One of the AM technologies playing a prominent role in orthopedics is direct metal printing (DMP). Through DMP, thin layers of metal powder are deposited on top of each other and melted together using a focused laser beam—also known as selective laser melting—in order to create a metal part (Figure 1). This printing technology can be used with a variety of biocompatible materials including several grades of titanium and cobalt-chrome.
Dental devices, patient-specific instruments (PSI), and prototyping comprise a small percentage of products produced via DMP. The vast majority of applications includes volume production of medical products. Over the past decade, 3D Systems has produced more than 600,000 medical devices using DMP technology.
While PSI accounts for a small percentage of total medical production, each printed part has a monumental impact on a person’s life. One example is the first jaw reconstruction surgery performed in the University Hospital of Leuven (UZ Leuven) in late 2016. Pre-operatively, the patient presented with a gaping hole in the lower jawbone due to osteonecrosis and a bone infection, which resulted in intense pain and immobility of the jaw and lip. As the patient’s body could not repair the bone, production of a patient-specific reconstruction plate was required. The plate was designed by engineers at UZ Leuven in close collaboration with surgeons and 3D Systems’ Precision Healthcare team. The final plate was printed in titanium (Figure 2).
There’s a great synergy created within 3D Systems. The company’s large R&D team focuses on the development and improvement of the DMP technology, its post processes, and the research of new materials; while the Precision Healthcare Team offers parts services to different fields within the medical industry.
As an end user of its own technology, a short feedback loop is created within the firm. Requests from the medical industry are shared with and reviewed by R&D immediately, while the application of new R&D improvements can be vetted and prioritized quickly by the healthcare business unit in close contact with the industry.
This synergy is undeniably a catalyst for continuous progression in the company’s machine portfolio and part services business. Long-term improvements focus on increasing productivity of the DMP printers, expanding the material portfolio by adding new options, and offering mass customization to healthcare customers. It also determines the focus areas for the short term, of which some are absolutely pioneering for the industry, such as in-process monitoring of the printing process, which offers the opportunity to check the quality of printed parts before they are in a customer’s hands. While DMP Vision detects macro phenomena during printing, a novel monitoring tool was developed that generates data about the presence of defects on a micro level. This means that internal porosity (like the typical lack-of-fusion porosity) can be detected and observed without needing to perform an extra imaging step after printing.
Meanwhile, a second patient has already been treated; this patient lost an eye during the terrorist attack at Brussels Airport in March 2016. The orbital floor was broken, causing an asymmetrical lower position of the artificial eye. The operation was successfully completed at UZ Leuven by a different surgical team using additive manufactured patient-specific implants.
Porous Metal Structures
As the number of orthopedic surgeries is increasing, so is the need for implants that can fully replace or help in reconstructing a mechanically stable joint. Implants also serve as bone replacement material since the availability of transplant bone is rather limited. Porous metal implants are a solution to address this need as they exhibit mechanical properties close to human bone with sufficient implant strength and stability.1 Additionally, bone can grow inside the pores, ensuring the implant will remain in place.
With the introduction of additive manufacturing techniques like direct metal printing, it is possible to fabricate porous metallic structures in large quantities in a consistent, repeatable manner. As such, an alternative method is offered to implant manufacturers for producing solid implants with porous coatings applied to the surface of them. The traditional processing techniques such as plasma spraying or foaming result in irregular structures that lack controlled geometries and mechanical properties.1 See Figure 3.
A reliable 3D printing/AM supplier firm that has experience and expertise in the orthopedic space can assist medical customers choose the best porous structure for their application, as well as optimize the design and manufacturing workflow. Porous structure design, build orientation, and post-processing steps all influence implant performance.1
- The deliberate choice in porous structure architecture is defined by the relative density of the structure and the unit cell geometry.
- The overall reproducibility and the influence of the build orientation can lead to improved porous implant designs and manufacturing with uniform properties.
- A proper selection of post-processing operations based on material influences the implant performance significantly.
A company with orthopedic experience can assist its customers in these phases, which ultimately impact implant performance and aesthetic appearance of the product.
While extensive research on porous structures has occurred, further investigation is required and ongoing. In some cases, software can be leveraged to enhance the overall design of an implant. For example, 3D Systems recently began offering a trabecular porous structure via 3DXpert—an all-in-one software package for metal additive manufacturing (Figure 4). This trabecular structure is a randomized stochastic structure that mimics the natural structure of bone (Figure 5). The software is commercially available and offers an integrated solution to import part data; position the part; optimize the geometry and create porous structures; design optimal supports; simulate printing and post-processing to verify the final part will match design intent; set printing strategies; calculate the scan-path; arrange the build platform; send parts to print; and even machine the final product when necessary.
Volume Production for a Continuous Supply of Medical Implants
The most well-known example of porous metal implants are spinal interbodies for interbody fusion. In this technique, the entire intervertebral disc between vertebrae is removed and a titanium device is placed between the vertebra, with or without a bone graft, to maintain spine alignment and disc height. Porous titanium implants are of interest since they exhibit improved strength and lower stiffness compared to the solid metals, and are more aligned with human bone properties (Figure 6). Traditionally, polyetheretherketone (PEEK) interbodies were used for interbody fusion; however, their lack of porous structure presents a disadvantage. By using porous titanium implants, initial fixation of the implant is improved. Additionally, long term stability is ensured due to the ability for bone to grow into the open, interconnected porosities.1
Another orthopedic product printed in volume is the revolutionary veterinary TTA RAPID implant, designed by Rita Leibinger Medical (Figure 7). These small, precise titanium implants have been implanted successfully in over 10,000 dogs diagnosed with cruciate ligament problems, ranging from Jack Russell Terriers to Great Danes. The key to this groundbreaking implant’s success is its complex open porous structure, which can only be created with additive manufacturing. This structure promotes rapid bone ingrowth for greater stability and a much faster recovery.1-2 Additionally, dogs are under anesthetic for less time and experience fewer infections than with previous solutions.
While durability of the device and improved patient outcomes are most important, cost of production is always an underlying consideration. Significant productivity improvements have been implemented to lower the production costs of porous implants manufactured via DMP. The best example is the cost competitiveness of spinal porous cages produced with selective laser melting, when compared to PEEK volume production of spinal cages and traditional manufactured titanium cages.
FDA Guidance for AM
Today, more than 100 FDA clearances have been granted for medical devices produced via additive manufacturing. This group includes a wide range of applications such as finished devices for the areas of cranio-maxillofacial, spinal, extremities, large joints, and sports medicine.
On Dec. 5, 2017, the U.S. Food and Drug Administration (FDA) released a guidance document for additive manufacturing of medical devices. This guidance document adds credibility to the technology and offers a risk-based, process-driven approach for design, development, and manufacturing of medical devices and instruments using additive manufacturing across a wide range of AM technologies. It also creates a roadmap for healthcare companies for composing all information needed for the premarket notification submission. This roadmap should align perfectly with a 3D printing/AM supplier’s quality approach, validation strategy, and quality management system. A well-established validation strategy can greatly reduce the amount of front-end testing required for a medical device submission. This combined with a long history of experience working with the FDA and other regulatory body submissions can enable a qualified supplier to greatly assist its healthcare customers. Ensure any 3D printing/AM partner is able to satisfy all regulatory requirements and deliver all necessary documentation to the manufacturer of the device in development. As a result, companies that team with an established medical AM supplier are able to accelerate their timeline for new market introductions to as little as nine months from concept through FDA approval.
- Wauthle, R. (2014). Industrialization of Selective Laser Melting for the Production of Porous Titanium and Tantalum implants.
- Samoy, Y., Verhoeven, G., Bosmans, T., Van der Vekens, E., de Bakker, E., Verleyen, P., & Van Ryssen, B. (2015). TTA rapid: description of the technique and short term clinical trial results of the first 50 cases. Veterinary Surgery, 44(4), 474–484.
As a project engineer within the Healthcare Division of 3D Systems, Hannelore Eykens is based in Leuven, Belgium. She supports medical device companies in bringing their products to the market by developing the manufacturing process using metal additive manufacturing, and by assisting them throughout the full development lifecycle, starting from prototyping up to volume manufacturing. In 2011, Eykens received her master’s in Biomedical Engineering from the University of Leuven. She worked at Materialise as a product development engineer for four years, focusing on mass customization solutions using additive manufacturing, for patient specific guides that assist in arthroplasty. In 2016, Eykens joined the Healthcare Division of 3D Systems, continuing her focus on additive manufacturing of medical devices.
As director of business development for the Healthcare division of 3D Systems, Ruben Wauthle is based in Leuven, Belgium, and leads the business development and project engineering activities in Europe. His work is focused on utilizing 3D System’s healthcare solutions platform to help medical device companies bring products to market more efficiently and effectively within the orthopedic, spine, and cardiovascular space. Wauthle worked with 3D Systems from 2010 to 2015 after receiving his masters in Mechanical Engineering from the University of Leuven. In 2014, he completed his Ph.D. on “The Industrialization of Porous Titanium and Tantalum” using 3D System’s Direct Metal Printing technology and contributed to more than 15 scientific publications. From 2015 to 2017, Wauthle set up and managed the Additive Manufacturing division for FMI Instrumed in the Netherlands, and joined 3D Systems again in December 2017.