design and fe analysis of heart valve for closure of atrial septal defect in heart

International Journal of Innovative Research in Advanced Engineering (IJIRAE) ISSN: 2349-2163 Issue 12, Volume 4 (December 2017) www.ijirae.com

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DESIGN AND FE ANALYSIS OF HEART VALVE FOR CLOSURE OF ATRIAL SEPTAL DEFECT IN HEART

Pushpashree N*, Manjunatha Babu N.S, Mohan Kumar K Department of Mechanical Engineering. Dr. T.T.I.T – KGF – 563120. Karnataka State, India

Visvesvaraya Technological University, Belgaum – Karnataka State, India [email protected]

Manuscript History Number: IJIRAE/RS/Vol.04/Issue12/DCAE10086 DOI: 10.26562/IJIRAE.2017.DCAE10086 Received: 22, November 2017 Final Correction: 02, December 2017 Final Accepted: 17, December 2017 Published: December 2017 Citation: Pushpashree, Babu, M. & Kumar, M. (2017). DESIGN AND FE ANALYSIS OF HEART VALVE FOR CLOSURE OF ATRIAL SEPTAL DEFECT IN HEART. IJIRAE::International Journal of Innovative Research in Advanced Engineering, Volume IV, 22-27. DOI: 10.26562/IJIRAE.2017.DCAE10086 Editor: Dr.A.Arul L.S, Chief Editor, IJIRAE, AM Publications, India Copyright: ©2017 This is an open access article distributed under the terms of the Creative Commons Attribution License, Which Permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

Abstract – Atrial Septal Defect is a congenital heart disease caused due to failure of closing septal which leads to hole or opening formation between left atria and right atria. In most of the cases, this type of defect gets cured by itself in childhood stage day by day before stepping to adult. If in case, the hole or opening between septum primum and septum secundum does not close before adult stage then this defect become permanent. Smart material has property to self-expand and self-contract which is special character compared to alloys. Due this special property it is used in ASD devices. The purpose of this study is to show that NITINOL alloy has better property than other alloys like titanium and nickel alloy with changes made in dimension of hole design. The design modification and geometry clean-up of the hole is made in Hypermesh and finite element analysis has been done using Ansys software for static analysis. Keywords — Smart Material; AS Defect; Design Modification; Hyper Mesh; Static Analysis; Finite Element; Analysis;

I. INTRODUCTION

Atrial septal defect is one of the congenital diseases where it is seen in heart with hole or opening in it. It is considered as one of the congenital cardiac anomalies occurs in adulthood. It is normally found as a defect in the atrial septum allowing pulmonary venous (veins that transfer oxygenated blood) which returns from the left atrium to pass directly to the right atrium. Based on the size of the defect and size of the shunt it is seen as one of the anomalies which leads to arterial hypertension and arrhythmias. Basically defect is formed at the development stage of embryonic heart. The heart is divided into two sides, separated by a wall which is called as septum [1]. A hole which is normally observed in the septum between the upper chambers of the heart is called atrial septal defect. There are two different methods which are used for closing defect.

A. Repair of ASD by Surgical method:

In surgical method, to expose the heart an incision is made and hole is closed by patch work. If the opening is large then it is closed by sewing a patch and if the hole is small then it is closed by stitches.

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B. Cardiac Catheterization by placing a Device closure (Valve Design): The device which is used for closing hole and this process is frequently performed for secundum ASD, depending on the size of the defect and weight of the person. The fig. 1 and fig. 2 shows the defect enclosed by implanting the device called Amplatzer Septal Occluder cardiac catheterization method. In this study the hole is closed by Amplatzer Septal Occluder, since this method is considered has best compared to surgery [2]. The defect is analysed in ANSYS and simulated the output results for titanium alloy, nickel alloy and Nitinol alloy for old design dimension and modified new dimension of hole.

Fig. 1 Atrial Septal Defect in Heart

Fig. 2 Amplatzer Septal Occluder has ASD device implanted

II. LITERATURE SURVEY

The defect was observed with many children without any symptoms and if in case they found, then medications is given. Commonly medications which are necessary and prescribed by the doctors include Digoxin. This helps to strengthen the heart muscle for pumping the blood more efficiently.

Professor Philipp Bonhoeffer developed an alternative method for replacement of heart halve instead of surgery (Bonhoeffer et al., 2000) [3]. During the development phases of the current PPVI device, preclinical testing was performed has simple bench and experiments were done on animal as part of routine. In clinical practice, the occurred function 20% stent fractures (Nordmeyer et al., 2007) [4]. The discrepancy was found here due to the fact that the in-vivo loading conditions could not be correctly reproduced with experimental set-ups, where the applied boundary conditions are simulated but does not match the real situation. Dr. Toumar A.J. and Pang S.D. created a finite element model which can be considered as the healthy aortic valve. To meet the desired results, model was analysed with stresses on the valve tissue during the performance of a cardiac cycle. The aortic valve is considered to be modelled and the analysis can be performed using finite element software like ANSYS [5]. Dr. Quan Yuan carried out geometrical design and finite element analysis on the bio prosthetic heart valve. By constructing the parametric models of bio prosthetic heart valves via computer aided design, a series of accurate dimension parameters are obtained [6]. Prof. Robert D. Howe studied that functionally heart valves complex and performing surgical repair will be difficult. Simulation based surgical planning could facilitate repair, but current finite element (FE) studies are prohibitively slow for rapid. The FE model is created to study a repair technique of generalized aortic valve that incorporates graft material into the native valve. Here the graft has significantly different mechanical properties compared to native leaflets [7]. After referring some of the medical journals related to this ASD device about tissue erosion among the patients who are implanted with this device, result was a serious problem inside the heart due to tissue erosion. If the device dimension is improper then it will create abrasion against the wall of the heart which leads to create hole / expand the existing hole [8]. FDA (Food and Drug Administration, U.S) reported that there will be 1 to 3 people approximately face an erosion problem out of 1000 patient. The case study was done on the incidence of erosion within body from day of implant to the seventh day and then one month, six months and finally at twelve months [9].

During this cardiac catheterization procedure, the person is sedated and a small incision is made at groin region as shown in fig. 3. And then catheter is inserted into a blood vessel in the groin and gently guided to the inside of the heart. The catheter is a small thin flexible tube with presence of imaging technique in it. Once the catheter is sent, the cardiologist passes Amplatzer device at defect region and open ASD to prevent blood from flowing through it as in fig. 4.





Fig. 3 Path way of Catheter through which Amplatzer is sent

Fig. 4 Valve design for closure of ASD

III. MODELLING AND ANALYSIS

The process involves importing the model IGES file in HYPER MESH 12, then geometry clean-up is performed. In most of the time the geometry of the mesh size will be different. So in order to get better results it needs to be meshed for appropriate mesh size. Once the meshing has been done, then assign boundary conditions and material properties. The material property details are mentioned in table (I), (II) and (III). Now apply the pressure load on the defect area ranging between 120mm of Hg to 139mm of Hg. Usually a normal human blood pressure ranges from 15kPa to 20kPa. Hence the pressure considered is higher than the normal range. After preparation of deck, export cdb file to ANSYS 16.2. Finally perform the static analysis and plot the result in HYPER VIEW. The steps involved in this process are as follows:

Import the IGES file in HYPER MESH 12 Perform geometry clean up Mesh the geometry for appropriate mesh size Assign the Boundary conditions and material properties Apply load on desired face After deck preparation export .cdb file to ANSYS 16.2 Evaluate in ANSYS 16.2 and plot the result in HYPER VIEW.

TABLE I - MATERIAL DETAILS OF NICKEL

S.No Property Value Unit 1 Density 4.5 x 10-9 Tonnes/mm3 2 Tensile strength 220 MPa 3 Young’s Modulus 1.16 x 105 MPa 4 Poisson’s Ratio 0.29 -

TABLE II -MATERIAL DETAILS OF NICKEL

S. No Property Value Unit 1 Density 8.89 x 10-9 Tonnes/mm32 Tensile strength 320 MPa 3 Young’s Modulus 2.0 x 105 MPa 4 Poisson’s Ratio 0.27 -

TABLE III - MATERIAL DETAILS OF NITINOL

Sl. No Property Value Unit 1 Density 7.58 x 10-9 Tonnes/mm3 2 Tensile strength 470 MPa 3 Young’s Modulus 1.15 x 105 MPa 4 Poisson’s Ratio 0.28 -

TABLE IV- MATERIAL DETAILS OF HEART

S. No Property Value Unit 1 Density 7.85 x 10-9 Tonnes/mm32 Tensile strength 60 MPa 3 Young’s Modulus 1000 MPa 4 Poisson’s Ratio 0.28 -

Finite Element analysis is a method that helps to simulate mechanical parts and systems to get information about failure, deformation and stresses under various kind of loadings. When a linear static analysis is carried out we can determine the stresses, strains, displacements and the reaction forces under any application of loads and boundary conditions. Always it is seen that when we are carrying out linear analysis it will make two assumptions as below:

Behaviour of structure is Linear (Obeys Hooke's Law) Loads are static





IV. RESULTS

Finite element analysis was carried out for different valve design and material considerations. Here analysis is done for two different hole dimensions to figure out which material yields the better results [10]. After completing the analysis, simulate the results for titanium alloy, nickel alloy and NITINOL for yield stress and factor of safety. The table V helps us to compare the results of stress and deformation obtained for the individual materials.

The two different defect dimensions considered as follows, Initially consider hole diameter has 11mm and simulate FE analysis for Titanium alloy, Nickel alloy and

Nitinol. Now change the dimension to 6.4mm and again perform the analysis for Ti alloy, Ni alloy and NITINOL.

A. Counter results plots for Titanium alloy with 2 different hole dimension: Plot the results for deformation and yield stress as done for the initial dimension and modified hole dimension. Please add material property details for titanium alloy then simulate the results. Here Max. Stress = 310MPa > 220MPa from fig. 11. 1) Initial Design:

Fig. 6 Deformation Plot for initial valve design

Fig. 7 Maximum stress plot in initial valve design

2) New modified Design:

Fig. 8 Deformation Plot for Modified valve design

Fig. 9 Maximum stress plot in modified valve design

B. Counter results plots for Nickel alloy with 2 different hole dimension: Repeat the same procedure has done for the previous material to plot the results for initial and modified dimension. Here Max. Stress = 223MPa > 220MPa from fig. 13.

1) Initial Design:

Fig. 10 Deformation Plot for initial valve design

Fig. 11 Maximum stress plot in initial valve design







Fig. 13 Maximum stress Plot in Modified Valve design

C. Contour plots for Nitinol alloy with 2 different hole dimension: Now plot results for final material which has considered has a smart material called NITINOL. Follow the same steps as followed to simulate results in ANSYS for initial and modified hole dimension. Here Max. Stress = 179MPa < 320MPa from fig. 17. 1) Initial Design:

Fig. 14 Deformation Plot for Initial valve design

Fig. 15 Maximum stress Plot in Modified Valve design



Fig. 17 Maximum stress Plot in Modified Valve





TABLE V - COMPARISON OF SIMULATION RESULTS

Sl No Valve material Initial Design Final Design Yield Stress (MPa)

Factor of Safety (Initial Design) (Final Design)

1 Titanium 310 223 220 0.71 0.99 2 Nickel 268 179 320 1.19 1.79 3 Nitinol 139 57 450 3.24 7.89

From the above finite element analysis by comparing the simulated results, it can concluded that NITINOL yields better result compared to Titanium and Nickel alloy. Hence, NITINOL can be used in Amplatzer Septal Occluder for closing Atrial Septal Defect.

V. CONCLUSIONS

Design of aortic valve and Finite Element Analysis (FEA) is performed on the valve. The aim of this study was to model a percutaneous valve and perform the finite element analysis. The design process was carried out to meet the functional and placing the valve in the premises of hole area. Finite element analysis and simulation of the model helped in optimizing the selection of exact valve design and the suitable material which enabled to have long term durability, low thrombogenicity, resistance to migration and paravalvular leak. After comparing the simulated results of titanium alloy, nickel alloy and NITINOL alloy, “Nitinol alloy was considered as the best material to use in Amplatzer Septal Occluder device for closing Atrial Septal Defect in heart”.

REFERENCES

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https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3461693/ 3. Bonhoeffer P., et al. Percutaneous replacement of pulmonary valve in a right-ventricle to pulmonary-artery prosthetic conduit with valve dysfunction. Lancet. 2000;356:1403–1405. https://www.ncbi.nlm.nih.gov/pubmed/11052583 4. Nordmeyer, Risk stratification, systematic classification and anticipatory management strategies for stent

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https://doi.org/10.1161/CIRCULATIONAHA.106.674259 5. Toumar AJ, Pang SD. Stress Analysis of the Aortic Valve Using Finite Element Modelling Software. https://www.esp.nus.edu.sg/undergraduate/UROP%20Projects/2008-Alex_Tourmar.pdf 6. Yuan, Quan (2007) - Geometrical design and finite element analysis on the bio prosthetic heart valve. Journal of

Clinical Rehabilitative Tissue Engineering Research. 11. 3480-3483. https://www.researchgate.net/publication/287852967 7. Peter E. Hammer, Michael S. Sacks, Pedro J. del Nido and Robert D. Howe – Mass-Spring Model for Simulation of

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https://doi.org/10.4103/0300-1652.129642

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3461693/

https://www.ncbi.nlm.nih.gov/pubmed/11052583

https://doi.org/10.1161/CIRCULATIONAHA.106.674259

https://www.esp.nus.edu.sg/undergraduate/UROP%20Projects/2008-Alex_Tourmar.pdf

https://www.researchgate.net/publication/287852967

https://doi.org/10.1007/s10439-011-0278-5

http://doi.org/10.1530/ERP-15-0023

http://www.fda.gov/AdvisoryCommittees/CommitteesMeetingMaterials/MedicalDevices/MedicalDevicesAdv