Mohammad Najafi

Confinement effect of graphene nanoplatelets on atom transfer radical polymerization of styrene: grafting through hydroxyl groups

Dual characteristics polystyrene chains were synthesized by “grafting through” atom transfer radical polymerization in the presence of surface-modified graphene nanoplatelets. After oxidation of graphene, it was functionalized by different amounts of 3-(trimethoxysilyl) propyl methacrylate (MPS) through the surface hydroxyl groups. Polymerization of styrene in the presence of modified graphene and initiator, ethyl alpha-bromoisobutyrate, was accomplished at 110xa0xa0C. Then, the effects of various graft densities and different graphene loadings on the heterogeneous graft and free polystyrene chains’ characteristics and also their kinetics of polymerization were studied by gas- and gel-permeation chromatographies. Linear increase of ln(M0/M) with time for all the samples shows that polymerization proceeds in a living manner. By increasing graphene content, Mn increases, and polydispersity index (PDI) decreases for free chains. However, a reverse behavior was observed for attached chains. Increasing graft density resulted in higher Mn and lower PDI values for free chains. Similar to the effect of graphene content, a reverse behavior was observed for the attached chains. Efficiency of grafting reactions along with the graft contents was studied by X-ray photoelectron spectroscopy (XPS), elemental analysis, and thermogravimetry analysis. The grafting ratio of MPS modifier was calculated to be 9.7xa0% via the data of Si contents in the XPS survey scan data. Finally, the morphology of the functionalized graphene was studied by transmission electron microscopy.

Prediction of Glioblastoma Multiform Response to Bevacizumab Treatment Using Multi-Parametric MRI

Glioblastoma multiform (GBM) is a highly malignant brain tumor. Bevacizumab is a recent therapy for stopping tumor growth and even shrinking tumor through inhibition of vascular development (angiogenesis). This paper presents a non-invasive approach based on image analysis of multi-parametric magnetic resonance images (MRI) to predict response of GBM to this treatment. The resulting prediction system has potential to be used by physicians to optimize treatment plans of the GBM patients. The proposed method applies signal decomposition and histogram analysis methods to extract statistical features from Gd-enhanced regions of tumor that quantify its microstructural characteristics. MRI studies of 12 patients at multiple time points before and up to four months after treatment are used in this work. Changes in the Gd-enhancement as well as necrosis and edema after treatment are used to evaluate the response. Leave-one-out cross validation method is applied to evaluate prediction quality of the models. Predictive models developed in this work have large regression coefficients (maximum R 2u200a=u200a0.95) indicating their capability to predict response to therapy.

Reversible addition fragmentation chain transfer polymerization of styrene from the edge of graphene oxide nanolayers

A graphene oxide modifier containing chain transfer agent moieties (CR) was synthesized by an esterification reaction between 1,4-butanediol and 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid. CR moieties were grafted at the edge of GO in low and high graft densities to yield GCRL and GCRH respectively. Then, GCRL and GCRH were used in grafting from reversible addition fragmentation chain transfer polymerization of styrene. Grafting of CR moieties was approved by Fourier transform infrared spectroscopy, X-ray photo electron spectroscopy, and Raman spectroscopy. Expansion of graphene oxide interlayer by oxidation and functionalization processes was evaluated by X-ray diffraction. Conversion values of styrene monomer were obtained from gas chromatography. Molecular weight and PDI values of attached polystyrene chains were studied by size exclusion chromatography. Thermogravimetric analysis was also used to investigate the degradation temperatures, char contents, and graft contents. The attached modifier content in GCRH and GCRL is estimated to be 7.6 and 4.0% respectively. Scanning electron and transmission electron microscopies show that flat and smooth layers of graphite are wrinkled during the oxidation and then turned to opaque layers as a consequence of polymer grafting.

Use of sourdough to reduce phytic acid and improve zinc bioavailability of a traditional flat bread ( sangak ) from Iran

In this study, effects of 8 different sourdough starters prepared with Saccharomyces cerevisiae, Lactobacillus plantarum, L. acidophilus, and Leuconostoc mesenteroides were investigated on the phytic acid level and mole ratio of phytic acid to zinc in a traditional Iranian bread (sangak). Different sourdough preparations were made and incubated at 30°C for 16 h and added to the dough at 10, 20, and 30% replacement levels. Use of sourdough resulted in a decrease in phytic acid level (also in a decrease in the phytic acid to zinc mole ratio) and corresponding increase in zinc bioavailability index when compared to the commercial sangak bread. The lowest phytic acid concentration and highest zinc bioavailability index were achieved when S. cerevisiae, L. plantarum, and Leu. mesenteroides were used at 30.0% dough replacement with sourdough. This study provides awareness about the negative impacts of higher phytic acid level in the breads, which is particularly the case for sangak bread, and also provides a solution for such issue.

Effects of several starter cultures on the anti-mold activity and sensory attributes of a traditional flat bread ( Sangak ) from Iran

Effects of 8 different sourdoughs and their replacement levels at 10, 20, and 30%(w/w) on the volume (of dough), crust hardness, organoleptic, and anti-mold properties of Iranian sangak bread were investigated. Saccharomyces cerevisiae, Lactobacillus plantarum, Lactobacillus acidophilus, and Leuconostoc mesenteroides were selected for the preparation of sourdough samples. The highest dough volume was achieved when sourdough (those having S. cerevisiae) was used at 30%. The highest taste scores were found with the bread sample using the above-mentioned starters at 30% sourdough replacement level. Considering the chewing, appearance, and overall quality of the new products, most of the samples maintained the favorite sensory aspects of sangak bread. Use of lactic acid bacteria and yeast strains as part of the sourdough formulation (followed by the use of sourdough in the dough formulation) resulted in improved crust properties and greater anti-mold activities.

Morphological, thermal and drug release studies of poly (methacrylic acid)-based molecularly imprinted polymer nanoparticles immobilized in electrospun poly (ε-caprolactone) nanofibers as dexamethasone delivery system

Electrospun poly (ε-caprolactone) (PCL) nanofibers containing molecularly imprinted polymer (MIP) nanoparticles based on methacrylic acid (MAA) were prepared for controlled release of dexamethasone (Dexa). First, the MIPs consisting of Dexa were synthesized via precipitation polymerization. Their recognition sites formation and thermal properties were investigated by FTIR and TGA tests, respectively. The results showed that by selecting a monomer: template (MAA:Dexa) molar ratio of 6 : 1, MIP nanoparticles were produced with imprinting factor of 1.80. The FESEM and TEM images showed the MIPs average diameter of 394±9.7 nm and appropriate immobilization of them in PCL nanofibers, respectively. Moreover, the cumulative release of Dexa from the MIP-loaded nanofibrous samples was studied by UV-vis spectrophotometry and revealed a suitable controlled release of the drug during four days. Afterward, Dexa release followed Higuchi model which indicated the main mechanism was governed by Fickian diffusion theory.

The impacts of feed fraction on copolymer microstructure in ATRcP: a kinetic Monte Carlo simulation

Abstract A research has been carried out to simulate an atom transfer radical copolymerization (ATRcP) system of styrene and n-butyl acrylate using the stochastic Monte Carlo method and to investigate the variation of reactant concentration, average molecular weight and molecular weight distribution, average sequence length and sequence length distribution, different dyad fractions and copolymer composition as a function of styrene feed fraction. To this end, a finely tuned program was written in C++ language to implement the simulation algorithm. It was observed that although styrene feed fraction alteration affected all the factors under review, weight-average molecular weight showed the least variation in its trend for styrene fractions higher than 5%. Finally, the outputs of the current work can be effectively used in tuning and controlling the topology and microstructure of copolymer chains.