The influence of 3D-printed PLA coatings on pure and fretting fatigue properties of AM60 magnesium alloys under cyclic bending loads.

A study was conducted to compare the pure fatigue and fretting fatigue properties of AM60 magnesium alloys, with and without 3D-printed PLA coatings. The PLA coating layers led to an increase in the fatigue lifetime in both pure and fretting conditions. They delayed the crack initiation time compared to uncoated samples, thereby increasing fatigue lifetime. Additionally, in the case of fretting fatigue, PLA coating caused the fretting pads to reach the magnesium alloy later, which also contributed to the longer lifetime of coated samples, compared to uncoated specimens. Using field emission scanning electron microscopy, all specimens exhibited the brittle fracture behavior, with the presence of both cleavage and quasi-cleavage marks. By the fractography, it was found that the number of cracks in coated samples decreased in both pure and fretting fatigue conditions. Remarkably, PLA coating during fretting fatigue resulted in a significant enhancement of the fretting fatigue lifetime, within 56%-2182 %.

Evaluation of stress-controlled high-cycle fatigue characteristics in PLA-wood fused deposition modeling 3D-printed parts under bending loads.

PLA (Poly-lactic acid)-wood provides more biodegradability through natural fibers, a significant advantage of pure PLA. Nevertheless, these bio-composites may have inferior mechanical properties compared to non-degradable polymer composites, considering the lower strength of natural particles compared to synthetic fibers. This research examines the fatigue behavior of additive-manufactured biopolymer PLA-wood and assesses its comparability with pure PLA. Therefore, solid fatigue test samples were printed using the FDM (fused deposition modeling) method. Afterward, fully reversed rotary bending fatigue experiments were performed at 4 different stress levels (7.5 to 15 MPa) to extract the S-N curve of PLA-wood. Moreover, the fatigue fracture surfaces of the PLA-wood were investigated and compared at the highest and lowest stress levels using an FE-SEM (Field Emission Scanning Electron Microscopy), indicating more ductile fracture marks at higher stress levels. The fatigue lifetime of the PLA-wood decreased by 87.48% at the highest stress level (15 MPa), rather than the result at the lowest stress level (7.5 MPa). Additionally, the results demonstrated that the fatigue characteristics of the printed pure PLA and PLA-wood were comparable, suggesting that the 3D-printed PLA-wood with the used printing parameters can be an alternative choice.

Optimization of 3D printing parameters in polylactic acid bio-metamaterial under cyclic bending loading considering fracture features.

3D printing has become a crucial additive manufacturing technique with the applications in various industries. Fused deposition modeling (FDM) is a common additive manufacturing process that offers considerable flexibility in the component fabrication through multiple parameters, which strongly influence the properties of the produced parts. This study focused on the impact of different printing parameters on the fatigue behavior of polylactic acid (PLA). The standard samples were 3D-printed with varying speed (5, 10, and 15 mm/s), print temperature (180, 210, and 240 °C), and nozzle diameter (0.2, 0.4, and 0.6 mm). The fatigue properties were evaluated through rotating bending fatigue tests, and a model was developed based on the results with a statistical analysis. The model accuracy was validated and the interactions between the parameters were analyzed. The optimization study found that a print speed of 5 mm/s, print temperature of 210 °C, and nozzle diameter of 0.2 mm were optimal. The fracture surfaces were also examined using a scanning electron microscopy, revealing the presence of crazing despite the brittle behavior of PLA.

Topology optimization on metamaterial cells for replacement possibility in non-pneumatic tire and the capability of 3D-printing.

One of the applications of mechanical metamaterials is in car tires, as a non-pneumatic tire (NPT). Therefore, to find a suitable cell to replace the pneumatic part of the tire, three different solution methods were used, including topology optimization of the cubic unit cell, cylindrical unit cell, and fatigue testing cylindrical sample (FTCS). First, to find the mechanical properties, a tensile test was conducted for materials made of polylactic acid (PLA) and then, the optimization was done based on the weight and overhang control for the possibility of manufacturing with 3D printers, as constraints, besides, the objective of minimum compliance. In the optimization of the cubic unit cell, the sample with a minimum remaining weight of 35% was selected as the optimal sample. However, for the cylindrical unit cell, a sample with a weight limit of 20% was the most optimal state. In contrast, in the FTCS optimization, a specimen with lower remaining weight equal to 60% of the initial weight was selected. After obtaining the answer, five cells in the FTCS and two mentioned cells were evaluated under compressive testing. The samples were also subjected to bending fatigue loadings. The results demonstrated that cellular structures with 15% of lower weight than the optimized samples had the same fatigue lifetime. In the compressive test, the line slope of the specimens with cellular structures in the elastic region of the force-displacement diagram was reduced by 37%, compared to the completely solid samples. However, the weight of these samples decreased by 59%. Furthermore, the fracture surface was also investigated by field-emission scanning electron microscopy. It was observed that a weak connection between the layers was the cause of failure.

Multi-objective numerical optimization of 3D-printed polylactic acid bio-metamaterial based on topology, filling pattern, and infill density via fatigue lifetime and mass.

Infill parameters are significant with regard to the overall cost and saving material while printing a 3D model. When it comes to printing time, we can decrease the printing time by altering the infill, which also reduces the total process extent. Choosing the right filling parameters affects the strength of the printed model. In this research, the effect of filling density and infill pattern on the fatigue lifetime of cylindrical polylactic acid (PLA) samples was investigated with finite element modeling and analysis. This causes the lattice structure to be considered macro-scale porosity in the additive manufacturing process. Due to the need for multi-objective optimization of several functions at the same time and the inevitable sacrifice of other objectives, the decision was to obtain a set of compromise solutions according to the Pareto-optimal solution technique or the Pareto non-inferior solution approach. As a result, a horizontally printed rectangular pattern with 60% filling was preferred over the four patterns including honeycomb, triangular, regular octagon, and irregular octagon by considering the sum of mass changes and fatigue lifetime changes, and distance from the optimal point, which is the lightest structure with the maximum fatigue lifetime as an objective function with an emphasis on mass as an important parameter in designing scaffolds and biomedical structures. A new structure was also proposed by performing a structural optimization process using computer-aided design tools and also, computer-aided engineering software by Dassault systems. Finally, the selected samples were printed and their 3D printing quality was investigated using field emission scanning electron microscopy inspection.

Multi-Material Metamaterial Topology Optimization to Minimize the Compliance and the Constraint of Weight: Application of Non-Pneumatic Tire Additive-Manufactured with PLA/TPU Polymers.

In non-pneumatic tires, metamaterial cells could replace the pneumatic part of the tire. In this research, to achieve a metamaterial cell suitable for a non-pneumatic tire with the objective function of increasing compressive strength and bending fatigue lifetime, an optimization was carried out for three types of geometries: a square plane, a rectangular plane, and the entire circumference of the tire, as well as three types of materials: polylactic acid (PLA), thermoplastic polyurethane (TPU), and void. The topology optimization was implemented by the MATLAB code in 2D mode. Finally, to check the quality of cell 3D printing and how the cells were connected, the optimal cell fabricated by the fused deposition modeling (FDM) method was evaluated using field-emission scanning electron microscopy (FE-SEM). The results showed that in the optimization of the square plane, the sample with the minimum remaining weight constraint equal to 40% was selected as the optimal case, while in the optimization of the rectangular plane and the entire circumference of tire, the sample with the minimum remaining weight constraint equal to 60% was selected as the optimal case. From checking the quality of 3D printing of multi-materials, it was concluded that the PLA and TPU materials were completely connected.

Evaluation of coronary stents: A review of types, materials, processing techniques, design, and problems.

In the world, one of the leading causes of death is coronary artery disease (CAD). There are several ways to treat this disease, and stenting is currently the most appropriate way in many cases. Nowadays, the use of stents has rapidly increased, and they have been introduced in various models, with different geometries and materials. To select the most appropriate stent required, it is necessary to have an analysis of the mechanical behavior of various types of stents. The purpose of this article is to provide a complete overview of advanced research in the field of stents and to discuss and conclude important studies on different topics in the field of stents. In this review, we introduce the types of coronary stents, materials, stent processing technique, stent design, classification of stents based on the mechanism of expansion, and problems and complications of stents. In this article, by reviewing the biomechanical studies conducted in this field and collecting and classifying their results, a useful set of information has been presented to continue research in the direction of designing and manufacturing more efficient stents, although the clinical-engineering field still needs to continue research to optimize the design and construction. The optimum design of stents in the future is possible by simulation and using numerical methods and adequate knowledge of stent and artery biomechanics.

Amazing epsilon-shaped trend for fretting fatigue characteristics in AM60 magnesium alloy under stress-controlled cyclic conditions at bending loads with zero mean stress.

In the present article, fatigue properties (pure and fretting) of magnesium alloys (AM60) under cyclic bending loading were compared. For this objective, a rotary fatigue testing device was utilized with a fretting module on standard cylindrical samples under bending loads with zero means stress. The fretting fatigue condition decreased fatigue lifetime compared with pure fatigue but in an amazing Epsilon-shaped trend. Comparatively speaking to the state of pure fatigue, the fatigue lifetime of the fretting fatigue condition reduced by 91.0% and 44.8%, respectively, between the lowest level of stress (80 MPa) and the greatest level of stress (120 MPa). To study the fracture behavior and the fractography analysis, field-emission scanning electron microscopy (FESEM) was utilized. In general, since both quasi-cleavage and cleavage were seen; therefore, the fracture behavior for all samples was brittle. In both test conditions (fretting fatigue and pure fatigue), at higher stress levels, the average crack length was higher than at low-stress levels. In addition, the number of cracks (in high- and low-stress levels) was observed to be less in fretting fatigue conditions than in pure fatigue conditions, but the average crack length in fretting fatigue conditions in high-stress levels and low-stress levels was 212.82% and 259.47% higher than the average crack length under the pure fatigue condition, respectively.

Microscopic study on the effect of nano-clay-particles on wear behaviors of piston aluminum-silicon alloy under various forces and speeds.

In the present article, a microscopic investigation was done on the effect of adding nano-clay-particles into the aluminum matrix on the wear behaviors of piston aluminum-silicon alloy under various forces and speeds. Then, the variation of the wear rate and the coefficient of friction (CoF) of the alloys was reported alongside the behavior of nano-reinforced composites. For this objective, the reciprocating wear tests were conducted under different conditions. Then, in order to evaluate the microstructural changes of the sample after the addition of the nano-clay-particles, optical and field-emission scanning electron microscopies (FESEM) were utilized. The obtained results demonstrated that the nano-reinforcement had an improvement in the wear behavior of the aluminum alloy. Furthermore, lower values of the CoF and wear rates were observed in the experiments, with lower normal forces or higher speeds.

Analyzing experimental data from reciprocating wear testing on piston aluminum alloys, with and without clay nano-particle reinforcement.

In the present experimental data, reciprocating wear testing was done on piston aluminum alloys. In some cases, this material was also reinforced by 1% wt. of clay nano-particles and also tested under wear conditions. For this objective, a permanent-mold casting process was done for the aluminum alloy sample. Besides, a stir-casting technique was used for the fabrication of aluminum-matrix nano-composite plus preheating of nano-particles. Then, for both material types (aluminum alloys, with and without nano-particle reinforcement), the weight, the wear rate, and the friction coefficient were measured during testing. Reciprocating wear testing was performed based on the ASTM-G133 standard for 500 m of the wear distance. Other factors were considered as 10, 20, and 30 N for the applied force with a linear velocity of 1 and 7 m/s (equal to 600 and 3600 rpm of the wear testing device). A nodular cast iron (MF-116) based on the piston ring material was utilized as the abrasive system with a hardness of 35-45 HRC in a dry environment. Finally, obtained experimental results were analyzed by a regression technique for the sensitivity analysis of outputs on inputs. Three input parameters were the force, the velocity, and the reinforcement. Moreover, the total wear rate and the average friction coefficient were the output factors. The effect of each input on all outputs was drawn in different contour and surface diagrams.

Data analysis of striation spacing, lifetime, and crack length in crankshaft ductile cast iron under cyclic bending loading through high-cycle fatigue regime.

In this dataset, experimental results of high-cycle bending fatigue testing on crankshaft ductile cast irons were presented both in raw and analyzed data. For this objective, EN-GJS-700-2 standard samples were cut and machined from the crankshaft of a gasoline engine. Then, stress-controlled rotary fatigue experiments were done on cast iron specimens under cyclic four-point bending loads in a fully-reversed condition (zero mean stress). These tests were considered under different cases of the loading rate and the applied stress, for both smooth and notched samples. The loading frequency was set to 12.5, 33.3, 58.3, and 100.0 Hz. The nominal stress was 226.6, 340.0, and 415.5 MPa in unnotched specimens. These values became 310.9, 513.6, and 642.4 MPa, respectively, when a notch was made on the specimens. After testing, field-emission scanning electron microscopy (FESEM) was utilized from the fracture surface of all samples to find the striation spacing and the crack length plus the fatigue lifetime. Obtained results from the sensitivity analysis illustrated that striation spacing was significantly affected by all three inputs of the loading frequency, the maximum stress, and the stress intensity factor. However, the loading frequency and the stress intensity factor had no effects on the fatigue lifetime and the crack length.

Influence of specimen geometry and notch on fatigue lifetime and fracture behavior of aluminum-based nanocomposite under stress-controlled fully-reversed bending loads.

INTRODUCTION: In the present article, the effect of the specimen geometry and the sample notch was studied on the high cycle fatigue lifetime and fracture behavior of the aluminum-based nanocomposite. METHODS: For such an objective, rotary fully-reversed bending fatigue tests were performed on smooth and notched specimens, with the frequency of 100 Hz. Then, simulated results using the MSC Fatigue software were calculated and compared to the fatigue lifetime in the experiments for validation. Moreover, scanning electron microscopy was utilized to observe the fracture surface of failed samples after testing. RESULTS: Obtained results indicated that the fatigue lifetime increased by enhancing the sample diameter. However, the fatigue lifetime reduced when the stress concentration factor changed from 1.0 to 2.9. CONCLUSIONS: All samples with three geometries had a brittle fracture due to cleavage and quasi-cleavage marks on the fracture surface.

Data analysis for investigating the tribological behaviors of aluminum-silicon alloys.

This dataset describes the tribological properties of aluminum-silicon alloys when reinforced with two types of nanoparticles: silica and clay. Moreover, two types of aluminum-silicon alloys were chosen as matrices. These alloys are used in the piston and cylinder-head parts of an automobile engine part. The percentage of nanoparticles was about 1 wt. %. All specimens were developed through the stir casting method. The range of casting temperature was about 700-850 °C. Stirring times for aluminum alloy melts were 2 and 4 min. Ageing heat treatment was also applied for some specimens after the casting process. The Vickers hardness instrument, a pin-on-disk tribometer, and compression test were utilized to collect the data. In addition, to analyze data, a Design-Expert software was used. The data contain hardness, wear rate, friction coefficient, and compression elastic module for aluminum-silicon alloy specimens.

Data analysis of high-cycle fatigue testing on piston aluminum-silicon alloys under various conditions: Wear, lubrication, corrosion, nano-particles, heat-treating, and stress.

In the present work, experimental datasets of high-cycle fatigue properties have been analyzed for aluminum-silicon alloys with the application of the engine piston. For such an objective, standard specimens were casted and machined to perform stress-controlled fatigue testing under fully-reversed cyclic bending loadings. These experiments were done under various conditions of the precorrosion after 100 and 200 h, with the wear (fretting) force of 10, 15, and 20 N, in the lubricated environment, the addition of 1 wt.% nano-clay-particles, T6 heat-treating, and under different applied stresses. All mentioned parameters were sensitively analyzed to find the effective or significant factor by the regression model on the fatigue lifetime. Obtained results illustrated that the stress, wear, corrosion, and nano-particles had negative effects and heat-treating and lubrication were positive variables on the high-cycle fatigue lifetime of aluminum alloys. Moreover, only the effect of the stress and the fretting force was more significant than others, when the sensitivity analysis was considered for the logarithmic value of the material lifetime. The least influence on fatigue properties was related to the lubrication and nano-particles.

Experimental fatigue dataset for additive-manufactured 3D-printed Polylactic acid biomaterials under fully-reversed rotating-bending bending loadings.

In this dataset, experimental fatigue testing results have been presented for the additive-manufactured 3D-printed Polylactic acid (PLA) biomaterials under fully-reversed rotating-bending loadings. For such an objective, a fused deposition modeling (FDM) 3D-printer was utilized to fabricate the standard cylindrical samples with different printing parameters in the horizontal direction. For the demonstration of printing parameter effects on the PLA fatigue lifetime, the nozzle diameters were from 0.2 to 0.6 mm, the extruder temperatures were from 180 to 240 °C, and finally, the printing speeds were from 5 to 15 mm/s. Then after 3D-printing of specimens, fatigue testing was performed on various samples under fully-reversed rotating-bending loadings. Then, the fatigue data were presented in tables through the high-cycle fatigue regime, under the load-controlled condition. For further works, these dataset tables could be used to draw the S-N (stress-lifetime) diagram, to find the fatigue strength coefficient and exponent.

Comparison of the effects of intramyocardial and intravenous injections of human mesenchymal stem cells on cardiac regeneration after heart failure.

OBJECTIVES: Existing studies have demonstrated that intravenous and intramyocardial-administrated mesenchymal stem cells (MSCs) lead to tissue repair after cardiac disorders. We compared the efficiency of both administration methods. MATERIALS AND METHODS: A rat model of isoproterenol-induced heart failure (ISO-HF) was established to compare the effects of intravenous and intramyocardial-administrated MSCs on cardiac fibrosis and function. The animals were randomly assigned into six groups: i) control or normal, ii) ISO-HF (HF) iii) ISO-HF rats treated with intramyocardial administration of culture medium (HF+IM/CM), iv) ISO-HF rats treated with intravenous administration of culture medium ( HF+IV/CM), v) ISO-HF rats treated with intravenous administration of MSCs (HF+IV/MSCs), vi) ISO-HF rats treated with intramyocardial administration of MSCs ( HF+IM/MSCs). Cultured MSCs and culture medium were administrated at 4 weeks after final injection of ISO. Heart function, identification of MSCs, osteogenic differentiation, adipogenic differentiation, cardiac fibrosis and tissue damage were evaluated by echocardiography, flow-cytometery, von Kossa, oil red O, Masson's trichrome and H & E staining, respectively. RESULTS: Both intravenous and intramyocardial MSCs therapy significantly improved heart function and reduced cardiac fibrosis and tissue damage (P<0.05), whereas the cultured medium had no beneficial effects. CONCLUSION: In sum, our results confirm the validity of both administration methods in recovery of HF, but more future research is required.

Leea macrophylla Roxb. leaf extract potentially helps normalize islet of ß-cells damaged in STZ-induced albino rats.

This research aims to investigate the protective effects Leea macrophylla Roxb polyphenols on streptozotocin-induced diabetic rats. Polyphenolic assays were undertaken through established methods. To conduct animal intervention study, forty Wistar albino male rats (average body weight 188.42 ± 7.13 g) of different groups were diabetized by streptozotocin (60 mg/kg) only in the animals of diabetic control (DC) and L. macrophylla extract (LM) groups. At the end of 4 weeks of intervention, serum was analyzed for insulin, liver and cardiac enzymes, lipid profiles, uric acid, and creatinine using ELISA method. In vitro α-amylase inhibition of LM was evaluated and compared with reference drug acarbose. Pancreatic tissues were undertaken for histopathological screening. Food and fluid intake, weekly blood glucose level, liver glycogen, aspartate transaminase (AST), creatinine kinase (CK-MB), cholesterol, and lactate dehydrogenase (LDH) were significantly decreased, whereas oral glucose tolerance (OGTT) ability, serum insulin concentration, and pancreatic islets morphology were significantly improved in the LM300 treatment group compared to the DC group. Alpha-amylase inhibition was not found to be very promising for guiding the α-amylase inhibition pathway. Results suggest that L. macrophylla can exert a potential effort to restore pancreatic ß-cell damaged by streptozotocin induction.

Fabrication and characterization of nanobiocomposite scaffold of zein/chitosan/nanohydroxyapatite prepared by freeze-drying method for bone tissue engineering.

In this investigation, porous composite scaffolds were prepared using a freeze-drying procedure by mixing zein (ZN), chitosan (CS) and nanohydroxyapatite (nHAp) in different inorganic/organic weight ratios. The gained nanocomposite scaffolds were studied using X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and N2-adsorption-desorption technique. Also, swelling, porosity, mechanical properties, biomineralization capability, degradation, cell attachment, and cell viability of the composite scaffolds were studied. The results showed a porous nature with acceptable pore dimensions and interconnections for cell penetration and colonization. In addition, the cytocompatibility of the ZN/CS/nHAp scaffolds was surveyed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) evaluation and cell attachment studies using human bone cancer cells. Studies indicated non- toxicity to the cells, and the cells were found to be attached to the pore walls within the scaffolds. The results related to physicochemical properties and superior cytocompatibility suggested that ZN/CS/nHAp scaffold could be potential candidate materials for the tissue engineering.

Soy isoflavone genistein attenuates lipopolysaccharide-induced cognitive impairments in the rat via exerting anti-oxidative and anti-inflammatory effects.

Systemic inflammation during infectious disorders usually accompanies chronic complications including cognitive dysfunction. Neuroinflammation and cognitive deficit are also observed in some debilitating neurological disorders like Alzheimer's and Parkinson's diseases. Genistein is a soy isoflavone with multiple beneficial effects including anti-inflammatory, anti-oxidative, and protective properties. In this research study, the effect of genistein in prevention of lipopolysaccharide (LPS)-induced cognitive dysfunction was investigated. LPS was given i.p. (500 µg/kg/day) and genistein was orally given (10, 50, or 100 mg/kg) for one week. Findings showed that genistein could dose-dependently attenuate spatial recognition, discrimination, and memory deficits. Additionally, genistein treatment of LPS-challenged group lowered hippocampal level of malondialdehyde (MDA) and increased activity of superoxide dismutase (SOD) and catalase and glutathione (GSH) level. Furthermore, genistein ameliorated hippocampal acetylcholinesterase (AChE) activity in LPS-challenged rats. Furthermore, genistein administration to LPS-injected group lowered hippocampal level of interleukin 6 (IL-6), nuclear factor-kappaB (NF-κB) p65, toll-like receptor 4 (TLR4), tumor necrosis factor α (TNFα), cyclooxygenase-2 (COX2), inducible nitric oxide synthase (iNOS), glial fibrillary acidic protein (GFAP), and increased hippocampal level of antioxidant element nuclear factor (erythroid-derived 2)-like 2 (Nrf2). In conclusion, genistein alleviated LPS-induced cognitive dysfunctions and neural inflammation attenuation of oxidative stress and AChE activity and appropriate modulation of Nrf2/NF-κB/IL-6/TNFα/COX2/iNOS/TLR4/GFAP.

Preparation and characterization of novel ß-chitin/nanodiopside/nanohydroxyapatite composite scaffolds for tissue engineering applications.

ß-chitin/nanodiopside/nanohydroxyapatite (CT/nDP/nHAp) composite scaffolds were synthesized from the combination of chitin, nDP, and nHAp in different inorganic/organic weight ratios by the freeze-drying technique. The prepared nHAp, and composite scaffolds were characterized by BET, TG, FT-IR, SEM, and XRD studies. The composite scaffolds had 50-75% porosities with well-defined interconnected porous networks. Moreover, investigation of the cell attachment and viability using MTT, DMEM solution, and mouse preosteoblast cell proved the cytocompatibile nature of the composite scaffolds with improved cell adhesion. All these results mainly illustrated that this composite could be a candidate for bone tissue engineering application.