The odontogenic differentiation of human dental pulp stem cells on hydroxyapatite-coated biodegradable nanofibrous scaffolds

The authors aimed to design nanofibrous (NF) scaffolds that facilitate odontogenic and osteogenic differentiation of human dental pulp-derived mesenchymal stem cells (DPSCs) in vitro. For this purpose, hydroxyapatite (HA)–loaded poly (L-lactic acid)/poly (?-caprolactone) (PLLA:PCL 2;1) blend NFs were prepared using the electrospinning method. Alizarin red activity and cell viability were evaluated by MTT assay, and SEM revealed the proliferation properties of NF scaffolds. QRT-PCR results demonstrated that HA-loaded PLLA/PCL can lead to osteoblast/odontoblast differentiation in DPSCs through the up-regulation of related genes, thus indicating that electrospun biodegradable PCL/PLA/HA has remarkable prospects as scaffolds for bone and tooth tissue engineering.     

Synthesis of highly isotactic poly 1-hexene using Fe-doped Mg(OEt)2/TiCl4/ED Ziegler–Natta catalytic system

In this article, polymerization of 1-hexene with FeCl_3-doped Mg(OET)₂/TiCl₄/electron donor (ED) catalytic system is presented. For this purpose, first a number of TiCl₄ catalysts supported on Mg(OEt)₂ and Fe-doped Mg(OEt)₂ supports were prepared with ethylbenzoate or dibutylphthalate as the internal EDs. After successive catalysts synthesis, they were employed in 1-hexene polymerization using cyclohexyl methyl dimethoxysilane as external ED as well as without it. The catalysts activity and molecular weight distribution (MWD) of poly 1-hexenes (PHs) were influenced strongly by both FeCl₃ doping and donor presence so that a remarkable increase in the catalyst activity was seen in doped catalysts. Deconvolution of MWD curves revealed that increase in the type of active centers by introducing FeCl₃ into the support should be responsible for the broadening of MWD of PHs. ¹³CNMR analysis indicated that while isotacticity does not change considerably by Fe doping, EDs increase its amount as high as 8–21%. Second, the stereoselective behavior of active Ti species in doped and undoped catalysts was fully explored by molecular modeling using density functional theory (DFT) method. Finally, with the aid of rheological measurements, the processability of polymers were evaluated and then the gel permeation chromatography (GPC) results were approved through the values obtained from model fitting as well as changes in moduli crossover modulus.     

Nonlinear Viscoelastic Response of Unidirectional Polymeric Laminated Composite Plates Under Bending Loads

Nonlinear bending analysis of polymeric laminated composite plate is examined considering material nonlinearity for viscoelastic matrix material through a Micro–macro approach. The micromechanical Simplified Unit Cell Method (SUCM) in three-dimensional closed-form solution is used for the overall behavior of the unidirectional composite in any combination of loading conditions. The elastic fibers are transversely isotropic where Schapery single integral equation in multiaxial stress state describes the matrix material by recursive-iterative formulation. The finite difference Dynamic Relaxation (DR) method is utilized to study the bending behavior of Mindlin annular sector plate including geometric nonlinearity under uniform lateral pressure with clamped and hinged edge constraints. The unsymmetrical laminated plate deflection is predicted for different thicknesses and also various pressures in different time steps and they are compared with elastic finite element results. As a main objective, the deflection results of viscoelastic laminated sector plate are obtained for various fiber volume fractions in the composite system.     

Dipyridamole recognition and controlled release by uniformly sized molecularly imprinted nanospheres

We used novel synthetic conditions of precipitation polymerization to obtain uniformly sized molecularly imprinted nanospheres of dipyridamole for application in the design of new drug delivery systems. In addition, the morphology, drug release, and binding properties of molecularly imprinted polymers (MIPs) were studied, and the effects of morphology on other properties were investigated. The MIPs prepared by acetonitrile/chloroform (19:1, v/v) were uniformly sized nanospheres with an average mean diameter of approximately 88 nm at a wetted state, 50 nm at a dry state, and a polydispersity index of 0.062. The imprinted nanospheres showed excellent binding properties and had 62.7% of template binding compared with 17.1% of its blank polymer. The imprinted nanospheres with 67.5 (mg template/of polymer) of binding capacity had better imprinting efficiency than the 50.5% of binding capacity shown by irregularly shaped MIP particles that were prepared by chloroform. The molecular binding abilities of imprinted nanospheres in human serum were evaluated by HPLC analysis (binding about 77% of dipyridamole). Results from release experiments of MIPs showed a very slow, controlled, and satisfactory release of dipyridamole. The loaded drug was released up to 99% in 17 days for nanospheres and 22 days for irregularly shaped particles.     

On the particle–particle contact effects on the hole cleaning process via a CFD–DEM model

ABSTRACT

The accurate and precise computational models in order to predict the hole cleaning process is one of the helpful assets in drilling industries. Besides the bulk properties such as the flow velocity, particles average size, cleaning fluid properties, etc., that will affect the cleaning process, there is an unanswered question about the microscopic properties of the particles, particularly those which determines the contact characteristics: Do those play a major role or not? The rudimentary answer is not. The first purpose of the present work is to answer this question via a developed computational fluid dynamics coupled with discrete element method (CFD–DEM) in which the six unknown rolling and sliding friction coefficients of particle–particle contact, particle–wall contact, and particle–drill contact are considered as the main microscopic properties of the contacts. The second purpose is to search for optimum values of these coefficients in order to calibrate the CFD–DEM model with the experimental data for a near horizontal well cleaning available in the literature. The verification of the calibrated CFD–DEM model is checked by simulation of the hole cleaning process for different inclination angles of the deviated well. The results indicate the pivotal role of the microscopic properties of the particles on the characteristics of the particle transport mechanism.