The researchers based their system

The researchers based their system on magnesium-based micromotors –– tiny spheres that react with water to produce hydrogen bubbles, which propel the motors. They coated the micromotors with hyaluronic acid, a joint lubricant, leaving a small opening for the magnesium to react with water. When placed in simulated joint fluid, the micromotors showed prolonged, sustained release of hydrogen bubbles and could move on their own. The team then injected the micromotors into the joints of rats that served as an animal model of rheumatoid arthritis and used ultrasound to visualize them. Compared with uninjected rats, the treated rats showed less-swollen paws, reduced bone erosion and lower levels of inflammatory cytokines. Although the micromotors still need to be tested in humans, they show great potential for the therapy of rheumatoid arthritis and other inflammatory diseases, the researchers say.