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Inspired by the natural motors capable of performing multiple tasks in complex living environments, synthetic nanomotors emerge as a potential vehicle for revolutionizing biomedical processes. Yet current motors suffer from decreased and even completely hindered motion in a complex physiological environment, shadowing the future of this booming field. To address this problem, a unimolecular nanomotor based on molecular bottlebrush (MBB) of sub-100 nm size is reported. This motor is constructed precisely via controlled radical polymerization and click chemistry and propelled with biocompatible catalase. Such a molecular nanomotor possesses tadpole-like asymmetry and is able to overcome Brownian motion, and demonstrates strong directional propulsion (linear and coiled cyclic trajectories) in a viscous tumor microenvironment gel model at an ultralow hydrogen peroxide level of 2 mM (0.006%). In addition, the molecular nanomotor exhibits superior stability in serum containing cell medium and good biocompatibility in blood. Such molecular bottlebrush based nanomotors may represent a unique platform for overcoming the tissue penetration barrier.

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Molecular bottlebrushes featuring brush-on-brush (BoB) architecture were prepared by combining azide–alkyne click chemistry, ring-opening polymerization (ROP), and atom transfer radical polymerization (ATRP). Primary side chains of diblock copolymers with a poly­(ε-caprolactone) (PCL) block and a poly­(α-bromo-ε-caprolactone) (P­(CL-Br)) block were synthesized by ROP and then grafted onto PCL backbone by the click reaction. Then the secondary side chains of poly­(oligo­(ethylene glycol) acrylate) (POEGA) were grafted from the P­(CL-Br) block by ATRP, yielding an amphiphilic core/shell structure. Imaging of individual macromolecules by atomic force microscopy (AFM) demonstrated dramatically thickened wormlike formation with distinct hairy side chains. Interestingly, for the BoB molecular bottlebrushes with enough long primary and secondary side chains, sufficient tension can be generated along the backbone and thus lead to its cleavage.

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