Australasian Physical & Engineering Sciences in Medicine Volume 29 Number 2, 2006 196 TECHNICAL REPORT An apparatus for studying the response of cultured endothelial cells to stresses L. Shen 1,2 , A. Qiao 1 , H. Ding 2 , G. Mo 2 , G. Xu 2 , Y. Du 2 , M. Li 2 , Z. Chen 2 and Y. Zeng 1 1 Biomechanics & Medical Information Institute, Beijing University of Technology, Beijing, China 2 The Medical Instrumentation College, University of Shanghai for Science and Technology, Shanghai, China Abstract In order to simulate the hemodynamic environment of human arteries in vivo, we designed a laminar flow apparatus which can precisely simulate the normal stress and shear stress to which cultured endothelial cells are exposed. Under both normal and abnormal physiological conditions, this apparatus can accurately control and adjust the values of normal stress and shear stress and the frequency of pulse waves, as well as the amplitude of pulsatile flow. This in vitro apparatus provides an experimental platform for studying the response of the biological characteristics of cultured endothelial cells in a hemodynamic environment. Key words endothelial cell, shear stress, normal stress, pulsatile flow, hemodynamic environment Introduction In the body’s normal cardiovascular system, the heart valves and blood vessels are covered with a layer of membrane formed from endothelial cells. In the past it was thought that the endothelial cell (EC) only provides a smooth surface for blood flow so that the EC form a barrier which blocks the transfer of materials through the blood vessel walls. In recent studies, researchers have found that vascular ECs play very important roles in the physiological and pathological activities of a blood vessel. Changes in the structure and function of ECs can influence immune system function and blood coagulation, which are key factors influencing the onset and development of various vascular diseases, including hypertension and atherosclerosis 1-5 . The ECs are always exposed to hemodynamic conditions in vivo. Previous research in this field has considered blood-flow-induced shear stress as the main parameter influencing ECs 6-7 . In fact, in addition to shear stress, normal stress (i.e. blood pressure), which is perpendicular to the blood vessel wall, also acts on ECs. Under normal physiological conditions in human beings, normal stress (15996/10664 Pa, or 120/80 mmHg) is 5300- 8000 times greater than the shear stress (2 Pa) 8,9 . Obviously, normal stress is an important factor affecting ECs and can not be neglected in studies on ECs. Corresponding author: Y. Zeng, Biomechanics & Medical Information Institute, Beijing University of Technology, Beijing, 100022, China, Email: yjzeng@bjut.edu.cn Received: 21 October 2004; Accepted: 11 April 2006 Copyright © 2006 ACPSEM/EA Some researchers have studied in vitro experimental approaches to cell culture under normal stress and shear stress respectively 10-17 . However, they rarely developed an apparatus that simultaneously analysed normal stress and shear stress for cell culture. The purpose of this design is to offer scientific researchers a test apparatus, which can be used to study the ECs’ environment as influenced by normal stress and shear stress simultaneously. Using the theories and methods of bio-fluid mechanics, we designed a laminar flow apparatus which can precisely control the level of normal stress and shear stress so as to simulate the hemodynamic environment of human arteries in vivo. This apparatus can accurately simulate steady flow and pulsatile flow in large arteries. Methodology and implementation of the design Methods Since the shear stress acting on the vascular endothelium is inaccessible in vivo, many experiments were conducted in vitro in order to obtain the shear stress indirectly. To the best of our knowledge, there is no method for the direct measurement of shear stress in vitro. The only method appears to be to indirectly calculate the shear stress using the pressure difference between two points on the flow path. The response of EC to shear stress depends on the level of shear stress, the nature of the flow (steady flow or pulsatile flow) and the type of flow (laminar or turbulent). Under normal physiological conditions, the blood flow remains in a laminar flow state except during the systolic phase of the cardiac cycle when turbulent flow can be observed in the aorta. Previous investigations were carried