Microfabricated Biomaterials for Engineering 3D Tissues

Mimicking natural tissue structure is crucial for engineered tissues with intended applications ranging from regenerative medicine to biorobotics. Native tissues are highly organized at the microscale, thus making these natural characteristics an integral part of creating effective biomimetic tissue structures. There exists a growing appreciation that the incorporation of similar highly organized microscale structures in tissue engineering may yield a remedy for problems ranging from vascularization to cell function control/determination. In this review, we highlight the recent progress in the field of microscale tissue engineering and discuss the use of various biomaterials for generating engineered tissue structures with microscale features. In particular, we will discuss the use of microscale approaches to engineer the architecture of scaffolds, generate artificial vasculature, and control cellular orientation and differentiation. In addition, the emergence of microfabricated tissue units and the modular assembly to emulate hierarchical tissues will be discussed.     

Numerical modeling the effects of overloading and underloading in fatigue crack growth

In this paper, the effects of overloading and underloading on fatigue crack growth were investigated. Numerical modeling was done by using finite element software. In this software, without using the remeshing technique, effect of crack tip plasticity in fatigue crack growth life was analyzed. Plasticity effects were considered by using three methods: COD method, U correction factor and J-integral. Calculated results for crack growth rates were compared with experimental data in literature. Results were obtained by COD method and U correction factor have good agreement but results form J-integral have not. We also study the effects of stress ratio (R) in plane stress and plane strain conditions. With increasing R, the fatigue life was increased. The extent of crack retardation is greater under plane stress than plane strain conditions. Underloading has not significant effects on fatigue crack growth rate. Underloading cause a little variation in plastic zones and so little effects on fatigue life.     

Energy intensity and greenhouse gases footprint of metallurgical processes: A continuous steelmaking case study

The demand on primary energy resources of three steelmaking technologies has been evaluated using an integrated energy analysis approach that takes into account the energy equivalent of major materials and supplies used in the process, as well as the inefficiency of electricity generation. Two new parameters, Material CO₂ Footprint (MCF) and Process CO₂ Footprint (PCF), are defined to provide unified measures for carbon footprint of the treated materials, and the process respectively. Using these measures, a comparative study of the three processes has been performed. It is demonstrated that a novel steelmaking technology that operates continuously leads to substantial reduction in the overall energy demand, when compared with the conventional batch processes. CO₂ reduction associated with the improvement of the energy efficiency is presented for several scenarios of power generation.     

Wrinkle free plaited knitted fabrics without pre-heat setting

Wrinkle free fabric at low cost is always a desirable aesthetic property. Different type of resins/finishes and pre-heat setting prior to processing are applied to avoid wrinkles in woven and hosiery, respectively. Current study is proposed to produce wrinkle free circular plaited knitted fabric by the elimination of a pre-boarding step. In this achievement, yarn covering parameters and compatibility of yarns with knitting machines are examined. Sock samples were analyzed for improved physical appearance (wrinkles) after various processes (pre-tumbling, dyeing, bleaching, and washing). Yarn specifications (sheath yarn fineness, sheath yarn texture i.e. shrink/un-shrink, covering air-knots) impact on socks physical appearance were also analyzed. The results clearly showed that by decreasing number of yarn covering air knots and sheath yarn fineness leads to prevention of wrinkle formation. The results also prove to be supportive for cost effectiveness by eliminating the pre-setting stage.     

Role of Heat Transfer in Early Stage Decarburization of DRI in Slag

The gas generation from reactions between direct reduced iron (DRI) pellets and steelmaking slags is known to take place in two stages; (1) the reaction of FeO and carbon within DRI, i.e., pellet internal reaction, followed by (2) the reduction of slag FeO with DRI carbon at the pellet?Cslag interface, if any carbon remains from the first step. To understand the controlling mechanism of the reaction between FeO and C inside DRI, the rate of the gas release and the temperature of pellets suspended in a slag-free atmosphere were quantified. The results were used to determine the apparent thermal conductivity of DRI that showed values of approximately 0.5 to 2 W.m^?1.K^?1 for a temperature range of 573?K to 1273?K (300?°C to 1000?°C). Furthermore, it was found that the experimental gas evolution rates are consistent with the values predicted by a heat?Ctransfer based model, confirming that the FeO-C reaction within pellet is controlled by the rate of heat transfer from the slag to the DRI pellet.     

Annealing effect on structural, optical and electrical properties of pure and Mg doped tin oxide thin films

This study describes the effect of annealing at different temperatures (400–600 °C) on structural, optical and electrical behaviors of pure and Mg doped tin oxide thin films grown on the glass substrate by electron beam evaporation technique. The transformation of tetragonal to orthorhombic form due to annealing, introduced a change in the optical and electrical properties of pure and Mg doped tin oxide thin films. X-ray diffraction studies or analysis revealed the phase transformation and change in the crystalline size with increase in the annealing temperature. The morphology and roughness of the thin films were studied by Atomic force microscopy. Optical band gap increased with annealing temperature confirms the improvements of crystallinity. The quality of thin films transparency was investigated by UV/Vis-spectroscopy. Photoluminescence of pure and Mg doped tin oxide thin films shows two extra peaks one at 486 nm and other at 538 nm is due to the crystal defect created as a result of annealing temperature. These peaks became stronger and shifted to longer wavelength with increasing the annealing temperature. The complex plot (Nyquist plot) showed the data point laying on two semicircles and the resistance of grains and grain boundaries increases with the increase in annealing temperature for both pure and Mg doped tin oxide thin films.     

The Effect of Base Metal Conditions on the Final Microstructure and Hardness of 2024 Aluminum Alloy Friction-Stir Welds

Aircraft aluminum alloys, such as 2024, generally present low weldability by traditional fusion welding processes. The development of friction-stir welding (FSW) has provided an improved alternative way to produce satisfactory aluminum joints in a faster and more reliable method. It has been demonstrated that the FSW process involves dynamic recrystallization, which leads to ultrafine and equiaxed grain structures due to the high temperatures and strains occurring during the process. In this study, the 2024 Al-alloy with annealed (O) and artificial aged (T6) conditions were friction-stir welded. Grain size distribution, hardness, and temperature profiles in the welded zones were determined to obtain the relationship between the base metal’s initial and final microstructures in these regions. The results showed that in both samples, the average grain sizes in the weld nugget were almost identical. The hardness of nugget zones in both samples was nearly the same due to their similar microstructures. According to the obtained results, the initial microstructure showed no considerable effect on the final microstructure and hardness of the weld nuggets. This may be attributed to the continuous dynamic recrystallization phenomenon that occurs during the FSW of aluminum alloys.     

The effect of granule microstructure on dissolution rate

The relationship between the microstructure of granules and their dissolution rate has been investigated. Granules consisting of mannitol primary particles and PVP aqueous binder have been prepared by top-spray fluid-bed granulation, and granules consisting of sucrose primary particles and PEG binder by in-situ melt fluid-bed granulation. Granule microstructure has been systematically varied by manipulating the primary particle size distribution and the binder content in each case. In both cases granule porosity was found to be a decreasing function of binder content and a minimum of porosity as function of the fine/coarse primary particle mixing ratio has been observed, in line with theoretical expectations. Granule microstructures have been analysed using X-ray computed micro-tomography and compared with three-dimensional “virtual granules” generated by a computer simulation of the agglomeration process. The dissolution rate of granules has then been measured. While porosity was found to have a strong effect on the dissolution rate of mannitol granules, the dissolution rate was found to be practically independent of porosity in the case of sucrose granules. The formulation-microstructure and microstructure-dissolution correlations established in course of this work are in line with previous computer simulation results and form part of a computer-aided granule design methodology.     

Synthesis of polyelectrolyte-modified ordered nanoporous carbon for removal of aromatic organic acids from purified terephthalic acid wastewater

In this work polyelectrolyte (polydiallyldimethylammonium chloride) modified ordered mesoporous carbon (CMK-1/PDDA) has been synthesized and has been employed in removal of major aromatic compounds present in purified terephthalic acid wastewater, such as p-toluic acid, benzoic acid, 4-carboxybenzaldehyde, phthalic acid and terephthalic. The adsorption behavior of these acidic impurities has been studied through batch experiments and using UV-spectrophotometric technique. The results show that CMK-1/PDDA is very effective in selective removal of acidic compounds from PTA-waste aqueous solutions. The electrostatic interaction was considered to be the main mechanism for the adsorption of acidic compounds. The effects of chemical modification, contact time, initial concentrations, adsorbent dose, agitation speed, solution pH and reaction temperature have been optimized. The sorption equilibrium was reached within 5 min. The sorption of acidic compounds on the CMK-1/PDDA slightly decreases with increasing pH, and temperature, indicating an exothermic process. The experimental isotherm data were analyzed using the Langmuir and Freundlich equations. The equilibrium data were best represented by the Langmuir isotherm.     

Desulphurization of Hot Metal and Ferronickel With Calcium Aluminate Fluxes

Traditionally, fluxes containing calcium fluoride and other additives are used for the treatment of hot metal and molten steel. Recently, magnesium powder or lime-Mg mixture is used more popularly in hot metal desulphurization. However, the use of calcium fluoride has been restricted due to environmental concerns, and the supply of magnesium is uncertain for the countries, which are short of magnesium resource. For those reasons, calcium aluminate fluxes are a possible alternative to replace slags containing calcium fluoride or magnesium. Calcium aluminate fluxes can be produced from three different raw materials: (1) high-quality bauxite, (2) residuals from aluminum dross treatment processes and (3) waste products from alumina production. Due to the limited amount and high cost associated with high-quality bauxite, the other two sources are preferred based on both economic and environmental considerations. The objective of this paper is to examine the use of waste slags and by-products from the aluminum industry as potential refining fluxes for the steel industry so that waste disposal from the aluminum industry can be reduced with economical and environmental benefits for both industrial sectors.