UNIVERSITY PARK, Pa. — Bacteria and other swimming microorganisms evolved to thrive in challenging environments, and researchers struggle to mimic their unique abilities for biomedical technologies, but fabrication challenges created a manufacturing bottleneck. Microscopic, 3D-printed tori — donuts — coated with nickel and platinum may bridge the gap between biological and synthetic swimmers, according to an international team of researchers.
These micro swimmers mimic biological behavior and might one day deliver targeted drugs or stir samples in labs-on-a-chip — a miniature device that mimics a full laboratory on a microchip.
"These donuts may eventually have medical applications as active materials," said Igor Aronson, Huck Chair Professor of Biomedical Engineering, Chemistry and Mathematics, Penn State.
Active materials are those that move on their own like bacteria or artificial micro swimmers.
"It's really hard to get things to mix when using a lab-on-a-chip," said Remmi Danae Baker, doctoral candidate in material science and engineering, Penn State. "These microtori, because they are active materials and move on their own, could be used to aid in micromixing.
The researchers manufacture these donuts using a Nanoscribe Photonic Professional GT machine that allows creation of the 3, 7 or 14 micrometer donuts with printed features of up to 200 nanometers. Spider silk is 3 to 10 micrometers in diameter. The Nanoscribe uses precise laser technology and specially designed photoresists to achieve this.
"We create two different designs, horizontal and vertical," said Baker. "Horizontal tori are printed flat on the supporting glass slide, glazed with nickel and then platinum. Vertical tori are 3D-printed upright and are then dipped in nickel and platinum."
The horizontal donuts are perfectly circular and look like iced donuts, with the icing thicker on top than on the sides. The vertical version has one flat end so that they stand for dipping and are only dipped halfway.
The nickel serves two purposes. Platinum will not stick to the plastic micro-donuts, but nickel will and platinum will stick to nickel. Also, nickel is magnetic, so the researchers can manipulate the donuts with magnetic fields.
"The lattices of the nickel and platinum layers match up pretty well," said Baker.
The researchers want the donuts to behave like living organisms — to swim in water and respond to signals. Living things need food or fuel for motion. For the experiment, the researchers placed the microtori in a hydrogen peroxide solution, which was the fuel. Platinum decomposes hydrogen peroxide and powers propulsion of the donuts.