When the press reports on additive manufacturing, the line between what’s possible now and what may be coming in the future is sometimes blurry. People love to read about breakthroughs taking place in university labs and company R&D centers—the reports of which always include Star Trek-like possibilities of what those breakthroughs may portend. Such reportage, however, needs to be parsed with care. (Newsflash: Nobody has 3D-printed complete, working human organs. Not yet.)
Moreover, the glare of that promised bright future can blind us to the technical marvels that medical device manufacturers are producing with additive technology now—and their contemporary challenges.
For example, Engineering Manager Travis Simpson and Production Manager Patrick Hare help to oversee the making of Individual Patient Solution (IPS) devices for KLS Martin Manufacturing LLC, Jacksonville, Fla. IPS leverages 3D printing of titanium, PEEK (polyether ether ketone) and other materials to make complex surgical implants used to repair and replace damaged or missing bone structures.
Imagine an accident victim with severe damage to the skull, say part of an eye socket or jaw destroyed. The IPS system lets the patient’s surgeons upload CT scans and other data to KLS Martin, where specialized software generates a virtual model of an implant customized for that specific patient. In fact, software enables virtual modeling of not only the implant but also of the surgery needed to place it simply and correctly.
The virtual model of the implant is used to make the CAM file for a 3D-printing system. The resulting implant corresponds precisely with the surgeons’ needs. After printing and inspection, the implant is shipped to the patient’s surgical team to be surgically inserted. Total time from CT scan data upload to shipping of the implant: five-to-10 days.
Additive manufacturing can create the structurally complicated shapes needed for implants such as those used in maxillofacial surgery—without the preparation time, development and material waste costs of subtractive techniques, according to Hare.
“We use additive-based production methods for nearly all of our products—not only the implants but also guides, models, and other tools, all designed to fit a particular patient’s anatomy,” said Hare. “The parts that result are as strong if not stronger than subtractive methods, with features and curvatures that are otherwise not reasonable or possible to produce.”
Simpson noted that the incremental improvements being made to 3D printing technology directly benefit the company’s customers. “The addition of automated preparation steps, improved software, faster manufacturing techniques, and larger machine capacity—all of these are allowing us to serve our patients and surgeons faster and more appropriately than ever,” he said.
“One such example is the development of multi-laser 3D printing systems and integrated material management, which substantially decrease manufacturing times.”
While additive materials and processes are improving, these are still early days, particularly when compared to the more mature subtractive technologies, Simpson and Hare agree.
“While many industries have not yet adopted this technology for more than prototyping and product development, our business is centered around the use of these systems for real, live patients,” Hare said.
Selective laser melting of metals, for example, is a process that may not yet be fully developed or understood, even by the additive equipment makers themselves, Hare said.
“Currently, much of the expertise for our use scenarios is developed in-house,” Simpson noted. Companies such as KLS Martin need to develop their own expertise with any given additive system because the additive equipment-maker may not know exactly what the equipment is capable of either. “We’re all still learning,” he said.
In other words, additive users seem to have to figure things out for themselves in a way that a buyer of a CNC mill or lathe perhaps wouldn’t.
At Smith+Nephew Inc., Memphis, Tenn., Senior Global Product Manager Cyndi Holland has observed such a learning curve in the production of the company’s Visionaire 3D-printed surgical guide for total knee replacement surgery. In April 2019, the company introduced an improved version of the guide—but the changes to the device led to new printing challenges.
The Visionaire guide is another system that uses the advantages of additive to create a customized, patient-specific solution. A patient’s knee is imaged using MRI and X-ray and the data is used to create a virtual 3D model with a sophisticated CAD program. As with KLS Martin’s IPS procedure, the model is used for virtual surgery—enabling the simplest, most effective and least invasive surgical procedure to be plotted out well before any scalpels are deployed. Throughout the process, an expert engineer is in communication with the surgeon to make sure “patient-specific parameters as well as surgeon-specific parameters” are accounted for, Holland said.
Once the model and the surgical plan are optimized, the data is used to 3D-print a surgical guide for the patient’s femur and another for the tibia (the leg bones above and below the knee, respectively).
During the surgery, the guides are placed directly on the patient’s bones, directing the surgeon to exactly where incisions need to be made in relation to where the knee is situated.
“It takes about 12 hours for each guide to be printed in Nylon 12 on one of our four EOS machines,” Holland said. After printing, each guide is scanned and its dimensions verified against the CAD model with a Romer arm, she noted.
The printers have large enough build spaces that the facility can print up to 50 individual guides at a time; with four machines, they can build up to 200 guides a day. On average, they build about 700 individual guides per week, Holland said.
When the company made some improvements to the product by further tailoring it to the individual patient, they ran into some headaches, however.
“The first iteration of the guides was static-sized,” Holland explained. Great care went into making sure that the area at the end of the tibia guide exactly matched the patient’s physiology. The problem was that the rest of the guide was less tailored.
“If a patient had what we called a size-2 tibia, for example, the guide would be created with a standard size-2 tibial guide. All of the size 2s were the same,” with only the small area that touched the patient’s anatomy being modified. “But there are different morphologies that the standard sizes didn’t capture. So, there were occasional issues with the way the old guides fit on the tibia because within a given size, individual patients’ bones could be thinner or thicker, longer or shorter.”
The new guides take those variations into account, she said, and are now automatically adjusted to the patient’s actual anatomy.
However, the greater variation in dimension has made the new guides more of a challenge to print.
“When we were first starting to build the new iteration, we found we couldn’t use the same build-space parameters that our old guides are able to use,” Holland said. “We had to bring the guide in much closer to the center of the printer’s build space.” For certain tibial guides, the features built near the edge of the printer’s build space ended up being “almost brittle” and prone to breaking—an issue not encountered with those built closer to the center of the build space.
She credits EOS with helping the facility adjust some parameters to improve print quality, because, of course, there can be no compromise on the quality of the finished guides.
Smith+Nephew’s surgical guides and KLS Martin’s IPS devices are individually customized for each user, a feature enabled by additive manufacturing. Other medical devices use additive in other ways. For example, Stryker Corp., Kalamazoo, Mich., uses a powder bed laser system to serially build orthopedic, spinal and other components.
According to Naomi Murray, senior manager, additive technologies at Stryker, the company had desired to use additive for full serial production of metal parts—not only for prototyping or patient-specific devices—since it began researching 3D printing in 2001.
“From the get-go, our thought process around this technology was for it to be a manufacturing technology—for making serial components, time and time again,” she said.
Also from early on, Stryker recognized that what was seen as a weakness in metal additive had the potential to be a strength for the company’s products.
“When we first started looking at the technology, we saw that people were trying to make all these fully dense components,” she said. “And we went to them and said, ‘Actually, could you just leave pores in there? We actually want it to be porous.’”
Porous, irregular surfaces on inserts promote osteoconductivity—successful bone growth around and into the insert. Back in the 1980s they’d begun coating their machined inserts with a beadlike surface to promote bone adhesion, a process that worked, she said, but had limits. The coating application usually requires high temperatures, which can compromise the mechanical properties of the substrate. “Which means that you have to limit where you put that porous material” she noted. “And these are also long processes, with lots of manufacturing steps.”
The better solution was to use metal additive to create porous titanium-alloy structures with complete control over the material’s strength and porosity. They call the material “Tritanium.”
Using additive enables a lot more flexibility in product designs, Murray said. “We can tailor the pore size and the porosity of our Tritanium to meet our product needs. We can interdigitate that with solid material or dense material and so not have everything be porous. We can put it in places that we could not have thought about before.”
Todd Andreoni, director of advanced operations at Stryker, noted that new additive materials, such as those used for surgical instrumentation, are now being validated for use, “giving both design and process engineers more options.”
Stryker has also made advancements in inspection, coatings and machining speed, he said. “And we are using automation and the data that comes along with it to help us enhance the repeatability of our products, reduce costs, and improve lead time.”
Additive technology developers would do well to keep in mind that medical device makers such as Stryker require quality not only to be high but also transparent and easy to document, according to Andreoni.
“Robust quality systems at the original equipment manufacturer can make a big difference,” he said. “At Stryker, we want to distribute a product that has been fabricated and documented using a process similar to our own standards.
“In some instances, the OEM’s quality management system may comply with one medical device company’s manufacturing processes, but not another’s, even though both processes may meet or exceed the ISO standards,” he noted. So, when medical manufacturers meet with an additive equipment vendor, “it’s important to discuss expectations up-front.”
One of the company’s most recent additive-built products is Trident II Tritanium, a new acetabular shell. The shell is a component in hip replacement operations: it goes inside the hip socket and holds the femur. It features not only the porous Tritanium surface structure but also additive-enabled features such as newly designed screw holes that allow the screws to go further into the implant—and which, in turn, allows the shell itself to be thinner.
“A thinner shell means we can maximize the ball joint head size and also maximize the polyethylene thickness,” Murray said. Polyethylene is the liner that goes into the shell. Inside that lined shell goes the ball head at the end of the femur.
This matters for the patient, Murray explained: The larger the head can be, the wider range of leg motion the patient can have. A thinner shell results in a range of motion that is closer to what the patient had before needing hip replacement surgery to begin with.
Medtronic Corp., Dublin, Ireland, is another company that uses metal additive for serial production. Keith Miller, a senior product development engineer at the company’s Memphis, Tenn., facility, said that: “We’ve learned that with additive manufacturing, in order to get the cost per product down to a reasonable level, you have to print a lot of product.” So, for the company’s metal implants, “it’s more cost-effective to print multiple sizes and let the surgeon pick the one that best fits a given patient.”
Medtronic’s proprietary titanium 3D printing platform—called TiONIC Technology—enables more complex designs and textured surface technologies for the company’s spine implants. The TiONIC system creates enhanced surface textures for the same reason Stryker does: To promote successful bone growth around and into the implant.
The company’s first product to be made with the TiONIC platform is the ARTiC-L spinal implant. It’s designed for surgeons to use in transforaminal lumbar interbody fusion (TLIF) spine surgery. The implant’s 3D printed honeycomb design acts as an osteoconductive scaffold for bony growth into the implant and provides improved mechanical load distribution across the implant. “It’s basically designed to give you more friction on the bone but also to promote bone growth onto the implant,” Miller said.
The product is made on slightly modified EOS M 290 3D printing systems, Miller said. “I’m not going to tell you the ‘secret recipe,’ but we actually did have to modify the laser parameters in order to create the rough surface.” EOS was an important contributor to the surface-build technology, he acknowledged.
Keith Miller is a 24-year veteran of manufacturing at Medtronic; as such, he is not the kind of person easily taken in by the hype about what additive may portend in the future. Nonetheless, when pressed, he can imagine some future applications for the technology that could be beneficial to the medical field.
For example, he is interested in the possibilities of lightweighting the instruments used in implant surgery.
“When a surgeon is doing some kinds of spinal implant surgery—as for scoliosis, for example, he may have to put in 20 screws, and tighten them to a pretty high torque,” he said. “I’ve had surgeons tell me that they’ve had a hard time driving home at the end of a long day because their hands are just so tired.”
On top of that, Medtronic ships the necessary surgical instruments free of charge along with the implants themselves—so lighter instruments would have the added benefit of lowering the company’s shipping costs. If Miller could find a cost-effective way—maybe by using latticed structures—to print lighter instruments, he would like to take a crack at it.Smith+Nephew’s Cyndi Holland is another realist regarding what additive is able to offer in the near future, but she can imagine a time coming when some hospitals will have production-ready 3D printers available on site, enabling on-the-fly building of some case-specific device. “There would be serious quality-control issues that would have to be addressed,” she acknowledged. But, she said, it can happen.
KLS Martin’s Travis Simpson is most excited about a process that he notes is well under way: The development of printable materials that mimic particular anatomic structures and their mechanical properties. “These enable not just virtual but physical simulation of patient-specific anatomy,” he said, “in a way previously not available without cadavers.”
Stryker’s Naomi Murray was less specific, though upbeat: “I think the industry has just scratched the surface,” she told her keynote audience at RAPID + TCT 2019 last May: “I love conferences like this, to see where we will be able to go next with additive technology.”
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