Over the last decade, collaborative teams of engineers, chemists, and biologists have diligently studied the physical and chemical properties of cicada wings, driven by the quest to unlock the enigmatic ability of these wings to eliminate microbes on contact. The hope is that if science can replicate this natural function, it may lead to the development of products with inherently antibacterial surfaces, surpassing the effectiveness of current chemical treatments.
At Stony Brook University’s Department of Materials Science and Chemical Engineering, researchers made significant progress when they developed a simple technique to replicate the nanostructure of cicada wings. However, they still lacked a crucial piece of information – the exact mechanism by which the nanopillars on the wing’s surface exterminate bacteria. Fortunately, their answer came in the form of assistance from Jan-Michael Carrillo, a researcher at the Center for Nanophase Materials Sciences in the Department of Energy’s Oak Ridge National Laboratory.
Carrillo plays a vital role in nanoscience research by providing large-scale, high-resolution molecular dynamics (MD) simulations on the powerful Summit supercomputer at the Oak Ridge Leadership Computing Facility. The researchers reached out to Carrillo, expressing their interest in conducting a simulation to understand the cicada wing’s mechanism. While they had a grasp of how MD simulations work, they lacked sufficient experience in conducting them.
Gaining access to Summit is no simple task. Nanoscience researchers must apply and undergo a peer review process to receive the simulation work at the Center for Nanophase Materials Sciences. Beyond computational simulations, Carrillo also assists researchers in requesting neutron beamtime at ORNL’s Spallation Neutron Source for future experiments.
The journey to replicate nature’s microbe killer began when Stony Brook’s researchers, Maya Endoh and Tadanori Koga, were inspired by a 2012 research article describing the cicada wings’ ability to puncture bacterial cells with deadly consequences. As experts in polymer material science, they sought to recreate the nanopillars of the wings through directed self-assembly using block copolymers.
Self-assembly involves using block copolymers composed of chemically distinct homopolymers connected by covalent bonds. This approach allows for the fabrication of dense, highly ordered periodic nanostructures with precise control over their geometric parameters across vast areas. By varying the dimensions of the nanopillars, the researchers sought to determine which geometric parameters were crucial in killing bacteria.
The team tested the nanosurfaces’ efficacy against bacteria in laboratory conditions, demonstrating that the nanosurfaces not only killed the bacteria that came into contact with them but also prevented the accumulation of dead bacteria and debris on their surfaces. This self-cleaning aspect is crucial as it avoids the creation of a better environment for bacteria to thrive.
The key to understanding how the nanosurface’s pillars achieve this bacterial extermination came through Jan-Michael Carrillo’s MD simulations. The simulations revealed how the bacteria’s cell membrane stretched and collapsed within the local structure of the pillars. Strong interaction between the bacterium and the nanosurface substrate caused the lipid heads to absorb onto the hydrophilic pillar surfaces, shaping the membrane to the structure of the pillars. Eventually, the simulations suggested that membrane rupture occurred due to tension generated within the lipid bilayer clamped at the edges of pillars.
Interestingly, the researchers found that the best-performing samples did not precisely mimic the height and structure of the cicada wing’s nanopillars, challenging their initial expectations. Even with shorter nanopillars, the bacteria were eradicated, and the surfaces remained self-cleaning. This discovery opens up new possibilities for the development of antibacterial nanosurfaces for biomedical devices.
The Stony Brook team plans to further investigate the mechanisms, particularly the self-cleaning functionality, through simulations before applying the nanosurface to biomedical devices. Meanwhile, Carrillo will continue his research on amphiphilic lipid-like bilayer systems and remain ready to assist other nanoscience researchers seeking help from the Center for Nanophase Materials Sciences, Oak Ridge Leadership Computing Facility, or Spallation Neutron Source.
By Impact Lab