Micromotors Go In Vivo: From Test Tubes to Live Animals

While synthetic micromotors have been evaluated extensively under in vitro conditions for over a decade, their in vivo function has rarely been explored. Recent research effort has resulted in micromotors that display fast movement in complex biological media, and possess efficient cargo loading, transport, and release, along with good biocompatibility. These new capabilities have made synthetic micromotors promising active delivery tools for in vivo applications including treatment of enteral diseases. This review highlights several examples of recent in vivo applications using different types of biocompatible and biodegradable chemically powered body-fuel-propelled micromotors, including precise micromotor tissue localization and retention, autonomous gastric fluid neutralization and cargo release, and enhanced drug delivery toward enhanced treatment of stomach bacterial infection. Zn and Mg-based micromotors, powered by body fluids, have shown unique advantages to operate at different regions of the gastrointestinal tract. This review also covers some early in vitro studies that paved the way for the current in vivo applications, along with future prospects and challenges.