Interaction between Cellulose and Xylan: An Atomic Force Microscope and Quartz Crystal Microbalance Study

Biobased Nanomaterials─The Role of Interfacial Interactions for Advanced Materials

This review presents recent advances regarding biomass-based nanomaterials, focusing on their surface interactions. Plant biomass-based nanoparticles, like nanocellulose and lignin from industry side streams, hold great potential for the development of lightweight, functional, biodegradable, or recyclable material solutions for a sustainable circular bioeconomy. However, to obtain optimal properties of the nanoparticles and materials made thereof, it is crucial to control the interactions both during particle production and in applications. Herein we focus on the current understanding of these interactions. Solvent interactions during particle formation and production, as well as interactions with water, polymers, cells and other components in applications, are addressed. We concentrate on cellulose and lignin nanomaterials and their combination. We demonstrate how the surface chemistry of the nanomaterials affects these interactions and how excellent performance is only achieved when the interactions are controlled. We furthermore introduce suitable methods for probing interactions with nanomaterials, describe their advantages and challenges, and introduce some less commonly used methods and discuss their possible applications to gain a deeper understanding of the interfacial chemistry of biobased nanomaterials. Finally, some gaps in current understanding and interesting emerging research lines are identified.

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.

Three-Dimensional Printing of Wood-Derived Biopolymers: A Review Focused on Biomedical Applications

Wood-derived biopolymers have attracted great attention over the past few decades due to their abundant and versatile properties. The well-separated three main components, i.e., cellulose, hemicelluloses, and lignin, are considered significant candidates for replacing and improving on oil-based chemicals and materials. The production of nanocellulose from wood pulp opens an opportunity for novel material development and applications in nanotechnology. Currently, increased research efforts are focused on developing 3D printing techniques for wood-derived biopolymers for use in emerging application areas, including as biomaterials for various biomedical applications and as novel composite materials for electronics and energy devices. This Review highlights recent work on emerging applications of wood-derived biopolymers and their advanced composites with a specific focus on customized pharmaceutical products and advanced functional biomedical devices prepared via three-dimensional printing. Specifically, various biofabrication strategies in which woody biopolymers are used to fabricate customized drug delivery devices, cartilage implants, tissue engineering scaffolds and items for other biomedical applications are discussed.

Role of (1,3)(1,4)-β-glucan in cell walls: interaction with cellulose

(1,3)(1,4)-β-D-Glucan (mixed-linkage glucan or MLG), a characteristic hemicellulose in primary cell walls of grasses, was investigated to determine both its role in cell walls and its interaction with cellulose and other cell wall polysaccharides in vitro. Binding isotherms showed that MLG adsorption onto microcrystalline cellulose is slow, irreversible, and temperature-dependent. Measurements using quartz crystal microbalance with dissipation monitoring showed that MLG adsorbed irreversibly onto amorphous regenerated cellulose, forming a thick hydrogel. Oligosaccharide profiling using endo-(1,3)(1,4)-β-glucanase indicated that there was no difference in the frequency and distribution of (1,3) and (1,4) links in bound and unbound MLG. The binding of MLG to cellulose was reduced if the cellulose samples were first treated with certain cell wall polysaccharides, such as xyloglucan and glucuronoarabinoxylan. The tethering function of MLG in cell walls was tested by applying endo-(1,3)(1,4)-β-glucanase to wall samples in a constant force extensometer. Cell wall extension was not induced, which indicates that enzyme-accessible MLG does not tether cellulose fibrils into a load-bearing network.

Spatial structure of plant cell wall polysaccharides and its functional significance

Plant polysaccharides comprise the major portion of organic matter in the biosphere. The cell wall built on the basis of polysaccharides is the key feature of a plant organism largely determining its biology. All together, around 10 types of polysaccharide backbones, which can be decorated by different substituents giving rise to endless diversity of carbohydrate structures, are present in cell walls of higher plants. Each of the numerous cell types present in plants has cell wall with specific parameters, the features of which mostly arise from the structure of polymeric components. The structure of polysaccharides is not directly encoded by the genome and has variability in many parameters (molecular weight, length, and location of side chains, presence of modifying groups, etc.). The extent of such variability is limited by the "functional fitting" of the polymer, which is largely based on spatial organization of the polysaccharide and its ability to form supramolecular complexes of an appropriate type. Consequently, the carrier of the functional specificity is not the certain molecular structure but the certain type of the molecules having a certain degree of heterogeneity. This review summarizes the data on structural features of plant cell wall polysaccharides, considers formation of supramolecular complexes, gives examples of tissue- and stage-specific polysaccharides and functionally significant carbohydrate-carbohydrate interactions in plant cell wall, and presents approaches to analyze the spatial structure of polysaccharides and their complexes.

Adsorption of arabinoxylan on cellulosic surfaces: influence of degree of substitution and substitution pattern on adsorption characteristics

This study presents results that show that the fine structure of arabinoxylan affects its interaction with cellulosic surfaces, an important understanding when designing and evaluating properties of xylan-cellulose-based materials. Arabinoxylan samples, with well-defined structures, were prepared from a wheat flour arabinoxylan with targeted enzymatic hydrolysis. Turbidity measurements and analyses using NMR diffusometry showed that the solubility and the hydrodynamic properties of arabinoxylan are determined not only by the degree of substitution but also by the substitution pattern. On the basis of results obtained from adsorption experiments on microcrystalline cellulose particles and on cellulosic model surfaces investigated with quartz crystal microbalance with dissipation monitoring, it was also found that arabinoxylan adsorbs irreversibly on cellulosic surfaces and that the adsorption characteristics, as well as the properties of the adsorbed layer, are controlled by the fine structure of the xylan molecule.

Modelling polymer interactions of the 'molecular Velcro' type in wood under mechanical stress

Trees withstand wind and snow loads by synthesising wood that varies greatly in mechanical properties: flexible in twigs and in the stem of the sapling, and rigid in the outer part of the mature stem. The 'molecular Velcro' model of Keckes et al. [2003. Cell-wall recovery after irreversible deformation of wood. Nat. Mater. 2, 810-814] permits the simulation of the tensile properties of water-saturated wood as found in living trees. A basic feature of this model is the presence of non-covalent interactions between hemicellulose chains attached to adjacent cellulose microfibrils, which are disrupted above a threshold level of interfibrillar shear. However, other evidence does not confirm the importance of hemicellulose-hemicellulose association in the cohesion of the interfibrillar matrix. Here, we present an alternative model in which hemicellulose chains bridging continuously from one microfibril aggregate (macrofibril) to the next provide most of the cohesion. We show that such hemicellulose bridges exist and that the stripping of the bridging chains from the cellulose surfaces under the tensile stress component normal to the macrofibrils can provide an alternative triggering mechanism for shear deformation between one macrofibril and the next. When one macrofibril then slides past another, a domain of the wood cell wall can extend but simultaneously it twists until the spacing between macrofibrils is reduced again and contact through hemicelluloses bridges is restored. Overall deformation therefore takes place through a series of local stick-slip events involving temporary twisting of small domains within the wood cell wall. Modelled load-deformation curves for this modified 'molecular Velcro' model are similar, although not identical, to those for the original model. However, the mechanism is different and more consistent with current views of the structure of wood cell walls, providing a framework within which the developmental control of rigidity in wood synthesised in different parts of a tree may be considered.

A survey of the 2001 to 2005 quartz crystal microbalance biosensor literature: applications of acoustic physics to the analysis of biomolecular interactions

The widespread exploitation of biosensors in the analysis of molecular recognition has its origins in the mid-1990s following the release of commercial systems based on surface plasmon resonance (SPR). More recently, platforms based on piezoelectric acoustic sensors (principally 'bulk acoustic wave' (BAW), 'thickness shear mode' (TSM) sensors or 'quartz crystal microbalances' (QCM)), have been released that are driving the publication of a large number of papers analysing binding specificities, affinities, kinetics and conformational changes associated with a molecular recognition event. This article highlights salient theoretical and practical aspects of the technologies that underpin acoustic analysis, then reviews exemplary papers in key application areas involving small molecular weight ligands, carbohydrates, proteins, nucleic acids, viruses, bacteria, cells and lipidic and polymeric interfaces. Key differentiators between optical and acoustic sensing modalities are also reviewed.

Cellulose—model films and the fundamental approach

This critical review describes the recent arrival of ultrathin films of cellulose. The methodology of preparation as well as the applications of the films for fundamental research is fully covered. The review places cellulose in a wider scientific context where cellulose research is no longer a field of interest for specialised scientists only. Cellulose and cellulosic materials should interest communities such as biochemists, physical chemists, surface chemists, organic chemists, polymer chemists and also physicists working close the disciplines mentioned. (149 references.).