“Tree-Ring” Patterns of Halloysite Nanotubes by Agitation-Assisted Assembly for Guiding Cell Alignment

Naturally occurring halloysite nanotubes (HNTs) are widely used in advanced materials area, but the preferred alignment of these nanotubes still lacks facile and versatile techniques. Here, we present a simple and efficient strategy for fabricating an ordered aligned HNT architecture on a glass substrate by drying their aqueous dispersion with the assistance of a magnetic rotor. The nanotubes were aligned into a “tree-ring” pattern, which was induced by a shear force provided by agitation during the water evaporation process. The factors, including nanotube charges, HNT concentrations, drying temperature, droplet volume, and rotor size, that influenced the formation of the HNT pattern were investigated. The birefringent phenomenon and micromorphology of the HNT tree-ring pattern were thoroughly studied with polarized optical microscopy and scanning electron microscopy. The perfectly ordered alignment of nanotube architectures can be achieved when the HNT concentration is above 5 wt %. The thickness and surface roughness of the HNT pattern increase with the HNT concentration. The macroscale topography of the HNT pattern can promote adhesion and proliferation of mouse fibroblast cells, and cells are grown along the nanotube’s alignment direction. This facile method for the fabrication of a patterned HNT array on a solid substrate has great potential in cellular-responsive templates such as tissue engineering scaffold materials.