Bioresorbable Composite Stents for Enhanced Response of Vascular Smooth Muscle Cells

Formation of arterial plaque and stenosis is one of the main cardiovascular disease risk factors. Stenting is a popular approach to increase the inner diameter of the artery and provide an acceptable lumen gain. This is achieved by applying internal pressure to the arterial wall. Despite the desirable outcomes of this procedure, there are complexities and challenges that are being discussed among scholars in this area. Restenosis is one of these complications, in which smooth muscles cell start proliferation and remodeling in response of induced mechanical stresses. Another important issue is the placement of the stent and possible migration due to the continuous deformation and special contact state between tissue and stent struts. Finally, the mechanical properties of the stent and application of novel materials in order to improve its performance are the critical topics that also have been elaborated in the current research work. First of all, we developed a multi-scale model which is able to calculate load distribution in RVE scale and can be useful to assess the mechanical stresses experienced by smooth muscle cells. Moreover, stent migration has been simulated by using finite element modeling, and the effect of stent structure on this complication has been explained. Finally, the application of novel nano composite materials in stent design has been discussed. Developing 3D printed steel-PLLA and MgPLLA particle composites and the effect of added phases in micromechanical properties of composites has been evaluated. Advisor: Linxia G

Bioresorbable Composite Stents for Enhanced Response of Vascular Smooth Muscle Cells

Formation of arterial plaque and stenosis is one of the main cardiovascular disease risk factors. Stenting is a popular approach to increase the inner diameter of the artery and provide an acceptable lumen gain. This is achieved by applying internal pressure to the arterial wall. Despite the desirable outcomes of this procedure, there are complexities and challenges that are being discussed among scholars in this area. Restenosis is one of these complications, in which smooth muscles cell start proliferation and remodeling in response of induced mechanical stresses. Another important issue is the placement of the stent and possible migration due to the continuous deformation and special contact state between tissue and stent struts. Finally, the mechanical properties of the stent and application of novel materials in order to improve its performance are the critical topics that also have been elaborated in the current research work. First of all, we developed a multi-scale model which is able to calculate load distribution in RVE scale and can be useful to assess the mechanical stresses experienced by smooth muscle cells. Moreover, stent migration has been simulated by using finite element modeling, and the effect of stent structure on this complication has been explained. Finally, the application of novel nano composite materials in stent design has been discussed. Developing 3D printed steel-PLLA and MgPLLA particle composites and the effect of added phases in micromechanical properties of composites has been evaluated. Advisor: Linxia G

Double-sided corrugated composite tube and axle protective mechanism for railway vehicles

Structural elements in transportation vehicles are exposed to different types of dynamic loadings and impact scenarios. Protecting passengers against injury and providing mechanisms to avoid impact induced damages to the critical components are the two hot topics in crashworthiness engineering. The presented research work includes two parts. The first part is about designing a novel double-sided composite corrugated tube that can be implemented in front chassis rail of ground vehicles to improve their crashworthiness against collision and car accidents. To maximize the controllable energy absorption of corrugation troughs as observed in the single sided corrugated (SSC) tube, we proposed and tested a new structure design, i.e., double-sided corrugated (DSC) tube made of Al 6060-T6 aluminum alloy or CF1263 carbon/epoxy composite. Finite element models were developed to test the DSC tube in comparison with both SSC and classical straight (S) tubes under axial crushing. Results have shown that the total absorbed energy of the DSC aluminum tube with 14 corrugations was 330% and 32% higher than that of the SSC tube with 14 corrugations and the S-tube, respectively. The second part of this research work is about designing a novel protective mechanism for railway car axle against ballast impact. The ice detached from the train body can fall on the track and form projectiles of ice and gravel (ballast); sharp, heavy, and at high impact energy. The main preventive mechanism in many countries such as Norway is to use protective coating on the axle. But when the coating is damaged by impact, bare steel of the axle can be exposed. The corrosion of these exposed impact zones can cause pits and cavities that become points of stress concentration where fatigue cracks can develop. Due to the current problems with coating technique we suggested a novel protective mechanism and used sandwich panel to protect railway axle against impact. Our results showed that the device can dissipate more than 70 % of impact energy without introducing any damage to the axle surface. Moreover, the rebounding velocity of projectile reduced by 97 % which eliminates the risk of second impact to the other vehicle components. The suggested device can be mounted by using a simple clamping system and unmount easily for potential inspections

Double-sided corrugated composite tube and axle protective mechanism for railway vehicles

Structural elements in transportation vehicles are exposed to different types of dynamic loadings and impact scenarios. Protecting passengers against injury and providing mechanisms to avoid impact induced damages to the critical components are the two hot topics in crashworthiness engineering. The presented research work includes two parts. The first part is about designing a novel double-sided composite corrugated tube that can be implemented in front chassis rail of ground vehicles to improve their crashworthiness against collision and car accidents. To maximize the controllable energy absorption of corrugation troughs as observed in the single sided corrugated (SSC) tube, we proposed and tested a new structure design, i.e., double-sided corrugated (DSC) tube made of Al 6060-T6 aluminum alloy or CF1263 carbon/epoxy composite. Finite element models were developed to test the DSC tube in comparison with both SSC and classical straight (S) tubes under axial crushing. Results have shown that the total absorbed energy of the DSC aluminum tube with 14 corrugations was 330% and 32% higher than that of the SSC tube with 14 corrugations and the S-tube, respectively. The second part of this research work is about designing a novel protective mechanism for railway car axle against ballast impact. The ice detached from the train body can fall on the track and form projectiles of ice and gravel (ballast); sharp, heavy, and at high impact energy. The main preventive mechanism in many countries such as Norway is to use protective coating on the axle. But when the coating is damaged by impact, bare steel of the axle can be exposed. The corrosion of these exposed impact zones can cause pits and cavities that become points of stress concentration where fatigue cracks can develop. Due to the current problems with coating technique we suggested a novel protective mechanism and used sandwich panel to protect railway axle against impact. Our results showed that the device can dissipate more than 70 % of impact energy without introducing any damage to the axle surface. Moreover, the rebounding velocity of projectile reduced by 97 % which eliminates the risk of second impact to the other vehicle components. The suggested device can be mounted by using a simple clamping system and unmount easily for potential inspections

Controllable energy absorption of double sided corrugated tubes under axial crushing

To maximize the controllable energy absorption of corrugation troughs as observed in the single sided corrugated (SSC) tube, we proposed and tested a new structure design, i.e., double-sided corrugated (DSC) tube made of Al 6060-T6 aluminum alloy or CF1263 carbon/epoxy composite. Finite element models were developed to test the mechanical advantage of the DSC tube in comparison with both SSC and classical straight (S) tubes under axial crushing. Results have shown that the total absorbed energy of the DSC aluminum tube with 14 corrugations was 330% and 32% higher than that of the SSC tube with 14 corrugations and the S-tube, respectively. The initiation and progression of the crushing process for different tube configurations were characterized, leading to the mechanism of energy absorption. Plastic deformation in terms of PPEQ is the key parameter correlating with the energy absorption capacity. To overcome the lower specific absorbed energy (SAE) in the DSC tube compared to that in the S-tube, the CF1263 carbon/epoxy composite laminate was adopted and the corresponding SAE was 5.9 times higher than that of the aluminum one. Moreover, the influence of the number of corrugations on the crushing behaviors of the DSC tube was also inspected. A minimal straight tube section was suggested for a controllable smooth crushing behavior regardless of its advantage in SAE. This work might shed light on designing future thin-walled energy absorber devices with better control of crushing behaviors for minimal injuries and damages

Controllable energy absorption of double sided corrugated tubes under axial crushing

To maximize the controllable energy absorption of corrugation troughs as observed in the single sided corrugated (SSC) tube, we proposed and tested a new structure design, i.e., double-sided corrugated (DSC) tube made of Al 6060-T6 aluminum alloy or CF1263 carbon/epoxy composite. Finite element models were developed to test the mechanical advantage of the DSC tube in comparison with both SSC and classical straight (S) tubes under axial crushing. Results have shown that the total absorbed energy of the DSC aluminum tube with 14 corrugations was 330% and 32% higher than that of the SSC tube with 14 corrugations and the S-tube, respectively. The initiation and progression of the crushing process for different tube configurations were characterized, leading to the mechanism of energy absorption. Plastic deformation in terms of PPEQ is the key parameter correlating with the energy absorption capacity. To overcome the lower specific absorbed energy (SAE) in the DSC tube compared to that in the S-tube, the CF1263 carbon/epoxy composite laminate was adopted and the corresponding SAE was 5.9 times higher than that of the aluminum one. Moreover, the influence of the number of corrugations on the crushing behaviors of the DSC tube was also inspected. A minimal straight tube section was suggested for a controllable smooth crushing behavior regardless of its advantage in SAE. This work might shed light on designing future thin-walled energy absorber devices with better control of crushing behaviors for minimal injuries and damages

Experimental study of corrugated metal-composite tubes under axial loading

In this study, crushing behavior of corrugated metal-composite tube was examined experimentally under axial loading condition. Six types of specimens, classified into two groups of metal and metal-composite, were tested under quasi static axial loading. The failure mechanism and failure history of the specimens were presented and discussed. The experimental result showed that corrugated metal composite tubes demonstrate perfect energy absorption characteristics in terms of uniformity of load-displacement diagram, reduction of initial peak load and controlling failure mechanism. Moreover, it was also found that adding filament wound layer of composite on the surface of metallic corrugated tube compensated weakness of corrugated metal tubes, which is low energy absorption capacity. Metal-composite corrugated showed high energy absorption capacity as well as preferable crushing characteristic under the axial loading

The Effect of Number of Corrugation on Crashworthiness of Aluminum Corrugated Tube under Lateral Loading

Thin-walled tubes have been developed and are growing in use as new energy absorber structures. The objective of this study is to investigate the energy absorption and crushing characteristics of corrugated tubes with different number of corrugation in a specific length exposed to lateral loading. At the first step, experimental tests were carried out on a corrugated tube with three con\u27ugations (two inner and one outer) and a tube without corrugation. After that, a finite element model was developed by means of ABAQUS software in order to study the effect of corrugation number on crushing properties of thin-walled tubes. The results show that tubes with corrugations have a higher mean crushing force which is directly proportional to the number of corrugations. Moreover, the plateau region in load-displacement curve decreases by increasing the number of corrugations and therefore the tube reaches its densification point earlier. Plastic strain variation pattern along the tubes were investigated as well

Multi-scale modeling of the lamellar unit of arterial media

The heterogeneity of the lamellar unit (LU) of arterial media plays an important role in the biomechanics of artery. Current two-component (fibrous component and a homogenous matrix) constitutive model is inappropriate for capturing the micro-structural variations in the LU, such as contraction/relaxation of vascular smooth muscle cells (VSMCs), fragmentation of the elastin layer, and deposition/disruption of the collagen network. In this work, we developed a representative volume element (RVE) model with detailed micro-configurations, i.e., VSMCs at various phenotypes, collagen fibers, and elastin laminate embedded in the ground substance. The fiber architecture was generated based on its volume fraction and orientations. Our multi-scale model demonstrated the relation between the arterial expansion and the micro-structural variation of the lamellar unit. The obtained uniaxial response of the LU was validated against the published experimental data. The load sharing capacity of fibrous component and VSMCs of the LU were obtained. We found that the VSMC could take 30% of the circumferential load when contracted until the collagen fibers were recruited, while this value was less than 2% for the relaxed VSMC. In addition, the contribution of collagen fibers at low stretch levels was negligible but became predominant when straightened in high stretches. Moreover, aging effects by collagen deposition was modeled to estimate the arterial stiffening. It was revealed that the aortic stiffness is mainly controlled by collagen fibers, instead of VSMCs. Our findings could shed some light about the contribution of VSMCs in arterial stiffness which has been under debate in recent year

Analysis of the Effects of Relative Price Changes as Supply Shocks on Inflation in Iran

This paper analyses the effects of relative price changes dispersion and skewness as aggregate supply shocks on inflation in iran. For this purpose, we used total and state urban price index, for period 2004-2012 and arellano and bover (1995), Blundell and Bond (1998) method. The results show that relative price changes dispersion and skewness have positive and significant effect on inflation. In addition, the interaction between the dispersion and skewness has negative effect on inflation