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Non-anatomical placement may occur during the surgical implantation of the meniscal implant, and its influence on the resulting biomechanics of the knee joint has not been systematically studied. The purpose of this study was to evaluate the biomechanical effects of non-anatomical placement of the meniscal implant on the knee joint during a complete walking cycle. Three-dimensional finite element (FE) analyses of the knee joint were performed, based on the model developed from magnetic resonance images and the loading conditions derived from the gait pattern of a healthy male subject, for the following physiological conditions: (i) knee joint with intact native meniscus, (ii) medial meniscectomized knee joint, (iii) knee joint with anatomically placed meniscal implant, and (iv) knee joint with the meniscal implant placed in four different in vitro determined non-anatomical locations. While the native menisci were modeled using the nonlinear hyperelastic Holzapfel-Gasser-Ogden (HGO) constitutive model, the meniscal implant was modeled using the isotropic hyperelastic neo-Hookean model. Placement of the meniscal implant in the non-anatomical lateral-posterior and lateral-anterior locations significantly increased the peak contact pressure in the medial compartment. Placement of the meniscal implant in non-anatomical locations significantly altered the tibial rotational kinematics and increased the total force acting at the meniscal horns. Results suggest that placement of the meniscal implant in non-anatomical locations may restrain its ability to be chondroprotective and may initiate or accelerate cartilage degeneration. In conclusion, clinicians should endeavor to place the implant as closest as possible to the anatomical location to restore the normal knee biomechanics.

Stenting of curved arteries is more challenging than straight vessels. There has been an increasing need for new techniques to treat lesions in highly curved locations. One generic idea is to use curved stents to treat lesions in such curved locations. Computational modeling of straight stent crimping which is being used to evaluate the structural performance of the stents has been done vastly in the past. However, there has not been much simulation work on crimping of curved stents due to the challenges associated with applying the boundary conditions. Here we propose a new method to crimp a curved stent to a smaller diameter by incorporating a simple algorithm to generate the required boundary conditions supplementing the finite element (FE) code. To achieve this, a curved crimper is modeled and used to apply crimping loading on the curved stent evaluate its crimpability. Our method provides a simple yet very useful tool which can be implemented in finite element packages to simulate crimping of curved stents using curved crimpers. This method can also be used to expand balloon expandable stents by inflating curved balloons.

Here, a prototypical metallic nanoglass is proposed as a new alloy for balloon expandable stents. Traditionally, the stainless steel SS 316L alloy has been used as a preferred material for this application due to its proper combination of mechanical properties, corrosion resistance, and biocompatibility. Recently, metallic glasses (MGs) have been considered as promising materials for biodevice applications. MGs often display outstanding mechanical properties superior to those of conventional metallic alloys and overcome some of the weaknesses of SS 316L, such as radiopacity, stainless steel allergy, and thrombosis-induced restenosis. However, commonly used monolithic MGs, which have an amorphous homogeneous microstructure, suffer from lack of ductility that is necessary for deployment of balloon expandable stents. In contrast, nanoglasses, that is, amorphous alloys with heterogeneous microstructure, exhibit enhanced ductility which makes them promising materials for balloon expandable stents. We evaluate the feasibility of a prototypical Zr64 Cu36 nanoglass with a grain size of 5 nm for balloon expandable stents by performing finite element method modeling of the stent deployment process in a coronary artery. We consider the BX-Velocity stent design and the nanoglass mechanical properties calculated from atomistic simulations. The results suggest that nanoglasses are suitable materials for balloon expandable stent applications. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 108B:73-79, 2020.

The emergence of bulk metallic glasses (BMGs) has been tantalizing in biomedical applications such as development of novel cardiovascular stents. Numerous investigations have confirmed the superior functional properties and biocompatibility of BMGs over conventional crystalline alloys as stent materials. However, a detailed understanding of the mechanical behavior of BMG-based stents during different stages of their application is still scarce. Here, by quantitative finite element analyses (FEA), we explore the deployment process of a BMG-based self-expandable stent in a patient specific descending aorta to evaluate the arterial stresses and the vessel deformation during the stent deployment. We further benchmark the performance of the BMG based stent by comparing the deployment results both with the results of a similar nitinol based stent and the experimental failure strength of the human arteries. Our detailed analyses confirm that the proposed BMG stent can be safely deployed in the artery without vessel overstretching and mechanical failure, preventing unexpected vessel injuries and resultant pathological responses. Our findings would be insightful for further investigations toward realization of novel BMG-based stent applications.

Bare metal stenting (BMS) does not adequately address the atheroembolic characteristic of carotid artery stenosis. While simple covered stents (CS) may prevent dislodged fragments of the atherosclerotic plaque from entering the blood stream, they also block blood flow into the major branches of the artery alongside the lesion, which is not desirable. Preferential covered stents (PCS) behave as a covered stent in a tubular part of a vessel but maintain side-branch flow over the bifurcation region by means of slits in the membrane. Stent design, membrane material, and slits configuration are the three main components contributing to stent performance. Optimization of PCS designs was conducted and tested.A newly designed BMS was developed and compared to a commercially available peripheral stent. Two materials (expanded poly(tetrafluoroethylene)) and silicone polyurethane co-polymers (Elast-eon E2A) were used as stent coverings with slits applied using various cutting methods to form the PCS. These PCS samples were tested for physical resilience, flexibility, ability to preserve side-branch flow, slit edge roughness, and platelet activation.Fabrication of E2A-coated stents required pretreatment of the stent with poly(ethylene glycol) to achieve firm attachment. The newly designed BMS with nine crowns design and larger cell size showed higher flexibility than commercially available stents. A combination of a larger stent cell size, E2A membrane coating, and three slits per stent cell unit configuration resulted in preserved side-branch flow similar to physiological conditions in the flow experiment. Slit edge roughness changed with different cutting methods and laser machine cutting parameters. In vitro studies showed platelet activation was minimal with lower slit edge roughness samples.An optimized PCS prototype was developed consisting of a newly designed stent, E2A membrane, and a three-slit pattern created by specific femtosecond laser cutting.

Artificial meniscal implants may replace severely injured meniscus and restore the normal functionality of the knee joint. Implant material stiffness and shape influence the longevity of implantations. This study, using 3D finite element analysis, aimed to evaluate the effects of material stiffness variations of anatomically shaped artificial meniscal implant in the knee joint. Finite element simulations were conducted on five different cases including intact knee, medial meniscectomized knee, and the knee joint with the meniscal implant with three distinct material stiffness. Cartilage contact pressures, compression stresses, shear stresses, and implant kinematics (medial-lateral and posterior-anterior displacement) were evaluated for an axial compressive load of 1150 N at full extension. Compared to the meniscectomized knee, the knee joint with the meniscal implant induced lower peak cartilage contact pressure and reduced the cartilage regions loaded with contact pressures greater than the peak cartilage contact pressure induced by the intact knee. Results of the current study also demonstrate that cartilage contact pressures and implant displacement are sensitive to the implant material stiffness. The meniscal implant with a stiffness of 11 MPa restores the intact knee contact mechanics, thereby reducing the risk of physiological damage to the articular cartilage.

To design a hooked self-expandable caval valve stent and determine the best crimping scenario for its percutaneous implantation in the Superior and Inferior Vena Cava (SVCIVC) for the treatment of tricuspid regurgitation (TR). A hooked, Nitinol based stent design was modeled using SOLIDWORKS and finite element analysis (FEA) was carried out using ABAQUS. The Nitinol material used in this study was modeled in ABAQUS as superelastic-plastic. Two cases were simulated. In case A, the stent model was crimped to 18 F by compressing the stent main body and then: (i) bending both the proximal and distal hooks; (ii) straightening the proximal hooks and bending the distal hooks. In case B, the stent model was crimped to 18 F by: (i) bending the proximal and distal hooks and then compressing the stent main body; (ii) straightening the proximal hooks and bending the distal hooks and then compressing the stent main body. The maximum strain after crimping was used to evaluate the best crimping scenario. Hook straightening produced strains of 10.7% and 10.96% as opposed to 12.6% and 13.0% produced by hook bending. From comparison of results of both cases simulated, it was found that straightening the hooks gave lower strain and thus was the best crimping procedure. The analysis performed in this paper may help understand the critical issue of crimpability of the new stent design. The best crimping scenario can be found based on finite element modeling and simulation. Identifying the best crimping way will also help the design team to optimize the delivery system that will eventually be used to deploy this caval valve stent.

Heterotopic implantation of transcatheter tricuspid valve is a new treatment option for tricuspid regurgitation. Transcatheter tricuspid valves (inferior and superior) are implanted at the cavo-atrial junctions (CAJ) in order to avoid the challenging task of anchoring the valve in the complex tricuspid valve annulus. However, little is known about the complex loading that the valve stent can withstand at the cavo-atrial junction, which is critical for fatigue life prediction and device development. In this study, we developed a finite element based fatigue model taking into account the major fatigue loads that may be acting upon the two caval stents, after deployment. The simulation results showed that both stent designs had a fatigue safety factor (FSF) greater than 1 under these complex loading conditions. It was also observed from our simulation that leaflets loads contributed more towards the fatigue of valved stents compared to the other loads. The fatigue model presented in this study provides a simple, fast and cost-effective tool to quantitatively determine the fatigue resistance of caval valved stents subjected to cyclic loads. The simulated bench testing proposed here can be of great value to the design and development of new prosthetic cava stented valves.

Heterotopic implantation of transcatheter tricuspid valve is a new treatment option for tricuspid regurgitation. Transcatheter tricuspid valves are implanted onto the cavoatrial junction in order to avoid the challenging task of anchoring the valve onto the complex tricuspid valve annulus. However, little is known about optimum extent of oversizing of the valved stent in a vena cava. In this study, we implanted valves of the same diameter onto the larger sized inferior vena cava (IVC) and a smaller sized superior vena cava (SVC). The valve in the IVC was oversized by 10.7% while the valve in the SVC was oversized by 21.6%. Finite element analysis was performed (i) to assess the strain on the nitinol stent during manufacturing and deployment; (ii) the stents were deployed in a patient-specific vena cava model and the intramural stress of the vena cava was calculated computationally. These valves were fabricated and placed in a silicone model of a patient-specific right atrium which was part of a mock circulatory system that emulated the patho-physiological flow rate and pressure of a patient with tricuspid regurgitation. Flow measurements were conducted by particle image velocimetry (PIV). It was found that the maximum crimping strain on the nitinol stent was 6.85% which was lower than the critical threshold of 10%. The maximum stress on the vena cava was located at the spot where the hooks met the wall. The maximum stress on the IVC was 0.5098 MPa while the maximum stress on the SVC was 0.7 MPa. The maximum Reynolds shear stress (mRSS) in the vena cava was found to be higher in the IVC than SVC with the highest mRSS being 1741 dynes/cm(2) found in the region of high flow during the peak flow phase. The overtly oversized valve in the SVC did not cause flow disturbances and exhibited mostly laminar flows. The mRSS at the downstream of the vena cava valve and the middle of the atrium remained at low magnitudes. However, velocity fluctuations were high in the IVC in all the time points measured. In conclusion, oversizing the valve may assist anchorage; yet, careful consideration should be taken in choosing the extent of oversizing as it may lead to adverse effects.

Self-expandable stents are widely used to restore blood flow in a diseased artery segment by keeping the artery open after angioplasty. Despite the prevalent use of conventional crystalline metallic alloys, for example, nitinol, to construct self-expandable stents, new biomaterials such as bulk metallic glasses (BMGs) are being actively pursued to improve stent performance. Here, we conducted a series of analyses including finite element analysis and molecular dynamics simulations to investigate the feasibility of using a prototypical Zr-based BMG for self-expandable stent applications. We model stent crimping of several designs for different percutaneous applications. Our results indicate that BMG-based stents with diamond-shaped crowns suffer from severe localization of plastic deformation and abrupt failure during crimping. As a possible solution, we further illustrate that such abrupt failure could be avoided in BMG-based stents without diamond shape crowns. This work would open a new horizon for a quest toward exploiting superior mechanical and functional properties of metallic glasses to design future stents. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1874-1882, 2017.

Thoracic endovascular aortic repair (TEVAR) has been introduced as a less invasive approach to the treatment of thoracic aortic aneurysm (TAA). However, the effectiveness of TEVAR in the treatment of TAA is often limited due to the complex anatomy of aortic arch. Flow preservation at the three supra-aortic branches further increases the overall technical difficulty. This study proposes a novel stent graft design with slit perforations that can positively alter the hemodynamics at the aortic arch while maintaining blood flow to supra-aortic branches. We carried out a computational fluid dynamic (CFD) analysis to evaluate flow characteristics near stented aortic arch in simplified TAA models, followed by in-vitro experiments using particle image velocimetry (PIV) in a mock circulatory loop. The hemodynamics result was studied in terms of time-averaged wall shear stress (TAWSS), oscillating shear index (OSI), and endothelial cell action potential (ECAP). The results showed that the stent graft with slit perforations can reduce the disturbed flow region considerably. Furthermore, the effect of the slits on flow preservation to the supra-aortic branches was simulated and compared with experimental results. The effectiveness of the stent graft with slit perforations in preserving flow to the branches was demonstrated by both simulated and experimental results. Low TAWSS and elevated ECAP were observed in the aortic arch aneurysm after the placement of the stent graft with slits, implying the potential of thrombus formation in the aneurysm. On the other hand, the effects of the stent grafts with full-slit design and half-slit design on the shear stress did not differ significantly. The present analysis indicated that not only could the stent graft with slit perforations shield the aneurysm from rupture, but also it resulted in a favorable environment for thrombus that can contribute to the shrinkage of the aneurysm.

Carotid artery stenosis can be treated by carotid endarterectomy operations (CEA) and carotid artery stenting procedures (CAS). Unlike other artery stents, the effectiveness and safety of carotid artery stenting is not prevailing though it has many advantages. Our group has been developing new generation carotid artery stent since 2011. The innovative carotid stent was named as preferential covered stent (PCS) as it could prevent both emboli release at internal carotid artery (ICA) and provide perfusion to external carotid artery (ECA). A series of studies have been carried out to verify the carotid stent design through modeling and simulation, in vitro loop testing, and in vivo pilot animal testing in our previous proof of concept (POC) stage. Here we report some recent findings on PCS development, including simulation and experimental work on stent crimpability, membrane material characterization, and the flow response for different slit designs in vitro.

Functional and mechanical properties of novel biomaterials must be carefully evaluated to guarantee long-term biocompatibility and structural integrity of implantable medical devices. Owing to the combination of metallic bonding and amorphous structure, metallic glasses (MGs) exhibit extraordinary properties superior to conventional crystalline metallic alloys, placing them at the frontier of biomaterials research. MGs have potential to improve corrosion resistance, biocompatibility, strength, and longevity of biomedical implants, and hence are promising materials for cardiovascular stent applications. Nevertheless, while functional properties and biocompatibility of MGs have been widely investigated and validated, a solid understanding of their mechanical performance during different stages in stent applications is still scarce. In this review, we provide a brief, yet comprehensive account on the general aspects of MGs regarding their formation, processing, structure, mechanical, and chemical properties. More specifically, we focus on the additive manufacturing (AM) of MGs, their outstanding high strength and resilience, and their fatigue properties. The interconnection between processing, structure and mechanical behaviour of MGs is highlighted. We further review the main categories of cardiovascular stents, the required mechanical properties of each category, and the conventional materials have been using to address these requirements. Then, we bridge between the mechanical requirements of stents, structural properties of MGs, and the corresponding stent design caveats. In particular, we discuss our recent findings on the feasibility of using MGs in self-expandable stents where our results show that a metallic glass based aortic stent can be crimped without mechanical failure. We further justify the safe deployment of this stent in human descending aorta. It is our intent with this review to inspire biodevice developers toward the realization of MG-based stents.

Percutaneous heart valve replacement is gaining popularity, as more positive reports of satisfactory early clinical experiences are published. However this technique is mostly used for the replacement of pulmonary and aortic valves and less often for the repair and replacement of atrioventricular valves mainly due to their anatomical complexity. While the challenges posed by the complexity of the mitral annulus anatomy cannot be mitigated, it is possible to design mitral stents that could offer good anchorage and support to the valve prosthesis. This paper describes four new Nitinol based mitral valve designs with specific features intended to address migration and paravalvular leaks associated with mitral valve designs. The paper also describes maximum possible crimpability assessment of these mitral stent designs using a crimpability index formulation based on the various stent design parameters. The actual crimpability of the designs was further evaluated using finite element analysis (FEA). Furthermore, fatigue modeling and analysis was also done on these designs. One of the models was then coated with polytetrafluoroethylene (PTFE) with leaflets sutured and put to: (i) leaflet functional tests to check for proper coaptation of the leaflet and regurgitation leakages on a phantom model and (ii) anchorage test where the stented valve was deployed in an explanted pig heart. Simulations results showed that all the stents designs could be crimped to 18F without mechanical failure. Leaflet functional test results showed that the valve leaflets in the fabricated stented valve coapted properly and the regurgitation leakage being within acceptable limits. Deployment of the stented valve in the explanted heart showed that it anchors well in the mitral annulus. Based on these promising results of the one design tested, the other stent models proposed here were also considered to be promising for percutaneous replacement of mitral valves for the treatment of mitral regurgitation, by virtue of their key features as well as effective crimping. These models will be fabricated and put to all the aforementioned tests before being taken for animal trials.

Vascular support structures are important devices for treating valve stenosis. Large population of patients is treated for valvular disease and the principal mode of treatment is the use of percutaneous valvuloplasty. Stent devices are proving to be an improved technology in minimal invasive cardiac surgery. This technology now accounts for 20% of treatments in Europe. This new technology provides highly effective results at minimal cost and short duration of hospitalization. During the development process, a number of specific designs and materials have come and gone, and a few have remained. Many design changes were successful, and many were not. This paper discusses the physical behavior of a hooked percutaneous aortic valve stent design using finite element analysis using a new Titanium alloy. The analysis performed in this paper may aid in understanding the stent's displacement ranges when subjected to the physiological pressures exerted by the heart and cardiac blood flow during abnormal cardiovascular conditions. It may also help to evaluate the suitability of a new titanium alloy for fabrication purposes.

Recently, percutaneous valve replacement has emerged as an alternative treatment for stenosis of mitral, aortic, and pulmonary valves, replacing the surgical approach and providing a new perspective on transcatheter placement of cardiac valves. The conventional open heart surgery does not suit most of the cardiothoracic patient population for various reasons. Percutaneous valve replacement has started becoming the first choice for surgical replacement of the cardiac valves. Under such a scenario where good potent porcine valves made from the pericardium of pigs are being made available, the real question is designing and developing cost effective stents to bear these valves. The ones that are imported are highly expensive which cannot be afforded by some of the Indian population. This also has substantial benefits from the standpoints of health, safety, and cost. The manufacturing of a stented aortic valve is an absolutely critical job, which requires proper designs, finite element analysis, and flow dynamics studies. This paper forms the base for an eventual manufacture of stented aortic valves, giving in-depth details pertaining to design and implantation of the bioprosthesis in the aorta with flow pattern analysis postimplantation and its hemodynamic efficacy analysis. Blood flow analysis and associated hemodynamic analysis help to understand the leakage resistance of the stented valve. A valve of this kind will enable minimal invasive cardiac surgeons to perform percutaneous aortic valve replacement with ease. This would also be an economic procedure allaying the high costs that are typically involved in conventional open heart surgery. We believe that this model has great potential for helping to set up a protocol for the growing of a tissue engineered heart valve construct.

To design against mechanical failure, most implants such as valve stents are assessed on the basis of survival on a long term. However, accurate investigation of the stress/strain distributions in such valve stents, which govern their deformation and fracture behavior, is essential for their prolonged, and safe use. With this background, an S–N type fatigue analysis was done on three stents with Von Mises stress component having the infinite life at 1.e + 006. The results of this study may aid a biomedical scientist to zero in on the material that could be used to analyze and fabricate percutaneous valve stents.

Objective: To design a new trileaflet aortic valve and investigate its mechanical behavior using finite ele- ment methods. Background: Quantification of aortic valve deformation during cardiac cycle is essential in understanding normal and pathological valvular function and eventually in the design of valves. We have designed and analyzed a new tissue valve model to investigate the mechanics of the valve and its components. Methods: Steps involves in 3D CAD based geometric modeling of a trileaflet aortic valve and the effects of different component dimensions on the mechanical behavior of valve is presented in this paper. Conceptual designing of individual components was used to build the total geometric model. Different physiological pressures were applied on the valve model and its deformation patterns were studied. Results: A new geometric model of a trileaflet aortic valve was designed. Its mechanical behavior was studied. Geometric analysis and simulation of these models enhanced the designer to optimize the geometry suitable for performance during and after implantation. Conclusion: The geometry-based model presented here allows determining quickly if the new set of valve component dimensions results in a functional valve. This is of great interest to designers of new prosthetic heart valve models, as well as to surgeons involved in valve- sparing surgery.

Our objective was to design a new trileaflet aortic valve using computer-aided design (CAD). Quantification of aortic valve geometries is essential in understanding normal and pathological valvular function and eventually in the design of valves. We have designed a new tissue valve model to investigate its suitability in aortic valve replacement. Steps involved in three-dimensional CAD-based geometric modeling of a trileaflet aortic valve and the effects of different component dimensions on the mechanical behavior of valve are presented in this article. Conceptual designing of individual components was used to build the total geometric model. A new geometric model of a trileaflet aortic valve was designed. This may be of great interest to designers of new prosthetic heart valve models, as well as to surgeons involved in valve-sparing surgery.

Background: Smoking has a number of well-documented negative effects on health. The seemingly common knowledge is that smoking causes low back pain. Cigarette smoking is associated with poor physical fitness and reduced muscle strength.1 The specific effects of smoking on the efficacy of the lumbar extensors have been previously investigated where individuals with chronic low back pain often have weaker lumbar extensor muscles.2 Rigorous exercises, however, reverse this weakness. Hypothesis: This study hypothesizes that cigarette smoking is associated with deficits in the lumbar extensor strength that make the back susceptible to mechanical stress and injury. Study Design: Cohort study. Methods: The objective of this study was to determine the isometric lumbar extensor strength before and after fatigue challenge amongst smokers and nonsmokers. A pre-test and post-test design was used to determine the differences in the lumbar extensor endurance between smokers and nonsmokers. Results: The result of the study confirms a relationship between reduced lumbar extensor strength and cigarette smoking. The negative impact of smoking on lumbar extensors suggests increased susceptibility to lumbar injuries and thereby low back pain. Conclusions: Smokers demonstrated reduced muscle strength and fatigability of the lumbar extensors and they may perhaps be vulnerable to lumbar spine injuries. The study also confirmed that spinal extension exercises increased the endurance time of the lumbar extensor muscles.

Valve stents are small cylindrical structures introduced in stenosed valves to replace them and restore blood flow. High radial force has become an essential feature of these stents. The primary aim of this investigation was to investigate the effects of varying stent "design parameters" on its radial force by using the finite element method (FEM). The improved model design was carried out to meet the functional and surgical requirements. The finite element model to evaluate radial force of stent was dependant on various design parameters. The results show that amplitude was the dominant parameter in this study. Increasing either strut circumference or thickness generally improved radial force of stent. However, increasing either amplitude or radius of curvature generally weakened it. In conclusion, FEM can quantify the compressive mechanical property of stent and help designers to optimize stent systems.

Objective: To design a novel percutaneous stented valve and model its implantation in the aorta.Background: The dimensions of stented aortic valve components govern its ability to prevent backflow of blood into the left ventricle. Whilst the theoretical parameters for the best stent performance have already been established, an effective valve model and its suitability along with the stent are lacking.Methods: This article discusses the design of a stented valve suitable for percutaneous aortic valve replacement. Steps involved in 3D CAD-based geometric modeling of the stented aortic valve and its implantation in the aorta are presented. Conceptual designing of individual components was used to build the total geometric model.Results: A novel geometric model of percutaneous stented aortic valve was generated. The improved design enhances its performance during and after implantation.Conclusion: The blunt hooks in the stent model prevent its migration in either direction by getting embedded in the aortic endothelium. This novel stent aortic valve may be of great interest to designers of future bioprosthetic heart valve models, as well as to surgeons involved in minimally invasive valve surgeries.

Background Vascular support structures are important devices for treating valve stenosis. Large population of patients are treated for valvular disease and the principal mode of treatment is the use of percutaneous valvuloplasty. Stent devices are proving to be an improved technology in minimal invasive cardiac surgery. This technology now accounts for 20% of treatments in Europe. This new technology provides highly effective results at minimal cost and short duration of hospitalization. Methods This paper discusses the design and finite element analysis (FEA) of a percutaneous aortic valve stent. The stent design was modeled and subjected to FEA. The improved model design was carried out to meet the functional and surgical requirements. Analysis was done with different materials with loads ranging from 50 to 73 kgf/mm 2 . These forces were selected because these values are far greater than the normal human blood pressure which ranges from 10 to 16 kPa. It was also to understand the mechanical behavior of different stent materials under such high pressures. Results A stent model was generated and its physical, mechanical, and behavioral properties were studied. Finite element analysis and simulation of the model help the designer to optimize the geometry suitable for performance during and after implantation. The design objective for the stent is to have long-term durability, low thrombogenicity, and resistance to migration and paravalvular leak. Conclusion The analysis performed in this paper may aid in understanding the stent's tolerable pressure ranges in comparison with the physiological pressures exerted by the heart and cardiac blood flow during abnormal cardiovascular conditions. It may also help in finding the material that will best suit the stent.

Vascular support structures are an important tool for treating valve stenosis. A large population of patients are treated for valvular disease and the principal mode of treatment is the use of percutaneous valvuloplasty. Stent devices are proving to be an improved treatment method; these devices now account for 20% of treatments in Europe. This new technology provides highly effective results at minimal cost and with reduced hospital stays. Accurate and reliable structural analysis provides essential information to the design team in an environment where in vivo experimentation is extremely expensive or impossible. This paper describes the design of a new vascular support structure (stent), to provide designers with estimates of the critical parameters which are essential. Stainless steel stents are preferred to be used as balloon-expanded prostheses as they are cost-effective.

Aim: This paper discusses the design and Finite Element Analysis (FEA) of a Percutaneous Aor-tic Valve Stent. The aim of this study was to model a percutaneous aortic valve stent and subject it to finite element analysis. The design process was carried out to meet the functional and surgical requirements. Methods and Results: Analysis was done with different materials with loads ranging from 50 kgf/mm² to 73 kgf/mm². These forces were selected because these val-ues are far greater than the normal human blood pressure which ranges from 10kPa to 16kPa. It was also to understand the mechanical behavior of different stent materials under such high pressures. A stent model was generated and its physical, mechanical and behavioral properties were studied. Finite element analysis and simulation of the model enhanced the designer to optimize the geometry suitable for perform-ance during and after implantation. The design objective for the stent is to have long term du-rability, low thrombogenicity, resistance to mi-gration and paravalvular leak. Conclusion: The analysis performed in this paper may aid in understanding the stent’s tolerable pressures ranges in comparison with the physiological pressures exerted by the heart and cardiac blood flow during abnormal cardiovascular conditions.

Vascular support structures are an important tool for treating valve stenosis. A large population of patients are treated for valvular disease and the principal mode of treatment is the use of percutaneous valvuloplasty. Stent devices are proving to be an improved treatment method; these devices now account for 20% of treatments in Europe. This new technology provides highly effective results at minimal cost and short duration of hospitalization. Accurate and reliable structural analysis provides essential information to the design team in an environment where in vivo experimentation is extremely expensive, or impossible. This paper describes the design of vascular support structure (stents), to provide designers with estimates of the critical parameters which are essential to restore the functions of the endothelium of the Aorta during and after implantation without injuring it.

Self-expandable stents are widely used to restore blood flow in a diseased artery segment by keeping the artery open after angioplasty. Despite the prevalent use of conventional crystalline metallic alloys, for example, nitinol, to construct self-expandable stents, new biomaterials such as bulk metallic glasses (BMGs) are being actively pursued to improve stent performance. Here, we conducted a series of analyses including finite element analysis and molecular dynamics simulations to investigate the feasibility of using a prototypical Zr-based BMG for self-expandable stent applications. We model stent crimping of several designs for different percutaneous applications. Our results indicate that BMG-based stents with diamond-shaped crowns suffer from severe localization of plastic deformation and abrupt failure during crimping. As a possible solution, we further illustrate that such abrupt failure could be avoided in BMG-based stents without diamond shape crowns. This work would open a new horizon for a quest toward exploiting superior mechanical and functional properties of metallic glasses to design future stents. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1874-1882, 2017.

Our group recently developed a novel covered carotid stent that can prevent emboli while preserving the external carotid artery (ECA) branch blood flow. However, our recent in vitro side-branch ECA flow preservation tests on the covered stents revealed the need for further stent frame design improvements, including the consideration to crimp the stent to a low profile for the delivery of the stent system and having bigger cells. Hence, the current work aims to design new bare metal stents with bigger cell size to improve the crimpability and to accommodate more slits so that the side-branch flow could be further increased. Three new stent designs were analyzed using finite element analysis and benchmarked against two commercially available carotid stents in terms of their mechanical performances such as crimpability, radial strength, and flexibility. Results indicated that the new bare metal stent designs matched well against the commercial stents. Hence our new generation covered stents based on these designs can be expected to perform better in side-branch flow preservation without compromising on their mechanical performances.

This work presents a numerical simulation of intraventricular flow after the implantation of a bileaflet mechanical heart valve at the mitral position. The left ventricle was simplified conceptually as a truncated prolate spheroid and its motion was prescribed based on that of a healthy subject. The rigid leaflet rotation was driven by the transmitral flow and hence the leaflet dynamics were solved using fluid-structure interaction approach. The simulation results showed that the bileaflet mechanical heart valve at the mitral position behaved similarly to that at the aortic position. Sudden area expansion near the aortic root initiated a clockwise anterior vortex, and the continuous injection of flow through the orifice resulted in further growth of the anterior vortex during diastole, which dominated the intraventricular flow. This flow feature is beneficial to preserving the flow momentum and redirecting the blood flow towards the aortic valve. To the best of our knowledge, this is the first attempt to numerically model intraventricular flow with the mechanical heart valve incorporated at the mitral position using a fluid-structure interaction approach. This study facilitates future patient-specific studies.

To evaluate and compare the effects of hold-relax technique and cyclic loading technique on increasing the resting length of hamstring muscles.Design and SettingThis was a randomised intervention trial. The setting was an academic rehabilitation centre, which provided physical therapist assistant programs under the supervision of a biomechanics expert. Thirty-six healthy male subjects who exhibited bilateral hamstring muscle tightness (18–30 years of age) volunteered to participate in this study. For each subject, one leg was randomised to receive the hold-relax technique, whereas the other side received the cyclic loading technique. The treatment was applied every alternate day for 3 consecutive weeks. Stretching sessions were supervised by the biomechanics specialist. Measurements were taken before and after the 3-week treatment period by the same investigator, who was blindfolded to the allocation of treatment. The popliteal angle and stretch pain (measured by the visual analogue scale) were the two parameters considered. The analysis was done using the paired t tests. The results showed that both the hold relax and cyclic loading stretch produced significant difference in the popliteal angle and stretch pain (p

Modern biomedical advances have propelled percutaneous valve replacement into an effective and powerful therapy for many heart valve diseases, especially aortic valve stenosis. Experiences so far suggest that outcomes for new percutaneous valve replacement surgery compare favorably with that of traditional valve surgery in selected patients with severe symptomatic aortic stenosis. The inception of percutaneous aortic valve replacement (PAVR) began in 1992 when the potential for treating valve diseases was demonstrated through a modern technique of endoluminal deployment of a catheter-mounted crimped stented heart valve in an animal model. The first successful demonstration of such novel technique of surgical replacement of a heart valve was performed in 2002, when valve implantation in a patient with aortic stenosis was reported. Despite initial stumbles and a perception of being an uphill task, PAVR has emerged as one of the breakthroughs in surgical procedures. More than 1500 citations were found in PubMed, half of which were available after 2011. This is primarily because more than 50,000 procedures are being performed in more than 40 countries worldwide, with encouraging outcomes, and several stented valves have been launched in the market. This review provides a detailed analysis of the current state of the art of PAVR. Moreover, a competitive landscape of various devices available in the market and their design considerations, biomaterial selections, and overall hemodynamic performance are presented.

Although percutaneous heart valve replacement is getting known amongst cardiovascular surgical procedures, as it was recently introduced, and reports of early clinical experience been published, this technique is limited to the replacement of pulmonary and aortic valves in old patients who cannot undergo open heart surgery. One of the reasons is the uphill challenges in the generation of an ideal design that would address anchorage and leakage issues. Stent anchorage and paravalvular leaks prove to the greatest challenge posed to biomedical design engineers. This paper describes a novel Nitinol based mitral valve stent that addresses migration and paravalvular leaks associated with the bioprosthetic mitral valve. The geometry-based model presented here specifically addresses issues of valve migration and paravalvular leaks This is of great interest to designers of new prosthetic heart valve models, as well as to surgeons involved in valve sparing surgery. Simulation results show that the studied stent design seemed to be good by virtue of its acceptable maximum crimping strain.Copyright © 2012 by ASME

Vascular support structures are important devices for treating valve stenosis. Large populations of patients are treated for valvular disease and the principal mode of treatment is the use of percutaneous valvuloplasty. Stent devices are proving to be imperative in minimally invasive cardiac surgery. This new technology provides highly effective results at minimal cost and short duration of hospitalization. This article discusses the finite element analysis (FEA) of various percutaneous aortic valve stent designs. The stent designs were modeled and subjected to FEA. Analysis was done on four models using three biomaterials, with loads ranging from 10,665.8 N/m(2) to 26,664 N/m(2). These pressures were selected as they are equivalent to human blood pressure, which ranges from 80 mm Hg to 200 mm Hg. They were also selected to understand the mechanical behavior of different stent designs under such high pressures. Four stent models were generated and their physical, mechanical, and behavioral properties were studied. FEA and simulation of these models encouraged the designer to select the geometry and the biomaterial suitable for performance during and after implantation. The analysis performed in this article may aid in understanding the stents' performance ranges when subjected to the physiological pressures exerted by the heart and cardiac blood flow during abnormal cardiovascular conditions. It may also help in finding the best design and the biomaterial that would be suitable under such conditions.

Piezoresistive actuation of a microcantilever induced by biomolecular binding such as DNA hybridization and antibody-antigen binding is an important principle useful in biosensing applications. As the magnitude of the forces exerted is small, increasing the sensitivity of the microcantilever becomes critical. In this paper, we are considering to achieve this by geometric variation of the cantilever. The sensitivity of the cantilever was improved so that the device can sense the presence of the antigen even if the magnitude of surface stresses over the microcantilever was very small. We consider a “T-shaped” cantilever that eliminates the disadvantages while improving the sensitivity simultaneously. An analysis of the cantilever using stainless steel and silicon has been performed using INTELLISUITE software (a microelectromechanical systems design and simulation package).

Our objective was to design a new trileaflet aortic valve using computer-aided design (CAD). Quantification of aortic valve geometries is essential in understanding normal and pathological valvular function and eventually in the design of valves. We have designed a new tissue valve model to investigate its suitability in aortic valve replacement. Steps involved in three-dimensional CAD-based geometric modeling of a trileaflet aortic valve and the effects of different component dimensions on the mechanical behavior of valve are presented in this article. Conceptual designing of individual components was used to build the total geometric model. A new geometric model of a trileaflet aortic valve was designed. This may be of great interest to designers of new prosthetic heart valve models, as well as to surgeons involved in valve-sparing surgery.

To design against mechanical failure, most implants such as valve stents are assessed on the basis of survival on a long term. However, accurate investigation of the stress/ strain distributions in such valve stents, which govern their deformation and fracture behavior, is essential for their prolonged, and safe use. Nitinol, a shape-memory alloy, can “remember” a previous shape and can recover strains as high as 10% by deformation (super-elasticity) or temperature change. As such, deformation mechanisms of Nitinol are more complex than the conventional modes of plastic deformation in traditional alloys. Consequently, the mechanical behavior of Nitinol under multi-axial conditions remains poorly understood. With this background, an S-N type fatigue analysis was done on three stents with Von Mises stress component having the infinite life at 1.e+008. The results of this study may aid biomedical scientist to zero in on the material that could be used to analyse and fabricate percutaneous valve stents.

Piezoresistive actuation of a microcantilever induced by biomolecular binding such as DNA hybridization and antibody-antigen binding is an important principle useful in biosensing applications. As the magnitude of the forces exerted is small, increasing the sensitivity of the microcantilever becomes critical. In this paper, we are considering to achieve this by geometric variation in the cantilever. The sensitivity of the cantilever was improved so that the device can sense the presence of antigen even if the magnitude of surface-stresses over the microcantilever was very small. We consider a “T-shaped” cantilever that eliminates the disadvantages while improving the sensitivity simultaneously. Simulations for validation have been performed using INTELLISUITE software (a micro-electromechanical system design and simulation package). The simulations reveal that the T-shaped microcantilever is almost as sensitive as a thin cantilever and has relatively very low buckling effect. Simulations also reveal that with an increase in thickness of the cantilever, there is a proportional decrease in the sensitivity.

Vascular support structures are important tools for treating valve stenosis. A large population of patients is treated for valvular disease and the principal mode of treatment is the use of percutaneous valvuloplasty. Stent devices are proving to be an improved treatment method; these devices now account for 20% of treatments in Europe. This new technology provides highly effective results at minimal cost and short duration of hospitalization. Accurate and reliable structural analysis provides essential information to the design team in an environment where in vivo experimentation is extremely expensive, or impossible. This paper describes the design of vascular support structures (stents), to provide designers with estimates of the critical parameters which are essential to restore the functions of the endothelium of the Aorta during and after implantation without injuring it.