Manufacturing technology
A: Schematic illustrating the as-deposited radial bimetallic structure arrangement, material removal boundaries for subsequent milling procedures, and the cut plane location used to provide microstructural analysis.
operative technique. Then there’s the prospect of printing components for machines in need of repair. This strategy proved particularly useful during the Covid-19 pandemic, when hospitals were able to print parts for their ventilators and respirators on site. According to GlobalData, the medical 3D printing market stood at $2bn globally in 2022 and is growing at more than 21% a year. This rise is being fuelled not only by more ‘traditional’ applications – orthopaedics, dental devices, and personalised devices – but also by its use within diagnosis and medical training. For instance, surgeons might hone their skills on a 3D-printed anatomical model before they operate on an actual patient. Many of the most exciting potential use cases, however, remain some way from the clinic. Research teams worldwide are working on everything from a programmable 3D-printed wound dressing to a 3D-printed heart replica that pumps just like the real thing. There is even a group working on 3D-printed hair follicles, set within lab- cultured human skin.
It would be remiss, too, not to mention the fast- emerging field of bioprinting – bodily tissue printed using the patient’s own cells. 3D-printed mini- organs have already been tested successfully in animals, and the hope is that 3D-printed organs could one day eliminate the need for organ donation. (Exciting though it is, that scenario is probably 20 years away or more.)
Stronger joint replacements At the less splashy – yet no less innovative – end of the spectrum, 3D printing is enabling big steps forward in material science. Amit Bandyopadhyay, Boeing Distinguished Professor of Mechanical and Materials Engineering at Washington State University, is developing a technique that could one day have profound implications for joint replacements. His team have found a way to 3D-print two types of steel in the same circular layer, creating a material that’s stronger than either metal alone. Their findings were published in the journal Nature Communications in June 2023. The team began by thinking about trees and bones – natural materials that derive their strength
Medical Device Developments /
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from layered rings of different materials. If you look at cross sections of cut wood, you will notice radial rings, formed by seasonal variations in wood growth. It’s a similar story with bone. “We hypothesise that such radial layering improves the mechanical properties of the overall structure,” says Bandyopadhyay.
Figuring that it might be possible to do the same thing with metals, the researchers used two welding machines of the type generally found in automotive shops. These machines were used to 3D-print two different metals in a circular layer, without any need to stop or change metal wires.
Although the metals were deposited at the same time, they cooled at different rates, and the resulting pressure fused the two together. The researchers think this pressure accounts for the increase in strength – in tests, the resulting composite material was 33–42% stronger than either metal taken alone. “This process is called wire arc-directed energy deposition,” says Bandyopadhyay. “We have also tried a powder-based directed energy deposition process and found that the concept works. So it is not process-dependent but design-dependent.” As he explains, the technique could be used with different materials depending on what you’re hoping to achieve. For instance, you could opt for a harder outer layer and a more ductile inner layer, providing high wear-resistance on the surface but good toughness overall. You could even start combining three or more materials, all 3D-printed within the same circular layer. Within the medical devices field, you might be able to create joint replacements that have titanium on the outside and magnetic steel on the inside. As Bandyopadhyay explains, magnetic fields have been shown to help in bone healing. “It’s a simple idea – titanium alloys offer excellent corrosion and fatigue resistance, but not such good biocompatibility,” he says. “Medical devices could be printed using the radial bimetallic structure concept, where the outside is titanium alloy and the inside is a magnetic material. So the overall device would offer better biocompatibility than a regular titanium implant, but similar corrosion and fatigue resistance.”
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B: Polished cross- sectional image showing build direction and the interlocking zig- zag pattern of wedge- shaped protrusions of stainless material in the core into the mild steel casing, and vice versa.
© Nature Communications/ Lile Squires, Ethan Roberts & Amit Bandyopadhyay - Washington State University
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