Researchers from the University of Science and Technology of China, working with outside collaborators, have developed shape-shifting microrobots that are designed to be guided to a target area in the body using magnets, and then release a drug cargo in response to the local environment. The application that the researchers have pursued involves guiding the microrobots to a solid tumor using magnets outside the body, and then the tumor’s naturally acidic microenvironment stimulates a shape change, resulting in the local release of a chemotherapy drug. Researchers are devising a variety of cunning ways to deliver drugs at precise locations in the body, and this latest technology is no exception. The microrobots consist of a 3D-printed hydrogel that is pH-responsive. The researchers tweaked the printing density at specific locations so that the small structures would change shape in predictable and useful ways in low pH conditions. This capability adds an additional ‘dimension,’ and has led the Chinese team to describe the process as 4D printing. For instance, one design consists of a fish-shaped microrobot that opens its mouth in an acidic environment, releasing a drug contained within its belly. Another is a crab that can hold something in its claw and then release it when required, and a third design is a butterfly that can move its wings. Another challenge involves maneuvering the microrobots to the area they are required, such as the site of a solid tumor. To address this, the researchers turned to magnets. They magnetized the tiny microrobots by soaking them in a suspension of iron oxide nanoparticles, allowing them to use magnets to move the tiny devices. In theory, this may mean that the microrobots can be controlled remotely and minimally invasively when they are in the body, by applying magnets or magnetic fields externally. So far, the team tested the microrobots in artificial blood vessels in a petri dish that also contained cancer cells. They successfully maneuvered the microrobots through the blood vessels and towards the cancer cells, where they reduced the pH to mimic the naturally acidic microenvironment of a tumor. The robots changed shape and released their drug payload, killing the cells. In future, the researchers will need to make the structures smaller so that they can traverse real blood vessels, but the technology certainly looks promising for targeted drug delivery. Check out the new microrobots in action: Source
