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Various different cell types in the body experience mechanical forces and the effect of cell stretch, compression or other mechanical stimuli has become a new and important scientific focus. Many devices have been developed to stretch cells. Usually the cells are cultivated on elastic membranes and the entire membrane is deformed to deform the attached cells. This approach has been proven useful but suffers one big disadvantage: If cells are to be imaged during or after the membrane is deformed, the cells are displaced relative to the optical axis of the microscope and a microscopic observation becomes virtually impossible. As shown in the figure below only the part in the center portion (red X) remains stable relative to the objective of the microscope, when the membrane is stretched.
When cells are grown on an elastic membrane and strain is applied to the membrane, only the center portion of the membrane can be used for imaging because only this part remains at its initial position relative to the objective of the microscope. This is a serious disadvantage as only those cells are available for microscopical investigation that have grow in this center portion of the membrane. We developed a computer- controlled stretch device that overcomes this impediment by using active motion compensation. With our new stretcher cells can either be subject to uni-axial strain or strain relaxation (compression) and it allows to simultaneously image the cells at high optical resolution. This is possible at any position on the membrane while strain or compression is applied. Numerous other features have been implemented to ensure easy handling of cells — during prolonged cell culture in the incubator as well as on the microscope.
detailed description of the device: summary
This compact cell strain device makes it possible to perform life cell imaging studies where a rapid image acquisition is required, such as observing changes of the intracellular Ca2+ concentration
Our dcCS10-compensation is moving the entire membrane during the stretch so that it counteracts this displacement. As a result the region of interest is still precisely positioned above the objective of the microscope during (and after) the stretch. The benefit: Cells can be imaged even during stretch!
when cells are mechanically stimulated. A big advantage of this cell strain device is its stretching chamber, which allows to use commercially available PDMS sheets. The sheets are transparent and as a consequence it is possible to perform regular bright field as well as epi-fluorescence microscopy with an inverted microscope. The commercially available PDMS substrates are thin enough to use even oil immersion objectives. The cell strain device is not operated by the microscope software but the program is running on a separate computer — a small laptop or even a net book with the appropriate interface is sufficient. This enables the scientist to use the stretcher on any microscope and regardless of the image acquisition software installed. Naturally the device can also be used without the microscope.
Figure 1 below shows a schematic of the device. The strain/compression device consists of two different components with different functions.
Figure 1. Schematic of the strain/compression (SC) device.
A: The SC-device with the membrane chamber attached is mounted on the microscope. The carrier plate is shown in gray with all attached components in matching colors. The SC motor is mounted on the carrier plate and deforms the mounted membrane chamber by moving the sliding blocks via a ball screw and a metal band (see also text). To compensate the stretch-induced lateral displacement the carrier plate is moved laterally with the ball screw driven by the compensation motor (both in blue). The red arrows show the movements of the membrane holders during deformation and the movement of the carrier plate to compensate the lateral displacement.
B: The membrane chamber shapes the elastic membrane into a tray that is used to cultivate the cells. In the view on the top right one of the holders is shown before assembly. Two double hooks of the prestrain holder (bottom) are holding the membrane chamber and can be moved freely along the plate rail and fastened at any position with two screws.
Observation of the membrane chamber with a regular cell culture microscope through the observation window allows inspection of the cells during cultivation of the cells without removing it from the prestrain holder.
C: Membrane chamber and prestrain holder are readily assembled. The next steps are usually autoclaving and coating of the membrane followed by seeding the cells into the tray.