Use Of Computational Models Research Articles

Reservoir implantation for flood dampening in the Macaé River basin using the Mohid Land model

The use of computational models of varied complexity helps to understand the hydrological dynamics studying different scenarios of urban flood. In this perspective, a hydrological model of the Macaé river basin (RH-VIII) was built using the MOHID Land platform to simulate the implementation of a hypothetical attenuation reservoir for flood mitigation in the Macaé urban region. The results indicate that the maximum flows obtained with the simulation from project rainfalls were compatible with values observed in the literature, in the region of interest. The analysis of the flood hydrograms (m3/s) indicates a high efficiency in flood mitigation near the reservoir region, higher than 50%, while at the lower part of the basin, more urbanized region, the attenuation was of the order of 10%.

P2439Reconstructing electrocardiograms from computational models of infarcted ventricles to determine the location of myocardial infarct scars based on features of the signal

Abstract Myocardial infarction can cause ventricular tachycardia as a result of reentrant electrical activation waves propagating around the infarct scar. The tachycardia can be treated by radiofrequency catheter ablation which requires the cardiologist to deliver radiofrequency, via an intracardiac catheter, to ablate a specific site within the scar, disrupting the reentrant circuit, to terminate the arrhythmia. Therefore, determining the location of the scar is an important step in the procedure. MRI and CT scans can show the region of scar but are costly and are contraindicated in many cases. Cardiologists observe ECG recordings of the patient's tachycardia, looking at the gross characteristics of the signal to determine an approximate location of the scar. However, this technique assumes a recording of the patient's tachycardia is available, and is only able to suggest a gross region of the heart. In addition, the method is based on studies which have identified characteristic features of the ECG using intracardiac mapping to determine the location of the scar, which may be unreliable. This study aims to determine features of the ECG which may be able to predict the location of an infarct scar with more accuracy and specificity than current methods allow. The use of computational models ensures that the true location of the scar is known, unlike in previous studies. Moreover, we aim to determine whether there are any characteristics of resting state ECG which may indicate the location of an infarct scar. An anatomically accurate finite element model of rabbit ventricles in a conductive bath was utilised in order to simulate electrical activation waves and generate ECG signals, by reconstructing the extracellular potentials. Scar regions comprising of non-conducting scar surrounded by tissue with altered electrophysiological properties to represent the borderzone were incorporated into the ventricular model at varying locations across the myocardium. The models were stimulated using an S1S2 protocol to produce wave block and reentry. ECGs were reconstructed and the differences between models were observed. Results suggest that differences in timing and amplitude of the R wave on the ECG could be an indication of scar location. Changes in the repolarisation phase of the ECG were also apparent, suggesting more features which could determine the location of the scar. Importantly, characteristic features of the ECG could also be determined from resting state ECG, generated from models where scar was present but no reentry occurred. Utilising computational models of rabbit ventricles with scars incorporated at a variety of locations around the myocardium, we were able to determine a set of features from the ECG which may be of use in determining the location of an infarct scar. Future validation of this study using patient data could indicate that this methodology may be of use in predicting scar location in ablation procedures. Acknowledgement/Funding YH is funded by the MRC (MR/R024995/1). JT acknowledges the financial support of the EPSRC (EP/N014391/1) and the Wellcome Trust WT105618MA.

Nanoindentation of Polyethylene/Polypropylene Tri-Layer Separator Under Dry and Wet Conditions

Polymer separators play an important role in lithium ion batteries by preventing contact between the positive and negative electrodes while allowing the ions to pass through. It is, therefore, important to study not only the chemical properties, but also mechanical properties of separators. Although mechanical properties of separators have been measured using, for example, tensile tests or dynamic mechanical analysis (DMA), local mechanical properties, especially when the separators are immersed in the electrolyte, are not well known. The local deformation behavior under compression is important since the separator is usually in contact with the porous electrode layer which has micro- and nano-meter length scale surface roughness. To study the mechanical properties in a more realistic environment, a polyethylene/polypropylene tri-layer separator (Celgard 2325) was investigated, under both dry and wet conditions, using a nanoindentation system. The indentation measurements were preformed inside of an argon filled glovebox which allowed for indentation in an organic electrolyte. A piece of separator was first saturated with several drops of electrolyte before several more drops were added to create a thin electrolyte layer in which the indenter tip remained submerged during indentation to avoid the surface tension effect on the measured load vs. displacement curves. By analyzing these curves, the elastic modulus and hardness were obtained. A t-test for two population means was conducted to ascertain whether there is a statistical significance between the dry and wet conditions. Under wet conditions, the separator displayed a larger elastic modulus of 0.884 GPa and hardness of 0.0478 GPa compared to 0.801 GPa and 0.0418 GPa under dry conditions, respectively. The incompressibility of the liquid electrolyte may be responsible for the measured differences. This study provides a more representative set of mechanical properties that should be considered especially for use in computational modeling and design of battery cells.

Modeling of the Human Cerebral Collateral Circulation: Evaluation of the Impact on the Cerebral Perfusion in Case of Ischemic Stroke

Abstract Stroke is the third-most cause of death in developed countries. A new promising treatment method in case of an ischemic stroke is selective intracarotid blood cooling combined with mechanical artery recanalization. However, the control of the treatment requires invasive or MRI-assisted measurement of cerebral temperature. An auspicious alternative is the use of computational modeling. In this work, we extended an existing 1D hemodynamics model including the characteristics of the anterior, middle and posterior cerebral artery. Furthermore, seven ipsilateral anastomoses were additionally integrated for each hemisphere. A potential stenosis was placed into the M1 segment of the middle cerebral artery, due to the highest risk of occlusion there. The extended model was evaluated for various degrees of collateralization (“poor”, “partial” and “good”) and degrees of stenosis (0%, 50%, 75% and 99.9%). Moreover, cerebral autoregulation was considered in the model. The higher the degree of collateralization and the degree of stenosis, the higher was the blood flow through the collaterals. Hence, a patient with a good collateralization could compensate a higher degree of occlusion and potentially has a better outcome after an ischemic stroke. For a 99.9% stenosis, an increased summed mean blood flow through the collaterals of +97.7% was predicted in case of good collateralization. Consequently, the blood supply via the terminal branches of the middle cerebral artery could be compensated up to 44.4% to the physiological blood flow. In combination with a temperature model, our model of the cerebral collateral circulation can be used for tailored temperature prediction for patients to be treated with selective therapeutic hypothermia.

A 1D computer model of the arterial circulation in horses: An important resource for studying global interactions between heart and vessels under normal and pathological conditions.

Arterial rupture in horses has been observed during exercise, after phenylephrine administration or during parturition (uterine artery). In human pathophysiological research, the use of computer models for studying arterial hemodynamics and understanding normal and abnormal characteristics of arterial pressure and flow waveforms is very common. The objective of this research was to develop a computer model of the equine arterial circulation, in order to study local intra-arterial pressures and flow dynamics in horses. Morphologically, large differences exist between human and equine aortic arch and arterial branching patterns. Development of the present model was based on post-mortem obtained anatomical data of the arterial tree (arterial lengths, diameters and branching angles); in vivo collected ultrasonographic flow profiles from the common carotid artery, external iliac artery, median artery and aorta; and invasively collected pressure curves from carotid artery and aorta. These data were used as input for a previously validated (in humans) 1D arterial network model. Data on terminal resistance and arterial compliance parameters were tuned to equine physiology. Given the large arterial diameters, Womersley theory was used to compute friction coefficients, and the input into the arterial system was provided via a scaled time-varying elastance model of the left heart. Outcomes showed plausible predictions of pressure and flow waveforms throughout the considered arterial tree. Simulated flow waveform morphology was in line with measured flow profiles. Consideration of gravity further improved model based predicted waveforms. Derived flow waveform patterns could be explained using wave power analysis. The model offers possibilities as a research tool to predict changes in flow profiles and local pressures as a result of strenuous exercise or altered arterial wall properties related to age, breed or gender.

Broadband lung dielectric properties over the ablative temperature range: Experimental measurements and parametric models.

Computational models of microwave tissue ablation are widely used to guide the development of ablation devices, and are increasingly being used for the development of treatment planning and monitoring platforms. Knowledge of temperature-dependent dielectric properties of lung tissue is essential for accurate modeling of microwave ablation (MWA) of the lung. We employed the open-ended coaxial probe method, coupled with a custom tissue heating apparatus, to measure dielectric properties of ex vivo porcine and bovine lung tissue at temperatures ranging between 31 and 150 C, over the frequency range 500MHz to 6GHz. Furthermore, we employed numerical optimization techniques to provide parametric models for characterizing the broadband temperature-dependent dielectric properties of tissue, and their variability across tissue samples, suitable for use in computational models of microwave tissue ablation. Rapid decreases in both relative permittivity and effective conductivity were observed in the temperature range from 94 to 108 C. Over the measured frequency range, both relative permittivity and effective conductivity were suitably modeled by piecewise linear functions [root mean square error (RMSE)=1.0952 for permittivity and 0.0650 S/m for conductivity]. Detailed characterization of the variability in lung tissue properties was provided to enable uncertainty quantification of models of MWA. The reported dielectric properties of lung tissue, and parametric models which also capture their distribution, will aid the development of computational models of microwave lung ablation.

Full-Scale Informal Settlement Dwelling Fire Experiments and Development of Numerical Models

While fire-related injuries and deaths decreased in the global north over the past few years, they have increased in the global south. With more than one billion people residing in informal settlements (sometimes known as slums, ghettos or shantytowns), it is necessary that greater effort be placed on addressing and developing means for improving fire safety in these areas. As a result of advances made in computer technologies, emerging performance-based regulations and an increase in building complexity in the global north, the use of computer models simulating enclosure fires have increased dramatically. In this work an experimental investigation is presented for (a) a full-scale corrugated steel sheeting clad informal dwelling experiment and (b) a full-scale timber clad informal dwelling experiment. The experimental results are then compared to numerical models consisting of both simple two-zone (OZone) and computational fluid dynamic models. Currently, there is negligible literature available on Fire Dynamic Simulator (FDS) modelling of informal settlement dwellings (sometimes known as shacks or shanties) fires. This paper evaluates the plausibility of using FDS v6.7 and zonal models to predict certain fire parameters (i.e. ceiling temperatures, heat fluxes, etc.) for Informal Settlement Dwellings (ISDs) and to study the plausibility of using FDS to estimate the probability of fire spread. In this paper an introduction to ISDs is given with details pertaining to construction materials and considerations needed for numerical modelling of informal dwellings (i.e. thin permeable boundaries or combustible boundaries). Models are based upon (a) a prescribed heat release rate per unit area in FDS using data obtained from a Fire Propagation Apparatus test, and (b) an empirical two-zone model using OZone. The FDS validation guide was used to quantify the model uncertainties in order to give a critical separation distance at which fire spread between dwellings will not occur. It was found that at 3 m spacing between ISDs there is a 6% chance (based on the model uncertainties) that fire spread can occur. This is an important finding that highlights the danger associated with these closely spaced dwellings and the hope is that it can guide local government and Non-Governmental Organizations in future decision making. Three meters spacing between dwellings, however, may not be possible due to the socio-cultural-political-economic issues associated with informal settlements. This is one of the first papers to demonstrate FDS models against full-scale ISD experiments.

An Early PDP Connectionist Model for Describing the Behavioral Phenomenon

The focus of modern neuroscience on cognitive processes has relegated to behavior the epiphenomenal status of neural processing and the difficulties generated by this interpretation have encouraged the use of computational models. However, the implementation based on inferred cognitive constructs has been inefficient. The objective of this work was to review the concept of behavior by a selectionist approach and propose a connectionist computational model that operates integrally with its neurophysiological bases. The behavioral phenomenon was functionally defined and described at different levels of analysis. Functional levels make it possible to understand why behavioral phenomena exist, while topographic levels describe how morphophysiological mechanisms implement the response. The connectionist notions of PDP ANNs formalizes the proposal. The model stands out for contextualizing neural processing as part of the response, addressing the behavioral phenomenon as a whole that needs to be explained in its most different levels of analysis.

Digital Model for Diagnosis of Postoperative Complications in Medicine Using Bioinformatics

Digital models are needed in medicine using bioinformatics for diagnosis and prediction. Such models are especially needed in personalized medicine using bioinformatics. In this area, it is necessary to evaluate and predict the patient's condition from a priori knowledge obtained from other patients. Therefore, a new direction appeared - predictive medicine using bioinformatics. Predictive medicine, or “in silico medicine” is the use of computer modelling and intelligent technologies in the diagnosis, treatment and prevention of diseases. Using predictive medicine, the doctor can determine the likelihood of the development of certain diseases and choose the optimal treatment using bioinformatics. Predictive medicine begins to be applied in surgery. The prognosis in surgery consists in the preoperative evaluation of various surgical interventions and in the evaluation of possible outcomes of surgical interventions.

Identification of effective stimulation parameters to abort epileptic seizures in a neural mass model.

Pathological brain activity can be modulated by using electrical stimulation. However, one major challenge is the identification of the optimal parameter values normalizing pathological activity towards more physiological patterns. One possible approach to address this challenge is the use of computational models. Here, we used a validated neural mass model (NMM) to simulate epileptiform activity and its modulation by electrical stimulation. Based on simple features of the simulated signals before and during stimulation within the time and frequency domains, we studied the effectiveness of a given stimulation parameters. Stimulations inducing a membrane polarization greater than 4 mV and a frequency over 25 Hz were identified as common effective parameters for the majority of epileptiform signals. This work provides further evidence for model-guided stimulation parameters optimization as a rationale for neuromodulation therapy refinement.

COMPUTER MODELING OF FINANCIAL CALCULATIONS

Within the implementation of the national strategy for improving financial competency and financial education in Russia, aimed at the broad masses of the population, any experience in promoting financial competency among young people, accumulated in the system of training bachelors of Economics, will be useful. The purpose of the article is to present the methodological and practical aspects of teaching the basics of financial calculations of future economists and the formation of computer modeling skills in the field of financial and economic activity. The reason for writing the article was the problem of interdisciplinary integration in the system of financial and economic education. The analysis of educational literature and curricula of the system of secondary and higher professional education, as well as the study and generalization of pedagogical experience showed weak integration of mathematical and economic disciplines with information technologies. The article also presents the problems associated with the calculations in the financial and economic activities with the use of computer modeling. The elements of the presented methods of teaching the basics of financial computing in conjunction with the modeling of financial problems on the computer can be useful for both school teachers and university teachers of mathematics and computer science.

Graphoanalytic determination of symmetry parameters and total compensation of reactive power for a three-phase power supply system

Problem. The simulation of currents and voltages in electric three-phase power supply systems is an important means of improving the quality of electrical supply. It is precisely the alignment of the values of currents in the phases of electricity supply lines, thus, the power supplies are loaded evenly. In addition to the symmetry to reduce losses in the transmission of electrical energy, it is necessary to provide transmission from the source to the loading of only active power. Therefore, it is necessary to determine the parameters of symmetric-compensating devices, which, given the fact that active-reactive line resistance is taken into account, is a rather complicated task. Numerical optimization algorithms are used to solve this problem, the disadvantage of which is the possibility of not receiving a solution due to unsuccessful selection of initial approximation of parameters and (or) excessive number of computational operations. To solve such problems, symmetro-compensating devices are used. The need to take into account the influence of active-reactive resistance of transmission lines with accurate calculation of the parameters of symmetro-compensating devices requires the use of computer models and numerical optimization methods and subroutines. Goal. Development of the method of determining the parameters of the symmetrical device for three-phase power supply systems, based on the analysis of the existing operating mode of the system with subsequent graph-analytical determination of the parameters of the symmetry and full compensation of reactive power. Methodology. The complex methods of analysis of linear electric circuits are used. To determine the requirements of symmetry and compensation, the method of symmetric components is used. To determine the parameters of the compensating device, methods of analytic geometry are used, as well as matrix methods for solving systems of linear algebraic equations. Results. The proposed method allows graphoanalytic way to obtain a numerical solution to the problem of symmetry of currents in the line and compensation of reactive power in a three-phase power supply system with asymmetric load. It has been established that the parameters of the symmetric device, determined from the data of the initial analysis of the mode of operation of the power supply system with an asymmetric load, do not always provide a sufficient effect of symmetry and compensation. To improve the efficiency of the symmetry and compensation parameters of the simulating device should be specified according to the primary compensation. Originality. It is proposed to make an initial assessment of the mode of operation of the power supply system. Based on the initial assessment, the primary requirements for the parameters of symmetry and compensation are determined. Approximate values of the parameters of the symmetry and compensation are determined by processing the initial requirements by methods of analytical geometry. The effect of primary symmetry and primary compensation was estimated, and the primary requirements were clarified. After the correction, the full effect of the symmetry of currents and the compensation of reactive power in the lines of the power supply system have been achieved. Practical value. The proposed method allows to calculate the parameters of the symmetric compensation devices with high accuracy taking into account the resistance of lines in power supply systems with a wide range of changes in asymmetry and reactivity of loads, which ensures reduction of losses due to excessive asymmetry and reactivity of consumers.Key words: three-phase system; asymmetry; symmetrical device; reactive power compensation.

Modulating reward learning with transcranial direct current stimulation: Applications for the treatment of depression

Background Negative attention biases are thought to be a causal factor in the development and maintenance of depression. It has been proposed that this bias may be caused by a belief that negative events are more informative than positive events. In the present study, it was investigated whether transcranial direct current stimulation (tDCS), a non-invasive brain stimulation technique, could modulate information content estimates for rewarding and aversive outcomes in healthy adults [1] , [2] . Methodology Forty healthy volunteers aged 18–45 participated in one sham and one active tDCS session in randomised order. During each session, participants completed an information bias learning task (IBLT) while receiving tDCS targeting bilateral dorsolateral prefrontal cortex (DLPFC) for 20 minutes at 2 mA. Information content estimates for positive and negative outcomes were reflected in participants’ learning rates on the IBLT, which were derived from the data with the use of computational models. Results Active bifrontal tDCS was associated with an increase in learning rates for positive but not negative outcomes on the IBLT (F = 5.47, P Conclusion These findings provide the first experimental evidence that modulating activity in the DLPFC can enhance learning from positive stimuli in healthy adults. This change in learning rates suggests an alteration in participants’ beliefs of how informative positive outcomes are compared to negative outcomes. Additional research is needed to assess whether this effect of tDCS can be harnessed to ameliorate negative attention biases associated with psychiatric disorders. The present results provide an exciting early step in the development of novel interventions for depression.

A hybrid discrete-continuum approach for modelling microcirculatory blood flow.

In recent years, biological imaging techniques have advanced significantly and it is now possible to digitally reconstruct microvascular network structures in detail, identifying the smallest capillaries at sub-micron resolution and generating large 3D structural data sets of size >106 vessel segments. However, this relies on ex vivo imaging; corresponding in vivo measures of microvascular structure and flow are limited to larger branching vessels and are not achievable in three dimensions for the smallest vessels. This suggests the use of computational modelling to combine in vivo measures of branching vessel architecture and flows with ex vivo data on complete microvascular structures to predict effective flow and pressures distributions. In this paper, a hybrid discrete-continuum model to predict microcirculatory blood flow based on structural information is developed and compared with existing models for flow and pressure in individual vessels. A continuum-based Darcy model for transport in the capillary bed is coupled via point sources of flux to flows in individual arteriolar vessels, which are described explicitly using Poiseuille's law. The venular drainage is represented as a spatially uniform flow sink. The resulting discrete-continuum framework is parameterized using structural data from the capillary network and compared with a fully discrete flow and pressure solution in three networks derived from observations of the rat mesentery. The discrete-continuum approach is feasible and effective, providing a promising tool for extracting functional transport properties in situations where vascular branching structures are well defined.

Prediction of thigh-calf contact parameters from anthropometric regression.

High knee flexion postures are common in industry and cultural practices, but the mechanical effect of intersegmental force, particularly thigh-calf contact force, on knee joint compressive force is poorly understood. Although some studies have measured thigh-calf contact parameters occurring in a number of high flexion postures, joint contact modeling would benefit from efforts to predict thigh-calf contact force for use in computational models. Therefore, this study assessed the strength of correlations and linear multiple regression models on the following five high flexion thigh-calf contact parameters in a young, healthy population: the onset angle of thigh-calf contact, maximum flexion angle, total thigh-calf contact force, center of force, and contact area at maximum flexion. Regressions used anthropometric values (and in some cases, maximum flexion angle). Overall, maximum flexion angle and center of force location had the most significant correlates and strong linear fits with regressive models. Thigh-calf contact onset, total force magnitude, and contact area had only moderate to weak relationships. An exploratory attempt at regression using grouped movements into gross patterns (e.g. two types of squatting were grouped into a general squatting category) using maximum flexion angle and center of force location as dependent variables resulted in similar model fitting. These findings suggest that a causal relationship between select anthropometrics and lower limb range of motion may exist, but further exploration is necessary to determine clinically reliable predictive models.

COMPASS: An Open-Source, General-Purpose Software Toolkit for Computational Psychiatry

Mathematical modeling of behavior during a psychophysical task, referred to as “computational psychiatry,” could greatly improve our understanding of mental disorders. One barrier to the broader adoption of computational methods, is that they often require advanced statistical modeling and mathematical skills. Biological and behavioral signals often show skewed or non-Gaussian distributions, and very few toolboxes and analytical platforms are capable of processing such signal categories. We developed the Computational Psychiatry Adaptive State-Space (COMPASS) toolbox, an open-source MATLAB-based software package. This toolbox is easy to use and capable of integrating signals with a variety of distributions. COMPASS has the tools to process signals with continuous-valued and binary measurements, or signals with incomplete—missing or censored—measurements, which makes it well-suited for processing those signals captured during a psychophysical task. After specifying a few parameters in a small set of user-friendly functions, COMPASS allows users to efficiently apply a wide range of computational behavioral models. The model output can be analyzed as an experimental outcome or used as a regressor for neural data and can also be tested using the goodness-of-fit measurement. Here, we demonstrate that COMPASS can replicate two computational behavioral analyses from different groups. COMPASS replicates and can slightly improve on the original modeling results. We also demonstrate the use of COMPASS application in a censored-data problem and compare its performance result with naïve estimation methods. This flexible, general-purpose toolkit should accelerate the use of computational modeling in psychiatric neuroscience.

A Large-Scale Semantic Analysis of Verbal Fluency Across the Aging Spectrum: Data From the Canadian Longitudinal Study on Aging

The present study aimed to characterize changes in verbal fluency performance across the lifespan using data from the Canadian Longitudinal Study on Aging (CLSA). We examined verbal fluency performance in a large sample of adults aged 45-85 (n = 12,686). Data are from the Tracking cohort of the CLSA. Participants completed a computer-assisted telephone interview that included an animal fluency task, in which they were asked to name as many animals as they could in 1 min. We employed a computational modeling approach to examine the factors driving performance on this task. We found that the sequence of items produced was best predicted by their semantic neighborhood, and that pairwise similarity accounted for most of the variance in participant analyses. Moreover, the total number of items produced declined slightly with age, and older participants produced items of higher frequency and denser semantic neighborhood than younger adults. These findings indicate subtle changes in the way people perform this task as they age. The use of computational models allowed for a large increase in the amount of variance accounted for in this data set over standard assessment types, providing important theoretical insights into the aging process.

Integration of hydraulic model (HEC-RAS) with Geographical Information System (GIS) in developing flood evacuation center along Sembrong River

Flood event create a continuing threat to lives, environment and infrastructure throughout the world. Recently, there is an increasing use of computer models in identifying floodprone area. Identification of floodprone area will assist in determining flood evacuation center in needs of protecting flood victims. The objective of this research is to develop flood evacuation center along Sembrong river of Batu Pahat using Hydraulic Model HEC-RAS integrated with Geographical Information System (GIS). HEC-RAS was used to produce an output of two-dimensional unsteady flow analysis to determine floodprone area. Integration of both softwares will determine the suitability of the existing flood evacuation center. By using GIS technology, 14 new locations of evacuation center with suitable criteria such as route network and capacity were proposed for rescuing and evacuating flood victims. The developed flood evacuation center can be a very useful information for flood evacuation planning.

The current trends of Mg alloys in biomedical applications-A review.

Magnesium (Mg) has emerged as an ideal alternative to the permanent implant materials owing to its enhanced properties such as biodegradation, better mechanical strengths than polymeric biodegradable materials and biocompatibility. It has been under investigation as an implant material both in cardiovascular and orthopedic applications. The use of Mg as an implant material reduces the risk of long-term incompatible interaction of implant with tissues and eliminates the second surgical procedure to remove the implant, thus minimizes the complications. The hurdle in the extensive use of Mg implants is its fast degradation rate, which consequently reduces the mechanical strength to support the implant site. Alloy development, surface treatment, and design modification of implants are the routes that can lead to the improved corrosion resistance of Mg implants and extensive research is going on in all three directions. In this review, the recent trends in the alloying and surface treatment of Mg have been discussed in detail. Additionally, the recent progress in the use of computational models to analyze Mg bioimplants has been given special consideration. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1970-1996, 2019.

An investigation of regional variations in the biaxial mechanical properties and stress relaxation behaviors of porcine atrioventricular heart valve leaflets

The facilitation of proper blood flow through the heart depends on proper function of heart valve components, and alterations to any component can lead to heart disease or failure. Comprehension of these valvular diseases is reliant on thorough characterization of healthy heart valve structures for use in computational models. Previously, computational models have treated these leaflet structures as a structurally and mechanically homogenous material, which may not be an accurate description of leaflet mechanical response. In this study, we aimed to characterize the mechanics of the heart valve leaflet as a structurally heterogenous material. Specifically, porcine mitral valve and tricuspid valve anterior leaflets were sectioned into six regions and biaxial mechanical tests with various loading ratios and stress-relaxation test were performed on each regional tissue sample. Three main findings from this study were summarized as follows: (i) the central regions of the leaflet had a more anisotropic nature than edge regions, (ii) the mitral valve anterior leaflet was more extensible in regions closer to the annulus, and (iii) there was variance in the stress-relaxation behavior among all six regions, with mitral valve leaflet tissue regions exhibiting a greater decay than the tricuspid valve regions. This study presents a novel investigation of the regional variations in the heart valve biomechanics that has not been comprehensively examined. Our results thus allow for a refinement of computational models for more accurately predicting diseased or surgically-intervened condition, where tissue heterogeneity plays an essential role in the heart valve function.