Surface modification of polyurethane via creating a biocompatible superhydrophilic nanostructured layer: role of surface chemistry and structure

Advanced surface modification approaches of biomaterials alongside the advent of sophisticated analytical techniques have provided a great opportunity to understand how the physicochemical characteristics of materials determine cell–surface dynamics at molecular and atomic scale. However, there are still many contradictory reports, which are mainly due to inadequate information about the role of the two parameters of surface chemistry and structure and their synergistic effect as an adequate predictor of biological performance. Here, surface parameters were altered by grafting of poly ethylene glycol (PEG) on polyurethane (PU) surfaces through a superhydrophilic modification method. In this study, surface modification of PU films by PEG thin layer via grafting technique and TiO2 nanoparticle entrapment in the brush polymers was investigated. The surface modification led to a reduction in protein adsorption and bacterial attachment by 8.7 times and 71% respectively with no cytotoxicity effect on HeLa cells. It was also observed that when PU surface became superhydrophilic the bacterial adhesion becomes independent of bacterium type. In general, it was observed that the impact of topographical changes on the biocompatibility and biofilm formation becomes significantly more profound than that of the surface chemistry alteration.     

Phase transformation from cubic ZnS to hexagonal ZnO by thermal annealing

We have investigated the mechanism of phase transformation from ZnS to hexagonal ZnO by hightemperature thermal annealing. The ZnS thin films were grown on Si(001) substrate by thermal evaporation system using ZnS powder as source material. The grown films were annealed at different temperatures and characterized by X-ray diffraction(XRD), photoluminescence(PL), four-point probe, scanning electron microscope(SEM) and energy dispersive X-ray diffraction(EDX). The results demonstrated that as-deposited ZnS film has mixed phases but high-temperature annealing leads to transition from ZnS to ZnO. The observed result can be explained as a twostep process:(1) high-energy O atoms replaced S atoms in lattice during annealing process, and(2) S atoms diffused into substrate and/or diffused out of the sample. The dissociation energy of ZnS calculated from the Arrhenius plot of 1000/T versus log(resistivity) was found to be 3.1 eV. PL spectra of as-grown sample exhibits a characteristic green emission at 2.4 eV of ZnS but annealed samples consist of band-to-band and defect emission of ZnO at 3.29 eV and 2.5 eV respectively. SEM and EDX measurements were additionally performed to strengthen the argument.     

Investigation and numerical analysis of strain distribution in the twist extrusion of pure aluminum

The effects of performing three twist extrusion passes on high purity aluminum samples were studied in this paper in regard to numerical analysis and experimental studies. The finite element analysis of the von-Mises stress and the equivalent plastic strain in the outer longitudinal and transverse cross-sections, which are parallel and normal to the billet axis respectively, was carried out. The simulation results showed that the end of the workpiece underwent more equivalent plastic strains in contrast to the head of the sample. Moreover, the corner regions experienced more strains than the center zone did. However, the heterogeneity in strain distribution in both longitudinal and transverse cross-sections decreased by performing the sequential twist extrusion passes. The experimental outcomes such as microstructure evolutions, microhardness and tensile tests validated the simulation results.     

Three-dimensional rigid multiphase networks providing high-temperature strength to cast AlSi10Cu5Ni1-2 piston alloys

The three-dimensional (3-D) architecture of rigid multiphase networks present in AlSi10Cu5Ni1 and AlSi10Cu5Ni2 piston alloys in as-cast condition and after 4?h spheroidization treatment is characterized by synchrotron tomography in terms of the volume fraction of rigid phases, interconnectivity, contiguity and morphology. The architecture of both alloys consists of α-Al matrix and a rigid long-range 3-D network of Al(7)Cu(4)Ni, Al(4)Cu(2)Mg(8)Si(7), Al(2)Cu, Al(15)Si(2)(FeMn)(3) and AlSiFeNiCu aluminides and Si. The investigated architectural parameters of both alloys studied are correlated with room-temperature and high-temperature (300?°C) strengths as a function of solution treatment time. The AlSi10Cu5Ni1 and AlSi10Cu5Ni2 alloys behave like metal matrix composites with 16 and 20?vol.% reinforcement, respectively. Both alloys have similar strengths in the as-cast condition, but the AlSi10Cu5Ni2 is able to retain ～15% higher high temperature strength than the AlSi10Cu5Ni1 alloy after more than 4?h of spheroidization treatment. This is due to the preservation of the 3-D interconnectivity and the morphology of the rigid network, which is governed by the higher degree of contiguity between aluminides and Si.     

Beam shaping design for coupling high power diode laser stack to fiber

A beam shaping technique that rearranges the beam for improving the beam symmetry and power density of a ten-bar high power diode laser stack is simulated considering a stripe mirror plate and a V-Stack mirror in the beam shaping system. In this technique, the beam of a high power diode laser stack is effectively coupled into a standard 550 μm core diameter and a NA=0.22 fiber. By this technique, compactness, higher efficiency, and lower cost production of the diode are possible.     

Pulsed plasma polymerization for controlling shrinkage and surface composition of nanopores

Solid-state nanopores have emerged as sensors for single molecules and these have been employed to examine the biophysical properties of an increasingly large variety of biomolecules. Herein we describe a novel and facile approach to precisely adjust the pore size, while simultaneously controlling the surface chemical composition of the solid-state nanopores. Specifically, nanopores fabricated using standard ion beam technology are shrunk to the requisite molecular dimensions via the deposition of highly conformal pulsed plasma generated thin polymeric films. The plasma treatment process provides accurate control of the pore size as the conformal film deposition depends linearly on the deposition time. Simultaneously, the pore and channel chemical compositions are controlled by appropriate selection of the gaseous monomer and plasma conditions employed in the deposition of the polymer films. The controlled pore shrinkage is characterized with high resolution AFM, and the film chemistry of the plasma generated polymers is analyzed with FTIR and XPS. The stability and practical utility of this new approach is demonstrated by successful single molecule sensing of double-stranded DNA. The process offers a viable new advance in the fabrication of tailored nanopores, in terms of both the pore size and surface composition, for usage in a wide range of emerging applications.     

Synthesis and Characterization of Nano-hydroxyapatite Powder Using Wet Chemical Precipitation Reaction

Hydroxyapatite(HA) nano-powder was synthesized via wet chemical technique in a used precipitation reaction,in which Ca(OH)_2 and H_3PO_4 were used as precursors.Deionised water was used as a diluting media for the reaction and ammonia was used to adjust the pH.The synthetic HA nano-powder has some medical applications such as a coating material in orthopaedic implants and in dental.HA powder has been studied at different temperatures from 100 to 800 ℃ to achieve the stoichiometric Ca/P ratio 1.667.The optimum temperature was found to be 600 ℃.Above this temperature,the HA powder decomposed to CaO.The crystallite size of HA powder was found to be in the range of 8.47—24.47 nm.The crystallographic properties were evaluated by X-ray diffraction,Fourier transform infrared spectroscopy,energy dispersive Xray spectroscopy and scanning electron microscopy.The results show that,high purity of nano-hydroxyapatite powders could be obtained at low temperatures,and the crystallinity,crystallite size and Ca/P ratio of the resulting nanoparticles were found to be dependent on the calcination temperature.When Ca/P ratio exceeded1.75,formation of CaO phase was observed.