pH- and near-infrared light-responsive, biomimetic hydrogels from aqueous dispersions of carbon nanotubes

Owing to their low flexibility, poor processability and a lack of responsiveness, inorganic materials are usually non-ideal for constructing a living organism. Hence, to date, lifelike materials with structural hierarchies and adaptive properties usually rely on light and soft organic molecules, although few exceptions have been acquired using two-dimensional (2D) inorganic nanosheets. Herein, with a systematic study on the gelation behavior of carbon-based 0D quantum dots, 1D nanotubes, and 3D fullerenes, we find that acidified 1D carbon nanotubes (CNTs) can serve as an alternative building block for fabricating purely inorganic biomimetic soft materials. The as-prepared CNT gels exhibit not only a pH- or photothermal-triggered mechanical and tribological adaptivity, which allows them to simulate the behavior of sea cucumbers, peacock mantis shrimps, and mammalian muscles or cortical bones, but also a unique damping property that is similar to spider's cuticular pad. Their high elasticity, effective lubrication, excellent biocompatibility, and controllable friction and wear also allow them to function as a new type of smart lubricants, whose tribological properties can be regulated either by its internal pH changes or spatiotemporally by near-infrared (NIR) light irradiations, free of any toxic and flammable base oils or additives.