Coastal and deep-sea biodegradation of polyhydroxyalkanoate microbeads.

Microbeads find widespread usage in personal care items and cosmetics, serving as exfoliants or scrubbing agents. Their micro-scale size poses challenges in effective drainage capture and given their origin from non-biodegradable oil-based plastics, this contributes substantially to marine pollution. In this study, microbeads were prepared by a simple yet scalable melt homogenization method using four types of polyhydroxyalkanoates (PHA), namely poly[(R)-3-hydroxybutyrate] (P(3HB)), poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate] (P(3HB-co-3HV)), poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate] (P(3HB-co-3HHx)) and poly[(R)-3-hydroxybutyrate-co-(R)-4-hydroxyvalerate] (P(3HB-co-4HB)). Microbeads with different surface smoothness, compressive strength (6.2-13.3 MPa) and diameter (from 1 ~ 150 µm) could be produced. The microbeads were subjected to a comprehensive degradation analysis using three techniques: enzymatic, Biochemical Oxygen Demand (BOD) evaluations, and in situ degradation tests in the deep-sea off Misaki Port in the northern Pacific Ocean (depth of 757 m). Qualitatively, results from enzymatic and in situ degradation demonstrated significant degradation within one week and five months, respectively. Quantitatively, BOD findings indicated that all PHA microbeads degraded similarly to cellulose (~ 85% biodegradability in 25 days). In conclusion, PHA microbeads from this study exhibit promising potential as alternatives to conventional non-biodegradable microbeads.

Elucidation of the Specific Ion Effects and Intermediate Structures of Cellulose Fibers Swollen in Inorganic Salt Solutions via In Situ X-ray Diffraction.

The solubilities of many substances are significantly affected by specific ions, as demonstrated by the Hofmeister series of proteins. Cellulose has a resistant fibrillar structure that hinders its swelling and dissolution. Certain inorganic salt solutions are effective swelling agents and solvents for cellulose. However, the precise effects of these ions on cellulose are not fully understood. In this study, we studied the intermediate structures of cellulose fibers during their swelling process in ZnCl2 and LiBr solutions via in situ X-ray diffraction. Two swollen phases with characteristic morphologies were observed for both salt treatments. Only the surfaces of the fibers were swollen in ZnCl2, whereas the ions penetrated the fibers and formed complexes with cellulose while the morphology of the fibers was maintained in LiBr. Our findings clarify the reasons that ZnCl2 has been used as an excellent swelling agent, whereas LiBr has been used as a good solvent for cellulose.

Low solid content mouldable chitin physical hydrogel prepared by atypical rupture-free swelling.

In this study, the atypical swelling gelation of chitin physical hydrogels was investigated. Just by tuning the amount of the N-acetylation reagent, the degree of acetylation varied and mouldable chitin hydrogels with a wide variety of gel concentrations (0.2-6.4 wt%) were obtained. In response to the gel concentration, the mechanical properties ranged from swollen soft gels to shrunken rigid gels (compressive moduli of 4-310 kPa). The thus-prepared chitin hydrogels, which were composed of only chitin and water, exhibited high transparency and integrity. The swelling gelation of chitin physical hydrogels was achieved owing to both the positive charges of the amino groups inducing the osmotic pressure and the toughness of the crystalline nanofibrous network structure of the chitin hydrogels that endured the large volume change. These previously unnoticed advantageous aspects of chitin have pioneered a novel area of swellable physical gels that has been exclusive to chemical gels so far.

Microbial decomposition of biodegradable plastics on the deep-sea floor.

Microbes can decompose biodegradable plastics on land, rivers and seashore. However, it is unclear whether deep-sea microbes can degrade biodegradable plastics in the extreme environmental conditions of the seafloor. Here, we report microbial decomposition of representative biodegradable plastics (polyhydroxyalkanoates, biodegradable polyesters, and polysaccharide esters) at diverse deep-sea floor locations ranging in depth from 757 to 5552 m. The degradation of samples was evaluated in terms of weight loss, reduction in material thickness, and surface morphological changes. Poly(L-lactic acid) did not degrade at either shore or deep-sea sites, while other biodegradable polyesters, polyhydroxyalkanoates, and polysaccharide esters were degraded. The rate of degradation slowed with water depth. We analysed the plastic-associated microbial communities by 16S rRNA gene amplicon sequencing and metagenomics. Several dominant microorganisms carried genes potentially encoding plastic-degrading enzymes such as polyhydroxyalkanoate depolymerases and cutinases/polyesterases. Analysis of available metagenomic datasets indicated that these microorganisms are present in other deep-sea locations. Our results confirm that biodegradable plastics can be degraded by the action of microorganisms on the deep-sea floor, although with much less efficiency than in coastal settings.

A simple microplastic splitter for subsampling expanded polystyrene particles.

With the high number of microplastic-like particles captured by net hauls including manta or neuston nets, it is often required to subsample in order to decrease sample volume for microplastic enumeration and analysis. Plankton splitter is commonly used to divide microplastic samples. However, current devices such as Folsom plankton splitter and Motoda box splitter have accuracy issues in separating highly buoyant microplastics, namely expanded polystyrene (EPS) as they tend to adhere to the inner walls. Inspired by an apple cutter, we have developed a simple radial splitter made of stainless steel that efficiently divides EPS microplastic samples into precise aliquots. With this simple device, we uniformly divided EPS microplastic samples from marine environments into eight aliquots with no significant differences. The device is a versatile tool to partition all buoyant microplastics including polypropylene and polyethylene microplastics.•The method developed facilitates the precise division of buoyant microplastics into equal aliquots.•The method is specifically effective in splitting expanded polystyrene particles with high buoyancy.

Chitin nanofiber-coated biodegradable polymer microparticles via one-pot aqueous process.

Tailoring the surface of biodegradable microparticles is important for various applications in the fields of cosmetics, biotechnology, and drug delivery. Chitin nanofibers (ChNFs) are one of the promising materials for surface tailoring owing to its functionality, such as biocompatibility and antibiotic properties. Here, we show biodegradable polymer microparticles densely coated with ChNFs. Cellulose acetate (CA) was used as the core material in this study, and ChNF coating was successfully carried out via a one-pot aqueous process. The average particle size of the ChNF-coated CA microparticles was approximately 6 µm, and the coating procedure had little effect on the size or shape of the original CA microparticles. The ChNF-coated CA microparticles comprised 0.2-0.4 wt% of the thin surface ChNF layers. Owing to the surface cationic ChNFs, the ζ-potential value of the ChNF-coated microparticles was +27.4 mV. The surface ChNF layer efficiently adsorbed anionic dye molecules, and repeatable adsorption/desorption behavior was exhibited owing to the coating stability of the surface ChNFs. The ChNF coating in this study was a facile aqueous process and was applicable to CA-based materials of various sizes and shapes. This versatility will open new possibilities for future biodegradable polymer materials that satisfy the increasing demand for sustainable development.

Identification of Chitin Allomorphs in Poorly Crystalline Samples Based on the Complexation with Ethylenediamine.

Chitin is a key component of hard parts in many organisms, but the biosynthesis of the two distinctive chitin allomorphs, α- and ß-chitin, is not well understood. The accurate determination of chitin allomorphs in natural biomaterials is vital. Many chitin-secreting living organisms, however, produce poorly crystalline chitin. This leads to spectrums with only broad lines and imprecise peak positions under conventional analytical methods such as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy, and solid-state nuclear magnetic resonance spectroscopy, resulting in inconclusive identification of chitin allomorphs. Here, we developed a novel method for discerning chitin allomorphs based on their different complexation capacity and guest selectivity, using ethylenediamine (EDA) as a complexing agent. From the peak shift observed in XRD profiles of the chitin/EDA complex, the chitin allomorphs can be clearly discerned. By testing this method on a series of samples with different chitin allomorphs and crystallinity, we show that the sensitivity is sufficiently high to detect the chitin allomorphs even in near-amorphous, very poorly crystalline samples. This is a powerful tool for determining the chitin allomorphs in phylogenetically important chitin-producing organisms and will pave the way for clarifying the evolution and mechanism of chitin biosynthesis.

Unusual bromine enrichment in the gastric mill and setae of the hadal amphipod Hirondellea gigas.

The hadal amphipod Hirondellea gigas is an emblematic animal of the Pacific trenches, and has a number of special adaptations to thrive in this 'extreme' environment, which includes the deepest part of the Earth's ocean. One such adaptation that has been suggested is the presence of an 'aluminum gel shield' on the surface of its body in order to prevent the dissolution of calcitic exoskeleton below the carbonate compensation depth. However, this has not been investigated under experimental conditions that sufficiently prevent aluminum artefacts, and the possibility of other elements with similar characteristic X-ray energy as aluminum (such as bromine) has not been considered. Here, we show with new electron microscopy data gathered under optimized conditions to minimize aluminum artefacts that H. gigas actually does not have an aluminum shield-instead many parts of its body are enriched in bromine, particularly gastric ossicles and setae. Results from elemental analyses pointed to the use of calcite partially substituted with magnesium by H. gigas in its exoskeleton, in order to suppress dissolution. Our results exemplify the necessity of careful sample preparation and analysis of the signals in energy-dispersive X-ray spectroscopic analysis, and the importance of analyses at different electron energies.

Uniaxial orientation of ß-chitin nanofibres used as an organic framework in the scales of a hot vent snail.

Organisms use various forms and orientations of chitin nanofibres to make structures with a wide range of functions, from insect wings to mussel shells. Lophotrochozoan animals such as snails and annelid worms possess an ancient 'biomineralization toolkit', enabling them to flexibly and rapidly evolve unique hard parts. The scaly-foot snail is a gastropod endemic to deep-sea hydrothermal vents, unique in producing dermal sclerites used as sites of sulfur detoxification. Once considered to be strictly proteinaceous, recent data pointed to the presence of chitin in these sclerites, but direct evidence is still lacking. Here, we show that ß-chitin fibres (approx. 5% of native weight) are indeed the building framework, through a combination of solid-state nuclear magnetic resonance spectroscopy, wide-angle X-ray diffraction, and electron microscopy. The fibres are uniaxially oriented, likely forming a structural basis for column-like channels into which the scaly-foot snail is known to actively secrete sulfur waste-expanding the known function of chitinous hard parts in animals. Our results add to the existing evidence that animals are capable of modifying and co-opting chitin synthesis pathways flexibly and rapidly, in order to serve novel functions during their evolution.

Massive occurrence of benthic plastic debris at the abyssal seafloor beneath the Kuroshio Extension, the North West Pacific.

The abyss (3500-6500 m) covers the bulk of the deep ocean floor yet little is known about the extent of plastic debris on the abyssal seafloor. Using video imagery we undertook a quantitative assessment of the debris present on the abyssal seafloor (5700-5800 m depth) beneath the Kuroshio Extension current system in the Northwest Pacific. This body of water is one of the major transit pathways for the massive amounts of debris that are entering the North Pacific Ocean from Asia. Shallower sites (1400-1500 m depth) were also investigated for comparison. The dominant type of debris was single-use plastics - mainly bags and food packaging. The density of the plastic debris (mean 4561 items/km2) in the abyssal zone was the highest recorded for an abyssal plain suggesting that the deep-sea basin in the Northwest Pacific is a significant reservoir of plastic debris.

Plastic additives in deep-sea debris collected from the western North Pacific and estimation for their environmental loads.

Plastic waste has become a growing concern in terms of marine pollution, but little information is available on plastic debris and its possible risks of chemical additives exposure in the deep-sea. This study focused on identification of polymer type and additive concentrations in 21 plastic debris collected from deep-sea of Sagami Bay, Japan and West Pacific Ocean under the Kuroshio Extension and its recirculation gyre (KERG) zone (water depth: 1388-5819 m). Polyethylene (PE) was dominant polymer (57% of the total) in samples, followed by polyvinylchloride (PVC), epoxy resin, polyester (PES), and polypropylene. In plastic additives, bis (2-ethylhexyl) phthalate (DEHP) was detected to be contained in a PVC sheet at concentration of 48%. Butylated hydroxytoluene (BHT) was also detected in PE plastic debris with median concentration of 12,000 ng/g. PES clothes were detected to contain dyeing mixtures, 1,2,4-trichlorobenzene (1,2,4-TCB), up to 42,000 ng/g. Knowing the estimated number of plastic debris under KE current, the minimum burden of chemical additives were estimated that 720 kg of dibutyl phthalate, 570 kg of BHT, 230 kg of DEHP, and 160 kg of 1,2,4-TCB exist on the seabed of KERG zone. This result strongly suggests that enormous amount of hazardous additives lie within plastic debris on abyssal level of the ocean.

Abundant Chitinous Structures in Chilostomella (Foraminifera, Rhizaria) and Their Potential Functions.

Benthic foraminifera, members of Rhizaria, inhabit a broad range of marine environments and are particularly common in hypoxic sediments. The biology of benthic foraminifera is key to understanding benthic ecosystems and relevant biogeochemical cycles, especially in hypoxic environments. Chilostomella is a foraminiferal genus commonly found in hypoxic deep-sea sediments and has poorly understood ecological characteristics. For example, the carbon isotopic compositions of their lipids are substantially different from other co-occurring genera, probably reflecting unique features of its metabolism. Here, we investigated the cytoplasmic and ultrastructural features of Chilostomella ovoidea from bathyal sediments of Sagami Bay, Japan, based on serial semi-thin sections examined using an optical microscope followed by a three-dimensional reconstruction, combined with TEM observations of ultra-thin sections. Observations by TEM revealed the presence of abundant electron-dense structures dividing the cytoplasm. Based on histochemical staining, these structures are shown to be composed of chitin. Our 3D reconstruction revealed chitinous structures in the final seven chambers. These exhibited a plate-like morphology in the final chambers but became rolled up in earlier chambers (toward the proloculus). These chitinous, plate-like structures may function to partition the cytoplasm in a chamber to increase the surface/volume ratio and/or act as a reactive site for some metabolic functions.

Primary structure of gum arabic and its dynamics at oil/water interface.

Gum arabic (GA), an arabinogalactan-based gum, is a well-known powerful emulsifier. However, the poor stability of emulsion has often been pointed out. In order to clarify the origin, the structure-property relationship of GA, especially the interfacial property at oil/water interface, needs to be investigated. Here, we tried to correlate the primary structure with interfacial property at oil/water interface. A series of structural analyses by SEC-MALLS, SAXS, etc. showed that the primary structure of GA was a disk-like star shaped nanoparticle. The dynamic interfacial tension measurement showed that GA molecules adsorb onto oil surface in 2 steps: Firstly, the micron-aggregates of GA approach onto the oil surface, and then the aggregates are dissociated into nano-particles so that they cover the oil surface. Therefore, the emulsification and emulsion stability are controlled not by the property of the primary structure of GA but by the higher-order molecular network structure made of GA molecules.

Salt-induced LCST-type thermal gelation of methylcellulose: quantifying non-specific interactions via fluctuation theory.

What drives the phase separation of water-soluble polymers in the presence of electrolytes was quantified on a molecular scale via statistical thermodynamic fluctuation theory. Quantifying polymer-water and polymer-salt interactions enabled us to identify the dominant interaction for phase separation. As a model system, the lower critical solution temperature (LCST) type thermal gelation of methylcellulose (MC) in aqueous salt solutions was chosen. The Kirkwood-Buff integrals for intermolecular interactions, calculated from the published calorimetric and volumetric data, showed that (1) the accumulation of salts around MC molecules (favourable interaction between salts and MC) inhibits thermal gelation and the depletion of salts from MC (unfavourable interaction between salts and MC) promotes the gelation, and (2) this salt-MC interaction is the dominant factor (50-100 times stronger than the water-MC interaction). This insight from the fluctuation theory is at odds with the age-old consensus regarding the driving force of thermal gelation: water structure change in the presence of salts induces the promotion or inhibition of thermal gelation. However, our conclusion is founded upon the ability of the fluctuation theory to quantify water-MC and salt-MC interaction independently via the Kirkwood-Buff integrals. Flory-Huggins (FH) theory, on the contrary, could not separate these two interactions owing to the lack of a thermodynamic degree of freedom because the lattice solution is assumed to be fully packed. In addition, the dominant contribution from salt depletion poses difficulty for the χ parameter, which is essentially the difference of contact energies. Our approach, requiring calorimetric and volumetric data alone as input, provides a simple and versatile method towards elucidating the effect of cosolvents on biopolymer phase separation of physiological importance.

Cellulose hydrogel with tunable shape and mechanical properties: From rigid cylinder to soft scaffold.

Cellulose hydrogel from aqueous solution of lithium bromide demonstrated excellent tunability of mechanical property and shape. A series of compression tests showed that cellulose hydrogel covered a wide range of mechanical property, where the compressive Young's modulus was controllable from 30 kPa to 1.3 MPa by changing the initial concentration of cellulose solution. Meanwhile, the diameter of the building block of gel, namely nano-fibrous cellulose, was constant at 15-20 nm irrelevant of the initial concentration of cellulose solution. Moreover, thanks to the biocompatibility of cellulose, the cultivation of cartilage tissue was successful in the micro-porous sponge-like cellulose hydrogel prepared by salt-leaching process. These findings show that this environmentally-benign versatile gel offers a new substrate for the biomaterial-based nanomaterial in biomedical applications.

Clearly Transparent Nanopaper from Highly Concentrated Cellulose Nanofiber Dispersion Using Dilution and Sonication.

Nanopaper prepared from holocellulose pulp is one of the best substrates for flexible electronics because of its high thermal resistance and high clear transparency. However, the clearness of nanopaper decreases with increasing concentration of the starting cellulose nanofiber dispersion-with the use of a 2.2 wt % dispersion, for example-resulting in translucent nanopaper with a high haze of 44%. To overcome this problem, we show that the dilution of this high-concentration dispersion with water followed by sonication for 10 s reduces the haze to less than 10% while maintaining the high thermal resistance of the nanopaper. Furthermore, the combination of water dilution and a short sonication treatment improves the clearness of the nanopaper, which would translate into cost savings for the transportation and storage of this highly concentrated cellulose nanofiber dispersion. Finally, we demonstrate the improvement of the electrical conductivity of clear transparent nanopaper prepared from an initially high-concentration dispersion by dropping and heating silver nanowire ink on the nanopaper. These achievements will pave the way toward the realization of the mass production of nanofiber-based flexible devices.

Solution-state structures of the cellulose model pullulan in lithium chloride/N,N-dimethylacetamide.

Pullulan is soluble in both N,N-dimethylacetamide (DMAc) and LiCl/DMAc. Here, the solution-state structures of pullulan in these two solvents were studied by size-exclusion chromatography with multi-angle laser light scattering (SEC/MALLS) and nuclear magnetic resonance (NMR) analyses. SEC/MALLS and off-line refractive index analyses revealed that the hydroxy groups of pullulan interact with LiCl in DMAc, as observed previously for cellulose. The nine different COH protons of pullulan in DMAc and LiCl/DMAc appeared independently in NMR spectra and were successfully assigned. When LiCl was present, the degree of dissociation of all COH protons of pullulan was increased by Li+ and Cl- ions, and the conformations of the COH groups became stable and restricted in DMAc. Based on the obtained results, the solution-state structures of cellulose in LiCl/DMAc are hypothesized to contain similar interactions between the cellulose hydroxy groups, and Li+ and Cl- in LiCl/DMAc to those observed for pullulan.

Clear transparent cellulose nanopaper prepared from a concentrated dispersion by high-humidity drying.

Optically transparent cellulose nanopaper is a promising candidate for flexible device substrates because of its light weight, surface smoothness, and high dimensional stability with respect to temperature. Conventionally, clear transparent nanopaper has been fabricated from cellulose nanofiber dispersions with quite low concentration: less than 0.5 wt%. However, this diluteness leads to several problems, such as huge energy consumption and long operation time for drying. Therefore, nanopaper should be fabricated from a concentrated dispersion to mitigate these problems. In this study, transparent nanopaper was fabricated from cellulose nanofiber dispersions with various concentrations (0.24-1.81 wt%). Optical experiments revealed that the haze of the transparent nanopaper increased monotonically with cellulose nanofiber dispersion concentration, when the cellulose nanofiber dispersion was prepared from holocellulose pulp and conventional over-drying was applied. Based on our insight into the origin of this increase in the haze of transparent nanopaper, we developed high-humidity drying, which successfully produced clear transparent nanopaper from a concentrated dispersion without prolonged drying time.

Statistical thermodynamics unveils the dissolution mechanism of cellobiose.

In the study of the cellulose dissolution mechanism opinion is still divided. Here, the solution interaction components of the most prominent hypotheses for the driving force of cellulose dissolution were evaluated quantitatively. Combining a rigorous statistical thermodynamic theory and cellobiose solubility data in the presence of chloride salts, whose cations progress in the Hofmeister series (KCl, NaCl, LiCl and ZnCl2), we have shown that cellobiose solubilization is driven by the preferential accumulation of salts around the solutes which is stronger than cellobiose hydration. Yet contrary to the classical chaotropy hypothesis, increasing salt concentration leads to cellobiose dehydration in the presence of the strongest solubilizer ZnCl2. However, thanks to cellobiose dehydration, cellobiose-salt interaction still remains preferential despite weakening salt accumulation. Based on such insights, the previous hypotheses based on hydrophobicity and polymer charging have also been evaluated quantitatively. Thus, our present study successfully paved a way towards identifying the basic driving forces for cellulose solubilization in a quantitative manner for the first time. When combined with unit additivity methods this quantitative information could lead to a full understanding of cellulose solubility.

TEMPO-oxidized cellulose hydrogel as a high-capacity and reusable heavy metal ion adsorbent.

Nitroxy radical catalyzed oxidation with hypochlorite/bromide (TEMPO-mediated oxidation) was performed on a cellulose hydrogel prepared using LiOH/urea solvent. TEMPO oxidation successfully introduced carboxyl groups onto the surface of the cellulose hydrogel with retention of the gel structure and its nanoporous property. The equilibrium measurement of Cu(2+) adsorption showed favorable interaction with Cu(2+) and high maximum adsorption capacity. In addition, over 98% of the adsorbed Cu(2+) was recovered using acid treatment, and the subsequent washing allowed the TEMPO-oxidized gels to be used repeatedly. Furthermore, the TEMPO-oxidized cellulose hydrogel showed high adsorption capacity for other toxic metal ions such as Zn(2+), Fe(3+), Cd(2+), and Cs(+).