Alginate hydrogel microbeads incorporated with Ag nanoparticles obtained by electrochemical method

An innovative method was developed for production of alginate hydrogel microbeads incorporated with silver nanoparticles (AgNPs) based on electrochemical synthesis followed by electrostatic extrusion. AgNPs were synthesized galvanostatically at different values of AgNO₃ concentration in the initial solution (0.5–3.9 mM), current density (5–50 mA cm⁻²), and implementation time (0.5–10 min). Increase in all of these parameters increased the concentration of AgNPs in alginate solution and was confirmed by TEM analysis and UV–vis spectroscopy. Cyclic voltammetry studies and Fourier transform infrared spectroscopy proved the alginate to be a good capping agent for the electrochemical synthesis of silver nanoparticles, due to coordination bonding between hydroxyl and ether groups, as well as ring oxygen atoms in uronic acid residues of alginate molecules, and Ag nanoparticles. Ag/alginate colloid solution was used for production of uniform hydrogel microbeads (with diameter of 487.75 ± 16.5 μm) by electrostatic extrusion technique. UV–vis spectroscopy confirmed retention and entrapment of AgNPs in microbeads during the production process. Alginate microbeads incorporated with AgNPs are attractive as biocompatible carriers and/or efficient donors of AgNPs as active components especially for potential biomedical applications, which was demonstrated by the antibacterial activity against Staphylococcus aureus.     

Novel PVP/PVA hydrogels for articular cartilage replacement

Poly(vinyl alcohol) (PVA) hydrogel has been considered as a very interesting and promising material for articular cartilage replacement. The most vital shortcoming of PVA hydrogels is that their mechanical properties are difficult to meet the requirements of articular cartilage. In the present work, blend hydrogels based on PVA and poly (vinyl pyrrolidone) (PVP) were prepared by repeated freezing and thawing method. Such hydrogel had similar internal three-dimensional structure and water content (approximately 75%) as nature articular cartilage. The mechanical and tribological properties were investigated to find out that change of mechanical and tribological properties of PVP/PVA hydrogels were significantly dependent on PVP content and freezing–thawing cycles. The blend hydrogel with 1 wt.% PVP had the best mechanical properties and the friction system consisting of such blend hydrogel and stainless steel ball exhibited a mixed lubrication regime especially under bovine serum lubrication. The results established that such hydrogel would be a novel attractive material for articular cartilage replacement.     

Assembly, characterization and swelling kinetics of Ag nanoparticles in PDMAA-g-PVA hydrogel networks

A series of poly(N,N-dimethylacrylamide)-g-poly(vinyl alcohol) (PDMAA-g-PVA) graft hydrogel networks were designed and prepared via a free radical polymerization route initiated by a PVA-(NH₄)₂Ce(NO₃)₆ redox reaction. Silver nanoparticles with high stability and good distribution behavior have been self-assembled by using these hydrogel networks as a nanoreactor and in situ reducing system. Meanwhile the PDMAA or PVA chains can efficiently act as stabilizing agents for the Ag nanoparticles in that Ag⁺ would form complex via oxygen atom and nitrogen atom, and form weak coordination bonds, thus astricting Ag⁺. The structure of the PDMAA-g-PVA/Ag was characterized by a Fourier transform infrared spectroscope (FTIR). The morphologies of pure PDMAA-g-PVA hydrogels and PDMAA-g-PVA/Ag nanocomposite ones were observed by a scanning electron microscopy (SEM) and transmission electron microscope (TEM). TEM micrographs revealed the presence of nearly spherical and well-separated Ag nanoparticles with diameters ranging from 10 to 20 nm, depending on their reduction routes. XRD results showed all relevant Bragg's reflection for crystal structure of Ag nanoparticles. UV–vis studies apparently showed the characteristic surface plasmon band at 410–440 nm for the existence of Ag nanoparticles within the hydrogel matrix. The swelling kinetics demonstrated that the transport mechanism belongs to non-Fickian mode for the PDMAA-g-PVA hydrogels and PDMAA-g-PVA/Ag nanocomposite ones. With increasing the DMAA proportion, the r₀ and S_∞ are enhanced for each system. The assembly of Ag nanoparticles and the swelling behavior may be controlled and modulated by means of the compositional ratios of PVA to DMAA and reduction systems.     

Rheological and thermal characteristics of a two phase hydrogel system for potential wound healing applications

Hydrogels fabricated from single polymers have been extensively investigated for wound healing applications. However, in many cases a single polymer cannot meet divergent demands in terms of both properties and performance. In this work, a two phase hydrogel was prepared by physically imbedding a xerogel in the core of a freeze thawed hydrogel. The outer hydrogel was prepared by freeze thawing poly (vinyl alcohol) (PVA) and poly (acrylic acid) (PAA) while the xerogels were prepared by UV polymerisation of 1-vinyl-2-pyrrolidinone (NVP). The rheological results indicated that the two phase hydrogels over a period of 2 weeks formed a strong interface and demonstrated greater physical strength. This suggested that the inner gel containing PVP diffused into the PVA/PAA hydrogel, which in turn increased hydrogen bonding, resulting in the overall increase in the stiffness of the gel. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) confirmed hydrogen bonding had occurred between the constituents of the two phase hydrogels. Thermal analysis suggested that T _g of each of the samples was above 80 °C, which indicated no impact on the behaviour of the gel at body temperature, but did however, give an indication of the stiffness of the dry polymer.     

聚乙烯醇/聚乙烯基吡咯烷酮复合水凝胶的结构与性能研究

用溶液共混法和冷冻解冻工艺制备聚乙烯醇(PVA)/聚乙烯基吡咯烷酮(PVP)二元复合水凝胶,通过红外、XRD、DSC、含水率与溶胀测试等对材料的结构与性能进行分析表征,并研究了材料的力学性能与细胞毒性.结果表明,PVP能与PVA通过化学键合形成分子级混合的PVA/PVP复合水凝胶.PVP含量可以影响PVA水凝胶的结构、结晶度、玻璃化转变温度、吸水率以及力学性能.该复合水凝胶具有高的吸水率和良好的细胞相容性,而且具有类似天然软骨的可渗透性.PVP/PVA复合水凝胶是一种有发展前景的人工软骨替代材料.     

Preparation and characterization of keratin-based biocomposite hydrogels prepared by electron beam irradiation

The biocompatible and highly porous keratin-based hydrogels were prepared using electron beam irradiation (EBI). The conditions for keratin-based hydrogel formation were investigated depending on several conditions, including the presence of poly(vinyl alcohol) (PVA), concentration of keratin solution, EBI dose, and poly(ethylene imine) (PEI) additives. The pure keratin (human hair and wool) aqueous solution was not gelled by EBI, while the aqueous keratin solutions blended with PVA were gelled at an EBI dose of more than 90 kGy. Furthermore, in the presence of PEI, the aqueous keratin solution blended with PVA could be gelled at a considerably lower EBI dose, even at 10 kGy. This finding suggests that the PEI additives significantly influence the rate of gelation and that PEIs function as an accelerator during gelation. The resulting keratin-based hydrogels were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), gel fraction, degree of swelling, gel strength, and kinetics of swelling analyses.     

Graphite/poly (vinyl alcohol) hydrogel composite as porous ringy skirt for artificial cornea

Graphite/poly (vinyl alcohol) (PVA) hydrogel composites, which were designed as the porous ringy skirt surrounding the transparent core of a novel artificial cornea, were prepared by using the freeze/thawing process and the particle-leaching technique. The properties of the composites, including the water content, the mechanical strength, the porous architecture and the interactions between the graphite and PVA, were investigated. The tissue responses to the composite and pure PVA hydrogel were studied by in vivo implantation in the dorsal muscles of mice. The results showed that chemical interactions were present between the graphite and PVA in the composite, which benefited the combination of the two phases and enhanced the uniform distribution of graphite particles in the PVA matrix. However, the present of graphites in the PVA hydrogels reduced the tensile strength, elongation at break and water content of the composite. Moreover, the porous graphite/PVA hydrogel composite had interconnective pore structure with high porosity and enough mechanical strength. According to the histological analysis of 1 week and 12 weeks post-implantation, the graphite/PVA hydrogel composites showed less inflammatory reactions than the PVA hydrogels at the 1 week post-implantation. Moreover, compared to pure PVA hydrogel, the graphite/PVA hydrogel composite exhibited enhanced migration and infiltration of cells, and more neovascularization and tissue ingrowth. These in vivo characteristics will be beneficial for the long-term biofixation of artificial cornea. Therefore, the porous graphite/PVA hydrogel composite has a potential to be used as novel artificial cornea skirt.     

Sustainable,Insoluble, and Photonic Cellulose Nanocrystal Patches for Calcium Ion Sensing in Sweat

Self-assembly of cellulose nanocrystals (CNCs) is invaluable for the development of sustainable optics and photonics. However, the functional failure of CNC-derived materials in humid or liquid environments inevitably impairs their development in biomedicine, membrane separation, environmental monitoring, and wearable devices. Here, a facile and robust method to fabricate insoluble hydrogels in a self-assembled CNC–polyvinyl alcohol (PVA) system is reported. Due to the reconstruction of inter- or intra-molecular hydrogen bond interactions, thermal dehydration makes an optimized CNC/PVA photonic film form a stable hydrogel network in an aqueous solution rather than dissolve. Notably, the resulting hydrogel exhibits superb mechanical performance (stress up to 3.3 Mpa and tough up to 0.73 MJ m⁻³) and reversible conversion between dry and wet states, enabling it convenient for specific functionalization. Sodium alginate (SA) can be adsorbed into the CNC photonic structure by swelling dry CNC/PVA film in a SA solution. The prepared hydrogel showcases the comprehensive properties of freezing resistance (−20°C), strong adhesion, satisfactory biocompatibility, and highly sensitive and selective Ca²⁺ sensing. The material could act as a portable wearable patch on the skin for the continuous analysis of calcium trends during different physical exercises, facilitating their development in precision nutrition and health monitoring.     

Fabrication of Ag nanoparticles dispersed in PVA nanowire mats by microwave irradiation and electro-spinning

In this study, the antimicrobial substance, silver nanoparticles (Ag NPs) loaded in poly (vinyl alcohol) (PVA) nanowire mats were fabricated by conjugation of the electro-spinning method and the microwave-assisted process. The best PVA nanowire mats were fabricated by through control of electro-spinning conditions, which were applied for fabrication of Ag NPs loaded in PVA nanowires. PVA was used not only as a carrier for loading of Ag NPs but also as a reduction agent with which the Ag⁺ ion was already reduced to a large number of Ag NPs by irradiation with a microwave. Ag NPs were synthesized inside the PVA solution depending on the time of microwave irradiation — whether for 60 s or 90 s. Size distribution of Ag NPs was 5–10 nm in diameter for 60 s; and 10–20 nm in diameter for 90 s of irradiation. Presence of Ag NPs acquired through microwave assisted irradiation was confirmed by X-ray diffraction profiles (XRD). Microstructure, particle size distribution, and morphology of both the nanowire mats and the Ag particles were investigated using SEM and TEM techniques. The effect of Ag-NPs on the PVA mechanical property of nano-fibrous mats was investigated according to tensile strength. Antibacterial activity of PVA loaded Ag NPs at different irradiation times was tested on Gram-positive bacteria, Staphylococcus aureus Gram-negative bacteria, and Escherichia coli.     

Black tea leaf extract derived Ag nanoparticle-PVA composite film: Structural and dielectric properties

Biosynthesized metal (Ag) nanoparticles have been used to prepare high dielectric polymer composite film of technological importance. Different amounts of the tea leaf extract (E) (mother leaker prepared by soaking 2 g tea leaf in 100 ml boiled water for 3 min) were used to synthesize silver nanoparticles from 10⁻³ M AgNO₃ solution. Such a resultant solution containing Ag nanoparticles was mixed with 20 ml PVA solution (5 g PVA in 100 ml water) was used to make anhydrous Ag/PVA composite film where spherical silver nanoparticles (AgNPs) of average diameter 10 nm are well dispersed in the composite. The Ag particle size in the composite was found to enhance with the increase of E content in PVA. XRD, SEM, TEM, FT-IR, UV–vis, TGA and DSC studies are made to characterize the nanoparticles. Detailed frequency and E concentration dependent electrical and dielectric properties of the nanocomposites have been made showing low loss (∼0.14) and high dielectric property of these films. Maximum value of dielectric permittivity (∼900 which is almost 170 times higher than that of pure PVA ∼ 5.2) have been observed for 15 ml E-AgNPs/PVA nanocomposite film at 1 kHz and room temperature. Present study establishes the importance of the biosynthesized metal nanoparticles for industrial applications as in capacitors.     

Evaluation of electrospun nanofiber formation of perfluorosulfonic acid and poly (<Emphasis Type="Italic">N</Emphasis>-vinylpyrrolidone) through solution rheology

Electrospinning performance of 5–52 wt% perfluorosulfonic acid (PFSA), poly (N-vinylpyrrolidone) (PVP), and PFSA/PVP blends in N,N-dimethylformamide (DMF) with various PFSA/PVP ratios were systematically investigated in respective of solutions properties, mainly surface tension and rheological properties. Mechanical relaxation time τ _M calculated from rheological results happens to be closely correlated with nanofiber morphology, and is used to evaluate the electrospinnability. Polymer solutions with higher τ _M show better electrospinnability. Morphologies of the electrospun samples were observed by Scanning electronic microscopy. The results show that the pure PFSA solutions, even with a quite high concentration up to 52 wt%, fail to be electrospun and possess a very low τ _M. Addition of PVP improves electrospinnability of PFSA and increases τ _M. The electrospinnability of PFSA/PVP/DMF solutions can be manipulated by changing the ratio of PFSA to PVP and the total polymer concentration of the mixed solutions. The PFSA nanofiber mats with a small fraction of PVP (<8 wt%) with the average diameter of 370 nm were successfully obtained.     

聚乙烯醇/聚丙烯酸/羟基磷灰石复合高吸水性树脂的制备及溶胀行为

以聚乙烯醇(PVA)、部分中和的丙烯酸(AA)和羟基磷灰石(HA)为原料,过硫酸铵(APS)为引发剂,N,N′-亚甲基双丙烯酰胺(MBA)为交联剂,采用水溶液聚合法制备了聚乙烯醇/聚丙烯酸/羟基磷灰石(PVA/PAA/HA)复合高吸水树脂。考察了PVA用量对吸水性能的影响,研究了树脂在不同pH值溶液和不同阳离子盐溶液中的溶胀行为。结果表明,引入适量的PVA有利于树脂吸水性能的改善;树脂在pH=4～11较宽的范围内都能保持较高的吸水倍率,在CaCl2溶液中的溶胀动力学行为表现出明显的"过溶胀平衡现象"。     

FTIR spectroscopy characterization of poly (vinyl alcohol) hydrogel with different hydrolysis degree and chemically crosslinked with glutaraldehyde

In this work, poly (vinyl alcohol) (PVA) hydrogels with different degree of hydrolysis (DH) were prepared by chemical crosslinking with glutaraldehyde (GA). The nanostructure of the resulting hydrogels was investigated by Fourier Transform Infrared Spectroscopy (FTIR) and Synchrotron small-angle X-ray scattering characterization (SAXS). In vitro tests were performed by swelling ratio assays in different pH solutions. The infrared spectra of the crosslinked PVA showed absorption bands of the acetal bridges resulted from the reaction of the GA with the OH groups from PVA. Also the FTIR spectroscopy was used to determine the crystallinity of the PVA film based on the relative intensity of the vibration band at 1141 cm^− 1. The results have showed an increase of hydrogel crystallinity with higher DH of PVA. SAXS patterns have clearly indicated important modifications on the PVA semicrystalline structure when it was crosslinked by GA. The swelling ratio was significantly reduced by chemically crosslinking the PVA network. PVA-derived hydrogel with chemically modified network was found to be pH-sensitive, indicating a high potential to be used in drug delivery polymer system.     

Radiation synthesis of PVP/alginate hydrogel containing nanosilver as wound dressing

Hydrogels with polyvinyl pyrrolidone (PVP) and alginate were synthesized and silver nanoparticles were incorporated in hydrogel network using gamma radiation. PVP (10?and 15?%) in combination with 0.5?and 1?% alginate was gamma irradiated at different doses of 25?and 40?kGy. Maximum gel percent was obtained with 15?% PVP in combination with 0.5?% alginate. The fluid absorption capacity for the PVP/alginate hydrogels was about 1881–2361?% at 24?h. Moisture vapour transmission rate (MVTR) of hydrogels containing nanosilver at 24?h was 278.44?g/(m²h). The absorption capacity and moisture permeability of the PVP/alginate–nanosilver composite hydrogel dressings show the ability of the hydrogels to prevent fluid accumulation in exudating wound. The hydrogels containing nanosilver demonstrated strong antimicrobial effect and complete inhibition of microbial growth was observed with 70?ppm nanosilver dressings. PVP/alginate hydrogels containing nanosilver with efficient fluid handling capacity and antimicrobial activity was found suitable for use as wound dressing.     

Preparation of water dispersible,fluorescent Ag–PAA–PVP hybrid nanogels and their optical properties

A simple method of synthesizing hybrid silver–polyacrylic acid–poly(N-vinylpyrrolidone) (Ag–PAA–PVP) nanogels was demonstrated through in situ reducing Ag⁺ inside PAA–PVP nanogels, which were formed by polymerization of acrylic acid in the PVP solution. Due to the ion exchange between Ag⁺ and acid protons of PAA, stable Ag⁺ clusters were formed inside the PAA–PVP nanogels, and hybrid nanogels were obtained by reducing Ag⁺ by ascorbic acid. Transmission electronic microscopic (TEM) images clearly showed the existence of silver nanoparticles inside the Ag–PAA–PVP nanogels. These hybrid nanogels showed typical surface plasma resonance absorption peak around 420 nm, and the size of the silver nanoparticles inside the Ag–PAA–PVP nanogels could be controlled from 9.5 ± 1.6 nm to 1.9 ± 0.4 nm by increasing the feeding amount of Ag⁺. In addition, these hybrid nanogels showed photoluminescent properties in fluorescent spectra. Considering the pH sensitive property of these hybrid nanogels, they will have potential application in drug delivery and biomedical imaging systems.     

Preparation and properties of a novel thermo-responsive poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide) hydrogel containing glycyrrhetinic acid

A novel thermo-responsive poly(N-isopropylacrylamide) (PNIPAAm) hydrogel containing glycyrrhetinic acid(GA) was synthesized by free radical copolymerization. The structure of the product was confirmed by FT-IR and ¹H-NMR spectra. The temperature responsibility and swelling properties of the copolymerized hydrogel were investigated by differential scanning calorimetry (DSC) and gravimetric methods. The results indicated that GA-incorporated hydrogel was still temperature responsive and the swelling ratio decreased with the increasing of temperature. The lower critical solution temperature (LCST) of GA-incorporated hydrogel and poly(N-isopropylacrylamide) hydrogel was 30.00 °C and 31.21 °C, respectively, in distilled water. However, these two values were shifted to 28.22 °C and 29.16 °C in cell culture media. The novel hydrogel also exhibited reversible temperature responsibility. Deswelling kinetics indicated that the copolymerized hydrogel deswelled more rapidly than poly(N-isopropylacrylamide) hydrogel. Since GA has specific binding capacity to asialoglycoprotein receptors on the membrane of hepatocyte, this novel hydrogel with GA could be expected as good candidate for hepatic cell culture.     

Swelling and mechanical behaviors of carbon nanotube/poly(vinyl alcohol) hybrid hydrogels

In this paper, carbon nanotubes (CNTs) were added into poly(vinyl alcohol) (PVA) hydrogels to modify their mechanical properties. A series of CNT/PVA hybrid hydrogels were prepared by freezing/thawing method. The mechanical and swelling properties of all hybrid hydrogels are better than those of the original PVA hydrogel. Especially, for CNTP-0.5 specimen with 0.5% w/w CNTs, its tensile modulus, tensile strength and strain at break are increased by 78.2%, 94.3% and 12.7%, respectively. And its swelling behavior is different from that of the pure PVA hydrogel. Its final swelling ratios at room temperature and 310 K are increased by 35.7% and 44.9%, respectively.     

Effect of PVP loading on pervaporation performance of poly(vinyl alcohol) membranes for THF/water mixtures

This work reports an experimental study on the pervaporative dehydration of an industrial solvent tetrahydrofuran (THF) using a blend membrane of PVA/PVP crosslinked with maleic acid. The influence of feed composition and permeate pressure on the pervaporation flux and selectivity has been investigated. The membrane was found to exhibit a water flux of 0.007 kg/m² h with a water selectivity of infinity for dehydration of 97% THF at 30 °C. FTIR of the blend was carried out to interpret its behavior on the basis of interactions between carbonyl groups of the cationic PVP and hydroxyl groups of the neutral PVA polymer. X-ray diffraction and sorption studies were carried out to study the degree of crystallinity and polymer–liquid interactions. The variation in film morphology was examined by scanning electron microscopy (SEM). Pervaporation experiments showed that high selectivity and promising permeability were obtained with a 9:1 blending ratio of PVA/PVP membrane crosslinked with 5 wt% maleic acid.     

Sodium alginate/poly(vinyl alcohol) alloy membranes for the pervaporation, vapour permeation and vapour permeation with temperature difference separation of dimethylformamide/water mixtures: A comparative study

In this study, sodium alginate (NaAlg)/poly(vinyl alcohol) (PVA) membranes were prepared for the separation of dimethylformamide (DMF)/water mixtures. The two polymer components were independently crosslinked chemically with glutaraldehyde. The crosslinked membranes were characterized by fourier transform infrared spectrometry (FTIR), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA) and scanning electron microscopy (SEM). The permeation and separation characteristics of water/DMF mixtures were investigated using the vacuum processes pervaporation (PV), vapour permeation (VP) and vapour permeation with temperature difference (TDVP) methods. The effects of NaAlg/PVA ratio, membrane thickness, operating temperature and temperature of the membrane surroundings, feed concentration on the transmembrane permeation rate and separation factor were investigated. Optimum NaAlg/PVA ratio was determined as 80/20 (w/w) for the separation. The permeation rate in VP was lower than those in PV, whereas the separation factors were higher. The activation energies of permeation in PV and VP were calculated to be 5.070 and 2.229 kcal/mol, respectively, for a 20 wt% of DMF solution.     

Thermosensitive solutions and gels consisting of poly(vinyl alcohol) and sodium silicate

We have investigated the transparency for visible light of a poly(vinyl alcohol) (PVA) aqueous solution in the presence of sodium silicates (SS). The transparency of the aqueous solution dramatically changed by varying temperature despite that neither aqueous solutions of PVA nor SS is sensitive to temperature. The aqueous solution showed a lower critical solution temperature (LCST) around 30 °C. The LCST depended on both concentrations of PVA and sodium silicate. Below the LCST, the transmittance was thermally irreversible. By a further increase in the temperature, the solution was separated into two phases consisting of a phase rich in solvent and that in solute; that is a coacervation. In the region of coacervation, the transmittance was thermally reversible. Reversible change in the transmittance was realized corresponding to stepwise temperature changes between 10 and 40 °C. A PVA gel swollen by the solution demonstrated transparency change in response to temperature changes as well as the solution.