Key points from article :
Millirobots responds to magnetic field generated by MRI scanners.
Bullet-shaped robot produces enough force to drive it into animal brains.
Contains a stainless-steel bead that is pulled back and forth.
Bead compresses a mechanical spring in one direction.
MRI machines' magnetic field orientation is fixed, limiting directional control.
Could performing minor medical interventions, e.g. piercing a cyst and biopsies.
The study was published in the IEEE Robotics and Automation Letters journal.
