All-printed and highly stable organic resistive switching device based on graphene quantum dots and polyvinylpyrrolidone composite

We propose all printed and highly stable organic resistive switching device (ORSD) based on graphene quantum dots (G-QDs) and polyvinylpyrrolidone (PVP) composite for non-volatile memory applications. It is fabricated by sandwiching G-QDs/PVP composite between top and bottom silver (Ag) electrodes on a flexible substrate polyethylene terephthalate (PET) at ambient conditions through a cost effective and eco-friendly electro-hydrodynamic (EHD) technique. Thickness of the active layer is measured around 97 nm. The proposed ORSD is fabricated in a 3 × 3 crossbar array. It operates switching between high resistance state (HRS) and low resistance state (LRS) with OFF/ON ratio ∼14 for more than 500 endurance cycles, and retention time for more than 30 days. The switching voltage for set/reset of the devices is ±1.8 V and the bendability down to 8 mm diameter for 1000 cycles are tested. The elemental composition and surface morphology are characterized by XPS, FE-SEM, and microscope.     

Dendrimer as nanocarrier for drug delivery

Dendrimers are novel three dimensional, hyperbranched globular nanopolymeric architectures. Attractive features like nanoscopic size, narrow polydispersity index, excellent control over molecular structure, availability of multiple functional groups at the periphery and cavities in the interior distinguish them amongst the available polymers. Applications of dendrimers in a large variety of fields have been explored. Drug delivery scientists are especially enthusiastic about possible utility of dendrimers as drug delivery tool. Terminal functionalities provide a platform for conjugation of the drug and targeting moieties. In addition, these peripheral functional groups can be employed to tailor-make the properties of dendrimers, enhancing their versatility. The present review highlights the contribution of dendrimers in the field of nanotechnology with intent to aid the researchers in exploring dendrimers in the field of drug delivery.     

液相化学还原法制备纳米银颗粒的研究

采用液相还原法,以PVP为分散剂,甲酸铵为还原剂,在30℃ AgNO3溶液高速搅拌下制备得到纳米银颗粒。采用X射线衍射（XRD）、透射电子显微镜（TEM）和紫外-可见光吸收光谱（UV-Vis）对所制备样品进行表征。当PVP 与AgNO3的质量比为2.2∶1,陈化时间24 h,得到立方块和六棱柱的银混合颗粒。     

Lonidamine Solid Dispersions: In Vitro and In Vivo Evaluation

ABSTRACT

Solid dispersions of lonidamine in PEG 4000 and PVP K 29/32 were prepared by the spray-drying method. Then, the binary systems were studied and characterized using differential scanning calorimetry, hot stage microscopy, and x-ray diffractometry. In vitro dissolution studies of the solid dispersed powders were performed to verify if any lonidamine dissolution rate or water solubility improvement occurred. In vivo tests were carried out on the solid dispersions and on the cyclodextrin inclusion complexes to verify if this lonidamine water solubility increase was really able to improve the in vivo drug plasma levels. Drug water solubility was increased by the solid dispersion formation, and the extent of increase depended on the polymer content of the powder. The greater increase of solubility corresponded to the highest content of polymer. Both the solid dispersions and the cyclodextrin complexes were able to improve the in vivo bioavailability of the lonidamine when administered per os. Particularly, the AUC of the drug plasma levels was increased from 1.5 to 1.9-fold depending on the type of carrier.     

Synthesis of highly dispersed MnOx–CeO2 nanospheres by surfactant-assisted supercritical anti-solvent (SAS) technique: The important role of the surfactant

In this work, highly dispersed mesoporous MnO_x–CeO₂ hollow nanospheres have been prepared using a surfactant-assisted supercritical anti-solvent (SAS) technique. The phase equilibria of methanol–CO₂, precursor-methanol–CO₂ and surfactant, precursor-methanol–CO₂ systems were measured to preliminarily screen suitable surfactants. The MnO_x–CeO₂ particles were characterized using N₂ adsorption/desorption, transmission electron microscopy (TEM) and X-ray diffraction (XRD). Polyvinylpyrrolidone (PVP) and poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (P123) both efficiently reduced the interconnectivity and agglomeration of MnO_x–CeO₂ particles and led to the formation of highly dispersed particles with higher specific surface areas, more uniform pores and larger pore volumes. The effects of the SAS process parameters including the surfactant to precursor mass ratio, the temperature and the pressure, on the morphology, particle size, particle size distribution, specific surface area and pore volume of the particles were also investigated. In addition, the catalytic activities of the synthesized hollow nanospheres for the low temperature denitrification (deNO_x) in the presence of NH₃ were evaluated. Over the entire experimental temperature range (100–220 °C), NO conversions of the MnO_x–CeO₂ particles prepared by introducing PVP or P123 during SAS were much higher than those for MnO_x–CeO₂ particles prepared without surfactants.     

Highly-reproducible nonvolatile memristive devices based on polyvinylpyrrolidone: Graphene quantum-dot nanocomposites

The properties of nonvolatile memristive devices (NMD) fabricated utilizing organic/inorganic hybrid nanocomposites were investigated due to their superior advantages such as mechanical flexibility, low cost, low-power consumption, simple technological process in fabrication and high reproducibility. The current-voltage (I-V) curves for the Al/polyvinylpyrrolidone (PVP): graphene quantum-dot (GQD)/indium-tin-oxide (ITO) memristive devices showed current bistability characteristics at 300 K. The window margins corresponding to the high-conductivity (ON) state and the low-conductivity (OFF) state of the devices increased with increasing concentration of the GQDs. The ON/OFF ratio of the optimized device was 1 × 10⁴, which was the largest memory margin among the devices fabricated in this research. The endurance number of ON/OFF switching was above 1 × 10² cycles, and the retention time was relatively constant, maintaining a value above 10⁴ s. The devices showed high reproducibility with the writing voltage being distributed between −0.5 and −1.5 V and the erasing voltage being distributed between 2 and 3 V. The ON state currents remained between 0.02 and 0.03 A, and the OFF state currents stayed between 10⁻⁶ and 10⁻⁴ A. The carrier transport mechanisms are illustrated by using both the results obtained by fitting the I-V curves and the energy band diagrams of the devices.     

Use of Sodium Alginate-Poly(vinyl pyrrolidone) Membranes for Pervaporation Separation of Acetone/Water Mixtures

Pervaporative separation of acetone from water at a concentration range of 0–100 wt% were studied using sodium alginate (NaAlg)/Poly vinyl pyrrolidone (PVP) membranes. Membranes were prepared in different ratios (w/w) (100/0, 95/5, 90/10, 85/15, 80/20, 75/25) of NaAlg/PVP by crosslinking with CaCl₂. Experimental studies were carried out to investigate the effects of the operating temperature, feed composition, and membrane thickness on the pervaporation performance. The optimum operating temperature, membrane thickness, NaAlg/PVP ratio, and feed composition were determined as 40°C, 70 µm, 75/25 (w/w), and 20 wt% acetone, respectively. The effect of PVP content in the membranes was investigated on pervaporation performance. The permeation rate was increased with increasing the PVP content; however, there was no appreciable change about the separation factor. The permeation rate and separation factor values were found to be in the range of 0.304–1.023 kg/m² h and 16–57, respectively. In addition, the sorption-diffusion properties of the alginate membranes were investigated at the operating temperature and the feed composition. It was found that the sorption selectivity was the dominant factor for the separation of acetone/water mixtures.     

聚乙烯吡咯烷酮的合成及其在定型剂啫喱中的应用

N-乙烯基吡咯烷酮(NVP)通过自由基溶液聚合方法合成聚乙烯基吡咯烷酮(PVP),通过调节引发剂偶氮二异丁腈(AIBN)的用量和催化剂NaHCO3溶液浓度调控PVP的质均分子量,制备出适用于定型剂啫喱所需的PVP。结果表明,当m(AIBN)∶m(NVP)为0.4%、NaHCO3溶液浓度为0.4 mol/L、聚合温度70℃、聚合时间2 h条件下,合成的PVP质均分子量为66 829;其所配制的定型剂啫喱对头发卷曲保持率为86.9%,且具有光泽度好、易清洗、不易发粘、梳理性好等性能。     

Chitosan—A versatile semi-synthetic polymer in biomedical applications

This review outlines the new developments on chitosan-based bioapplications. Over the last decade, functional biomaterials research has developed new drug delivery systems and improved scaffolds for regenerative medicine that is currently one of the most rapidly growing fields in the life sciences. The aim is to restore or replace damaged body parts or lost organs by transplanting supportive scaffolds with appropriate cells that in combination with biomolecules generate new tissue. This is a highly interdisciplinary field that encompasses polymer synthesis and modification, cell culturing, gene therapy, stem cell research, therapeutic cloning and tissue engineering. In this regard, chitosan, as a biopolymer derived macromolecular compound, has a major involvement. Chitosan is a polyelectrolyte with reactive functional groups, gel-forming capability, high adsorption capacity and biodegradability. In addition, it is innately biocompatible and non-toxic to living tissues as well as having antibacterial, antifungal and antitumor activity. These features highlight the suitability and extensive applications that chitosan has in medicine. Micro/nanoparticles and hydrogels are widely used in the design of chitosan-based therapeuticsystems. The chemical structure and relevant biological properties of chitosan for regenerative medicine have been summarized as well as the methods for the preparation of controlled drug release devices and their applications.     

在不同保护剂存在下合成纳米银线(粒子)

常温常压下、在水溶液中,在PVP、PEG、PVA、P123、吐温等不同的保护剂存在下,用二苯胺磺酸钠(DPAS)还原AgNO3(SN),制备了纳米银线(粒子),并且用X-射线衍射(XRD),扫描电镜(SEM),透射电镜(TEM)和紫外-可见光谱等手段对产物进行了表征。纳米银线(粒子)的形态特征和大小可以通过改变反应物浓度,保护剂品种、用量等条件来控制。对纳米银线的生长机理也进行了探讨。