Double bubbles pierce with less problems

Two microscopic bubbles are better than one in penetrating soft materials, concludes a new study by engineers at the University of California, Riverside.

Optical cavitation, which uses a laser to bubble into a liquid that expands rapidly and then collapses, could be a safe way to deliver therapeutic agents, such as drugs or genes, quickly and efficiently, directly into living cells. Current methods for introducing foreign materials into cells, known as transfection, are based on piercing the outer membrane with a laser, which risks damaging the heat of the cell, or a pipette, which risks contamination.

Although not yet ready for primetime, scientists are improving optical cavitation techniques. The new document shows that two bubbles produce long, fine jets that penetrate enough with just five pulses to make cavitation potentially suitable for transfection or needle-free injections.

“The study of cavitation bubbles has evolved relatively quickly, from learning how to avoid damaging ship propellers to benefiting drug delivery,” said Vicente Robles, a doctoral student at Marlan and Rosemary College of Engineering Bourns, who led the study. . “The biggest limitation in your applications is our creativity.”

Cavitation bubbles are microns in size and live only for a fraction of a second, but they generate strong local changes in the physical properties of the surrounding medium, making them the prime candidates for cleaning localized surfaces, cell selection and heating or cooling.

In double bubble configurations, a bubble collapses faster and accelerates the neighboring bubble to invert and pierce itself, emitting a rapid jet that could, if strong enough, also pierce a cell membrane and possibly be used to transfect a cell. However, the speed, force and trajectory of the jet are highly influenced by the mechanical properties of the surrounding medium and the spatial and temporal separations of the bubbles.

Robles began by using lasers to create bubbles that form jets of water directed at a medium. He then compared single and double bubble jets targeting both petrolatum and a transparent agar gel widely used to model human tissue.

The double bubble process created elongated, fast and focused jets that increased in length and volume when directed at the agar gel. Only five pulses penetrated 1.5 millimeters, enough to pierce human skin. This was accomplished without the special micro nozzles used in existing laser injection systems. In petroleum jelly, the double bubble jet produced the same penetration length as the single bubble jet, but with a 45% reduction in the area of ​​damage, which could result in less thermal and shock wave damage in the surrounding environment, and three times as far.

“The use of a laser-induced double bubble arrangement is a significant advantage over previous studies, which rely on a converging nozzle or a pressurized cavity to produce strong jets,” said mechanical engineering professor and lead author Guillermo Aguilar. “Here, we take advantage of the inherent physics of asynchronous collapse of two bubbles to accelerate the jet that pierces the nearby surface.”

The study concludes that double bubble cavitation could offer compact, deviceless alternatives for needleless applications after further study and improvement.

The article, “Drilling Soft Material Using Double Bubble Laser-Induced Cavitation Microjets,” is published in Fluid Physics.