Millimeter-Scale Magnetic Carrier for On-Demand Delivery of Magnetic and Non-Magnetic Microparticles Suspensions

The use of magnetic microparticles (MMPs) has recently proven a great potential for biomedical applications, i.e. for drug delivery or magnetic hyperthermia. However, MMPs are typically delivered passively through systemic injection or exploiting tethered drug delivery systems which require percutaneous medical procedures. Here we propose an untethered magnetic carrier for MMPs suspension delivery. This wireless millirobot is capable of precisely releasing MMPs that after delivery are completely decoupled from the carrier and can be manipulated independently by separate magnetic sources. Experiments were performed in an aqueous environment to validate carrier locomotion and controlled release capabilities. The prototyped carrier (overall 41 mm long and 10 mm in diameter) can be wirelessly moved by an external magnet at a distance larger than 10 cm, and, when fixed magnetically, can be triggered by another external magnet (around 6 mm apart) to release a cargo. Magnetic navigation and release activation well fit model predictions with actuation distance errors below 10% based on experimental performance. The carrier proved able to perform controlled release of non-magnetic and magnetic cargoes and was recorded to release approximately 25% of the loaded MMPs suspension with no premature release.