Going for a Spin: Simultaneously Pulling and Spinning Microrods Speeds Transport through Collagen Matrices.

Magnetic drug targeting requires particles to move through the complex viscoelastic environments of tissues and biological fluids. However, these environments often inhibit particle motion, making it difficult for magnetically guided particles to reach their intended targets. Magnetic microrods are easy to grow and manipulate, but experience significant hindrance to transport in complex, tortuous, tissue-like environments. Simple magnetic force translation ("pulling" or "pushing") is often insufficient or inefficient for long-range transport of microrods through such environments. Designing microrods capable of rotating while being pulled with a magnetic force may enable rods to overcome hindrances to transport. We present microrods with orthogonally magnetized segments, actuated by simultaneous magnetic force and magnetic torque. By simultaneously pulling and rotating our rods we create smooth-surfaced magnetic drilling microrods (MDMRs) capable of enhanced motion through protein-dense biopolymers. We model magnetic force and torque on MDMRs, characterize MDMR dynamics during transport, and demonstrate enhanced MDMR transport through protein-dense matrices in vitro.