Nature Helps: Toward Bioinspired Bactericidal Nanopatterns

Abstract

Development of synthetic bactericidal surfaces is a drug‐free route to the prevention of implant‐associated infections. Surface nanotopographies with specific dimensions have been shown to kill various types of bacterial strains through a mechanical mechanism, while regulating stem cell differentiation and tissue regeneration. The effective ranges of dimensions required to simultaneously achieve both aims are in the <200 nm range. Here, a nanoscale additive manufacturing (=3D printing) technique called electron beam induced deposition (EBID) is used to fabricate nanopillars with reproducible and precisely controlled dimensions and arrangements that are within those effective ranges (i.e. a height of 190 nm, a diameter of 80 nm, and an interspacing of 170 nm). When compared to the flat surface, the nanopatterned surfaces show a significant bactericidal activity against both Escherichia coli and Staphylococcus aureus (with respective killing efficiencies of 97 ± 1% and 36 ± 5%). Direct penetration of nanopatterns into the bacterial cell wall leads to the disruption of the cell wall and cell death. The more rigid cell wall of S. aureus is consistent with the decreased killing efficiency. These findings support the development of nanopatterns with precisely controlled dimensions that are capable of killing both Gram‐negative and Gram‐positive bacteria.

Deciphering the Roles of Interspace and Controlled Disorder in the Bactericidal Properties of Nanopatterns against Staphylococcus aureus

“…The results of this study showed that the cell wall of S. aureus could be mechanically penetrated by nanopatterns ( Figure 5) and be severely damaged with an unrecognizable morphology (Figure 3), as reported previously [25,30,37]. However, changing the interspacing of nanopatterns could drastically affect the percentage of the damaged cells.…”

“…EBID was used to fabricate the desired nanopatterns on silicon substrates as described before [25]. Briefly, 1 × 1 cm 2 samples were prepared by cutting double-sided polished 4-inch (diameter = 10.16 cm) silicon wafers (thickness = 525 ± 25 µm, p-type), cleaning with nitric acid, and rinsing with deionized water subsequently.…”

“…A volume of 2 µL liquid with a falling rate of 1667 µL min −1 was placed on the surface and the average contact angle was recorded within 30 s after the droplet touched the surface. The measured contact angle was further used to calculate the Cassie-Baxter contact angle (Table 1) [25].…”

“…As previously explained [25], fabricating large areas of nanopatterned surfaces using EBID is not time-efficient yet, but patterning a small area would suffice for systematically studying the bactericidal effects of highly controlled nanopatterns. However, it hinders the use of certain assessment methods such as live/dead staining and CFU counting.…”

“…However, it hinders the use of certain assessment methods such as live/dead staining and CFU counting. We therefore exploited a method applied previously in several other studies [25,[30][31][32][33] in which morphological evaluation of bacterial cells through SEM imaging is used to distinguish between disrupted and healthy bacterial cells. The validity of this technique has been demonstrated before in studies that have used and compared different evaluation techniques in determining the bactericidal properties of nanopatterned surfaces [30,33].…”