A Tetherless Microdriller for Maneuverability and On-Board Cargo Delivery Inside Viscoelastic Media

Abstract

Untethered microrobots capable of drilling offer an attractive alternative to conventional surgical tools due to their lower invasiveness and maneuverability in subsurface tissue. This work presents a magnetically actuated microdriller (250µm in width and 1.25mm in length) capable of drilling at speeds of up to 780µm/s under a 10mT rotational magnetic field in an agar gel tissue phantom. The microdriller consists of a neodymium cube attached onto a driller printed via two-photon polymerization. Under sufficiently high static and rotational magnetic fields, the microdriller could reorient itself and travel a targeted trajectory inside the viscoelastic material. To demonstrate drug delivery capabilities, the microdriller could carry an attached pH-sensitive, fluorescein-loaded hydrogel along its path. In slightly acidic solutions similar to extracellular tumor environments, the hydrogel package selectively swelled and released the molecules held inside it. These results document one of the smallest microdrillers fabricated to date and the first to carry an on-board, pH-sensitive hydrogel for drug delivery and microsurgery applications.