Relaxation phenomenon and swelling behavior of regenerated cellulose fibers affected by water

Optimizing carboxylated nanocellulose preparation: A kinetic and mechanistic study on the enhancement of TEMPO-mediated oxidation via swelling treatment

This study explored the application of swelling pretreatment as a solution to the high cost and contamination associated with the process of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation for nanocellulose preparation. The results demonstrated that swelling significantly expanded the fibers while preserving the degree of polymerization (DP) of cellulose (approximately 95 %). The native crystal structure and hydrogen bonding of cellulose were disrupted after swelling, leading to a reduction in crystallinity and crystallite size, and the decrease of bonding energy and content of intermolecular O6-H⋯O3'. The TEMPO-mediated oxidation processes of cellulose fibers with or without swelling were successfully fitted using a consecutive first-order reaction kinetic model. The fitting results indicated that swelling significantly reduced the activation energy of TEMPO-mediated oxidation and enhanced the reaction rate. Among three swelling systems, the NaOH/thiourea/water system exhibited the optimal promotion effect. Consequently, the swelling treatment enables a significant reduction of 30 % in the catalyst dose for the TEMPO-mediated oxidation while preserving a competitive reaction rate, yield, and product performance. Lower catalyst dosage helps to reduce cost and environmental impact, facilitating the industrial application of the TEMPO-mediated oxidation process.

β-Glucan-based superabsorbent hydrogel acts as a gastrointestinal exoskeleton enhancing satiety and interfering fat hydrolysis

Fat and its hydrolysis products, fatty acids, are indispensable nutritional components; however, prolonged excessive fat consumption, particularly in western diets, contributes to the onset of obesity and multiple metabolic disorders. In this study, we propose a daily-ingestible hydrogel (denoted as βC-MA hydrogel) composed of natural β-glucan and sodium carboxymethylcellulose crosslinked by malic acid at 120 °C. This hydrogel exhibits rapid swelling performance, up to 24-fold within 1 min and 176-fold after 1 h in deionized water. It also lengthens gastric retention and increases endogenous satiety signal levels, potentially controlling appetite and reducing food intake. Furthermore, βC-MA hydrogels that enter the small intestine can effectively inhibit fat hydrolysis and decrease triglyceride synthesis and transport. Specifically, the hydrogels inhibit the release of free fatty acids (FFAs) by approximately 50 % during digestion, influence the translocation of triglycerides and FFAs across the intestinal epithelium, and reduce the serum triglyceride levels by 22.2 %. These findings suggest that βC-MA hydrogels could serve as a noninvasive gastrointestinal device for weight control, with the advantage of reducing food intake and restoring lipid metabolism homeostasis.

Antimicrobial Wound Dressings based on Bacterial Cellulose and Independently Loaded with Nutmeg and Fir Needle Essential Oils

The aim of the present study was to obtain antimicrobial dressings from bacterial cellulose loaded with nutmeg and of fir needle essential oils. The attractive properties of BC, such as biocompatibility, good physicochemical and mechanical stability, and high water absorption, led to the choice of this material to be used as a support. Essential oils have been added to provide antimicrobial properties to these dressings. The results confirmed the presence of oils in the structure of the bacterial cellulose membrane and the ability of the materials to inhibit the adhesion of Staphylococcus aureus and Escherichia coli. By performing antibacterial tests on membranes loaded with fir needle essential oil, we demonstrated the ability of these membranes to inhibit bacterial adhesion to the substrate. The samples loaded with nutmeg essential oil exhibited the ability to inhibit the adhesion of bacteria to the surface of the materials, with the 5% sample showing a significant decrease. The binding of essential oils to the membrane was confirmed by thermal analysis and infrared characterization.

Synthesis and Characterization of Ciprofloxacin Loaded Star-Shaped Polycaprolactone-Polyethylene Glycol Hydrogels for Oral Delivery

The administration of poorly water-soluble drugs represents a relevant problem due to the low body fluids transport efficiency through hydrophilic hydrogels. Star-shaped co-polymers, i.e., amphiphilic polymers such as those with a hydrophobic core and a hydrophilic outer shell, can be used to improve weak interactions with drugs, with relevant benefits in terms of administration and controlled delivery. In this work, two different co-polymers, four-arm star-shaped PCL-PEG and six-arm star-shaped PCL-PEG, were synthesized via ring-opening polymerization to be loaded with ciprofloxacin. ¹H-NMR and FTIR analyses confirmed that PCL arms were successfully grafted to the mPEG backbone, while DSC analysis indicated similar crystallinity and melting point, ranging from 56 to 60 °C, independent of the different co-polymer architecture. Therefore, both star-shaped PCL-PEGs were investigated as cargo device for ciprofloxacin. No significant differences were observed in terms of drug entrapment efficiency (>95%) and drug release, characterized by a pronounced burst followed by a slow sustained release, only slightly affected by the co-polymer architecture. This result was also confirmed with curve fitting via the Korsmeyer-Peppas model. Lastly, good antibacterial properties and biocompatibility exhibited in both star-shaped PCL-PEG co-polymers suggest a promising use for oral delivery applications.

Oxygen permeability of regenerated cellulose films with different water regains

The effect of water regain on the oxygen permeability coefficient (OP) of regenerated cellulose film was investigated. The OP of the dry film was extremely low, which was classified as a "very high" performance gas barrier; however, the OP increased with increasing water regain, and reached to the OP similar to that of low-density polyethylene film, which was categorized as a "poor" gas barrier. The film thickness increased with increasing water regain, and edge-view small-angle X-ray scattering revealed widening of the space between microcrystals in the thickness direction. Oxygen molecules likely passed through the space between cellulose molecules, which was widened with increasing water regain. The viscoelastic measurements indicated that regenerated cellulose existed in a rubbery state under wet conditions. Overall, the OP of regenerated cellulose was increased because of the widening and micro-Brownian motion of cellulose main chains caused by water.

Isolation and characterization of cellulose nanocrystals from Chinese medicine residues

Nanocellulose has become a vital material with excellent and crucial properties in the field of nanotechnology and advanced materials science. Plant-based traditional Chinese medicines are mostly plant rhizomes, which contain a large amount of cellulose, hemicellulose, and lignin. In this study, carboxylated cellulose nanocrystals (CNCs) were prepared from traditional Chinese medicine residues (CMR) by sequential periodate-chlorite oxidation without mechanical treatment. The obtained nanocelluloses were analyzed by transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and X-ray diffractometry (XRD); the carboxyl content and specific surface area were also measured, simultaneously. XRD results revealed that the crystallinity index decreased after sequential oxidation; however, the cellulose I structure was maintained. From the morphology analysis, the average length and width of CNCs were 139.3 and 10 nm, respectively. From the FTIR analysis, with the particle size decreasing, hydrogen bonds were broken and recombined. TGA results showed that the thermal property was decreased with a reduction of nanocellulose particle size and crystallinity index. This study is the first to refine utilization of traditional Chinese medicine residues as a potential source of cellulose, that is, to prepare nanocellulose efficiently with high carboxyl content which finds its application in nanomaterials.

Supervised Learning for Predictive Pore Size Classification of Regenerated Cellulose Membranes Based on Atomic Force Microscopy Measurements

Nanoporous dialysis membranes made of regenerated cellulose are used as molecular weight cutoff standards in bioseparations. In this study, mesoporous standards with Stokes' radii (50 kDa/2.7 nm, 100 kDa/3.4 nm and 1000 kDa/7.3 nm) and overlapping skewed distributions were characterized using AFM, with the specific aim of generating pore size classifiers for biomimetic membranes using supervised learning. Gamma transformation was used prior to conducting discriminant analysis in terms of the area under the receiver operating curve (AUC) and classification accuracy (Acc). Monte Carlo simulations were run to generate datasets (n = 10) on which logistic regression was conducted using a constant ratio of 80:20 (measurement:algorithm training), followed by algorithm validation by WEKA. The proposed algorithm can classify the 1000 kDa vs. 100 kDa (AUC > 0.8) correctly, but discrimination is weak for the 100 kDa vs. 50 kDa (AUC < 0.7), the latter being attributed to the instrument accuracy errors below 5 nm. As indicated by the results of the cross-validation study, a test size equivalent to 70% (AUC_tapping = 0.8341 ± 0.0519, Acc_tapping = 76.8% ± 5.9%) and 80% (AUC_fluid = 0.7614 ± 0.0314, Acc_tfluid = 76.2% ± 1.0%) of the training sets for the tapping and fluid modes are needed for correct classification, resulting in predicted reduction of scan times.

Relaxation phenomenon and swelling behavior of regenerated cellulose fibers affected by organic solvents

Regenerated cellulose fibers are extremely sensitive to water. In particular, their mechanical properties are greatly affected by water. Recently, it was clarified that the glass transition temperatures of regenerated cellulose over 500 K can be shifted to room temperature, and small-angle X-ray scattering (SAXS) showed the maxima and shoulders on the equator line in the wet state. In this study, glass transition caused by organic solvents was observed, although the peak heights of tangent δ (tan δ) were low, which suggested the regions affected by organic solvents were small. SAXS showed the maxima and shoulders, suggesting that organic solvents decreased the density of the amorphous region, i.e., widened space between cellulose molecules, creating sufficient space for the micro-Brownian motion of cellulose main chains. However, alkanes with molecular weight larger than n-nonane did not show tan δ peaks, which suggests that the solvent is hard to enter between microfibrils.

Facile preparation and performance study of antibacterial regenerated cellulose carbamate fiber based on N-halamine

With the outbreak of coronavirus disease (COVID-19) which has incalculable disasters and economic losses, people have given increasing attention to the health and safety of textile and fiber materials. In this study, an eco-friendly, facile, and cost-effective wet-spinning cellulose carbamate fiber technology was developed, and N-halamine regenerated cellulose fiber (RCC-Cl) with rechargeable and rapid bactericidal properties were prepared by the Lewis acid-assisted chlorination method. The chemical properties of the fibers were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetric analysis, and energy-dispersive X-ray spectroscopy. The mechanical and surface topography of the treated fiber was investigated by tensile testing and scanning electron microscopy. The results showed that the mechanical properties of RCC-Cl fibers can reach a breaking strength of 12.1 cN/tex and a breaking elongation of 41.4% with the optimized spinning process. Furthermore, RCC-Cl showed excellent antimicrobial activities, which can inactivate Escherichia coli and Staphylococcus aureus at a concentration of 10⁷ CFU/mL within 1 min. This work provided a novel approach to produce regenerated cellulose fibers with antibacterial properties, showing great potential in the field of functional textiles.

Simple conversion of 3D electrospun nanofibrous cellulose acetate into a mechanically robust nanocomposite cellulose/calcium scaffold

Cellulose and its derivatives are widely used as nanofibrous biomaterials, but obtaining 3D cellulose nanofibers is difficult and relevant research is scarce. In the present study, we propose a simple method for converting electrospun 3D cellulose acetate/lactic acid nanofibers via calcium hydroxide treatment into a 3D cellulose/calcium lactate nanocomposite matrix. The conversion resulted in producing a stronger nanofibrous matrix (1.382 MPa vs. 0.112 MPa) that is more hydrophilic and cell-friendly compared to the untreated cellulose acetate/lactic acid group. The successful conversion was verified via FTIR, XPS, TGA, DTG, and XRD. The ability of the scaffolds to provide a suitable environment for cell growth and infiltration was verified by CCK assay and confocal microscopy. The porous nature, mechanical strength, and presence of calcium make the 3D cellulose/calcium lactate matrix a promising material for bone tissue engineering.

Synthesis of bimetallic silver-gold nanoparticle composites using a cellulose dope: Tunable nanostructure and its biological activity

Introducing functional metal nanoparticles (NPs) into flexible substrate is being increasingly attempted to expand their application. Here, we extend the synthesis of cellulose to its unmodified dope achieving freestanding nanocomposite decorated with bimetallic Ag-Au NPs through the one pot reaction. In the procedure, cellulose chain not only acts as a reducing agent but also a biocompatible support for NPs with a mean size of 7.9-9.7 nm. Meanwhile, changing the addition order of Ag⁺ and AuCl₄^- generated different atom arrangement in the bimetallic NPs. Moreover, the correlation of bioactivity to NP atom arrangement was studied. The result revealed that the nanocomposite containing NPs with an ultrathin Ag-rich outermost shell around an Au-rich core showed better bactericidal ability while lower cytotoxicity. In addition, the nanocomposite exhibited a sensitive SERS property for determination of R6G with a high enhancement factor of 10⁸.