Cell loading with laser-generated stress waves: the role of the stress gradient.

Purpose: To determine the dependence of the permeabilzation of the plasma membrane on the characteristics of laser-generated stress waves.
Methods: Laser pulses can generate stress waves by ablation. Depending on the laser wavelength, fluence, and target material, stress waves of different characteristics (rise time, peak stress) can be generated. Human red blood cells were subjected to stress waves and the permeability changes were measured by uptake of extracellular dye molecules.
Results: A fast rise time (high stress gradient) of the stress wave was required for the permeabilization of the plasma membrane. While the membrane was permeable, the cells could rapidly uptake molecules from the surrounding medium by diffusion.
Conclusions: Stress waves provide a potentially powerful tool for drug delivery.