Microrheological study of PVA/borax physical gels: Effect of chain length and elastic reinforcement by sodium hydroxide addition

Development of polyvinyl alcohol/carrageenan hydrogels and fibers via KOH treatment for Morse code information transmission

To solve the inherent problems of conductive hydrogels, such as relatively low mechanical properties and fatigue resistance, inability to work after water loss, and difficulty weaving. In this study, the borax-crosslinked polyvinyl alcohol/k-carrageenan (kC) conducting hydrogels (BPKKOH) were prepared by a simple one-pot method, and KOH treatment was used instead of the cumbersome and time-consuming freeze-thaw cycle to improve the comprehensive properties. The KOH treatment increased the hydrogel hydrogen bonding content by 7.72 % and synergized with the induction of kC by K+ to enhance the tensile and compressive strengths by 8.12 and 34.6 times, respectively. Meanwhile, the BPKKOH hydrogel's fatigue resistance and shape recovery after water loss were improved. Additionally, the BPKKOH hydrogels can be monitored for finger bending, showing clear and stable differences in electrical signals. BPKKOH hydrogels combined with Morse code realize applications in information transmission and encryption/decryption. Notably, introducing KOH ensures the molding and preparation of BPKKOH hydrogel fibers while having good signal responsiveness and monitoring ability. More importantly, it can be woven into fabrics that can be loaded with heavy weights, which has the potential to be directly applied in smart wearables. This work provides new ideas for applying flexible sensors and wearable smart textiles.

Nanocellulose-Based Ecofriendly Nanocomposite for Effective Wastewater Remediation: A Study on Its Process Optimization, Improved Swelling, Adsorption, and Thermal and Mechanical Behavior

A nanocellulose (NC)-based cross-linked adsorbent has been employed herein for the removal of dye pollutants (e.g., methylene blue) from the textile industry. The synthesized hydrogel was optimized to achieve the best concentrations of the adsorbent constituents, i.e., 1.55% guar gum, 1.46% NC, and 0.84% borax for achieving the maximum swelling index (SI, 3741.42%) and higher adsorption capacity (qe, 24.05 mg g-1). 98.8% of dye qe was achieved at optimal conditions of pH 8 within 30 min at 30 °C. Adsorption isotherms and kinetics investigations showed good correlation with the Freundlich adsorption isotherm model (R2 > 0.9889; ΔG° = -4.71; ΔH° = -12.30; ΔS° = -0.025) as well as the pseudo-second-order kinetics model, indicating multilayered and intricate adsorption mechanisms for dye removal. The study of thermodynamic parameters confirmed the exothermic nature of the adsorption process. The adsorption-desorption study of the resulting hydrogel exhibited 64.58% dye removal efficiency even after 4 consecutive cycles of reuse. Further, scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction analysis revealed the surface morphology, functional moieties, thermal behavior, and crystallinity pattern of the hydrogel. Rheological analysis demonstrated pseudoplastic flow and improved mechanical behavior for the hydrogel. The current study found that the synthesized adsorbent with a higher SI and qe has a noticeable potential for the removal of dye pollutants from wastewater.

Preparation and Evaluation of Composite Hydrogel for Reducing the Leakage Rate of Lost Circulation

Fractured reservoirs are widely distributed and rich in hydrocarbon resources. When encountering fractured reservoirs during the drilling process, it is often accompanied by formation losses characterized by high leak-off rates, causing severe damage to the reservoir and hindering the detection of oil and gas layers, which is not conducive to the accurate and efficient development of the reservoirs. Conventional plugging materials have poor retention effects in the fractures, resulting in the low stability of the sealing layer. The treatment of malignant lost circulation in fractured formations is an urgent problem to be solved in drilling engineering. This article focuses on improving the success rate of formation plugging through the combined use of multiple plugging materials and develops a composite hydrogel that can effectively reduce leakage rates. This hydrogel is mainly composed of materials such as polyvinyl alcohol, borax, and sodium silicate. It has good temperature resistance, maintains good gel strength at 60 °C, and can maintain long-term performance stability under simulated geological water conditions with salinity of 12,500 mg/L. For immersion corrosion by water or gasoline, the amount of corrosion is small and its fundamental performance remains largely unchanged. Through indoor simulation of a leak formation scenario, the hydrogel demonstrates commendable sealing pressure-bearing capacity. In terms of delaying fluid leakage, mixing the hydrogel with cement slurry at a ratio of 1:1 can delay the leakage rate of the cement slurry by a factor of 5.29.

A facile strategy to fabricate high-barrier, water- and oil-repellent paper with carboxymethyl cellulose/collagen fiber/modified polyvinyl alcohol

Due to the increasingly serious environmental and human health hazards brought by traditional food packaging materials, paper-based packaging materials have become increasingly popular among consumers in recent years. Currently, the fabrication of fluorine-free degradable water- and oil-repellent paper using low-cost bio-based polymers by a simple method is a hot subject in the field of food packaging. In this work, we used carboxymethyl cellulose (CMC), collagen fiber (CF), and modified polyvinyl alcohol (MPVA) to create coatings that were impervious to water and oil. The homogeneous mixture of CMC and CF generated electrostatic adsorption to impart excellent oil repellency to the paper. PVA was chemically modified by sodium tetraborate decahydrate, and the MPVA coating imparted excellent water-repellent properties to the paper. Finally, the water- and oil-proof paper showed excellent water repellency (Cobb value: 1.12 g/m²), oil repellency (kit rating: 12/12), low air permeability (0.3 μm/Pa·s), and stronger mechanical properties (4.19 kN/m). This non-fluorinated degradable water- and oil-repellent paper with high barrier properties prepared by a convenient method is expected to be in widespread use in the food packaging field.

Facile fabrication of Bi-layered Perfusable Hydrogel Tubes as Biomimetic 3D arterial construct

Small-diameter arterial conduits with native physiological and biological equivalence continues to be a constant global demand posing critical challenges in fabrication. Advent of various strategies towards mimicking the structural hierarchy of a native blood vessel, often involve complex instrumentation and template-assistance with post-processing complications eventually compromising structural fidelity. In the present research, we report a template-free, facile strategy- '3D wet writing' by peripheral-core differential ionic gelation to fabricate perfusable customizable constructs of any dimension, thickness and length in <5 mins. Dual-crosslinking using di-diol complexation of borax with Alginate-PVA was performed to enhance the stability of fabricated bi-layered tubular constructs (BLT). These fabricated BLTs demonstrated non-liner mechanical characteristics of native blood vessels in withstanding physiological (120/80 mmHg) hemodynamic loading conditions with cyclic strain (5.82 ± 0.88 %). The BLTs also ensured adequate longitudinal (0.176 ± 0.03 MPa) & circumferential (0.29 ± 0.012 MPa) tensile strength and burst pressure strength of 353.875± 22.69 mmHg. Hemocompatible characteristics of BLT were clearly evident with lower hemolytic index (0.21±0.03 %) and maintenance of erythrocyte structural integrity under dynamic conditions. Further, non-thrombogenic and non-inflammatory characteristics of BLTs were confirmed by in-activated platelets and monocytes under dynamic conditions. The developed wet-writing technique exhibited facile integration of layer-specific cells concurrently with the BLT fabrication. The spatial cell-specific expressions of smooth muscle (α-SMA) and endothelial (CD-31) cells in BLT were comparable to native hierarchical cellular organization with the multi-layered medial and mono-layered intimal layers. Further, ex-vivo dynamic studies on anastomotic interface between BLT and rat abdominal aorta clearly evidenced the functional efficacy of fabricated BLTs as physiologically relevant small-diameter vascular construct.

Microrheological Approach for Probing the Entanglement Properties of Polyelectrolyte Solutions

The entanglement dynamics and viscoelasticity of polyelectrolyte solutions remain active research topics. Previous studies have reported conflicting experimental results when compared to Dobrynin's scaling predictions derived from the Doi-Edwards (DE) tube model for entangled polymers. Herein, by combining classical bulk shear rheometry with diffusing wave spectroscopy (DWS) microrheometry, we investigate how the key viscoelastic parameters (the specific viscosity η_sp, the plateau modulus G_e, and the ratio of the reptation time to the Rouse time of an entanglement strand τ_rep/τ_e) depend on the polymer concentration for semidilute entangled (SE) solutions containing poly(sodium styrenesulfonate) with high molecular weight. Our experimental measurements yield G_e ∝ c^1.51±0.04, in good agreement with the scaling of G_e ∝ c^1.5 predicted by Dobrynin's model for salt-free polyelectrolyte SE solutions, suggesting that the electrostatic interaction influences the viscoelastic properties of polyelectrolyte SE solutions. On the other hand, the deviation in the scaling exponent for η_sp ∝ c^2.56±0.04 and τ_rep/τ_e ∝ c^1.82±0.28 is observed between our DWS experiments and Dobrynin's model prediction (∝ c^1.5), likely due to the fact that Dobrynin's scaling model does not account for mechanisms such as the contour length fluctuation, the constraint release, and the retardation of solvent dynamics, which are known to occur for SE solutions of neutral polymers. Our results demonstrate that DWS serves as a powerful rheological tool to study the entanglement dynamics of polyelectrolyte solutions. The scaling relationships obtained in this study provide new insights to the long-standing debate on the entanglement dynamics of polyelectrolyte solutions.

Formulation and Characterization of a New Injectable Bone Substitute Composed PVA/Borax/CaCO3 and Demineralized Bone Matrix

The occurrence of bone-related disorders and diseases has dramatically increased in recent years around the world. Demineralized bone matrix (DBM) has been widely used as a bone implant due to its osteoinduction and bioactivity. However, the use of DBM is limited because it is a particulate material, which makes it difficult to manipulate and implant with precision. In addition, these particles are susceptible to migration to other sites. To address this situation, DBM is commonly incorporated into a variety of carriers. An injectable scaffold has advantages over bone grafts or preformed scaffolds, such as the ability to flow and fill a bone defect. The aim of this research was to develop a DBM carrier with such viscoelastic properties in order to obtain an injectable bone substitute (IBS). The developed DBM carrier consisted of a PVA/glycerol network cross-linked with borax and reinforced with CaCO3 as a pH neutralizer, porosity generator, and source of Ca. The physicochemical properties were determined by an injectability test, FTIR, SEM, and TGA. Porosity, degradation, bioactivity, possible cytotoxic effect, and proliferation in osteoblasts were also determined. The results showed that the developed material has great potential to be used in bone tissue regeneration.

Symmetry breakdown in the sol-gel transition of a Guar gum transient physical network

The gelation of the mixture of guar gum and borax in an aqueous solution was studied by diffusing-wave spectroscopy microrheology. The Winter and Chambon power-law domain was evidenced at high-frequency range. The time-cure superposition was applied to the mean square displacement of the probe particles and the critical power-law behavior of the shifting factors was revealed close to the percolation threshold. Morphological characterization revealed the emergence of ribbon-like structures at high borax concentrations. The Rubinstein and Semenov plateau was demonstrated. The correlations between the critical exponents that govern the gelation of the transient networks were reviewed with regard to the scaling laws of both permanent and transient networks. Unlike permanent networks, the relation n₊= n_- was assumed as the unique condition to establish the hyperscaling laws in transient networks. Whereas, the symmetry breakdown of the longest relaxation time was found to be a common feature of the flowable gels.