(Nanowerk Spotlight) Bacterial eye infections blind millions globally each year, and current antibiotics increasingly fail to stop them. When bacteria develop resistance to drugs, they can withstand our most powerful medications – leaving doctors with few options to save patients’ vision. This crisis hits hardest in cases of endophthalmitis, a severe infection inside the eye that can destroy retinal tissue within days if untreated.
Scientists studying cicada wings discovered an intriguing phenomenon in 2012: the microscopic spikes on these insects’ surfaces could physically rupture bacterial cells on contact, without using any chemical agents (Small, “Natural Bactericidal Surfaces: Mechanical Rupture of Pseudomonas aeruginosa Cells by Cicada Wings”). This mechanical approach to killing bacteria sparked interest because it bypasses the resistance mechanisms that bacteria develop against antibiotics. However, translating this concept from static wing surfaces to practical medical treatments proved challenging. Early attempts using spiked nanomaterials showed potential but relied on random particle movement, making them ineffective at penetrating the protective biofilm barriers that bacteria create around themselves.
A research team at Shandong First Medical University in China has now developed a solution that actively hunts down and destroys resistant bacteria. They created microscopic particles that combine the bacteria-killing spikes found on insect wings with the ability to propel themselves through infected tissue.
Schematic depiction of constructing a virus-like mechano–bactericidal nanomotor (VMSNT) and its use against bacterial infections. a) Steps in producing biomimetic VMSNT with bactericidal mechanical action. b) Fundamental concepts behind the bactericidal mechanical operations. (Image: Adapted with permission from Wiley-VCH Verlag)
These nanoscale robots, which the researchers call VMSNTs (virus-like mechano-bactericidal nanomotors), measure just 200 nanometers across – smaller than most bacteria. They feature a spiky silica core partially coated with gold, giving them two crucial capabilities: their sharp spikes can pierce bacterial cell membranes, while their gold coating converts near-infrared light into directional motion through temperature differences in the surrounding fluid.
The researchers modified the particles’ surface with molecules that specifically bind to bacterial cell walls but not human cells. When exposed to near-infrared light – which can safely penetrate eye tissue – the gold coating creates temperature gradients through a process called self-thermophoresis, propelling the particles through liquid environments toward bacteria. This active motion allows them to penetrate bacterial biofilms and reach protected infection sites.
In controlled laboratory cultures, the system eliminated over 99% of antibiotic-resistant Staphylococcus aureus and Pseudomonas aeruginosa, two bacterial species commonly responsible for severe eye infections. These initial results in isolated test conditions demonstrated the technology’s potential effectiveness. Microscopic imaging revealed how the particles pierce bacterial cell membranes and disrupt their internal structures. At the concentrations needed to kill bacteria, the treatment showed minimal toxicity to human cells.
The researchers then tested their system in mice with bacterial eye infections, including both surface corneal infections and internal eye infections. The VMSNT treatment significantly reduced bacterial levels and inflammation. Eyes treated with the nanomotors showed dramatic improvement compared to untreated controls, with near-complete recovery of tissue structure and function.
Detailed analysis revealed why the system works so effectively. The force generated by the moving particles, combined with their sharp surface features, creates enough localized pressure to rupture bacterial cell membranes. The active motion helps the particles break through bacterial biofilms – a crucial advantage over static treatments.
The technology marks an important step toward non-antibiotic treatments for bacterial infections. By combining mechanical bacteria-killing capabilities with active motion and specific targeting, the system addresses key limitations of previous approaches. The use of near-infrared light provides precise control over the treatment while remaining safe for eye tissue.
Several hurdles remain before human testing could begin. The complex environment of human infections contains proteins and other molecules that might affect the particles’ performance. The researchers acknowledge the need for extensive safety studies in larger animals and optimization of the treatment protocol.
The next phase of research will focus on these challenges while exploring applications beyond eye infections. The ability to create microscopic robots that actively seek and destroy resistant bacteria without antibiotics opens new possibilities for treating infections throughout the body.
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