Dan Sorin Vasilescu

Porous calcium alginate–gelatin interpenetrated matrix and its biomineralization potential

Artificial bone composites exhibit distinctive features by comparison to natural tissues, due to a lack of self-organization and intimate interaction apatite-matrix. This explains the need of “bio-inspired materials”, in which hydroxyapatite grows in contact with self-assembling natural polymers. The present work investigates the function of a rational design in the hydroxyapatite-forming potential of a common biopolymer. Gelatin modified through intrinsic interactions with calcium alginate led through freeze-drying to porous hydrogels, whose architecture, constitutive features and chemistry were investigated with respect to their role on biomineralization. The apatite-forming ability was enhanced by the porosity of the materials, while the presence of alginate-reinforced Gel elastic chains, definitely favored this phenomenon. Depending on the concentration, polysaccharide chains act as “ionic pumps” enhancing the biomineralization. The mineralization-promoting effect of the peptide-polysaccharide network strictly depends on the hydrogels structural, compositional and morphological features derived from the interaction between the above mentioned two components.

Synthesis and Characterization of Novel Azobenzene Methacrylate Monomers

New methacrylic monomers containing pendant azobenzene structures have been prepared by reacting azobenzene assemblies possessing phenolic functions with methacryloyl chloride. The most favorable synthetic routes are described together with the yields obtained. The new monomers have been purified and completely characterized by elemental analysis and melting points, as well as by recording their UV, FT-IR and NMR spectra.

Synthesis and characterization of some polymers with applications in non-linear optics II. Copolymerization of styrene with some monomers containing azo-dyes

The present work describes the evolution of binary copolymerization of a monomer containing an azoic chromophore with styrene. Reactivity ratios have been computed using several methods. The sequential analysis suggests a favourable case for the use of azoic structures in electro-optical applications.

The Effect of Silver Nanoparticles on the Collagen Secondary Structure

Attenuated Total Reflection - Fourier Transform Infrared (ATR-FTIR) spectroscopy is a label-free, non-destructive analytical technique that can be used extensively to study a wide variety of molecules in different conditions. Proteins have very complicated three dimensional structures with multi-level conformations, which are highly correlated with their biological activities. Recently, there is a significant increase of materials based on interaction between proteins and nanoparticles. The aim of this paper is to highlight the understanding of protein interaction with silver nanoparticles (AgNPs) surfaces. Information about the secondary structures of collagen with and without AgNPs was obtained from atomic force microscopy (AFM) measurements.ATR-FTIR spectroscopy was used for monitoring the changes in the secondary structures of collagen upon interaction with AgNPs. Amide I is the most sensitive band for detecting changes in the protein secondary structures. Its characteristic absorption band is located at 1600–1700 cm-1. Comparing the spectra of collagen with and without AgNPs in this region, information about the different types of secondary structures such as α-helix, β-sheets, turns and random coil can be obtained. The conjugation of AgNPs-collagen occurred mainly through electrostatic interactions. Based on these data, the effects of AgNPs stability and the conformational changes of collagen upon interaction with the AgNPs are discussed.

New side-chain azo-polymers for optical applications: synthesis and characterization

In this paper we report a series of side-chain polymers bearing a push-pull azo-moiety, from pseudo-stylbene type molecules. The azobenzene monomer is chemically incorporated through radical copolymerization in: poly(methacrylate), poly(styrene); and poly(oxazoline) matrices. The different classes of azo-polymers are discussed comparatively to one another from the point of view of: solubility, molecular weights, glass transition temperatures and thermal stability, chromophore contents, and as well as from the point of view of their spectral features.

Copolymerization of vinyl acetate with acrylic monomers in microemulsion

Abstract Composition domains corresponding to “one phase microemulsions” have been studied for the monomer mixtures consisting in vinyl acetate (VAc)–2-ethyl-hexyl acrylate (EHA) and VAc–ethyl acrylate (EtA). Maleic monoester with nonyl phenol ethoxylated with 25 mol ethylene oxide has been used as surfactant; n-propanol (n-PrOH), t-butanol (t-BuOH) and 2-ethyl-hexanol have been employed as cosurfactants. The number of microemulsions formed in the frame of the existing systems (as shown in ternary diagrams) is higher for polar monomers and cosurfactants: EtA>EHA; n-PrOH>t-BuOH. Refractometric and conductometric studies have proved the reality of three types of microemulsions: O/W, bicontinuous and W/O respectively. The homogeneous domains lessen after radical copolymerization. However, for the zone with a bicontinuous microstructure the conversion for the comonomer mixture reaches a minimum; a degradative chain transfer of the growing radicals with the cosurfactant might explain this phenomenon. It has been proved by GPC, that the concentration of unreacted surfactant increases when the concentration of the acrylic monomer increases as well.

Establishing proper scanning conditions in atomic force microscopy on polyimide and polyurethane samples and their effect on 3D surface texture parameters

Several atomic force microscopy (AFM) tests have been carried out on both smooth (polyimide) and rough (polyurethane) surfaces so that to obtain the best results; subsequently, the optimization of experiments performed is presented. A special emphasis has been put on the effect of tip geometry, image pre-processing procedure, scanning area, resolution, pixel size, and cantilever oscillation amplitude in tapping mode, as well as on the quality of the topographical images and 3D surface texture parameters. After viewing the scanning tip and finding out its sharpness, degradation, and contamination, a simultaneous calibration in X, Y, and Z directions, lateral calibration of SPM scanners and detection of lateral non-linearity, hysteresis, creep, and cross-coupling effects has been made. We have established the following experimental parameters: proper scanning resolution (512 × 512 pixels), adequate pixel size (between 2.9 and 19.5 nm) and suitable intermittent contact region (moderate tapping) for which the AFM images present good contrast and resolution. Using these parameters, the values of 3D texture parameters remain constant. These kinds of measurements are extremely important to conduct further AFM experiments on polyimide and polyurethane surfaces under optimal conditions, thus avoiding unwanted artifacts on the morphological images or unrealistic values for the 3D surface texture parameters that might occur.

Copolymerization of the Pair Maleic Anhydride‐Dicyclopentadiene: II. Kinetics at Low Conversion

Kinetic investigations regarding the copolymerization of the pair maleic anhydride (MA)–di‐cyclo‐pentadiene (DCPD) are presented. It has been shown that copolymerization takes place mainly by cross‐propagation, implying both free monomers and charge transfer complexes (CTC) as well. In this case, homo‐propagation of MA, even minor, can no longer be overlooked; termination is due to a degradative transfer. A suitable kinetic model has been devised, on this basis; the proposed model has been checked against experimental measurements.

Three-Dimensional Nanostructures with Biocidal Activity Created on a Siloxane-Containing Copolyimide Film

Surface morphological characteristics of a copolyimide film prepared from a fluorine-based dianhydride combined with an aliphatic siloxane-based diamine and an aromatic containing ether linkages one, were studied before and after oxigen plasma treatment using atomic force microscopy (AFM). The three-dimensional texture parameters calculated from the AFM data have highlighted a more pronounced surface morphology (higher average roughness and developed interfacial area ratio), improved bearing properties and no predominant orientation, as the plasma exposure time was increased from 6 to 10 minutes, using the same power (40 W). The reactive groups generated on the binding surface have facilitated the interaction with a biocidal agent, such as silver nitrate. This creates silver-containing nanoparticles, of about 120-150 nm, uniformly distributed on the copolymer surface, with a density of 10±2 particles/μm2. The functionalization with the biocidal agent of the flourinated copolyimide surface was conducted for testing its antimicrobial properties, namely the inhibition/destruction of Escherichia coli bacterium.

The impact of three-dimensional morphological changes and local properties induced by plasma treatment on polyimide films at the interface with some electronic components

The morphological features and local properties of an semi-alicyclic polyimide film were closely evaluated by atomic force microscopy (AFM). These characteristics were optimized by applying high frequency plasma treatment, in order to increase their suitability for electronic purposes. Starting from the surface texture parameters, a deep analysis of the surface topographies at the interface with certain compounds was performed. The action of the plasma species generates a prevalent granular surface morphology, with higher roughness, improved bearing characteristics and minimal surface orientation. In addition, after the plasma treatment, a greater interaction between the AFM silicon tip and the polyimide film occurred, reflecting an increased surface adhesion. The obtained data reveal that the processed semi-alicyclic polyimide exhibits optimal features for microelectronic applications such as silicon/polyimide interfaces for flexible electronics.