulose fiber diameter. The high abundance of BcsD and the accessory proteins CmcAx, CcpAx, and BglxA emphasizes their importance for the proper formation of the cellulosic network. Characterization of deletion mutants lacking the DGC genes dgcA and dgcB suggests a new regulatory mechanism of cellulose synthesis and cell motility in K. hansenii ATCC 53,582. Our findings form the basis for rational tailoring of the characteristics of BC. Key points • BcsAB1 induces formation of microcrystalline cellulose fibers. • Modifications by BcsAB2 and BcsAB3 alter diameter of cellulose fibers. • Complex regulatory network of DGCs on cellulose pellicle formation and motility.

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The fabrication of green optical waveguides based on cellulose and spider silk might allow the processing of novel biocompatible materials. Regenerated cellulose fibers are used as the core and recombinantly produced spider silk proteins eADF4(C16) as the cladding material. A detected delamination between core and cladding could be circumvented by using a modified spider silk protein with a cellulose-binding domain-enduring permanent adhesion between the cellulose core and the spider silk cladding. The applied spider silk materials were characterized optically, and the theoretical maximum data rate was determined. The results show optical waveguide structures promising for medical applications, for example, in the future.

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