University:University of Mons (UMons)
Team Members (with year of graduation): Kamil J. Chodzyński, Daniel Ribeiro de Sousa
Faculty Advisers:Prof. Gregory Coussement, Prof. Karim Zouaoui Boudjeltia
Submission Language: English
Title: In vitro testbed to study cardiovascular diseases
Nowadays, cardiovascular diseases are still among the top causes of mortality and morbidity in the world (the 2012 World Health Report). The number of deaths caused by cardiovascular diseases in 2008 is estimated at 17 million.
The object is to provide a device capable of reproducing in vitro, the exact pulsatile signals encountered in the blood vessels. This ability should enable signals to be generated and applied to ECs (endothelial cells) or bilayer culture systems containing ECs and VSMCs (vascular smooth muscle cells) seeded in a transparent test chamber or any geometry that allows observation under the microscope, recording of flow parameters and cell harvest after treatments. Moreover, the system must enable to study different pulsatile hemodynamic patterns in different geometries such as aneurysms (an aneurysm is a balloon-like expansion of weakened blood vessels which can rupture causing haemorrhages). The root of the development is to supply a flexible in vitro tool that can bring us closer to the real human body and patient’s specific conditions, where physicians can test in a safe environment, the best treatment approach. The flexibility of an in vitro testbed should enable different kinds of tests to be performed without requiring large changes in the system.
The interest of in vitro testing is:
1. To study endothelial cells’ behaviour under near physiological pulsatile flow conditions,
2. To examine the geometry of different vessels i.e. aneurysms, branches, with/without stents etc. under physiological hemodynamic conditions.
3. To enable work with supported measurement equipment to be carried out. In order to perform additional training for physicians and/or test medical equipment.
In vivo measurements
In order to achieve the sustainable development of a new in vitro model that would reproduce the mechanical constraints induced by pulsatile blood flows, a link between many disciplines such as Medicine, Mechanics, Fluids–Mechanics, Electronics, Automatics and/or Computer Sciences is required. Through the collaboration with a medical team in vivo data such as blood velocity and additional information to better understand the problem and help with the conception of the system was provided (Fig.1). Moreover, the aim is to collect and post-process as much hemodynamic data as possible from various patients for future in vitro tests.
Fig.1. During in vivo measurements (left), An angiography picture which presents the position of the Doppler flow ComboWire®, (right).
In vitro testbed design
The aim of this project was:
Based on the description outlined above the in vitro testbed was conceived and built (Fig.2). The testbed is designed to be easily tuned for performing different type of tests such as a test with ECs and a microscope visualisation (Fig.2, left) or tests with different type of vessels (aneurysm presented) and/or additional supported measurement equipment such as a laser PIV (Particle Image Velocimetry) measurements or a CT (Computed tomography) scanning (Fig.2, right).
Fig.2. The in vitro testbed for testing ECs responses (left) and for testing different shape of vessels such as aneurysms (right).
In the in vitro testbed, it is crucial to control the pulsatile flow rate that would fit the hemodynamic in vivo data while mimicking the physiological conditions as accurately as possible. Based on that objective for the in vitro testbed design, the problem become very complex and requires multiple controls in order to reproduce the speed and the complexity of pulsatile hemodynamic flows. In order to control the whole system a proper tool is needed. This tool has to allow us to communicate with the equipment, monitor desired variables and control necessary signals. Therefore to fit these multiple constraints, we decided that the control strategy will be implemented in the LabVIEW environment, (Fig.3 and 4). The following control strategy was implemented:
1. A main loop controls the flow and temperature (speed of loop 200Hz). The principle of the control loop is shown in Fig.3 and 4. The reference signal (controlled flow) is divided into two signals: the mean flow and
the pulsatile fluctuations of the flow.
2. A control for a microscope camera (speed of loop 100Hz). In order to visualize and/or record ECs evolution during online testing a microscope with USB camera was incorporated. The control loop which is
responsible for taking picture in desire time period is presented in Fig.5. For controlling NI LabVIEW Vision module is required.
3. A control for the cooling of the system in order to keep a safe temperature for the electric equipment (speed of loop 100Hz)
4. A process to save measured data such as flow, pressure or temperature signals on the hard drive disc for post – processing (speed of loop 200Hz)
5. A visualization of the measured data on the computer (speed of loop 100Hz)
Fig.3. The control strategy of the pulsatile flow. Fig.4. The block diagram panel in Labview– the main control loop (200Hz).
Fig.5. The block diagram panel in Labview - the control of the camera and taking pictures.
Results and some features of the device
The results obtained for in vivo patient's data with the real-time in vitro testbed satisfy the condition of a maximum relative error set at 5%. We have to bear in mind that we are dealing with very fast control loops. LabVIEW executes one cycle for all the input/output signals in a time period of 5ms (200Hz). It is much higher than the one in most industrial control systems. In addition, the system is highly non-linear and depends on the external conditions such as compositions of the medium that can vary significantly with the plasma used and/or the mixing of additional substances such as Red Blood Cells (RBCs). Moreover, it also varies with the properties of the equipment and experimental variability such as diaphragm age, external temperature that are difficult to predict and to model. Examples of some flows obtained using our in vitro testbed are presented in Fig.6 for the controlled flow and in Fig.7 for the controlled temperature.
Fig.6. Examples of reproduced flows by the in vitro testbed.
Fig.7. The control results of the medium temperature.
In addition in the movie below, the concept and some features of the device are presented.
Conclusions and future perspectives:
The challenge of the design and the control of an in vitro testbed to mimic pulsatile hemodynamic lies on the fact that:
1. The system is highly non-linear.
2. In order to reproduce accurately in vivo flow patterns:
The in vitro testbed take benefit of LabVIEW capabilities to accurately reproduce the speed and the complexity of in vivo hemodynamic signals measured in patients within the aims defined by the researchers and medical practitioners. Physicians were pleased with the performance of the machine and original experiments were designed to further explore the potentialities of this system.
The use of this testbed by the medical research community has triggered new and exciting prospects. These future perspectives can be divided into two groups:
1. Those consisting in the improvement of the design of the existing system
2. Those that can advance the control of the system
- To put a touch panel computer or a tablet with direct implementation of LabVIEW program that will be able to make the system completely independent, easier to use and even more mobile. It will decrease the number of cables and external control equipment that are necessary to start the system. Especially, it would be more convenient to work with a tablet while the experiment with CT scanner will be performed in order to avoid unwanted radiation during the start process. For this a wireless connection is also required. Moreover a reduction of the size of the system will improve its transportability.
- By implementing the newest technology, such as a shear stress sensor, a pressure sensor, a temperature sensor based on the MEMS sensors (Micro Electro-Mechanical Systems), huge improvements could be brought to the system. The typical MEMS sensor is less than 100 um in size. This can help to gain addition space or make the system even more compact. Moreover, by miniaturisation of the sensors the system becomes more sensitive on the measurements. The small spatial extension implies that both the inertia mass and the thermal capacity are reduced. It also reduces power consumption and working costs.
- One of the future objectives in order to improve the reality of the system is to control an in vivo pressure signal. Therefore, an additional control loop for the instantaneous pulsatile pressure has to be introduced.
- Finally, in vivo signal i.e. the flow rate, the pressure signals as well as the shift between them will be a huge challenge to be able to control continuously together. To do so, a combination of the control flow strategy as well as the control pressure strategy has to be implemented.