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3-D Printing

The 3-D printing industry tries to make body parts

Polymer and device makers brave obstacles to establish themselves in the medical market

by Alexander H. Tullo
November 24, 2019 | APPEARED IN VOLUME 97, ISSUE 46

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Credit: Carbon
Carbon is developing a bioresorbable elastomer that may be used in surgical and other applications.

One in every 2,000 children is born with tracheobronchomalacia, a life-threatening weakness of the walls of the trachea that can collapse the airway, making it difficult or impossible to breathe.

In 2012, Glenn Green, a pediatric otolaryngologist at C.S. Mott Children’s Hospital in Ann Arbor, Michigan, was treating five people—four babies and one adolescent—with the condition. He teamed up with Scott Hollister, a professor of biomedical engineering at the University of Michigan, to create splints that would support the trachea.

Guided by computed tomography scans of the patients, the pair 3-D printed splints out of the ductile and bioresorbable polymer polycaprolactone for the babies and out of high-performance polyether ketone ketone (PEKK) for the teenager.

The splints allowed the children to breathe normally until their own tissues grew strong enough for them to do so unassisted. To date, some 60 splints have been placed in 30 people.

Green, who sees the most severe tracheobronchomalacia cases, says 3-D printing is a lifesaver where none existed before. “There was no treatment,” he says. “The patients died.”

While 3-D printing is fast becoming a technology of choice for making industrial tools, prototypes, and finished goods, medicine may turn out to be the application with the most impact on the lives of everyday people.

I can count on one hand the number of 3-D printing companies focused on medical that have received or are pursuing FDA approval.
Dayton Horvath, 3-D printing consultant

With 3-D printers, medical device makers or hospitals can churn out parts as diverse as their patients themselves, mimicking even their most complex anatomy. To date, 3-D printers have fashioned artificial bones, prosthetic limbs, customized medical equipment, surgical tools, orthopedic devices, dentures, and models for surgeons to plan and perform operations.

Medicine is only beginning to exploit 3-D printing. Polymer and printing equipment companies are eagerly introducing materials and devices that could bring further big changes to how people are treated.

But exploiting this technology will take a lot more than just drawing a picture on a screen and hitting the Print button. In the US, new medical devices created with 3-D printing, even if they are made with materials familiar to medicine, have to be approved, one at a time, by the Food and Drug Administration. Regulations, experts say, pose the biggest hurdle to widespread adoption of the technology.

Medicine and 3-D printing are a natural fit. Personalization is chief among the advantages of the fabrication process. Using a scan of a person as a template for a printed implant is a big improvement over machining injection-molded or extruded parts down to size. And 3-D printed parts can be made with surface textures that promote tissue growth or with functional interior channels and cavities that molding and extrusion just cannot duplicate.

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Credit: EOS
EOS's 3-D printing machines have been used widely in medicine, including to make this hand brace.

The medical benefits of 3-D printing go beyond implants like the tracheal splint. Patient-specific cutting guides for knee replacement are a favorite example of Laura Gilmour, global medical business development manager at EOS, a German company whose 3-D printing systems are widely used in medicine, including for Green’s tracheal splints. The firm’s printers use laser sintering, a process in which lasers fuse fine powders of metal or polymer into shapes one layer at a time.

The cutting guides are in wide use—one EOS customer makes 650 of them per week. The precise cuts they enable help surgeons avoid breaching the intramedullary canal inside the bone, which eases a person’s recovery. And they reduce the amount of time surgeons need to prepare for and complete an operation. “The less time you have under anesthesia, the better it is for the patient,” Gilmour says.

As in other fields, the advantages of 3-D printing in medicine are also economic. For example, Oxford Performance Materials (OPM) makes 3-D printed spinal implants. These are standardized parts, but they come in many varieties. Old-school machine shops require a minimum number of parts before they’ll fill an order, creating expensive inventories. “In our system we can make all the different shapes in all the different sizes simultaneously,” says Scott DeFelice, OPM’s CEO.

The South Windsor, Connecticut–based PEKK specialist has been in polymer-based medical implants longer than any other company and boasts the first FDA approval for a 3-D printed plastic device—a cranial implant used to repair the skulls of people who have suffered trauma or have had tumors removed.

The company, which DeFelice founded in 2000 with PEKK technology from DuPont, started investigating 3-D printing of industrial parts around 2005 after its scientists realized that PEKK’s adhesive properties would create strong bonds between the 3-D printed layers.

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Credit: OPM
Oxford Performance Materials makes cranial implants out of polyether ketone ketone.

Separately, the company began selling PEKK for conventionally fabricated medical implants, in which the adhesive properties help promote bone growth. In 2008, after it was approached by doctors who wanted 3-D printed parts made with the material, OPM began to develop the cranial implants.

Surgeons at the time were working with titanium mesh and polyethylene shapes that they would cut and forge by hand to fit the patient’s skull, DeFelice recalls. Titanium implants were beginning to be 3-D printed, and PEKK—not as stiff as metal and more like bone—offered advantages.

Moreover, EOS’s Gilmour says, PEKK is translucent to X-rays, unlike metals. “When you do a fusion in your spine, the surgeon wants to be able to see that your bone has grown from one vertebral body to another,” she says.

OPM received FDA clearance for the cranial implants in 2013. Now, at its facility in South Windsor, it prints them using laser sintering and CT scans sent by hospitals. “We receive a file, and in 3 days it’s by the side of a hospital bed getting implanted,” DeFelice says.

The firm makes up to 50 cranial and maxillofacial implants per month. It has produced 2,000 altogether. And it continues to launch new devices. In April, for example, OPM received clearance for 3-D printed suture anchors for fixing soft tissue to bone.

The fact that PEKK was already being used to make implants helped the company win the first FDA approval to print them, DeFelice says. “If you’re coming out of the woodwork with an entirely new material that no one has ever implanted in a human, to get the clearances, you better have 10 years,” he says.

Indeed, FDA approval is a “huge barrier” for companies trying to develop 3-D printed medical devices, according to Dayton Horvath, a principal at the investment bank NewCap Partners and an independent 3-D printing consultant. “I can count on one hand the number of 3-D printing companies focused on medical that have received or are pursuing FDA approval,” he says.

The criteria, Horvath says, are stringent. “You can’t just take the same material from traditional fabrication methods and drop it into 3-D printers,” he says.

Marc Knebel, director of polyether ether ketone (PEEK) for medical markets at the chemical maker Evonik Industries, agrees. “The key will be the validation of the printing process,” he says.

Conventional fabrication processes, such as machining stock shapes, are predictable and repeatable, Knebel explains. But when parts are 3-D printed layer by layer, quality depends on factors such as the temperature and speed of the printing run and in what orientation the print is being conducted. Depending on these factors, from the same drawing, “you could get different results,” he says.

In 2017, seeking to clear up confusion for the emerging industry, the FDA put out a guidance document. In it, the agency promises to regulate 3-D printed devices like it would any other, while taking into consideration the nuances of the new technology, often called additive manufacturing, or AM. “The innovative potential of AM may introduce variability into the manufacturing process that would not be present when using other manufacturing techniques,” the FDA says in the document.

As part of the approval process, the FDA seeks information on machine parameters such as temperature. It looks at the effects that being processed through a 3-D printer might have on polymer chemistry. It evaluates how consistently photocurable materials cross-link. It considers how interlayer binding of the material influences the strength and reliability of finished parts.

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Credit: Evonik
Evonik Industries is developing 3-D printing filaments made of bioresorbable polymers that might be used in breast implants.

The guidance came at a time when multiple companies were trying to break into medical 3-D printing. Evonik is doing so with a strategy similar to OPM’s. Like OPM, it has been selling polyaryl ether ketones for implants for many years—PEEK, in its case. Evonik started a 3-D printing initiative several years ago in response to customer interest.

Although Evonik sells nylon 12 powders for laser-sintering machines, the company’s focus in the medical market is on fused deposition modeling (FDM). FDM printers melt a filament of plastic rather than a powder to create each layer of a 3-D printed object. FDM yields PEEK objects with better mechanical properties than laser sintering does, Knebel says.

The company is focusing on selling filaments for applications such as maxillofacial implants that require geometries that cannot be achieved with traditional molding. Aligning with this effort, Evonik’s venture capital arm invested in Meditool, which is developing cranial and spinal implants made of PEEK.

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Credit: Wacker Chemie
Wacker Chemie has silicone printing technology that is being used for models, such as this aortic valve, that aid surgeons.

Knebel says Evonik’s polymers have been used in a couple of special circumstances that received emergency clearances, but they are not yet in approved applications.

In addition to its efforts with PEEK, Evonik is starting a business in 3-D printed bioresorbable implants that are made to dissolve into the body over 6–36 months as tissues heal and grow around them. The company has offered bioresorbable resins such as poly(l-lactide), poly(l-lactide-co-glycoside), polycaprolactone, and polydioxanone for conventionally fabricated implants for decades. They go into applications such as orthopedic screws and cardiac stents.

Last summer, Evonik launched bioresorbable filaments for 3-D printed implants, which complement its line of PEEK filaments. Cost was a factor in its choice of FDM over laser sintering, according to Balaji Prabhu, head of Evonik’s Medical Device Competence Center in Birmingham, Alabama. FDM machines are cheaper for medical device customers to buy and operate than laser-sintering machines, sometimes going for only a few thousand dollars. “We see a greater pull in FDM, primarily because of the capital investment costs,” he says.

FDM lends an ability to tune the porosity of finished parts, Prabhu notes. “You want the cells to start growing into the pores because that is how the fixation becomes stronger,” he says.

One of the company’s early applications targets tissue growth. With the German firm BellaSeno, Evonik is working on a 3-D scaffolding for breast implants. Human trials for the 3-D printed pads—which will be used for breast reconstruction, revision, and augmentation—will begin later this year.

Carbon, a Redwood City, California–based start-up, is also taking the plunge into the medical market, starting with the dental field. Rather than use laser sintering or FDM, the company prints shapes out of liquid photocurable resins in machines with an oxygen-permeable window that allows for fast, continuous curing.

Customers already use Carbon’s machines to make dentures, replacing traditional fashioning by hand. Its technology is also being used to build forms for making orthodontic aligners. “Dental has been a great starting point for us,” says Steven Pollack, a science fellow at Carbon.

One of the company’s first medical efforts outside of dental printing is based on a polyurethane material it calls MPU 100. Carbon provides polymers and printers to firms that make medical equipment and single-use surgical tools.

For components that require many iterations of a design prototype, 3-D printing can cut development time from 18 months to about 10 weeks, says Elle Meyer, Carbon’s director of life sciences. Additionally, the same Carbon machines that made the prototypes can manufacture the final part.

The company took this approach when it worked with the medical equipment maker Becton, Dickinson, and Company to develop a single-cell genomic analysis system. Carbon is working with other firms to make parts for surgical robots.

And it’s developing a bioresorbable elastomer with Johnson & Johnson, which is an investor in Carbon. The material will be based on a polyester that Carbon made ultraviolet curable.

Meyer won’t disclose the application the partners are pursuing, but she says one area Carbon is interested in generally is spacers that would shield healthy tissue during radiation therapy.

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Additional applications can take advantage of other properties of the bioresorbable elastomer. For example, Carbon can design pores into the printed object, allowing for better blood flow to injured areas. The material can also be used to fabricate drug-delivery devices.

We receive a file, and in 3 days it’s by the side of a hospital bed getting implanted.
Scott DeFelice, CEO, Oxford Performance Materials

The German firm Wacker Chemie is cultivating a business in 3-D printing of silicone elastomers with its Aceo technology. The company’s latest machine, the Aceo Imagine Series K2 printer, can print multiple materials at a time with different colors or different physical properties, such as hardness and elasticity.

Wacker says its technology is already being used to make prototypes for aerospace and automotive markets and for small-scale machinery production runs. It also has been used to make spare parts for classic cars.

In the medical market, Wacker has its eye on surgical models that help surgeons plan and rehearse for surgery. Multimaterial printing is important for this application. “Tumors or diseased blood vessels that have been scanned using imaging methods can now be distinguished in color and copied extremely realistically in different hardnesses,” says Egbert Klaassen, Wacker’s global marketing director at Aceo.

Separately, medical device makers are using the technology to test their products on structures that mimic human tissue, Wacker says. The company has also experimented with prosthetics, such as ears, and has made grips for surgical equipment. The company has a policy against using its materials for permanent implants.

Ultimately, polymer and printer companies want no less than to revolutionize medicine with the broad adoption of 3-D printing. “The dream, at least for the 3-D printer manufacturer, would be to have 3-D printing equipment in the hospital able to help doctors in a very short amount of time print a patient-specific device,” Evonik’s Knebel says.

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