Zorica Kačarević-Popović

Bioreactor validation and biocompatibility of Ag/poly(N-vinyl-2-pyrrolidone) hydrogel nanocomposites

Silver/poly(N-vinyl-2-pyrrolidone) (Ag/PVP) nanocomposites containing Ag nanoparticles at different concentrations were synthesized using γ-irradiation. Cytotoxicity of the obtained nanocomposites was determined by MTT assay in monolayer cultures of normal human immunocompetent peripheral blood mononuclear cells (PBMC) that were either non-stimulated or stimulated to proliferate by mitogen phytohemagglutinin (PHA), as well as in human cervix adenocarcinoma cell (HeLa) cultures. Silver release kinetics and mechanical properties of nanocomposites were investigated under bioreactor conditions in the simulated body fluid (SBF) at 37°C. The release of silver was monitored under static conditions, and in two types of bioreactors: perfusion bioreactors and a bioreactor with dynamic compression coupled with SBF perfusion simulating in vivo conditions in articular cartilage. Ag/PVP nanocomposites exhibited slight cytotoxic effects against PBMC at the estimated concentration of 0.4 μmol dm(-3), with negligible variations observed amongst different cell cultures investigated. Studies of the silver release kinetics indicated internal diffusion as the rate limiting step, determined by statistically comparable results obtained at all investigated conditions. However, silver release rate was slightly higher in the bioreactor with dynamic compression coupled with SBF perfusion as compared to the other two systems indicating the influence of dynamic compression. Modelling of silver release kinetics revealed potentials for optimization of Ag/PVP nanocomposites for particular applications as wound dressings or soft tissue implants.

On the Use of Radiation Technology for Nanoscale Engineering of Silver/Hydrogel Based Nanocomposites for Potential Biomedical Application

For nanoscience to become true nanotechnology, there is a need for breakthroughs in the engineering science of processing and manufacturing at the nanoscale. The radiation technology may offer a novel approaches to solving the problems of placement, high throughput, as well as integration across multiple length scales. Furthermore, there are critical needs for advanced materials in the area of biomaterial engineering, primarily in generating biomaterials of enhanced specific functionalities, which can be achieved by introduction of proper functionalities at the nanoscale dimensions. The radiation techniques are uniquely suited for such task, due to their favorable characteristics and in most cases not possible by other methods of synthesis. Therefore, we are systematically developing novel synthetic strategies for incorporation of noble metal nanoparticles in hydrogel networks by gamma irradiation, for possible biomedical application, using liquid filled cavities in hydrogels as nanoreactors (template synthesis). The radiation process has various advantages, such as easy process control, the possibility of joining synthesis and sterilization in one technological step. The radiation technique does not require any extra substances, and does not need any further purification. On the other hand, in recent years nanoscale antibacterial materials, such as nanocrystalline silver, as novel antimicrobial species have been seen as promising candidates for application owing to their high surface to volume ratio and their novel physical and chemical properties on the nanoscale level. Silver can be safely used even for patients who have diseases like Diabetes Mellitus that interfere with wound healing. The recent emergence of nanotechnology has provided a new therapeutic modality in silver nanoparticles for healing wounds.

Properties of Ag/PVP Hydrogel Nanocomposite Synthesized In Situ by Gamma Irradiation

Metal nanoparticles embedded in crosslinking polymer matrices i.e. hydrogels are novel class of materials which have attracted great attention due to applications in catalysis, photonics, optic, pharmaceutics and biomedicine. This work describes novel, simple and facile radiolytic synthesis of silver nanoparticles (AgNPs) within the poly(N-vinyl-2-pyrrolidone) (PVP) hydrogel. The hydrogel matrix was previously obtained by gamma irradiation induced crosslinking, while the in situ reduction of (mathrm{Ag}^{+}) ions was performed using strongly reducing species formed under the radiolysis of water. Absorption spectrum of Ag/PVP hydrogel shows the presence of surface plasmon band with maxima at 400 nm, which confirms formation of AgNPs (diameter less than 10 nm). Swelling properties of synthesized hydrogels, neat PVP and Ag/PVP nanocomposite, were investigated in the SBF (simulated body fluid) solution at (37^{circ}mathrm{C}). Obtained results show that Ag/PVP hydrogel nanocomposite has higher equilibrium swelling compared with neat PVP hydrogel. Moreover, kinetics parameters were calculated from the swelling curves. The fluid transport mechanism is non-Fickian for both PVP and Ag/PVP hydrogels, meaning that both diffusion and polymer relaxation control the fluid transport.

Thermal properties of radiolytically synthesized PVA/Ag nanocomposites

The radiolytic method was used to synthesize two types of nanocomposites with silver, PVA/Ag by film casting and PVA hydrogel/Ag nanocomposites. This method is particularly suitable for generating metal nanoparticles in solution. The radiolytic species (solvated electrons and secondary radicals) exhibit strong reducing properties such that metal ions are reduced at each encounter. Metal atoms then tend to grow into larger clusters. It was found that solid or swollen polymers are able to stabilize small crystallites against spontaneous growth via aggregation. Using differential scanning calorimetry (DSC), the melting behavior and kinetics of the PVA/Ag nanocomposites were investigated and compared to those of pure PVA. The melting as well as crystallization behavior of polymers is crucial because it governs the thermal properties, impact resistance and stress strain properties. Understanding the melting behavior is significant not only to tailor the properties of nanocomposites but to investigate the interactions between the constituents. The DSC curves of pure PVA and prepared nanocomposites show only one melting peak between 175 and 230 °C, indicating that the melting behavior of these two systems are analogous. In both cases, with increasing heating rate, the melting peak shifts to a higher temperature, but with increasing Ag content the peak melting temperature is lower. When specimens are heated at high heating rate, the motion of PVA molecular chains cannot follow the heating temperature on time due to the influence of heat hysteresis, which leads to a higher peak melting temperature. When Ag nanoparticles are added they increase the heat transfer among the PVA molecular chains decreasing the melting temperature. The Ag content is a major factor affecting the degree of crystallinity. It was observed that at low nanofiller content, up to the 0.5 wt%, the degree of crystallinity of the nanocomposites increased, while at a higher content the crystallization was retarded. The half time of melting is non-linearly dependent on the amount of nanofiller. In the range from 0.25 to 1 wt% Ag it slightly increases, because at a low Ag content the nanoparticles act as a heterogeneous nucleation agent during the crystallization process. For large amounts of nanofiller, the half time of melting is markedly higher than for pure PVA. At a higher Ag content, the nanoparticles act as a barrier that restricts the thermal motion of PVA molecular chains and the half time of complete melting increases. The significantly lower melting activation energy of the nanocomposites with high amount of nanofiller compared to pure PVA, calculated by the Kissinger method, indicated that nanoparticles reduced the heat barrier for the melting process. .

Nanocomposite Hydrogels Obtained by Gamma Irradiation

During the past decades hydrogels have gained considerable interest and reviewed from different points of view, because of their unique properties. The hydrogel 3D structure, porosity, swelling behavior, stability, gel strength, as well as biodegradability, nontoxicity, and biocompatibility are properties which are widely variable and easily adjusted, making them suitable for many versatile applications, especially in the field of medicine and biotechnology. Generally, hydrogels possess the huge potential to be used as a matrix for incorporation of different types of nanoparticles. Namely, hydrogels in the swollen state provide free space between cross-linked polymer chains, in which the nucleation and A. Radosavljević (*) · J. Spasojević · J. Krstić · Z. Kačarević-Popović Laboratory for Radiation Chemistry and Physics, Vinča Institute of Nuclear Sciences, University of Belgrade, Belgrade, Serbia e-mail: krkljes@vin.bg.ac.rs # Springer International Publishing AG, part of Springer Nature 2018 Md. I. H. Mondal (ed.), Cellulose-Based Superabsorbent Hydrogels, Polymers and Polymeric Composites: A Reference Series, https://doi.org/10.1007/978-3-319-76573-0_21-1 1 growth of nanoparticles occurs. In this way, the carrier-hydrogel system acts as a nanoreactor that also immobilizes nanoparticles and provides easy handling with obtained hydrogel nanocomposites. It is well known that the properties of nanocomposite materials are dependent on the method of synthesis. Among various techniques, the radiation-induced synthesis offers a number of advantages over the conventional physical and chemical methods. Radiolytic method is a highly suitable way for formation of three-dimensional polymer network, i.e., hydrogels, as well as for generation of nanoparticles in a solution (especially metal nanoparticles). This method provides fast, easy, and clean synthesis of hydrogel nanocomposites. Moreover, and probably the most important from the biomedical point of view, is the possibility of simultaneous formation of nanocomposite hydrogel and its sterilization in one technological step. Despite all the mentioned advantages of radiolytic method, there are not so many investigations related to nanocomposite materials based on nanoparticles incorporated in a hydrogel matrix.

Flexible and high-efficiency Sb2S3/solid carrier solar cell at low light intensity

Producing green and efficient energy sources is a major challenge. As a consequence, the use of photovoltaic devices for conversion of light into electricity is growing worldwide. A lot of effort had been invested to create high-efficient solar cells, but their durability, stability, flexibility and efficiency at low light intensities are still unexplored. Here, we built a flexible solar cell made of p-doped, amorphized a-undoped and n-doped Sb2S3 solid carrier loaded with electrolyte. Indium tin oxide glass was the working electrode, and aluminium was the counter electrode. Every (p–a–n) flexible Sb2S3/solid carrier layers were obtained using a cheap casting/solvent evaporation technique, from a blend consisted of chitosan, polyethylene glycol and electrolyte containing 0.5xa0M potassium iodide and 0.05xa0M iodine, and corresponding synthesized amorphized a-undoped and p and n-doped Sb2S3 semiconductor. Results show that flexible Sb2S3 solar cell possesses good stability and efficiency ofxa0about 10% at 5% sun. Overall, our findings demonstrate for the first time that flexible solar cell can be made and used for low light intensity applications.

Electroanalytical Sensing of Bromides Using Radiolytically Synthesized Silver Nanoparticle Electrocatalysts

Monitoring bromides (Br−) is of crucial importance since bromates, potential human carcinogens, are formed during ozonation of water containing bromides in concentrations >100u2009μgu2009L−1. Within this study, silver (Ag) and four carbon-supported Ag catalysts were synthesized by the γ-radiation method and their morphology and structure examined using transmission electron microscopy, X–ray diffraction, and UV-Vis analysis. The nanocatalysts were tested for Br− sensing in aqueous media using cyclic voltammetry. All five Ag materials exhibited electroactivity for sensing of Br− ions, with pure Ag catalyst giving the best response to Br− ions presence in terms of the lowest limit of detection. Sensing of bromides was also explored in tap water after addition of bromides suggesting that herein prepared catalysts could be used for bromides detection in real samples. Furthermore, sensing of other halogen ions, namely, chlorides and iodides, was examined, and response due to chloride presence was recorded.

Radiolytic synthesis and characterization of PVA and chitosan based conductive polymer membranes for alkaline fuel cells

Poly(vinyl alcohol) (PVA) and chitosan (CS) based polymer membranes for alkaline fuel cells were synthesized by gamma irradiation method. They were swollen with 6 M KOH solution and their ionic conductivity and gas permeance were investigated as a function of temperature. They show high ionic conductivities at room temperature, which wasnt reduced over a period of few months. No gas flow through membranes was detected at any temperature and pressure. These properties show that the membranes could be potentially applied in alkaline fuel cells.

Silver/poly(N-vinyl-2-pyrrolidone) nanocomposites obtained by the electrochemical synthesis

Silver/poly(N-vinyl-2-pyrrolidone) (Ag/PVP) nanocomposites were obtained by n electrochemical reduction of Ag+ ions at a constant voltage, by the in situ n synthesis of silver nanoparticles inside poly(N-vinyl-2-pyrrolidone) matrix, n previously crosslinked by γ-irradiation. Optimal values of synthesis n parameters were investigated: the composition of the solution for swelling of n PVP hydrogel, implementation time and applied voltage. Ag/PVP nanocomposites n were characterized by UV-visible spectroscopy, and IR spectroscopy. n UV-visible spectroscopy results shown that the reduction of silver ions was n more efficient when the more conductive solution for swelling of PVP hydrogel n was used, i.e. the solution containing 3.9 mM AgNO3 with 0.1 M KNO3. Also, it n was shown that the concentration of the reduced silver increases with the n increase in implementation time and applied voltage, up to the values of 4 n min, and 200 V, respectively. The Ag nanoparticle size was estimated to be 25 n nm, by comparison of the experimental results of UV-vis spectroscopy with the n theoretical predictions obtained by the calculations in “MiePlot v.3.4” n computer program, having the algorithm based on Mie scattering from a sphere. n The results of FTIR spectroscopy have shown that Ag nanoparticles are mainly n bonded to PVP by coordination bondages between Ag nanoparticles and N from n the pyrrolidone ring of PVP.

Corrosion behavior of duplex polyaniline/epoxy coating on mild steel in 3% NaCl

The corrosion behavior and thermal stability of epoxy coatings electrodeposited on mild steel and on mild steel with electrochemically deposited polyaniline (PANI) film were investigated by electrochemical impedance spectroscopy (EIS) and thermo gravimetric analysis (TGA). The aim of the paper was to present new findings on the corrosion protection of mild steel by a duplex PANI/-epoxy coating in 3% NaCI solution and to determine the effect of thin PANI film on the protective properties of the coating. PANI film was deposited electrochemically on mild steel from an aqueous solution of 0.5 mol dm3 sodium benzoate and 0.1 mol dm3 aniline at a constant current density of 1.5 mA cm2. Non-pigmented epoxy coatings on mild steel and on mild steel with PANI film were obtained by cathodic electrode position at constant voltage and stirring conditions. The resin concentration in the electrode position bath was 10 wt.% solid dispersion in water at pH 5.7. The applied voltage was 250 V, the temperature 26°C and the deposition time 3 min. It was shown that thin PANI film could be used to modify the surface of mild steel prior to epoxy coating deposition, due to the increased corrosion protection of a duplex PANI/epoxy coating comparing to an epoxy coating on mild steel in 3% NaCl solution.