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.     

Fabrication and characterisation of α-chitin nanofibers and highly transparent chitin films by pulsed ultrasonication

α-Chitin nanofibers were fabricated with dried shrimp shells via a simple high-intensity ultrasonic treatment under neutral conditions (60 KHz, 300 W, pH = 7). The diameter of the obtained chitin nanofibers could be controlled within 20–200 nm by simply adjusting the ultrasonication time. The pulsed ultrasound disassembled natural chitin into high-aspect-ratio nanofibers with a uniform width (19.4 nm after 30 min sonication). The EDS, FTIR, and XRD characterisation results verified that α-chitin crystalline structure and molecular structure were maintained after the chemical purification and ultrasonic treatments. Interestingly, ultrasonication can slightly increase the degree of crystallinity of chitin (from 60.1 to 65.8). Furthermore, highly transparent chitin films (the transmittance was 90.2% at a 600 nm) and flexible ultralight chitin foams were prepared from chitin nanofiber hydrogels.     

Application of a water jet system to the pretreatment of cellulose

Plant cellulose is the most abundant organic compound on earth. Technologies for producing cellulose fiber or improving the enzymatic saccharification of cellulose hold the key to biomass applications. A technology for atomizing biomass without strong acid catalysis remains to be developed. The water jet is a well-known device used in machines (e.g., washing machines, cutters, and mills) that use high-pressure water. In this study, we examined whether a water jet system could be used to atomize crystalline cellulose, which comprises approximately 50% of plant biomass. The Star Burst System manufactured by Sugino Machine Limited (Sugino Machine; Toyama, Japan) is a unique atomization machine that uses a water jet to atomize materials and thereby places lower stress on the environment. After treatment with this system, the crystalline cellulose was converted into a gel-like form. High-angular annular dark-field scanning transmission electron microscopy showed that the cellulose fibers had been converted from a solid crystalline into a matrix of cellulose nanofibers. In addition, our results show that this system can improve the saccharification efficiency of cellulases by more than three-fold. Hence, the Star Burst System provides a new and mild pretreatment system for processing biomass materials.     

Influential factors to enhance the moving rate of Acetobacter xylinum due to its nanofiber secretion on oriented templates

Acetobacter xylinum, a bacterium which secretes a cellulose nanofiber, moves due to the inverse force of extrusion of the fiber, which accordingly correlates with the fiber production rate. To improve the production, the moving rate of the bacterium was focused to examine the influential factors on the substrates for culture and additives in the culture medium. From the real-time video analysis, the oriented template having a strong interaction with the secreted cellulose nanofibers proved to be suitable for the bacteria to move faster. Furthermore, addition of carboxymethylcellulose sodium salt (CMC) to the culture medium cause the bacteria to move faster in the culture medium. In this case, secreted cellulose nanofiber formed different from a normal cellulose nanofiber. The above result could provide an understanding how the formation of cellulose nanofibers contributes to the production rate as well as the bacterial moving rate.     

Structure and mechanical properties of wet-spun fibers made from natural cellulose nanofibers

Cellulose nanofibers were prepared by TEMPO-mediated oxidation of wood pulp and tunicate cellulose. The cellulose nanofiber suspension in water was spun into an acetone coagulation bath. The spinning rate was varied from 0.1 to 100 m/min to align the nanofibers to the spun fibers. The fibers spun from the wood nanofibers had a hollow structure at spinning rates of >10 m/min, whereas the fibers spun from tunicate nanofibers were porous. Wide-angle X-ray diffraction analysis revealed that the wood and tunicate nanofibers were aligned to the fiber direction of the spun fibers at higher spinning rates. The wood spun fibers at 100 m/min had a Young's modulus of 23.6 GPa, tensile strength of 321 MPa, and elongation at break of 2.2%. The Young's modulus of the wood spun fibers increased with an increase in the spinning rate because of the nanofiber orientation effect.     

Viscoelastic evaluation of average length of cellulose nanofibers prepared by TEMPO-mediated oxidation

Dynamic viscoelasticity measurements were performed for aqueous dispersions of cellulose nanofibers prepared by TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidation and subsequent mechanical disintegration in water. The frequency dependence of the storage and loss moduli of 0.02% (w/v) dispersions of TEMPO-oxidized cellulose nanofibers in water showed terminal relaxation behavior at relatively lower angular frequencies. This strongly suggests that each cellulose nanofiber in the dispersion behaves as a semiflexible rod-like macromolecular chain or colloidal particle. Furthermore, a clear boundary was observed between the terminal relaxation and rubbery plateau regions. The longest viscoelastic relaxation time, τ, was estimated from the angular frequency, corresponding to the boundary point, and the average length of the cellulose nanofibers, L, was estimated using the equation τ = πη(s)L(3)/[18k(B)T ln(L/d)]. The equation gave a value of L = 2.2 μm, which was in good agreement with TEM observations.     

Fine structure and enzymatic degradation of poly[(R)-3-hydroxybutyrate] and stereocomplexed poly(lactide) nanofibers

Fiber morphology and crystalline structure of poly[(R)-3-hydroxybutyrate] (P(3HB)) and stereocomplexed poly(lactide) (PLA) nanofibers were investigated by using scanning and transmission electron microscopies and X-ray and electron diffractions. In the P(3HB) nanofibers spun from less than 1 wt% 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) solution, planar zigzag conformation (beta-form) as well as 2(1) helix conformation (alpha-form) structure was formed. Based on the electron diffraction measurement of single P(3HB) nanofiber, it was revealed that the molecular chains of P(3HB) align parallel to the fiber direction. From the enzymatic degradation test of P(3HB) nanofiber, it was shown that beta-form molecular chains are degraded more preferentially than alpha-form chains. Stereocomplexed PLA nanofibers were electrospun from 1 wt% poly(l-lactide)/poly(d-lactide) (PLLA/PDLA) solution in HFIP, which contains equal amounts of PLLA and PDLA. While as-spun stereocomplexed PLA nanofiber was amorphous, PLA nanofiber annealed at 100 degrees C contained only racemic crystal. It was supposed that the crystallization behavior of stereocomplexed PLA in the nanofiber is affected by the electrospinning process, which forcibly exerts the strain onto the polymer chains.     

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.     

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.     

Nanofiber adsorbents for high productivity downstream processing

Electrospun polymeric nanofiber adsorbents offer an alternative ligand support surface for bioseparations. Their non‐woven fiber structure with diameters in the sub‐micron range creates a remarkably high surface area. To improve the purification productivity of biological molecules by chromatography, cellulose nanofiber adsorbents were fabricated and assembled into a cartridge and filter holder format with a volume of 0.15 mL, a bed height of 0.3 mm and diameter of 25 mm. The present study investigated the performance of diethylaminoethyl (DEAE) derivatized regenerated cellulose nanofiber adsorbents based on criteria including mass transfer and flow properties, binding capacity, and fouling effects. Our results show that nanofibers offer higher flow and mass transfer properties. The non‐optimized DEAE‐nanofiber adsorbents indicate a binding capacity of 10% that of packed bed systems with BSA as a single component system. However, they operate reproducibly at flowrates of a hundred times that of packed beds, resulting in a potential productivity increase of 10‐fold. Lifetime studies showed that this novel adsorbent material operated reproducibly with complex feed material (centrifuged and 0.45 µm filtered yeast homogenate) and harsh cleaning‐in‐place conditions over multiple cycles. DEAE nanofibers showed superior operating performance in permeability and fouling over conventional adsorbents indicating their potential for bioseparation applications. Biotechnol. Bioeng. 2013; 110: 1119–1128. © 2012 Wiley Periodicals, Inc.     

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.     

Incorporation of the Tat cell‐penetrating peptide into nanofibers improves the respective antitumor immune response

A major challenge for the development of anticancer vaccines is the induction of a safe and effective immune response, particularly mediated by CD8+ T lymphocytes, in an adjuvant‐free manner. In this respect, we present a simple strategy to improve the specific CD8+ T cell responses using KFE8 nanofibers bearing a Class I (Kb)‐restricted peptide epitope (called E. nanofibers) without the use of adjuvant. We demonstrate that incorporation of Tat, a cell‐penetrating peptide (CPP) of the HIV transactivator protein, into E. nanofibers remarkably enhanced tumor‐specific CD8+ T cell responses. E. nanofibers containing 12.5% Tat peptide (E.Tat_12.5 nanofiber) increased antigen cross‐presentation by bone marrow‐derived dendritic cells as compared with E. nanofibers, or E. nanofibers containing 25 or 50% the Tat peptide. Uptake of KFE8.Tat_12.5 nanofibers by dendritic cells (DCs) was significantly increased compared with KFE8 nanofiber lacking Tat. Peritoneal and lymph node DCs of mice immunized with E.Tat_12.5 nanofibers exhibited increased presentation of the H2kb‐epitope (reminiscent for cross‐presentation) compared with DCs obtained from E. nanofiber vaccinated mice. Tetrameric and intracellular cytokine staining revealed that vaccination with E.Tat_12.5 triggered a robust and specific CD8+ T lymphocyte response, which was more pronounced than in mice vaccinated with E. nanofibers alone. Furthermore, E.Tat_12.5 nanofibers were more potent than E. nanofiber to induce antitumor immune response and tumor‐infiltrating IFN‐γ CD8 T lymphocyte. In terms of cancer vaccine development, we propose that harnessing the nanofiber‐based vaccine platform with incorporated Tat peptide could present a simple and promising strategy to induce highly effective antitumor immune response.     

Self-assembly of amylose-grafted carboxymethyl cellulose

In this study, we performed the self-assembly of the amylose-grafted carboxymethyl cellulose sodium salt (NaCMC) for the formation of nanofiber films under aqueous conditions. The introduction of amylose graft chains was conducted by the chemoenzymatic approach including phosphorylase-catalyzed enzymatic polymerization. The product had the rigid NaCMC main chain, which further assembled leading to nanofibers by the formation of double helix between the long amylose graft chains in the intermolecular NaCMC chains of the products. The lengths of the fibers were depended on degrees of polymerization of amylose chains. The nanofiber films were constructed by drying the alkaline solutions of the amylose-grafted NaCMC. The lengths of the nanofibers strongly affected their arrangements in the films. The nanofibers were merged further by washing out alkali to produce the robust nanofiber films.     

Selective molecular adsorption using electrospun nanofiber affinity membranes

Molecularly imprinted nanoparticles were encapsulated into polymer nanofibers with a simple electrospinning method. The composite nanofibers form non-woven mats that can be used as affinity membrane to greatly simplify solid phase extraction of drug residues in analytical samples. Upward 100% of propranolol-imprinted nanoparticles can be easily encapsulated into poly(ethylene terephthalate) nanofibers, ensuring the composite materials to have a high specific binding capacity. As confirmed by radioligand binding analysis, the specific binding sites in the composite materials remain easily accessible and are chiral-selective. Using the new composite nanofiber mats as solid phase extraction materials, trace amount of propranolol (1 ng mL(-1)) in tap water can be easily detected after a simple sample preparation. As validated in this study, there is no problem of template leakage from the composite nanofibers. Without the solid phase extraction, the existence of propranolol residues in water cannot be confirmed with even tandem HPLC-MS/MS analysis.     

Fibrous cellulose nanocomposite scaffolds prepared by partial dissolution for potential use as ligament or tendon substitutes

Fibrous cellulose nanocomposites scaffolds were developed and evaluated for their potential as ligament or tendon substitute. The nanocomposites were prepared by partial dissolution of cellulose nanofiber networks using ionic liquid at 80 °C for different time intervals. Scanning electron microscopy study indicated that partial dissolution resulted in fibrous cellulose nanocomposites where the dissolved cellulose nanofibers formed the matrix phase and the undissolved or partially dissolved nanofibers formed the reinforcing phase. Mechanical properties of the composites in simulated body conditions (37 °C and 95% RH) after sterilization using gamma rays was comparable to those of natural ligaments and tendons. Stress relaxation studies showed stable performance towards cyclic loading and unloading, further confirming the possibility for using these composites as ligament/tendon substitute. In vitro biocompatibility showed a positive response concerning adhesion/proliferation and differentiation for both human ligament and endothelial cells. Prototypes based on the cellulose composite were developed in the form of tubules to be used for further studies.     

Activation of crystalline cellulose to cellulose III(I) results in efficient hydrolysis by cellobiohydrolase

The crystalline polymorphic form of cellulose (cellulose I(alpha)-rich) of the green alga, Cladophora, was converted into cellulose III(I) and I(beta) by supercritical ammonium and hydrothermal treatments, respectively, and the hydrolytic rate and the adsorption of Trichoderma viride cellobiohydrolase I (Cel7A) on these products were evaluated by a novel analysis based on the surface density of the enzyme. Cellobiose production from cellulose III(I) was more than 5 times higher than that from cellulose I. However, the amount of enzyme adsorbed on cellulose III(I) was less than twice that on cellulose I, and the specific activity of the adsorbed enzyme for cellulose III(I) was more than 3 times higher than that for cellulose I. When cellulose III(I) was converted into cellulose I(beta) by hydrothermal treatment, cellobiose production was dramatically decreased, although no significant change was observed in enzyme adsorption. This clearly indicates that the enhanced hydrolysis of cellulose III(I) is related to the structure of the crystalline polymorph. Thus, supercritical ammonium treatment activates crystalline cellulose for hydrolysis by cellobiohydrolase.     

Polymorphism of cellulose I family: reinvestigation of cellulose IVI

Polymorphs of cellulose I, III(I), and IV(I) have been investigated by X-ray diffraction, FT-IR, and solid-state (13)C NMR spectroscopy. Highly crystalline cellulose III(I) samples were prepared by treating cellulose samples in supercritical ammonia at 140 degrees C for 1 h, and conventional cellulose III(I) samples were prepared by liquid ammonia treatment. The cellulose IV(I) sample of highest crystallinity was that prepared from Cladophora cellulose III(I) in supercritical ammonia, followed by the sample treated in glycerol at 260 degrees C for 0.5 h, whereas the lowest crystallinity was observed in ramie cellulose prepared by conventional liquid ammonia treatment followed by glycerol annealing. In general, the perfection of cellulose IV(I) depends on the crystallinity of the original material: either of the starting cellulose I or of the cellulose III(I) after ammonia treatment. The product thus obtained was analogous to cellulose I(beta), which is what it should be called rather than cellulose IV(I). If the existence of the polymorph cellulose IV(I) is not accepted, the observations on which it has been based may be explained by the fact that the structure termed cellulose IV(I) is cellulose I(beta) which contains lateral disorder.     

Preparation of carboxylic acid-bearing polysaccharide nanofiber made from euglenoid β-1,3-glucans

This paper introduces a new strategy for creating surface modified polysaccharide nanofibers. To demonstrate proof of principle, the synthesis, structure, and self-assembly behavior of a carboxylic acid-bearing polysaccharide made from paramylon (β-1,3-glucan) and succinic anhydride were investigated. Examination by a combination of NMR, FT-IR, and SEC-MALLS confirmed that successful preparation of the desired succinylated paramylon without significant depolymerization. NMR, SEC-MALLS, visible absorption and CD spectroscopic analyses indicated that the paramylon derivative forms the triplex structure in solutions. SEM observation revealed that succinylated paramylon forms a nanofiber that has carboxylic acid on the surface.     

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.     

一株产细菌纤维素菌株的筛选鉴定及其产物分析

从红茶菌液中筛选获得一株产细菌纤维素的菌株BC-41,经生理生化分析和分子生物学鉴定,现证实该菌株为中间葡糖酸醋杆菌(Gluconacetobacter intermedius)。对该菌株所产生的细菌纤维素进行了物理特性的表征和分析,获得以下数据:BC-41所产的纤维素纯度达到91.32%,湿纤维素膜含水率达99.16%,每克干纤维素膜能吸水28.59 g;扫描电子显微镜观察,显示该纤维素具有网状结构,且纤维束宽度分布在40-100 nm之间;X射线衍射分析,证实该纤维素的晶型为纤维素I型,结晶指数为48.8%;通过黏度测定法,得出该纤维素的平均聚合度达2 100。