Effects of pressure characteristics on transfection efficiency in laser-induced stress wave-mediated gene delivery

Abstract

Laser-induced stress waves (LISWs) generated by irradiating a light-absorbing medium with a pulsed laser can transiently increase the permeability of cell membranes for gene delivery. In this study, we investigated the effects of pressure characteristics of LISWs upon gene transfection efficiency using lasers with different pulse durations: a 6-ns pulsed Nd:YAG laser and 20-ns and 200-µs pulsed ruby lasers. LISWs were generated by irradiating a black rubber disk, on which a transparent plastic sheet was adhered for confinement of the laser-produced plasma. Rat dorsal skin was injected with plasmid DNA coding for luciferase, to which LISWs were applied. With nanosecond laser pulses, transfection efficiency increased linearly with increasing positive peak pressure in the range of 35 to 145 MPa, the corresponding impulse ranging from 10 to 40 Pa⋅s. With 200-µs laser pulses, on the other hand, efficient gene expression was observed by the application of LISWs even with a 10-fold-lower peak pressure (∼5 MPa), the corresponding impulse being as large as 430 Pa⋅s. These results indicate that even at low peak pressures, efficient transfection can be achieved by extending the pressure duration and hence by increasing the impulse of LISWs, while the averaged expression efficiencies were relatively low.