Oct 31, 2015 | By Benedict

Researchers at Harvard have developed an innovative anti-fouling material which is able to vastly reduce the corrosion and fouling of steel. Their research could have a valuable knock-on effect for the 3D printing community, with the lifespan and functionality of steel nozzles predicted to improve significantly when equipped with the special material.

The researchers, part of the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), have used rough nanoporous tungsten oxide to create a new surface coating for steel, which can make the alloy stronger, safer and more durable. The coating is purportedly the most durable anti-fouling and anti-corrosive material yet produced, and can effectively repel any kind of liquid. “This research is an example of hard core, classic material science,” said Joanna Aizenberg, the Amy Smith Berylson Professor of Materials Science and core faculty member of the Wyss Institute for Biologically Inspired Engineering at Harvard University. “We took a material that changed the world and asked, how can we make it better?”

The material’s potential benefit to the durability and longevity of 3D printer nozzles could be significant. The steel components of 3D printers are as vulnerable to corrosion and fouling as all steel objects, which is a particularly big problem when attempting to 3D print with highly viscous materials. Stickier filaments require minimal friction from the inside of the printing nozzle, else they cannot be dispersed effectively and evenly.

Fouled steel nozzles are also a no-go when 3D printing with biological materials. Researchers continue to look for ways of 3D printing human tissue in order to provide synthetic organs for patients, but such an operation would be extremely dangerous were the tissue to become contaminated from a fouled steel nozzle. Philseok Kim, co-author of the paper and co-founder and vice president of technology at SEAS spin-off SLIPS Technologies Inc., does not think that this kind of contamination would be problem with the new material. “Because we show that this material successfully repels bacteria and blood, small medical implants, tools and surgical instruments like scalpels and needles that require both significant mechanical strength and anti-fouling property are high value-added products we are exploring for application and commercialization.”

The surface coating could be used in a wide range of circumstances besides 3D printing. Steel, a low cost alloy made up of iron, carbon and other elements, is an extremely valuable material in many fields, including construction, medicine and transport.

Aizenberg, one of the team’s principal researchers, has a distinguished history of creating non-stick, anti-fouling materials. Since developing Slippery Liquid-Infused Porous Surfaces (SLIPS) in 2011, Aizenberg has demonstrated many uses for the material. “Our slippery steel is orders of magnitude more durable than any anti-fouling material that has been developed before,” she explained. “So far, these two concepts – mechanical durability and anti-fouling – were at odds with each other. We need surfaces to be textured and porous to impart fouling resistance but rough nanostructured coatings are intrinsically weaker than their bulk analogs. This research shows that careful surface engineering allows the design of a material capable of performing multiple, even conflicting, functions, without performance degradation.”

Aizenberg and co. used an established method to provide the material with its seemingly paradoxical dual function. An electrochemical technique was used to grow an ultrathin film made up of hundreds of thousands of small, rough, tungsten-oxide islands onto a steel surface. The technique is common practice in steel manufacturing, but Aizenberg believes that her team have perfected the art. Furthermore, using an established technique encourages scalability without being disruptive to current industry practices. “I don’t want to create another line that would cost millions and millions of dollars and that no one would adopt,” she explained.

Alexander B. Tesler, former postdoctoral fellow at SEAS, current research fellow at Weizmann Institute of Science in Israel, and the paper’s first author, explained the electrochemical process in layman’s terms. “If one part of an island is destroyed, the damage doesn’t propagate to other parts of the surface because of the lack of interconnectivity between neighboring islands,” he explained. “This island-like morphology combined with the inherent durability and roughness of the tungsten oxide allows the surface to keep its repellent properties in highly abrasive applications, which was impossible until now.”

a-h images show corrosion evolution as a function of contact time. Unmodified stainless steel (300 grade) (right sample) and TO-SLIPS sample with a 600-nm-thick porous TO film on steel (left sample) exposed to very corrosive Glyceregia stainless steel etchant. ©Harvard SEAS

The material has already been thoroughly tested. Its durability was tested with intense scratching and pummelling, whilst a variety of liquids, including water, oil, highly corrosive media, biological fluids containing bacteria and blood, were applied to the material to test its anti-wetting properties.

We hope that the researchers’ findings can be used to speed up developments in medical 3D printing and other fields. The team’s full findings can be found in Nature Communications.



Posted in 3D Printer Accessories



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