In August 2022, global medical and orthopedic device maker Stryker inaugurated a 156,000-square-foot facility in Cork, Ireland, with the aim of fortifying its leadership in additive manufacturing (AM). The facility shares grounds with the AMagine Institute, the company’s global development hub and one of the most extensive AM facilities for orthopedic implants.

“Our initial implant projects focused on designing, developing, and delivering complex shapes that were challenging to create using traditional manufacturing technology,” said Josh Johnson, VP and GM of Core Spine at Stryker. “AMagine has been game-changing for product technologies such as our Tritanium, a novel porous titanium material designed for biological fixation and bone in-growth.”¹

The company’s Triathlon Tritanium tibial baseplate and patella features a design that can only be made using AM. The design features include strategic placement of Stryker’s highly porous, biologic fixation Tritanium technology. The company’s AMagine technology is also used in other joint replacement, spine, shoulder, and ankle products.

“AMagine, our proprietary approach to implant manufacturing using additive manufacturing, enables us to continue to innovate and develop new footprints, structures, and solutions to help meet the evolving needs of surgeons,” said Josh Johnson.

A few months later in October, Stryker rolled out Monterey AL, a standalone interbody fusion device for anterior lumbar interbody fusion (ALIF). The additively manufactured interbody cage features both solid and porous structures in one implant and its Tritanium material mimics cancellous bone to promote bone regeneration and fusion. They’re all built using the AMagine manufacturing process.

“Monterey AL cages feature an anterior cam lock, which was designed to provide audible, tactile, and visual locking feedback while helping to prevent screw backout,” said Josh Johnson. “Its robust medial inserter connection is designed to allow for secure inserter-to-cage connection, and surgeon control during placement. The cage is also designed with lateral windows, allowing visualization on CT and X-ray.”²

Monterey AL is designed for indirect compression without neural foraminal impingement with a wide variety of footprints, heights, and lordotic options. Hyperlordotic implant options—from 10 degrees to 30 degrees—facilitate restoration of sagittal balance, according to Stryker.

Additive Assistance

With AM, new designs that were not previously feasible can become possible. AM technology can produce complex features like ordered or disordered lattice configurations, which can add function to joint replacement, spinal, and craniomaxillofacial (CMF) implants. It can also be used to create patient-specific instrumentation and implants.

Also known as 3D printing, AM can offer expedited development times, keeping the period between design and manufacture as low as possible.

“One of the key advantages of additive manufacturing, particularly in our context, is the opportunity to leverage topology optimization tools that allow us to simplify designs that can only be achieved through additive manufacturing,” said Juan Chafino, development manager at Intech, a France-based manufacturing partner for orthopedic devices. “Indeed, while keeping a device’s requirements in mind (such as constraints and loads), we can enhance the design by leveraging materials’ flexibility to create moving parts within a single piece. This not only streamlines the production process and reduces costs but also enhances sterilization and cleanliness due to the absence of assembly joints.”

Some of the benefits of using AM to manufacture orthopedic devices are obvious—there are device configurations being designed that simply aren’t possible using anything besides an AM process. The features possible only by using AM are creating improvements to products that revolutionize the way some surgical procedures are performed.

“Take cementless knees as an example,” said John Ruggieri, senior VP of business development at ARCH Medical Solutions, a contract manufacturer for orthopedic and dental implants and instruments, plus components and subassemblies for robotic-assisted surgical equipment and medical devices. “Lattice surface geometry manufactured into a single-piece implant component allows for improved connections to bone and eliminates the need for cementing the implant in place during the procedure.”

Another, more subtle benefit of using AM to manufacture orthopedic devices is the ability to scale volumes to be larger or smaller with more flexibility.

“When starting off with low to mid-size volumes, it is often difficult to justify the cost of setting up a conventional manufacturing process that can support rapid growth and potentially future volumes that may not have been predicted,” said Ruggieri. “When using AM as the method, we can produce the initial batches at 10 pieces and use the identical process when the demand reaches batch sizes of 1,000 pieces or more.”

Orthopedic manufacturers can leverage a number of benefits from using AM to manufacture parts and devices. They can create patient-matched designs and devices, and create complex, porous scaffolds and lattices to increase bone ingrowth. More sizes can be created with design freedom to serve a wider range of patients, with limited or no tooling costs. “Just in time” production can also occur with AM’s use to lower inventory requirements and move toward what AM expert 3D Systems calls “case in a box.”

The company has a strong reputation as an AM solutions provider for the orthopedic device and healthcare industries.

“We have manufactured over 2 million implants and instruments for 100-plus CE-marked and FDA-cleared devices from our ISO 13485-certified facilities in both North America and Europe,” said Ben Johnson, VP of portfolio and regulatory, healthcare, at 3D Systems. “We also facilitate the transfer of manufacturing technology to customers who prefer in-house device production. This adaptable approach empowers device manufacturers to choose the optimal path to market while mitigating the risks associated with investing in AM solutions.”

The company’s FDA-cleared VSP surgical planning solutions marry digital workflows with expertise in diagnostic imaging segmentation, surgical planning, device design, and 3D printing. 3D Systems revealed VSP Connect, a centralized, cloud-based surgical planning portal that integrates automated workflows and artificial intelligence, in March 2023 and showcased it at that year’s American Academy of Orthopaedic Surgeons annual meeting.

VSP Connect is powered by Enhatch, with whom 3D Systems entered a partnership in 2022 to scale personalized medical device delivery. It empowers device manufacturers and surgeons with real-time patient case visualization and improved abilities to collaborate.

“The 3D Systems VSP Connect planning portal allows clinicians and engineers to track cases, view 3D patient anatomies, and approve the surgical plan with the associated patient-matched models, instruments, and implants,” said Ben Johnson. “From there, the patient-specific case outputs are fabricated from our fleet of printing technologies that are validated to produce robust, accurate, and biocompatible medical devices, delivered directly to the clinic to translate the digital surgical plan into the operating room.”

In November 2020, orthopedic device maker Exactech earned FDA clearance for Vantage Ankle PSI, its patient-specific, total ankle surgical planning and 3D-printed instruments. The innovation was a result of collaboration between Exactech and 3D Systems.

The product includes pre-surgical planning and a patient-specific, 3D-printed instrument set that guides tibial and talar resections for total ankle replacement using Exactech’s Vantage total ankle. Based on medical imaging data from the patient, 3D Systems produces biocompatible, sterilizable, and patient-specific osteotomy guides.

“Orthopedic surgery has been exploring the benefits of patient-specific instrumentation for some time now, but solutions like the Vantage Ankle PSI are making these cases more practical and efficient,” said Ben Johnson.

In October 2023, Exactech gained an FDA nod for its new 3D-printed tibial implants, Vantage ankle 3D and 3D+, which offer additional tibial height options in total ankle replacements. They are also compatible with 3D Systems’ PSI cutting guides.

Making Moves with Metal

In AM, material properties are being established in tandem with the part’s geometry. The raw material has an impact but process parameters also affect factors like strength, ductility, porosity, and surface finish of the final part.

Polymers are still widely used 3D-printed materials. Thermoplastics like PLA and ABS are commonly used in filament-based systems, but high-performance materials like PEEK and PEKK are expanding.

Nylons and TPU have also found use in powder bed fusion processes. Composite polymers reinforced with chopped carbon and glass fibers are also being used, as well as ceramics to a lesser degree.

On the metals side, common materials include aluminum, titanium, stainless steel, and cobalt chrome. Metals for 3D printing are usually provided in wire or powder formats, but can also be mixed with other materials.

“Currently, titanium (Ti64ELI) is the material of choice for additive manufacturing. The majority—more than 95%—of the FDA-approved 3D-printed medical devices are printed using Ti64ELI,” said Gaurav Lalwani, Ph.D., who works in strategic business and applications development at Carpenter Technology Corp., a Philadelphia-headquartered developer of high-performance specialty alloy-based materials and process solutions. “Other alloys such as stainless steels, cobalt chrome molybdenum (CCM), BioDur 108, and Nitinol are still in their infancy for adoption in AM.”

In order to adopt AM beyond the use of typical titanium alloys, other alloys of AM-optimized powders must become available. One such example is CCM, which is used for conventional medical implant manufacturing. However, wrought CCM’s standard chemistry renders it brittle and causes it to crack when 3D printed.

“We have optimized the trace elemental composition that confines to the ASTM standard and developed a CCM powder optimized for 3D printing,” said Dr. Lalwani. “Another example of our materials innovation in additive manufacturing powders is Ti Grade 23+, which provides ~15%-20% improvement in mechanical properties vs. standard Ti Grade 23 material. This enables the design of ultra-fine and complex device features that typically fail with regular Ti Grade 23 powder. Additionally, availability of alloys like BioDur 108 (cobalt and nickel-free FDA-approved implantable alloy) and Nitinol in AM-optimized powders will enable new applications via 3D printing.”

Powder bed fusion (PBF) for AM includes the commonly used printing techniques direct metal laser sintering (DMLS), electron beam melting (EBM), selective heat sintering (SHS), selective laser melting (SLM), and selective laser sintering (SLS). The methods use either a laser or electron beam to melt and fuse material powder together. All PBF processes involve spreading of powder material over previous layers.

There are different mechanisms for this, including a roller or a blade. A hopper or reservoir below or beside the bed provides a fresh supply of material. The powdered material is selectively fused using thermal energy, layer by layer on a powder bed. Both metal and plastic PBF parts usually have high strength and stiffness, as well as mechanical properties that are comparable to the bulk material.

“Implantable metal components obtained through PBF-AM offer benefits for unprecedented complexity in both geometrical shape and surface topography,” said Francesco Robotti, technology and business development manager at Lincotek Medical. The company promotes the use of AM for large-scale manufacturing and further evolved by adding essential post-processing and regulatory support in a “one-stop shop” approach.

“Cavities and canals can be fabricated along with the solid portion of the piece, which does not add cost to the construct—the opposite of traditional technologies,” continued Robotti. “Complex topography can be supportive to osseointegration, avoiding post-processes like porous coatings.”

Know Your Limits

The advantages of using additive manufacturing are undeniable—speed, complex parts, patient-specific devices, flexible volumes, and the list goes on. However, as with any burgeoning technology, there are some limitations to navigate when considering AM to manufacture medical and orthopedic devices.

Although its cost has been dropping in recent years, in some cases, AM can be more expensive than traditional methods. The initial cost of creating an in-house additive manufacturing operation can be high because investments need to be made in the right equipment and materials, and staff must be trained on how to operate the machines. The cost can be a barrier for small businesses or startups and switching to AM can be costly and disruptive for companies already using a traditional manufacturing operation.

Some additively manufactured components also still require post-processing. The main reasons for the need to refine the printed parts depends on the type of AM process used—resolution limitations or tolerance accuracy issues are usually the culprits. Some AM processes aren’t yet able to meet the stringent requirements needed for critical part features.

“This results in the need for additional processing using conventional machines and machining practices to ensure that components fall well within their specified tolerance ranges and their associated assemblies function as intended,” said Cody Bonk, sales engineer at Able Medical Devices, a Gwinn, Mich.-based provider of precision-machined surgical implants and instruments. “We have seen situations where the additive manufacturing processes specified are incapable of producing certain unique geometries. This forces the need for traditional post-processing machining to ensure conformance without requiring pivoting to a more costly additive manufacturing process that would be capable of meeting said requirements.”

AM is also limited to a handful of materials, meaning there can be circumstances where it’s not an appropriate procedure. This isn’t much of a problem for rapid prototyping purposes because parts are being produced for early testing and review before final production can begin.

However, with parts that are being manufactured for use in final assembly, it’s crucial to ensure the materials selected have the right properties for their application.

“Current PBF AM tech runs with one material only; the parts are homogeneous in material composition,” said Robotti. “This can be a limitation when you need a certain portion of the device offering properties like osseointegration and another portion must offer wear resistance. In one example, a titanium-based AM part may need a further post-process like a TiN coating to improve the sliding side’s wear resistance. In another case, a CoCr-based AM part having a porous lattice may need a CaP coating to improve the lattice’s bone ingowth potential.”

A printed implant has the attractive design potential to have unique, porous structures integrated into the implant surface. This can be done through a single process and of the same continuous material, with the goal of improving osseointegration. It’s not possible to achieve this with subtractive machining of titanium implants. There are, however, risks that still exist when implants are manufactured this way.

“One such risk is the capacity of printing residue, which may be harmful to the patient to be trapped in the porous matrix and eventually escape into the patient tissue,” said Nathan Wright, MS, RAC, engineer and regulatory specialist at Empirical Technologies, a partner for mechanical testing that specializes in medical device testing services. “The FDA began requesting new cleaning validations for suspect porous patterns to mitigate concerns for this potential risk.”

Empirical has worked with many companies during their regulatory testing and regulatory submission for additively manufactured implants. The company is on the front line of learning the new risks and how the FDA is addressing them—the agency’s expectations have evolved rapidly in a short period of time. The FDA and other regulatory bodies have exacting expectations of evaluating implant materials for biocompatibility, strength, electromagnetic properties, and sterility.

“Damage of the additive implant’s porous layer during implantation or from fatigue loading has also led to the FDA’s treatment of a printed porous layer as a separate coating. The FDA has increasingly required as part of the 510(k) submission to conduct coating characterization and testing of the porous structure when that layer is a bone-contacting surface, in order to ensure integrity of the porous structure.”


References

1. Stryker data on file; PROJ 43909 Tritanium technology claim support memo, Rev-1. 
2. Stryker data on file; PROJ 71050 Tritanium AL imaging marketing memo.