Table 4.
Natural nanostructures and bio-inspired Ti structures modified from [155,184,185,186,187]. In contrast to hydrophilic surfaces hydrophobic surfaces prohibit bacterial growth as the bacteria cannot stick to the surface. Defined nanostructured surfaces can stretch and rupture the relatively thin bacterial cell wall. This rapid morphological change of the adhered bacteria induce its death within a few minutes (approximately 3–5 min, “contact killing mechanism”). However, the peptidoglycan layer of the cell wall of Gram-positive (G+) bacteria is 4–5 times thicker than that of Gram-negative (G−). Here, defined surface textures of the nanostructure are required to enfold its bacteriostatic effects which are based on reduced adhesion forces. A special challenge and exception are mycobacteria. In contrast to many other bacteria their cell wall is thicker, hydrophobic, and rich in mycolic acids. It is believed that, for this reason, there has not been any study on the bactericidal efficiency of nanostructured surfaces. HY: hydrophobic, HP: hydrophilic, CA: contact angle.
| Surface | Surface Feature | Method | Wettability (CA) | Bactericidal and Fungicidal Efficacy |
|---|---|---|---|---|
| Cicada wing | Nanoneedles, height 200 nm, diameter 60 nm size at the top, 100 nm at the base of the pillar, and spacing 170 nm | natural | HY [159°] | Lethal to P. aeruginosa (G−) |
| Gecko skin | Hair (spinules) like structures with sub-micron spacing and a tip radius of curvature <20 nm | natural | HY [151°–155°] | Lethal to Porphyromonas gingivalis (G−) |
| Dragon fly wing | Nanograss, diameter 50–70 nm, height 240 nm | natural | HY [153°] | Lethal to P. aeruginosa (G−), S. aureus (G+), B. subtilis (G+) |
| Periodical cicada | Hemispherical nano features with height 83.5 nm, diameter 167 nm, pitch 252 nm | natural | HP [80.1°] | Caused cell wall rupturing of Saccharomyces cerevisiae |
| Annual DD cicada | Spherical nanocones with height 183 nm, base diameter 104 nm, cap diameter 104 nm, pitch 175 nm | natural | HY [132°] | Caused cell wall rupturing of Saccharomyces cerevisiae |
| Sanddragon dragonfly | High-aspect ratio spherical capped nanocylinders with height 241 nm, diameter 53 nm, pitch 123 nm | natural | HY [119°] | Caused cell wall rupturing of Saccharomyces cerevisiae |
| Megapomponia intermedia | Nanopillars with height 241 nm, diameter 156 nm, pitch 165 nm | natural | HY [135.5°] | Bactericidal against Pseudomonas fluorescens (G−) |
| Cryptotympana aguila | Nanopillars with height 182 nm, diameter 159 nm, pitch 187 nm | natural | HY [113.2°] | Bactericidal against G− P. fluorescens |
| Ayuthia spectabile | Nanopillars with height 182 nm, diameter 207 nm, pitch 251 nm | natural | HY [95.65°] | Bactericidal against P. fluorescens (but more than Megapomponia intermedia and Cryptotympana aguila) |
| Titania nanowire arrays | Nanowires, brush type: Diameter 100 nm | Hydrothermal | - | Effective in killing motile bacteria (P. aeruginosa, Escherichia coli (G−), B. subtilis), less lethal against non-motile bacteria (S. aureus, Enterococcus faecalis (G+), K. pneumoniae (G−)) |
| Titania nanowire arrays | Nanowires, niche type: Diameter 10–15 μm | Hydrothermal | - | Effective in killing motile bacteria (P. aeruginosa, Escherichia coli and B. subtilis), less lethal against non-motile bacteria (S. aureus, Enterococcus faecalis, and Klebsiella pneumoniae) |
| Ti nanopatterned arrays | Nanopatterned arrays, average diameter 40.3 nm | Hydrothermal etching | HP [73°] | Effective in killing P. aeruginosa, less lethal against S. aureus |
| Ti alloy nanospike surface | Nanospikes, average diameter 10 nm, spacing 2 μm, height 2 μm | Anodization | - | Lethal to S. aureus |
| Ti alloy anospike surface | Nanospikes, average diameter 20 nm | Thermal oxidation | - | Lethal to E. coli |