Synthesis by gamma irradiation of hyaluronic acid-polyvinyl alcohol hydrogel for biomedical applications.

Hyaluronic acid (HA) is one of the most attractive natural polymers employed in biomaterials with biological applications. This polysaccharide is found in different tissues of the body because it is a natural component of the extracellular matrix; furthermore, it has crucial functions in cell growth, migration, and differentiation. Since its biological characteristics, HA has been utilized for the new biomaterial's development for tissue engineering, such as hydrogels. These hydrophilic macromolecular networks have gained significant attention due to their unique properties, making them potential candidates to be applied in biomedical fields. Different mechanisms to obtain hydrogels have been described. However, the research of new non-toxic methods has been growing in recent years. In this study, we prepared a new hydrogel of HA and polyvinyl alcohol by the cost-effective technique of cross-linking by gamma irradiation. The hydrogel was elaborated for the first time and was characterized by several methods such as Fourier Transform Infrared Spectroscopy, Differential Scanning Calorimetry, Thermogravimetric Analysis, and Scanning Electron Microscopy. Likewise, we evaluated the cytotoxicity of the biomaterial and its influence on cell migration in human fibroblasts. Furthermore, we provide preliminary evidence of the wound closure effect in a cellular wound model. The novel hydrogel offers an increase of HA stability with the potential to expand the useful life of HA in its different medical applications.

Near-Infrared Light-Triggered Unfolding Microneedle Patch for Minimally Invasive Treatment of Myocardial Ischemia.

It is hard to achieve safe, effective, and minimally invasive therapies on myocardial infarction (MI) via conventional treatments. To address this challenge, a vascular endothelial growth factor (VEGF)-loaded and near-infrared (NIR)-triggered self-unfolding graphene oxide (GO)-poly(vinyl alcohol) (PVA) microneedle (MN) patch was designed and fabricated to treat MI through a minimally invasive surgery (MIS). The folded MN patch can be easily placed into the chest cavity through a small cut (4 mm) and quickly recover to its original shape with 10 s of irradiation of NIR light (1.5 W/cm2, beam diameter = 0.5 cm), thanks to its excellent shape memory effect and fast shape recovery ability. Meanwhile, the unfolded MN patch can be readily punctured into the heart and wrap the heart tightly, thanks to its sufficient mechanical strength and adjustable morphological structure, thus ensuring a high fixation strength to withstand the high-frequency pulsation of the heart. In addition, the prepared MN patch has low cytotoxicity and controllable and sustainable release of VEGF. More importantly, the MN patch can effectively promote neovascularization, reduce myocardial fibrosis, and restore cardiac function, which indicates its promising application prospects in MIS.

Bimodal microwave and ultrasound phantoms for non-invasive clinical imaging.

A precise and thorough methodology is presented for the design and fabrication of bimodal phantoms to be used in medical microwave and ultrasound applications. Dielectric and acoustic properties of human soft tissues were simultaneously mimicked. The phantoms were fabricated using polyvinyl alcohol cryogel (PVA-C) as gelling agent at a 10% concentration. Sucrose was employed to control the dielectric properties in the microwave spectrum, whereas cellulose was used as acoustic scatterer for ultrasound. For the dielectric properties at microwaves, a mathematical model was extracted to calculate the complex permittivity of the desired mimicked tissues in the frequency range from 500 MHz to 20 GHz. This model, dependent on frequency and sucrose concentration, was in good agreement with the reference Cole-Cole model. Regarding the acoustic properties, the speed of sound and attenuation coefficient were employed for validation. In both cases, the experimental data were consistent with the corresponding theoretical values for soft tissues. The characterization of these PVA-C phantoms demonstrated a significant performance for simultaneous microwave and ultrasound operation. In conclusion, PVA-C has been validated as gelling agent for the fabrication of complex multimodal phantoms that mimic soft tissues providing a unique tool to be used in a range of clinical applications.

High performance of alginate/polyvinyl alcohol composite film based on natural original melanin nanoparticles used as food thermal insulating and UV-vis block.

Light is a major factor in promoting food aging and deterioration, especially for ultraviolet (UV) light. Herein, bioinspired dopamine-melanin solid nanoparticles with strong absorption at a wide range of 200-2500 nm were first incorporated into alginate/polyvinyl alcohol to fabricate film materials in this work for UV-vis block, and this also brings excellent thermal insulating properties to the materials. In addition, in order to obtain a material with excellent performance, particles of uniform size of about 100 nm are obtained by fractional centrifugation. It was found the mechanical, UV-vis block and thermal insulating properties were improved significantly compared with the control samples. This study provides a strategy to design a non-polluting, biodegradable, biocompatible film with excellent mechanical properties that can be used in UV-vis barriers and has potential applications in thermal insulating materials for food preservation.

Composite Films with UV-Barrier Properties of Bacterial Cellulose with Glycerol and Poly(vinyl alcohol): Puncture Properties, Solubility, and Swelling Degree.

The aim of this study was to develop composite films based on bacterial cellulose, glycerol, and poly(vinyl alcohol) with improved optical and mechanical properties and good UV-barrier property. The interaction among the compounds was analyzed using Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetry, and differential scanning calorimetry. The mechanical properties (toughness, burst strength, and distance to burst), solubility, water adsorption, and light barrier properties of the composite films were evaluated. Polynomial models obtained allowed us to predict the behavior of these properties. Poly(vinyl alcohol) showed a reinforcing effect on the bacterial cellulose matrix, while glycerol showed a noticeable plasticizing behavior. The bacterial cellulose-based composites showed toughness values ranging from 0.22 to 2.60 MJ/m3. The burst strength values obtained ranged between 43.74 and 2105.52 g. The distance to burst ranged from 0.39 to 4.94 mm. The film solubility on water ranged from 9.37 to 31.65%, and the water retention ranged from 78.26 to 364.78%. Glycerol decreased the transmittance in the UV region, improving the UV-barrier properties of the films, while poly(vinyl alcohol) improved the transparency and opacity values of the samples. The transmittance in the UV regions (A, B, and C) ranged from 1 to 48.51%, increasing with the poly(vinyl alcohol) concentration.

Characterization of bacterial cellulose films combined with chitosan and polyvinyl alcohol: Evaluation of mechanical and barrier properties.

Bacterial cellulose (BC) produced by Komagataeibacter xylinus is a biomaterial with a unique three-dimensional structure. To improve the mechanical properties and reinforce the BC films, they were immersed in polyvinyl alcohol (0-4%) and chitosan (0-1%) baths. Moisture content, mechanical properties and water vapour permeability were measured to assess the effect of polyvinyl alcohol and chitosan. The morphology, optical, structural and thermal properties were evaluated by scanning electron microscopy, spectral analysis, thermogravimetry and differential scanning calorimetry. Results showed that moisture content was significantly affected by the chitosan presence. Tensile strength values in the 20.76-41.65 MPa range were similar to those of synthetic polymer films. Percentage of elongation ranged from 2.28 to 21.82% and Young's modulus ranged from 1043.88 to 2247.82 MPa. The water vapour permeability (1.47 × 10-11-3.40 × 10-11 g/m s Pa) decreased with the addition of polyvinyl alcohol. The developed films own UV light barrier properties and optimal visual appearance.

Photopolymerized water-soluble maleilated chitosan/methacrylated poly (vinyl alcohol) hydrogels as potential tissue engineering scaffolds.

Photocrosslinkable water-soluble maleilated chitosan and methacrylated poly (vinyl alcohol) were synthesized and therefore maleilated chitosan/methacrylated poly (vinyl alcohol) (MCS/MPVA) hydrogels were prepared under UV radiation. Series of properties of the hydrogels including rheological property, swelling behavior, morphology and mechanical test were investigated. The main results showed that the MCS/MPVA hydrogels had fast gel-forming rate (complete transformation to gel within 150s), improved compressive strength at 0.169±0.011MPa and rapid absorbent capacity. These behaviors could be tunable via the control of weight ratio of MCS to MPVA. The indirect cytotoxicity assessments demonstrated the photocrosslinked hydrogels was compatible to mouse fibroblasts (L929 cells), indicating their potential as tissue engineering scaffolds.

pH-degradable PVA-based nanogels via photo-crosslinking of thermo-preinduced nanoaggregates for controlled drug delivery.

pH-Degradable PVA nanogels, which are prepared by photo-crosslinking thermo-preinduced PVA nanoaggregates in water without any surfactants or toxic organic solvents, are used for intracellular PTX release and anticancer treatment. These nanogels fast degraded at mildly acidic conditions with a pH-triggered PTX release, and the degradation products are only native PVA and poly(hydroxyethyl acrylate) (PHEA) as well as acetaldehyde without any toxic byproducts. The nanogel sizes could be tailored by different temperatures during the crosslinking process. The results of confocal microscopy and flow cytometry revealed that smaller nanogels exhibited enhanced internalization with MCF-7 cells than the ones treated with larger nanogels, by which the smaller PTX-loaded nanogels induced a more significant cytotoxicity against MCF-7 cells. GRAPHIC ABSTRACT: pH-Degradable PVA nanogels can be prepared by photo-crosslinking of thermo-preinduced nanoaggregates with tailored nanogel sizes given their pH-triggered PTX release and fast acid-degradation into native PVA and cell-compatible poly(hydroxyethyl acrylate) (PHEA) as well as acetaldehyde.

Coupled electron beam radiation and MBR treatment of textile wastewater containing polyvinyl alcohol.

Advanced oxidation processes (AOP) can be combined with biological treatments for recalcitrant organic pollutant decomposition. However, there has been no thorough investigation on the coupling of AOPs and membrane bioreactors (MBR) to treat polymer organic pollutants. This study proposes a new AOP that couples electron beam (EB) radiation and MBR treatment. This method was applied to treat real textile effluents containing polyvinyl alcohol (PVA). During the stable operation stage, 31 ± 7% (n = 28) COD was removed by the EB-MBR process. COD removal was enhanced to 45% at the end of the research period without process optimization. In addition, both the membrane flux and activated sludge system exhibited good stability. Only a 2% membrane flux decreased was observed after a 46 d operation period. PVA radiolysis and biofacies analysis mechanisms are also discussed. By contrast, PVA degradation using only the MBR treatment was ineffective in this study. This ineffectiveness was caused by membrane interception and floccule formation by PVA and activated sludge.

Effects of hydrogen peroxide feeding strategies on the photochemical degradation of polyvinyl alcohol.

The performance of batch and fed-batch photoreactors with that of continuous photoreactor for the treatment of aqueous polyvinyl alcohol (PVA) solutions is compared. Hydrogen peroxide feeding strategies, residence time, and [H2O2]/[PVA] mass ratio are examined for their impacts on the molecular weight distribution (MWD) of PVA and the total organic carbon (TOC) removal. The results prove that a continuous addition of H2O2 during the degradation reaction ensures the utilization of the produced radicals to minimize the oxidant consumption and maximize the TOC removal and the PVA degradation in a short irradiation time. Also, the MWD of PVA is found to be bimodal and shifted towards lower molecular weights with small shoulder peak indicating a progressive disappearance of the higher molecular weight fractions that is in accordance with the random chains scission mechanism. Besides, the hydrogen peroxide feeding strategies are found to have a great effect on the reduction in H2O2 residuals in the effluent.

Clusters of neural stem/progenitor cells cultured on a soft poly(vinyl alcohol) hydrogel crosslinked by gamma irradiation.

Neural stem/progenitor cells (NSPCs) in the central nervous system (CNS) have the capacity to self-renew by proliferation and are multipotent, giving rise to neurons, astrocytes, and oligodendrocytes. NSPCs can be amplified in neurosphere suspension cultures for cell transplantation therapy to treat CNS diseases as well as for in vitro pharmacological/toxicological assays; however, these suspension cultures have certain limitations, including the inconvenience of changing the culture medium as well as difficulty of live imaging. In the present study, we prepared a gamma-crosslinked poly(vinyl alcohol) (PVA) hydrogel and assessed its suitability as a substrate for adherent NSPC cultures. Differentiation was determined by evaluating the expression of the markers nestin (progenitors), ßIII tubulin (neurons), and glial fibrillary acidic protein and S100ß (glia) by immunocytochemistry and quantitative reverse transcriptase PCR. The levels of the marker genes were similar between the two types of culture; although some variability was observed, there were no fold differences in expression. NSPCs adhered to the PVA gel as clusters and grew without differentiating into neurons and glia. The proliferation rate of cells grown on the soft PVA gel [3.75-7.5% (w/v) PVA] was approximately 70% of that of neurospheres in suspension. We conclude that gamma-crosslinked PVA hydrogels can function as a novel scaffold for maintaining adherent NSPCs in an undifferentiated state.

Photoinduced conformational changes in DNA by poly(vinyl alcohol) carrying a malachite green moiety for protecting DNA against attack by nuclease.

Light is a highly advantageous means of specific cell targeting. Though targeted gene delivery is an important characteristic of an ideal delivery vehicle, there has been little effort to develop a photoresponsive vector. Among nonviral vectors, cationic substances interact effectively with negatively charged DNA. With this property in mind, we designed copolymers of poly(vinyl alcohol) carrying a malachite green moiety (PVAMG) with different molecular weights. Though PVAMG has no affinity for DNA in the absence of light, it undergoes photoionization in the presence of light to afford cationic DNA binding sites. The DNA-PVAMG complex was investigated with respect to DNA conformational changes and its protective nature, which are important properties for nonviral vectors. PVAMG irradiation promoted DNA conformational transitions from coils to partial globules to compacted globules. The complex had a protective effect against DNase I after PVAMG irradiation, while DNA was degraded under dark conditions. The effect on DNA transition and the protective nature were sensitive to the molecular weight of PVAMG. The data regarding binding constants and binding mode provided insight into the structure of the DNA-PVAMG complex. To withstand DNase I attacks, complexation results in the compaction of DNA, which is further covered with PVAMG.

Optoelectronic logic gates based on photovoltaic response of bacteriorhodopsin polymer composite thin films.

We present designs of optoelectronic OR, AND, NOR, and NAND logic gates with multiple pulsed pump laser beams based on the photovoltaic response of bacteriorhodopsin (BR) molecules embedded in a polyvinyl matrix coated on ITO. A detailed experimental study of the photovoltaic response reveals that continuous pulsed exposure to 532 nm and 405 nm laser light results in a large photocurrent/photovoltage, due to rapid reprotonation and chromophore reisomerization, taking BR to the ground state in hundreds of nanoseconds. It also helps in sustaining the photovoltage at higher frequencies and in maintaining the shape of the photovoltage. It is shown experimentally that for a pulsed laser beam at 532 nm with peak pump intensity of 1.19 W/cm (2), a photovoltage of 50 mV is generated. A detailed numerical simulation of the photovoltaic response of BR has been carried out taking into account all the six states (B, K, L, M, N, and O) in the BR photocycle to ascertain the effect of various parameters such as lifetime of the M-state, the pump pulse-width, pump intensity, lifetime of excited protons, and rate constant of excited protons. Experimental results are in good agreement with theoretical simulations. The present study opens up new prospects for protein-based optoelectronic computing.

Improvement of biodegradability of PVA-containing wastewater by ionizing radiation pretreatment.

BACKGROUND: Polyvinyl alcohol (PVA) has been widely used as sizing agents in textile and manufacturing industry, and it is a refractory compound with low biodegradability. OBJECTIVE: The objective of this paper was to treat the PVA-containing wastewater using gamma irradiation as a pretreatment strategy to improve its biodegradability and to determine the roles of different kinds of radical species played during pretreatment. METHODS: Gamma radiation was carried out in a (60)Cobalt source station, PVA concentration was analyzed by using a visible spectrophotometer and specific oxygen uptake rate (SOUR, milligram of O(2) per gram of mixed liquor volatile suspended solids (MLVSS) per hour) was measured by a microrespirometer. RESULTS: The results showed that the biodegradability of PVA-containing wastewater with low initial concentration (e.g., 327.8 mg/l) could be improved greatly with increasing irradiation dose. However, PVA gel formation was observed at higher initial PVA concentration (e.g., 3,341.6 mg/l) and higher irradiation dose, which inhibited PVA degradation by aerobic microorganisms. However, the formed gel could be separated by microfiltration, which led to more than 90% total organic carbon (TOC) removal. CONCLUSION: Ionizing radiation could be used as a pretreatment technology for PVA-containing wastewater, and its combination with biological process is feasible.

Silk fibroin/poly(vinyl alcohol) photocrosslinked hydrogels for delivery of macromolecular drugs.

Hydrogels are three-dimensional polymer networks widely used in biomedical applications as drug delivery and tissue engineered scaffolds to effectively repair or replace damaged tissue. In this paper we demonstrate a newly synthesized cytocompatible and drug releasing photo-crosslinked hydrogel based on poly(vinyl alcohol) methacrylate and silk fibroin which possesses tailorable structural and biological properties. The initial silk fibroin content was 0%, 10%, 20%, 30%, 40% and 50% with respect to the weight of poly(vinyl alcohol) methacrylate. The prepared hydrogels were characterized with respect to morphology, crystallinity, stability, swelling, mass loss and cytotoxicity. FITC-dextrans of different molecular weights were chosen as model drugs molecules for release studies from the hydrogels. The hydrogels containing different silk fibroin percentages showed differences in pore size and distribution. X-ray diffraction analysis revealed that amorphous silk fibroin in poly(vinyl alcohol) methacrylate is crystallized to ß-sheet secondary structure upon gelation. The sol fraction increased with increasing fibroin concentration in the co-polymer gel (from 18% to 45%), although the hydrogel extracts were non-cytotoxic. Similarly, the addition of silk fibroin increased water uptake by the gels (from 7% to 21%). FITC-dextran release from the hydrogels was dependent on the silk fibroin content and the molecular weight of encapsulated molecules. The study outlines a newer type of photo-crosslinked interpenetrating polymer network hydrogel that possess immense potential in drug delivery applications.

Preparation of nanocrystalline cellulose via ultrasound and its reinforcement capability for poly(vinyl alcohol) composites.

Rod-shaped nanocrystalline cellulose (NCC) was prepared from microcrystalline cellulose (MCC) using the purely physical method of high-intensity ultrasonication. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction was used for the characterization of the morphology and crystal structure of the material. The thermal properties were investigated using thermogravimetric analysis. The reinforcement capabilities of the obtained NCC were investigated by adding it to poly(vinyl alcohol) (PVA) via the solution casting method. The results revealed that the prepared NCC had a rod-shaped structure, with diameters between 10 and 20 nm and lengths between 50 and 250 nm. X-ray diffraction results indicated that the NCC had the cellulose I crystal structure similar to that of MCC. The crystallinity of the NCC decreased with increasing ultrasonication time. The ultrasonic effect was non-selective, which means it can remove amorphous cellulose and crystalline cellulose. Because of the nanoscale size and large number of free-end chains, the NCC degraded at a slightly lower temperature, which resulted in increased char residue (9.6-16.1%), compared with that of the MCC (6.2%). The storage modulus of the nanocomposite films were significantly improved compared with that of pure PVA films. The modulus of PVA with 8 wt.% NCC was 2.40× larger than that of pure PVA.

Comparison of a new self developing photopolymer with AA/PVA based photopolymer utilizing the NPDD model.

The development of suitable recording media for applications such as holographic optical elements and holographic data storage are of significant research and commercial interest. In this paper, a photopolymer material developed by Bayer MaterialScience is examined using various optical techniques and then characterised using the Non-local Photo-polymerization Driven Diffusion model. This material demonstrates the capabilities of a new class of photopolymer offering high index modulation, full colour recording, high light sensitivity and environmental stability. One key result of this study is the material's high spatial frequency resolution, indicating a very low non-local effect, thus qualifying it as a very good storage medium.

An elastically compressible phantom material with mechanical and x-ray attenuation properties equivalent to breast tissue.

We have developed a novel phantom material: a solution of polyvinyl alcohol (PVAL) in ethanol and water, freeze-thawed to produce a solid yet elastically compressible gel. The x-ray attenuation and mechanical properties of these gels are compared with published measurements of breast tissue. Gels with PVAL concentrations from 5 to 20% w/v were produced. The linear x-ray attenuation coefficients of these gels range from 0.76 to 0.86 cm(-1) at 17.5 keV, increasing with PVAL concentration. These values are very similar to the published values of breast tissue at this energy, 0.8-0.9 cm(-1). Under compression cancerous breast tissue is approximately ten times stiffer than healthy breast tissue. The Young's moduli of the gels increase with PVAL concentration. Varying the PVAL concentration from 7.5 to 20% w/v produces gels with Young's moduli from 20 to 220 kPa at 15% strain. These values are characteristic of normal and cancerous breast tissue, respectively.

Separation of copper ions from iron ions using PVA-g-(acrylic acid/N-vinyl imidazole) membranes prepared by radiation-induced grafting.

Acrylic acid (AAc), N-vinyl imidazole (Azol) and their binary mixtures were graft copolymerized onto poly(vinyl alcohol) membranes using gamma irradiation. The ability of the grafted membranes to separate Cu ions from Fe ions was investigated with respect to the grafting yield and the pH of the feed solution. The data showed that the diffusion of copper ions from the feed compartment to the receiver compartment depends on the grafting yield of the membranes and the pH of the feed solution. To the contrary, iron ions did not diffuse through the membranes of all grafting yields. However, a limited amount of iron ions diffused in strong acidic medium. This study shows that the prepared membranes could be considered for the separation of copper ions from iron ions. The temperature of thermal decomposition of pure PVA-g-AAc/Azol membrane, PVA-g-AAc/Azol membrane containing copper ions, and PVA-g-AAc/Azol membrane containing iron ions were determined using TGA analyzer. It was shown that the presence of Cu and Fe ions increases the decomposition temperature, and the membranes bonded with iron ions are more stable than those containing copper ions.