Skip to content

Medical Materials: Not Your Father’s Titanium

Kip Hanson
By Kip Hanson Contributing Editor, SME Media

The past year has offered several painful illustrations of all that additive manufacturing brings to the medical community and its patients. Within weeks of the COVID-19 outbreak, 3D printing hobbyists, service bureaus, and shops both large and small began printing face shields and other critical personal protective equipment (PPE.) Additive machine builders often played a leading role in these efforts, supplying the makerspace with part designs and distribution assistance.

They also applied their considerable resources to the medical emergency. Surf over to the websites of those interviewed for this article and you’ll see countless COVID-19 success stories, everything from nasopharyngeal swabs to air-purifying respirator (PAPR) hoods to the tooling and components needed to produce ventilators. All of these companies and individuals deserve our heartfelt thanks as we navigate towards the end of this global pandemic.

A Proud 3D-Printed Legacy

And yet, 3D printing has been an active player in the health care industry for decades. It will become even more so in the years to come. “Additive manufacturing with medical grade materials provides personalization, biocompatibility, and sterilizable components,” said Tim Weber, global head of 3D metals at HP Inc. in Palo Alto, Calif. “It also enables doctors to perform their jobs more effectively with custom tools and models designed to fit the needs of each patient.”

Nashville, Tenn.-based SmileDirectClub has deployed dozens of HP Jet Fusion 3D printing systems to produce more than 50,000 unique mouth molds per day. (Provided by HP Inc.)

Additive supports a wide array of applications, he added, including prosthetics, implants, orthodontics, and many more. For example, HP worked with CGX recently to design and manufacture electroencephalogram (EEG) headsets. The company has also collaborated with other cutting-edge medical firms, such as Glaze Prosthetics, a startup that uses HP Multi Jet Fusion technology to provide bespoke custom 3D-printed prosthetic devices.

There’s also Rady Children’s Hospital, a pediatric medical and research center in San Diego that brought HP’s Multi Jet Fusion technology in-house to reduce turnaround time and enable medical innovations. (See Child Adaptable Manufacturing at Rady Children’s on page 82 of this yearbook.)

Assuring safety

Here again, most 3D printer manufacturers can cite similar examples of their work with the medical community, and all of them say that projects like these are only growing more commonplace. They’ll also suggest that the raw materials needed for these implants and prosthetics are just as important as the technology used to 3D print them. “Given that many of these components are intended for use within the human body, they must have a variety of properties, biocompatibility chief among them,” said Weber.

This heart model was created using Stratasys’ J750 Digital Anatomy 3D printer. How long will it be until medical device manufacturers are printing the real thing? (Provided by Stratasys Ltd.)

There’s that term again: biocompatibility. It’s an essential aspect of medical components, 3D-printed or otherwise. But what does biocompatibility actually mean, and how can manufacturers be sure that the resins and powders used to make 3D printed parts are safe for humans? Fortunately, any such concerns are addressed in the International Organization for Standardization’s (ISO) standard 10993-1:2018, which lists five definitions of biocompatibility and covers everything from contact lenses and dental implants to stents, joint replacements, surgical mesh, and heart valves.

Oren Zoran, the head of PJ materials business for Eden Prairie, Minn.-based Stratasys Ltd., said the company currently has seven materials that have passed one or more of these biocompatibility tests. These include evaluations for cytotoxicity, sensitization, and carcinogenicity, most of which determine how long a given polymer or metal can remain in contact with the human body, and where it can be used.

“Think about something as routine as a tooth replacement,” Zoran said. “Of course, the tooth and the metal post it is attached to must be biocompatible, since they will hopefully stay in for years. But the 3D-printed guide used to drill the hole for that post must also be biocompatible, even though it will only be in contact with the patient during the procedure. It’s also worth noting that these materials can be sterilized using steam or gamma radiation, a property that’s critical for patient safety.”

Keep It Clean

Jessica Coughlin, head of global healthcare marketing and market development at Stratasys, carried that concept one step further. She noted that the packaging materials used for medical products are often required to be biocompatible, as are the jigs and fixtures needed to machine these components. “There are situations where a shop would 3D print this tooling from a biocompatible material, just to assure that they avoid contamination during the manufacturing process,” she said.

Biocompatible materials and 3D printing provides medical health practitioners with patient-specific replicas of the human body and its various organs. (Provided by Formlabs Inc.)

Such requirements imply that CNC machinery and even the 3D printer itself must meet a certain level of cleanliness if they’re to come in contact with biocompatible materials. This helps explain Coughlin’s suggestion that medical device manufacturers follow approved operating and maintenance procedures for their equipment, especially if they’re switching between biocompatible materials and those used for non-medical purposes.

“We certify the biocompatibility of our raw materials when used per our established guidelines, just as other suppliers do for theirs,” she said. “Achieving and maintaining certification of the final product, however, is entirely the responsibility of the medical device manufacturer.”

Kyle Babbitt shares this position. A medical sales engineer for Formlabs Inc., Somerville, Mass., he said any medical material provider should be able to provide its customers with whatever US Pharmacopeia Convention (USP) and ISO standards their products have met. But before printing with these materials, Babbitt said, it’s best to understand their mechanical and chemical properties. “Make sure you look at the safety data sheets (SDS) and technical data sheets (TDS) to check on any harmful interactions that could occur. Also, be sure to verify that the material can be sterilized and, if so, which sterilization technique is most appropriate.”

Tracing One’s Roots

Traceability is another important topic for any mission-critical application, medical or otherwise. Babbitt listed a host of potential questions in this regard, ones that will gain steam as printer fleets become common for medical facilities and their suppliers. Which printer made this part? Which version of the software were we using when it was made? Which lot of material did it come from? Was additional material required during the print job? What operator was working at the time, and were there any build problems?

These questions will only multiply as the number of medical materials grows. “We’re constantly getting requests from our users for novel resins for their unique applications,” Babbitt said. “These materials must be tested for printability by the materials team while the software group hones in on the perfect settings. It’s a lengthy process involving many departments, starting with feasibility and ending with user testing.”

Existing materials receive regular updates as well, he added, via more effective print settings and slightly altered formulations that give customers exactly what they need. “These shouldn’t be concerns for the users, as the printer and materials manufacturers do whatever testing and validation is required before launching their products.”

Material Mojo

So what are these materials? The answer depends entirely on the provider and the type of 3D printing process. As already mentioned, Stratasys offers seven grades of biocompatible polymers, its MED-series Polyjet materials among them. And Babbitt said that Formlabs has more than 25 resins to choose from, all of which are suitable for its healthcare-focused printer, the Form 3B. It also offers Nylon PA-12, an SLS (selective laser sintering) compatible powder used to produce lightweight and durable medical models.

These nasopharyngeal swabs were developed with Carbon’s Digital Light Synthesis (DLS) technology, and use a soft, flexible material for patient comfort. (Provided by Carbon Inc.)

So does HP, whose High Reusability PA-12 boasts biocompatibility certifications that meet USP Class I-VI and US FDA guidance for Intact Skin Surface Devices. In addition to this and its High Reusability PA-11, the company has partnered with material suppliers BASF, Evonik, and Lubrizol to offer new materials, including a “first of its kind” PP (polypropylene), Ultrasint TPU01 (thermoplastic polyurethane), and a new grade of TPA (thermoplastic amide).

Jason Lopes, global market development engineer at Carbon Inc., Redwood City, Calif., listed several more—like most 3D printing materials, however, they are proprietary, intended for use in the equipment of whatever 3D printer manufacturer supplied them.

“We can’t divulge most of the products made with our technology,” he said. “Speaking broadly, though, we enable the manufacturing of devices where rapid production of complex geometries is critical to companies that can’t afford the time or investment needed to create injection mold tooling, at least for initial product feasibility studies. That said, I know of several devices in the regulatory review process that use our MPU 100, RPU 70, or SIL 30, all of which are medical-grade, biocompatible materials.”

Although the first two of these offer properties similar to that of ABS, and SIL 30 is advertised as a silicone urethane, additive manufacturers should be aware that there are no conventional equivalents to these and other 3D printed polymers—they can be considered analogous to their rod, sheet, plate, and pellet counterparts, but not as exact replacements.

Metal Magic

“Achieving the desired mechanical properties with an additive polymer may require that engineers design parts differently than they would with injection-molded polymers, but this is often offset by 3D printing’s greater design freedom,” said Ed Hortelano, senior vice president, materials engineering and development at 3D Systems Inc., Rock Hill, S.C. “Despite this, the types of polymeric materials available to AM users continues to grow, so the gap between conventional polymers and those used in additive processes is getting smaller.”

This spinal cage inserter was rapidly designed and 3D-printed from 17-4 stainless steel in partnership with 3D Systems. (Provided by 3D Systems Inc.)

Hortelano added that this statement is less true with metals, in that there’s not much difference between AM metals and traditional feedstock. Additive titanium, for instance, has properties comparable to those of machined titanium, a factor that helps explain why this well-known superalloy has become the most widely used material for the production of orthopedic implants.

Using additive rather than subtractive processes to make these components allows manufacturers to reduce cost while improving the device’s quality and performance, he said. Further, when you 3D print a spinal cage or similar orthopedic implant, it’s possible to design osteoconductive features into the part, greatly facilitating bone integration.

This last part is a big deal to anyone facing a knee or hip implant over the coming years. “AM is well-suited for medical uses because it allows design freedoms that traditional technologies do not,” said Hortelano. “With additive manufacturing, we like to say that complexity is free; it allows us to manufacture designs that provide enhanced product features like latticed bone ingrowth surfaces and tuned mechanical performance. Additionally, AM is a very efficient, cost-effective technology to manufacture low-volume production parts, which is ideal for patient-specific devices.”

Road to Approval

He said, however, that the qualification process for new 3D printing materials in health care presents challenges at multiple levels. The material has to be evaluated for its biocompatibility and mechanical properties, and depending on the application, some materials must also have a master file with the FDA to provide confidential detailed information about the facilities, processes, and various materials used in medical device and drug applications.

The regulatory and financial burden of this qualification and the associated time requirements can be significant, seemingly outweighing their benefits. “Although still a challenging task from a logistics and technology standpoint, it is faster, easier, and less-expensive to qualify already proven materials like 17-4 PH stainless steel and validate those for new printing applications,” Hortelano said.

And yet, none of these hurdles are stopping or even slowing down the adoption of 3D-printed materials and devices. As proof, Sandvik AB recently opened a metal atomizer plant in Sandviken, Sweden, devoted to the production of titanium powder for 3D printing, making it clear that the manufacturing industry overall is gearing up for skyrocketing demand from the medical, aerospace, and energy sectors.

Sandvik’s new $20 million factory in Sandviken promises to be a major contributor to the world’s supply of medical-grade titanium. (Provided by Sandvik AB)

Taking a Powder

“Sandvik offers a broad portfolio of metal powders such as tool steel, aluminum, stainless and duplex steels, and nickel-based superalloys,” said Keith Murray, head of global sales. “The use of Grade 5 and Grade 23 titanium aluminum alloys (Ti-6Al-4V and Ti-6Al-4V ELI) for permanent body implants represents a key target market, which is why we invested $20 million into a new factory and worked closely with regulators to certify that our materials meet the ISO 13485 standard.”

The certification process doesn’t end there for Sandvik. Medical device manufacturers are typically looking for partnerships with their material providers, as are those who build 3D printing equipment. All must work closely together to determine the correct process parameters needed to reliably and predictably fuse tiny bits of metal powder together.

“The raw material itself has to be tightly controlled during the manufacturing process, but even more so when you actually start melting it back together again,” said Mikael Schuisky, business unit manager for additive manufacturing at Sandvik. “Collaborating with our customers allows us to better understand how our materials behave during the 3D printing process, and provides opportunities for everyone involved to further optimize their products.”

They’re just getting started. Schuisky noted that Sandvik and others are researching new titanium alloys, ones designed to further promote bone growth. Some are even looking at the addition of magnesium, a highly flammable metal that presents some alarming possibilities in the context of laser-based printing technologies.

He said, “Titanium and aluminum can be quite reactive, but magnesium is even more so. We’re not directly involved in this, but it might be possible to sinter magnesium in a vacuum chamber or print it using a different, less energetic technology. Whatever the case, the industry continues to develop novel materials for 3D printing applications, most of which present some very exciting opportunities.”

Scott’s Favorite Molecule

Tony DeCarmine agreed. The chief technical officer for Oxford Performance Materials (OPM), South Windsor, Conn., he offered numerous insights from a company that pioneered the use of poly-ether-ketone-ketone (PEKK), a high-performance polymer ideally-suited for a range of 3D-printed medical components (and said to be founder Scott Defelice’s favorite molecule). “To manufacture items in highly regulated spaces like medical device production, one must have sufficient confidence in the end product,” he said. “Achieving that with 3D printing, however, requires that we take a different approach.”

For instance, it’s common knowledge that 3D printed items—even if made with the same materials as those used in CNC machining and injection molding—do not enjoy the same performance profiles as their conventional counterparts. Making matters worse, different additive technologies and even specific machines within those technologies often give different results when processing identical feedstock. “For this reason, we cannot address materials, methods, and machines as separate, like we do with traditional processes—with 3D printing, they represent a symbiotic ecosystem that must be considered as a whole.”

Because of this, DeCarmine affirmed what others here have suggested, that process management and consistency are integral to 3D-printed part quality. Vetted methods of tracking and tracing all aspects of a project—material lots, operational parameter sets, machine status, and any other details—must be implemented. The “days of cowboy operators spinning the knobs are indeed numbered,” he added. 

Despite titanium’s extensive use in medical implants, the high-performance polymer poly-ether-ketone-ketone (PEKK) often proves better-suited for a range of 3D-printed components. (Provided by Oxford Performance Materials)

The 3D-Printed Future

Complicating matters further is the fact that there are many thousands of polymer compositions that can be used on existing additive machines, be they photocuring resins, thermoplastic resins in powder (PBF) or strand (FDM), or any other macromolecular material. With 3D printers often able to only work with a narrow material set, however, one usually provided by the machine vendor, it is consequently difficult to determine which of these might be most useful for a given application.

“When end users are granted the freedom to explore the true capabilities of the machines they paid for, running resins freely chosen, we will see a rapid expansion of the field of usable materials in additive,” he said. “The untapped potential is enormous. And looking to the future, there are a cornucopia of chemico-physical processes that could be harnessed to create shapes through the addition of material. Perhaps biologically growing devices like a coral reef? Or reactive extrusion to create chemically cured systems in situ? Drexler’s molecular assembler? I only know that I cannot wait to see it.”

  • View All Articles
  • Connect With Us

Always Stay Informed

Receive the latest manufacturing news and technical information by subscribing to our monthly and quarterly magazines, weekly and monthly eNewsletters, and podcast channel.