TEMPO-oxidized Cellulose Nanofibrils Research Articles

Preparation and Evaluation of Undaria pinnatifida Nanocellulose in Fabricating Pickering Emulsions for Protection of Astaxanthin.

Pickering emulsions stabilized from natural sources are often used to load unstable bio-active ingredients, such as astaxanthin (AXT), to improve their functionality. In this study, AXT-loaded Pickering emulsions were successfully prepared by 2,2,6,6-tetramethy-1-piperidine oxide (TEMPO)-oxidized cellulose nanofibers (TOCNFs) from Undaria pinnatifida. The morphology analysis showed that TOCNFs had a high aspect ratio and dispersibility, which could effectively prevent the aggregation of oil droplets. The stable emulsion was obtained after exploring the influence of different factors (ultrasonic intensity, TOCNFs concentration, pH, and ionic strength). As expected, AXT-loaded Pickering emulsions showed good stability at 50 °C and 14 days of storage. The results of simulated in vitro digestion showed that the emulsions exhibited higher release of free fatty acids (FFAs) and bioaccessibility of AXT than those in sunflower oil. Hence, our work brought new insights into the preparation of Pickering emulsions and their applications in protection and sustained, controlled release of AXT.

Tb-coordination polymer-anchored nanocellulose composite film for selective and sensitive detection of ciprofloxacin

In recent years, along with the extensive application of ciprofloxacin (CIP), it has gradually become one of key environmental issues to be solved urgently. A novel fluorescent responsive nanocellulose composite film was successfully prepared by combining TEMPO-oxidized cellulose nanofibers (TOCNF) and terbium coordination polymer (Tb-AMP), in aqueous medium at room temperature via in-situ synthesis to detect CIP. CIP could supply energy for terbium ion through antenna effect to achieve the green fluorescence of Tb-AMP@TOCNF under 365 nm UV lamp. The transparency of the Tb-AMP@TOCNF was 88% when the deposition ratio of Tb-AMP on TOCNF was 7.2% and the environmental stability was good, which was conducive to fluorescent detection. As CIP concentration increased, the fluorescence intensity of Tb-AMP@TOCNF increased, and fluorescence intensity had a good linear relationship with CIP concentration in the range of 1–8 μM (y = 4.57 + 3.17x, R2 = 0.999, LOD = 0.0392 μM). It was a new way to realize future quantitative colorimetric analysis of pollutants.

Detection of Human Neutrophil Elastase by Fluorescent Peptide Sensors Conjugated to TEMPO-Oxidized Nanofibrillated Cellulose.

Peptide–cellulose conjugates designed for use as optical protease sensors have gained interest for point-of-care (POC) detection. Elevated serine protease levels are often found in patients with chronic illnesses, necessitating optimal biosensor design for POC assessment. Nanocellulose provides a platform for protease sensors as a transducer surface, and the employment of nanocellulose in this capacity combines its biocompatibility and high specific surface area properties to confer sensitive detection of dilute biomarkers. However, a basic understanding of the spatiotemporal relationships of the transducer surface and sensor disposition is needed to improve protease sensor design and development. Here, we examine a tripeptide, fluorogenic elastase biosensor attached to TEMPO-oxidized nanofibrillated cellulose via a polyethylene glycol linker. The synthetic conjugate was found to be active in the presence of human neutrophil elastase at levels comparable to other cellulose-based biosensors. Computational models examined the relationship of the sensor molecule to the transducer surface. The results illustrate differences in two crystallite transducer surfaces ((110) vs. (1−10)) and reveal preferred orientations of the sensor. Finally, a determination of the relative (110) vs. (1−10) orientations of crystals extracted from cotton demonstrates a preference for the (1−10) conformer. This model study potentiates the HNE sensor results for enhanced sensor activity design.

Biomimetic, Highly Reusable and Hydrophobic Graphene/Polyvinyl Alcohol/Cellulose Nanofiber Aerogels as Oil-Removing Absorbents.

Aerogels have great potential in oil absorption applications; however, many reported aerogels have the drawbacks of a low oil-recovery rate and poor mechanical properties, which limit their application. In this study, highly reusable graphene oxide (GO)/TEMPO-oxidized cellulose nanofiber (TOCN)/polyvinyl alcohol (PVA) aerogels with excellent mechanical properties and with an architecture similar to that of Thalia dealbata stems were fabricated through a three-step process of bidirectional-freezing, freeze-drying, and chemical vapor deposition (CVD) modification. After CVD modification, the modified GTPA (MGTPA) accorded hydrophobicity. The synergistic effects of the three components and the unique biomimetic structure conferred biomimetic-MGTPA (b-MGTPA) with excellent compressible properties. As an adsorbent, b-MGTPA showed a high adsorption capacity (75–151 g/g) for various types of organic solvents. In addition, its high compressibility enables b-MGTPA to have fast and highly efficient recovery of absorbed oil through simple mechanical squeezing and it possesses excellent reusable stability (the oil recovery rate and oil retention rate reached 80% and 91.5%, respectively, after 10 repeated absorption–compression cycles).

Nanocellulose/Nisin Hydrogel Microparticles as Sustained Antimicrobial Coatings for Paper Packaging

Hydrogels composed of biomaterials are promising drug delivery systems. In this study, we prepared an antibacterial hydrogel by incorporating the antimicrobial peptide nisin into bagasse cellulose nanofibrils, followed by mechanic shearing to obtain hydrogel microparticles as antimicrobial coatings for paper packaging. The concept of combining nisin with a hydrogel network helps to reduce the nisin depletion disadvantage in a nisin alone coating while achieving a prolonged antibacterial efficacy in application. First, antimicrobial hydrogels were constructed by electrostatic attraction between TEMPO-oxidized cellulose nanofibrils (TOCNF) and nisin. The rheological analysis confirmed that the hydrogel with a TOCNF/nisin ratio of 3:1 formed a good gel network accompanied by a high nisin loading efficiency. The obtained hydrogel exhibited controlled release of nisin in response to pH, with a slower rate at pH 7 than that of pH 5 and pH 9. Then, the obtained hydrogel has been processed to microparticles to facilitate its application as coating on paper packaging. Highly stable TOCNFs/nisin hydrogel microparticles were obtained under a water/hydrogel ratio of 4:1 and a mechanical shearing rate of 8000 rpm. The paper with hydrogel microparticles coating displayed an enhanced tensile strength by 14.67% compared to uncoated paper. As a packaging for cheese in storage at 4 °C for 7 days, the hydrogel microparticle coating paper can significantly reduce the growth of Listeria monocytogenes on the surface of cheese and show a sustained inhibition advantage over a nisin alone coating. The utilization of hydrogel microparticles as the coating slurry provides a versatile approach for paper treatment and endows the paper with a sustained release characteristic in actively preventing the bacterial proliferation on food surfaces during storage. The finding from this work is expected to broaden the application of nanocellulose and nisin into the field of food active packaging.

Cellulose nanofibrils (CNFs) in uniform diameter: Capturing the impact of carboxyl group on dispersion and Re-dispersion of CNFs suspensions

The poor dispersibility and re-dispersibility of cellulose nanofibrils (CNFs) in various solvents and polymers have been recognized as the key factors limiting their potential applications. TEMPO oxidation, as the most common surface modification, can greatly improve the dispersion and re-dispersion of CNFs. However, the diameter of TEMPO-oxidized cellulose nanofibers (TOCNFs) has not been regulated in most researches, which was an important factor determining the dispersion and re-dispersion of TOCNFs. Herein, this work explored the effect of carboxyl groups on dispersion and re-dispersion of TOCNFs with uniform diameter in various solvents. Notably, fractal dimension was innovatively introduced to characterize the distribution of TOCNFs diameter. The fractal dimension and statistic diameter of TCONFs with different carboxyl group contents are ~1.56 and ~22 nm, demonstrating that the diameter of TOCNFs has been regulated in the same range. When the carboxyl group content is up to 1.58 mmol/g, the dispersion and re-dispersion of TOCNFs suspension in water and different organic solvents are the most uniform and stable. In a word, this work explores the dispersion and re-dispersion of TOCNFs with the uniform diameter and different carboxyl group contents, which can provide the theoretical guidance for various potential applications of nanofibrils in polymer matrix composites.

Role of nanocellulose in colored paper preparation

Colored paper is an important industrial paper grade that has applications in various industrial sectors. The increase in coloring efficiency is a key in decreasing the use of dyes, thus can be considered as a “green” process concept; the coloring efficiency depends on the dye retention and dispersion. This work explores the use of nanocellulose, specifically, TEMPO-oxidized cellulose nanofibers (TOCNF), on the coloring efficiency of the preparation of colored paper. Two dyes (i.e. direct blue GL and reactive red 195 (RR195)) were used. Thanks to the large specific surface area and abundant active sites of TOCNF, its use largely improves the direct blue GL retention during the process. The coloring difference (∆E*ab) reached 5.334 with the addition of 13.6 wt% TOCNF and 1.8 wt% direct blue GL in the pulp furnish. The functional group in the dye is a vital factor in determining the dye retention when one chooses TOCNF to enhance the coloring efficiency in the production of colored paper. Furthermore, TOCNF significantly improved the strength properties of both direct blue GL and RR 195 dyed papers. This work demonstrates the potential of nanocellulose in the production of colored paper in improving the coloring efficiency, thus decreasing the environmental impact of the manufacturing process.

SI ATRP for the Surface Modifications of Optically Transparent Paper Films Made by TEMPO-Oxidized Cellulose Nanofibers.

Applications of cellulose nanofibers currently match the demands of biodegradable and renewable constituent biocomposites. In this study, we studied the process of preparing TEMPO-oxidized cellulose nanofibers (TOCNs). These nano-sized cellulose fibers (ca. 11 nm) can be fabricated to high transmittance and optically transparent paper (OP) films. Then the OP films can be facilely immobilized initiating sites for the subsequent surface-initiated atom transfer radical polymerization (SI ATRP). We investigated SI ATRP with styrene (St) kinetics and monitored chemical structure changes of the OP surfaces. The obtained OP-g-PSt significantly led to enhance thermal stability and alter the OP surface with hydrophobic compared to that of pristine OP film. Characterization was studied by Fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV–Vis spectroscopy, thermogravimetric analyzer (TGA), and water contact angle (WCA) measurements.

Adjustable film properties of cellulose nanofiber and cellulose nanocrystal composites

A novel nanocomposite comprised of cellulose nanocrystals (CNCs) and 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) oxidized cellulose nanofibers (TOCNFs) was prepared through solution casting to evaluate potential improvements of the mechanical performance compared to individual reinforcements alone. Such materials can be implemented as mechanical reinforcements in polymer composites, especially when less weight is desired. Dissipative particle dynamics (DPD) simulations, in combination with polarized light microscopy and atomic force microscopy, were analyzed to evaluate the morphology of these combined cellulose nanomaterial (CNM) films. Our results indicate that TOCNFs provide enhanced translational mobility to CNCs which become incorporated near the crystalline domains of TOCNFs. This mobility enables CNCs to increase the rigidity of the network without sacrificing elongation and toughness. The combination of these materials provides improved ultimate tensile strength and elongation without sacrificing the Young's modulus. Therefore, a combination of these materials can be used to develop nanocomposites with enhanced mechanical properties.

An osteogenic bioink composed of alginate, cellulose nanofibrils, and polydopamine nanoparticles for 3D bioprinting and bone tissue engineering

Bioprinting is an emerging technology for manufacturing cell-laden three-dimensional (3D) scaffolds, which are used to fabricate complex 3D constructs and provide specific microenvironments for supporting cell growth and differentiation. The development of bioinks with appropriate printability and specific bioactivities is crucial for bioprinting and tissue engineering applications, including bone tissue regeneration. Therefore, to produce functional bioinks for osteoblast printing and bone tissue formation, we formulated various nanocomposite hydrogel-based bioinks using natural and biocompatible biomaterials (i.e., alginate, tempo-oxidized cellulose nanofibrils (TOCNF), and polydopamine nanoparticles (PDANPs)). Rheological studies and printability tests revealed that bioinks containing 1.5% alginate and 1.5% TOCNF in the presence or absence of PDANP (0.5%) are suitable for 3D printing. Furthermore, in vitro studies of 3D-printed osteoblast-laden scaffolds indicated that the 0.5% PDANP-incorporated bioink induced significant osteogenesis. Overall, the bioink consisting of alginate, TOCNF, and PDANPs exhibited excellent printability and bioactivity (i.e., osteogenesis).

Multifunctional Nanocellulose/Carbon Nanotube Composite Aerogels for High-Efficiency Electromagnetic Interference Shielding

Bio-based specialized components have emerged as a promising trend to limit the use of petroleum derivatives. Conversely, the current use of electronic systems has conditioned the emission of electromagnetic waves that interfere with high-precision devices and harm human health. Thus, robust, ultralight, and conductive nanocellulose-based aerogels paired with carbon nanotubes appear as an electromagnetic interference (EMI) shielding biomaterial to reduce the dispersion of microwaves emitted or received from a device. This study proposes a reliable aerogel system to deflect radiation by integrating TEMPO-oxidized cellulose nanofibrils, cationic cellulose nanocrystals, and sodium alginate, with carbon nanotubes at various concentrations. After inducing gelation, the aerogels were obtained by freeze drying. According to zeta potential and FTIR analysis data of nanocellulose, the aerogel frame was induced by electrostatic attraction and hydrogen bonds between the cellulosic matrix and the nanofillers. Finally, lightweight (density < 0.075 g/cm3), highly porous (porosity > 95.47%), conductive (up to 26.2 S/m), mechanically resistant, and EMI-protective aerogels were obtained, proving their potential to be used as green and lightweight shielding elements against electromagnetic radiation.

Nanofibrillated cellulose/glucosamine 3D aerogel implants loaded with rosuvastatin and bioactive ceramic for dental socket preservation

Recycling of agro-wastes presents a great economic and ecologic value. In this study, TEMPO-oxidized nanofibrillated cellulose (TONFC) originating from sugarcane bagasse pulp was exploited in regenerative medicine. TONFC in combination with glucosamine HCl (G) were used to prepare a 3D aerogel implant loaded with rosuvastatin as an integrative approach for extraction-socket healing. Comparing the prepared devices, aerogel composed of TONFC: G (4:1 wt ratio) had the best mechanical properties and integrity. Strontium borate-based bioactive ceramic particles were prepared and characterized for crystal structure, shape, porosity, and zeta potential. The particles had a crystalline diffraction pattern relative to Sr3B2O6, and they were rod in shape with nanopores with a zeta potential value of −16 mV. The prepared bioactive ceramic (BC) was then added in different concentrations (3 or 6% w/w) to the selected aerogel implant. The BC had a concentration-dependent effect on the aerogel properties as it ameliorated its mechanical performance (compressive strength = 90 and 150 kPa for 3 and 6%, respectively) and retarded drug release (mean release time = 2.34 and 3.4 h for 3 and 6%, respectively) (p < 0.05). The microphotograph of the selected aerogel implant loaded with BC showed a rough surface with an interconnective porous structure. During cell biology testing, the selected implant loaded with the lower BC concentration had the highest ability to increase MG-63 cells proliferation. In conclusion, TONFC is a promising material to formulate rosuvastatin-loaded aerogel implant with the aid of glucosamine and bioactive ceramic for dental socket preservation.

Strong, tough and degradable cellulose nanofibers-based composite film by the dual crosslinking of polydopamine and iron ions

It is urgently needed to develop an eco-friendly composite films with excellent mechanical properties for biomedicine, optoelectronics, and water treatment applications. Here, we acquired a strong, tough, and sustainable TEMPO-oxidized cellulose nanofiber (TOCN)-based composite film by the dual crosslinking of polydopamine (PDA) and iron ions (Fe3+). The ultimate TOCN/PDA/Fe3+ ternary composites exhibited outstanding mechanical properties with a strength of 220 MPa, a strain of 13.26% and a toughness of 17.73 MJ m−3, increasing by 113%, 149%, and 417% compared to pure TOCN film, respectively. This result was caused by the coordination bonds and covalent bonds. Moreover, the TOCN/PDA/Fe3+ composite film also showed excellent degradability, thermal stability and UV-shielding capability.

Multifunctional silk fibroin/PVA bio-nanocomposite films containing TEMPO-oxidized bacterial cellulose nanofibers and silver nanoparticles

Multifunctional silk fibroin/PVA bio-nanocomposite films containing TEMPO-oxidized bacterial cellulose nanofibers and silver nanoparticles

Combination of Polysaccharide Nanofibers Derived from Cellulose and Chitin Promotes the Adhesion, Migration and Proliferation of Mouse Fibroblast Cells.

Extracellular matrix (ECM) as a structural and biochemical scaffold to surrounding cells plays significant roles in cell adhesion, migration, proliferation and differentiation. Herein, we show the novel combination of TEMPO-oxidized cellulose nanofiber (TOCNF) and surface-N-deacetylated chitin nanofiber (SDCtNF), respectively, having carboxylate and amine groups on each crystalline surface, for mouse fibroblast cell culture. The TOCNF/SDCtNF composite scaffolds demonstrated characteristic cellular behavior, strongly depending on the molar ratios of carboxylates and amines of polysaccharide NFs. Pure TOCNF substrate exhibited good cell attachment, although intact carboxylate-free CNF made no contribution to cell adhesion. By contrast, pure SDCtNF induced crucial cell aggregation to form spheroids; nevertheless, the combination of TOCNF and SDCtNF enhanced cell attachment and subsequent proliferation. Molecular blend of carboxymethylcellulose and acid-soluble chitosan made nearly no contribution to cell culture behavior. The wound healing assay revealed that the polysaccharide combination markedly promoted skin repair for wound healing. Both of TOCNF and SDCtNF possessed rigid nanofiber nanoarchitectures with native crystalline forms and regularly-repeated functional groups, of which such structural characteristics would provide a potential for developing cell culture scaffolds having ECM functions, possibly promoting good cellular adhesion, migration and growth in the designated cellular microenvironments.

Mineralized Polyvinyl Alcohol/Sodium Alginate Hydrogels Incorporating Cellulose Nanofibrils for Bone and Wound Healing.

Bio sustainable hydrogels including tunable morphological and/or chemical cues currently offer a valid strategy of designing innovative systems to enhance healing/regeneration processes of damaged tissue areas. In this work, TEMPO-oxidized cellulose nanofibrils (T-CNFs) were embedded in alginate (Alg) and polyvinyl alcohol (PVA) solution to form a stable mineralized hydrogel. A calcium chloride reaction was optimized to trigger a crosslinking reaction of polymer chains and mutually promote in situ mineralization of calcium phosphates. FTIR, XRD, SEM/EDAX, and TEM were assessed to investigate the morphological, chemical, and physical properties of different mineralized hybrid hydrogels, confirming differences in the deposited crystalline nanostructures, i.e., dicalcium phosphate dehydrate (DCPDH) and hydroxyapatite, respectively, as a function of applied pH conditions (i.e., pH 4 or 8). Moreover, in vitro tests, in the presence of HFB-4 and HSF skin cells, confirmed a low cytotoxicity of the mineralized hybrid hydrogels, and also highlighted a significant increase in cell viability via MTT tests, preferentially, for the low concentration, crosslinked Alg/PVA/calcium phosphate hybrid materials (<1 mg/mL) in the presence of hydroxyapatite. These preliminary results suggest a promising use of mineralized hybrid hydrogels based on Alg/PVA/T-CNFs for bone and wound healing applications.

Zinc- and Copper-Loaded Nanosponges from Cellulose Nanofibers Hydrogels: New Heterogeneous Catalysts for the Synthesis of Aromatic Acetals.

Herein we report the synthesis of cellulose-based metal-loaded nano-sponges and their application as heterogeneous catalysts in organic synthesis. First, the combination in water solution of TEMPO-oxidized cellulose nanofibers (TOCNF) with branched polyethyleneimine (bPEI) and citric acid (CA), and the thermal treatment of the resulting hydrogel, leads to the synthesis of an eco-safe micro- and nano-porous cellulose nano-sponge (CNS). Subsequently, by exploiting the metal chelation characteristics of CNS, already extensively investigated in the field of environmental decontamination, this material is successfully loaded with Cu (II) or Zn (II) metal ions. Efficiency and homogeneity of metal-loading is confirmed by scanning electron microscopy (SEM) analysis with an energy dispersive X-ray spectroscopy (EDS) detector and by inductively coupled plasma-optical emission spectrometry (ICP-OES) analysis. The resulting materials perform superbly as heterogeneous catalysts for promoting the reaction between aromatic aldehydes and alcohols in the synthesis of aromatic acetals, which play a fundamental role as intermediates in organic synthesis. Optimized conditions allow one to obtain conversions higher than 90% and almost complete selectivity toward acetal products, minimizing, and in some cases eliminating, the formation of carboxylic acid by-products. ICP-OES analysis of the reaction medium allows one to exclude any possible metal-ion release, confirming that catalysis undergoes under heterogeneous conditions. The new metal-loaded CNS can be re-used and recycled five times without losing their catalytic activity.

A honeycomb-like hydrogel in-situ constructed by Streptococcus zooepidemicus and TOCN for the proliferation of bacteria

Cellulose, as a significant natural carbohydrate polymer, can be transformed into polysaccharide nanofiber. A novel in-situ hydrogel was constructed using TEMPO-oxidized cellulose nanofiber (TOCN) and metabolites of Streptococcus zooepidemicus, such as hyaluronic acid (HA) and lactic acid (LA). In the presence of LA, HA underwent a gelation process, and S. zooepidemicus was embedded in the skeleton of the hydrogel network. This in-situ hydrogel accommodated the bacteria by providing a suitable environment for their growth and protecting them from external stress. The elastic modulus of the in-situ hydrogel was maintained at 4000 G′ in Pa, thus ensuring that it was protected from damage even after being immersed in the medium. The hydrogel continued to show normal fermentation activities upon being transferred into the seed or fermentation medium. These findings indicated that the in-situ hydrogel could act as a wellspring that spills out the scattered bacteria.

Synthesis and characterization of TEMPO-oxidized peptide-cellulose conjugate biosensors for detecting human neutrophil elastase

Here we describe the synthesis and characterization of a peptide-cellulose conjugate biosensor based on TEMPO-oxidized nanofibrillated cellulose (tNFC) for detecting elevated levels of human neutrophil elastase (HNE) in chronic wounds. The fluorescent peptide HNE substrate constructed from n-succinyl-Ala-Pro-Ala-7-amino-4-methyl-coumarin was attached to the TEMPO-oxidized cellulose surface via polyethylene glycol linker. The characterization of the biosensor conjugate shows a high degree of peptide incorporation onto the surface with the degree of substitution of 0.057. The relatively small crystallite size of 26.0 Å compared to other cellulose- and nanocellulose-based materials leads to a large specific surface area which can promote access of HNE to the enzyme substrates due to decreased steric interactions. Likewise, the porosity for tNFC was found to be higher than all other samples, including the nanocellulosic aerogel, lending to its hydrogel-like nature. The properties of tNFC were compared to other cellulose-based materials. The volume of each crystallite and volume ratio to the largest sample was calculated. tNFC was found to occupy the smallest space resulting in high amounts of sensors per crystallite unit volume. With a small crystallite volume and large number of sensors, the tNFC peptide-cellulose conjugate biosensor could provide a more sensitive system and is a good candidate for point of care diagnostic devices for detecting elevated protease levels in humans.

3d-Printed Polylactic Acid-Based Biocomposite Filters Reinforced with Tempo-Oxidized Cellulose Nanofibers and Chitin Nanofibers for Removal of Metal Ions and Microplastics from Water

3d-Printed Polylactic Acid-Based Biocomposite Filters Reinforced with Tempo-Oxidized Cellulose Nanofibers and Chitin Nanofibers for Removal of Metal Ions and Microplastics from Water