نشریه مهندسی متالورژی و مواد
سال سی و پنجم شماره 2 (پیاپی 34، تابستان 1403)

In the present study, a design for the construction of poly-caprolactone (PCL)/gelatin (GEL)/chitosan (CS) scaffolds has been proposed in order to increase performance in tissue engineering. The artificial polymer PCL is used to increase the mechanical properties of the scaffold, and two natural polymers GEL and CS are used as factors in the proliferation of cells. Polycaprolactone-gelatin-chitosan ternary composites with different weight ratios of polycaprolactone (70, 80, 90 and 60) were made by double-sided electrospinning method. The samples were cross-linked in glutaraldehyde vapor with 25% by weight. Microscopic evaluation indicates the proper formation of the composite. FTIR analysis confirmed the bonding between the components in the composite samples. Also, the results of the water contact angle test showed promotion the hydrophilicity of the PCL scaffold by adding gelatin and chitosan. So that the contact angle of pure PCL reaches from 98 degrees to about 22 degrees with the presence of gelatin and chitosan. The evaluation of degradability in phosphate buffered saline solution showed that the weight loss of the fabricated scaffolds occurs with the passage of time from 1 to 28 days for all scaffolds. Because of the nature of poly-caprolactone and gelatin-chitosan, the highest degradation rate after 28 days in gelatin-chitosan fibers is more than 50% and the lowest degradation rate related to the sample containing 70 wt% PCL is less than 23%.

Foam materials are a family of new and advanced materials that due to their unique characteristics, will have a lot of potential for development in the coming years. The current research deals with the production of metal foams made of 316L stainless steel, which has a relatively wide application in the medical industry (especially in the production of implants). For this purpose, the methods of powder metallurgy and dissolving spherical urea particles in water has been used as a spacer have been employed. Porosity measurement, cell wall evaluation by scanning electron microscope and pressure test on steel specimens have been investigated. The effect of porosity and applied pressure during the production of the foams on their mechanical behavior have been studied. In addition to conducting experimental tests, the compressive test was simulated using an explicit finite element model for a steel foam with 30 percent of porosity. The results indicate that the failure mechanism of both experimental and simulated specimens occur approximately similar.

In this work, lead foams containing alumina nano-particles (contains from 0, 0.1, 0.2, 0.4 and 0.8 wt. %) are manufactured through powder metallurgy using urea granules as leachable space holders. The leaching behavior of urea granules, porosity contents and compression properties of lead foams and also, microstructure of cell walls by optical and field emission scanning electronic microscopes are investigated. The results show in the multi-stage of leaching processes, about 80% of urea granules dissolved in seven stages. The optical images prove the good agglomeration of lead powder particles. By increasing the alumina particles, the porosity content of manufactured foams that is in the range of 80-83% is increased. The images of FESEM and X-ray spectroscopic maps show the uniform distribution of alumina nano-particles in the cell walls. The compression properties of manufactured foams, by increasing the alumina nano-particles to 0.1 wt.% first decreases, then after 0.4 wt.% enhanced, and finally in the 0.8 wt.% of nano-particles goes down again.

In the present study, magnesium aluminate bio-ceramic (MgAl2O4) with particle size of 27 to 40 nm was produced by combustion synthesis method. Also, PLA/MgAl2O4 polymer matrix composites were made using FDM and slurry welding methods and their properties were studied and compared. X-ray diffraction (XRD), scanning electron microscope (FE-SEM), infrared spectrometer (FT-IR) and inductively coupled plasma spectroscopy (ICP) were used to investigate the properties of the produced composites. XRD results showed that in the composite samples synthesized by FDM method, PLA has more crystallinity than the slurry method, which is caused by relatively slow cooling of the polymer melt. To investigate the bioactive properties of this composite, the simulated body solution (SBF) was used and the results of the ICP test showed that the amount of calcium and phosphorus in the fourth week in the PLA/MgAl2O4 printed sample was the highest and equal to 77 mg/L and respectively were 40 mg/L. These results show that the processing of these composites by the 3D printing method brings more degradability than the slurry method and has a higher quality for biological uses.

The application of conductive particles with segregated distribution in the polymeric matrices is one of the most effective ways to reduce percolation threshold, increase conductivity, and improve electromagnetic interference (EMI) shielding properties. In this study, mechanical mixing and hot compression molding were used to fabricate polyethylene/carbon black composite with segregate structure and random distributions. Scanning electron microscope images showed that during the mechanical mixing process, the polymeric granules were well coated with carbon black. besides, there is good relation between conductivity and well dispersed of carbon black on the surface of HDPE granules. The electrical conductivity of segregated structure composite ( 2 wt% carbon black) increased about 3000 times compared to the random structure(2%wt carbon black). Using the vector network analyzer, it was revealed that by increasing the black carbon content from 2 to 5 wt%, the maximum EMI shielding effectiveness of the composite increased from 6 dB to 16 dB, respectively.

In this research, the effect of adding silicon carbide nanoparticles, zirconium carbide, and carbon nanofibers at different sintering temperatures and times on fracture toughness and hardness of ZrB2 ceramics has been investigated. Due to the high number of required samples (four variables in three levels) to optimize the fracture toughness and hardness, the design of the experiment (DOE) by the Taguchi method was used. The hardness and fracture toughness of the composites fabricated by spark plasma sintering (SPS) were evaluated by macro-Vickers and crack length measurement methods respectively. The results showed that sample 8 with the chemical composition of ZrB2-25Vol%SiC-15ZrC-10CNF sintered at 1875°C for 7 minutes has the maximum amount of HV hardness (400±33) and fracture toughness (7.3±0.4) Mpa.m1/2. Also, analysis of variance (ANOVA) indicated that temperature and time are the most effective variables on fracture toughness (with contributions of 84% and 10.5% respectively) and hardness (with contributions of 74.3% and 15.9% respectively).