We have put together some illustrations of our experience, and we've organized them according to both area of application and service type. Some of the work we've done and clients we've worked with remain confidential. We will continue to populate this list as intellectual property gets secured or we find novel applications we think you'll be interested in.
Our Work in Cardiovascular Devices
Client:Faculty of Medicine, University of Calgary
There is clinical demand from vascular surgeons for a better method to assess risk of aneurysm rupture in their patients. Rupture of aortic aneurysms has high mortality; yet many patients present with aneurysms that do not lead to rupture, and the surgical treatment of aneurysm is high risk in itself. The currently accepted practice is to monitor the size of the aneurysm from regular imaging.
Dr. Elena DiMartino has developed a novel computational method to estimate the mechanical properties of the aorta from dynamic CT or MR images. She is working with vascular surgeon, Dr. Jehangir Appoo, to apply the method to assessment of aneurysms for surgical planning. Mechanical validation of the model is required to support its clinical usage. The Zymetrix Planar Biaxial system is a key element of the validation as it is being used to measure the anisotropic mechanical properties of arterial tissue for comparison to model predictions.
- Specimens are collected recording the location and orientation in vivo.
- Tests are performed under deformation control up to 40% and 60% deformation.
- An equibiaxial test (protocol 1:1) is followed by 4 additional protocols applying 1:0.75, 1:0.5, 0.5:1 and 0.75:1. These 5 protocol explores the behaviour of the tissue in different loading conditions so that the whole range of physiological response can be modelled.
G. Martufi, T.C. Gasser, J.J. Appoo, E.S. Di Martino, Mechanobiology in the Thoracic Aortic Aneurysm: a review and case study, Biomechanics and Modeling in Mechanobiology, 13, 917-928, 2014.
C. Bellini, J. Ferruzzi, S. Roccabianca, E.S. Di Martino, J.D. Humphrey, A Microstructurally-Motivated Model of Arterial Wall Mechanics with Mechanobiological Implications, Annals of Biomedical Engineering: Vol. 42, Issue 3:488-502, 2014.
G. Martufi, A. Satriano, R.D. Moore, D.A. Vorp, E.S. Di Martino, Local quantification of wall thickness and intraluminal thrombus offer insight into the mechanical properties of the aneurysmal aorta, under revision, the Annals of Biomedical Engineering.
C. Bellini, E.S. Di Martino, S. Federico, Mechanical behavior of the human atria, Vol. 41(7):1478-1490 DOI: 10.1007/s10439-012-0699-9, Annals of Biomedical Engineering, 2013.
Client:JC Medical Inc.
The client was developing a finite element model of their valve to determine the worst case size to use in durability testing according to ISO 5840. Given that the valve was transcatheter, deformations for the valve frame could not be determined from measurement on a pulse duplicator. As a result, the model was developed to include the valve leaflets and simulate stresses during valve closure.
The client did not have the resources and expertise to specify and develop an appropriate material model for the valve leaflets.
Porcine heart valves were shipped from China and received from the client. Tissue samples were selectively cut from the supplied valves. The material properties of each sample were determined using the Electroforce Planar Biaxial system. From these properties, it was determined that an anisotropic Fung model best fit this particular tissue. A constitutive equation was developed and provided to the client.
Service(s):Medical Device Testing , Planar/Biaxial Testing , Structural Imaging , Tensile Testing
Client:University of Calgary
Heart valve replacement occurs in over 100,000 patients annually in the US alone. Bioprosthetic valve replacements have an advantage over mechanical valves in that they do not require blood thinners. However, the lifespan of a bioprosthetic valve is generally limited to around 15 years. This lifespan is sufficient for much of the mostly elderly patient population; but for a sizeable younger subset of patients, it is not. Furthermore, one indicator of valve performance is pressure drop across the valve as this is related to how hard the heart has to work to move blood through the circulatory system; and improvements in pressure drop should result in reduced morbidity post treatment.
Dr. Yaghoub Dabiri and Dr. Kishan Narine have been applying an advanced computational method known as fluid-structure interaction to design a new bioprosthetic heart valve that will both reduce the long term calcification of the valve that limits its lifespan and reduce the pressure drop across the valve allowing it to perform like a normal valve.
This method is has also allowed Dr. Dabiri to utilize an innovative approach for manufacturing that preserves the complex 3D geometry of the valve leaflets.
Dr. Dabiri has been utilizing a novel computational method known as fluid-structure interaction to iteratively determine the effect of design parameters on valve stresses (related to calcification) and pressure drop across the valve.
The accuracy of the computational methods used by Dr. Dabiri rely on having accurately defined material properties for the valve leaflet materials (typically bovine or porcine pericardium). These materials have strong anisotropy which requires measurement on the planar biaxial system, and Zymetrix supported Dr. Dabiri in obtaining these measurements.
Zymetrix has also supported this project by developing high resolution 3D geometric models of existing valves through microCT imaging and Simpleware reconstruction, as well as by using Simpleware to develop complex structural meshes for Dr. Dabiri’s fluid structure model.
Dr. Dabiri’s computational model was validated by comparing simulated pressure drop across an existing bioprosthetic valve with a measurement of the pressure drop taken in a Vi Vitro pulse duplicator.
Dabiri, Y., Paulson, K., Tyberg, J.V., Ronsky, J.L., Ali, I. and Narine, K. (2015) Aortic Valve Design Optimized by Integration of Three-Dimensional Two-Way Fluid Structure Interaction and Transverse. Computer Methods in Biomechanics and Biomedical Engineering, Montreal, Canada.
Dabiri, Y., Paulson, K., Tyberg, J.V., Ronsky, J.L., Ali, I., Di Martino, E. and Narine, K. (2015) Design of Bioprosthetic Aortic Valves using Biaxial Test Data. 37th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Milan, Italy.
Dabiri, Y., Anderson, T.J., Tyberg, J.V., Ronsky, J.L., Ali, I., Wong, M. and Narine, K. (2014) Novel CALP Pericardium Shows Superior Hydrodynamics and Fluid Structure Interaction Compared to Current Bioprosthetic Valve Tissues: A Computer Simulation. 6th Biennial Heart Valve Biology & Tissue Engineering Meeting, London, UK.
Service(s):Biological Testing , Medical Device Testing , Physiological Models , Structural Imaging
Endovascular repair of the aorta is associated with reduced morbidity compared to open repair. However, a long term complication can be thrombosis of the stent graft, necessitating open removal of the stent graft and aortic replacement. The purpose of this project was to develop in vitro methods that are capable of assessing the potential for development of thrombosis in endovascular stent graft designs.
This was a multidisciplinary project that merged expertise in both biology and mechanics to understand how mechanical design influences mechanical and biological processes in the body.
The project incorporated three primary parts:
- A physical, in vitro system was developed that allowed the deployment of a stent graft and simulation of blood flow and platelet activation. Zymetrix assisted with the design of experiments to examine blood coagulation and platelet involvement, and conducted blood analysis.
- A novel system was developed to simulate the effect of blood on the detailed geometry of the stent graft. Zymetrix then imaged the stent graft in a micro CT and developed a 3D high resolution geometric model in Simpleware.
- A 3D computational fluid dynamics (CFD) model was developed and validated against the physical system (Dr. Elena Di Martino). The CFD model identified wall shear stress as a strong indicator of thrombotic potential.
- Robert D. Shepherd1 , Elena S. Di Martino1 , Steven K. Boyd1 , Randy D. Moore2 , Kristina D. Rinker1 (2015) A Novel In Vitro Model Predicts Aortic Stent Graft Hemodynamic Alterations After Endovascular Repair. 1Schulich School of Engineering, University of Calgary, Calgary, Alberta, Canada; 2 Division of Vascular Surgery, Department of Surgery, University of Calgary, Calgary, Alberta, Canada.
- The project was a research collaboration between the University of Calgary and Vascutek-Terumo.