Template and template-free preparation of one-dimensional metallic nanostructures

In this article, we have studied and developed two approaches for organizing metallic nanoparticles into one-dimensional assemblies. The first uses DNA as a ‘template’ and allows the preparation of various silver nanostructures (‘beads-on-a-string’ or rod-like wires). The conductance of such nanostructures was demonstrated by employing a powerful technique, Electrostatic Force Microscopy (EFM). This technique gave us ‘contactless’ information about the electrical properties of silver nanostructures, aligned on a SiO₂/Si surface. Additionally, I–V characteristics of a single silver nanowire crossing two microelectrodes were recorded. The nanowire resistivity was estimated at 1.46 × 10⁻⁷ Ω m (at 300 K), which is one order of magnitude higher than that of bulk silver (1.6 × 10⁻⁸ Ω m). The second approach is a ‘template-free’ one, and exploits the binding ability of l-arginine, which favours the self-assembling of capped gold nanoparticles into gold nanochains. The results suggest that gold nanochains were formed due to dipole–dipole interaction between adjacent nanoparticles, which fuse together through an oriented attachment mechanism. Atomic force microscopy, TEM, UV–vis spectroscopy and X-ray diffraction were used to characterize the morphological, optical and structural properties of these metallic nanostructures.     

pH- and temperature-sensitive polymeric microspheres for drug delivery: the dissolution of copolymers modulates drug release

Most pH-/temperature-responsive polymers for controlled release of drugs are used as cross-linked hydrogels. However, the solubility properties of the linear polymers below and above the lower critical solution temperature (LCST) are not exploited. Here, the preparation and characterization of poly (N-isopropylacrylamide-co-methacrylic acid-co-methyl methacrylate) (poly (NIPAAm-co-MA-co-MM)) and poly (N-isopropylacrylamide-co-acrylamide) (poly (NIPAAm-co-AAm)), known as “smart” polymers (SP), is reported. Both poly (NIPAAm-co-MA-co-MM) and poly (NIPAAm-co-AAm) display pH- and temperature-responsive properties. Poly (NIPAAm-co-MA-co-MM) was designed to be insoluble in the gastric fluid (pH = 1.2), but soluble in the intestinal fluid (pH = 6.8 and 7.4), at the body temperature (37°C). Poly (NIPAAm-co-AAm) was designed to have a lower critical solution temperature (LCST) corresponding to 37°C at pH = 7.4, therefore it is not soluble above the LCST. The solubility characteristics of these copolymers were exploited to modulate the rate of release of drugs by changing pH and/or temperature. These copolymers were solubilized with hydrophobic cellulose acetate butyrate (CAB) and vitamin B₁₂ (taken as a water soluble drug model system) in an acetone/methanol mixture and dispersed in mineral oil. By a progressive evaporation of the solvent, the liquid droplets were transformed into loaded CAB/SP microspheres. Differential scanning calorimetric studies and scanning electron microscopy analysis demonstrated that the polymeric components of the microspheres precipitated separately during solvent evaporation forming small microdomains. Moreover, vitamin B₁₂ was found to be molecularly dispersed in both microdomains with no specific affinity for any polymeric component of microspheres. The release of vitamin B₁₂ was investigated as a function of temperature, pH, and the CAB/SP ratio.     

Investigation of carbon nanofibers as support for bioactive substances

In this paper we have studied the adsorption properties of various bio-active systems onto the surface of carbon nanofibers (CNF) synthesized by chemical vapor deposition (CVD). Amino acids (alanine, aspartic acid, glutamic acid) and glucose oxidase (GOx) were adsorbed on CNF and the results were compared with those obtained when activated carbon (AC) was used as support. CNF and AC properties (hydrophilic or hydrophobic properties) were characterized by the pH value, the concentration of acidic/basic sites and by naphthalene adsorption. CNF with immobilized GOx was additionally investigated as a highly sensitive glucose biosensor. An amperometric method was used in an original manner to detect the changes in the specific activity of GOx, immobilized longer time on CNF. The method demonstrates that not the whole enzyme adsorbed onto CNF can catalyze the oxidation of glucose from the solution.     

A comparison of two- and four-electrode techniques to characterize blood impedance for the frequency range of 100 Hz to 100 MHz

Measurement setups that characterize the impedance of suspensions of blood over the wide frequency range of 100 Hz to 100 MHz are presented in this paper. The performance of the two- and four-electrode techniques have been compared and evaluated. By applying a combination of the two measurement techniques the best result is achieved when taking into account the main nonidealities, such as electrode polarization impedance and parasitic capacitances. It has been found that the conventional three-element model for the impedance of blood can be used for frequencies up to 1 MHz. For frequencies exceeding 1 MHz, an extended model is introduced where a constant phase angle element is used for modeling the cell membrane and a capacitor C(liq) is added for modeling the electrical capacitance of water in blood.     

UV light copolymerization of dimethyl vinylphosphonate with bisphenol A ethoxylate dimethacrylate

Dimethyl vinylphosphonate (DMVP), a very promising monomer, was copolymerized with acrylic monomer bisphenol A ethoxylate dimethacrylate (BEMA), in different molar ratios, by radical photoinitiated polymerization in the presence of photoinitiator Darocur 4265 (3 wt%) and in the absence of solvent. The UV light polymerization was an efficient method to obtain polymers in a green procedure. The molar ratio between DMVP and acrylic monomer BEMA varied between 1:1 and 5:1. The copolymers were characterized by FTIR, thermal analysis, water uptake and conductivity. From the ATR-FTIR spectra of DMVP-BEMA copolymers at the molar ratios of 1:1–5:1, it was observed that the intensity of P-O-C aliphatic band increased with increases in DMVP content. The synthesized copolymers showed good thermal stability in the range of 335–390 °C. DMVP:BEMA copolymer at 1:1 molar ratio displayed the highest stability, with decomposition temperature above 390 °C, the highest temperature in the series. The water uptake decreased with increases in DMVP content and this behavior was correlated with the ionic conductivity. Based on the Bode diagrams, the ionic conductivity of DMVP:BEMA of 1:1 molar ratio was 6.15 × 10^?8 S cm^?1 and that of DMVP:BEMA of 2:1 molar ratio was 3.69 × 10^?8 S cm^?1 which were considered promising as valuable conducting materials.     

Comparative analysis of the processes of collagen concentration by ultrafiltration using different types of membranes

Tangential flow filtration of the collagen protein solutions with a molecular weight 12, 14, and 24 kDa is investigated using flat sheet membranes. The effects of tangential ultrafiltration (UF) on the permeate properties using two regenerated celluloses (RCs) and two polyethersulfone (PES) membranes with molecular weight cut-off (MWCO) of 5 and 10 kDa are reported. The permeate and concentrate obtained in the UF experiments are characterized from a physical–chemical point of view by determining the temperature, pH, electrical conductivity, nitrogen content, and protein concentration. In addition, the experimental data are modeled using Hermia's model. The UF experiments demonstrated that permeate flux declined with increasing molecular weight of collagen at constant concentration (1%). Regardless of the molecular weight of collagen, the rejections decrease in the following order: PES 5 kDa > RC5kDa > RC10kDa > PES10kDa. In case of membrane with higher MWCO, the clogging phenomenon is mainly due to the blockage of the internal pores of the membrane than the formation of a polarization layer. Morphologies and characteristics of the membranes are characterized using scanning electron microscopy.     

In vitro study of BSA gel/polyelectrolite complexes core shell microcapsules encapsulating doxorubicin for antitumoral targeted treatment

Abstract

The aim of this study is to develop core shell microcapsules of bovine serum albumin (BSA) gel with a complex polyelectrolite multilayer shell of natural polysaccharides with opposite charges, pectin (P), chitosan (Chi), and hyaluronic acid (HA) respectively, encapsulating Doxorubicin (Dox) as a carrier for targeted anti-tumoral treatment of hepatic cell carcinoma (HCC). A sacrificial CaCO₃ template method was used in order to obtain microcapsules with a BSA gel core and a layer-by-layer (Lbl) deposition technique of polyelectrolite complexes formed between P/Chi in the inner layers and HA/Chi in the outer shell layers. The preformed microcapsules, BSA gel/P/Chi/HA, noted as ms, have been applied for Dox encapsulation (ms-Dox). Dox encapsulation and release in different pH media were studied in order to elucidate the interactions between pH dependently charged species involved in the Dox loading/releasing processes. The structure characterization of ms/ms-Dox was evaluated by FTIR and UV-Vis spectroscopy, X-ray diffraction, thermal analy sis, optical microscopy, confocal laser scanning microscopy, and scanning electron microscopy. The in vitro study for citotoxicity assessment on normal and tumoral cells of both ms and ms-Dox was performed using mesenchymal stem cells (MSCs) and Hep2G HCC cell lines. Results of physical-chemical analyses confirm the successful encapsulation of Dox in ms, and the in vitro biological study recommends ms-Dox as a candidate for future in vivo research as a targeted anti-tumoral treatment modality applications.     

Formation of CoFe2O4/PVA-SiO2 nanocomposites: Effect of diol chain length on the structure and magnetic properties

The paper presents the influence of diol (1,2-ethanediol, 1,2-propanediol, 1,3-propanediol and 1,4-butanediol) on the formation of magnetic crystalline cobalt ferrite embedded in polyvinyl alcohol-silica hybrid matrix at 200?°C. Formation of crystalline oxides (CoFe₂O₄, Co₃O₄ and Co₂SiO₄) was studied by X-ray diffraction and Fourier transformed infrared spectroscopy. The effect of annealing temperature and diol chain length on the cobalt ferrite nanocrystallites size was investigated. Using transmission electron microscopy, the size and shape of particles obtained at 200?°C were recorded and compared to those obtained by annealing at 500, 800 and 1100?°C. The saturation magnetization (M_s) and coercive field were calculated from the magnetic hysteresis loops of nanocomposites. The M_s was influenced by the particle size and crystallinity only for nanocomposites annealed at 800 and 1100?°C, when the magnetic domains started to form and to be larger than the critical particle size. The diols used in the synthesis influence both the oxidic phase formation and its properties.     

Kinetic studies on the irinotecan release based on structural properties of functionalized mesoporous-silica supports

Building a detailed kinetic model for the drug release from an ordered mesoporous support is a difficult task due to various physico-chemical processes involved, including complex adsorption-desorption and diffusion steps. A compartmented mechanistic model for the drug release from a silica mesoporous (functionalized) support is elaborated to correlate the experimental drug release data under various release conditions. The identified model parameters are interpreted in relationship to the delivery system characteristics (drug, support, and linker properties) to be used for designing a system with a controlled release. Extended model predictions are compared with those of various semi-empirical or overall diffusion models in terms of quality (adequacy, validity, reliability) and parameter significance to determine the information loss when simplified models are used for design purposes. Exemplification is made for the release of irinotecan from a MCM-41 support unfunctionalized vs. functionalized with 3-aminopropyl triethoxysilane or triethoxyvinylsilane in a synthetic intestinal fluid.