An assistant professor of mechanical engineering at the University of California has embarked on a study to explore innovative micro-manufacturing processes that could strengthen tiny titanium-based medical devices in order to improve their performance and reliability.

Masaru Rao, an assistant professor in the Department of Mechanical Engineering, has for the past 10 years been working on a novel manufacturing technique that allows machining of titanium at an unprecedentedly small scale. This is particularly groundbreaking as titanium is a material that is well proven to be compatible in the human body and so can be used in various chronic medical implants.

However, Rao’s new study, which has received a five-year, $400,000 award from the National Science Foundation in the US, will focus on developing techniques to strengthen these titanium-based micro- and nano-scale medical devices, which has not been carried out up until now. “This is due, in large part, to limitations imposed by the micro-machining techniques that must be used to access these reduced length scales,” says Rao.

For example, Rao’s own technique only works with pure titanium and so prevents it from working with other biomedical alloys such as stainless steel. This also means that coating a machined part to increase its hardness is also constrained at the micro- and nano-scale because of challenges of coating uniformity and quality over complex structures.

Rao is going to try and attempt to address these limitations by exploring the use of gas nitriding, a technique that is widely used in the automotive field to increase the wear resistance of metal parts such as engine camshafts. Essentially, the surfaces of machined parts are heated in a nitrogen atmosphere resulting in a strong nitrogen-based titanium alloy.

“While pure titanium has adequate strength for many applications, device performance and reliability could be enhanced significantly if we can increase strength,” explains Rao. “Gas nitriding may provide a means for doing so, since it can be applied to our devices after they have been fabricated, it won’t suffer from the limitations of coating-based processes, and the diminutive dimensions of our devices will make it easy to diffuse nitrogen throughout the entire structure, thus allowing through-thickness strengthening.”

A project currently being worked on in his lab that will benefit from this micro-machining process are titanium-based microneedle devices that can be used, for instance, to deliver drugs to the eye. “Since these devices are intended for penetration of relatively robust but also highly sensitive tissues, such as cornea and sclera, strength is crucial,” Rao says. “Increased strength will allow us to make smaller devices, which will reduce tissue trauma and insertion force, both of which are important performance metrics.”

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