The Intrinsic Incompressibility of Osteoblast-like Cells

This paper presents a new methodology, apparatus design, and the experimental results of ongoing research into the measurement of the mechanical properties of musculoskeletal tissue at the cellular level. A microchamber was constructed that provides a controlled hydrostatic pressure environment for these cells where optical sectioning, via epifluorescence microscopy, was used to acquire volume information about the individual cell. The microchamber was integrated into a hydraulic system that, via computer control, provided a regulated adjustable hydrostatic pressure environment for living cells suspended in culture media. The techniques applied in this study include fluorescent labeling of the cell volume, hydrostatic pressure application, optical sectioning, and digital volume reconstruction. To determine the mechanical response (compressibility) of cultured MG-63 osteoblast-like cells under physiologically high hydrostatic pressures two experiments were devised: In the first experiment changes in volume of 10 cells were measured as the applied hydrostatic pressure was increased from 0 to 7 MPa. Volume changes in response to pressure magnitudes were not significant (p > 0.49). In the second experiment, the mechanical role of the plasma membrane to act as a supportive component in cell compressibility was studied by permeabilizing the membrane of six cells and again applying hydrostatic pressure. Again, no significant volume differences between pressurized and unpressurized cells were found (p > 0.46). A retrospective power analysis of the results of the first and second experiments indicates that the sample size was sufficient. The results of this study show that MG-63 osteoblast-like cells are intrinsically incompressible in the 0-7 MPa hydrostatic pressure range. They also support the hypothesis that the plasma membrane plays an insignificant mechanical role in terms of cell compressibility.