Briefly, cavitation is the process whereby collapsing bubbles create shock waves. Usually, these waves radiate out in all directions and cannot be tightly controlled. Zhong and his team got the idea of using two bubbles in tandem to direct the energy flow in a specific direction, namely to puncture and inject a nearby cell.
The team used lasers to precisely create tiny bubbles of blue dye within a liquid surrounding a target cell. First, one bubble is created and allowed to expand. Exactly at the point when that bubble would normally collapse, a second bubble is created. The expansion of the second bubble puts pressure on the first. Instead of dissipating in a radial fashion, the first bubble now accelerates toward the cell, puncturing it and injecting it with the blue dye.
The timed expansion and collapse of two bubbles creates a liquid jet that can penetrate a fine hole in the membrane of a cell. From left to right: A laser (green circle) focused inside a water bath locally vaporizes the liquid, creating an expanding bubble (light blue). Just after the first bubble reaches its maximum size, a second laser (red circle) generates another bubble. As the second bubble expands and the first bubble collapses, a rush of liquid forms along the vertical line between the two, creating a high-speed liquid jet that accelerates toward the cell with enough force to penetrate the membrane.
Credit: Alan Stonebraker, American Physical SocietyThe mammalian cells that the researchers used have membranes that are impervious to the blue dye unless they are first perforated. The clear evidence of blue dye within the cells indicates that the bubble technique was successful. Unfortunately, the toxic blue dye also happened to kill the cells. Hopefully, that won’t be the case with any therapeutic agents that are injected in this manner. The ability to deliver drugs to specific cells is expected to be an especially useful tool for scientists working with stem cells.