Formation of a ZnO nanorods-patterned coating with strong bactericidal capability and quantitative evaluation of the contribution of nanorods-derived puncture and ROS-derived killing.

Abstract

To endow Ti-based orthopedic implants with strong bactericidal activity, a ZnO nanorods-patterned coating (namely ZNR) was fabricated on Ti utilizing a catalyst- and template-free method of micro-arc oxidation (MAO) and hydrothermal treatment (HT). The coating comprises an outer layer of ZnO nanorods and a partially crystallized inner layer with nanocrystalline TiO₂ and Zn₂TiO₄ embedded amorphous matrix containing Ti, O and Zn. During HT, Zn²⁺ ions contained in amorphous matrix of the as-MAOed layer migrate to surface and react with OH^- in hydrothermal solution to form ZnO nuclei growing in length at expense of the migrated Zn²⁺. ZNR exhibits intense bactericidal activity against the adhered and planktonic <i>S. aureus in vitro</i> and <i>in vivo</i>. The crucial contributors to kill the adhered bacteria are ZnO nanorods derived mechano-penetration and released reactive oxygen species (ROS). Within 30 min of <i>S. aureus</i> incubation, ROS is the predominant bactericidal contributor with quantitative contribution value of ∼20%, which transforms into mechano-penetration with prolonging time to reach quantitative contribution value of ∼96% at 24 h. In addition, the bactericidal contributor against the planktonic bacteria of ZNR is relied on the released Zn²⁺. This work discloses an in-depth bactericidal mechanism of ZnO nanorods.