A D V A N C E D M A T E R I A L S & P R O C E S S E S | M A Y / J U N E 2 0 2 0 1 4 NANOTECHNOLOGY NANOSTRUCTURED SURFACES THAT CAN KILL BACTERIA Engineers at Purdue University, West Lafayette, Ind., have developed a laser treatment method with the po- tential to transform metal surfac- es into bacteria killers. The research- ers demonstrated that this techni- que allows the surface of copper to instantaneously kill off super- bugs such as MRSA (Methicillin- resistant Staphylococcus aureus). “Copper has been used as an an- timicrobial material for centuries. But it typically takes hours for native copper surfaces to kill off bacteria,” says lead researcher Rahim Rahimi. The technique is not yet tailored to killing viruses, such as the one re- sponsible for the COVID-19 pandemic, which are much smaller than bacteria. The method developed by Ra- himi’s team uses a laser to create na- noscale patterns on the metal’s surface. The patterns produce a rugged texture that increases surface area, allowing more opportunity for bacteria to hit the surface and rupture on the spot. The research team has begun test- ing the technology on the surfaces of other metals and polymers that are used to reduce risks of bac- terial growth and biofilm formation on devices such as orthopedic implants or wearable patches for chron- ic wounds. The technique might apply to metallic alloys that also are known to have anti- microbial properties. “We’ve created a robust process that selectively gen- erates micron and nanoscale patterns directly onto the targeted surface without al- tering the bulk of the cop- per material,” says Rahimi, whose lab develops innovative materi- als and biomedical devices to address health care challenges. The laser-texturing has a dual ef- fect—it not only improves direct con- tact but also makes a surface more hydrophilic. For orthopedic implants, such a surface allows bone cells to more strongly attach, improving how well the implant integrates with bone. The Purdue team observed this effect with fibroblast cells. Due to the simplicity and scalabili- ty of the technique, the researchers be- lieve that it could easily be translated into existing medical device manufac- turing processes. . DISINFECTING WITH NANOMATERIALS A new electromechanical depo- sition method out of Iowa State Uni- versity, Ames, can fabricate nanoma- terials on cloth and paper. The Univer- sity’s Sonal Padalkar discovered the process through studying metal-oxide nanomaterials for use in biosensors and antimicrobial agents. “The implications of our present antimicrobial studies are enormous,” Padalkar says. “We can find ... many very specific applications, like surgi- cal units in hospitals.” More studies are needed to determine if this technique, which is effective on bacteria, can work for tiny viruses, too. The key contribution from her lab has been figuring out how to grow nanostructures of metal oxides on cheap, lightweight, flexible cloth and paper. Padalkar’s fabrication tech- niques are based on electrochemical deposition—applying electricity to the cloth or paper while also applying a solution containing precursors to the metal oxides. Tests show the resulting nano- structures are consistent, stable, and robust. She says the technology could be scaled up for larger surfaces and scaled all the way down to a single thread. In the time of social distancing and hand sanitizer shortages, there’s high demand for all kinds of antimicro- bial products. Padalkar says the anti- microbial cloth and paper products made possible by this fabrication tech- nology could be useful in homes, hos- pitals, clinics, workplaces, schools, and farms. A carbon cloth is coated with zinc oxide nanomaterials that are just billionths of a meter in size. Courtesy of Sonal Padalkar/Iowa State University. A laser prepares to texturize the surface of copper, enhancing its antimicrobial properties. Courtesy of Purdue University photo/Kayla Wiles.