Polyvinyl Alcohol-polyacrylic Acid Research Articles

Harnessing synergy: Polydopamine-hBN integration in electrospun nanofibers for Co (II) ion, methylene blue and crystal violet dyes adsorption

In today's world, major pollutants, such as cationic dyes and heavy metals, pose a serious threat to human health and the environment. In this study, a novel adsorbent was created through the electrospinning of polyvinyl alcohol/polyacrylic acid (PVA/PAA), incorporated with hexagonal boron nitride (hBN) coated with polydopamine (PDA). The integration of hBN and PDA substantially enhanced the adsorption capacity of the PVA/PAA fibers, making them highly effective in adsorbing cationic dyes such as methylene blue and crystal violet, as well as cobalt (II) ions, from contaminated water. The adsorbents were assessed to understand how their adsorption behavior varies with pH, as well as to examine their adsorption kinetics and isotherms. The results indicate that the PVA/PAA-hBN@PDA adsorbent has maximum adsorption capacities of 1029.57 mg/g, 793.65 mg/g, and 62.46 mg/g for methylene blue, crystal violet, and cobalt (II) ions, respectively. This underscores the superior performance of the PVA/PAA-hBN@PDA adsorbent when compared to both the PVA/PAA and PVA/PAA-hBN adsorbents. The adsorption kinetics adhered to a pseudo-second-order model, indicating chemisorption, whereas the Langmuir model implied a monolayer adsorption. Overall, the findings of this study highlight the efficacy of harnessing the synergistic capabilities of hBN and PDA within the PVA/PAA-hBN@PDA adsorbents, providing an efficient and eco-friendly approach to removing cationic dyes and heavy metals from contaminated water, and thereby contributing to a cleaner and safer environment for all.

Introducing self-healing properties to polyethersulfone (PES) membrane via poly(vinyl alcohol)/ polyacrylic acid (PVA/PAA) surface coating

During membrane filtration, it is inevitable that a membrane will experience physical damage, leading to a loss of its integrity and a decrease in separation efficiency. Hence, the development of a water-responsive membrane capable of healing itself autonomously after physical damage is significantly important in the field of water filtration. Herein, a water-enabled self-healing composite polyethersulfone (PES) membrane was synthesized by coating the membrane surface using a mixed solution composed of poly (vinyl alcohol) and polyacrylic acid (PVA-PAA). The self-healing efficiency of the coated PES membrane was examined based on the changes in water flux at three stages which are pre-damaged, post-damaged, and post-healing. The self-healing process was initiated by the swelling of the water-responsive PVA and PAA, followed by the formation of reversible hydrogen bonds, completing the self-healing process. The coated PES membrane with three layers of PVA-PAA coatings (at 3:1 ratio) demonstrated high water flux and remarkable self-healing efficiency of up to 98.3%. The self-healing capability was evidenced by the morphology of the membrane observed via scanning electron microscope (SEM). The findings of this investigation present a novel architecture approach for fabricating self-healing membranes using PVA-PAA, in addition to other relevant parameters as reported.

Preparation of an ultrasensitive electrochemical immunosensor for the rapid detection of 19-nortestosterone based on polyvinyl alcohol/polyacrylic acid electrospun nanofiber mat

19-nortestosterone (19-NT), being regarded as the residual marker of banned synthetic steroid hormone nandrolone phenylpropionate, could cause adverse effects when consumed by human. To ensure food safety and minimize 19-NT toxicity, herein, an innovative electrochemical immunosensor for detection of 19-NT was constructed based on the modified polyvinyl alcohol/polyacrylic acid (PVA/PAA) nanofiber mat (NFM). The detection was achieved via a direct competition for binding to horse radish peroxidase-tagged anti-19-NT nanobody between free 19-NT and the 19-NT-ovalbumin covalently immobilized onto the NFM, and the amperometric response of immunosensor was analyzed using cyclic voltammetry. Under the optimal preparation conditions, the PVA/PAA NFM with appropriate hydrophilicity and ultra-high surface was obtained and characterized, and its electrochemical performance exhibited a 20-times increased response compared to the PVA/PAA casting membrane. The established immunosensor possessed high sensitivity towards 19-NT with a detection limit of 2.14 pg/mL, a 46-fold times lower compared to the traditional ic-ELISA of pure anti-19-NT nanobody. Recovery rates from the spiked animal urine samples ranged from 97.09 % to 117.32 %. Moreover, the sensor showed good reproducibility and stability over 6 weeks, suggesting that the nanofiber-based biosensor is a promising alternative for the fast and sensitive determination of 19-NT.

Drying-enhanced polyvinyl alcohol-polyacrylic acid double-network hydrogel and its application in flexible strain sensors

Polyvinyl alcohol (PVA) based hydrogels, are generally prepared by freeze–thaw cycling methods. However, water loss and shrinkage of the gel over time should be prevented during the freeze–thaw cycles. Herein, a polyvinyl alcohol-polyacrylic acid (PVA-PAA) double-network hydrogel was fabricated through the strategy of “freezing-drying-swelling” (FDS) cycle, where the moisture retention was unnecessary. By a freezing-drying treatment, the formation of PVA crystalline domains and hydrogen bonds in freezing step was further improved by the drying treatment, and subsequently enhanced the mechanical properties of the hydrogel. The FDS hydrogel with the cross-linker content of 0.1% and one FDS cycle (FDS-0.1-1) could reach the ultimate tensile stress as high as 1.1 MPa with high stretchability of 648% strain. Thanks to the combination of PAA and conductive ions, the FDS-0.1-1 hydrogel strain sensor possessed excellent conductivity with a wide strain monitoring range of 0–250%, high sensitivity with a gauge factor (GF) up to 3.985, a fast response (75 ms) and excellent long-term stability without any decay for 5000 cycles of continuous loading–unloading between 0 and 100% strain. Besides, the FDS hydrogel strain sensor can be used for real-time monitoring various movements of the human body, including large movements (finger, wrists, elbows, and back of the neck) and subtle motions (smile and swallow).

Dramatically enhancing mechanical properties of hydrogels by drying reactive polymers at elevated temperatures to introduce strong physical and chemical crosslinks

Mechanically strong and tough hydrogels have a wide range of practical applications, and many preparation methods have been developed in recent two decades. However, facile and convenient methods for preparing hydrogels with excellent mechanical properties are still lacking. In this work, we report a strategy for preparing hydrogels with very high mechanical strengths by utilizing the strong physical and chemical crosslinks formed by drying reactive polymers at elevated temperatures. The obtained polyvinyl alcohol-polyacrylic acid (PVA-PAA) hydrogels show very high tensile strengths and elastic moduli up to 28.9 MPa and 26.6 MPa, which are several tens and hundreds of times those of PVA-PAA hydrogels prepared with freezing-thawing method, respectively. And the mechanical properties of the hydrogels can be adjusted by controlling drying temperature and PAA content. The crosslinking nature of the hydrogels are studied and proved with swelling and rheology measurements as well as structural characterizations. The drying at elevated temperatures enables the occurrence of esterification reaction and promotes the crystallization of PVA chains and the formation of stronger hydrogen bonds between PVA and PAA chains. This work provides a simple and facile method to prepare high-strength hydrogels for wide potential applications.

Anisotropic hydrogels with enhanced mechanical and tribological performance by magnetically oriented nanohybrids

Most current hydrogels have weak mechanical properties and unordered structures, which limits their applications. However, soft tissues with highly ordered hierarchical nanocomposite structures exhibit anisotropic mechanical performance and function to adapt the complex environments. Therefore, the introduction of an ordered nanocomposite structure into hydrogel is an effective strategy to endow the hydrogel with superb mechanical strength and excellent anisotropic functions. Here, we develop a method to create anisotropic hydrogels with significantly enhanced mechanical and tribological properties. Based on mussel adhesion chemistry, polydopamine (PDA) was used as a mediator to control the formation of Fe3O4 nanoparticles on the surface of montmorillonite (MMT). Subsequently, the obtained PDA-Fe3O4-MMT nanohybrids in the polyvinyl alcohol/polyacrylic acid (PVA/PAA) hydrogel matrix were aligned to form an ordered structure using magnetic-induced technology and then frozen in hydrogel form by freezing-thawing and annealing methods. The resulting hydrogels showed an anisotropic microstructure and exhibited outstanding mechanical properties with a tensile strength of 10.65 MPa, toughness of 52.2 MJ/m3, and compressive strength of 4.86 MPa, which is higher than that of the corresponding isotropic hydrogel. More interestingly, the friction coefficient of hydrogel is significantly reduced to as low as 0.038 due to the presence of ordered structure. This work not only improves magnetic induction technology for the preparation of anisotropic hydrogels but also provides a simple and effective method to obtain hydrogels with anisotropic structure, high mechanical strength, and anisotropic properties for potential application in tissue engineering.

Effect of thermal annealing on a bilayer polyvinyl alcohol/polyacrylic acid electrospun hydrogel nanofibres loaded with doxorubicin and clarithromycin for a synergism effect against osteosarcoma cells

Polyvinyl alcohol/polyacrylic acid (PVA/PAA) bilayer hydrogel nanofibres were successfully fabricated by electrospinning and physically crosslinked via heat treatment. The effects of the thermal annealing process on the structure, morphology, swelling, thermal properties and hydrophilicity of electrospun nanofibres were investigated. In addition, these membranes were also used to incorporate doxorubicin and clarithromycin for osteosarcoma treatment, one in each layer. These drugs were used because it is hypothesized in this work that a synergism occurs between both drugs. So, these membranes were analyzed towards their dual-drug release and potential cytotoxicity towards the U2OS human osteosarcoma cell line. Moreover, the water contact angle, disintegration, swelling and weight loss studies confirmed the rapid swelling and improved water stability of the annealed PVA/PAA bilayer nanofibres. The annealed bilayer nanofibres exhibited an increase in the average diameter and degree of crystallinity. In addition, the results revealed that a variation occurred in the degree of hydrophilicity of annealed PVA/PAA bilayer nanofibres. The PAA nanofibres surface exhibited higher hydrophilicity than the PVA nanofibres surface. Drug delivery presented to be as fast rate release for clarithromycin and slow-rate release for doxorubicin, which may be advantageous because both drugs exhibited to be synergetic for certain dosages presenting the combination of the drugs higher than 50% of cell inhibition, while these membranes had higher inhibition values (up to 90%), which was attributed to the PAA but also the drugs. These unique properties are of potential interest in drug delivery applications for dual drug delivery where the tunability of surfaces is desirable.

No-core fiber interferometry pH sensor based on a polyvinyl alcohol/polyacrylic acid and silica/polyvinyl alcohol/polyacrylic acid hydrogel coating.

In this paper, we present an investigation on the sensing performance of a pH sensor based on a modal interferometer formed by a simple NO-core fiber interferometer (NCFI) that operates in transmission mode. The fundamental configuration of this sensor encompasses a single-mode-no-core-single-mode fiber (SMF-NCF-SMF "SNCS") segment chain. The chemical etching method has been used with hydrofluoric (HF) acid to prepare diverse NCF diameters. This was proposed to expand the evanescent fields and enhance sensor sensitivity. Then, the two diverse segments of etched NCF were cladded with polymeric composite fabricated by polyvinyl alcohol/polyacrylic acid (PVA/PAA) hydrogel and pure silica nanoparticles embedded in polyvinyl alcohol/polyacrylic acid (SiO2@PVA/PAA) hydrogel, respectively, for more sensing enhancement. Our results reveal that the PAA/PVA coating is a candidate coating material for acidic sensing, while SiO2@PVA/PAA is more appropriate for the base sensing, in which these coating materials show enhancement in the sensitivity above the NCF structure before an uncoated sensor due to greater enhancement of the evanescent field affected by the coating layer. The experimental results demonstrate a high average sensitivity of 3.42 nm/pH unit for the 11 w.t.% PVA/PAA coated sensor in the pH range from 1 to 7 and 3.2 nm/pH unit in the pH range from 8 to 14. The sensor also displays high repeatability and stability and low cross-sensitivity to temperature. The simple fabrication and high sensitivity of this sensor may prompt many potential applications in the fields of biology and chemistry.

One-step removal of lead from water using an electricity-free and sustainable membrane filtration

Lead (Pb) is a typical contaminant in water with adverse effects on human health. Hong Kong’s incident of drinking water contamination by Pb in 2015 caused severe public concerns regarding drinking water safety. Conventional treatment methods for Pb removal generally require electricity, chemical dosage, and considerable time and space, which significantly restrict their use for rapid water purification under emergency situations. In this study, a polyvinyl alcohol/polyacrylic acid (PVA/PAA) composite nanofibrous membrane was developed for the rapid and effective removal of Pb from water. The PVA/PAA membrane had a high water permeability of 550 L/m2/h/kPa - 710 L/m2/h/kPa, which allowed the filtration to be driven by gravity (e.g. with a water height of 10.0 cm). The membrane showed consistently high removal efficiency of Pb (> 95%) with a volumetric loading up to 3000 L/m2. This high removal efficiency was attributed to the combined effects of complexing and electrostatic attraction between Pb and PAA. An esculent citric acid was used to regenerate the exhausted PVA/PAA membrane. The regenerated membrane maintained its removal efficiency of Pb over a five-cycle filtration. These results imply that the PVA/PAA composite membrane can be repeatedly used in electricity-free filtration devices for rapid elimination of Pb under emergency situations.

High strength polyvinyl alcohol/polyacrylic acid (PVA/PAA) hydrogel fabricated by Cold-Drawn method for cartilage tissue substitutes

Poly (vinyl alcohol) (PVA) hydrogel has been considered as promising cartilage replacement materials due to its excellent characteristics such as high water content, low frictional behavior and excellent biocompatibility. However, lack of sufficient mechanical properties and cytocompatibility are two key obstacles for PVA hydrogel to be applied as cartilage substitutes. Herein, Polyacrylic acid (PAA) has been introduced into PVA hydrogel to balance these problems. Compared with pure PVA hydrogel, PVA/PAA hydrogel has the equal excellent biocompatibility, and its cell adhesion is significantly improved. In order to further improve the mechanical properties of hydrogels, Cold-Drawn treatment of hydrogels is performed in this paper. Compared to pure 12% PVA hydrogel, 40.8‐fold, 50.8‐fold, and 46.8‐fold increase in tensile strength, tensile modulus, and toughness, respectively, which can be obtained from 12% PVA/PAA Cold-Drawn hydrogel. These biocompatible composite hydrogels have a great application potential as cartilage tissue substitutes.

Adsorptive filtration of lead by electrospun PVA/PAA nanofiber membranes in a fixed-bed column

Poly(vinyl) alcohol/poly(acrylic) acid (PVA/PAA) nanofiber membranes were fabricated using electrospinning and showed good water stability and mechanical strength. Their application in lead (Pb(II)) removal from water was evaluated in a continuous fixed-bed column under varying conditions. The filtration was more efficient with a low feed concentration and low flow rate in terms of the elevated adsorption capacity and better bed utilization efficiency. The dynamic adsorption process was independent of bed height, so the fibers can be used as multilayer membranes in a fixed-bed column. The saturated column material could be regenerated and reused. The breakthrough curves were well fitted with the dose-response model, and the maximum adsorption capacity was 288 mg/g with the initial Pb(II) concentration of 1 mg/L. When tap water was used, the amount of water that can be treated before the effluent reached 15 μg/L increased by three times compared to the treatment of NaCl solutions, and a very high improvement was observed at pH 7 (4.5 L) than pH 5 (2.0 L) in tap water. These differences were further confirmed by the extended X-ray absorption fine structure (EXAFS) spectroscopy, where a decreased coordination number and decreased interatomic distance between Pb and C were observed for tap water. This study provides valuable insights in the application of PVA/PAA nanofiber membranes in a dynamic system for Pb(II) removal, and sheds light on the interatomic behavior between Pb(II) and the nanofiber membranes in a flow-through system.

Cost-Effective Double-Layer Hydrogel Composites for Wound Dressing Applications.

Although poly vinyl alcohol-poly acrylic acid (PVA-PAA) composites have been widely used for biomedical applications, their incorporation into double-layer assembled thin films has been limited because the interfacial binding materials negatively influence the water uptake capacity of PVA. To minimize the effect of interfacial binding, a simple method for the fabrication of a double-layered PVA-PAA hydrogel was introduced, and its biomedical properties were evaluated in this study. Our results revealed that the addition of PAA layers on the surface of PVA significantly increased the swelling properties. Compared to PVA, the equilibrium swelling ratio of the PVA-PAA hydrogel increased (p = 0.035) and its water vapour permeability significantly decreased (p = 0.04). Statistical analysis revealed that an increase in pH value from 7 to 10 as well as the addition of PAA at pH = 7 significantly increased the adhesion force (p < 0.04). The mechanical properties—including ultimate tensile strength, modulus, and elongation at break—remained approximately untouched compared to PVA. A significant increase in biocompatibility was found after day 7 (p = 0.016). A higher release rate for tetracycline was found at pH = 8 compared to neutral pH.

Photonic crystal fiber interferometric pH sensor based on polyvinyl alcohol/polyacrylic acid hydrogel coating.

We present a simple photonic crystal fiber interferometer (PCFI) that operates in reflection mode for pH measurement. The sensor is made by coating polyvinyl alcohol/polyacrylic acid (PVA/PAA) hydrogel onto the surface of the PCFI, constructed by splicing a stub of PCF at the distal end of a single-mode fiber with its free end airhole collapsed. The experimental results demonstrate a high average sensitivity of 0.9 nm/pH unit for the 11 wt.% PVA/PAA coated sensor in the pH range from 2.5 to 6.5. The sensor also displays high repeatability and stability and low cross-sensitivity to temperature. Fast, reversible rise and fall times of 12 s and 18 s, respectively, are achieved for the sensor time response.

Miniature pH optical fiber sensor based on waist-enlarged bitaper and mode excitation

A polyvinyl alcohol/poly-acrylic acid (PVA/PAA) hydrogel coated optical fiber interferometer was been evaluated as a pH sensor. The interferometer, which comprises a waist-enlarged bitaper, a round tip and a tantalum pentoxide layer displays high refractive index (RI) sensitivity. With the hydrogel coated, the sensor's optical interference fringes shifted with exposure to varying pH solutions. High pH sensitivity of 1.58nm/pH was achieved for pH 2.48–6.47. The miniature sensor demonstrates little hysteresis, high repeatability and low cross-sensitivity to temperature. A rising/falling time of 10/11s for the sensor time response was acquired, respectively.