Spray-Dried Cellulose Nanofibers as Novel Tablet Excipient

The purpose of this study was to evaluate the potential of cellulose nanofibers (also referred as microfibrillated cellulose, nanocellulose, nanofibrillated, or nanofibrillar cellulose) as novel tabletting material. For this purpose, physical and mechanical properties of spray-dried cellulose nanofibers (CNF) were examined, and results were compared to those of two commercial grades of microcrystalline cellulose (MCC), Avicel PH101 and Avicel PH102, which are the most commonly and widely used direct compression excipients. Chemically, MCC and CNF are almost identical, but their physical characteristics, like mechanical properties and surface-to-volume ratio, differ remarkably. The novel material was characterized with respect to bulk and tapped as well as true density, moisture content, and flow properties. Tablets made of CNF powder and its mixtures with MCC with or without paracetamol as model compound were produced by direct compression and after wet granulation. The tensile strength of the tablets made in a series of applied pressures was determined, and yield pressure values were calculated from the measurements. With CNF, both wet granulation and direct compression were successful. During tablet compression, CNF particles were less prone to permanent deformation and had less pronounced ductile characteristics. Disintegration and dissolution studies showed slightly faster drug release from direct compression tablets with CNF, while wet granulated systems did not have any significant difference.     

Biomimetic repeat protein derived from Xenopus tropicalis for fibrous scaffold fabrication

Collagen, silk, and elastin are the fibrous proteins consist of representative amino acid repeats. Because these proteins exhibited distinguishing mechanical properties, they have been utilized in diverse applications, such as fiber‐based sensors, filtration membranes, supporting materials, and tissue engineering scaffolds. Despite their infinite prevalence and potential, most studies have only focused on a few repeat proteins. In this work, the hypothetical protein with a repeat motif derived from the frog Xenopus tropicalis was obtained and characterized for its potential as a novel protein‐based material. The codon‐optimized recombinant frog repeat protein, referred to as ‘xetro’, was produced at a high rate in a bacterial system, and an acid extraction‐based purified xetro protein was successfully fabricated into microfibers and nanofibers using wet spinning and electrospinning, respectively. Specifically, the wet‐spun xetro microfibers demonstrated about 2‐ and 1.5‐fold higher tensile strength compared with synthetic polymer polylactic acid and cross‐linked collagen, respectively. In addition, the wet‐spun xetro microfibers showed about sevenfold greater stiffness than collagen. Therefore, the mass production potential and greater mechanical properties of the xetro fiber may result in these fibers becoming a new promising fiber‐based material for biomedical engineering. © 2015 Wiley Periodicals, Inc. Biopolymers 103: 659–664, 2015.     

Electrospinning of highly porous scaffolds for cartilage regeneration

This study presents a new innovative method where electrospinning is used to coat single microfibers with nanofibers. The nanofiber-coated microfibers can be formed into scaffolds with the combined benefits of tailored porosity for cellular infiltration and nanostructured surface morphology for cell growth. The nanofiber coating is obtained by using a grounded collector rotating around the microfiber, to establish an electrical field yet allow collection of nanofibers on the microfiber. A Teflon tube surrounding the fibers and collector is used to force the nanofibers to the microfiber. Polycaprolactone nanofibers were electrospun onto polylactic acid microfibers and scaffolds of 95 and 97% porosities were made. Human chondrocytes were seeded on these scaffolds and on reference scaffolds of purely nanofibers and microfibers. Thereafter, cellular infiltration was investigated. The results indicated that scaffold porosity had great effects on cellular infiltration, with higher porosity resulting in increased infiltration, thereby confirming the advantage of the presented method.     

In situ synthesis of CdS nanoparticles on bacterial cellulose nanofibers

CdS nanoparticles have been synthesized and stabilized on unique bacterial cellulose (BC) nanofibers in situ. The obtained nanocomposite material have been characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), fourier transformed infrared (FTIR), thermogravimetric analysis (TGA), ultraviolet–visible (UV–Vis) and photoluminescence (PL) spectroscopy. The results indicated that CdS nanoparticles of about 30 nm diameter deposited on BC nanofibres are well-dispersed in the BC nanofibre-network and the uniform spherical CdS nanoparticles are comprised of nano-sized CdS crystal. Moreover, the crystallite sizes of CdS crystals are about 8 nm. The nanocomposites would have potential application as photocatalyst, novel luminescence and photoelectron transfer devices.     

Structure, morphology and thermal characteristics of banana nano fibers obtained by steam explosion

In this work, cellulose nanofibers were extracted from banana fibers via a steam explosion technique. The chemical composition, morphology and thermal properties of the nanofibers were characterized to investigate their suitability for use in bio-based composite material applications. Chemical characterization of the banana fibers confirmed that the cellulose content was increased from 64% to 95% due to the application of alkali and acid treatments. Assessment of fiber chemical composition before and after chemical treatment showed evidence for the removal of non-cellulosic constituents such as hemicelluloses and lignin that occurred during steam explosion, bleaching and acid treatments. Surface morphological studies using SEM and AFM revealed that there was a reduction in fiber diameter during steam explosion followed by acid treatments. Percentage yield and aspect ratio of the nanofiber obtained by this technique is found to be very high in comparison with other conventional methods. TGA and DSC results showed that the developed nanofibers exhibit enhanced thermal properties over the untreated fibers.     

Surface modification of bacterial cellulose nanofibers for property enhancement of optically transparent composites: dependence on acetyl-group DS

Bacterial cellulose (BC) nanofibers were acetylated to enhance the properties of optically transparent composites of acrylic resin reinforced with the nanofibers. A series of BC nanofibers acetylated from degree-of-substitution (DS) 0 to 1.76 were obtained. X-ray diffraction profiles indicated that acetylation proceeded from the surface to the core of BC nanofibers, and scanning electron microscopy images showed that the volume of nanofibers increases by the bulky acetyl group. Since acetylation decreased the refractive index of cellulose, regular transmittance of composites comprised of 63% BC nanofiber was improved, and deterioration at 580 nm because of fiber reinforcement was suppressed to only 3.4%. Acetylation of nanofibers changed their surface properties and reduced the moisture content of the composite to about one-third that of untreated composite, although excessive acetylation increased hygroscopicity. Furthermore, acetylation was found to reduce the coefficient of thermal expansion of a BC sheet from 3 x 10(-6) to below 1 x 10(-6) 1/K.     

Effect of deacetylation on wicking behavior of co-electrospun cellulose acetate/polyvinyl alcohol nanofibers blend

Cellulose acetate (CA) nanofibers webs deserve a special attention because of their very good water retention properties. CA nanofibers based biosensor in certain application come into contact with various liquids and requires high degree of wicking rate to transport liquid to its destination. Cellulose acetate (CA)/polyvinyl alcohol (PVA) blended nanofibers were prepared via co-electrospinning using double nozzle for jetting cellulose acetate and polyvinyl alcohol independently. The CA/PVA blend nanofibers webs were deacetylated in aqueous alkaline solution to convert CA in to regenerated cellulose and to remove PVA nanofibers from the raw web. The resultant nanofibers webs were characterized by wicking rate, water contact angle, SEM and FTIR analysis. The results revealed that by varying concentration of PVA solution enhances the wicking rate. Such a nanofibers web may be used in biosensor strip and other medical applications where the high wicking rates are desired.     

Preparation of chitin nanofibers from squid pen beta-chitin by simple mechanical treatment under acid conditions

A procedure for preparing individualized chitin nanofibers 3-4 nm in cross-sectional width and at least a few microns in length was developed. The key factors to prepare the chitin nanofibers with such high aspect ratios are as follows: (1) squid pen beta-chitin is used as the starting material and (2) ultrasonication of the beta-chitin in water at pH 3-4 and 0.1-0.3% consistency for a few minutes. Transparent and highly viscous dispersions of squid pen beta-chitin nanofibers in water can be obtained by this method. No N-deacetylation occurs on the chitin molecules during the nanofiber conversion procedure. Moreover, the original crystal structure of beta-chitin is maintained, although crystallinity index decreases from 0.51 to 0.37 as a result of the nanofiber conversion. Cationization of the C2 amino groups present on the crystallite surfaces of the squid pen beta-chitin under acid conditions is necessary for preparing the nanofibers.     

PVA based nanofiber containing cellulose modified with graphitic carbon nitride/nettles/trachyspermum accelerates wound healing

Today, bacterial cellulose has received a great deal of attention for its medical applications due to its unique structural properties such as high porosity, good fluid uptake, good strength, and biocompatibility. This study aimed to fabricate and study bacterial cellulose/graphitic carbon nitride/nettles/trachyspermum nanocomposite by immersion and PVA/BC/g-C₃N₄/nettles/trachyspermum nanofiber by electrospinning method as a wound dressing. The g-C₃N₄ and g-C₃N₄ solution were synthesized and then were characterized using Fourier transform infrared, X-ray diffraction, Zeta Potential, and scanning electronic microscope analyzes. Also, the antibacterial properties of the synthesized materials were proved by gram-positive and gram-negative bacteria using the minimum inhibitory concentration method. Besides, the toxicity, migration, and cell proliferation results of the synthesized materials on NIH 3T3 fibroblasts were evaluated using MTT and scratch assays and showed that the BC/PVA/g-C₃N₄/nettles/trachyspermum composite not only had no toxic effect on cells but also contributed to cell survival, cell migration, and proliferation has done. To evaluate the mechanical properties, a tensile strength test was performed on PVA/BC/g-C₃N₄/nettles/trachyspermum nanofibers, and the results showed good strength of the nanocomposite. In addition, in vivo assay, the produced nanofibers were used to evaluate wound healing, and the results showed that these nanofibers were able to accelerate the wound healing process so that after 14 days, the wound healing percentage showed 95%. Therefore, this study shows that PVA/BC/g-C₃N₄/nettles/trachyspermum nanofibers effectively inhibit bacterial growth and accelerate wound healing.     

Vaccination of biological cellulose fibers with glucose: a gateway to novel nanocomposites

This work introduces, for the first time worldwide, the means to preserve and protect the natural nanoporous structure of the never-dried plant cell wall, against the irreversible collapse, which occurs due to drying. Simultaneously, these means, used for the above-mentioned aim, provide a gateway to novel nanocomposite materials, which retain the super reactive and super absorbent properties of the never-dried biological cellulose fibers. The present work showed, for the first time worldwide, that glucose can be vaccinated into the cell wall micropores or nanostructure of the never-dried biological cellulose fibers, by simple new techniques, to create a reactive novel nanocomposite material possessing surprising super absorbent properties. Inoculation of the never dried biological cellulose fibers, with glucose, prevented the collapse of the cell wall nanostructure, which normally occurs due to drying. The nanocomposite, produced after drying of the glucose inoculated biological cellulose, retained the super absorbent properties of the never dried biological cellulose fibers. It was found that glucose under certain circumstances grafts to the never dried biological cellulose fibers to form a novel natural nanocomposite material. About 3-8% (w/w) glucose remained grafted in the novel nanocomposite.     

Isolation and characterization of nanofibers from agricultural residues: wheat straw and soy hulls

Cellulose nanofibers were extracted from the agricultural residues, wheat straw and soy hulls, by a chemi-mechanical technique to examine their potential for use as reinforcement fibers in biocomposite applications. The structure of the cellulose nanofibers was investigated by transmission electron microscopy. The wheat straw nanofibers were determined to have diameters in the range of 10-80 nm and lengths of a few thousand nanometers. By comparison, the soy hull nanofibers had diameter 20-120 nm and shorter lengths than the wheat straw nanofibers. Chemical characterization of the wheat straw nanofibers confirmed that the cellulose content was increased from 43% to 84% by an applied alkali and acid treatment. FT-IR spectroscopic analysis of both fibers demonstrated that this chemical treatment also led to partial removal of hemicelluloses and lignin from the structure of the fibers. PXRD results revealed that this resulted in improved crystallinity of the fibers. After mechanical treatments of cryocrushing, disintegration and defibrillation, the thermal properties of the nanofibers were studied by the TGA technique and found to increase dramatically. The degradation temperature of both nanofiber types reached beyond 290 degrees C. This value is reasonably promising for the use of these nanofibers in reinforced-polymer manufacturing.     

Ultrafine polysaccharide nanofibrous membranes for water purification

Ultrafine polysaccharide nanofibers (i.e., cellulose and chitin) with 5-10 nm diameters were employed as barrier layers in a new class of thin-film nanofibrous composite (TFNC) membranes for water purification. In addition to concentration, the viscosity of the polysaccharide nanofiber coating suspension was also found to be affected by the pH value and ionic strength. When compared with two commercial UF membranes (PAN10 and PAN400), 10-fold higher permeation flux with above 99.5% rejection ratio were achieved by using ultrafine cellulose nanofibers-based TFNC membranes for ultrafiltration of oil/water emulsions. The very high surface-to-volume ratio and negatively charged surface of cellulose nanofibers, which lead to a high virus adsorption capacity as verified by MS2 bacteriophage testing, offer further opportunities in drinking water applications. The low cost of raw cellulose/chitin materials, the environmentally friendly fabrication process, and the impressive high-flux performance indicate that such ultrafine polysaccharide nanofibers-based TFNC membranes can surpass conventional membrane systems in many different water applications.     

Cellulose‐based Supercapacitors: Material and Performance Considerations

One of the biggest challenges we will face over the next few decades is finding a way to power the future while maintaining strong socioeconomic growth and a clean environment. A transition from the use of fossil fuels to renewable energy sources is expected. Cellulose, the most abundant natural biopolymer on earth, is a unique, sustainable, functional material with exciting properties: it is low‐cost and has hierarchical fibrous structures, a high surface area, thermal stability, hydrophilicity, biocompatibility, and mechanical flexibility, which makes it ideal for use in sustainable, flexible energy storage devices. This review focuses on energy storage applications involving different forms of cellulose (i.e., cellulose microfibers, nanocellulose fibers, and cellulose nanocrystals) in supercapacitors, with particular emphasis on new trends and performance considerations relevant to these fields. Recent advances and approaches to obtaining high capacity devices are evaluated and the limitations of cellulose‐based systems are discussed. For the first time, a combination of device‐specific factors such as electrode structures, mass loadings, areal capacities, and volumetric properties are taken into account, so as to evaluate and compare the energy storage performance and to better assess the merits of cellulose‐based materials with respect to real applications.     

Nanocomposite films based on xylan-rich hemicelluloses and cellulose nanofibers with enhanced mechanical properties

Interest in xylan-rich hemicelluloses (XH) film is growing, and efforts have been made to prepare XH films with improved mechanical properties. This work described an effective approach to produce nanocomposite films with enhanced mechanical properties by incorporation of cellulose nanofibers (CNFs) into XH. Aqueous dispersions of XH (64-75 wt %), sorbitol (16-25 wt %), and CNF (0-20 wt %) were cast at a temperature of 23 °C and 50% relative humidity. The surface morphology of the films was revealed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The thermal properties and crystal structure of the films were evaluated by thermal analysis (TG) and X-ray diffraction (XRD). The surface of XH films with and without CNF was composed primarily of nanonodules, and CNFs were embedded in the XH matrix. Freeze-dried XH powder was amorphous, whereas the films with and without CNF showed a distinct peak at around 2θ = 18°, which suggested that XH molecules aggregated or reordered in the casting solution or during water evaporation. Furthermore, the nanocomposite films had improved thermal stability. XH film with 25 wt % plasticizer (sorbitol, based on dry XH weight) showed poor mechanical properties, whereas incorporation of CNF (5-20 wt %, based on the total dry mixture) into the film resulted in enhanced mechanical properties due to the high aspect ratio and mechanical strength of CNF and strong interactions between CNF and XH matrix. This effective method makes it possible to produce hemicellulose-based biomaterials of high quality.     

Bacterial cellulose nanocrystals exhibiting high thermal stability and their polymer nanocomposites

Nanocrystals prepared from bacterial cellulose are considered as 'green nanomaterials' depending on their renewable nature and ease of production without the involvement of hazardous chemical treatments. In this investigation, a top down approach was followed for the preparation of bacterial cellulose nanocrystals (BCNC) using a commercially available cellulase enzyme so as to retain native properties of bacterial cellulose even in its nanodimensional form. The morphological and dimensional parameters of BCNC were studied using atomic force microscope (AFM) and transmission electron microscope (TEM). Thermal properties of BCNC produced using the novel enzyme treatment and conventional sulfuric acid hydrolysis were compared. The thermal stability of enzyme processed BCNC was almost two fold higher than sulfuric acid processed ones. Further, the activation energy required for decomposition of enzyme processed BCNC was much higher than the other. Using this enzyme processed BCNC, Polyvinylalcohol (PVA) nanocomposite films were prepared and characterized. Incorporation of these nanocrystals in polymer matrix resulted in a remarkable improvement in the thermal stability as well as mechanical properties of nanocomposite films. These nanocomposites exhibited higher melting temperature (Tm) and enthalpy of melting (ΔHm) than those of pure PVA, suggesting that the addition of nanocrystals modified the thermal properties of PVA. The effective load transfer from polymer chains to the BCNC resulted in an improved tensile strength from 62.5 MPa to 128 MPa, by the addition of just 4 wt% of BCNC. Furthermore, the elastic modulus was found to increase from 2 GPa to 3.4 GPa. The BCNC obtained through cellulose treatment under controlled conditions were associated with several desirable properties and appear to be superior over the conventional methods of nanocrystals production. The enzymatic method followed in this study is expected to contribute the fabrication of high performance polymer nanocomposites in a much greener and innovative manner.     

New nanocomposite materials reinforced with flax cellulose nanocrystals in waterborne polyurethane

New nanocomposite films were prepared from a suspension of cellulose nanocrystals as the filler and a polycaprolactone-based waterborne polyurethane (WPU) as the matrix. The cellulose nanocrystals, prepared by acid hydrolysis of flax fiber, consisted of slender rods with an average length of 327 +/- 108 nm and diameter of 21 +/- 7 nm, respectively. After the two aqueous suspensions were mixed homogeneously, the nanocomposite films were obtained by casting and evaporating. The morphology, thermal behavior, and mechanical properties of the films were investigated by means of attenuated total reflection Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, and tensile testing. The results indicated that the cellulose nanocrystals could disperse in the WPU uniformly and resulted in an improvement of microphase separation between the soft and hard segments of the WPU matrix. The films showed a significant increase in Young's modulus and tensile strength from 0.51 to 344 MPa and 4.27 to 14.86 MPa, respectively, with increasing filler content from 0 to 30 wt %. Of note is that the Young's modulus increased exponentially with the filler up to a content of 10 wt %. The synergistic interaction between fillers and between the filler and WPU matrix played an important role in reinforcing the nanocomposites. The superior properties of the new nanocomposite materials could have great potential applications.     

"Nanocellulose" as a single nanofiber prepared from pellicle secreted by Gluconacetobacter xylinus using aqueous counter collision

This study attempted to prepare a single cellulose nanofiber, "nanocellulose", dispersed in water from 3D networks of nanofibers in microbial cellulose pellicle using aqueous counter collision (ACC), which allows biobased materials to be down-sized into nano-objects only using water jets without chemical modification. The nanocellulose thus prepared exhibited unique morphological properties. In particular, the width of the nanocellulose, which could be controlled as desired on nanoscales, was smaller than that of just secreted cellulose nanofiber, resulting in larger specific surface areas. Moreover, ACC treatment transformed cellulose I(α) crystalline phase into cellulose I(β) phase with the crystallinity kept >70%. In this way, ACC method depending on the treatment condition could provide the desired fiber width at the nanoscale and the different ratios of the two crystalline allomorphs between cellulose I(α) versus I(β), which thus opens further pathways into versatile applications as biodegradable single nanofibers.     

Cellulose nanofibers prepared by TEMPO-mediated oxidation of native cellulose

Never-dried and once-dried hardwood celluloses were oxidized by a 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated system, and highly crystalline and individualized cellulose nanofibers, dispersed in water, were prepared by mechanical treatment of the oxidized cellulose/water slurries. When carboxylate contents formed from the primary hydroxyl groups of the celluloses reached approximately 1.5 mmol/g, the oxidized cellulose/water slurries were mostly converted to transparent and highly viscous dispersions by mechanical treatment. Transmission electron microscopic observation showed that the dispersions consisted of individualized cellulose nanofibers 3-4 nm in width and a few microns in length. No intrinsic differences between never-dried and once-dried celluloses were found for preparing the dispersion, as long as carboxylate contents in the TEMPO-oxidized celluloses reached approximately 1.5 mmol/g. Changes in viscosity of the dispersions during the mechanical treatment corresponded with those in the dispersed states of the cellulose nanofibers in water.     

A new approach to obtain cellulose nanocrystals and ethanol from eucalyptus cellulose pulp via the biochemical pathway

The feasibility of integration of cellulosic ethanol production with the manufacture of cellulose nanofibers (CNF) and cellulose nanocrystals (CNC) was evaluated using eucalyptus cellulose pulp as feedstock and employing the biochemical route alone. For the enzymatic hydrolysis step, experimental central composite design (CCD) methodology was used as a tool to evaluate the effects of solids loading (SL) and enzymatic loading (EL) on glucose release and cellulose conversion. Glucose concentrations from 45 to 125 g/L were obtained after 24 h, with cellulose conversions from 35 to 96%. Validation of the statistical model was performed at SL of 20% and EL of 10 mg protein/g, which was defined by the desirability function as the optimum condition. The sugars released were used for the production of ethanol by Saccharomyces cerevisiae, resulting in 62.1 g/L ethanol after 8 h (yield of 95.5%). For all the CCD experimental conditions, the residual solids presented CNF characteristics. Moreover, the use of a new strategy with temperature reduction from 50 to 35°C after 24 h of enzymatic hydrolysis enabled CNC to be obtained after 144 h. The CNC showed a crystallinity index of 83%, length of 260 nm, diameter of 15 nm, and aspect ratio (L/D) of 15. These characteristics are suitable for many applications, such as reinforcement in polymeric materials and other lower volume higher value bio‐based products. The findings indicate the viability of obtaining ethanol and CNC using the biochemical route exclusively, potentially contributing to the future implementation of forest biorefineries. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:1085–1095, 2017     

High performance edible nanocomposite films containing bacterial cellulose nanocrystals

Bacterial cellulose obtained from Gluconacetobacter xylinus in the form of long fibers were acid hydrolyzed under controlled conditions to obtain cellulose nanocrystals. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) confirmed the formation of rod like cellulose nanocrystals having an average diameter and length of 20 ± 5 nm and 290 ± 130 nm respectively. These nanocrystals were used to prepare gelatin nanocomposite films and characterized for elucidating its performance. The formation of percolated networks of cellulose nanocrystals within gelatin matrix resulted in improving the mechanical properties of nanocomposites. The moisture sorption and water vapor permeability (WVP) studies revealed that the addition of cellulose nanocrystals reduced the moisture affinity of gelatin, which is very favorable for edible packaging applications. Results of this study demonstrated the use of bacterial cellulose nanocrystals (BCNCs) in the fabrication of edible, biodegradable and high-performance nanocomposite films for food packaging applications at relatively low cost.