Micropatterning of biologically derived surfaces with functional clay nanotubes.

Micropatterning of biological surfaces performed via assembly of nano-blocks is an efficient design method for functional materials with complex organic-inorganic architecture. Halloysite clay nanotubes with high aspect ratios and empty lumens have attracted widespread interest for aligned biocompatible composite production. Here, we give our vision of advances in interfacial self-assembly techniques for these natural nanotubes. Highly ordered micropatterns of halloysite, such as coffee rings, regular strips, and concentric circles, can be obtained through high-temperature evaporation-induced self-assembly in a confined space and shear-force brush-induced orientation. Assembly of these clay nanotubes on biological surfaces, including the coating of human or animal hair, wool, and cotton, was generalized with the indication of common features. Halloysite-coated microfibers promise new approaches in cotton and hair dyeing, medical hemostasis, and flame-retardant tissue applications. An interfacial halloysite assembly on oil microdroplets (Pickering emulsion) and its core-shell structure (functionalization with quantum dots) was described in comparison with microfiber nanoclay coatings. In addition to being abundantly available in nature, halloysite is also biosafe, which makes its spontaneous surface micropatterning prospective for high-performance materials, and it is a promising technique with potential for an industrial scale-up.

This international group of authors unites researchers who pioneered halloysite clay nanotubes for biomaterials, and discloses a new strategy for this nanoclay composite design through interfacial architecture. These results confirm Dr. K. Ariga concept of nanoarchitectonics, and demonstrate promising applications. Assembly of the clay nanotubes on biosurfaces, including the coating of human or animal hair, wool, and cotton, was generalized for the process optimization. Halloysite-coated microfibers promise new approaches in cotton and hair dyeing, and medical hemostasis and flame-retardant tissue applications. Related techniques of interfacial halloysite assembly on oil microdroplets (Pickering emulsion) and its quantum dots core­shell structure for cell imaging are also described. Contrary to many other synthetic nanomaterials, described natural halloysite nanotubes are environmentally safe and abundantly available, thus allowing for scale up of the suggested functional biocomposites.