A current challenge in the field of artificial molecular machines is the synthesis and implementation of systems that can produce useful work when fuelled with a constant source of external energy. The first experimental achievements of this kind consisted of machines with continuous unidirectional rotations and translations that make use of 'Brownian ratchets' to bias random motions. An intrinsic limitation of such designs is that an inversion of directionality requires heavy chemical modifications in the structure of the actuating motor part. Here we show that by connecting subunits made of both unidirectional light-driven rotary motors and modulators, which respectively braid and unbraid polymer chains in crosslinked networks, it becomes possible to reverse their integrated motion at all scales. The photostationary state of the system can be tuned by modulation of frequencies using two irradiation wavelengths. Under this out-of-equilibrium condition, the global work output (measured as the contraction or expansion of the material) is controlled by the net flux of clockwise and anticlockwise rotations between the motors and the modulators.

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Microarrays of living cells are an emerging tool in systems such as reverse transfection. These studies are limited to adherent cells partly because of the difficulty of cell immobilization. Using a newly developed reagent, the biocompatible anchor for membrane (BAM), we show herein the rapid and strong attachment of living nonadherent cells and adherent cells on BAM-modified surfaces. Normal cellular growth was observed for over 7 days on BAM-modified surfaces. We expect this methodology to greatly expand the scope of current cell microarray technology.