Bactericidal Anisotropic Nanostructures on Titanium Fabricated by Maskless Dry Etching

Abstract

Bioinspired nanostructured antibacterial surfaces are among the most promising recent discoveries in nanotechnology to tackle microbial colonization of surfaces, especially with the growing challenge of antimicrobial resistance. Reactive ion etching (RIE) is one of the few nanofabrication techniques that has been demonstrated to be capable of generating biomimetic nanostructures on large substrates through a combination of physical and chemical etching. However, the physics behind the formation of these structures and their spatiotemporal evolution is poorly understood, primarily limited by the challenges associated with placing in situ characterization instruments inside the process chamber. The limited understanding in the field leads to poor reproducibility, constraining the widespread acceptance and application of this technique. This work describes maskless RIE of commercially pure titanium substrates using chlorine and fluorine plasma. It is demonstrated that the chamber condition plays a critical role toward determining the morphology of the nanostructures generated, and high aspect ratio (HAR) nanostructures can be generated reproducibly by following proper cleaning protocols involving fluorine plasma by scavenging the SiOCl species that accumulate in the chamber walls over time. Furthermore, the control of several process parameters to reproducibly fabricate various types of nanostructures such as nanoridges, nanopillars, and nanowires are demonstrated, along with insights into the underlying physical principles. HAR nanopillars are generated, and their bactericidal mechanism and efficiency are shown to be primarily dependent on their aspect ratio. This study provides insights to resolve the hitherto poorly understood events of fabrication of bioinspired nanostructures by RIE with important implications for reliably and reproducibly engineering biomaterial surfaces with bactericidal activity.

Antibacterial Designs for Implantable Medical Devices: Evolutions and Challenges

“…Such antibacterial surfaces are promising for orthopedic devices and dental implants, which are intended to be integrated into bone tissues. In addition, topographical nanostructures, such as nanopillars [216][217][218], nanosheets [219], nanorod [220,221], and nano-roughness [222,223], with the efficacy of physical sterilization represent an innovative pathway toward antibacterial surfaces. Among these designs, nanopillars received the most attention because their puncture-based biocidal actions are material composition and bacterial species independent.…”

Controlled Metal Crumpling as an Alternative to Folding for the Fabrication of Nanopatterned Meta-Biomaterials

“…The introduction of nanotopographies to the surface of bone substitutes is particularly appealing, because well-designed surface ornaments may be able to (simultaneously) kill bacteria [3,[14][15][16][17][18][19] and induce osteogenesis [2,16,20]. In this regard, introducing holes to the flat sheet not only regulates the mechanical properties of such 3D structures but could also address the morphology-based aspects that are required for bone tissue regeneration, such as suitable mass transport properties for the transportation of oxygen, nutrients, and metabolites [21] and cell settlement.…”

Mechanobactericidal Nanotopography on Nitrile Surfaces toward Antimicrobial Protective Gear

“…As the pressure is increased, the availability and density of reactive species in the chamber also increase, thereby increasing the etching rate. This also results in a decrease in anisotropy of etching due to the reduced mean free path of the ions, which causes more frequent collision events and deviation of the ions from their original straight path and an increase in their angular distribution . However, in this study, chamber pressure (0.05 mbar) was kept constant.…”

“…Standard micro- and nanofabrication processes, such as nanoimprint lithography and a hybrid of colloidal lithography and plasma etching, are multistep, slow, and limited to thermoplastics . In contrast, reactive ion etching (RIE) is a one-step simple and elegant procedure that can generate random nanotopography on a wide range of materials . However, the applicability of this manufacturing process to engineer mechanobactericidal nanostructures on polymers for medical products and protective gear has not been demonstrated before.…”

“…Notably, the above-mentioned processes are limited to flat surfaces due to the use of masks/molds, whereas maskless RIE can easily be applied to curved surfaces. The random nanostructures generated by RIE have demonstrated excellent mechanobactericidal activity against several strains of bacteria along with the added advantage of cost-effective scalability. ,, In contrast to periodic structures, the random nanostructures are more densely packed, and owing to their random arrangements, the bacteria are exposed in many different directions to the pillar tips. , …”