Nanoparticle hydrogel heats up to release drugs in active cartilage

Researchers in France have come up with a novel way to treat damaged cartilage after a joint injury, using the friction produced by the active joint in combination with a nanoparticle-based hydrogel to release drugs when and where they will be most effective.

Cartilage in a joint such as the knee is slow to heal after an injury, partly because it has no blood vessels. This lack of blood flow in the connective tissue also makes it difficult to administer growth factors there, making many cartilage injuries chronic and irreversible. But scientists at the French École Polytechnique Fédérale de Lausanne (EPFL) have developed a hydrogel that delivers a drug while a patient's cartilage is in motion. They published their work in the journal Biomaterials.

Cells called chondrocytes produce cartilage in the body, but when a joint is at rest, these cells are mostly inactive, according to an EPFL report. And so for a treatment to work, it must release drugs not only at the site of the injury, but while the joint is in motion. By developing a hydrogel that releases drugs when a joint creates friction and release heat, the team was able to treat the cartilage right at the moment it is needed.

"The receptors involved only appear after 5-20 minutes of repetitive movement," said team member Dominique Pioletti in a statement. "We therefore had to develop a way to time the release of the medication."

To do this, the hydrogel comprises liposomal nanoparticles that contain TGF-beta growth factor. When heat is generated in the cartilage for up to 5 to 10 minutes, EPFL reports, the nanoparticles shrink, producing gaps that release the drug. Presently, the team has proven the mechanics of the delivery using colored dye in place of the growth factor, and by arthroscopically implanting the hydrogel directly into the cartilage.

- here's the EPFL report
- and the research abstract