Localized pain caused by disease, injury, or surgery can be hard to control, and it leads too many people to use opioids. Though there are electronic and physical methods that can help manage some pain, these are typically only marginally effective and usually only work on targets close to the skin. Now a team from Boston Children’s Hospital has come up with a way to use ultrasound to trigger the release of an anesthetic previously injected into the affected region.

The anesthetic is encapsulated within liposomes, tiny sacks made of lipids derived from cellular membranes. The walls of the liposomes are also seeded with sono-sensitizer molecules that produce reactive oxygen species when shaken by ultrasound waves. After the anesthetic loaded liposomes are injected, they stay put for a few days near their original delivery point and don’t interact much with nearby tissue. But when ultrasound is introduced, the liposomes break up and release their pain-killing cargo.

The intensity and length of time of the projection of ultrasound control how much anesthetic is released, allowing for a fairly easy and accurate management of pain symptoms.

Hopefully soon patients post-surgery will be leaving the hospital not with a bottle of oxycodone, but with an ultrasound transducer and instructions on how to use it.