Nanocellulose as a sustainable biomass material: structure, properties, present status and future prospects in biomedical applications

Construction of Nanocrystalline Cellulose-Based Composite Fiber Films with Excellent Porosity Performances via an Electrospinning Strategy

Cellulose nanocrystals (CNCs) not only have environmental protection characteristics of being lightweight, degradable, green, and renewable but also have some nanocharacteristics of high strength, large specific surface area, and obvious small size effect, so they are often used as a reinforcing agent in various polymers. However, the hydrogen bonding between CNC molecules is relatively strong, and they can easily aggregate and get entangled with each other. In this work, several large-porosity composite nanofiber films, KH550-CNC/waterborne polyurethane (WPU)/poly(vinyl alcohol) (PVAL) with KH550-modified CNCs, are prepared using poly(vinyl alcohol) (PVAL) solution and electrospinning technology. A variety of characterization methods are used to discuss and analyze the nanofiber materials, and the effects of the added amount of CNCs modified with KH550, spinning voltage, curing distance, and advancing speed on the morphology and performance of composite fibers are discussed separately. The results show that when the content of KH550-CNC is 1%, the composite fiber film obtained has the most regular morphology and the best spinnability, which is convenient for the specific application of fiber materials in a later period. In addition, the porosity of the obtained composite fiber film is 62.61%. Therefore, this work provides a theoretical basis and research strategy for the preparation of higher-porosity composite films as well as the development of new textile materials.

Nanocellulosics: Benign, Sustainable, and Ubiquitous Biomaterials for Water Remediation

Water is critical for all lives to thrive. Access to potable and safe water has been argued to rank top among the prerequisites for defining the standard of living of a nation. However, there is a global decline in water quality due to human activities and other factors that severely impact freshwater resources such as saltwater intrusion and natural disasters. It has been pointed out that the millions of liters of industrial and domestic wastewater generated globally have the potential to help mitigate water scarcity if it is appropriately captured and remediated. Among the many initiatives to increase access to clean water, the scientific community has focused on wastewater remediation through the utilization of bioderived materials, such as nanocellulosics. Nanocellulosics, derived from cellulose, have the advantages of being ubiquitous, nontoxic, and excellent adsorbents. Furthermore, the surface properties of nanocellulosic materials can easily be modified. These advantages make them promising materials for water remediation applications. This perspective highlights the most important new developments in the application of nanocellulosics in water treatment technologies, such as membrane, adsorption, sensors, and flocculants/coagulants. We also identify where further work is urgently required for the widespread industrial application of nanocellulosics in wastewater treatment.

Jatropha Oil as a Substituent for Palm Oil in Biobased Polyurethane

Polyurethanes (PUs) are unique polymers that can be tailored to suit certain applications and are increasingly used in many industrial fields. Petrochemicals are still used as the main compound to synthesize PUs. Today, environmental concerns arise in the research and technology innovations in developing PUs, especially from vegetable polyols which are having an upsurge. These are driven by the uncertainty and fluctuations of petroleum crude oil price and availability. Jatropha has become a promising substituent to palm oil so as to reduce the competition of food and nonfood in utilizing this natural resource. Apart from that, jatropha will solve the problem related to the European banning of palm oil. Herein, we review the literature on the synthesis of PUs using different vegetable oils and compare it with jatropha oil and its nanocomposites reinforced with cellulose nanocrystals. Given the potential of vegetable oil PUs in many industrial applications, we expect that they will increase commercial interest and scientific research to bring these materials to the market soon.

Nanocellulose: Recent Fundamental Advances and Emerging Biological and Biomimicking Applications

In the effort toward sustainable advanced functional materials, nanocelluloses have attracted extensive recent attention. Nanocelluloses range from rod-like highly crystalline cellulose nanocrystals to longer and more entangled cellulose nanofibers, earlier denoted also as microfibrillated celluloses and bacterial cellulose. In recent years, they have spurred research toward a wide range of applications, ranging from nanocomposites, viscosity modifiers, films, barrier layers, fibers, structural color, gels, aerogels and foams, and energy applications, until filtering membranes, to name a few. Still, nanocelluloses continue to show surprisingly high challenges to master their interactions and tailorability to allow well-controlled assemblies for functional materials. Rather than trying to review the already extensive nanocellulose literature at large, here selected aspects of the recent progress are the focus. Water interactions, which are central for processing for the functional properties, are discussed first. Then advanced hybrid gels toward (multi)stimuli responses, shape-memory materials, self-healing, adhesion and gluing, biological scaffolding, and forensic applications are discussed. Finally, composite fibers are discussed, as well as nanocellulose as a strategy for improvement of photosynthesis-based chemicals production. In summary, selected perspectives toward new directions for sustainable high-tech functional materials science based on nanocelluloses are described.

Nanocellulose-based lightweight porous materials: A review

Nanocellulose has been widely concerned and applied in recent years. Because of its high aspect ratio, large specific surface area, good modifiability, high mechanical strength, renewability and biodegradability, nanocellulose is particularly suitable as a base for constructing lightweight porous materials. This review summarizes the preparation methods and applications of nanocellulose-based lightweight porous materials including aerogels, cryogels, xerogels, foams and sponges. The preparation of nanocellulose-based lightweight porous materials usually involves gelation and drying processes. The characteristics and influencing factors of three main drying methods including freeze, supercritical and evaporation drying are reviewed. In addition, the mechanism of physical and chemical crosslinking during gelation and the effect on the structure and properties of the porous materials in different drying methods are especially focused on. This contribution also introduces the application of nanocellulose-based lightweight porous materials in the fields of adsorption, biomedicine, energy storage, thermal insulation and sound absorption, flame retardancy and catalysis.

Functionalized Cellulose Nanocrystals for Cellular Labeling and Bioimaging

Cellulose nanocrystals (CNCs) are unique and promising natural nanomaterials that can be extracted from native cellulose fibers by acid hydrolysis. In this study, we developed chemically modified CNC derivatives by covalent tethering of PEGylated biotin and perylenediimide (PDI)-based near-infrared organic dye and evaluated their suitability for labeling and imaging of different cell lines including J774A.1 macrophages, NIH-3T3 fibroblasts, HeLa adenocarcinoma cells, and primary murine dendritic cells. PDI-labeled CNCs showed a superior photostability compared to similar commercially available dyes under long periods of constant and high-intensity illumination. All CNC derivatives displayed excellent cytocompatibility toward all cell types and efficiently labeled cells in a dose-dependent manner. Moreover, CNCs were effectively internalized and localized in the cytoplasm around perinuclear areas. Thus, our findings demonstrate the suitability of these new CNC derivatives for labeling, imaging, and long-time tracking of a variety of cell lines and primary cells.

Plant celluloses, hemicelluloses, lignins, and volatile oils for the synthesis of nanoparticles and nanostructured materials

A huge variety of plants are harvested worldwide and their different constituents can be converted into a broad range of bionanomaterials. In parallel, much research effort in materials science and engineering is focused on the formation of nanoparticles and nanostructured materials originating from agricultural residues. Cellulose (40-50%), hemicellulose (20-40%), and lignin (20-30%) represent major plant ingredients and many techniques have been described that separate the main plant components for the synthesis of nanocelluloses, nano-hemicelluloses, and nanolignins with divergent and controllable properties. The minor components, such as essential oils, could also be used to produce non-toxic metal and metal oxide nanoparticles with high bioavailability, biocompatibility, and/or bioactivity. This review describes the chemical structure, the physical and chemical properties of plant cell constituents, different techniques for the synthesis of nanocelluloses, nanohemicelluloses, and nanolignins from various lignocellulose sources and agricultural residues, and the extraction of volatile oils from plants as well as their use in metal and metal oxide nanoparticle production and emulsion preparation. Furthermore, details about the formation of activated carbon nanomaterials by thermal treatment of lignocellulose materials, a few examples of mineral extraction from agriculture waste for nanoparticle fabrication, and the emerging applications of plant-based nanomaterials in different fields, such as biotechnology and medicine, environment protection, environmental remediation, or energy production and storage, are also included. This review also briefly discusses the recent developments and challenges of obtaining nanomaterials from plant residues, and the issues surrounding toxicity and regulation.

Preparation of Cellulose Nanofibers from Bagasse by Phosphoric Acid and Hydrogen Peroxide Enables Fibrillation via a Swelling, Hydrolysis, and Oxidation Cooperative Mechanism

Due to the natural cellulose encapsulated in both lignin and hemicellulose matrices, as well as in plant cell walls with a compact and complex hierarchy, extracting cellulose nanofibers (CNFs) from lignocellulosic biomass is challenging. In this study, a sustainable high yield strategy with respect to other CNF preparations was developed. The cellulose was liberated from plant cell walls and fibrillated to a 7-22 nm thickness in one bath treatment with H₃PO₄ and H₂O₂ under mild conditions. The cellulose underwent swelling, the lignin underwent oxidative degradation, and the hemicellulose and a small amount of cellulose underwent acid hydrolysis. The CNFs' width was about 12 nm, with high yields (93% and 50% based on cellulose and biomass, respectively), and a 64% crystallinity and good thermal stability were obtained from bagasse. The current work suggests a strategy with simplicity, mild conditions, and cost-effectiveness, which means that this method can contribute to sustainable development for the preparation of CNFs.

Growing Pd NPs on cellulose microspheres via in-situ reduction for catalytic decolorization of methylene blue

Dyeing industry highly contributes to environmental pollution and this needs to be addressed on priority. Pd NPs/CMs, a highly efficient and reusable catalyst for methylene blue (MB) decolorization, were fabricated by in-situ reduction method based on the cellulose microspheres (CMs). Pd NPs/CMs were characterized for the structure and catalytic performance by spectroscopic techniques such as SEM, EDS, XRD, IR, XPS, porosity, zeta potential, MS, and UV-visible spectroscopy, which all demonstrated that Pd NPs were distributed on the cellulose microspheres uniformly and exhibited excellent catalytic performances to decolorize a model organic dye MB in the presence of NaBH₄ with catalytic efficiency higher than 99.8%. More importantly, Pd NPs/CMs were proven to show excellent reusability for at least five cycles. Decolorization mechanism of MB, via the destruction of the chromophores (CN and S) of MB, was established with the help of MS combined with IR and XPS. Blank experiments using pure cellulose microspheres were carried out simultaneously to estimate the level of catalytic capacity achieved to Pd NPs/CMs. These materials proved themselves having great potential in large scale applications to treat dye-containing wastewater.

Nanocellulose in biomedical and biosensing applications: A review

Cellulose is abundant in the nature and nanocellulose (NC) in particular is regarded as a credible green substrate to be used in bio nanocomposites for various applications. NC exhibits excellent mechanical reinforcement properties comparable to conventionally used materials due to its high specific surface area and tunable surface chemistry. Additionally, low toxicity, biodegradability and biocompatibility of NC deem it a promising material for use in different biomedical applications. In this review, we highlight the biomedical applications of NC based hydrogels and aerogels/nanocomposites and advancements of their employment in the areas of wound dressing, drug delivery, tissue engineering, scaffolds and biomedical implants. This review also explores the recent use of NC in making biosensors for the detection of cholesterol, various enzymes and diseases, heavy metal ions in human sweat and urine, and for general health monitoring.

Dual-responsive carboxymethyl cellulose/dopamine/cystamine hydrogels driven by dynamic metal-ligand and redox linkages for controllable release of agrochemical

The utilization of agrochemicals in crop production is often inefficient due to lack of appropriate carriers, raising in the significant concerns of ecological environment and public health. To enhance the efficiency of agrochemical delivery, a novel cellulose-based hydrogel was constructed in this work by cross-linking dopamine (DA)-modified carboxymethyl cellulose (CMC) with cystamine (CYS) in the presence of Fe³⁺ ions. The hydrogels displayed reversible sol-gel transitions upon exposure to stimulation of changes in pH and redox, leading to the controllable release of model agrochemical (6-benzyladenine). Compared with single-triggered condition, the hydrogel doubled the cumulative release when co-triggered by pH and redox. The dynamic metal/catechol complexation and disulfide bonding coexist in the hydrogel networks, enabling occurrence of dynamic reaction under a variety of environmental conditions. The finite element method (FEM) was employed to simulate the hydrogel to provide a theoretical insight into the tested drug delivery. Benefitting from the reversibly cross-linked networks and the excellent biodegradability of the hydrogels, we anticipate that this dual-responsive, polysaccharide-based hydrogel will offer diverse applications to reach the full potential in sustainable advancement of crop production.

Physicochemical Characterization of Bilayer Hybrid Nanocellulose-Collagen as a Potential Wound Dressing

The eminent aim for advance wound management is to provide a great impact on the quality of life. Therefore, an excellent strategy for an ideal wound dressing is being developed that eliminates certain drawbacks while promoting tissue regeneration for the prevention of bacterial invasion. The aim of this study is to develop a bilayer hybrid biomatrix of natural origin for wound dressing. The bilayer hybrid bioscaffold was fabricated by the combination of ovine tendon collagen type I and palm tree-based nanocellulose. The fabricated biomatrix was then post-cross-linked with 0.1% (w/v) genipin (GNP). The physical characteristics were evaluated based on the microstructure, pore size, porosity, and water uptake capacity followed by degradation behaviour and mechanical strength. Chemical analysis was performed using energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectrophotometry (FTIR), and X-ray diffraction (XRD). The results demonstrated a uniform interconnected porous structure with optimal pore size ranging between 90 and 140 μm, acceptable porosity (>70%), and highwater uptake capacity (>1500%). The biodegradation rate of the fabricated biomatrix was extended to 22 days. Further analysis with EDX identified the main elements of the bioscaffold, which contains carbon (C) 50.28%, nitrogen (N) 18.78%, and oxygen (O) 30.94% based on the atomic percentage. FTIR reported the functional groups of collagen type I (amide A: 3302 cm^-1, amide B: 2926 cm^-1, amide I: 1631 cm^-1, amide II: 1547 cm^-1, and amide III: 1237 cm^-1) and nanocellulose (pyranose ring), thus confirming the presence of collagen and nanocellulose in the bilayer hybrid scaffold. The XRD demonstrated a smooth wavy wavelength that is consistent with the amorphous material and less crystallinity. The combination of nanocellulose with collagen demonstrated a positive effect with an increase of Young's modulus. In conclusion, the fabricated bilayer hybrid bioscaffold demonstrated optimum physicochemical and mechanical properties that are suitable for skin wound dressing.

Phosphorylase-catalyzed bottom-up synthesis of short-chain soluble cello-oligosaccharides and property-tunable cellulosic materials

Cellulose-based materials are produced industrially in countless varieties via top-down processing of natural lignocellulose substrates. By contrast, cellulosic materials are only rarely prepared via bottom up synthesis and oligomerization-induced self-assembly of cellulose chains. Building up a cellulose chain via precision polymerization is promising, however, for it offers tunability and control of the final chemical structure. Synthetic cellulose derivatives with programmable material properties might thus be obtained. Cellodextrin phosphorylase (CdP; EC 2.4.1.49) catalyzes iterative β-1,4-glycosylation from α-d-glucose 1-phosphate, with the ability to elongate a diversity of acceptor substrates, including cellobiose, d-glucose and a range of synthetic glycosides having non-sugar aglycons. Depending on the reaction conditions leading to different degrees of polymerization (DP), short-chain soluble cello-oligosaccharides (COS) or insoluble cellulosic materials are formed. Here, we review the characteristics of CdP as bio-catalyst for synthetic applications and show advances in the enzymatic production of COS and reducing end-modified, tailored cellulose materials. Recent studies reveal COS as interesting dietary fibers that could provide a selective prebiotic effect. The bottom-up synthesized celluloses involve chains of DP ≥ 9, as precipitated in solution, and they form ~5 nm thick sheet-like crystalline structures of cellulose allomorph II. Solvent conditions and aglycon structures can direct the cellulose chain self-assembly towards a range of material architectures, including hierarchically organized networks of nanoribbons, or nanorods as well as distorted nanosheets. Composite materials are also formed. The resulting materials can be useful as property-tunable hydrogels and feature site-specific introduction of functional and chemically reactive groups. Therefore, COS and cellulose obtained via bottom-up synthesis can expand cellulose applications towards product classes that are difficult to access via top-down processing of natural materials.

Sponges with Janus Character from Nanocellulose: Preparation and Applications in the Treatment of Hemorrhagic Wounds

The development of a rapid and effective hemostatic dressing is highly desired in the treatment of hemorrhagic wounds. In this study, sponges with Janus character are developed using cellulose nanofibers (CNFs) that exhibit materials facets of different wettability characteristics using heterogeneous mixing and freeze-drying. The bonding of the interface between the hydrophilic and hydrophobic facets is achieved by using interpenetrating chemical cross-linking between CNFs and organosilanes. The hydrophilic layer absorbs water from blood and works synergistically with the inherent hemostatic chitosan-rich complementary layer to accelerate blood clotting, displaying both active and passive hemostatic mechanisms. The hydrophobic layer prevents blood penetration into the construct and exerts proper pressure on the wound. Compared with the hydrophilic control samples and commercial gauzes, the Janus sponges can achieve effective bleeding control with nearly 50% less blood loss in a femoral artery injury model and prolong the survival time in a carotid artery injury model. Compared with the only hydrophilic layer, the time to hemostasis of Janus sponge are reduced from 165 ± 20 to 131 ± 26 s in femoral artery injury model and from 102 ± 21 to 83 ± 15 s in liver femoral artery injury model.

Multivalent ion-induced re-entrant transition of carboxylated cellulose nanofibrils and its influence on nanomaterials' properties

In this work, we identify and characterize a new intriguing capability of carboxylated cellulose nanofibrils that could be exploited to design smart nanomaterials with tuned response properties for specific applications. Cellulose nanofibrils undergo a multivalent counter-ion induced re-entrant behavior at a specific multivalent metal salt concentration. This effect is manifested as an abrupt increase in the strength of the hydrogel that returns upon a further increment of salt concentration. We systematically study this phenomenon using dynamic light scattering, small-angle X-ray scattering, and molecular dynamics simulations based on a reactive force field. We find that the transitions in the nanofibril microstructure are mainly because of the perturbing actions of multivalent metal ions that induce conformational changes of the nanocellulosic chains and thus new packing arrangements. These new aggregation states also cause changes in the thermal and mechanical properties as well as wettability of the resulting films, upon water evaporation. Our results provide guidelines for the fabrication of cellulose-based films with variable properties by the simple addition of multivalent ions.

Biomedical Applications of Hemicellulose-Based Hydrogels

Background:

Hydrogel has a three-dimensional network structure that is able to absorb a large amount of water/liquid and maintain its original structure. Hemicellulose (HC) is the second most abundant polysaccharide after cellulose in plants and a heterogeneous polysaccharide consisting of various saccharide units. The unique physical and chemical properties of hemicellulose make it a promising material for hydrogels.

Methods:

This review first summarizes the three research hotspots on the hemicellulose-based hydrogels: intelligence, biodegradability and biocompatibility. It also overviews the progress in the fabrication and applications of hemicellulose hydrogels in the drug delivery system and tissue engineering (articular cartilage, cell immobilization, and wound dressing).

Results:

Hemicellulose-based hydrogels have many unique properties, such as stimuliresponsibility, biodegradability and biocompatibility. Interpenetrating networking can endow appropriate mechanical properties to hydrogels. These properties make the hemicellulose-based hydrogels promising materials in biomedical applications such as drug delivery systems and tissue engineering (articular cartilage, cell immobilization, and wound dressing).

Conclusion:

Hydrogels have been widely used in biomedicine and tissue engineering areas, such as tissue fillers, drug release agents, enzyme encapsulation, protein electrophoresis, contact lenses, artificial plasma, artificial skin, and tissue engineering scaffold materials. This article reviews the recent progress in the fabrication and applications of hemicellulose-based hydrogels in the biomedical field.

Cellulose Nanofibrils-based Hydrogels for Biomedical Applications: Progresses and Challenges

Background:

Cellulose Nanofibrils (CNFs) are natural nanomaterials with nanometer dimensions. Compared with ordinary cellulose, CNFs own good mechanical properties, large specific surface areas, high Young's modulus, strong hydrophilicity and other distinguishing characteristics, which make them widely used in many fields. This review aims to introduce the preparation of CNFs-based hydrogels and their recent biomedical application advances.

Methods:

By searching the recent literatures, we have summarized the preparation methods of CNFs, including mechanical methods and chemical mechanical methods, and also introduced the fabrication methods of CNFs-based hydrogels, including CNFs cross-linked with metal ion and with polymers. In addition, we have summarized the biomedical applications of CNFs-based hydrogels, including scaffold materials and wound dressings.

Results:

CNFs-based hydrogels are new types of materials that are non-toxic and display a certain mechanical strength. In the tissue scaffold application, they can provide a micro-environment for the damaged tissue to repair and regenerate it. In wound dressing applications, it can fit the wound surface and protect the wound from the external environment, thereby effectively promoting the healing of skin tissue.

Conclusion:

By summarizing the preparation and application of CNFs-based hydrogels, we have analyzed and forecasted their development trends. At present, the research of CNFs-based hydrogels is still in the laboratory stage. It needs further exploration to be applied in practice. The development of medical hydrogels with high mechanical properties and biocompatibility still poses significant challenges.

Crystal and Supramolecular Structure of Bacterial Cellulose Hydrolyzed by Cellobiohydrolase from Scytalidium Candidum 3C: A Basis for Development of Biodegradable Wound Dressings

The crystal and supramolecular structure of the bacterial cellulose (BC) has been studied at different stages of cellobiohydrolase hydrolysis using various physical and microscopic methods. Enzymatic hydrolysis significantly affected the crystal and supramolecular structure of native BC, in which the 3D polymer network consisted of nanoribbons with a thickness T ≈ 8 nm and a width W ≈ 50 nm, and with a developed specific surface S_BET ≈ 260 m²·g⁻¹. Biodegradation for 24 h led to a ten percent decrease in the mean crystal size D_hkl of BC, to two-fold increase in the sizes of nanoribbons, and in the specific surface area S_BET up to ≈ 100 m²·g⁻¹. Atomic force and scanning electron microscopy images showed BC microstructure “loosening“after enzymatic treatment, as well as the formation and accumulation of submicron particles in the cells of the 3D polymer network. Experiments in vitro and in vivo did not reveal cytotoxic effect by the enzyme addition to BC dressings and showed a generally positive influence on the treatment of extensive III-degree burns, significantly accelerating wound healing in rats. Thus, in our opinion, the results obtained can serve as a basis for further development of effective biodegradable dressings for wound healing.

Effects of ingested nanocellulose on intestinal microbiota and homeostasis in Wistar Han rats

Micron scale cellulose materials are "generally regarded as safe" (GRAS) as binders and thickeners in food products. However, nanocellulose materials, which have unique properties that can improve food quality and safety, have not received US-Food and Drug Administration (FDA) approval as food ingredients. In vitro and in vivo toxicological studies of ingested nanocellulose revealed minimal cytotoxicity, and no subacute in vivo toxicity. However, ingested materials may modulate gut microbial populations, or alter aspects of intestinal function not elucidated by toxicity testing, which could have important health implications. Here, we report the results of studies conducted in a rat gavage model to assess the effects of ingested cellulose nanofibrils (CNF) on the fecal microbiome and metabolome, intestinal epithelial expression of cell junction genes, and ileal cytokine production. Feces, plasma, and ilea were collected from Wistar Han rats before and after five weeks of biweekly gavages with water or cream, with or without 1% CNF. CNF altered microbial diversity, and diminished specific species that produce short chain fatty acids, and that are associated with increased serum insulin and IgA production. CNF had few effects on the fecal metabolome, with significant changes in only ten metabolites of 366 measured. Exposure to CNF also altered expression of epithelial cell junction genes, and increased production of cytokines that modulate proliferation of CD8 T cells. These perturbations likely represent initiation of an adaptive immune response, however, no associated pathology was seen within the duration of the study. Additional studies are needed to better understand the health implications of these changes in long term.

Electrospun Nanocomposites Containing Cellulose and Its Derivatives Modified with Specialized Biomolecules for an Enhanced Wound Healing

Wound healing requires careful, directed, and effective therapies to prevent infections and accelerate tissue regeneration. In light of these demands, active biomolecules with antibacterial properties and/or healing capacities have been functionalized onto nanostructured polymeric dressings and their synergistic effect examined. In this work, various antibiotics, nanoparticles, and natural extract-derived products that were used in association with electrospun nanocomposites containing cellulose, cellulose acetate and different types of nanocellulose (cellulose nanocrystals, cellulose nanofibrils, and bacterial cellulose) have been reviewed. Renewable, natural-origin compounds are gaining more relevance each day as potential alternatives to synthetic materials, since the former undesirable footprints in biomedicine, the environment, and the ecosystems are reaching concerning levels. Therefore, cellulose and its derivatives have been the object of numerous biomedical studies, in which their biocompatibility, biodegradability, and, most importantly, sustainability and abundance, have been determinant. A complete overview of the recently produced cellulose-containing nanofibrous meshes for wound healing applications was provided. Moreover, the current challenges that are faced by cellulose acetate- and nanocellulose-containing wound dressing formulations, processed by electrospinning, were also enumerated.

A Review on Surface-Functionalized Cellulosic Nanostructures as Biocompatible Antibacterial Materials

As the most abundant biopolymer on the earth, cellulose has recently gained significant attention in the development of antibacterial biomaterials. Biodegradability, renewability, strong mechanical properties, tunable aspect ratio, and low density offer tremendous possibilities for the use of cellulose in various fields. Owing to the high number of reactive groups (i.e., hydroxyl groups) on the cellulose surface, it can be readily functionalized with various functional groups, such as aldehydes, carboxylic acids, and amines, leading to diverse properties. In addition, the ease of surface modification of cellulose expands the range of compounds which can be grafted onto its structure, such as proteins, polymers, metal nanoparticles, and antibiotics. There are many studies in which cellulose nano-/microfibrils and nanocrystals are used as a support for antibacterial agents. However, little is known about the relationship between cellulose chemical surface modification and its antibacterial activity or biocompatibility. In this study, we have summarized various techniques for surface modifications of cellulose nanostructures and its derivatives along with their antibacterial and biocompatibility behavior to develop non-leaching and durable antibacterial materials. Despite the high effectiveness of surface-modified cellulosic antibacterial materials, more studies on their mechanism of action, the relationship between their properties and their effectivity, and more in vivo studies are required.

Functional biohybrid materials based on halloysite, sepiolite and cellulose nanofibers for health applications

Biohybrid materials were prepared by co-assembling the three following components: nanotubular halloysite, microfibrous sepiolite, and cellulose nanofibers dispersed in water, in order to exploit the most salient features of each individual component and to render homogeneous, flexible, yet strong films. Indeed, the incorporation of halloysite improves the mechanical performance of the resulting hybrid nanopapers and the assembly of the three components modifies the surface features concerning wetting properties compared to pristine materials, so that the main characteristics of the resulting materials become tunable with regard to certain properties. Owing to their hierarchical porosity together with their diverse surface characteristics, these hybrids can be used in diverse biomedical/pharmaceutical applications. Herein, for instance, loading with two model drugs, salicylic acid and ibuprofen, allows controlled and sustained release as deduced from antimicrobial assays, opening a versatile path for developing other related organic-inorganic materials of potential interest in diverse application fields.

A study of TiO2 nanocrystal growth and environmental remediation capability of TiO2/CNC nanocomposites

Nanocellulose, which can be derived from any cellulosic biomass, has emerged as an appealing nanoscale scaffold to develop inorganic-organic nanocomposites for a wide range of applications. In this study, titanium dioxide (TiO₂) nanocrystals were synthesized in the cellulose nanocrystal (CNC) scaffold using a simple approach, i.e., hydrolysis of a titanium oxysulfate precursor in a CNC suspension at low temperature. The resulting TiO₂ nanoparticles exhibited a narrow size range between 3 and 5 nm, uniformly distributed on and strongly adhered to the CNC surface. The structure of the resulting nanocomposite was evaluated by transmission electron microscopy (TEM) and X-ray diffraction (XRD) methods. The growth mechanism of TiO₂ nanocrystals in the CNC scaffold was also investigated by solution small-angle X-ray scattering (SAXS), where the results suggested the mineralization process could be described by the Lifshitz-Slyozov-Wagner theory for Ostwald ripening. The demonstrated TiO₂/CNC nanocomposite system exhibited excellent performance in dye degradation and antibacterial activity, suitable for a wide range of environmental remediation applications.

Additive Printed All-Cellulose Membranes with Hierarchical Structure for Highly Efficient Separation of Oil/Water Nanoemulsions

To expand the application of commercial membranes in oily wastewater separation, in this work, all-cellulose membranes were fabricated by depositing cellulose nanocrystals onto the surface of mixed-cellulose esters via a large-scale additive printing strategy. The thickness, pore size, surface wettability, and water flux of all-cellulose membranes can be well tuned by controlling the printing cycles of cellulose nanocrystal inks. Under optimal printing conditions, the resultant all-cellulose membranes with nanoporous architecture (76-91 nm) exhibit superhydrophilicity and underwater superoleophobicity, which benefits the separation of oil/water nanoemulsions with a high water flux (>1500 L m^-2 h^-1 bar^-1) and an ultrahigh efficiency (>99%). Moreover, these all-cellulose membranes exhibit excellent stability and reusability for long-term separation and retains their inherent properties under various acidic, basic, and salty conditions, as well as mechanical abrasion. The presented scalable additive printing is a facile, economical, and sustainable strategy to construct all-cellulose membranes with excellent separation performance for oil/water nanoemulsions.

Cellulose-based biomaterials integrated with copper-cystine hybrid structures as catalysts for nitric oxide generation

Bionanocomposite materials were developed from the assembly of polymer-coated copper-cystine high-aspect ratio structures (CuHARS) and cellulose fibers. The coating of the metal-organic materials with polyallylamine hydrochloride (PAH) allows their covalent linkage to TEMPO-oxidized cellulose by means of EDC/NHS. The resulting materials can be processed as films or macroporous foams by solvent casting and lyophilization, respectively. The films show good mechanical behavior with Young's moduli around 1.5 GPa as well as resistance in water, while the obtained foams show an open network of interconnected macropores with average diameters around 130 μm, depending on the concentration of the initial suspension, and compression modulus values around 450 kPa, similar to other reported freeze-dried nanocellulose-based aerogels. Based on these characteristics, the cellulose/PAH-CuHARS composites are promising for potential biomedical applications as implants or wound dressing materials. They have proved to be effective in the decomposition of low molecular weight S-nitrosothiols (RSNOs), similar to those existing in blood, releasing nitric oxide (NO). This effect is attributed to the presence of copper in the crystalline structure of the CuHARS building unit, which can be gradually released in the presence of redox species like ascorbic acid, typically found in blood. The resulting biomaterials can offer the interesting properties associated with NO, like antimicrobial activity as preliminary tests showed here with Escherichia coli and Staphylococcus epidermidis. In the presence of physiological concentration of RSNOs the amount of generated NO (around 360 nM) is not enough to show bactericidal effect on the studied bacteria, but it could provide other properties inherent to NO even at low concentration in the nM range like anti-inflammatory and anti-thrombotic effects. The cytotoxic effect recorded of the films on rat brain endothelial cells (BMVECs) is least significant and proves them to be friendly enough for further biological studies.

Characterization of Hydrothermal Deposition of Copper Oxide Nanoleaves on Never-Dried Bacterial Cellulose

Bacterial cellulose (BC) has attracted a great deal of interest due to its green synthesis and biocompatibility. The nanoscale dimension of BC nanofibers generates an enormous surface area that enhances interactions with water and soluble components within aqueous solution. Recent work has demonstrated that BC is a versatile platform for the formation of metal/metal oxide nanocomposites. Copper oxide (CuO) is a useful material to compare nanomaterial deposition on BC with other cellulosic materials because of copper’s colorimetric reaction as it forms copper hydroxide (Cu(OH)₂) and transitions to CuO. In this research, we found that never-dried BC readily deposits CuO into its matrix in a way that does not occur on cotton, dried BC, or regenerated cellulose fibers. We conclude that hydroxyl group availability does not adequately explain our results and that intrafibrillar pores in never-dried BC nanofibers play a critical role in CuO deposition.

Methods and applications of nanocellulose loaded with inorganic nanomaterials: A review

Nanocellulose obtained from natural renewable resources has attracted enormous interests owing to its unique morphological characteristics, excellent mechanical strength, biocompatibility and biodegradability for a variety of applications in many fields. The template structure, high specific surface area, and active surface groups make it feasible to conduct surface modification and accommodate various nano-structured materials via physical or chemical deposition. The review presented herein focuses on the methodologies of loading different nano-structured materials on nanocellulose, including metals, nanocarbons, oxides, mineral salt, quantum dots and nonmetallic elements; and further describes the applications of nanocellulose composites in the fields of catalysis, optical electronic devices, biomedicine, sensors, composite reinforcement, photoswitching, flame retardancy, and oil/water separation.

Complex Aerogels Generated from Nano-Polysaccharides and Its Derivatives for Oil-Water Separation

The complex aerogel generated from nano-polysaccharides, chitin nanocrystals (ChiNC) and TEMPO-oxidized cellulose nanofibers (TCNF), and its derivative cationic guar gum (CGG) is successfully prepared via a facile freeze-drying method with glutaraldehyde (GA) as cross-linkers. The complexation of ChiNC, TCNF, and CGG is shown to be helpful in creating a porous structure in the three-dimensional aerogel, which creates within the aerogel with large pore volume and excellent compressive properties. The ChiNC/TCNF/CGG aerogel is then modified with methyltrichlorosilane (MTCS) to obtain superhydrophobicity/superoleophilicity and used for oil–water separation. The successful modification is demonstrated through FTIR, XPS, and surface wettability studies. A water contact angle of 155° on the aerogel surface and 150° on the surface of the inside part of aerogel are obtained for the MTCS-modified ChiNC/TCNF/CGG aerogel, resulting in its effective absorption of corn oil and organic solvents (toluene, n-hexane, and trichloromethane) from both beneath and at the surface of water with excellent absorption capacity (i.e., 21.9 g/g for trichloromethane). More importantly, the modified aerogel can be used to continuously separate oil from water with the assistance of a vacuum setup and maintains a high absorption capacity after being used for 10 cycles. The as-prepared superhydrophobic/superoleophilic ChiNC/TCNF/CGG aerogel can be used as a promising absorbent material for the removal of oil from aqueous media.

Nanomaterials for the theranostics of obesity

As a chronic and lifelong disease, obesity not only significant impairs health but also dramatically shortens life span (at least 10 years). Obesity requires a life-long effort for the successful treatment because a number of abnormalities would appear in the development of obesity. Nanomaterials possess large specific surface area, strong absorptivity, and high bioavailability, especially the good targeting properties and adjustable release rate, which would benefit the diagnosis and treatment of obesity and obesity-related metabolic diseases. Herein, we discussed the therapy and diagnosis of obesity and obesity-related metabolic diseases by using nanomaterials. Therapies of obesity with nanomaterials include improving intestinal health and reducing energy intake, targeting and treating functional cell abnormalities, regulating redox homeostasis, and removing free lipoprotein in blood. Diagnosis of obesity-related metabolic diseases would benefit the therapy of these diseases. The development of nanomaterials will promote the diagnosis and therapy of obesity and obesity-related metabolic diseases.

A strategy of tailoring polymorphs and nanostructures to construct self-reinforced nonswelling high-strength bacterial cellulose hydrogels

A serious decline in mechanical properties of polysaccharide hydrogels caused by swelling has always been a difficult problem which greatly limited their application especially in the medical field. Herein, nonswelling high-strength natural hydrogels based on self-reinforced double-crosslinked bacterial cellulose (SDBC) were prepared. Inspired by the concept of homogeneous composite materials, by regulating the ratio of LiOH/urea alkaline solvent, the aggregation structure and nanostructure of SDBC hydrogels can be controlled, thereby a unique nanofiber-network-self-reinforced (FNSR) structure was constructed and a new self-reinforcing mechanism is proposed. The prepared SDBC hydrogels have excellent mechanical properties at a high water content (>91%) for the combination of double-crosslinking and a unique FNSR structure, which can effectively prevent crack propagation and dissipate a large amount of energy. In particular, the compressive strength can reach 3.17 MPa which is 56 times that of native bacterial cellulose (BC). It is worth mentioning that no swelling occurs for the hydrogel, and the mechanical strength still remains in excess of 90% for 15 days in water, which is favorable for promising application in underwater equipment, implantable ionic devices, and tissue engineering scaffolds. This study also opens up a new horizon for the preparation of self-reinforced hydrogels.

Advances in tissue engineering of nanocellulose-based scaffolds: A review

Scaffolds based on nanocellulose (NC) have crucial applications in tissue engineering (TE) owing to the biocompatibility, water absorption, water retention, optical transparency, and chemo-mechanical properties. In this review, we summarize the scaffolds based on nanocellulose, including nanocrystalline cellulose and nanofibrillated cellulose. We compare four representative methods to prepare NC-based scaffolds, containing electrospinning, freeze-drying, 3D printing, and solvent casting. We outline the characteristics of scaffolds obtained by different methods. Our focus is on the applications of NC-based scaffolds to repair, improve or replace damaged tissues and organs, including skin, blood vessel, nerve, skeletal muscle, heart, liver, and ophthalmology. NC-based scaffolds are attractive materials for regeneration of different tissues and organs due to the remarkable features. Finally, we propose the challenges and potentials of NC-based TE scaffolds.

Using cellulose fibers to fabricate transparent paper by microfibrillation

Fabricating transparent paper from cellulose nanofibers (CNFs) normally involves high energy or the use of expensive chemicals for the extraction of CNFs from cellulose fibers and time-consuming paper formation processes because of the slow filtration rate of CNFs. In this study, we reported a strategy for the fabrication of transparent paper using microfibrillated cellulose fibers (MFCFs), which were prepared by extracting nanosized fibrils from the cellulose fiber surfaces by a two-step refining process. The paper made from MFCFs has hierarchical structures of microsized fiber/nanosized fibril networks, where the microsized fiber skeletons are buried in the nanosized fibril networks. Consequently, the paper shows a light transmittance of 82.4% at 550 nm; this is comparable to the light transmittance (89.1%) of papers made from CNFs. Meanwhile, the filtration time of the paper made from MFCFs is less than 2 min, which is much shorter than the time (longer than 180 min) required for the formation of nanopaper made from commercial CNFs. In addition, the transparent paper made from MFCFs shows higher thermal stability, higher tensile strength, higher resistance to deformation, and more flexibility than the nanopaper made from commercial CNFs. This work provides a promising method for the manufacture of transparent paper from cellulose fibers.

Biomass-Templated Fabrication of Metallic Materials for Photocatalytic and Bactericidal Applications

In this paper, we report a simple, feasible and low-cost method to fabricate self-standing metallic materials using cellulose-based biomass as sacrificial templates. This process involves the impregnation of metallic precursors to the cellulose fibers of biomass templates and the transformation of the precursors to corresponding metals or metal oxides (as well as the removal of the cellulose framework) at an elevated temperature. The structures of the metallic materials as fabricated take the form of architectures of biomass templates (e.g., chromatography paper, medical absorbent cotton, catkins of reed, seed balls of oriental plane, and petals of peach blossom), and the various kinds of metals and metal oxides fabricated with these templates include silver, gold, anatase, cupric oxide, zinc oxide, etc. We have demonstrated photocatalytic and bactericidal applications of such metallic materials, and they should find more applications in electronics, catalysis, energy storage, biomedicine and so on.

Commercial application of cellulose nano-composites - A review

Cellulose is the biosynthetic product from plants, animals and bacteria. Cellulose is the most abundant polymer having long linear chain like structure composed of (1,4) linked β-D glucopyranosyl units assembled into hierarchical structures of microfibrils with excellent strength and stiffness. And 'nanocellulose' refers to the cellulosic materials with defined nano-scale structural dimensions. They may be cellulose nanocrystal (CNC or NCC), cellulose nanofibers (CNF) or bacterial nanocellulose. Nanocellulose is non-toxic, biodegradable and biocompatible with no adverse effects on health and environment. Due to its low thermal expansion coefficient, high aspect ratio, better tensile strength, good mechanical and optical properties, they find many applications in thermo-reversible and tenable hydrogels, paper making, coating additives, food packaging, flexible screens, optically transparent films and light weight materials for ballistic protection, automobile windows. It also find potential in biopharmaceutical applications such as in drug delivery and for fabricating temporary implants with PHB like sutures, stents etc.

Cellulose nanocrystals and cellulose nanofibrils based hydrogels for biomedical applications

The production of cellulose nanomaterials from lignocellulosic biomass opens an opportunity for the development and application of new materials in nanotechnology. Over the last decade, cellulose nanomaterials based hydrogels have emerged as promising materials in the field of biomedical applications due to their low toxicity, biocompatibility, biodegradability, as well as excellent mechanical stability. In this review, recent progress on the preparation of cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) based hydrogels and their biomedical applications is summarized and discussed based on the analyses of the latest studies (especially for the reports in the past five years). We begin with a brief introduction of the differences in preparation methods and properties of two main types of cellulose nanomaterials: CNCs and CNFs isolated from lignocellulosic biomass. Then, various processes for the fabrication of CNCs based hydrogels and CNFs based hydrogels were elaborated, respectively, with the focus on some new methods (e.g. 3D printing). Furthermore, a number of biomedical applications of CNCs and CNFs based hydrogels, including drug delivery, wound dressings and tissue engineering scaffolds were highlighted. Finally, the prospects and ongoing challenges of CNCs and CNFs based hydrogels for biomedical applications were summarized. This work demonstrated that the CNCs and CNFs based hydrogels have great promise in a wide range of biomedical applications in the future.

Biomass and waste materials as potential sources of nanocrystalline cellulose: Comparative review of preparation methods (2016 - Till date)

Nanocrystalline cellulose (NCC) has gained much popularity over the last decade as a preferred nanomaterial in varied applications, despite its laborious industrial production and higher cost. Its production methods have undergone a great deal of metamorphosis lately. The main emphasis has been on the environment-friendly and green processes, in addition to the sustainable and renewable feedstock. Globally, the researchers have explored biomass and waste cellulosic materials as renewable sources for NCC extraction. Newer and/or improved process alternatives, e.g., ultrasonication, enzymatic hydrolysis and mechanical treatments have been applied successfully for producing high-quality material. Detailed investigations on optimizing the overall yield from cheaper feedstock have yielded obvious benefits. This is still work in progress. The present review majorly focuses on the advances made in the NCC preparation field from biomass and waste cellulosic materials in last three years (2016 - till date). Collaborative efforts between chemical engineers and research scientists are crucial for the success of this really amazing nanomaterial.

Friction-Active Surfaces Based on Free-Standing Anchored Cellulose Nanofibrils

A specific feature of fibrous surfaces is the dependence of their mechanical properties on the alignment of the fibers. Vertically aligned fibers enhance friction and adhesion, whereas horizontal fibers are known to act as a lubricant reducing the friction. Many plants form a specific fibrous mucilage cover around their seeds upon hydration. This mucilage consists of cellulose, hemicelluloses, and strongly hydrophilic pectins. We show that the controlled critical-point drying of hydrated seed mucilage of three exemplary seed mucilage-rich plant species results in the exposure of free-standing cellulose nanofibers with a very high aspect ratio and anchored to the seed surface. The structural dimensions of the cellulose nanofibers are similar to the vertically aligned carbon nanotubes and the contact elements in the adhesion system of the gecko that show an outstanding high dry friction and adhesion. Tribological experiments demonstrate very high average friction coefficients when sliding a smooth and stiff probe over the surface of such arrays of dry free-standing cellulose nanofibrils in the range from 1.4 to 1.8. The high friction values most likely arise from bending of the single cellulose fibers and their alignment with the counterpart surface in close contact. We suggest the potential of free-standing cellulose nanofibrils of plant seed mucilage as a natural and ecologically friendly material where high contact forces to surfaces in dry environments are desired.

Hierarchical Assembly of Nanocellulose-Based Filaments by Interfacial Complexation

In the present study, interfacial complexation spinning of oppositely charged cellulose-materials is applied to fabricate hierarchical and continuous nanocellulose based filaments under aqueous conditions by using cationic cellulose nanocrystals with different anionic celluloses including soluble sodium carboxymethyl cellulose and insoluble 2,2,6,6-tetramethylpiperidinyl-1-oxy radical-oxidized cellulose nanofibers and dicarboxylated cellulose nanocrystals (DC-CNC). The morphologies of the wet and dry nanocellulose based filaments are further investigated by optical and electron microscopy. All fabricated continuous nanocellulose based filaments display a hierarchical structure similar to the natural cellulose fibers in plant cells. As far as it is known, this is not only the first report about the fabrication of nanocellulose based filaments by interfacial complexation of cationic CNCs with anionic celluloses but also the first demonstration of fabricating continuous fibers directly from oppositely charged nanoparticles by interfacial nanoparticle complexation (INC). This INC approach may provide a new route to design continuous filaments from many other oppositely charged nanoparticles with tailored characteristics.

The Rise of Hierarchical Nanostructured Materials from Renewable Sources: Learning from Nature

Mimicking Nature implies the use of bio-inspired hierarchical designs to manufacture nanostructured materials. Such materials should be produced from sustainable sources ( e.g., biomass) and through simple processes that use mild conditions, enabling sustainable solutions. The combination of different types of nanomaterials and the implementation of different features at different length scales can provide synthetic hierarchical nanostructures that mimic natural materials, outperforming the properties of their constitutive building blocks. Taking recent developments in flow-assisted assembly of nanocellulose crystals as a starting point, we review the state of the art and provide future perspectives on the manufacture of hierarchical nanostructured materials from sustainable sources, assembly techniques, and potential applications.

Well-dispersed cellulose nanocrystals in hydrophobic polymers by in situ polymerization for synthesizing highly reinforced bio-nanocomposites

In nanocomposites, dispersing hydrophilic nanomaterials in a hydrophobic matrix using simple and environmentally friendly methods remains challenging. Herein, we report a method based on in situ polymerization to synthesize nanocomposites of well-dispersed cellulose nanocrystals (CNCs) and poly(vinyl acetate) (PVAc). We have also shown that by blending this PVAc/CNC nanocomposite with poly(lactic acid) (PLA), a good dispersion of the CNCs can be reached in PLA. The outstanding dispersion of CNCs in both PVAc and PLA/PVAc matrices was shown by different microscopy techniques and was further supported by the mechanical and rheological properties of the composites. The in situ PVAc/CNC nanocomposites exhibit enhanced mechanical properties compared to the materials produced by mechanical mixing, and a theoretical model based on the interphase effect and dispersion that reflects this behavior was developed. Comparison of the rheological and thermal behaviors of the mixed and in situ PVAc/CNC also confirmed the great improvement in the dispersion of nanocellulose in the latter. Furthermore, a synergistic effect was observed with only 0.1 wt% CNCs when the in situ PVAc/CNC was blended with PLA, as demonstrated by significant increases in elastic modulus, yield strength, elongation to break and glass transition temperature compared to the PLA/PVAc only material.

Cellulose Nanofiber Biotemplated Palladium Composite Aerogels

Noble metal aerogels offer a wide range of catalytic applications due to their high surface area and tunable porosity. Control over monolith shape, pore size, and nanofiber diameter is desired in order to optimize electronic conductivity and mechanical integrity for device applications. However, common aerogel synthesis techniques such as solvent mediated aggregation, linker molecules, sol⁻gel, hydrothermal, and carbothermal reduction are limited when using noble metal salts. Here, we present the synthesis of palladium aerogels using carboxymethyl cellulose nanofiber (CNF) biotemplates that provide control over aerogel shape, pore size, and conductivity. Biotemplate hydrogels were formed via covalent cross linking using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) with a diamine linker between carboxymethylated cellulose nanofibers. Biotemplate CNF hydrogels were equilibrated in precursor palladium salt solutions, reduced with sodium borohydride, and rinsed with water followed by ethanol dehydration, and supercritical drying to produce freestanding aerogels. Scanning electron microscopy indicated three-dimensional nanowire structures, and X-ray diffractometry confirmed palladium and palladium hydride phases. Gas adsorption, impedance spectroscopy, and cyclic voltammetry were correlated to determine aerogel surface area. These self-supporting CNF-palladium aerogels demonstrate a simple synthesis scheme to control porosity, electrical conductivity, and mechanical robustness for catalytic, sensing, and energy applications.