Probing adhesion between nanoscale cellulose fibres using AFM lateral force spectroscopy: The effect of hemicelluloses on hydrogen bonding

Deep-eutectic-solvent modulation of self-assembled multi-responsive films based on polyvinyl alcohol/cellulose nanocrystal and grape skin red for highly sensitive food monitoring

To enhance the mechanics performance, sensitivity and response range of multi-responsive photonic films, herein, a facile method for fabricating multi-responsive films is demonstrated using the evaporative self-assembly of a mixture of grape skin red (GSR), cellulose nanocrystal (CNC), polyvinyl alcohol (PVA) and deep eutectic solvent (DES). The prepared materials exhibited excellent thermal stability, strain properties, solvent resistance, ultraviolet (UV) resistance and antioxidant activity. Compared to a pure PVA film, the presence of GSR strengthened the antioxidant property of the film by 240.1 % and provided excellent UV barrier capability. The additional cross-linking of DES and CNC promoted more efficient phase fusion, yielding a film strain of 41.5 %. The addition of hydrophilic compound GSR, wetting and swelling due to the DES and the surface inhomogeneity of the films rendered the multi-responsive films high sensitivity, wide response range and multi-cyclic stability in environments with varying pH and humidity. A sample application showed that a PVA/CNC/DES film has the potential to differentiate between fresh, sub-fresh and fully spoiled shrimps. The above results help in designing intelligent thin film materials that integrate antioxidant properties, which help in monitoring the changes in food freshness and food packaging.

Coarse-grained molecular dynamics model to evaluate the mechanical properties of bacterial cellulose-hemicellulose composites

The plant cell wall (PCW) inspires the preparation of fiber-based biomaterials, particularly emphasizing exploiting the intrinsic interactions within the load-bearing cellulose and hemicellulose network. Due to experimental difficulties in studying and interpreting the interaction between these polysaccharides, this research presents a numerical model based on coarse-grained molecular dynamics that evaluates the mechanical properties of fiber composites. To validate the model and explain the structural and mechanical role of hemicelluloses, bacterial cellulose (BC) was synthesized in the presence of different concentrations of xylan, arabinoxylan, xyloglucan, or glucomannan and subjected to nano- and macroscale structural and mechanical characterization. The data obtained were used to interpret the effects of each hemicellulose on the mechanics of the BC-hemicellulose composite based on the sensitivity of the model. The mechanical properties of the resulting simulated networks agreed well with the experimental observations of the BC-hemicellulose composites. Increased xylan and arabinoxylan contents increased the macroscale mechanical properties, fiber modulus (xylan), and fiber width (arabinoxylan). The addition of xyloglucan increased the mechanical properties of the composites in the elastic deformation phase, associated with an increase in the fiber modulus. Adding glucomannan to the culture medium decreased all the mechanical properties studied while the fiber width increased.

Polymeric hydrogels-based materials for wastewater treatment

Low-cost and reliable wastewater treatment is a relevant issue worldwide to reduce the concentration of environmental pollutants. Industrial effluents containing dyes, heavy metals, and other inorganic and organic compounds can pollute water resources; therefore, novel technologies are required to mitigate and control their release into the environment. Adsorption is one of the simplest methods for treating contaminated water in which a wide spectrum of adsorbents can be used to remove emerging compounds. Hydrogels are interesting materials with high adsorption capacities that can be synthesized via green routes. These adsorbents are promising for large-scale industrial wastewater treatment applications; however, gaps still exist in achieving sustainable commercial implementation. This review focuses on the discussion and analysis of preparation, characterization, and adsorption properties of hydrogels for water purification. The advantages of these polymeric materials for water treatment were analyzed, including their performance in the removal of different organic and inorganic contaminants. Recent advances in the functionalization of hydrogels and the synthesis of novel composites have also been described. The adsorption capacities of hydrogel-based adsorbents are higher than 500 mg/g for different organic and inorganic pollutants, and can reach values of up to >2000 mg/g for organic compounds, significantly outperforming other materials reported for water cleaning. The main interactions involved in the adsorption of water pollutants using hydrogel-based adsorbents were described and explained to allow the interpretation of their removal mechanisms. The current challenges in the implementation of hydrogels for water purification in real-life operations are also highlighted. This review provides an updated picture of hydrogels as interesting materials to address water depollution worldwide.

Significance of glycans in cellulolytic enzymes for lignocellulosic biorefinery - A review

Lignocellulosic (LC) biomass is the most abundant renewable resource for mankind gravitating society towards sustainable solution for energy that can reduce the carbon footprint. The economic feasibility of 'biomass biorefinery' depends upon the efficiency cellulolytic enzymes which is the main crux. Its high production cost and low efficiencies are the major limitations, that need to be resolved. As the complexity of the genome increases, so does the complexity of the proteome, further facilitated by protein post-translational modifications (PTMs). Glycosylation is regarded the major PTMs and hardly any recent work is focused on importance of glycosylation in cellulase. By modifying protein side chains and glycans, superior cellulases with improved stability and efficiency can be obtained. Functional proteomics relies heavily on PTMs because they regulate activity, localization, and interactions with protein, lipid, nucleic acid, and cofactor molecules. O- and N- glycosylation in cellulases influences its characteristics adding positive attributes to the enzymes.

In silico studies of plant primary cell walls - structure and mechanics

Primary plant cell wall (PCW) is a highly organized network, its performance is dependent on cellulose, hemicellulose and pectic polysaccharides, their properties, interactions and assemblies. Their mutual relationships and functions in the cell wall can be better understood by means of conceptual models of their higher-order structures. Knowledge unified in the form of a conceptual model allows predictions to be made about the properties and behaviour of the system under study. Ongoing research in this field has resulted in a number of conceptual models of the cell wall. However, due to the currently limited research methods, the community of cell wall researchers have not reached a consensus favouring one model over another. Herein we present yet another research technique - numerical modelling - which is capable of resolving this issue. Even at the current stage of development of numerical techniques, due to their complexity, the in silico reconstruction of PCW remains a challenge for computational simulations. However, some difficulties have been overcome, thereby making it possible to produce advanced approximations of PCW structure and mechanics. This review summarizes the results concerning the simulation of polysaccharide interactions in PCW with regard to network fine structure, supramolecular properties and polysaccharide binding affinity. The in silico mechanical models presented herein incorporate certain physical and biomechanical aspects of cell wall architecture for the purposes of undertaking critical testing to bring about advances in our understanding of the mechanisms controlling cells and limiting cell wall expansion.

Tea extracts inhibit the attachment of streptococci to oral/dental substrata by reducing hydrogen bonding energies

Previous work in the authors' lab demonstrated that tea extracts significantly suppressed streptococcal colonization of abiotic substrata by coating the bacterial cell surfaces with tea components. In this study, the physico-chemical mechanisms by which the tea coating inhibits cellular attachment are demonstrated. The changes in the cell surface physico-chemical properties of streptococci, induced by tea extracts, were measured. Using these results, surface interaction energies were calculated between streptococcal cells and hard surfaces (glass, stainless steel, hydroxyapatite and titanium) within the cellular attachment system exploiting the extended Derjaguin-Landau-Verwey-Overbeek theory. The net energy outcomes were compared with experiment results of attachment assays to validate the predictability of the model. The results showed that the tea extracts inhibited the attachment of the bacteria by 11.1%-91.5%, and reduced the interaction energy by 15.4%-94.9%. It was also demonstrated that the abilities of the bacteria to attach to hard surfaces correlated well with their net interaction energies. The predominant interaction in the systems was found to be hydrogen bonding. In conclusion, tea extracts suppress streptococcal attachment to hard substrata by limiting the formation of hydrogen bonds.

Fungal cellulases: protein engineering and post-translational modifications

Enzymatic degradation of lignocelluloses into fermentable sugars to produce biofuels and other biomaterials is critical for environmentally sustainable development and energy resource supply. However, there are problems in enzymatic cellulose hydrolysis, such as the complex cellulase composition, low degradation efficiency, high production cost, and post-translational modifications (PTMs), all of which are closely related to specific characteristics of cellulases that remain unclear. These problems hinder the practical application of cellulases. Due to the rapid development of computer technology in recent years, computer-aided protein engineering is being widely used, which also brings new opportunities for the development of cellulases. Especially in recent years, a large number of studies have reported on the application of computer-aided protein engineering in the development of cellulases; however, these articles have not been systematically reviewed. This article focused on the aspect of protein engineering and PTMs of fungal cellulases. In this manuscript, the latest literatures and the distribution of potential sites of cellulases for engineering have been systematically summarized, which provide reference for further improvement of cellulase properties. KEY POINTS: •Rational design based on virtual mutagenesis can improve cellulase properties. •Modifying protein side chains and glycans helps obtain superior cellulases. •N-terminal glutamine-pyroglutamate conversion stabilizes fungal cellulases.

The influence of alkaline treatment on the mechanical and structural properties of bacterial cellulose

The unique mechanical properties of hydrated bacterial cellulose make it suitable for biomedical applications. This study evaluates the effect of concentrated sodium hydroxide treatment on the structural and mechanical properties of bacterial cellulose hydrogels using rheological, tensile, and compression tests combined with mathematical modelling. Bacterial cellulose hydrogels show a concentration-dependent and irreversible reduction in shear moduli, compression, and tensile strength after alkaline treatment. Applying a poroelastic biphasic model to through-thickness compressive stress-relaxation tests showed the alkaline treatment to induce no significant change in axial compression, an effect was observed in the radial direction, potentially due to the escape of water from within the hydrogel. Scanning electron microscopy showed a more porous structure of bacterial cellulose. These results show how concentration-dependent alkaline treatment induces selective weakening of intramolecular interactions between cellulose fibres, allowing the opportunity to precisely tune the mechanical properties for specific biomedical application, e.g., faster-degradable materials.

High-Performanced Hemicellulose Based Organic-Inorganic Films with Polyethyleneimine

For the high-value utilization of hemicellulose-based composite films, the poor film-forming and mechanical properties of hemicellulose-based composite films must be surmounted crucially. Based on this, hemicellulose-based organic-inorganic composite films with good mechanical properties were prepared from quaternized hemicelluloses (QH), bentonite, and polyethyleneimine (PEI). The QH/PEI/bentonite composite films were prepared by vacuum filtration, and the properties of the composite film were investigated. The results showed that the QH was inserted into bentonite nanosheets through hydrogen bonding and electrostatic interactions. PEI was cross-linked with hemicellulose by hydroxyl groups, electrostatically attracted by the bentonite flake layers. The mechanical properties of the composite films were significantly increased by the incorporation of PEI. When the PEI content was 20%, the tensile stress of the composite film was increased by 155.18%, and the maximum tensile stress was reached 80.52 MPa. The composite films had strong UV absorption ability with the transmittance was almost 0 in the UV region from 200 to 300 nm. The thermal property of composite film was also improved, and the residual mass increased by three times compared to QH. These results provide a theoretical basis for the use of hemicellulose-based composite films in packaging applications.

Mechanical Characteristics and Adhesion of Glass-Kevlar Hybrid Composites by Applying Different Ratios of Epoxy in Lamination

Hybrid composites have great potential for specific strength and specific stiffness, effective in aerospace industries, submarines, and light-weight automotives. The mechanical strength and adhesiveness of hybrid laminates can be enhanced by effective use of matrix materials in different ratios of epoxy resin and epoxy hardener. Gentle use of resin and hardener in the fabrication of hybrid composites can alter tensile modulus, the bonding strength between matrix and fabric. Spectacular progress has been achieved by the selection of appropriate amounts of resin and hardener in the hybridization of composite laminate. Hybridization was made by Kevlar inorganic/organic fabrics and glass fabrics stacked with epoxy matrix material. To achieve the combination of mechanical properties and bonding strength, transparent epoxy resin and hardener of commercial grades mixed in various ratios are incorporated as matrix material to fabricate laminate. Three different sheets, named A (3:2), B (4:1), and C (2:3), were embedded by the hand layup method to prepare a hybrid composite. Experimental tests, according to ASTM 3039, were performed to determine the tensile mechanical properties. Peel tests, according to ASTM 6862-11, were performed to investigate the interlaminar strength between Kevlar and glass layers. Shore A and Shore C hardness durometers were used to find out the hardness of the specimens at different spots using the ASTM D-2240 standard. Finally, physical testing, such as density and then water absorption, was carried out using the ASTM D-570 standard to check the swelling ratio of the different specimens. The results obtained highlight that the specimen of the glass/Kevlar hybrid embedded in the ratio 3:2 in lamination has the best mechanical properties (tensile strength and hardness) and the lowest swelling ratio, while the material system in the ratio 4:1 shows the best interlaminar properties and adhesion capabilities.

Wood hemicelluloses exert distinct biomechanical contributions to cellulose fibrillar networks

Hemicelluloses, a family of heterogeneous polysaccharides with complex molecular structures, constitute a fundamental component of lignocellulosic biomass. However, the contribution of each hemicellulose type to the mechanical properties of secondary plant cell walls remains elusive. Here we homogeneously incorporate different combinations of extracted and purified hemicelluloses (xylans and glucomannans) from softwood and hardwood species into self-assembled networks during cellulose biosynthesis in a bacterial model, without altering the morphology and the crystallinity of the cellulose bundles. These composite hydrogels can be therefore envisioned as models of secondary plant cell walls prior to lignification. The incorporated hemicelluloses exhibit both a rigid phase having close interactions with cellulose, together with a flexible phase contributing to the multiscale architecture of the bacterial cellulose hydrogels. The wood hemicelluloses exhibit distinct biomechanical contributions, with glucomannans increasing the elastic modulus in compression, and xylans contributing to a dramatic increase of the elongation at break under tension. These diverging effects cannot be explained solely from the nature of their direct interactions with cellulose, but can be related to the distinct molecular structure of wood xylans and mannans, the multiphase architecture of the hydrogels and the aggregative effects amongst hemicellulose-coated fibrils. Our study contributes to understanding the specific roles of wood xylans and glucomannans in the biomechanical integrity of secondary cell walls in tension and compression and has significance for the development of lignocellulosic materials with controlled assembly and tailored mechanical properties.

Hemicelluloses are an essential constituent of plant cell walls, but the individual biomechanical roles remain elusive. Here the authors report on the interaction of wood hemicellulose with bacterial cellulose during deposition and explore the resultant fibrillar architecture and mechanical properties.

High Molecular Weight Mixed-Linkage Glucan as a Mechanical and Hydration Modulator of Bacterial Cellulose: Characterization by Advanced NMR Spectroscopy

Bacterial cellulose (BC) consists of a complex three-dimensional organization of ultrafine fibers which provide unique material properties such as softness, biocompatibility, and water-retention ability, of key importance for biomedical applications. However, there is a poor understanding of the molecular features modulating the macroscopic properties of BC gels. We have examined chemically pure BC hydrogels and composites with arabinoxylan (BC-AX), xyloglucan (BC-XG), and high molecular weight mixed-linkage glucan (BC-MLG). Atomic force microscopy showed that MLG greatly reduced the mechanical stiffness of BC gels, while XG and AX did not exert a significant effect. A combination of advanced solid-state NMR methods allowed us to characterize the structure of BC ribbons at ultra-high resolution and to monitor local mobility and water interactions. This has enabled us to unravel the effect of AX, XG, and MLG on the short-range order, mobility, and hydration of BC fibers. Results show that BC-XG hydrogels present BC fibrils of increased surface area, which allows BC-XG gels to hold higher amounts of bound water. We report for the first time that the presence of high molecular weight MLG reduces the density of clusters of BC fibrils and dramatically increases water interactions with BC. Our data supports two key molecular features determining the reduced stiffness of BC-MLG hydrogels, that is, (i) the adsorption of MLG on the surface of BC fibrils precluding the formation of a dense network and (ii) the preorganization of bound water by MLG. Hence, we have produced and fully characterized BC-MLG hydrogels with novel properties which could be potentially employed as renewable materials for applications requiring high water retention capacity (e.g. personal hygiene products).

Boron and calcium deficiency disturbing the growth of trifoliate rootstock seedlings (Poncirus trifoliate L.) by changing root architecture and cell wall

Boron (B) and calcium (Ca) are essential elements for plant growth. Both deficiencies inhibit root growth. However, the mechanism of inhibition is not well clear. Morphological characteristics of roots and changes in root cell wall grown at different B and Ca deficiencies were examined by using a hydroponic culture system. Both B and Ca deficiencies caused reduced plant biomass and root growth. Ca deficiency significantly decreased the fresh weight of root, stem, and leaves by 47%, 50%, and 62%, respectively, while B deficiency only reduced root fresh weight. The PCA combined with Pearson correlation analysis showed that there was significant different correlation among root parameters under B and Ca deficiency treatments when compared to control. The results of observation of transmission electron microscope showed that Ca deficiency reduced but B deprivation increased the thickness of the cell wall. Combining these technologies like X-ray diffraction, fourier transform infrared spectroscopy, homogalacturonan epitopes (JIM5 and JIM7), we confirmed that those changes above may be due to different changes in the degree of methyl esterification of pectin and glycoprotein of the cell wall. Taken together, we concluded that B deficiency can promote the formation of more low methyl esterified pectin to increase cell wall thickness, and then affect the morphological development of root system, while the formation of more highly methyl esterified pectin to increase cell wall degradation under Ca deficiency, which inhibited root elongation and formation of root branches.