Does 3D Printing Add Value in Orthopedics?

At the beginning of the spring 2019 semester, we asked our students where they believe 3D printing was being used most effectively. The top answers were prototyping and hobby activities. These answers illustrated a common misconception about 3D printing—that it only has limited appeal in manufacturing. The term “rapid prototyping” is an outdated expression that doesn’t fully capture the value unlocked by 3D printing. Today, additive manufacturing is a rapidly evolving field that utilizes 3D printing to shape the entire fabrication process from an initial concept to production to a product’s end-of-life.

Technology Options
3D printing is considered an additive process, as a part is built one layer at a time and material is added to each layer. This is in contrast to conventional “subtractive” manufacturing methods such as machining, which removes material to create a part. This process of layer-by-layer addition can be achieved in numerous ways. Extrusion of a thermoplastic polymer filament (i.e., ABS, PEKK, or PEEK) through a nozzle is common and the most affordable way to enter the 3D printing market. Quality extrusion printers can be purchased for less than $5,000 (for options, review the companies MakerBot, Lulzbot, or Prusa).

Photopolymerization curing of acrylics can be achieved by exposing a resin bath to light and can produce parts with intricate details and smooth finish. Invisalign is a well-known manufacturer that uses this technique to produce orthodontic aligners. Entry-level photopolymerization systems can be purchased for approximately $5,000 (one company offering this type of technology is FormLabs).

Other methods can involve deposition of a curable ink or binding agent, as well as the use of lasers to sinter together a polymer or metal powder. It is exciting to note that common biomedical materials such as titanium, stainless steel, cobalt, PEEK, PLA, acrylics, and more can now be 3D printed.

The Value for Orthopedic Manufacturing
There are two features of additive manufacturing that are attractive to medical device manufacturers in order to unlock value from the process. First, the cost-per-part curve as a function of the number of parts manufactured is relatively flat (Figure 1). This enables companies only selling several thousand devices per year to keep their manufacturing costs down without the expense of machining or molding. While injection molding is currently the most cost-effective way to mass produce a large number of polymer components, the cost curve for additive manufacturing is steadily decreasing. It is expected in the next decade that additive manufacturing will rival conventional manufacturing costs at large volumes.

The second feature to unlock value is that complexity comes for free (or close to free). Traditional design for manufacturing must take into account how tooling is made (i.e., molds), the steps needed for machining, or how an assembly may fit together from individual components. These rules mostly do not apply in design for additive manufacturing (DfAM). From a part perspective, the layer-by-layer building process can easily produce complex features, such as representative trabecular networks or surface patterning. Depending upon the design, these features may improve the performance of the device and save money compared to machining (Figure 2).


One of the best examples of a success story attributed to this technology is from the fabrication of acetabular cups (the socket side of the ball-and-socket structure of the human hip). This component is printed from titanium with a trabecular-patterned surface for bone ingrowth, which has now been used for approximately 10 years. From a tooling perspective, stereolithography techniques can produce highly accurate and complex investment casting molds, while entire assemblies can often be consolidated into a single printed part. Another area where this “free complexity” adds value is for making patient-specific devices. Current imaging techniques allow for quick development of 3D medical models that can be manipulated and used to produce patient-specific implants and surgical guides.

The value created by additive manufacturing is allowing new companies to develop innovative business models that challenge traditional concepts of running an orthopedic device company. There are two small companies (<50 employees) using 3D printing at the heart of their businesses that serve as excellent examples of the opportunity created through the involvement of the fabrication process.

restor3D
restor3D Inc., headquartered in Durham, N.C., was founded in the summer of 2017 based on the Ph.D. work of founder and CEO Andy Miller. While the company’s first product was focused around developing patient-specific airway stents using 3D-printed soft polymers, it has used 3D printing as a platform to rapidly develop new products using a wide range of printed materials—including PEEK, titanium, and cobalt chromium alloys—for patient-specific cases and FDA 510(k)-cleared products. This rapid R&D process allowed restor3D to start manufacturing devices such as midfoot wedges and distal tibia replacements from 3D-printed titanium (Figure 3). Most impressive, restor3D is able to design, manufacture, and deliver a patient-specific device in an average of two weeks.


Nathan Evans, Ph.D., the company’s vice president of technology and strategy, believes the company’s extremely fast turnaround time in the creation of a patient-specific and surgeon-specified device is its most significant value proposition. Further, they “never want to compromise on turnaround time.” When asked about how this has shaped the company’s business, Dr. Evans said, “Our product is low volume; however, design complexity is enabled by 3D printing, which helps command a higher price point. This makes more financial sense for small companies, which aren’t competing in commoditized markets.”

Another area that he believes is advantageous for the firm’s business is its lack of inventory cost. As a medical device manufacturer, devices are only made on demand, and traditional “static” inventory is not needed. Rather, the employees of restor3D refer to the products as “dynamic” inventory that can be rapidly manufactured to fit the requirements of the surgeon and patient.

Mighty Oak Medical
Mighty Oak Medical Inc., based in Englewood, Colo., is a company that utilizes 3D printing to aid in presurgical planning and accurate guidance of instrumentation for spine surgery. The firm’s signature product, FIREFLY, was invented by George Frey, M.D., husband of the company’s CEO, Heidi Frey. The technology is a pedicle screw guidance system aimed at eliminating surgical complexity associated with image guidance systems or robotics (Figure 4). While 3D printing is often cited as a technique for producing the actual implantable devices in orthopedics, the FIREFLY system is an excellent example of the process being used to instead improve a surgical procedure.


Heidi Frey described the FIREFLY product as an “open-platform system that works with virtually all pedicle screw systems.” She added, “The guides are patient-specific to each vertebral level to be instrumented, and we work with the surgeon on a surgical plan to incorporate their preferences regarding screw trajectory and size.”

Heidi Frey echoed many sentiments offered by Evans. “All of our guides are made to order; it is advantageous not to have company capital tied to inventory. 3D printing allows us to continually incorporate customer feedback into the product and be responsive to our customer’s needs,” she explained.

Learning New Skills and Techniques
Mighty Oak Medical and restor3D serve as just two examples of innovating orthopedic companies unlocking the value of additive manufacturing to create viable businesses. Without the use of 3D printing, it would be difficult to envision either firm being able to manufacture customized devices rapidly or successfully. Companies utilizing additive manufacturing may wish to design and print entirely in-house or rely on third-party service bureaus. In addition, companies in this space need to recognize that conventional inventory could become obsolete as “dynamic” or “digital” inventory will be increasingly relied upon.

Regardless of whether a business is an orthopedic device manufacturer or service provider, this rapid change in the medical device manufacturing industry will require a workforce with a new set of skills. Engineers should understand the variety, benefits, and drawbacks of the different 3D printing techniques. Furthermore, they should appreciate a new set of skills revolving around DfAM.

In addition to the skills needed for DfAM, the creation of patient-specific devices also requires the know-how for combining a digital version of a patient’s real anatomy with a computer-generated device. Medical imaging techniques like computed tomography and magnetic resonance imaging provide highly-detailed, 3D images of a patient’s internal anatomy. Starting with an image of a patient, a process called “segmentation” is used to identify specific structures (e.g., bones or internal airways) for which a device is to be custom fitted. Once these structures have been isolated, a 3D digital version of the device can be added to the model, creating a 3D representation of the product as it would be connected to the patient’s body. The device can then be modified to produce a seamless, custom fit to the patient.

Recent advances in material jetting technology allow for multi-material printing using “digital materials.” These materials are defined digitally for color and stiffness and are applied to the final part. While it is not currently available, the technology is being developed to produce visually and physically accurate anatomical models for surgical planning and education.

Using additional digital techniques like finite element analysis (FEA; an engineering tool for analyzing the mechanics of complex structures), the patient-specific device can even be “virtually tested” before it is printed to ensure it will work as intended. The Department of Mechanical Engineering at The University of Colorado Denver has specialized in patient-specific FEA to analyze the stress distribution in existing and proposed medical devices for the ankle and spine (Figure 5). These joints have complex structures and movement, which would be hard to analyze in a cadaver study.


So where can employees go to learn these skills? Universities are increasingly offering more curriculum focused on additive manufacturing. Penn State has a variety of online offerings for graduate curriculum, while MIT Online offers an introductory additive manufacturing certificate. At CU Denver, we are planning to launch an additive manufacturing minor in our department of mechanical engineering.

Conclusion
Overall, 3D printing should no longer be viewed as a prototyping and hobbyist activity, but rather, as a valuable tool to influence manufacturing in many areas. It can create value for businesses seeking to develop highly customized orthopedic products. 3D printing unlocks the ability to quickly design and manufacture a patient- and surgeon-specific device. Furthermore, it allows companies to develop new products rapidly without the expense of housing traditional inventory. This process of digital manufacturing can be combined with other areas of digital analysis, such as patient-specific models for surgical planning or even FEA to test devices virtually. It is safe to say there is added value in additive manufacturing. 

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Dr. Chris Yakacki, associate professor of Mechanical Engineering, received his Ph.D. in Mechanical Engineering from the University of Colorado Boulder in 2007. During his graduate studies, he helped co-found MedShape Inc.—a biomedical device company focused on using novel shape-memory materials for orthopedic applications. Dr. Yakacki served as the principal scientist for MedShape from 2007 to 2011, supporting the development of suture anchors, interference fixation devices, and intramedullary nails for ankle fusion. In 2012, he joined the Department of Mechanical Engineering at the University of Colorado Denver and has continued his pursuit of novel materials to improve human health. His research on  biomimicking, energy absorbing liquid-crystal elastomers has been funded by the National Science Foundation, Army Research Office, National Football League, and the PAC-12 Conference. Dr. Yakacki is the founder and CEO of Impressio Inc.—another university-based startup aimed at commercializing liquid-crystal materials to improve human health. He has received over $2 million in federal funding, including small business innovation grants as well as the National Science Foundation’s CAREER award. He has published over 50 peer-reviewed research articles ranging from smart materials to biomedical device performance.

Samuel T. Mills received his BS in mechanical engineering from the University of Kansas in 2014, and his MS in mechanical engineering from University of Colorado Denver in 2017. His research is focused on image-based modeling, biomechanics, and finite element analysis. Mills began working as an instructor at CU Denver in 2017, teaching CAD, and helped develop new courses using additive manufacturing. His master’s research into the strength of bone daggers was picked up by multiple news organizations, including CNN. He is currently the assistant director of Additive Manufacturing for the Department of Mechanical Engineering at CU Denver.

Dr. Dana Carpenter, associate professor of mechanical engineering, received his Ph.D. in mechanical engineering from Stanford University in 2006. He then worked as a research engineer in the Department of Radiology and Biomedical Imaging at the University of California, San Francisco, before joining the Department of Mechanical Engineering at the University of Colorado Denver in 2011. Dr. Carpenter’s research focuses on understanding the mechanical implications of aging, disease, exercise, and implanted devices on the human skeleton. This work combines medical imaging and finite element modeling to uncover interactions between biology and mechanics. His work has been funded by organizations including the National Institutes of Health, the U.S. Department of Veterans Affairs, and the PAC-12 Conference.