Numerical model of a valvuloplasty balloon: in vitro validation in a rapid‑prototyped phantom

Background Patient-specific simulations can provide insight into the mechanics of cardiovascular procedures. Amongst cardiovascular devices, non-compliant balloons are used in several minimally invasive procedures, such as balloon aortic valvuloplasty. Although these balloons are often included in the computer simulations of these procedures, validation of the balloon behaviour is often lacking. We therefore aim to create and validate a computational model of a valvuloplasty balloon. Methods A finite element (FE) model of a valvuloplasty balloon (Edwards 9350BC23) was designed, including balloon geometry and material properties from tensile testing. Young’s Modulus and distensibility of different rapid prototyping (RP) rubber-like materials were evaluated to identify the most suitable compound to reproduce the mechanical properties of calcified arteries in which such balloons are likely to be employed clinically. A cylindrical, simplified implantation site was 3D printed using the selected material and the balloon was inflated inside it. The FE model of balloon inflation alone and its interaction with the cylinder were validated by comparison with experimental Pressure–Volume (P–V) and diameter–Volume (d–V) curves. Results Root mean square errors (RMSE) of pressure and diameter were RMSE P = 161.98 mmHg (3.8 % of the maximum pressure) and RMSE d = 0.12 mm (<0.5 mm, within the acquisition system resolution) for the balloon alone, and RMSE P = 94.87 mmHg (1.9 % of the maximum pressure) and RMSE d = 0.49 mm for the balloon inflated inside the simplified implantation site, respectively. Conclusions This validated computational model could be used to virtually simulate more realistic valvuloplasty interventions

Numerical model of a valvuloplasty balloon:in vitro validation in a rapid-prototyped phantom

BACKGROUND: Patient-specific simulations can provide insight into the mechanics of cardiovascular procedures. Amongst cardiovascular devices, non-compliant balloons are used in several minimally invasive procedures, such as balloon aortic valvuloplasty. Although these balloons are often included in the computer simulations of these procedures, validation of the balloon behaviour is often lacking. We therefore aim to create and validate a computational model of a valvuloplasty balloon. METHODS: A finite element (FE) model of a valvuloplasty balloon (Edwards 9350BC23) was designed, including balloon geometry and material properties from tensile testing. Young’s Modulus and distensibility of different rapid prototyping (RP) rubber-like materials were evaluated to identify the most suitable compound to reproduce the mechanical properties of calcified arteries in which such balloons are likely to be employed clinically. A cylindrical, simplified implantation site was 3D printed using the selected material and the balloon was inflated inside it. The FE model of balloon inflation alone and its interaction with the cylinder were validated by comparison with experimental Pressure–Volume (P–V) and diameter–Volume (d–V) curves. RESULTS: Root mean square errors (RMSE) of pressure and diameter were RMSE(P) = 161.98 mmHg (3.8 % of the maximum pressure) and RMSE(d) = 0.12 mm (<0.5 mm, within the acquisition system resolution) for the balloon alone, and RMSE(P) = 94.87 mmHg (1.9 % of the maximum pressure) and RMSE(d) = 0.49 mm for the balloon inflated inside the simplified implantation site, respectively. CONCLUSIONS: This validated computational model could be used to virtually simulate more realistic valvuloplasty interventions

Pressure Regulator for a High-Altitude Balloon

High altitude balloons are large latex balloons filled with gas that carry payloads to near space. They provide a convenient way to study the Earth’s atmosphere. Per Boyle’s Law, the pressure and volume of a confined gas are inversely proportional. Thus, as the balloon ascends and the atmospheric pressure decreases, the gas inside the balloon expands. This pressure difference allows the balloon to ascend, but it also causes it to continuously expand until it bursts. For some observations, one might want their balloon to remain at constant altitude for a period of time. One way to achieve this is to periodically decrease the volume of the balloon by releasing some of the gas. The objective of this project was to design a valve with a sensor to periodically release gas during flight. The valve was designed in SolidWorks and was 3D printed. A push-pull solenoid was mounted to the inside of the valve and wired to a microprocessor, along with an altimeter sensor to measure altitude. The microprocessor code was written based on altitude and the known pressure gradient versus altitude on Earth. The pressure valve has proven to be fully autonomous. However, testing determined that the valve could not successfully hold helium with leakage of less than one percent per hour. Therefore, the valve could not be tested in actual flight

A study of balloon type, system constraint and artery constitutive model used in finite element simulation of stent deployment

This paper carried out a comparative study of different practices used in finite element simulation of stent deployment, with a focus on the choice of balloon type, system constraint and artery constitutive model. Folded balloon produces sustained stent expansion under a lower pressure when compared to rubber balloon. The maximum stresses on the stent and stenotic artery are considerably higher for simulations using a folded balloon, due to the assumed elastic behaviour of the folded balloon which signified the contact stresses between the balloon and the stent. The achieved final diameter is larger for folded balloon than that for rubber balloon, with increased dogboning and decreased recoiling effects. Fully constrained artery reduces the final expansion when compared to a free artery and a partially constrained artery due to the increased recoiling effect. The stress on the plaque-artery system has similar distribution for all three types of artery constraints (full, partial and free of constraints), but the magnitude is higher for a free artery as a result of more severe stretch. Stenotic plaque model plays a dominant role in controlling stent expansion, and calcified plaque model leads to a considerably lower expansion than hypocellular plaque model. Simulations using Ogden and 6-parameter polynomial models generate different behaviour for stent expansion. For Ogden model, stent expansion approaches the saturation at a certain stage of balloon inflation, while saturation is not observed for 6- 2 parameter polynomial model due to the negligence of the second stretch invariant in the strain energy potential. The use of anisotropic model for the vessel layers reduced the expansion at peak pressure when compared to the simulation using an isotropic model, but the final diameter increased due to the significantly reduced recoiling effect. The stress distribution in the arteryplaque system is also different for different combination of artery and plaque constitutive models. In conclusion, folded balloon should be used in the simulation of stent deployment, with the artery partially constrained using spring elements with a proper stiffness constant. The blood vessel should be modelled as a three-layer structure using a hyperelastic potential that considers both the first and second stretch invariants as well as the anisotropy. The composition of the plaque also has to be considered due to its major effect on stent deployment

Simulation and pre-design of a controlled super-pressure balloon

In this document a deep study of the trajectory of a weather balloon is developed. Making use of a simulator coded in Matlab, it will be possible to predict the flight path prior launch. The starting point is a pre-existing code which assumes that the properties inside the balloon are the same as in the outside; the first part of the project focuses on integrating the formulas needed to compute the temperature and pressure inside, together with the appropriate radius evolution. The simulator will make use of an external data supplier, NOAA, which will provide the wind data based on predictions. The second part of the project is devoted to make an experimental launch: once the system has been recovered and the data measured has been analyzed, a comparison between the simulator and the data obtained from the experiment can be done. The real trajectory of the balloon will be reconstructed from the data measured by the GPS.Ingeniería Aeroespacia

Computational modelling of stent deployment and mechanical performance inside human atherosclerotic arteries

Atherosclerosis is the obstruction of blood stream caused by the formation of fatty plaques (stenosis) within human blood vessels. It is one of the most common cardiovascular conditions and the primary cause of death in developed countries. Nowadays stenting is a standard treatment for this disease and has been undergoing a rapid technological development. The aim of this PhD is to simulate the deployment of stents within atherosclerotic arteries in order to understand the mechanical performance of these devices. To this purpose, specific objectives were identified to study: (i) the effects of stent design, material and coating on stent deployment; (ii) the influence of balloon type, arterial constraints and vessel constitutive models in stenting simulation; (iii) the importance of plaque thickness, stenosis asymmetry and vessel curvature during the process of stent deployment; (iv) the necessity of considering vessel anisotropy and post-deployment stresses to assess stents mechanical behaviour; (v) the performance of biodegradable polymeric stents in comparison with metallic stents. Finite element (FE) analyses were employed to model the deployment of balloon-expandable stents. The balloon-stent-artery system was generated and meshed using finite element package Abaqus. Individual arterial layer and stenosis were modelled using hyperelastic Ogden model, while elastic-plastic behaviour with nonlinear hardening was used to describe the material behaviour of stents. The expansion of the stent was obtained by application of pressure inside the balloon, with hard contacts defined between stent, balloon and artery. The FE model was evaluated by mesh sensitivity study and further validated by comparison with published work. Comparative study between different commercially available stents (i.e. Palmaz-Schatz, Cypher, Xience and Endeavor stents) showed that open-cell design tends to have easier expansion and higher recoiling than closed-cell design, with lower stress level on the plaque after deployment. Also, stents made of materials with lower yield stress and weaker strain hardening experience higher deformation and recoiling, but less post-deployment stresses. Folded balloon produces sustained stent expansion under a lower pressure when compared to rubber balloon, with also increased stress level on the stent and artery. Simulations with different arterial constraints showed that stress on the plaque-artery system is higher for a free artery as a result of more severe stretch. Study of arterial constitutive models showed that saturation of expansion could not be noticed for models that neglect the second stretch invariant in the strain energy potential. Stent expansion is highly affected by plaque thickness, and stresses and recoiling increased considerably with the increasing level of stenosis. Asymmetry of the plaque causes non-uniform stent expansion and high levels of vessel wall stresses are developed in the regions covered by thin layer of plaque. Also, a reduction in stent expansion is observed with the increase of artery curvature, accompanied by an elevation of stresses in the plaque and arterial layers. Vessel anisotropic behaviour reduces the system expansion at peak pressure, and also lowers recoiling effect significantly. The post-deployment stresses caused by stent expansion increase the system flexibility during in-plane bending and radial compression. Comparative study of a PLLA stent (Elixir) and a Co-Cr alloy stent (Xience) showed that polymeric stent has a lower expansion rate and a reduction in final expansion than metallic stent

Cute Balloons with Thickness

Based on the fnite element method, we present a simple volume-preserved thin shell deformation algorithm to simulate the process of inflating a balloon. Diff erent from other thin shells, the material of balloons has special features: large stretch, small bend and shear, and incompressibility. Previous deformation methods often focus on typical three-dimensional models or thin plate models such as cloth model. The rest thin shell methods are complex or ignore the special features of thin shells especially balloons. We modify the triangle element to simple three-prism element, ignore bending and shearing deformation, and use volume preservation algorithm to match the incompressibility of balloons. Simple gas model is used, which interacts with shells to make the balloons inflated. Di different balloon examples have been tested in our experiments and the results are compared with those of other methods. The experiments show that our algorithm is simple and effective

Design of a pneumatic soft robotic actuator using model-based optimization

In this thesis, the design and optimization process of a novel soft intelligent modular pad (IntelliPad) for the purpose of pressure injury prevention is presented. The structure of the IntelliPad consists of multiple individual multi-chamber soft pneumatic-driven actuators that use pressurized air and vacuum. Each actuator is able to provide both vertical and horizontal motions that can be controlled independently. An analytical modeling approach using multiple cantilever beams and virtual springs connected in a closed formed structure was developed to analyze the mechanical performance of the actuator. The analytical approach was validated by a finite element analysis. For optimizing the actuator\u27s mechanical performance, firefly algorithm and deep reinforcement learning-based design optimization frameworks were developed with the purpose of maximizing the horizontal motion of the top surface of the actuators, while minimizing its corresponding effect on the vertical motion. Four optimized designs were fabricated. The actuators were tested and validated experimentally to demonstrate their required mechanical performance in order to regulate normal and shear stresses at the skin-pad interface for pressure injury prevention applications