Drug delivery system slowly releases pain-relieving nerve block over weeks
· Medical Xpressedited by Sadie Harley, reviewed by Robert Egan
Sadie Harley
Scientific Editor
Meet our editorial team
Behind our editorial process
Robert Egan
Senior Editor
Meet our editorial team
Behind our editorial process Editors' notes
This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility:
fact-checked
peer-reviewed publication
trusted source
proofread
The GIST Add as preferred source
Most local anesthetics used in medicine last only eight to 12 hours, or a day at most. Now, Boston Children's Hospital researchers have formulated a more effective slow-release injectable drug delivery system that achieved pain-numbing anesthetic effects lasting two to three weeks in rats, compared with a commercial formulation lasting about four to eight hours.
Given that nerve blocks in humans tend to work longer than in rats, this advancement, published in Nature Biomedical Engineering, could substantially extend the effective duration of currently used anesthetics and have implications for other types of pain.
Rethinking liposome drug release
For decades, physicians have used liposomes, tiny balls of fatty compounds known as lipids, as gradual drug delivery systems in the body. Liposome composition determines how fast drugs leak out, with faster release leading to a more potent drug effect over a shorter period and potentially greater toxicity.
Until now, researchers believed that molecules leaked fastest from liposomes made of more "fluid" lipids. However, Yuan Wang, Ph.D., a research engineer in the laboratory of Daniel Kohane, MD, Ph.D., overturned this theory by showing that liposomes made of more fluid lipids release drugs that mix well with or dissolve in water, known as "hydrophilic" drugs, extremely slowly.
One way to make lipids more fluid is by adding many double chemical bonds to their tails. The double bonds mean that the lipids can't pack together as tightly.
With a series of complex experiments, the team demonstrated that liposomes with many double bonds had a structure with multiple compartments, while those without them had a simple spherical structure. As a result, in liposomes with many double bonds, hydrophilic drugs had more lipid barriers to cross, leading to slower drug release.
"The more fluid membranes in liposomes with many double bonds may be easier to cross, but the greater number of barriers slows the drug's release," Wang says. "The more fluid liposomes with more double bonds may form concentric spheres that are like onions with many layers or could potentially be spheres within spheres."
Testing a longer-lasting anesthetic
Knowing a hydrophilic drug will leak more slowly from a more fluid liposome, the researchers tested a proof-of-principle experiment. The team filled its more fluid liposomes with potent tetrodotoxin—a powerful neurotoxin found in pufferfish and blue-ringed octopuses that serves as a powerful numbing agent.
When injected near a nerve in the leg of rats, the formulation provided prolonged local anesthesia, but no toxicity at the injection site or throughout the body. This means the drug released slowly enough to be cleared by the body, but still at sufficiently high levels to be an effective anesthetic. Tetrodotoxin is not yet commercially used in patients but could one day be developed as a therapeutic.
"This extended-release combination could be used for longer-term perioperative pain instead of opioids, and we are starting to consider using these potentially for chronic pain as well," says Kohane, senior associate in pediatric critical care at Boston Children's and director of Laboratory for Biomaterials and Drug Delivery. "These liposomes can also provide slow release of a wide range of hydrophilic molecules."
Publication details
Ultra-slow release of hydrophilic drugs via multilamellar–multivesicular liposomes formed by unsaturated phospholipids, Nature Biomedical Engineering (2026). DOI: 10.1038/s41551-026-01793-6
Journal information: Nature Biomedical Engineering
Key medical concepts
Clinical categories
AnesthesiologyClinical pharmacology Provided by Children's Hospital Boston Who's behind this story?
Sadie Harley
BSc Life Sciences & Ecology. Microbiology lab background with pharmaceutical news experience in oil, gas, and renewable industries. Full profile →
Robert Egan
Bachelor's in mathematical biology, Master's in creative writing. Well-traveled with unique perspectives on science and language. Full profile →
Citation: Drug delivery system slowly releases pain-relieving nerve block over weeks (2026, September 23) retrieved 23 September 2026 from https://medicalxpress.com/news/2026-09-drug-delivery-slowly-pain-relieving.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.