MOF Coating Enhances the Ion Tolerance of Micromotors

Abstract

Electrophoretic-driven micro/nanomotors (EMNMs) offer great potential for biomedical applications due to their design flexibility. However, they face challenges in high-salt environments, where ionic quenching disrupts propulsion by collapsing the electrical double layer. This study introduces a versatile strategy by coating EMNMs with a MOF porous scaffold (ZIF-8), which acts as ion-conductive channels that replace the electrical Debye layers and support propulsion in high-salt solutions. Through a heteroepitaxial growth process, ZIF-8 was precisely coated on silicon micromotors, a typical model for EMNMs, significantly enhancing their ion tolerance. By optimizing both the MOF layer and the geometry factor, the micromotors achieved effective motion in PBS solution, comparable to blood salt levels, with their ion tolerance (EI₅₀) improving by up to 266 times compared to uncoated micromotors. Additionally, the micromotors maintained stable, controllable motion under 980 nm NIR light, even when passing through an artificial blood vessel covered with biological tissues. In addition, the ZIF-8 coating offers drug-loading capabilities and pH-responsive release, along with biocompatibility, making these micromotors suitable for targeted drug delivery. This MOF coating strategy is versatile and scalable, and can be extended to other types of EMNMs, significantly enhancing their ion tolerance and unlocking new possibilities for biomedical applications.