The findings could help researchers make local anesthetics last longer in people.

Patients recovering from surgery may need pain relief beyond the eight to 12 hours, or about a day at most, that most local anesthetics provide.

Seeking a longer-lasting option, researchers at Boston Children’s Hospital have redesigned liposomes, microscopic carriers made from fatty molecules, to release a numbing drug more gradually. In rats, the formulation sustained local anesthesia for two to three weeks, compared with about four to eight hours for a commercial formulation.