Composition dependent structural modulations in transparent poly(vinyl alcohol) hydrogels

Adhesive Antibacterial Moisturizing Nanostructured Skin Patch for Sustainable Development of Atopic Dermatitis Treatment in Humans

Atopic dermatitis (AD) is a chronic inflammatory skin disease with a complex etiology that lacks effective treatment. The therapeutic goals include alleviating symptoms, such as moisturizing and applying antibacterial and anti-inflammatory medications. Hence, there is an urgent need to develop a patch that effectively alleviates most of the AD symptoms. In this study, we employed a "green" cross-linking approach of poly(vinyl alcohol) (PVA) using glycerol, and we combined it with polyacrylonitrile (PAN) to fabricate core-shell (CS) nanofibers through electrospinning. Our designed structure offers multiple benefits as the core ensures controlled drug release and increases the strength of the patch, while the shell provides skin moisturization and exudate absorption. The efficient PVA cross-linking method facilitates the inclusion of sensitive molecules such as fermented oils. In vitro studies demonstrate the patches' exceptional biocompatibility and efficacy in minimizing cell ingrowth into the CS structure containing argan oil, a property highly desirable for easy removal of the patch. Histological examinations conducted on an ex vivo model showed the nonirritant properties of developed patches. Furthermore, the eradication of Staphylococcus aureus bacteria confirms the potential use of CS nanofibers loaded with argan oil or norfloxacin, separately, as an antibacterial patch for infected AD wounds. In vivo patch application studies on patients, including one with AD, demonstrated ideal patches' moisturizing effect. This innovative approach shows significant promise in enhancing life quality for AD sufferers by improving skin hydration and avoiding infections.

Synthesis and characterization of an innovative sodium alginate/polyvinyl alcohol bioartificial hydrogel for forward-osmosis desalination

Recently, hydrogels have been widely applied as draw agents in forward osmosis (FO) desalination. This work aims to synthesize bioartificial hydrogel from a blend of sodium alginate (SA) and polyvinyl alcohol (PVA) using epichlorohydrin (ECH) as a crosslinker. Then this prepared hydrogel was applied as a draw agent with cellulose triacetate membrane in a batch (FO) cell. The effects of the PVA content in the polymer blend and the crosslinker dose on the hydrogel's swelling capacity were investigated to optimize the hydrogel's composition. Furthermore, the water flux and the reverse solute flux of the optimum SA/PVA hydrogel were evaluated in a batch (FO) unit under the effect of the hydrogel's particle size, feed solution (FS) temperature, FS concentration, and membrane orientation. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD) and compression strength tests were used to characterize the prepared hydrogel. Results revealed that the equilibrium swelling ratio (%) of 5228 was achieved with a hydrogel that had 25% PVA and a crosslinking ratio of 0.8. FO experiments revealed that the maximum water flux of 0.845 LMH achieved, when distilled water was used as FS, average hydrogel's particle size was 60 µm, and the FS temperature was 40 °C.

Reinforced hydrogel building via formation of alginate-chitosan double network with pH & salt-responsiveness and electric conductivity for soft actuators

Aiming at green and friendly environmental protection, polyvinyl alcohol/sodium alginate/chitosan (PSCS) double network hydrogel was successfully prepared through diffusing the high molecular weight chitosan into PVA/sodium alginate (PS) hydrogel without any other toxic reagents. The polyanion hydrogels could be significantly enhanced by immersing the polyanion hydrogel in high molecular weight chitosan solution without requiring specific structure. The PSCS hydrogel had a compact and rough surface structure with the smaller porosities and larger crystallization degree compared with polyvinyl alcohol/sodium alginate hydrogels and polyvinyl alcohol/sodium alginate/Ca2+ (PSCa) hydrogels. The PSCS hydrogel possessed excellent hydrolysis resistance, the significant pH-sensitive and salt-sensitive swelling. In addition, the flexibility, Young's modulus and mechanical properties of PSCS hydrogel can be adjusted through the changing the content of sodium alginate. Moreover, PS, PSCa and PSCS had electric conductivity, and PSCS showed twice the conductivity compared to PS hydrogel. Based on differences of swelling ratio, a PSCS bilayer hydrogel was designed and showed excellent pH-driven deformation ability. The PSCS hydrogel is expected to expand the application of hydrogels in conditions involving stimulus response, and might serve as a promising intelligent actuators or soft robots.

Composite Hydrogel of Poly(vinyl alcohol) Loaded by Citrus hystrix Leaf Extract, Chitosan, and Sodium Alginate with In Vitro Antibacterial and Release Test

Citrus hystrix leaves have been used traditionally as a spice, a traditional medicine for respiratory and digestive disorders, and a remedy for bacterial infections. This study reports on the synthesis of composite hydrogels using the freeze-thaw method with poly(vinyl alcohol) (PVA) as the building block loaded by C. hystrix leaf extract (CHLE). Additionally, chitosan (CS) and sodium alginate (SA) were also loaded, respectively, to increase the antibacterial activity and to control the extract release of the composite hydrogels. The combinations of the compositions were PVA, PVA/CHLE, PVA/CHLE/CS, PVA/CHLE/SA, and PVA/CHLE/SA/CS. The internal morphology of the hydrogels shows some changes after the PVA/CHLE hydrogel was loaded by CS, SA, and SA/CS. The analysis of the Fourier transform infrared (FTIR) spectra confirmed the presence of PVA, CHLE, CS, and SA in the composite hydrogels. From the X-ray diffraction (XRD) characterization, it was shown that the composite hydrogels maintained their semicrystalline properties with decreasing crystallinity degree after being loaded by CS, SA, and SA/CS, as also supported by differential scanning calorimetry (DSC) characterization. The compressive strength of the PVA/CHLE hydrogel decreases after the loading of CS, SA, and SA/CS, so that it becomes more elastic. Despite being loaded in the composite hydrogels, the CHLE retained its antibacterial activity, as evidenced in the in vitro antibacterial test. The loading of CS succeeded in increasing the antibacterial activity of the composite hydrogels, while the loading of SA resulted in the decrease of the antibacterial activity. The release of extract from the composite hydrogels was successfully slowed down after the loading of CS, SA, and SA/CS, resulting in a controlled release following the pseudo-Fickian diffusion. The cytotoxic activity test proved that all hydrogel samples can be used safely on normal cells up to concentrations above 1000 μg/mL.

Formulation and characterization of polyvinyl alcohol/chitosan composite nanofiber co-loaded with silver nanoparticle & luliconazole encapsulated poly lactic-co-glycolic acid nanoparticle for treatment of diabetic foot ulcer

Chronic wounds are prone to fungal infections, possess a significant challenge, and result in substantial mortality. Diabetic wounds infected with Candida strains are extremely common. It can create biofilm at the wound site, which can lead to antibiotic resistance. As a result, developing innovative dressing materials that combat fungal infections while also providing wound healing is a viable strategy to treat infected wounds and address the issue of antibiotic resistance. Present work proposed anti-infective dressing material for the treatment of fungal strains Candida-infected diabetic foot ulcer (DFU). The nanofiber was fabricated using polyvinyl Alcohol/chitosan as hydrogel base and co-loaded with silver nanoparticles (AgNP) and luliconazole-nanoparticles (LZNP) nanoparticles, prepared using PLGA. Fabricated nanofibers had pH close to target area and exhibited hydrophilic surface suitable for adhesion to wound area. The nanofibers showed strong antifungal and antibiofilm properties against different strains of Candida; mainly C. albicans, C. auris, C. krusei, C. parapsilosis and C. tropicalis. Nanofibers exhibited excellent water retention potential and water vapour transmission rate. The nanofibers had sufficient payload capacity towards AgNP and LZNP, and provided controlled release of payload, which was also confirmed by in-vivo imaging. In-vitro studies confirmed the biocompatibility and enhanced proliferation of Human keratinocytes cells (HaCaT). In-vivo studies showed accelerated wound closure by providing ant-infective action, supporting cellular proliferation and improving blood flow, all collectively contributing in expedited wound healing.

Investigation of human hair keratin-based nanofibrous scaffold for skin tissue engineering application

Keratin-based nanofibers were fabricated using the electrospinning technique, and their potential as scaffolds for tissue engineering was investigated. Keratin, extracted from the human hair, was blended with poly(vinyl alcohol) (PVA) in an aqueous medium. Morphological characterizations of the fabricated PVA-keratin nanofiber (PK-NF) random and aligned scaffolds performed using a scanning electron microscope (SEM) revealed the formation of uniform and randomly oriented nanofibers with an interconnected three-dimensional network structure. The mean diameter of the nanofibers ranged from 100 to 250 nm. Functional groups and structural studies were done by infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis. FTIR study suggested that PVA interacted with keratin by hydrogen bonding. Moreover, the in vitro cell culture study could suggest that PK-NF scaffolds were non-cytotoxic by supporting the growth of murine embryonic stem cells (ESCs), human keratinocytes (HaCaT), and dermal fibroblast (NHDF) cell lines. Further, the immunocytochemical characterization revealed the successful infiltration, adhesion, and growth of ESCs, HaCaT, and NHDF cells seeded on PK-NF scaffolds. However, there was no noteworthy difference observed concerning cell growth and viability irrespective of the random and aligned internal fibril arrangement of the PK-NF scaffolds. The infiltration and growth pattern of HaCaT and NHDF cells adjacent to each other in a 3D co-culture study mimicked that of epidermal and dermal skin cells and indeed underscored the potential of PK-NFs as a scaffold for skin tissue engineering.

Nanostructured N/S doped carbon dots/mesoporous silica nanoparticles and PVA composite hydrogel fabrication for anti-microbial and anti-biofilm application

Regarding the convergence of the worldwide epidemic, the appearance of bacterial infection has occasioned in a melodramatic upsurge in bacterial pathogens with confrontation against one or numerous antibiotics. The implementation of engineered nanostructured particles as a delivery vehicle for antimicrobial agent is one promising approach that could theoretically battle the setbacks mentioned. Among all nanoparticles, silica nanoparticles have been found to provide functional features that are advantageous for combatting bacterial contagion. Apart from that, carbon dots, a zero-dimension nanomaterial, have recently exhibited their photo-responsive property to generate reactive oxygen species facilitating to enhance microorganism suppression and inactivation ability. In this study, potentials of core/shell mesoporous silica nanostructures (MSN) in conjugation with carbon dots (CDs) toward antimicrobial activity against Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli have been investigated. Nitrogen and sulfur doped CDs (NS/CDs) conjugated with MSN which were cost effective nanoparticles exhibited much superior antimicrobial activity for 4 times as much as silver nanoparticles against all bacteria tested. Among all nanoparticles tested, 0.40 M NS/CDs@MSN showed the greatest minimal biofilm inhibitory at very low concentration (< 0.125 mg mL-1), followed by 0.20 M NS/CDs@MSN (0.5 mg mL-1), CD@MSN (25 mg mL-1), and MSN (50 mg mL-1), respectively. Immobilization of NS/CDs@MSN in polyvinyl alcohol (PVA) hydrogel was performed and its effect on antimicrobial activity, biofilm controlling efficiency, and cytotoxicity toward fibroblast (NIH/3 T3 and L-929) cells was additionally studied for further biomedical applications. The results demonstrated that 0.40 M NS/CDs-MSN@PVA hydrogel exhibited the highest inhibitory effect on S. aureus > P. aeruginosa > E. coli. In addition, MTT assay revealed some degree of toxicity of 0.40 M NS/CDs-MSN@PVA hydrogel against L-929 cells by a slight reduction of cell viability from 100% to 81.6% when incubated in the extract from 0.40 M NS/CDs-MSN@PVA hydrogel, while no toxicity of the same hydrogel extract was detected toward NIH/3 T3 cells.

Structural, Optical, and Electrical Parameters of Doped PVA/PVP Blend with TPAI or THAI Salt

The 70% polyvinyl alcohol/30% polyvinyl pyrrolidone (PVA/PVP) polymer blends, with different weight ratios of tetrapropylammonium iodide (TPAI) or tetrahexylammonium iodide (THAI) salt, were prepared using dimethyl sulfoxide (DMSO) as a solvent. The X-ray diffraction technique was used to trace the crystalline nature of the formed blends. The SEM and EDS techniques were applied to figure out the morphology of the blends. The variation in the FTIR vibrational bands was used to investigate the chemical composition and the effect of different salt doping on the functional groups of the host blend. The influence of the salt type (TPAI or THAI) and its ratio on the linear and nonlinear optical parameters for the doped blends were investigated in detail. Absorbance and reflectance are highly enhanced in the UV region reaching a maximum for the blend with 24% TPAI or THAI; so, it can be employed as shielding materials for UVA and UVB types. The direct (5.1 eV) and indirect (4.8 eV) optical bandgaps were reduced continuously to (3.52, 3.63 eV) and (3.45, 3.51 eV) while increasing the content of TPAI or THAI, respectively. The blend doped with 24% wt TPAI exhibited the highest refractive index (around 3.5 in 400-800 nm). The DC conductivity is affected by the content and type of salt, its dispersion, and blend-salt interaction. The activation energies of different blends were obtained by applying the Arrhenius formula.

Fluorescent-based biodegradable microneedle sensor array for tether-free continuous glucose monitoring with smartphone application

Continuous glucose monitoring (CGM) allows patients with diabetes to manage critical disease effectively and autonomously and prevent exacerbation. A painless, wireless, compact, and minimally invasive device that can provide CGM is essential for monitoring the health conditions of freely moving patients with diabetes. Here, we propose a glucose-responsive fluorescence-based highly sensitive biodegradable microneedle CGM system. These ultrathin and ultralight microneedle sensor arrays continuously and precisely monitored glucose concentration in the interstitial fluid with minimally invasive, pain-free, wound-free, and skin inflammation-free outcomes at various locations and thicknesses of the skin. Bioresorbability in the body without a need for device removal after use was a key characteristic of the microneedle glucose sensor. We demonstrated the potential long-term use of the bioresorbable device by applying the tether-free CGM system, thus confirming the successful detection of glucose levels based on changes in fluorescence intensity. In addition, this microneedle glucose sensor with a user-friendly designed home diagnosis system using mobile applications and portable accessories offers an advance in CGM and its applicability to other bioresorbable, wearable, and implantable monitoring device technology.

Natural Cellulose Fiber-Derived Photothermal Aerogel for Efficient and Sustainable Solar Desalination

Aerogels are becoming a promising platform to fabricate photothermal materials for use in solar steam generation (SSG), which have remarkable application potential in solar desalination, due to their excellent thermal management, salt resistance, and considerable water evaporation rate. In this work, a novel photothermal material is fabricated by forming a suspension between sugarcane bagasse fibers (SBF) and poly(vinyl alcohol), tannic acid (TA), and Fe³⁺ solutions via hydrogen bonds of hydroxyl groups. After freeze drying, the fabricated SBF aerogel-based photothermal (SBFAP) material possesses a 3D interconnected porous microstructure, which could enhance water transportation ability, reduce thermal conductivity, and quickly dissolve salt crystals on the SBFAP surface. Thanks to the formation of micro/nanosized complexes between TA and Fe³⁺ ions on the SBFAP material, the SBFAP exhibits high light capture and water evaporation rate (2.28 kg m^-2 h^-1). In particular, due to strong hydrogen bonding and the SBF, the SBFAP material is reinforced, thereby exhibiting excellent structural stability in seawater. Moreover, the high salt tolerance of SBFAP favors its high desalination performance for at least 76 days of continuous evaporation under actual conditions. This research paves the way for the fabrication of natural cellulose fiber-based photothermal materials for application in solar desalination.

Controlled Release of Felodipine from 3D-Printed Tablets with Constant Surface Area: Influence of Surface Geometry

In this study, 3D-printed tablets with a constant surface area were designed and fabricated using polylactic acid (PLA) in the outer compartment and polyvinyl alcohol and felodipine (FDP) in the inner compartment. The influences of different surface geometries of the inner compartment, namely, round, hexagon, square, and triangle, on drug release from 3D-printed tablets were also studied. The morphology and porosity of the inner compartment were determined using scanning electron microscopy and synchrotron radiation X-ray tomographic microscopy, respectively. Additionally, drug content and drug release were also evaluated. The results revealed that the round-shaped geometry seemed to have the greatest total surface area of the inner compartment, followed by square-shaped, hexagon-shaped, and triangle-shaped geometries. FDP-loaded 3D-printed tablets with triangle and hexagon surface geometries had the slowest drug release (about 80% within 24 h). In the round-shaped and square-shaped 3D-printed tablets, complete drug release was observed within 12 h. Furthermore, the drug release from triangle-shaped 3D-printed tablets with double the volume of the inner compartment was faster than that of a smaller volume. This was due to the fact that a larger tablet volume increased the surface area contacting the medium, resulting in a faster drug release. The findings indicated that the surface geometry of 3D-printed tablets with a constant surface area affected drug release. This study suggests that 3D printing technology may be used to develop oral solid dosage forms suitable for customized therapeutic treatments.

Investigation of Transport Mechanism and Nanostructure of Nylon-6,6/PVA Blend Polymers

A casting technique was used to prepare poly(vinyl alcohol) (PVA) blend polymers with different concentrations of Nylon-6,6 to increase the free-volume size and control the ionic conductivity of the blended polymers. The thermal activation energy for some blends is lower than that of pure polymers, indicating that their thermal stability is somewhere in between that of pure Nylon-6,6 and pure PVA. The degree of crystallinity of the blend sample (25.7%) was lower than that of the pure components (41.0 and 31.6% for pure Nylon-6,6 and PVA, respectively). The dielectric properties of the blended samples were investigated for different frequencies (50 Hz-5 MHz). The σ_ac versus frequency was found to obey Jonscher's universal power law. The calculated values of the s parameter were increased from 0.53 to 0.783 for 0 and 100 wt.% Nylon-6,6, respectively, and values less than 1 indicate the hopping conduction mechanism. The barrier height (Wm) was found to increase from 0.33 to 0.72 for 0 and 100 wt.% Nylon-6,6, respectively. The ionic conductivity decreases as the concentration of Nylon-6,6 is blended into PVA because increasing the Nylon-6,6 concentration reduces the number of mobile charge carriers. Positron annihilation lifetime (PAL) spectroscopy was used to investigate the free volume's nanostructure. The hole volume size grows exponentially with the concentration of Nylon-6,6 mixed with PVA. The Nylon-6,6/PVA blends' free-volume distribution indicates that there is no phase separation in the blended samples. Mixing PVA and Nylon-6,6 resulted in a negative deviation (miscible blends), as evidenced by the interaction parameter's negative value. The strong correlation between the free-volume size and other macroscopic properties like ionic conductivity suggests that the free-volume size influences these macroscopic properties.

Hollow and porous TiO2 in PVA matrix nanocomposite green synthesis using ionic liquid micelle for Congo red removal from contaminated water

A new green procedure has been applied to prepare TiO₂ nanocomposite in polyvinyl alcohol (PVA) matrix using an aqueous micelle solution of ionic liquid 1-methyl-3-octylimidazolium bromide by determining critical micelle concentration (CMC). The COSMO-SAC model has been used to calculate the activity coefficient of water and understand the water molecules' behavior in the synthesis mixture. The prepared nanocomposite was porous and layered that has been characterized using FT-IR, XRD, DSC, TGA, SEM, EDX, and elemental mapping. The prepared nanocomposite has been used to remove Congo red dye from contaminated water with the adsorption process. The Langmuir, Freundlich, and Temkin isotherms have been used for modeling equilibrium adsorption of dye removal. Also, the optimized process factors have been evaluated that could achieve 97% dye removal in the following conditions: pH = 12, T = 25 ℃, and t = 45 min using 0.2 g TiO₂@PVA (Mesh 100)/L of 10 ppm Congo red aqueous solution. Also, the efficiency of the nanocomposite was 88% after 5 recovery cycles from the optimized condition.

Constructions of synergistic photothermal therapy antibacterial hydrogel based on polydopamine, tea polyphenols and polyvinyl alcohol and effects on wound healing in mouse

Hydrogels with significant antibacterial efficacy have enormous potential in wound healing. This work reported a series of effective antibacterial and antioxidant hydrogels based on tea polyphenols (TP), polydopamine (PDA), and polyvinyl alcohol (PVA). PDA-TP molecular chains are formed from oxidized TP and PDA. These molecular chains, which were cross-linked with PVA by cyclic freeze-thaw (FT), formed the PVA/PDA-TP hydrogel (PPTP). The number of freezing-thawing cycles and the amount of TP would affect the mechanical properties and swelling properties of hydrogel. The PPTP hydrogel exhibited high photo thermal conversion efficiency, high antibacterial efficacy, antioxidant properties, good cellular compatibility and short wound closure time. The PPTP hydrogel leaded to wound closure in approximately 10 d in a full-thickness skin defect mouse model. The preparation method of hydrogel with non-chemical cross-linked and ability of rapid high temperature generation provided a new way to apply TP to wound healing and proved that synergistic chemical and photothermal therapy can effectively inhibit resistant bacteria and accelerate wound healing.

Enhancing Photoluminescence Intensity and Spectral Bandwidth of Hybrid Nanofiber/Thin-Film Multilayer Tm3+-Doped SiO2-HfO2

Multilayering of optical thin films is widely used for a range of purposes in photonic technology, but the development of nanofiber structures that can outperform thin films and nanoparticles in optical applications cannot simply be disregarded. Hybrid structures composed of Tm³⁺-doped SiO₂-HfO₂ in the form of nanofibers (NFs) and thin films (TFs) are deposited on a single substrate using the electrospinning and dip-coating methods, respectively. Ultrafine nanofiber strands with a diameter of 10-60 nm were fabricated in both single and multilayer samples. Enhanced photoluminescence emission intensity of about 10 times was attained at wavelengths of around 457, 512 and 634 nm under an excitation of 350 nm for NF-TF-NF* hybrid structures when compared with single-layered NF and TF structures. The arrangement of nanofibers and thin films in a multilayer structure influenced the luminescence intensity and spectral bandwidth. High transparency in the range of 75-95% transparency across the wavelength of 200-2000 nm was achieved, making it ideal for photonic application. Theoretical findings obtained through IMD software were compared with experimental results, and they were found to be in good agreement.

Enzyme-Triggered Crosslinked Hybrid Hydrogels for Bone Tissue Engineering

The quest to develop state-of-the-art hydrogels for bone tissue engineering has accompanied substantial innovation and significant progression in the field of bioactive hydrogels. Still, there is scope for advancement in this cell-friendly and biocompatible scaffold system. The crosslinking approaches used for hydrogel synthesis plays a decisive role in guiding and regulating the mechanical stability, network framework, macroscopic architect, immunological behaviors, and cellular responses. Until recently, enzyme-based crosslinking strategies were considered as the pinnacle in designing efficient hybrid hydrogel systems. A variety of enzymes have been explored for manufacturing hydrogels while taking the advantage of the biocompatible nature, specificity, ability to produce nontoxic by products and high efficiency of enzymes. The current review focuses on the utility of different enzymes as crosslinking agents for hydrogel formation with their application in bone tissue engineering. The field of enzyme crosslinked hydrogel synthesis is rapidly maturing with a lot of opportunities to be explored in bone tissue engineering. Enzyme-based in situ and externally crosslinked hydrogels for bone regeneration is an attractive field, and with innovation in using engineered enzymes this field will continue to flourish with clinical orientation.

Efficient Removal of Organic Dye from Aqueous Solution Using Hierarchical Zeolite-Based Biomembrane: Isotherm, Kinetics, Thermodynamics and Recycling Studies

Bio adsorbents have received tremendous attention due to their eco-friendly, cheap and non-toxic nature. Recently, bio-adsorbent-based membranes have been frequently employed for water treatment. The work reports the preparation of a novel adsorbent membrane from hierarchical zeolite, polyvinyl alcohol, carboxymethyl cellulose and agar. The fabricated membrane was characterized spectroscopically and microscopically with several techniques such as XRD, UTM, TGA, optical microscopy and FT-IR, as well as contact-angle studies. The result showed that the hierarchical-zeolite-loaded membrane is superior in terms of thermal stability, mechanical properties and surface roughness. The fabricated membrane was investigated for its efficiency in the removal of Congo red dye in aqueous conditions. The influence of pH, temperature, contact period and the initial concentration of dye and zeolite loading on the adsorption process are also explored. The adsorption results highlighted the maximum sorption property of Congo red on agar/zeolite/carboxymethyl cellulose/polymer biomembrane was found to be higher (15.30 mg/g) than that of zeolite powder (6.4 mg/g). The adsorption isotherms and kinetic parameters were investigated via Langmuir, Freundlich and pseudo-first order, pseudo-second order and the intraparticle diffusion model, respectively. The adsorption isotherms fitted well for both considered isotherms, whereas pseudo-second order fitted well for kinetics. The thermodynamic parameter, ΔG at 303 K, 313 K and 323 K was −9.12, −3.16 and −0.49 KJ/mol, respectively. The work further explores the antibacterial efficacy of the prepared membrane and its reusability.

Preparation of citric acid-modified poly(vinyl alcohol) films for effectively precipitating calcium phosphate particles

Development of a technology for effectively controlling the precipitation of CP particles on PVA films via a biomimetic process was achieved using the CA-modification technique.

Properties of the PVA-VAVTD KOH Blend as a Gel Polymer Electrolyte for Zinc Batteries

Rechargeable zinc-air batteries are promising for energy storage and portable electronic applications because of their good safety, high energy density, material abundance, low cost, and environmental friendliness. A series of alkaline gel polymer electrolytes formed from polyvinyl alcohol (PVA) and different amounts of terpolymer composed of butyl acrylate, vinyl acetate, and vinyl neodecanoate (VAVTD) was synthesized applying a solution casting technique. The thin films were doped with KOH 12M, providing a higher amount of water and free ions inside the electrolyte matrix. The inclusion of VAVTD together with the PVA polymer improved several of the electrical properties of the PVA-based gel polymer electrolytes (GPEs). X-ray diffraction (XRD), thermogravimetric analysis (TGA), and attenuated total reflectance- Fourier-transform infrared spectroscopy (ATR-FTIR) tests, confirming that PVA chains rearrange depending on the VAVTD content and improving the amorphous region. The most conducting electrolyte film was the test specimen 1:4 (PVA-VAVTD) soaked in KOH solution, reaching a conductivity of 0.019 S/cm at room temperature. The temperature dependence of the conductivity agrees with the Arrhenius equation and activation energy of ~0.077 eV resulted, depending on the electrolyte composition. In addition, the cyclic voltammetry study showed a current intensity increase at higher VAVTD content, reaching values of 310 mA. Finally, these gel polymer electrolytes were tested in Zn-air batteries, obtaining capacities of 165 mAh and 195 mAh for PVA-T4 and PVA-T5 sunk in KOH, respectively, at a discharge current of -5 mA.

Dual Cross-Linked Chitosan/PVA Hydrogels Containing Silver Nanoparticles with Antimicrobial Properties

Stable chitosan/PVA-based hydrogels were obtained by combining covalent and physical cross-linking methods. As covalent cross-linkers, epoxy agents with different chain lengths were used, while freeze-thaw cycles were applied for additional physical cross-linking. The chemical structure of the hydrogel was examined by FTIR spectroscopy whereas the morphology was analyzed by SEM, showing well-defined pores with dimensions of around 50 μm in diameter. It was proved that gel fraction and the network morphology were deeply influenced by the synthesis conditions. Chitosan/PVA hydrogel showed a relative high swelling rate, reaching equilibrium in the first hour. The values obtained for the elastic modulus were relatively low (3-30 kPa); as a result, these hydrogels are soft and very flexible, and are ideal candidates for medical applications as wound or oral dressings. In addition, the natural antimicrobial activity of chitosan was enhanced by in situ generation of silver nanoparticles (AgNPs) under UV irradiation. The total amount of Ag from hydrogel was determined by elemental analyses and its crystalline state was confirmed by XRD. The CS/PVA hydrogels entrapped with AgNPs exhibited high inhibitory activity against S. aureus and K. pneumonia. The vitality tests confirmed the lack of cytotoxicity of CS/PVA hydrogels without and with AgNPs.

Tailor-made shape memory stents for therapeutic enzymes: A novel approach to enhance enzyme performance

Herein, our suggestion is to immobilize enzymes in-situ on absorbable shape-memory stents instead of injecting therapeutic enzymes into the blood. Chitosan (CHI)-based stents were tailored as novel support and the enzyme-immobilizing ability was elucidated using L-asparaginase (L-ASNase). For developing shape-memory stents, CHI-glycerol (GLY) solution was prepared and further blended with different ratios of polyethylene glycol (PEG), and polyvinyl alcohol (PVA). Afterward, the blends were modified by ionic crosslinking with sodium tripolyphosphate to obtain a shape-memory character. L-ASNase was included in the blends by using in-situ method before ionic crosslinking. The prepared stents, with or without L-ASNase, were comprehensively characterized by using several techniques. Collectively, immobilized L-ASNase exhibited much better performance in immobilization parameters than free one, thanks to its improved stability and reusability. For instance, CHI/GLY/PEG-3@L-ASNase retained about 70% of the initial activity after storage at 30 °C for 2 weeks, whereas the free form lost half of its initial activity. Besides, it retained 73.4% residual activity after 15 consecutive cycles. Most importantly, stent formulations exhibited ~60% activity in the bioreactor system after 4 weeks of incubation. Given the above results, shape-memory stents can be a promising candidate as a new platform for immobilization, especially in the blood circulation system.

Fabrication and Characterization of Poly (vinyl alcohol) and Chitosan Oligosaccharide-Based Blend Films

In the present study, we report the development of poly (vinyl alcohol) (PVA) and chitosan oligosaccharide (COS)-based novel blend films. The concentration of COS was varied between 2.5-10.0 wt% within the films. The inclusion of COS added a brown hue to the films. FTIR spectroscopy revealed that the extent of intermolecular hydrogen bonding was most prominent in the film that contained 5.0 wt% of COS. The diffractograms showed that COS altered the degree of crystallinity of the films in a composition-dependent manner. As evident from the thermal analysis, COS content profoundly impacted the evaporation of water molecules from the composite films. Stress relaxation studies demonstrated that the blend films exhibited more mechanical stability as compared to the control film. The impedance profiles indicated the capacitive-dominant behavior of the prepared films. Ciprofloxacin HCl-loaded films showed excellent antimicrobial activity against Escherichia coli and Bacillus cereus. The prepared films were observed to be biocompatible. Hence, the prepared PVA/COS-based blend films may be explored for drug delivery applications.

Propolis-Based Nanofiber Patches to Repair Corneal Microbial Keratitis

In this research, polyvinyl-alcohol (PVA)/gelatin (GEL)/propolis (Ps) biocompatible nanofiber patches were fabricated via electrospinning technique. The controlled release of Propolis, surface wettability behaviors, antimicrobial activities against the S. aureus and P. aeruginosa, and biocompatibility properties with the mesenchymal stem cells (MSCs) were investigated in detail. By adding 0.5, 1, and 3 wt.% GEL into the 13 wt.% PVA, the morphological and mechanical results suggested that 13 wt.% PVA/0.5 wt.% GEL patch can be an ideal matrix for 3 and 5 wt.% propolis addition. Morphological results revealed that the diameters of the electrospun nanofiber patches were increased with GEL (from 290 nm to 400 nm) and Ps addition and crosslinking process cause the formation of thicker nanofibers. The tensile strength and elongation at break enhancement were also determined for 13 wt.% PVA/0.5 wt.% GEL/3 wt.% Ps patch. Propolis was released quickly in the first hour and arrived at a plateau. Cell culture and contact angle results confirmed that the 3 wt.% addition of propolis reinforced mesenchymal stem cell proliferation and wettability properties of the patches. The antimicrobial activity demonstrated that propolis loaded patches had antibacterial activity against the S. aureus, but for P. aeruginosa, more studies should be performed.

Tribomechanical Comparison between PVA Hydrogels Obtained Using Different Processing Conditions and Human Cartilage

Designing materials for cartilage replacement raises several challenges due to the complexity of the natural tissue and its unique tribomechanical properties. Poly(vinyl alcohol) (PVA) hydrogels have been explored for such purpose since they are biocompatible, present high chemical stability, and their properties may be tailored through different strategies. In this work, the influence of preparation conditions of PVA hydrogels on its morphology, water absorption capacity, thermotropic behavior, mechanical properties, and tribological performance was evaluated and compared with those of human cartilage (HC). The hydrogels were obtained by cast-drying (CD) and freeze-thawing (FT), in various conditions. It was found that the method of preparation of the PVA hydrogels critically affects their microstructure and performance. CD gels presented a denser structure, absorbed less water, were stiffer, dissipated less energy, and withstood higher loads than FT gels. Moreover, they led to friction coefficients against stainless steel comparable with those of HC. Overall, CD hydrogels had a closer performance to natural HC, when compared to FT ones.

Hydrogel beads bio-nanocomposite based on Kappa-Carrageenan and green synthesized silver nanoparticles for biomedical applications

This paper describes the fabrication and characterization of bio-nanocomposite hydrogel beads based on Kappa-Carrageenan (κ-Carrageenan) and bio-synthesized silver nanoparticles (Ag-NPs). The silver nanoparticles were prepared in aqueous Citrullus colocynthis seed extract as both reducing and capping agent. Cross-linked κ-Carrageenan/Ag-NPs hydrogel beads were prepared using potassium chloride as the cross-linker. The hydrogel beads were characterized using XRD and FESEM. Moreover, swelling property of the hydrogel beads was investigated. The Ag release profile of the hydrogels was obtained by fitting the experimental data to power law equation. The direct visualization of the green synthesized Ag-NPs using TEM shows particle size in the range of 23±2nm. The bio-nanocomposite hydrogels showed lesser swelling behavior in comparison with pure κ-Carrageenan hydrogel. Regardless the slow Ag release, κ-Carrageenan/Ag-NPs presented good antibacterial activities against Staphylococcus aureus, Methicilin Resistant Staphylococcus aurous, Peseudomonas aeruginosa and Escherichia coli with maximum zones of inhibition 11±2mm. Cytotoxicity study showed that the bio-nanocomposite hydrogels with non-toxic effect of concentration below 1000μg/mL have great pharmacological potential and a suitable level of safety for use in the biological systems.

Fabrication of transparent quaternized PVA/silver nanocomposite hydrogel and its evaluation as an antimicrobial patch for wound care systems

Grafting of quaternary nitrogen atoms into the backbone of polymer is an efficient way of developing new generation antimicrobial polymeric wound dressing. In this study, an elastic, non-adhesive and antimicrobial transparent hydrogel based dressing has been designed, which might be helpful for routine observation of wound area without removing the dressing material along with maintaining a sterile environment for a longer period of time. Green synthesized silver nanoparticles have been loaded into the quaternized PVA hydrogel matrix to improve its antimicrobial property. Silver nanoparticles loaded quaternized PVA hydrogel showed enhanced mechanical and swelling properties compared to native quaternized PVA hydrogel. Release kinetics evaluated by atomic absorption spectroscopy revealed that the release mechanism of silver nanoparticles from the hydrogel follows Fickian diffusion. Antimicrobial efficacy of the hydrogels was evaluated by disk diffusion test on Pseudomonas aeruginosa, Staphylococcus aureus and Escherichia coli. After 96 h of release in phosphate buffer, the growth inhibition zone created by silver nanoparticless loaded quaternized PVA hydrogel is comparable to that created by ampicillin. These observations assert that the silver nanoparticles loaded quaternized PVA hydrogel acts as a reservoir of silver nanoparticles, which helps in maintaining a sterile environment for longer time duration by releasing Ag nanocrystallite in sustained manner.

Poly(vinyl alcohol)/chitosan/montmorillonite nanocomposites for food packaging applications

Poly(vinyl alcohol) (PVA)/chitosan (CS)/montmorillonite (C30B) materials for food packaging applications were prepared by using a noninvasive and low-cost freeze/thawing method. Cloisite 30B nanoclay content in PVA/CS gels was varied in order to establish optimum amount to obtain improved properties. The structural, morphological, rheological aspects, thermal stability, and antimicrobial activity were investigated using various techniques as Fourier transform infrared, scanning electron microscopy, rheology, thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical thermal analysis, and antibacterial tests. It was noticed that the obtained materials show an intercalated structure with specific interactions between components and nanoclay incorporation led to an increased thermal stability, mechanical properties, and excellent antimicrobial activity against Escherichia coli, Listeria monocytogenes, and Salmonella typhimurium due to synergistic action of CS and nanoclay.

Fabrication and properties of irradiation-cross-linked poly(vinyl alcohol)/clay aerogel composites

Poly(vinyl alcohol) (PVOH)/clay aerogel composites were fabricated by an environmentally friendly freeze-drying of the aqueous precursor suspensions, followed by cross-linking induced by gamma irradiation without chemical additives. The influences of cross-linking conditions, i.e., absorbed dose and polymer loading as well as density on the aerogel structure and properties, were investigated. The absorbed dose of 30 kGy was found to be the optimum dose for fabricating strong PVOH composites; the compressive modulus of an aerogel prepared from an aqueous suspension containing 2 wt % PVOH/8 wt % clay increased 10-fold, and that containing 1 wt % PVOH/9 wt % clay increased 12 times upon cross-linking with a dose of 30 kGy. Increasing the solids concentration led to an increase in the mechanical strength, in accordance with the changes in microstructure from layered structure to network structure. The increase of absorbed dose also led to decreased porous size of the network structure. Cross-linking and the increase of the PVOH lead to decreased thermal stability. The strengthened PVOH/clay aerogels possess very low flammability, as measured by cone calorimetry, with heat, smoke, and volatile products release value decreasing as increasing clay content. The mechanism of flame retardation in these materials was investigated with weight loss, FTIR, WAXD, and SEM of the burned residues. The proposed mechanism is that with decreasing fuel content (increasing clay content), increased heat and mass transport barriers are developed; simultaneously low levels of thermal conductivity are maintained during the burning.