Printing People Parts

Replacement knees, hips, and other joints are just the beginning for 3D printing

It's a sad fact of life that the older we get, the more our bodies begin to break down. In days past, this might have meant a one-way trip to sea on the nearest ice floe. But, thanks to modern medical technology, humans can look forward to longer, more ache-free lives.

One of the coolest, most advanced enablers of these modern medical technologies? Additive manufacturing (AM), of course.

With AM, physicians can design patient-specific replacement parts for aging hips and knees. They can develop custom orthoses, repair various physical injuries, print 3D-realistic models for training and surgical planning, and produce medical devices that were previously impractical or downright impossible to manufacture. While this results in lower costs and improved patient outcomes, in many cases, 3D printing can also be a life or death differentiator.

Diana Hall doesn't claim to print any life-saving devices, but she’ll tell you that wearing one of her company's products improves the healing process and is more comfortable, convenient, and less smelly than a traditional plaster cast.

Hall is the founder and CEO of ActivArmor Inc., a startup changing the way physicians treat broken bones. Rather than encase the affected area in a fiberglass or plaster shell—which blocks skin visibility and treatment, and has to be sawed off for routine examinations—medical personnel can simply scan the patient's arm, wrist, leg, or ankle with a free smartphone app and send the resulting data to practically any 3D printer.

Depending on where the 3D printer is located—in the practitioner's office, at a regional fabrication site, or among dozens of similar machines at ActivArmor's facility in Pueblo, Colo.—the custom-fitted, reusable cast is available for use within a few hours or a few days. If the latter, ActivArmor also provides 3D-printed splints that can be worn while waiting.

"There's a high rate of noncompliance with plaster casts," said Hall. "They get soggy and dirty. The wrapping comes loose. Stuff gets trapped inside so the patient takes it off because it's bugging them and they can't shower. Oftentimes, patients are cut or burned during removal.

"With our solution, patient compliance improves greatly," Hall continued. "It locks into place using zip ties and does not need to be removed for showering or swimming, and because it's made of sanitizable plastic, is easy to keep clean. It's also much more breathable, and there's no need for multiple casts as there is with plaster—in most situations, a single 3D-printed device carries the patient completely through the healing process, as it converts from a long-arm to a short-arm cast, and from a locked-on cast to a removable splint, so the costs are much lower."

EastPoint Prosthetics and Orthotics Inc. doesn't make any life-saving medical products either, although its work can certainly be life changing. Like many medical practitioners, the Kinston, N.C., clinic has taken manufacturing matters into its own hands by investing in several Multi Jet Fusion (MJF) printers from HP Inc. The company also is learning how to design and build a wide range of custom devices.

EastPoint began working with 3D-printing service bureaus in 2018, but within a year, decided to get a machine of its own. The main reason: quality.

"Contract manufacturers are generally quite good, but they also try to maximize profit, so they might build something in a suboptimal orientation or use a super dense nesting strategy that could introduce defects," explained Brent Wright, a certified prosthetist and orthotist for EastPoint. "But the orthotics and prosthetics we produce go on people. It's not like a consumer good, where if something goes wrong, you just print a new one. Bottom line, we can't have any failures."

The stakes are admittedly high, but there was much more to EastPoint's endeavor than learning to build knee braces and shoe inlays. Many of the 3D-printed devices it makes are load bearing—such as a socket used to join an amputee to a prosthetic limb, or a post-operative fitting.

Wright and the team had to learn how to physically test the mechanical properties and structural integrity of the plastic parts they produce. The process might begin with what ActivArmor is trying to eliminate: a plaster cast.

However, Wright is quick to point out that EastPoint works with whatever it receives from clinicians, be it a series of 3D scans, a fiberglass mold, or a digital model of the patient's body part.

Depending on the device and the necessary design modifications, the file might then move to one of several software packages for tasks such as mesh cleanup, finite element analysis, and pre-build processing. Nylon12 and thermoplastic urethane (TPU ) are the most commonly used polymers for load-bearing parts, but Wright noted that new applications and materials are emerging, some of which receive additional processing in the clinic's vapor polishing machine (for smoothness).

When asked why 3D printing is needed for devices that specialists have been producing by hand for centuries, Wright's answer was unsurprising. "We have an aging population of super-experienced, highly skilled orthotic and prosthetic technicians, and we’re unable to replace them," he noted. "Additive manufacturing allows us to utilize their talent in more effective ways and fill a critical gap in our industry."

Turning to metal 3D printing, there's Marle Tangible Solutions Inc. of Fairborn, Ohio, where executives Adam Clark and Chris Collins spend their days printing and post processing a wide range of orthopedic implants. "Spinal components have long been our bread and butter, but we’ve expanded into new markets recently," Collins said. "We now manufacture a host of foot and ankle parts as well as screws, anchors, and other Class One, Two, and Three devices, all of which are made of Ti-6Al4V Grade 23 titanium alloy."

Tangible has grown rapidly since it was launched in 2013. The company added 10 pieces of capital equipment over the past year and is currently producing nearly 200,000 implants annually, according to Collins. The success gained the attention of France's Marle Group, a medical device contract manufacturer, that purchased a majority stake in Tangible last year.

None of the parts that Tangible prints are novel, and anyone who has spent time in a medical machine shop will recognize the different spinal cages, tibial trays, and acetabular cups, all of which have been around for decades. Given that AM is admittedly much slower than legacy processes, the question then becomes: why print?

"We’re pretty cost competitive, but the reasons for 3D printing's success in this area go far beyond cost," Clark said. "For example, a traditionally made shoulder stem has plasma spray added to provide roughness for improved bone adhesion. But we’re able to design and build that roughness in ways that other processes can't. We can shape it into cones or triangles, or make it smoother in certain areas for a less aggressive bite. And there's no need for masking or a costly secondary operation.

"There's also huge potential to tune the mechanical properties of the components—you might want different stiffness levels based on the weight of the patient, for example, as well as the possibility to make implants or corrective devices based on CT scans of the affected area," Clark continued. "In fact, we helped one of our customers clear the first custom cage to go through the 510(k) approval process."

Dan Crawford knows all about turning the DICOM data obtained through CT, MRI, and PET scans into patient-specific medical devices. The founder of Axial Medical Printing Ltd.—trademarked as Axial3D and a partner company to 3D-printing giant Stratasys Ltd.—he manages day-to-day operations at the company's headquarters in Ireland.

DICOM is short for digital imaging and communications in medicine. Crawford has built a business on making it as easy as possible for surgeons, hospitals, and medical device companies to segment or convert DICOM data into patient-specific models that can be 3D printed or used with other solutions, such as augmented and virtual reality (AV/VR) technologies.

"The vast majority of our company is made up of software engineers, biomedical engineers, and machine learning engineers, whose job it is to support and further develop what is essentially ‘segmentation-as-a-service,’" Crawford explained. "This eliminates the need for medical providers to invest in expensive software and then learn how to use it. Instead, we have created a series of machine learning algorithms that automate much of the process that normally requires a highly trained technician—the surgeon simply uploads the two-dimensional image files to our cloud platform and receives a print-ready CAD model back within a day or less. It's also pay-as-you-go, so there are no upfront costs."

For hospitals and clinics that don't have access to a 3D printer, Axial3D's partnership with Stratasys has led to the creation of a service bureau that will be more than happy to print whatever DICOM images are sent its way. These might be similar to the custom-fitted orthoses that EastPoint Prosthetics makes each day, or they could be replicas of a patient's spine, heart, or other body parts a surgeon uses to practice and plan an upcoming medical procedure.

That's music to the ears of physicians and patients alike, because affordable, easily procured and customized medical devices will surely lead to better results for all involved. But what about Crawford's earlier comment about AR/VR? Will these newer technologies soon make the 3D printing of surgical planning tools obsolete?

Not at all, according to Crawford. "The two are entirely complementary. An orthopedic surgeon wants to practice on an object that feels like bone and muscle, and 3D printing gets better at replicating the texture and color of human tissues all the time," he explained. "AR/VR can't replicate that touch and feel—not yet anyway—but what it can do is let a cardiovascular surgeon zoom into blood vessels and see tiny details that a 3D-printed model can't provide. .... Both are necessary, and both will continue to provide benefits only dreamed of even a decade ago."

Speaking of continually evolving technologies, meet Mattia Brodar, head of sales at Zurich-based Spectroplast AG, a company that has developed a productive, repeatable way to 3D print an important medical and industrial material—silicone—and built a service bureau around it. That's welcome news for anyone who wishes to produce parts from liquid silicone rubber (LSR) without the tooling expense and lead times that come with injection molding or casting, but it could soon lead to even better news for those who would rather take AM matters into their own hands.

"Our business model is based on producing parts for our customers," Brodar noted. "To explore opportunities for commercializing our AM technology, we did manufacture a dozen or so desktop printers as a turnkey solution called the SAM, which stands for Silicone Additive Manufacturing. So while we are still evaluating that product's future, we’ve also developed a new printing solution for our on-demand service that is much larger—offering a build platform of one meter by 30 cm—and has applications well beyond the medical industry."

What's the big deal about 3D printing silicone? And given the hundreds, perhaps thousands of polymers available, why bother inventing a silicone-specific machine in the first place? For starters, LSR has the consistency of peanut butter, and until now, processing it for AM has proven nearly impossible while offering diminished characteristics.

Spectroplast claims to have built a proprietary, light-based system that doesn't have any significant changes from the known processes. More importantly, the machine cracks the nut in terms of part quality and accuracy, according to Brodar.

As for the material, Brodar insists that it uses the same silicone rubbers as those known in the industry for more than a century. He will not discuss how the company managed to make the silicone light curable, nor will he go into great detail on mitigation of the peeling forces that plague all printers of high-viscosity materials. What he will tell you is that there's no risk of layer delamination and that Spectroplast's printed parts exhibit near-uniform strength in all axes.

This opens the door to all manner of biocompatible parts, including the surgical models described previously as well as hearing aids, physical therapy tools, wrist bands, tubing connectors, and the gaskets and seals found in medical machinery. Until recently, the build platform was limited to about the size of a smartphone, but this looks to change with the imminent release of Spectroplast's large-scale, industrial SAM.

What about the elephant in the operating room: FDA certification? "The problem here is that the whole process has to be certified to, in turn, certify a specific product," Broadar said. "As a service provider, we manufacture a wide variety of parts so we cannot yet achieve this, but we do work closely with our partners to ensure that they can. That said, response from the medical OEMs and other silicone product developers has been very positive."

Whether medically oriented or not, implementing any 3D printing technology can be a difficult road, one filled with costly potholes and prohibitively long learning curves. Shannon VanDeren, owner and president of Layered Manufacturing and Consulting Inc., Cornelius, N.C., suggested that the best way to navigate these challenges is to find a knowledgeable partner for guidance.

"I’ve watched over the years as a number of large providers—some of whom I’ve worked for—offer solutions to potential customers before they even understand the problem," VanDeren said. "If they only sell a printer that's great for titanium, then that's the answer, even if the customer might also need to print aluminum or ABS (acrylonitrile butadiene styrene). That approach always felt backward to me."

Fortunately, VanDeren made a lot of connections along the way, thus was well prepared when she struck out on her own. That was in 2015, and she continues to see sales processes that don't include touring the production floor or gaining a full understanding of the client's needs and future goals. In one notable non-medical instance, she received a call from a company that had recently purchased a 3D printer that couldn't produce its core oil-tight parts. "Thanks to an uninformed salesman, they now have a very expensive coat rack."

Her advice? Educate yourself the best you can, expand your network to include those with 3D-printing experience, and consider enlisting the counsel of someone like herself. She’ll also tell you not to despair: While AM may seem daunting to an early adopter, it's growing more streamlined and cost effective all the time.

"I think the industry's competence level is going up, for several reasons," VanDeren added. "One is that, post COVID, people are changing jobs again and they’re taking their 3D-printing knowledge with them. That's not so great for their former employers, but it will definitely help those who’ve hired them get up to speed more quickly. And trade shows are back in full swing. People can come and learn and see what's been churning over the last three years while we were all in seclusion.

"Lastly, I think people and companies are warming a little bit to sharing how they’re using additive," VanDeren continued. "Of course, no one's giving away any secret sauces, but any level of information sharing is positive. It's that old saying about how a rising tide lifts all boats."

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