Caltech researchers have developed spherical microrobots made of hydrogel polymers for targeted drug delivery in complex biological fluids like blood and urine. These 30-micron diameter structures incorporate magnetic nanoparticles and therapeutic drugs, allowing precise navigation using external magnetic fields and ultrasound for propulsion and real-time imaging. The microrobots feature an innovative design with a hydrophilic exterior and hydrophobic interior to trap air bubbles for extended in vivo stability. In tests on mice with bladder tumors, these microrobots delivered drugs effectively, showing significant therapeutic potential. Researchers aim to further evaluate the system for various medical applications.