TEMPO-oxidized Bacterial Cellulose Research Articles

Concentrated O/W Pickering emulsions stabilized by soy protein/cellulose nanofibrils: Influence of pH on the emulsification performance

In this work, concentrated Pickering emulsions had been prepared by using soybean protein isolate (SPI) and TEMPO-oxidized bacterial cellulose (TOBC) complex as solid stabilizers. The effects of solid particle content, pH and oil phase volume fraction on the morphology, stability and rheological behaviors of the emulsions had been investigated. It indicated that the emulsion droplets had uniform particle size distribution when the ratio of SPI/TOBC was controlled to 12.5:1 (wt/wt). The emulsification performance could be improved with the increase of solid complex particles content from 1.0% to 3.0%. Moreover, the pH played an important role in regulating the structure and properties of the emulsions. With microscopic observation, the emulsions at pH 7.0 had smaller droplet size (10–15 μm) than that (15–40 μm) of the emulsions at pH 3.0. While the emulsions at pH 3.0 maintained a low creaming index (CI) value than those at pH 7.0, and uniform cellular network structure could be seen by SEM observation. It suggested that the electrostatic complexation between soy proteins and anionic bacterial cellulose nanofibrils at pH 3.0 was more favorable for stabilizing emulsions than those at pH 7.0. This work would provide some guidance for regulating the properties of emulsions that stabilized by soy protein and cellulose nanofibrils.

A 3D-printable TEMPO-oxidized bacterial cellulose/alginate hydrogel with enhanced stability via nanoclay incorporation

Three-dimensional (3D) printing offers a novel approach to manufacture repeatable personalized structures for mass customization in medical fields. Considering the resemblance of materials in composition and microstructure to biological tissues, polysaccharide-based hydrogel is a promising printing material. However, its long-term stability of structure has always been a problem. In this work, we showed a green nanocomposite printing ink based on 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO)-oxidized bacterial cellulose (TOBC), sodium alginate (SA) and laponite nanoclay (Xls). The TOBC/SA/Xls hydrogel prepared by the 3D printing ink not only exhibited structural stability, but also performed a long-term release behavior of protein which could be attractive in medical application of drug release, biomedical devices and tissue engineering.

TEMPO-oxidized bacterial cellulose nanofiber membranes as high-performance separators for lithium-ion batteries

In this paper, 2, 2, 6, 6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized bacterial cellulose (TOBC) nanofiber membranes as separators of lithium-ion batteries were successfully prepared from a water dispersion of TOBC nanofibers via a vacuum filtration approach. The TOBC membranes had adequate porosity and desirable affinity with the liquid electrolyte and lithium electrode, giving rise to superior electrolyte uptake and small interfacial resistance. Among the TOBC nanofiber samples, the TOBC1.0 membrane exhibited the best properties, including high electrolyte uptake (339 %), superior electrochemical stability window (>6.0 V), outstanding ionic conductivity (13.45 mS cm−1) and small interfacial resistance (96 Ω). The half cells obtained using the TOBC1.0 membrane achieved a discharge capacity of 166 mA h g−1 (0.2 C), corresponding to 97.6 % of the theoretical value of LiFePO4 (170 mA h g−1), excellent cycle stability (with capacity retention of 94 % after 100 cycles) at 0.2 C and good C-rate performance. Thus, the TOBC nanofiber membranes could be considered as a promising high-performance separator used in lithium-ion batteries.

Preparation of polylactic acid/TEMPO-oxidized bacterial cellulose nanocomposites for 3D printing via Pickering emulsion approach

The aim of this study is to produce a novel TEMPO-oxidized bacterial cellulose (TOBC) reinforced Polylactic acid (PLA), fully biodegradable composites for fused deposition molding (FDM). In order to get uniform dispersion of BC in PLA matrix, TEMPO-mediated oxidation reaction and Pickering emulsion were used. The PLA composite microspheres were found uniformly coated by TOBC, via Pickering emulsion approach. And screw extrusion was used to prepare PLA/TOBC filaments for FDM. The mechanical properties, crystallinity, fluidity and thermal stability of PLA/TOBC nanocomposites were systematically investigated. It was found that the addition of a small amount of TOBC could effectively improve the mechanical properties and crystal properties of PLA. Uniform dispersion of TOBC in PLA matrix is helpful for forming a three-dimensional network and cross-linking structure which acts as a nucleating agent to promote the crystallization of PLA. In this paper, the mechanical properties and crystallization properties of the composites were optimized when TOBC content up to 1.5 wt%, and with further increasing TOBC, TOBC accumulates were found in PLA matrix, which were defects for PLA composites, the mechanical properties and crystallinity of the nanocomposites were reduced. • Pickering emulsion approach can achieve good dispersion of BC in PLA. • TEMPO-mediated oxidation to improve the compatibility of BC with PLA matrix. • The addition of BC improves the crystallinity PLA nanocomposites. • 3D printed PLA/BC nanocomposites have good mechanical properties and designability.

Surface modification of cellulose nanofibrils with protein nanoparticles for enhancing the stabilization of O/W pickering emulsions

In order to enhance the surface hydrophobicity and emulsifying capacity of cellulose nanofibrils, a ‘green’ surface-modification with protein nanoparticles was conducted. The adsorption of soy protein isolate (SPI) nanoparticles on the bacterial cellulose oxidized by 2,2,6,6-tetramethylpiperidine-nitrogen-oxide (TEMPO) through electrostatic attraction at pH 3 was investigated. The experimental results demonstrated that the modification increased the surface hydrophobicity of TEMPO-oxidized bacterial cellulose (TOBC), and the complexes expressed the improved interfacial rheological properties. Accordingly, with the increasing contents of complexes, the Pickering emulsions exhibited the smaller droplets size, higher viscosity, and better physical stability. Moreover, the emulsions showed good anti-oxidative stability, where both primary (POVs) and secondary (TBARS) products of lipid oxidation were significantly lower than those of oil without coverage. The results of in vitro digestion indicated the improved anti-lipid hydrolysis performance of emulsions with tunable interfacial structure formed by complexes.

One-Pot Method of Synthesizing TEMPO-Oxidized Bacterial Cellulose Nanofibers Using Immobilized TEMPO for Skincare Applications.

In the skincare field, water-dispersed bacterial cellulose nanofibers synthesized via an oxidation reaction using 2,2,6,6–tetramethyl–1–piperidine–N–oxy radical (TEMPO) as a catalyst are promising bio-based polymers for engineered green materials because of their unique properties when applied to the surface of the skin, such as a high tensile strength, high water-holding capacity, and ability to block harmful substances. However, the conventional method of synthesizing TEMPO-oxidized bacterial cellulose nanofibers (TOCNs) is difficult to scale due to limitations in the centrifuge equipment when treating large amounts of reactant. To address this, we propose a one-pot TOCN synthesis method involving TEMPO immobilized on silica beads that employs simple filtration instead of centrifugation after the oxidation reaction. A comparison of the structural and physical properties of the TOCNs obtained via the proposed and conventional methods found similar properties in each. Therefore, it is anticipated that due to its simplicity, efficiency, and ease of use, the proposed one-pot synthesis method will be employed in production scenarios to prepare production quantities of bio-based polymer nanofibers in various potential industrial applications in the fields of skincare and biomedical research.

Rheological behaviors of Pickering emulsions stabilized by TEMPO-oxidized bacterial cellulose

The present study assesses the rheological behaviors of TEMPO-oxidized bacterial cellulose (TOBCs) with diverse oxidation degrees to explore the potential relationship between the rheology and stability of the emulsions. The TOBCs with different oxidation degrees were prepared at the NaClO dosages of 2, 6, and 10 mmol/g, designated 2-TOBC, 6-TOBC, and 10-TOBC, respectively. The small amplitude dynamic rheology and diffusing wave spectroscopy results showed that 2-TOBC emulsion had higher storage modulus G’ and loss modulus G’’ with lower tan δ than 6-TOBC emulsion and possessed the lowest solid-liquid balance among all of the TOBC Pickering emulsions, indicating the highest emulsion stability of 2-TOBC emulsion. Positive correlations existed between the viscoelasticity and stability of the TOBCs Pickering emulsions, with the coefficients of correlation over than 0.6. These results should improve understanding of the relationships between emulsions’ stability and rheological characteristics, and lead to a potential application of TEMPO-oxidized bacterial cellulose as an emulsion stabilizer.

TEMPO-Oxidized Bacterial Cellulose Pellicle with Silver Nanoparticles for Wound Dressing.

Biocompatible bacterial cellulose pellicle (BCP) is a candidate for biomedical material such as wound dressing. However, due to lack of antibacterial activity, to grant BCP with the property is crucial for its biomedical application. In the present study, BCP was modified by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation using TEMPO/NaClO/NaBr system at pH 10 to form TEMPO-oxidized BCP (TOBCP) with anionic C6 carboxylate groups. The TOBCP was subsequently ion-exchanged in AgNO3 solution and silver nanoparticles (AgNP) with diameter of ∼16.5 nm were in situ synthesized on TOBC nanofiber surfaces by thermal reduction without using a reducing agent. Field emission scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectra, Fourier transform infrared spectroscopy, and thermogravimetric analysis were carried out to confirm morphology and structure of the pellicles with AgNP. The AgNP continuously released Ag+ with a rate of 12.2%/day at 37 °C in 3 days. The TOBCP/AgNP exhibited high biocompatibility according to the result of in vitro cytotoxicity test (cell viability >95% after 48 h of incubation) and showed significant antibacterial activities of 100% and 99.2% against E. coli and S. aureus, respectively. Hence, the highly biocompatible and highly antibacterial TOBCP/AgNP prepared in the present study is a promising candidate for wound dressing.

Physical properties of TEMPO-oxidized bacterial cellulose nanofibers on the skin surface

Water-dispersed bacterial cellulose nanofibers were prepared via an oxidation reaction using 2,2,6,6-tetramethyl-1-piperidine-N-oxy radical (TEMPO) as a catalyst. It was found that TEMPO-oxidized bacterial cellulose nanofibers (TOCNs) synthesized via sodium bromide-free methods are similar to those synthesized using sodium bromide. The TOCNs retained their unique structure in water as well as in emulsion. TOCNs adhere to the skin surface while maintaining nanofibrous structures, providing inherent functions of bacterial cellulose, such as high tensile strength, high water-holding capacity, and blockage of harmful substances. When gelatin gels as model skin were coated with TOCNs, the hardness representing the elasticity was increased by 20% compared to untreated gelatin gel because TOCNs could tightly hold the gelatin structure. When porcine skin was treated with TOCNs, carboxymethyl cellulose, and hydroxyethyl cellulose, the initial water contact angles were 26.5°, 76.5°, and 64.1°, respectively. The contact angle of TOCNs dramatically decreased over time as water penetrated the fibrous structure of the TOCN film. When observed by scanning electron microscopy and confocal microscopy, TOCNs on the skin surface provided physical gaps between particles and the skin, blocking the adsorption of particulate matter to the skin surface. On the contrary, the structure of water-soluble polymers was disrupted by an external environment, such as water, so that particulate matter directly attached to the skin surface. Characterization of TOCNs on the skin surface offered insight into the function of nanofibers on the skin, which is important for their applications with respect to the skin and biomedical research.

Effect of carboxylic acid groups on the supercapacitive performance of functional carbon frameworks derived from bacterial cellulose

Three-dimensional (3D) carbonaceous materials derived from bacterial cellulose (BC) has been introduced as electrode for supercapacitors in recent. Here, we report a simple strategy for the synthesis of functional carbon frameworks through 2,2,6,6-tetramethylpilperidine l-oxyl radical (TEMPO) −mediated oxidation of bacterial cellulose (BC) followed by carbonization. TEMPO-mediated oxidation can efficiently convert the hydroxyls on the surface of BC to carboxylate groups to improve electrochemical activity. Because of its high porosity, good hydrophilicity, rich oxygen groups, and continuous ion transport in-between sheet-like porous network, the TEMPO-oxidized BC delivers a much higher gravimetric capacitance (137.3F/g) at low annealing temperature of 500°C than that of pyrolysis BC (31F/g) at the same annealing temperature. The pyrolysis modified BC obtained at 900°C shows specific capacitance (160.2F/g), large current stability and long-term stability (84.2% of its initial capacitance retention after 10,000 cycles).

TEMPO-oxidized bacterial cellulose nanofibers-supported gold nanoparticles with superior catalytic properties

A novel nanohybrid was successfully fabricated by deposition of gold nanoparticles (AuNPs) onto the surface of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized bacterial cellulose nanofibers (TOBCNs). The prepared AuNPs/TOBCNs nanohybrids were characterized by UV–vis spectral analysis, XRD, TEM and HRTEM. Their catalytic activity for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) was estimated by UV–vis spectrometry. The results showed that the AuNPs/TOBCNs nanohybrids possessed AuNPs with an average diameter of 4.30±0.97nm exhibited superior catalytic properties for the reduction of 4-NP to 4-AP. The influences of the content of reducing agent and system temperature on the catalytic property were studied. Moreover, the turnover frequency of AuNPs/TOBCNs was 750h−1, which is higher than most recently reported AuNPs-based catalysts. This work reported a heterogeneous catalyst based on TOBCNs supported AuNPs with superior catalytic properties.

Strong, thermal-stable, flexible, and transparent films by self-assembled TEMPO-oxidized bacterial cellulose nanofibers

Research on bacterial cellulose (BC), an all-purpose biomaterial widely used in various applications, often focuses on the pellicle type. To apply BC to flexible devices such as solar cells and displays, flowability is necessary for manufacturing processes. Fabrication of a BC fiber (BCF) suspension by treating BC pellicles in water using a homogenizer is a fast and easy pathway. However, it is difficult for BCF suspensions to form a transparent film that has sufficient strength that would arise from the BC nanofibers bound by hydrogen bonds. To solve the problem, the BCF suspension was treated by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation followed by mild mechanical treatment. The individual TEMPO-oxidized BC nanofibers (TOBCNs) with a C6-carboxylate group content of 1.1 mmol g−1 cellulose were successfully dispersed in water. The TOBCN maintained the high crystallinity of the original BC pellicle (BCP) and had two classes of fiber width: 30–60 and 4–10 nm. Interestingly, the TOBCN dispersion exhibited much more concentrated, wide and lengthy birefringence than the TEMPO-oxidized cellulose nanofibers prepared from wood cellulose, implying their different roles in liquid crystal applications. The TOBCN film prepared by cast-drying the TOBCN dispersion was flexible and transparent, showing a high Young’s modulus of 9 GPa, a high tensile strength of 163 MPa and a considerably low coefficient of thermal expansion of 3.2 ppm K−1. In addition, to discuss the effect of TEMPO-mediated oxidation on material properties, the following films were also prepared: TOBCN film with carboxylate group content of 0.7 mmol g−1 cellulose, heat-dried BCP and BCF films without oxidation. With development of mass production of BC, the TOBCN and TOBCN-based nanomaterials are promising for flexible devices, such as substrates of solar cells and displays, in the future.

Surfactant-free emulsions stabilized by tempo-oxidized bacterial cellulose

In order to seek a safe, biodegradable, and sustainable solid stabilizer for food, topical and pharmaceutical emulsions, individualized cellulose nanofibers were prepared by oxidizing bacterial cellulose (BC) in a Tempo-mediated system; their ability to stabilize oil/water interface was investigated. Significant amounts of C6 carboxylate groups were selectively formed on each cellulose microfibril surface, so that the hydrophilicity was strengthened, leading to lower contact angles. Meanwhile, both the length and width of fibrils were decreased significantly, by partial cleavage of numerous numbers of inter- and intra-fibrillar hydrogen bonds. Tempo-oxidized BC (TOBC) was more effective than BC in stabilizing oil-water interface, attributing to the much smaller size. Fibril dosage and oxidation degree exerted a great influence on the stability and particle size distribution of emulsion samples. When the fibril dosage was 0.7wt.%, the sample was so stable that it did not experience creaming and coalescence over 8 months. The 2-TOBC coated droplets showed the greatest stability, although both the zeta potential and the electric repulsion were the largest for the 10-TOBC analogue, which was manipulated by the wettability of fibrils. In addition, the stability of samples was analyzed from the viewpoint of particle size distribution. Consequently, fibril size and wettability are two counterbalanced factors influencing the stability of TOBC-stabilized emulsions; a combination of suitable wettability and size imparts TOBC-stabilized emulsion high stability. As a kind of biomass-based particle stabilizer, TOBC showed great potential applications in food, topical and pharmaceutical formulations.

Effect of negatively charged cellulose nanofibers on the dispersion of hydroxyapatite nanoparticles for scaffolds in bone tissue engineering

Nanofibrous 2,2,6,6-tetramethylpiperidine-1-oxyl(TEMPO)-oxidized bacterial cellulose (TOBC) was used as a dispersant of hydroxyapatite (HA) nanoparticles in aqueous solution. The surfaces of TOBC nanofibers were negatively charged after the reaction with the TEMPO/NaBr/NaClO system at pH 10 and room temperature. HA nanoparticles were simply adsorbed on the TOBC nanofibers (HA–TOBC) and dispersed well in DI water. The well-dispersed HA–TOBC colloidal solution formed a hydrogel after the addition of gelatin, followed by crosslinking with glutaraldehyde (HA–TOBC–Gel). The chemical modification of the fiber surfaces and the colloidal stability of the dispersion solution confirmed TOBC as a promising HA dispersant. Both the Young's modulus and maximum tensile stress increased as the amount of gelatin increased due to the increased crosslinking of gelatin. In addition, the well-dispersed HA produced a denser scaffold structure resulting in the increase of the Young's modulus and maximum tensile stress. The well-developed porous structures of the HA–TOBC–Gel composites were incubated with Calvarial osteoblasts. The HA–TOBC–Gel significantly improved cell proliferation as well as cell differentiation confirming the material as a potential candidate for use in bone tissue engineering scaffolds.

Nanocellulose-alginate hydrogel for cell encapsulation.

TEMPO-oxidized bacterial cellulose (TOBC)-sodium alginate (SA) composites were prepared to improve the properties of hydrogel for cell encapsulation. TOBC fibers were obtained using a TEMPO/NaBr/NaClO system at pH 10 and room temperature. The fibrillated TOBCs mixed with SA were cross-linked in the presence of Ca(2+) solution to form hydrogel composites. The compression strength and chemical stability of the TOBC/SA composites were increased compared with the SA hydrogel, which indicated that TOBC performed an important function in enhancing the structural, mechanical and chemical stability of the composites. Cells were successfully encapsulated in the TOBC/SA composites, and the viability of cells was investigated. TOBC/SA composites can be a potential candidate for cell encapsulation engineering.

Novel electroactive PVA-TOCN actuator that is extremely sensitive to low electrical inputs

A novel electroactive biopolymer actuator was developed based on a cross-linked ionic networking membrane of TEMPO-oxidized bacterial cellulose nanofibers (TOCNs) and polyvinyl alcohol (PVA). Ionic liquids were added to develop an air-working artificial muscle and to enhance the performance of the PVA-TOCN actuator. Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) conducting layers were deposited on the top and bottom surfaces of the PVA-TOCN membrane via a simple dipping and drying method. The electroactive PVA-TOCN actuator under both step and harmonic electrical inputs shows much larger tip displacements and faster bending deformation than the pure TOCN actuator. The cross-linking reaction between PVA and TOCN was observed in the Fourier transform–near-infrared (FT-IR) spectrum of the PVA-TOCN networking membrane. Scanning electron microscopy (SEM), x-ray diffusion (XRD), thermogravimetric analysis (TGA) and tensile and ion conductivity testing results for the PVA-TOCN membrane were compared with those of pristine TOCN. Most important, the PVA-TOCN actuator shows much larger bending deformation under even extremely low input voltages, and this could be attributed to the cross-linking mechanism and the greater flexibility resulting from the synergistic effects between PVA and TOCN.

Characterization of TEMPO-oxidized bacterial cellulose scaffolds for tissue engineering applications

Introduction of active groups on the surface of bacterial cellulose (BC) nanofibers is one of the promising routes of tailoring the performance of BC scaffolds for tissue engineering. This paper reported the introduction of aldehyde groups to BC nanofibers by 2,2,6,6-tetramethylpyperidine-1-oxy radical (TEMPO)-mediated oxidation and evaluation of the potential of the TEMPO-oxidized BC as tissue engineering scaffolds. Periodate oxidation was also conducted for comparison. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses were carried out to determine the existence of aldehyde groups on BC nanofibers and the crystallinity. In addition, properties relevant to scaffold applications such as morphology, fiber diameter, mechanical properties, and in vitro degradation were characterized. The results indicated that periodate oxidation could introduce free aldehyde to BC nanofibers and the free aldehyde groups on the TEMPO-oxidized BC tended to transfer to acetal groups. It was also found that the advantageous 3D structure of BC scaffolds remained unchanged and that no significant changes in morphology, fiber diameter, tensile structure and in vitro degradation were found after TEMPO-mediated oxidation while significant differences were observed upon periodate oxidation. The present study revealed that TEMPO-oxidation could impart BC scaffolds with new functions while did not degrade their intrinsic advantages.