ZnO Nanowires-PLA Fiber Hierarchical Structure for Antibacterial Surface

Biominerals are composite materials that are generally based on organic templates and appear as organic-inorganic heterostructures with unique structures and functions such as stretchability, hydrophobicity, mechanical and thermal properties. [1] Recently, Significant advances in microfabrication and heterogeneous crystallization have made it possible to artificially realize a variety of nano architectures like those found in exoskeletons. However, emulating complex natural biominerals with topographical features is still challenging. [2,3]<br/>In this study, we proposed an approach to construct ZnO nanowires on the polylactic acid (PLA) templates to artificially implement natural urchin spicule structures in nanoscale and their protective functions. ZnO is an excellent candidate to simulate the urchin spicules since its bactericidal effect by generating reactive oxygen species (ROS) and potentially induces physical interaction. The growth of ZnO nanowires was inspired by the mineralization process of the sea-urchin spicule, in which a CaCO3-extracellular matrix exterior grows from internalized seeds. In natural mineralization, intermolecular interaction between CaCO3-extracellular matrix induces the migration of internalized CaCO3 seeds to the surface. This study found that we could expose ZnO nanoparticle seeds to the polymer surface with an interfacial assembly mechanism driven by free energy reduction. Based on the proposed mechanism, the macroscale spicule structure can be artificially realized in nanoscale after further growing ZnO nanowires via the hydrothermal method. [4]<br/>Based on insights into the protective function of the urchin spicule against external invasion, the topography of the heterostructure with nanowires represents a surface that efficiently inhibits the adhesion and proliferation of bacteria. The wettability of the ZnO-PLA heterostructure becomes super-amphiphilic, which aids bacteria in approaching the surface of the ZnO nanowires but not adhering to it, allowing bactericidal ZnO to function efficiently. The synergistic effect of the topography-induced super-amphiphilicity and bactericidal ZnO leads to unprecedented results of bactericidal activities.<br/><b>Reference</b><br/>[1] S. Yao <i>et al</i>., <i>Adv. Mater</i>. 29, 1605903 (2017)<br/>[2] L. Li <i>et al</i>., <i>Proc. Natl. Acad. Sci. U. S. A. </i>115, 3575 (2018)<br/>[3] T. Nishimura <i>et al</i>., <i>Polym. J.</i> 47, 235 (2015)<br/>[4] B. C. Park <i>et al</i>., <i>Adv. Funct. Mater. </i>31, 2100844 (2021)