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The promise of producing personalized implants first drew Andy Christensen to additive manufacturing and inspired him to purchase Medical Modeling’s first 3D printer in 2006. His goal at the additive manufacturing service provider was to produce personalized titanium parts for use in orthopedic applications.
It was a great idea that was ahead of its time.
“The concept was too complicated, and producing one-off parts was difficult then — and still is,” said Christensen, now the President of Fingerprint Additive, a consulting firm for the 3D printing and medical device industries.
Despite that initial setback, Christensen’s passion for 3D printing continued to grow, leading to a respected career in additive manufacturing and him staying abreast of the technology’s latest developments. He sees growth in printing applications involving fatigue-sensitive parts, particularly in spine devices, and said implant designers often need to strike a balance between achieving structural support and allowing for some mechanical play. It’s what is referred to as the “mechanobiology” concept.
“The idea involves designing implants that aren’t as rigid as a traditional interbody device,” Christensen said. “That concept has always been around, but most applications have focused on parts that weren’t fatigue sensitive.”
Part of that is due to the material properties that were previously possible. Christensen said designers of 3D-printed devices could meet cast-grade titanium specs without issue. Eventually, they also hit wrought specs.
“They made parts that met or exceeded those strength requirements,” he added. “But forging remains a higher bar. Forged properties are around 20% to 30% stronger than wrought, and that gap has always felt somewhat insurmountable. We may never completely bridge it.”
That doesn’t mean orthopedic companies aren’t trying to cross the chasm. “One of the primary ways companies are working to close that gap is through post-processing, specifically advanced heat treatments and hot isostatic pressing (HIP),” Christensen said.
One of the most interesting developments he’s observed is the work being done to tweak HIP cycles. He said these processes are achieving their intended purpose of improving fatigue strength and pushing mechanical properties much closer to those of forged parts.
According to Christensen, the groups doing impressive work in this area include Quintus Technologies, a HIP vessel manufacturer based in Sweden.
On the commercial side, Paragon Medical is using HIP to improve the fatigue performance of 3D-printed implants and employing “clean HIP,” which avoids the formation of alpha case, a layer that typically develops on HIP-processed parts and can negatively impact surface properties. The company’s process helps parts retain their intended appearance and functionality and enhances their performance, according to Christensen.
“HIP is a really exciting area of innovation,” he said. “Companies that successfully fine-tune their cycles will gain a real competitive advantage. That’s worth monitoring.”
Christensen identified a focus on increasing production speed as another important trend in additive manufacturing and said a growing number of companies are using multi-laser systems to accelerate build times.
As machine speeds increase, the cost per part — at least the portion tied to machine amortization — goes down. “That’s likely opening the door to new applications,” Christensen said. “Faster machines, equipped with two, four or even 16 lasers are becoming more common. The move toward faster, multi-laser machines is a positive development for the industry.”
Traditional manufacturing involves prototyping and then translating that prototype into a full-scale production process. AM, on the other hand, often involves prototyping directly on the same equipment that’s used to produce the parts.
“So, while you’re dialing in your design, you’re also figuring out machine parameters, post-processing and all the other production variables,” Christensen said. “That makes the transition from prototype to production much smoother than it used to be.”
Additive manufacturing offers flexibility in terms of inventory and stock management. Although it’s not always easy to hit precise production targets, orthopedic companies can order 10 or 50 implants instead of batches of a thousand. “That helps reduce inventory levels, and I think we’ll continue to see more of that as the technology makes it easier to mix and match sizes and components within smaller production runs,” Christensen said.
He noted that laser-based systems have largely dominated the production landscape, but electron beam melting (EBM) is being used to complete some compelling work. Christensen attended Formnext, the international 3D printing show, last November in Germany. GE provided interesting updates on the ways the company is advancing EBM technology to improve surface finishing, enable supportless part production and move toward eliminating the need for a build plate.
“At first, I was skeptical,” Christensen said. “But what GE showed was impressive.”
The company introduced a new scanning technique called Point Melt. This technique involves melting metal powder through small points instead of lines, enabling a more accurate temperature and reducing temperature gradients when printing a part.
“Visually, it doesn’t look like it should work, but GE is achieving the same or even better strength as traditionally printed parts, and is doing it without supports,” Christensen said. “What’s even more interesting is that they’ve figured out how to print porous structures with downward- or sideways-facing surfaces, something that’s usually a major challenge. But with this new method, they’re making part orientation almost irrelevant.”
Christensen noted that eliminating support structures and part orientation would allow companies to fully utilize a build chamber’s Z height.
“Most spine and hip implants fill only a thin slice of that vertical space. With this new technology, companies could stack parts in a more efficient way, dramatically increasing throughput and lowering the cost per part,” he said. “From a usability and cost-efficiency standpoint, that’s a game-changer.”
