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Show Design And Manufacturing Of Cell Stretch Device For Visualization Of Cytoskeltal Restructuring Research Department of Bioengineering Mechanical forces influence the structure of tissues and organs. For example, a person with high blood pressure experiences thickening of the arteries because of the pressure being exerted on the vessel walls. Also, exercise increases the hearts muscle mass. Mechanical signals are sensed by cells, and activate a cascade of signals inside the cell called mechano-transduction. Through mechano-transduction, the cells alter the cytoskeletal proteins, which give the cell its size and shape. An interesting phenomenon that can be observed is that cells will align perpendicular to their stretch direction. First of all, what is the sensor? How can the cells sense an external mechanical force such as pressure or shear forces? There are several possibilities of how a cell is able to sense these forces via mechano-sensors. (1) First is the cytoskeletal protein itself. The cytoskeleton is the framework of the cell, which determines the shape of the cell. Very much like the walls in a house, which hold it together and give it its shape. In this first hypothesis, cytoskeletal proteins function as the mechano-sensors when they are deformed. Thus the actual framework sends the signal for change. (2) The second candidate is the idea that the contacts between cells or contact to the extra cellular matrix creates a signal. In the second hypothesis, mechanical force alters the contact between cells or extra cellular matrix, and the altered contacts function as mechano-sensors. To answer these questions, the first step is to design a device that can exert forces which approximate those found in the body. Normal human cells in the arterial wall experience around 10% stretch overall. The device exerts only a linear stretch, whereas arterial cells experience some radial stretching as well. Vascular Smooth Muscle cells are grown on a silicon rubber membrane and placed inside the device (see graphic depiction in Figure 1). During the course of the summer we designed and manufactured this stretch device which would allow us to stretch the cells on the microscope stage and then visualize them immediately. Previous to this device, stretching occurred inside an incubator and then had to be removed, and then placed on the microscope stage. The ultimate goal is to quantitatively measure the total deformation incurred to the cells as a result of stretching over roughly the following data sets: Preliminary images captured show the type of strain which we are going to need to calculate. The cells below (See Figure 2) have micro beads inserted (red dots) which allow us to get an idea of which parts of the cell are moving due to the stretching. By understanding which focal points are under the most stress, it may be possible to understand what particular proteins are responsible for allowing that change. The work to create software which will calculate the strain with image processing techniques is under way. Below are 2 preliminary images of a cell before and after stretching. Shown with stretch direction arrows. By calculating over a number of micro beads, the distance that they travel we can get an idea of the strain being exerted on the individual cell. The next step is to precisely calculate the deformation of the cellular structure. Paul Murdock Assist. Professor Masaaki Yoshigi |
