Ana M. Díez-Pascual

Wound Healing Bionanocomposites Based on Castor Oil Polymeric Films Reinforced with Chitosan-Modified ZnO Nanoparticles

Castor oil (CO), which is a readily available, relatively inexpensive, and environmentally benign nonedible oil, has been successfully used as matrix material to prepare biocompatible and biodegradable nanocomposite films filled with chitosan (CS)-modified ZnO nanoparticles. The biocomposites were synthesized via a simple and versatile solution mixing and casting method. The morphology, structure, thermal stability, water absorption, biodegradability, cytocompatibility, barrier, mechanical, viscoelastic, antibacterial, and wound healing properties of the films have been analyzed. FT-IR spectra were used to obtain information about the nanoparticle-matrix interactions. The thermal stability, hydrophilicity, degree of porosity, water absorption, water vapor transmission rate (WVTR), oxygen permeability (Dk), and biodegradability of the films increased with the CS-ZnO loading. The WVTR and Dk data obtained are within the range of values reported for commercial wound dressings. Tensile tests demonstrated that the nanocomposites displayed a good balance between elasticity, strength, and flexibility under both dry and simulated body fluid (SBF) environments. The flexibility increased in a moist atmosphere due to the plasticization effect of absorbed water. The nanocomposites also exhibited significantly enhanced dynamic mechanical performance (storage modulus and glass transition temperature) than neat CO under different humidity conditions. The antibacterial activity of the films against Escherichia coli, Staphylococcus aureus, and Micrococcus luteus bacteria was investigated in the presence and the absence of UV light. The biocide effect increased progressively with the CS-ZnO content and was systematically stronger against Gram-positive cells. Composites with nanoparticle loading ≤5.0 wt % exhibited very good in vitro cytocompatibility and enabled a faster wound healing than neat CO and control gauze, hence showing great potential to be applied as antibacterial wound dressings.

Nano-TiO2 Reinforced PEEK/PEI Blends as Biomaterials for Load-Bearing Implant Applications

Biocompatible ternary nanocomposites based on poly(ether ether ketone) (PEEK)/poly(ether imide) (PEI) blends reinforced with bioactive titanium dioxide (TiO2) nanoparticles were fabricated via ultrasonication followed by melt-blending. The developed biomaterials were characterized using FT-IR, SEM, XRD, DSC, TGA, and DMA. Further, their water-absorption, tensile, tribological, dielectric, and antibacterial properties were evaluated. PEI acts as a coupling agent, since it can interact both with PEEK via π-π stacking and polar interactions as well as with the nanoparticles through hydrogen bonding, as corroborated by the FT-IR spectra, which resulted in a homogeneous titania dispersion within the biopolymer blend without applying any particle surface treatment or polymer functionalization. A change from promotion to retardation in the crystallization rate of the matrix was found with increasing TiO2 concentration, while its crystalline structure remained unaltered. The nanoparticles stiffened, strengthened, and toughened the matrix simultaneously, and the optimal properties were achieved at 4.0 wt % TiO2. More interesting, the tensile properties were retained after steam sterilization in an autoclave or exposure to a simulated body fluid (SBF). The nanocomposites also displayed reduced water absorption though higher thermal stability, storage modulus, glass transition temperature, dielectric constant, and dielectric loss compared to the control blend. Further, remarkable enhancements in the tribological properties under both SBF and dry environments were attained. The nanoparticles conferred antibacterial action versus Gram-positive and Gram-negative bacteria in the presence and the absence of UV light, and the highest inhibition was attained at 4.0 wt % nanoparticle concentration. These nanocomposites are expected to be used in long-term load-bearing implant applications.

Effect of layer-by-layer confinement of polypeptides and polysaccharides onto thermoresponsive microgels: A comparative study

The confinement of polyelectrolyte multilayers of poly-L-lysine (PLL)/poly-L-glutamic acid (PGA) and chitosan (CHIT)/dextran sulfate (DEX) onto soft and porous thermoresponsive poly(N-isopropylacrylamide-co-methacrylic acid) (P(NiPAM-co-MAA)) microgel was studied by dynamic light scattering (DLS) and electrophoretic measurements. DLS demonstrates an odd-even effect in the hydrodynamic radius depending on the type of polyelectrolyte in the outermost layer and that coated microgels retain their native thermoresponsive property. Strong hysteresis is found between the swelling and deswelling processes of microgels coated with polypeptides, whilst for those coated with polysaccharides are nearly reversible. Electrophoretic mobility results indicate charge reversal after each layer deposition, which magnitude decreases with increasing number of layers. Microgels coated with polysaccharides exhibit higher mobility values. Stability studies reveal spatial and temporal reorganization of the polymer chains over several weeks. Upon increasing time, the hydrodynamic radius of polypeptide-terminated microgels decreases, whereas that of polysaccharide-terminated increases to almost the original size of the uncoated microgel. Both systems exhibit an exponential growth of the bilayer thickness with the number of deposition steps, more pronounced for microgels coated with polypeptides. Our results demonstrate the feasibility of the layer-by-layer assembly of these biopolymers onto microgels, which could have potential application for storage and release of biomolecules.

Study of Layer-by-Layer Films on Thermoresponsive Nanogels Using Temperature-Controlled Dual-Focus Fluorescence Correlation Spectroscopy

While a few studies have reported on the layer-by-layer (LbL) assembly of polyelectrolytes on soft and porous templates, none have really demonstrated direct proof that the layers are actually on the template. Thermoresponsive nanogels present challenges that render a quantitative proof of successful polyelectrolyte deposition extremely difficult. Additionally, the fate of the polyelectrolyte has never been investigated during the phase transition of the coated nanogel. Here, the auto- and cross-correlation functions of a labeled polyelectrolyte assembled via the LbL technique onto soft and porous thermoresponsive labeled nanogels using dual-focus fluorescence correlation spectroscopy (2f-FCS) are presented. Performing 2f-FCS as a function of temperature, hydrodynamic radii of nanogels coated with various numbers of layers are determined, which are found to be in excellent agreement with values obtained from dynamic light scattering. This study presents irrefutable quantitative evidence of successful LbL assembly on thermoresponsive nanogels and demonstrates that the layers are not stripped off during the phase transition of the nanogels. Forster Resonance Energy Transfer (FRET) detection also supports our findings.

Determination of riboflavin based on fluorescence quenching by graphene dispersions in polyethylene glycol

The effect of graphene (G) dispersions in a biodegradable polymer, polyethylene glycol (PEG), on the fluorescence emission of vitamin B2 (riboflavin) has been studied. The ultrasonication time and power used for the preparation of the dispersions have been optimized, and their quality has been evaluated by measuring the thickness of the G flakes and their distribution within the polymer by scanning electron microscopy (SEM), and by determining their defect content and degree of exfoliation by Raman spectroscopy. A quenching phenomenon of riboflavin fluorescence has been observed, attributed to π–π stacking interactions between the aromatic rings of the vitamin and G combined with PEG-riboflavin H-bonding interactions. The analysis of the fluorescence spectra confirms that, for mild ultrasonication conditions, the quenching becomes more effective on increasing G concentration, whilst for more intense conditions it is almost independent on the nanomaterial loading. Moreover, for a given G concentration, the fluorescence intensity increases slightly at low PEG contents, while it remains almost constant at high concentrations. The ratio data between the fluorescence intensity in the absence and in the presence of G fit to a second-order polynomial equation, suggesting a combined mechanism of static and dynamic quenching. The analytical characteristics of the fluorimetric method have been calculated for PEG aqueous solutions, for G dispersions in PEG and for the differences of intensities between them, and the best results were obtained in the presence of G. The proposed method was successfully applied to the analysis of riboflavin in multivitamin tablets, and the recoveries found in fortified samples were higher than 90%. The quenching phenomenon observed in this work could be employed for the development of new optical sensors for riboflavin determination.

Development of linseed oil–TiO2 green nanocomposites as antimicrobial coatings

This study deals with the preparation and characterization of acrylated epoxidized linseed oil (AELO) based bionanocomposites for antimicrobial coating applications. AELO was synthesized from epoxidized vegetable oils, crosslinked with an acrylic monomer, reinforced with anatase TiO2 nanoparticles and then subjected to UV irradiation to yield the cured nanocomposite coatings. The effect of TiO2 loading on the morphology, barrier, thermal, mechanical, tribological and antibacterial performance of the coatings has been comprehensively investigated. FT-IR spectra indicated the existence of strong TiO2-AELO hydrogen bonding interactions. The nanoparticles were randomly dispersed within the bioresin, significantly reducing its water absorption and gas permeability whilst increasing its thermal stability. They also promoted remarkable enhancements of both static and dynamic mechanical properties such as storage and Youngs moduli, hardness, impact resistance and glass transition temperature. Strong reductions in the coefficient of friction and the wear rate were attained in the nanocomposites with the highest TiO2 loadings. The coatings were found to display antimicrobial activity even in the absence of UV light, and the bactericidal effect against Staphylococcus aureus was higher than on Escherichia coli. Furthermore, the antimicrobial activity improved with increasing nanoparticle concentration. The use of these green nanocomposite coatings could be a suitable and inexpensive method to prevent microbial proliferation in public places, particularly in medical centers where there is higher risk of infections.

Layer-by-layer assembly of biopolyelectrolytes onto thermo/pH-responsive micro/nano-gels

This review deals with the layer-by-layer (LbL) assembly of polyelectrolyte multilayers of biopolymers, polypeptides (i.e., poly-l-lysine/poly-l-glutamic acid) and polysaccharides (i.e., chitosan/dextran sulphate/sodium alginate), onto thermo- and/or pH-responsive micro- and nano-gels such as those based on synthetic poly(N-isopropylacrylamide) (PNIPAM) and poly(acrylic acid) (PAA) or biodegradable hyaluronic acid (HA) and dextran-hydroxyethyl methacrylate (DEX-HEMA). The synthesis of the ensembles and their characterization by way of various techniques is described. The morphology, hydrodynamic size, surface charge density, bilayer thickness, stability over time and mechanical properties of the systems are discussed. Further, the mechanisms of interaction between biopolymers and gels are analysed. Results demonstrate that the structure and properties of biocompatible multilayer films can be finely tuned by confinement onto stimuli-responsive gels, which thus provides new perspectives for biomedical applications, particularly in the controlled release of biomolecules, bio-sensors, gene delivery, tissue engineering and storage.

Antimicrobial and sustainable food packaging based on poly(butylene adipate-co-terephthalate) and electrospun chitosan nanofibers

Antimicrobial packaging systems are developed to increase the shelf life of foods by inhibiting the growth of microorganisms. In this work, antimicrobial poly(butylene adipate-co-terephthalate) (PBAT) films incorporating different amounts of chitosan nanofibers (CS-NF) have been prepared via solution casting technique. Their morphology, structure, thermal stability, crystallization and melting behaviour, water absorption, hydrophilicity, barrier, migration, antibacterial, mechanical and viscoelastic properties have been investigated. Uniform films without pores were attained, as revealed by SEM, suggesting good compatibility between the matrix and nanofiller phases. Further, IR spectra demonstrated the existence of strong H-bonding interactions between PBAT and CS-NF. The nanofibers acted as nucleating agents, raising the crystallization temperature and the degree of crystallinity of the copolyester, and also increased its thermal stability and flammability. Compared to neat PBAT, the biocomposites showed higher stiffness, strength and glass transition temperatures whilst reduced ductility, oxygen and water vapour permeability. For all the nanocomposites, the migration levels in both non-polar and polar simulants were considerably below the overall limits established by the current legislation on food contact materials. The films displayed antibacterial activity against common foodborne pathogens: Gram-positive S. aureus and B. subtilis as well as Gram negative S. enteritidis and E. coli bacteria, and the biocide effect was systematically stronger against Gram-negative cells. These sustainable and biodegradable antimicrobial films meet the growing demand for green packaging from the food and beverage industry.

Recent Developments in Graphene/Polymer Nanocomposites for Application in Polymer Solar Cells

Graphene (G) and its derivatives, graphene oxide (GO) and reduced graphene oxide (rGO) have enormous potential for energy applications owing to their 2D structure, large specific surface area, high electrical and thermal conductivity, optical transparency, and huge mechanical strength combined with inherent flexibility. The combination of G-based materials with polymers leads to new nanocomposites with enhanced structural and functional properties due to synergistic effects. This review briefly summarizes recent progress in the development of G/polymer nanocomposites for use in polymer solar cells (PSCs). These nanocomposites have been explored as transparent conducting electrodes (TCEs), active layers (ALs) and interfacial layers (IFLs) of PSCs. Photovoltaic parameters, such as the open-circuit voltage (Voc), short-circuit current density (Jsc), fill factor (FF) and power-conversion efficiency (PCE) are compared for different device structures. Finally, future perspectives are discussed.

Quenching of fluorene fluorescence by single-walled carbon nanotube dispersions with surfactants: application for fluorene quantification in wastewater

AbstractThe fluorescence of fluorene in aqueous solutions of surfactants of different natures, anionic sodium dodecylsulphate (SDS), cationic cetyltrimethyl ammonium chloride (CTAC) and non-ionic polyoxyethylene-23-lauryl ether (Brij 35), as well as in single-walled carbon nanotube (SWCNT) dispersions in these surfactants, has been studied and compared. A fluorescence quenching phenomenon has been observed in the presence of SWCNT, the effect being stronger for dispersions in CTAC, related to the improved dispersion capability of this surfactant as revealed by microscopic observations and its stronger adsorption onto the SWCNT surfaces as inferred from the Raman spectra. SWCNT interact with fluorene causing a fluorescence quenching. The fluorescence intensity ratio, calculated in the absence and in the presence of SWCNT, follows the Stern-Volmer equation. For the CTAC concentration that provides the highest quenching effect, the analytical characteristics of the fluorimetric method like sensitivity, detection and quantification limits, repeatability, reproducibility and robustness have been calculated. Results demonstrate that it is possible to determine fluorene in a fortified wastewater sample in aqueous solutions of CTAC and SWCNT/CTAC dispersions, showing recoveries close to 100xa0%. The quenching effect found in this work could be useful for the development of an optical device that uses SWCNT-based receptors for fluorene detection and quantification in aqueous surfactant solutions.n Graphical abstractDistribution of fluorene between single-walled carbon nanotubes and micelles