PVA Network Research Articles

Supercooling-Driven Homogenization and Strengthening of Hydrogel Networks.

By leveraging principles from metal grain refinement, we introduce a transformative technique for fabricating poly(vinyl alcohol) (PVA) hydrogels via supercooling-coupled wet annealing, significantly enhancing their mechanical robustness and isotropy while maintaining their exceptionally high water content. Our methodology involves the dissolving PVA in water at elevated temperatures, mirroring the homogeneity achieved with a molten metal, in order to ensure a uniform distribution of polymer chains. This uniformity facilitates a rapid cooling phase that generates ultrafine ice crystals, setting the stage for a crucial solvent exchange with ethylene glycol (EG). The EG-mediated supercooling technique ensures the polymer homogeneity and structure integrity and induces the PVA chains to aggregate and form high-density hydrogen bonds, leading to a uniformly distributed, interconnected PVA network with high crystallinity. The process is further strengthened by EG-enabled wet annealing, which promotes the formation of densely packed crystalline domains within the polymer network. This rigorous process yields PVA hydrogels with superior mechanical properties, including a tensile strength of 13.65 MPa and a fracture toughness of 35.39 MJ m-3, alongside remarkable water content nearing 80%. These advances not only surpass the capabilities of conventional hydrogels but also broaden their application potential, highlighting the innovative integration of supercooling principles in polymer science.

Probing variation of the structure and electrical conductivity of functionalized PVA based composite films doped with silver nanoparticles and irradiated by gamma rays

Polyvinyl alcohol/sulfuric acid/ethanol films doped with nano-silver particles are prepared using in-situ chemical reduction method. The as-prepared films are irradiated with gamma rays at dose range 0–50 kGy. The elemental analysis of as-prepared samples using energy dispersive x-ray spectroscopy (EDXS) showed presence of oxygen and silver peaks which refers to the probable formation of silver oxide nano-particle (Ag2O NPs) phase. Moreover, scanning electron microscope (SEM) analysis confirmed that the inserted Ag nanoparticles have regular and uniformly distributed pores within the PVA network. X-ray diffraction (XRD) measurements indicated that of Ag2O and Ag nanoparticles are embedded in the PVA matrix in cubic face-centered structure. Structural variations due to gamma irradiation are also probed by high-resolution transmission electron microscopy (HR-TEM) which displayed that the diameter of encapsulated Ag nanoparticles increases from ∼15 nm up to 34 nm against irradiation dose. The measured dc electrical conductivity results indicated that the thermal activation energy decreased from 0.95 eV to 0.56 eV as a sequence of irradiation dose in the range 0–50 kGy The evaluation of the frequency exponent factor, s, derived from the measured ac conductivity data indicated that correlated barrier hopping (CBH) is the most probable conduction mechanism for the present films. The measured dielectric constants and Cole-Cole diagrams are employed in the analysis of the dependence of the dielectric constant on the irradiation dose.

Maleic acid crosslinked starch/polyvinyl alcohol blend films with improved barrier properties for packaging applications

Incorporating starch, which is a potential biodegradable substitute for petroleum-based polymers, into conventional polymers is challenging owing to limitations in processability and weak-performing resulting materials. Herein, corn starch/polyvinyl alcohol (PVA) blend films (starch: PVA ratio of 50:50) were prepared via the solvent casting method using glycerol as a plasticizer and with varying concentrations of maleic acid as the crosslinking agent. Fourier transform infrared spectroscopy revealed the molecular interactions of the maleic acid crosslinker with the polymeric network of starch and PVA through an ester linkage. The properties of the films were strongly dependent on the maleic acid concentration. An increasing maleic acid concentration imparted hydrophobicity to the film; therefore, water swelling was significantly reduced, and water resistance was enhanced. The film containing 20 wt% maleic acid exhibited excellent barrier properties, with the lowest oxygen and water vapor transmission rates of 0.5 ± 0.2 cc/m2⋅day and 232.3 ± 5.4 g/m2⋅day, respectively. Moreover, the mechanical properties of the film improved with increasing crosslinking. This study demonstrates that the addition of maleic acid leads to an improvement in the overall performance of starch/PVA blend films. Therefore, maleic acid-crosslinked films can be used as barrier materials in food packaging applications.

Thermally stable, mechanically strong, easily biodegradable and water-resistant Poly(vinyl alcohol) composites crosslinked by supported crosslinker

Water-resistant Poly(vinyl alcohol) (PVA) materials integrated with excellent mechanical strength and simultaneously high thermal stability would be of great use in many fields, however their fabrication has been proven to be a big challenge. Here, the concept of supported crosslinker for PVA crosslinking was proposed and prepared by using halloysite nanotubes (HNTs) as supporter and reactive 3-glycidyloxypropyltrimethoxysilane (KH560) grafted on HNTs surface as crosslinker. The resultant PVA composites (c-PVA/HNTs-s-560) crosslinked with supported crosslinker (HNTs-s-560) shows high tensile strength (which is 20% higher than PVA composites with physically blended HNTs-s-560 (PVA/HNTs-s-560) and 40% higher than pure PVA) and excellent thermal stability (the maximum decomposition temperature is 21 °C higher than that of PVA/HNTs-s-560). Moreover, c-PVA/HNTs-s-560 has higher weight loss after soil burial tests for 90 days and higher tensile strength (110%) after immersion in water at room temperature for 15 days than that of PVA/HNTs-s-560, indicating the easy biodegradability and excellent water resistance of c-PVA/HNTs-s-560. The smart design of making mechanically strong and thermally stable inorganic nanofiller as building blocks of the crosslinked PVA network using a supported crosslinker is responsible for the excellent comprehensive performance of c-PVA/HNTs-s-560 and this work may open an avenue toward the development of PVA-based smart materials.

Porous polypyrrole Nanotube-Based Organohydrogels: Versatile materials for robust electromagnetic interference shielding in harsh environments

Wearable and multi-functional electromagnetic interference (EMI) shielding materials are an inevitable trend in order to cope with increasingly complex practical applications. In the present work, polypyrrole nanotube (PNT)-based organohydrogels (POGs) with excellent electromagnetic shielding effectiveness (SE) were synthesized through a facile sol–gel strategy. The obtained POGs offer distinct shielding performance, anti-drying, anti-freezing, plasticity and recyclable ability. The POG with a 20 wt% PNTs filling exhibits a SET of 63.6 dB in the X-band at a thickness of 2.0 mm. After being placed at ambient temperature for 30 days and − 40 ℃ for 4 h, its SE values still retained at 50.3 dB and 59.3 dB, respectively. Moreover, after being immersed in the solvents, the POG (left in the air for 30 days) can recover flexibility and 92 % of its original EMI shielding performance. Importantly, crushing the fully dried organohydrogels into the powder and placing it again in the solvents fully restores its flexibility and EMI shielding properties. The glorious shielding and mechanical characteristics can be ascribed to the superior conductivity of PNTs and the highly crosslinked stable network of PVA, as well as the further enhancement of the crosslinked network by cellulose nanofibers. In addition, ​sensors based on POGs can effectively detect human movement and strain deformations. This work thus provides fresh insight into exploring the sustainability of flexible and wearable EMI shielding materials for handling extreme environments.

Effects of glycerol and PVA on gelatin/Gum Arabic aerogels: Microstructure, mechanical properties, and applications for food monitoring

Smart labels are a hot research topic in the field of food science, but the low sensitivity of film smart labels limits the on-site and visual detection of seafood freshness. To address these challenges, betacyanin (BET) as a response signal and an aerogel smart label based on gelatin/gum arabic (Gel/GA) were designed. The labels produced a visually observable color change in the presence of volatile ammonia (2500 ppm) and displayed an immediate colorimetric response to food spoilage when packaged shrimp was used as an example. The results showed that the smart aerogel labels were better than the film smart labels in the response sensitivity test of volatile ammonia. In addition, the addition of a small amount of plasticizers (glycerol) or hardeners (polyvinyl alcohol, PVA) further enhanced the responsiveness of the aerogel to volatile ammonia. Notably, the addition of a small amount of PVA further increased the hardness of the aerogels. The scanning electron microscopy (SEM), infrared spectroscopy, and X-ray diffraction (XRD) results showed that these results may be caused by the interpenetration of the PVA network and the Gel/GA network to form a new type of interpenetrating polymer network structure. Therefore, the developed smart aerogel labels play an important role in ensuring food quality and reducing food waste and inspire new ideas for the development of additional functional smart labels.

A dual physical crosslinking starch-based hydrogel exhibiting high strength, fatigue resistance, excellent biocompatibility, and biodegradability.

Simultaneous realization of high strength, toughness, and fatigue resistance in natural starch-based hydrogel materials is challenging. A facile method of in situ self-assembly and a freeze-thaw cycle was proposed to construct double-network nanocomposite hydrogels of debranched corn starch/polyvinyl alcohol (Gels). Rheology, chemical structure, microstructure, and mechanical property of Gels were investigated. Notably, short linear starch chains were self-assembled into nanoparticles and subsequently into 3D microaggregates, which were tightly wrapped by starch and PVA network. Compared with corn starch single-network and starch/PVA double-network hydrogels, the Gels reached up to a higher compressive strength (ca. 1095.7kPa), and then achieved to ∼20-30-fold improvement in compressive strength. Recovery efficiency exceeded 85% after 20 successive compression loading-unloading cycle tests. Furthermore, the Gels had good biocompatibility to L929 cells. Hence, the high-performance starch hydrogels are thought to serve as a biodegradable and biocompatible material to replace synthetic hydrogels, which can broaden their application fields.

Effect of Composition and Freeze-Thaw on the Network Structure, Porosity and Mechanical Properties of Polyvinyl-Alcohol/Chitosan Hydrogels.

We report the synthesis and characterization of poly (vinyl alcohol) (PVA)/Chitosan (CT) cryogels for applications involving the uptake and entrapment of particulate and bacterial colonies. In particular, we systematically investigated the network and pore structures of the gels as a function of CT content and for different freeze-thaw times, combining Small Angle X-Ray Scattering (SAXS), Scanning Electron Microscopy (SEM), and confocal microscopy. The nanoscale analysis obtained from SAXS shows that while the characteristic correlation length of the network is poorly affected by composition and freeze-thaw time, the characteristic size of heterogeneities associated with PVA crystallites decreases with CT content. SEM investigation evidences a transition to a more homogeneous network structure induced by the incorporation of CT that progressively builds a secondary network around the one formed by PVA. A detailed analysis of confocal microscopy image stacks allows to characterize the 3D porosity of the samples, revealing a significantly asymmetric shape of the pores. While the average volume of single pores increases with increasing CT content, the overall porosity remains almost unchanged as a result of the suppression of smaller pores in the PVA network with the progressive incorporation of the more homogeneous CT network. Increasing the freezing time in the FT cycles also results in a decrease of porosity, which can be associated with a growth in the crosslinking of the network due to PVA crystallization. The linear viscoelastic moduli measured by oscillatory rheology show a qualitatively comparable frequency-dependent response in all cases, with a moderate reduction with increasing CT content. This is attributed to changes in the structure of the strands of the PVA network.

Nanocomposite hydrogels flexible sensors with functional cellulose nanocrystals for monitoring human motion and lactate in sweat

Cellulose nanocrystals (CNCs) are envisioned as superior building blocks for the manufacture of green functional materials and show great potential in flexible electronics. However, the development of a new generation of sensors with the ability to monitor human motion and sweat composition in an integrated manner holds significant promise. In this manuscript, an executable strategy was provided to construct the flexible sensors both for human motion monitoring and sweat sensing detection. The biocompatible, stretchable and self-healing hydrogels were proposed by introducing CNCs modified by polydopamine (PDA) and gold nanoparticles (AuNPs) into the poly (vinyl alcohol) PVA network, which provided enhanced conductivity and mechanical strength. The prepared hydrogels strain sensors displayed a high gauge factor (GF = 0.99) and fast response (160 ms). In addition, taking lactate oxidase (LOx) as a model enzyme, the obtained sweat sensors exhibited a low detection limit (0.31 mM) and an excellent linear correlation (0.9987) in a range of 0.5– 30 mM. The multifunctional sensing strategy provides a new and convenient approach to enable the sensitive detection of multiple components in sweat, as well as small or large human motion monitoring in the near future.

Engineered Highly Porous Polyvinyl Alcohol Hydrogels with Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and Graphene Nanosheets for Musculoskeletal Tissue Engineering: Morphology, Water Sorption, Thermal, Mechanical, Electrical Properties, and Biocompatibility.

Electroactive composite materials are very promising for musculoskeletal tissue engineering because they can be applied in combination with electrostimulation. In this context, novel graphene-based poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/polyvinyl alcohol (PHBV/PVA) semi-interpenetrated networks (semi-IPN) hydrogels were engineered with low amounts of graphene (G) nanosheets dispersed within the polymer matrix to endow them with electroactive properties. The nanohybrid hydrogels, obtained by applying a hybrid solvent casting-freeze-drying method, show an interconnected porous structure and a high water-absorption capacity (swelling degree > 1200%). The thermal characterization indicates that the structure presents microphase separation, with PHBV microdomains located between the PVA network. The PHBV chains located in the microdomains are able to crystallize; even more after the addition of G nanosheets, which act as a nucleating agent. Thermogravimetric analysis indicates that the degradation profile of the semi-IPN is located between those of the neat components, with an improved thermal stability at high temperatures (>450 °C) after the addition of G nanosheets. The mechanical (complex modulus) and electrical properties (surface conductivity) significantly increase in the nanohybrid hydrogels with 0.2% of G nanosheets. Nevertheless, when the amount of G nanoparticles increases fourfold (0.8%), the mechanical properties diminish and the electrical conductivity does not increase proportionally, suggesting the presence of G aggregates. The biological assessment (C2C12 murine myoblasts) indicates a good biocompatibility and proliferative behavior. These results reveal a new conductive and biocompatible semi-IPN with remarkable values of electrical conductivity and ability to induce myoblast proliferation, indicating its great potential for musculoskeletal tissue engineering.

Highly conductive and tough double‐network hydrogels for smart electronics

AbstractDevelopment and understanding of highly mechanically robust and electronically conducting hydrogels are extremely important for ever‐increasing energy‐based applications. Conventional mixing/blending of conductive additives with hydrophilic polymer network prevents both high mechanical strength and electronic conductivity to be presented in polymer hydrogels. Here, we proposed a double‐network (DN) engineering strategy to fabricate PVA/PPy DN hydrogels, consisting of a conductive PPy‐PA network via in‐situ ultrafast gelation and a tough PVA network via a subsequent freezing/thawing process. The resultant PVA/PPy hydrogels exhibited superior mechanical and electrochemical properties, including electrical conductivity of ~6.8 S/m, mechanical strength of ~0.39 MPa, and elastic moduli of ~0.1 MPa. Upon further transformation of PVA/PPy hydrogels into supercapacitors, they demonstrated a high capacitance of ~280.7 F/g and a cycle life of 2000 galvanostatic charge/discharge cycles with over 94.3% capacity retention at the current density of 2 mA/cm2 and even subzero temperatures of −20 °C. Such enhanced mechanical performance and electronic conductivity of hydrogels are mainly stemmed from a synergistic combination of continuous electrically conductive PPy‐PA network and the two interpenetrating DN structure. This in‐situ gelation strategy is applicable to the integration of ionic‐/electrical‐conductive materials into DN hydrogels for smart‐soft electronics, beyond the most commonly used PEDOT:PSS‐based hydrogels.

High performance and multifunctional Janus bio-nanocomposite film for underwater actuators with excellent sensitivity and controllability

Stimuli-responsive materials have been increasingly explored to construct actuators and develop soft robots. Herein, one strategy via regulating lignin-containing cellulose nanofibrils (LCNF) distribution in PVA network followed by alkaline treatment (AT) and pre-stretching to fabricate bio-nanocomposite derived Janus films with stimulus response is proposed. LCNF/PVA-AT film displays obvious asymmetric structure, good mechanical properties, and water-resistance. Based on Janus structure and Hofmeister effect of PVA in salt solution, the applied pre-stretching treatment further enables the as-prepared LCNF/PVA-AT film with an excellently smart and controllable responsiveness to salt solutions. In addition, by adjusting some factors including length–width ratio of the film, salt type and concentration, the deformation degree and response/recovery time of LCNF/PVA-AT film and its based actuators can be controllably designed. The study will enrich the development of green, sustainable and biodegradable polymers derived Janus films, and expand their wide potential applications in multifunctional actuators.

Thermogalvanic hydrogel electrolyte for harvesting biothermal energy enabled by a novel redox couple of SO4/32- ions

Thermoelectric hydrogels can be used as energy conversion devices to convert low-grade heat into practical electricity for sustainable energy supply. However, current redox couple-based thermogalvanic gel electrolytes contain toxic metal elements, limiting their non-toxic and environmentally sustainable development. Here, a stretchable, flexible gel thermoelectric device is created by introducing a novel non-toxic redox couple of SO42-/SO32- for the first time, which exhibits a high Seebeck coefficient (Se) of 1.63 mV K−1 at the optimal redox couple concentration of 0.1 M. The tensile/compressive stress and deformation at break of the hydrogel electrolyte achieves a superior index due to the hybrid structure formed between PEDOT: PSS and SO42-/SO32- ion-promoted crosslinking PVA network. By subtly doping additional electrolyte ions, the gel affords a favorable ionic conductivity and thermoelectric performance. Furthermore, this PVA-SO4/32- hydrogel shows the capacity of harvesting biothermal energy for operating small electronics at body temperature. This work breaks with conventional redox couples and represents a step towards green sustainable self-powered wearables using a new redox couple with a favorable thermoelectric performance.

A robust photoswitchable dual-color fluorescent poly (vinyl alcohol) composite hydrogel constructed by photo-responsive FRET effect

Stimuli responsive fluorescence characteristics are significant in some fields, such as sensors, information encryption, and bionic camouflage. In this work, a robust poly(vinyl alcohol) (PVA) hydrogel with photoswitchable dynamic fluorescence behaviors was constructed by incorporating dual-color fluorescent nanoparticles (DCFNs). The DCFNs were composed of the spiropyran-modified β-cyclodextrin (β-CD-SP) and nitrobenzoxadiazolyl (NBD) derivatives, which could exist in the PVA network through non-covalent interaction. The SP moiety functioned as an acceptor and realized the photoisomerization to further quench or recover the fluorescence of the NBD moiety based on the fluorescence resonance energy transfer (FRET) effect. Therefore, under the irradiation of ultraviolet light (UV) or visible light (Vis), the hydrogel showed a fluorescence emission peak of merocyanine (MC) at 660 nm (red) or NBD at 550 nm (green), respectively. Additionally, the pH responsive characteristic of the MC chromophore also endowed the hydrogel with pH responsive fluorescence behaviors. Utilizing these advantages, specific patterns can be displayed on the hydrogel in dual mode through a hollowed-out photomask. The hydrogel could also be utilized as dual-color “building blocks” to construct various 2D or 3D structures. This composite hydrogel has potential application in various fields, such as sensors, optical switch, information storage, and biomimetic components.

Nanostructured fluids confined into Highly Viscous Polymeric Dispersions as cleaning tools for artifacts: A rheological, SAXS, DSC and TOF-SIMS study

The development, and the structural and mechanical characterization of an new complex system composed by an oil-in-water microemulsion (μE) embedded in a aqueous 3D Highly Viscous Polymeric Dispersion (HVPD) of poly(vinyl alcohol) (PVA) cross-linked by borax, is here presented together with its possible implications in paintings conservation. The HVPD/μE was characterized by Small Angle X-Rays Scattering (SAXS), Differential Scanning Calorimetric (DSC) and rheology to obtain information about the mutual effect of the μE and of the PVA network on both the nanostructure of the μE, and on the mechanical behavior of the system. Experimental data indicate that the nanostructure of the μE is retained even in the presence of the PVA/borax network whose mechanical properties are enhanced by the presence of the nanofluid. The effect of HVPD/μE on organic molecules thin films of varnish coatings usually used on easel paintings, was studied by Attenuated Total Reflection Fourier Transform InfraRed spectroscopy (ATR-FTIR) and Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS). The results showed that an interaction occurred leading to the extraction of the organic molecules within the HVPD/μE. The applicative consequence was that the HVPD/μE complex fluid revealed itself to be a potential, very powerful and “green” tool for selective cleaning of easel paintings affected by artificial aged coatings, with very low environmental impact and leaving no residues onto the painting surface.

Acid catalyzed cross‐linking of polyvinyl alcohol for humidifier membranes

AbstractPolyvinyl alcohol (PVA) is a hydrophilic polymer well known for good film forming properties, high water vapor permeance JW, and low nitrogen permeance. However, depending on molar mass and temperature, PVA swells strongly in water until complete dissolution. This behavior affects the usability of PVA in aqueous environments and makes cross‐linking necessary if higher structural integrity is envisaged. In this work, PVA networks are formed by thermal cross‐linking in the presence of p‐toluenesulfonic acid (TSA) and investigated in a design of experiments approach. Experimental parameters are the cross‐linking period tc, temperature ϑ and the TSA mass fraction wTSA. Cross‐linking is found to proceed via ether bond formation at all reaction conditions. Degradation is promoted especially by a combination of high wTSA, tc and ϑ. Thermal stability of the networks after preparation is strongly improved by neutralizing residual TSA. Humidification membranes with a JW of 6423 ± 63.0 gas permeation units (GPU) are fabricated by coating PVA on polyvinyliden fluoride hollow fibers and cross‐linking with TSA. Summarizing, the present study contributes to a clearer insight into the cross‐linking of PVA in presence of TSA, the thermal stability of the resulting networks and the applicability as selective membrane layers for water vapor transfer.

SILICON-CONTAINING OLIGOMERIC AZOINITIATORS IN THE SYNTHESIS OF BLOCK COPOLYMERS

A solvothermal synthetic pathway and functional polymer styabilizers was used for synthesis of fine silver structures of different architecture. Using polyvinylpyrrolidone as a stabilizer silver micronized wires with a diameter of 3,8–4,2 μm and aspect ratio of up to 30 were prepared. XRD technique was applied for qualitative determination of silver metal structures. New thermoresponse composite hydrogels with a structure of semi-IPNs were prepared from cross-linked polyvinyl alcohol, linear highly hydrophilic poly(2-ethyl-2-oxazoline) (PEtOx) and as-synthesized silver micro-sized wires. Effect of a structure and a composition of the polymer matrix, and inorganic anisotropic filler on structure arrangement of composite hydrogels were evaluated by DMA studies. A presence of linear hydrophilic PEtOx and anisotropic metal filler in PVA matrix reduces storage modulus Е’ from 275 to 222–230 MPa and increases loss modulus Е” up to 45,5 MPa at room temperature measurements that partially initiated by poor structuration ability of the composites under high solvation level of polymer matrices. Increasing temperature leads to redistribution of hydrogen bonds network and hybridization of PVA nad PEtOx macrochains and enhances energy dissipation ability of unfilled hydrogel. A filler due to conjugation with amine-functionalized PEtOx chains and its localization closed to a surface of metal supresses polymer-polymer interactions and elasticity parameters of composite matrix drops down. As a result, diffusion and permeability coefficients of composite hydrogels reaches 1,06–1,52·10–9 cm2/s and 0,83–1,09·10-9 g/(cm·s), respectively, that higher in comparison with cross-linked PVA matrices. A presence of hydrogen bonds of different energy in hydrogels provides an appearance of multiple relaxation transitions due to different macrochain mobility in a bulk of polymer matrix. Differences of temperature interval of LCTS for hydrogels were found from analysis Е”(T)/dT (62–70 °С) and Δχ(T)/dT (67–70 °С) dependencies are interrelated with kinetic pecularities of diffusion processes that are able to suppress a phase separation at the temperatures closed to LCTS. Phase inversion processes for hydrogel containing 5 % of PEtOx at LCTS are accompanied by desorption of 32–73 % of sorbate. Moreover, thermoresponsive properties of the hydrogels filled with metallic silver wires are higher than that of the unfilled semi-IPNs.

Marriage of 2D Covalent-Organic Framework and 3D Network as Stable Solar-Thermal Still for Efficient Solar Steam Generation.

In this work, a diketopyrrolopyrrole-based 2D covalent-organic framework (COF) is realized and featured with broadband optical absorption and high solar-thermal conversion performance. Moreover, a 3D hierarchical structure, referred to as COF-based hierarchical structure (COFHS), is rationally designed to achieve an enhanced photothermal conversion efficiency. In this water evaporator, diketopyrrolopyrrole is immobilized into conjugated COF to achieve enhanced light absorption, whereas a porous PVA network scaffold is utilized to support COF sheets as well as to enhance the hydrophilicity of the evaporator. Due to this structural advantage, COFHS displays a high solar-to-vapor energy conversion efficiency of 93.2%. Under 1 sun AM1.5 G irradiation, a stable water evaporation rate of 2.5kg m-2 h-1 can be achieved. As a proof-of-concept application, a water collection device prepared with the COFHS can achieve high solar-thermal water collection efficiency of 10.2L m-2 d-1 under natural solar irradiation. The good solar-thermal conversion properties and high-water evaporation rate make the COFHS a promising platform for solar-thermal water production.

In vitro biological activity of Zn substituted hydroxyapatite/ polyvinyl alcohol composite for orthopaedic applications

Zinc substituted hydroxyapatite (Zn-HAP) Ca5-xZnx(PO4)3OH (x = 0, 0.05, 0.2 and 1.0) was synthesized by hydrothermal method. Different weight ratio (30:70, 50:50 and 70:30) of polymer composite (parent HAP and Zn-HAP/PVA (poly vinyl alcohol)) were prepared by solvent casting method. The developed parent and Zn-HAP/PVA composites were characterized by XRD, FTIR and SEM-EDAX to examine the phase composition, functional groups and morphology. Porosity, swelling percentage, mechanical strength, antibacterial activity, hemocompatibility, bioactivity and cytotoxicity were studied. Increase in porosity (88.90 ± 1.20–97.25 ± 1.12 %) and mechanical strength (44.45–98.94 MPa) were observed with the increase in the wt% of Zn-HAP in the PVA network. Furthermore, In-vitro hemocompatibility assay showed that all composites were hemocompatible with less than 2% hemolytic ratio. In-vitro biomineralization of the optimized composite (Zn-HAP/PVA with 30:70 (w/w)) showed a new apatite formation on the surface of the composite after soaking in simulated body fluid (SBF) for 28 days. Further, the cytotoxicity of the optimized composite was evaluated against human osteoblast cells (HOS). Zn-HAP/PVA with 30:70 was found to have higher cell viability (p < 0.01) compared to the pure (HAP/PVA) composite.

Fabrication of hydrogels with nanoparticles as surface-enhanced Raman scattered (SERS) substrates and their application in Raman imaging

A polyvinyl alcohol–silver nanoparticle (PVA–Ag NP) hydrogel was fabricated using a simple and facile method; it was used as a substrate for surface-enhanced Raman scattering (SERS). The Ag+ ions dispersed uniformly in the PVA network were reduced by NaBH4; this process was termed dipping method. Compared with conventional SERS substrates (e.g., colloidal suspensions), the prepared PVA–Ag NP hydrogel has prominent Raman enhancement effects for crystal violet (CV), and the detection limit was 10−12 M. It could also help detect rhodamine B, methylene blue, and 4-mercaptobenzoic acid. In addition to SERS, the reliable 3D porous structure was utilized in the Raman imaging of CV at 1621 cm−1 in a nude mouse.