Cell permeabilization using
shock waves may be a way of introducing macromolecules and small polar molecules into the cytoplasm, and may have applications in gene therapy and anticancer
drug delivery. The pressure profile of a
shock wave indicates its energy content, and
shock-wave propagation in tissue is associated with cellular displacement, leading to the development of cell deformation. In the present study, three different
shock-wave sources were investigated;
argon fluoride excimer laser,
ruby laser, and
shock tube. The duration of the pressure pulse of the
shock tube was 100 times longer than the
lasers. The uptake of two fluorophores,
calcein (molecular weight: 622) and
fluorescein isothiocyanate-dextran (molecular weight: 71,600), into HL-60 human promyelocytic
leukemia cells was investigated. The intracellular fluorescence was measured by a spectrofluorometer, and the cells were examined by confocal fluorescence microscopy. A single
shock wave generated by the
shock tube delivered both fluorophores into approximately 50% of the cells (p < 0.01), whereas
shock waves from the
lasers did not. The cell survival fraction was >0.95. Confocal microscopy showed that, in the case of
calcein, there was a uniform fluorescence throughout the cell, whereas, in the case of
FITC-dextran, the fluorescence was sometimes in the nucleus and at other times not. We conclude that the impulse of the
shock wave (i.e., the pressure integrated over time), rather than the peak pressure, was a dominant factor for causing fluorophore uptake into living cells, and that
shock waves might have changed the permeability of the nuclear membrane and transferred molecules directly into the nucleus.