An improved stretching device has been developed for use in research on the effects of unidirectional loading on human and animal cells. The device is capable of applying or removing a load (a controlled amount of stretch) on command to mimic the loading or unloading experienced by skeletal muscles and other tissues of interest.
This device is designed to overcome the deficiencies of three cell-stretching devices that were commercially available at the time of reporting the information for this article. In the present device as in the commercial devices, a cell culture is grown on a coated sheet of silicone rubber that is immersed in a culture medium and the sheet is stretched to apply the desired load. One of the commercial devices can apply the load only in discrete steps and must be removed from the culture medium to change to a different load step. The other two commercial devices contain circular silicone membranes that are deformed in such ways that the resulting stretches include radial components and are thus not the desired unidirectional stretches. The present device need not be removed from the culture medium and produces a continuously adjustable, truly unidirectional stretch.
The silicone rubber sheets in the present device are in the form of rectangular strips coated with an extracellular matrix compound (i.e., collagen Type I). The strips are arranged parallel to each other with their long axes laid out along the axis of a round cylindrical ram (see figure). By use of removable pins, the ends of the strips are attached to the ends of the ram at equal circumferential intervals. This design makes it possible to grow cells on the strips in standard tissue culture plates to the required cell density or differentiation state before placing the strip in the cell stretcher. This design also offers the advantage of ease of removal of the cells for examination at the end of the stretching procedure.
The ram assembly with the strips attached is inserted in a tissue-culture vessel that contains a culture medium. The stretching actuator in the ram is a sealed-chamber piston. Stretching along the cylindrical axis is effected by injection of a sterile fluid into the sealed chamber by use of a pump controlled by a microprocessor. (The pump is situated outside the culture vessel.) Reversal of the injection flow results in a decrease in the amount of stretch. The rate of stretching or unstretching is controlled by controlling the rate of flow.
According to a proposed alternative design of this device, the ram would be advanced by a screw drive actuated by a microprocessor-controlled stepping motor. According to another proposed alternative design, the cell stretcher would be built into a tissue-culture vessel that would include a heater, a temperature sensor, ports for exchange and/or sampling of the culture medium, a port for infusion of gas, a pressure sensor, gas sensors, and optical ports for observation of cells during the loading procedure.
This work was done by Daniel L. Feeback of Johnson Space Center and Mark S. F. Clarke of the National Research Council. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Bio-Medical category.
This invention is owned by NASA, and a patent application has been filed. Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to
the Patent Counsel
Johnson Space Center
Refer to MSC-22834.