Sharif Digital Repository

Background and Objective: During the manufacture and storage of probiotic products, there are always possibilities that probiotics be exposed to harmful stresses such as high temperature, low pH, various osmotic pressures and high oxygen levels, which can decrease the number of living cells. Encapsulation is one of the methods used to protect living cells such as probiotic bacteria from environmental challenges. Up-to-date, various compounds with abilities to protect bacteria during freeze-drying and to increase viability during storage have been identified. In this study, alginate with calcium chloride was used to encapsulate probiotic bacteria using extrusion method. Then, effects of... 

Porous scaffolds composed of gelatin/poly (vinyl alcohol), (Gel/PVA), were prepared using combination of freeze gelation and freeze drying methods. The effect of polymer concentration, gelatin/PVA ratio, and glutaraldehyde/gelatin ratio (GA/Gel) was investigated on morphology of pores, swelling ratio, biodegradation, and skin cell culture. At optimum preparation conditions the scaffolds had uniform pore size distributions showing high swelling ratio of 23.6. The scaffolds were of biodegradable nature and almost degraded in 28 days. Human dermal fibroblast cells (HDF) were cultured on the scaffolds and MTS assay was conducted to evaluate the influence of PVA on growth and proliferation of the... 

A drug delivery system based on poly (vinyl alcohol) (PVA) hydrogels containing ibuprofen-loaded poly (lactic acid) (PLA) microspheres was developed to improve the release kinetics of this model drug. Gamma-irradiation and freeze-thawing were applied to prepare poly (vinyl alcohol) hydrogels. Properties and morphology of these composite hydrogels were investigated using FTIR, DSC, and SEM. In vitro release indicated that entrapment of the microspheres into the PVA hydrogels causes a reduction in both the release rate and the initial burst effect. PLA microspheres entrapped into the PVA hydrogels showed more suitable controlled release kinetics for drug delivery  

There are very limited researches carried out to investigate the influence of saturation degrees, freezing-thawing, and curing times on geotechnical properties of lime concrete (LC) and lime-cement concrete (LCC) due to the capillary action and changes in groundwater table. Subsequently, the primary goal of this research is to investigate the influence of these parameters on mechanical properties of LC and LCC using unconfined compression tests, namely uniaxial compressive strength (UCS), stress-strain behavior, deformability index (I D ), secant modulus (E S ), failure strain, bulk modulus (K), resilient modulus (M R ), brittleness index (I B ), and shear modulus (G). At first, the... 

Access to potable water with standard quality is an inevitable component of human's lives. Freeze desalination, by consuming lower energy compared to other techniques, relies on the exertion of a cold source which is then accompanied by simultaneous rejection of impurities from water. Regarding this, a numerical study on freeze desalination in a hollow cylinder is carried out to determine the effects of the design variables such as heat flux, hydraulic diameter, initial salt concentration, and freezing time on the ice mass, ice salinity, ice generation speed, and Nusselt number on the cold surface of the inner tube. Results show that increasing the value of heat flux from −250 [Formula... 

In this research work, different devices made of glutaraldehyde cross-linked chitosan hydrogels loaded by amoxicillin, have been prepared using freeze-drying method. Effects of system parameters such as cross-linker concentration, pH, and gel structure on the morphology and release behavior of devices have been investigated using standard methods. Morphological studies were performed using SEM instrument and controlled releases are followed via spectrophotometeric method. Reaction of glutaraldehyde with chitosan has been studied using FTIR instrument. SEM micrographs have shown that with increasing cross-linker percentage in hydrogel, pore sizes increased where pore size distribution... 

Porous scaffolds composed of gelatin/poly (vinyl alcohol), (Gel/PVA), were prepared using combination of freeze gelation and freeze drying methods. The effect of polymer concentration, gelatin/PVA ratio, and glutaraldehyde/gelatin ratio (GA/Gel) was investigated on morphology of pores, swelling ratio, biodegradation, and skin cell culture. At optimum preparation conditions the scaffolds had uniform pore size distributions showing high swelling ratio of 23.6. The scaffolds were of biodegradable nature and almost degraded in 28 days. Human dermal fibroblast cells (HDF) were cultured on the scaffolds and MTS assay was conducted to evaluate the influence of PVA on growth and proliferation of the... 

A novel approach for particles size separation based on dielectrophoresis (DEP) method is introduced and analyzed both computationally and experimentally. The proposed technique has been utilized for the separation of polystyrene (PS) particles with 8, 6 and 2 μm diameters passing through microchannels with planar electrodes. The performance of the technique has been computationally analyzed using the finite element method (FEM). Considering the structure of the planar electrodes, we propose an approach based on applying an electric potential between one of the global electrodes, and a needle touched the top of the cell suspension. Results of both simulation and experiment show that by... 

In today's global economy, the automotive design engineer's responsibilities are made more complex by the differences between regulatory requirements of the various global markets. This paper compares instrument panel head impact requirements of FMVSS 201 with its European counterparts, ECE 21. The behavior during a head impact test has been studied. Due to the gravity of the cockpit module, the sag has been analyzed to simulate shipping, loading, and assembly conditions. The interior parts of the vehicle cabin are exposed to temperature variations due to radiation effect of sun ray or freezing temperature in winter. Plastic parts appear to be more thermally susceptible than steel parts in... 

Blood vessels, especially large vessels have a greater thermal effect on freezing tissue during cryosurgery. Vascular networks act as heat sources in tissue, and cause failure in cryosurgery and reappearance of cancer. The aim of this study is to numerically simulate the effect of probe location and multiprobe on heat transfer distribution. Furthermore, the effect of nanoparticles injection is studied. It is shown that the small probes location near large blood vessels could help to reduce the necessary time for tissue freezing. Nanoparticles injection shows that the thermal effect of blood vessel in tissue is improved. Using Au, Ag and diamond nanoparticles have the most growth of ice ball... 

Starch based scaffolds are considered as promising biomaterials for bone tissue engineering. In this study, a highly porous starch/polyvinyl alcohol (PVA) based nanocomposite scaffold with a gradient pore structure was made by incorporating different bio-additives, including citric acid, cellulose nanofibers, and hydroxyapatite (HA) nanoparticles. The scaffold was prepared by employing unidirectional and cryogenic freeze-casting and subsequently freeze-drying methods. Fourier transform infrared (FTIR) spectroscopy confirmed the cross-linking of starch and PVA molecules through multiple esterification phenomenon in the presence of citric acid as a cross-linking agent. Field emission scanning... 

Assessing the durability of concrete is of prime importance to provide an adequate service life and reduce the repairing cost of structures. Freeze-thaw is one such test that indicates the ability of concrete to last a long time without a significant loss in its performance. In this study, the freeze-thaw resistance of polymer concrete containing different polymer contents was explored and compared to various conventional cement concretes. Concretes’ fresh and hardened properties were assessed for their workability, air content, and compressive strength. The mass loss, length change, dynamic modulus of elasticity, and residual compressive strength were determined for all types of concretes... 

Improving the discharge process of phase change materials (PCMs) is of great importance and can be effective for thermal energy storage (TES) systems. In this research, the direct-contact method for acetone droplet on molten paraffin is optimized to enhance the efficiency of the discharge process of PCMs and TES systems working with intermediate boiling fluid (IBF). In order to improve the storage rate and increase the freezing rate in the system, the NSGA-II algorithm is used. When the acetone droplet hits, owing to its low boiling point relative to the temperature of molten paraffin, the acetone evaporates, causing the creation of solidified paraffin area. The main goal of the current...