Understanding the Dispersion and Assembly of Bacterial Cellulose in Organic Solvents

Opportunities for bacterial nanocellulose in biomedical applications: Review on biosynthesis, modification and challenges

Bacterial nanocellulose (BNC) is a natural polysaccharide produced as extracellular material by bacterial strains and has favorable intrinsic properties for primary use in biomedical applications. In this review, an update on state-of-the art and challenges in BNC production, surface modification and biomedical application is given. Recent insights in biosynthesis allowed for better understanding of governing parameters improving production efficiency. In particular, introduction of different carbon/nitrogen sources from alternative feedstock and industrial upscaling of various production methods is challenging. It is important to have control on the morphology, porosity and forms of BNC depending on biosynthesis conditions, depending on selection of bacterial strains, reactor design, additives and culture conditions. The BNC is intrinsically characterized by high water absorption capacity, good thermal and mechanical stability, biocompatibility and biodegradability to certain extent. However, additional chemical and/or physical surface modifications are required to improve cell compatibility, protein interaction and antimicrobial properties. The novel trends in synthesis include the in-situ culturing of hybrid BNC nanocomposites in combination with organic material, inorganic material or extracellular components. In parallel with toxicity studies, the applications of BNC in wound care, tissue engineering, medical implants, drug delivery systems or carriers for bioactive compounds, and platforms for biosensors are highlighted.

Nanocellulose for Sustainable Water Purification

Nanocelluloses (NC) are nature-based sustainable biomaterials, which not only possess cellulosic properties but also have the important hallmarks of nanomaterials, such as large surface area, versatile reactive sites or functionalities, and scaffolding stability to host inorganic nanoparticles. This class of nanomaterials offers new opportunities for a broad spectrum of applications for clean water production that were once thought impractical. This Review covers substantial discussions based on evaluative judgments of the recent literature and technical advancements in the fields of coagulation/flocculation, adsorption, photocatalysis, and membrane filtration for water decontamination through proper understanding of fundamental knowledge of NC, such as purity, crystallinity, surface chemistry and charge, suspension rheology, morphology, mechanical properties, and film stability. To supplement these, discussions on low-cost and scalable NC extraction, new characterizations including solution small-angle X-ray scattering evaluation, and structure-property relationships of NC are also reviewed. Identifying knowledge gaps and drawing perspectives could generate guidance to overcome uncertainties associated with the adaptation of NC-enabled water purification technologies. Furthermore, the topics of simultaneous removal of multipollutants disposal and proper handling of post/spent NC are discussed. We believe NC-enabled remediation nanomaterials can be integrated into a broad range of water treatments, greatly improving the cost-effectiveness and sustainability of water purification.

Hierarchically Designed Three-Dimensional Composite Structure on a Cellulose-Based Solar Steam Generator

The emerging water purification technology represented by solar water evaporation has developed rapidly in recent years and is widely used in seawater desalination. However, the high reflectivity of sunlight and low efficiency of photothermal conversion greatly hinder its application prospects. In this paper, the hierarchical structure of the film was designed and optimized by the addition of carbon materials in the process of bacterial cellulose culture. A cellulose-based composite film material with a microporous structure was obtained, which can improve the photothermal evaporation rate and photothermal conversion efficiency from the structural principle to improve the stability of floating on the water. Bacterial cellulose (BC) as a three-dimensional carrier was combined with one-dimensional and two-dimensional (1D/2D) compounds of carbon nanotubes (CNT) and reduced graphene oxide (RGO) to form composite films for solar evaporation. By the addition of CNT-RGO (21.8 wt %), the composite showed prominent photothermal evaporation rate and photothermal conversion efficiency properties. Through in situ culture of BC, not only a tight structure can be obtained but also the surface of BC contains a large number of hydroxyl groups, which have many active sites to load photothermal materials. BC nanofibers, CNT, and RGO cooperate to form a porous network structure, which provides continuous double channels for the rapid transmission of water molecules and light paths, so as to form an excellent photothermal layer. The photothermal conversion efficiency is 90.2%, and the photothermal evaporation rate is 1.85 kg m^-2 h^-1 to achieve efficient solar interface evaporation. This is a high level of photothermal properties in a cellulose-based solar steam generator. The superior photothermal performance of this hybrid film possesses scalability and desalination ability.

Bacterial cellulose-based composites for biomedical and cosmetic applications: Research progress and existing products

Bacterial cellulose (BC) is a promising unique material for various biomedical and cosmetic applications due to its morphology, mechanical strength, high purity, high water uptake, non-toxicity, chemical controllability, and biocompatibility. Today, extensive investigation is into the manufacturing of BC-based composites with other components such as nanoparticles, synthetic polymers, natural polymers, carbon materials, and biomolecules, which will allow the development of a wide range of biomedical and cosmetic products. Moreover, the addition of different reinforcement substances into BC and the organized arrangement of BC nano-fibers have proven a promising improvement in their properties for biomedical applications. This review paper highlights the progress in synthesizing BC-based composites and their applications in biomedical fields, such as wound healing, drug delivery, tissue engineering, and cancer treatment. It emphasizes high-performance BC-based materials and cosmetic applications. Furthermore, it presents challenges yet to be defeated and future possibilities for BC-based composites for biomedical and cosmetic applications.

Bacterial nanocellulose papers with high porosity for optimized permeance and rejection of nm-sized pollutants

Access to clean potable water is increasingly becoming a struggle for whole humankind, thus water treatment to remediate wastewater and fresh water sources is an important task. Pollutants in the nanoscale, such as viruses and macromolecules, are usually removed by means of membrane filtration processes, predominantly nanofiltration or ultrafiltration. Cellulose nanopapers, prepared from renewable resources and manufactured by papermaking, have recently been demonstrated to be versatile alternatives to polymer membranes in this domain. Unfortunately, so far nanopaper filters suffer from limited permeance and thus efficiency. We here present nanopapers made from bacterial cellulose dispersed in water or different types of low surface tension organic liquids (alcohol, ketone, ether) through a simple papermaking process. Nanopapers prepared from organic liquids (BC-org) exhibited 40 times higher permeance, caused by a lower paper density hence increased porosity, compared to conventional nanopapers produced from aqueous dispersions, ultimately enhancing the efficiency of bacterial cellulose nanopaper membranes. Despite their higher porosity, BC-org nanopapers still have pore sizes of 15-20 nm similar to BC nanopapers made from aqueous dispersions, thus enabling removal of contaminants the size of viruses by a size-exclusion mechanism at high permeance.

Redispersion and structural change evaluation of dried microfibrillated cellulose

Commercializing dried microfibrillated cellulose (MFC) has always been a challenge mainly due to the tendency of MFC to aggregate. In this study MFC samples were submitted to drying/redispersion cycles at different temperatures. Morphology, crystallinity and mechanical performance of films were analyzed throughout the cycles. Microscopy images, particle size and stability in water showed that aggregation happens more severely with 5 drying/redispersion cycles and at drying temperatures of 75 and 100 °C. Particles once-dried at 20 °C formed the same size and web-like structure as the MFC-control. Crystallinity and crystallite sizes increased with drying/redispersion cycles especially when dried at 75 and 100 °C, however drying/redispersion cycles also led to a reduction in mechanical performance due to aggregation. While oven-drying is not the most suitable method, milder action at room temperature once-drying led to suspension stability in water, morphology and mechanical properties close to never-dried MFC, which makes this treatment a feasible option to maintain cellulose quality.

Oleanolic Acid Suppressed DMBA-Induced Liver Carcinogenesis through Induction of Mitochondrial-Mediated Apoptosis and Autophagy

Phytochemicals appeared as a rich source of efficient and safe agents against many diseases like cancer. Various herbal sources are rich in oleanolic acid (OA). The scope of this study was to assess the biochemical and molecular mechanisms implicated in the ameliorative potency of OA against DMBA-induced liver carcinogenesis. Forty-eight male albino mice were assigned randomly to five groups (eight mice each) as follows: control healthy group, olive oil group, OA group, DMBA group, and DMBA with OA. Apoptosis, autophagy, inflammation, proliferation, and angiogenesis were investigated in the tissue samples. Histopathological examination was carried out as well as liver enzymes activity and other hepatic antioxidant and inflammatory biomarkers. The treatment with OA effectively suppressed the DMBA-initiated liver carcinogenesis via modulation of antioxidant status, induction of apoptosis and autophagy through modulating the expression of Caspase-3, Bcl-2 and Beclin-1, inhibiting angiogenesis (VEGF), proliferation (PCNA), and improved liver function and histological picture with a reduction in AFP level. Additionally, OA applies its antitumor effects by inhibition of proinflammatory transcription factor NF-κB and inflammatory markers (TNF-α and Cox-2) associated with DMBA administration. The present study shows that OA treatment efficiently suppressed the DMBA-initiated liver carcinogenesis through induction of mitochondrial-mediated apoptosis and autophagy and modulating inflammation.

7,8-Dihydroxyflavone alleviated the high-fat diet and alcohol-induced memory impairment: behavioral, biochemical and molecular evidence

RATIONALE

Alcoholism and obesity impart a deleterious impact on human health and affects the quality of life. Chronic consumption of alcohol and western diet has been reported to cause memory deficits. 7,8-dihydroxyflavone (7,8-DHF), a TrkB agonist, comprises antioxidant and anti-inflammatory properties in treating various neurological disorders.

OBJECTIVES

The current study was aimed to determine the protective effect and molecular mechanism of 7,8-DHF against alcohol and high-fat diet (HFD)-induced memory deficits in rats.

METHODS

The adult male Wistar rats were given alcohol (3-15%) and HFD ad libitum for 12 weeks in different experimental groups. 7,8-DHF (5 mg/kg) was intraperitoneally injected daily for the last 4 weeks (9th-12th week).

RESULTS

The alcohol and HFD administration caused cognitive impairment as evaluated through the Morris water maze (MWM) test in alcohol, HFD, and alcohol + HFD-fed animals. The last 4-week treatment of 7,8-DHF (5 mg/kg; i.p.) attenuated alcohol and HFD-induced memory loss. 7,8-DHF treatment also restored the glutathione (GSH) level along with attenuation of nitrite, malondialdehyde content (markers of oxidative and nitrosative stress), and reduction of the acetylcholinesterase activity in the hippocampus of alcohol and HFD-fed animals. Furthermore, the administration of 7,8-DHF caused downregulation of NF-κB, iNOS, and caspase-3 and upregulation of Nrf2, HO-1, and BDNF mRNA level in rat hippocampus.

CONCLUSION

7,8-DHF administration conferred beneficial effects against alcohol and HFD-induced memory deficit via its unique antioxidant, anti-inflammatory, anti-apoptotic potential, along with the activation of TrkB/BDNF signaling pathway in the hippocampus.

Highly transparent, highly flexible composite membrane with multiple antimicrobial effects used for promoting wound healing

In recent years, bacterial cellulose (BC)-based dressings or patches for skin or soft tissue repair have become investigative emphasis. However, most of the BC-based products used for biomedical applications present limitations due to their low flexibility, poor gas permeability and no inherent antibacterial activity. Herein, we proposed and designed a novel composite composed of natural bacterial cellulose (BC), polyethylene glycol (PEG) and polyhexamethylene biguanidine (PHMB) through new synthetic approaches. The composite membrane exhibited favorable physicochemical performance, especially transparency, water retention ability, flexibility as well as the characteristic of anti-adhesion. In vitro biochemical experiment results indicated that the composite had excellent biocompatibility and exhibited strong and sustained antibacterial effect. In vivo test further demonstrated that the composite could efficiently promote skin wound healing and regeneration in a rat model. This composite membrane possesses multiple mechanisms of promoting cutaneous wound healing and will provide new ideas for future development of wound dressings.

Rapid Water Softening with TEMPO-Oxidized/Phosphorylated Nanopapers

Water hardness not only constitutes a significant hazard for the functionality of water infrastructure but is also associated with health concerns. Commonly, water hardness is tackled with synthetic ion-exchange resins or membranes that have the drawbacks of requiring the awkward disposal of saturated materials and being based on fossil resources. In this work, we present a renewable nanopaper for the purpose of water softening prepared from phosphorylated TEMPO-oxidized cellulose nanofibrils (PT-CNF). Nanopapers were prepared from CNF suspensions in water (PT-CNF nanopapers) or low surface tension organic liquids (ethanol), named EPT-CNF nanopapers, respectively. Nanopaper preparation from ethanol resulted in a significantly increased porosity of the nanopapers enabling much higher permeances: more than 10,000× higher as compared to nanopapers from aqueous suspensions. The adsorption capacity for Ca²⁺ of nanopapers from aqueous suspensions was 17 mg g^-1 and 5 mg g^-1 for Mg²⁺; however, EPT-CNF nanopapers adsorbed more than 90 mg g^-1 Ca²⁺ and almost 70 mg g^-1 Mg²⁺. The higher adsorption capacity was a result of the increased accessibility of functional groups in the bulk of the nanopapers caused by the higher porosity of nanopapers prepared from ethanol. The combination of very high permeance and adsorption capacity constitutes a high overall performance of these nanopapers in water softening applications.

Flexible Amoxicillin-Grafted Bacterial Cellulose Sponges for Wound Dressing: In Vitro and in Vivo Evaluation

In this study, we report the design and fabrication of a novel biocompatible sponge with excellent antibacterial property, making it a promising material for wound dressings. The sponge is formed by grafting amoxicillin onto regenerated bacterial cellulose (RBC). It was observed that the grafted RBC could enhance the antibacterial activity against fungus, Gram-negative, and Gram-positive bacteria. The morphology of strains treated with the grafted RBC and fluorescent stain results further demonstrated the antibacterial ability of the fabricated sponge. Moreover, a cytocompatibility test evaluated in vitro and in vivo illustrates the nontoxicity of the prepared sponge. More importantly, the wound infection model reveals that this sponge can accelerate the wound healing in vivo. This work indicates the novel sponge has the huge potential in wound dressing application for clinical use.

Better together: synergy in nanocellulose blends

Cellulose nanopapers have gained significant attention in recent years as large-scale reinforcement for high-loading cellulose nanocomposites, substrates for printed electronics and filter nanopapers for water treatment. The mechanical properties of nanopapers are of fundamental importance for all these applications. Cellulose nanopapers can simply be prepared by filtering a suspension of nanocellulose, followed by heat consolidation. It was already demonstrated that the mechanical properties of cellulose nanopapers can be tailored by the fineness of the fibrils used or by modifying nanocellulose fibrils for instance by polymer adsorption, but nanocellulose blends remain underexplored. In this work, we show that the mechanical and physical properties of cellulose nanopapers can be tuned by creating nanopapers from blends of various grades of nanocellulose, i.e. (mechanically refined) bacterial cellulose or cellulose nanofibrils extracted from never-dried bleached softwood pulp by chemical and mechanical pre-treatments. We found that nanopapers made from blends of two or three nanocellulose grades show synergistic effects resulting in improved stiffness, strength, ductility, toughness and physical properties.This article is part of a discussion meeting issue 'New horizons for cellulose nanotechnology'.

Highly Nitrogen-Doped Three-Dimensional Carbon Fibers Network with Superior Sodium Storage Capacity

Inspired by the excellent absorption capability of spongelike bacterial cellulose (BC), three-dimensional hierarchical porous carbon fibers doped with an ultrahigh content of N (21.2 atom %) (i.e., nitrogen-doped carbon fibers, NDCFs) were synthesized by an adsorption-swelling strategy using BC as the carbonaceous material. When used as anode materials for sodium-ion batteries, the NDCFs deliver a high reversible capacity of 86.2 mAh g^-1 even after 2000 cycles at a high current density of 10.0 A g^-1. It is proposed that the excellent Na⁺ storage performance is mainly due to the defective surface of the NDCFs created by the high content of N dopant. Density functional theory (DFT) calculations show that the defect sites created by N doping can strongly "host" Na⁺ and therefore contribute to the enhanced storage capacity.

Cellulose nanocrystals by acid vapour: towards more effortless isolation of cellulose nanocrystals

Cellulose nanocrystals (CNCs) are topical in materials science but their full potential is yet to be fulfilled because of bottlenecks in the production: the process consumes huge amounts of water, recycling the strong acid catalyst is difficult, and purification steps are cumbersome, particularly with lengthy dialysis. Production of CNCs with HCl vapour overcomes many of these difficulties but the dispersion of CNCs from the already hydrolysed fibre matrix is a formidable challenge. This study is a fundamental effort to explore very basic means to facilitate CNC dispersion from cotton linter fibres (filter paper), hydrolysed to levelling off degree of polymerization by HCl vapour. The introduction of carboxylic groups on the cellulose crystal surface proved the most efficient method to alleviate dispersion with good yields (ca. 50%) and a provisional possibility to tune the CNC length. By contrast, attempts to directly disperse untreated hydrolysed fibres in various organic solvents and aqueous surfactant solutions were unsuccessful. The results showed that hydrolysis of native cellulose fibres by HCl vapour is indeed a viable method for producing CNCs but it has more potential as a pre-treatment step rather than a full-fledged process on its own.