Additive-Manufactured Orthopedic Implants Under MDR

Regardless whether they are produced through subtractive or additive manufacturing technologies, implantable orthopedic devices generally fall under the highest risk class in Europe following the rules of the Medical Device Regulation (EU) 2017/745 (MDR) and amended by the Regulation (EU) 2020/561. They are classified as either Class IIb implantable or Class III implantable devices. In the case of implantable custom-made devices (CMD), Annex XIII of the MDR must be selected and followed by the manufacturer when conducting the conformity assessment under the MDR. For Class III implantable CMD, the involvement of a Notified Body is also mandatory. Regardless of such an involvement, medical devices must fulfill all the applicable provisions of the MDR, comprising topics like process controls.

This article aims to provide a short overview on key aspects of additive manufacturing (AM) impacting the orthopedic device industry. Additionally, process control challenges will be highlighted and discussed by showing potential solutions toward compliance with the regulatory requirements.

Background and Key Engineering Principles
For more than a decade, the number of patient-specific orthopedic implants produced by AM technology has increased significantly. What has evolved is the robustness and monitoring capabilities of the process as well as the knowledge about the applicability of this new technology for implantable orthopedic devices. Furthermore, there is a clearer understanding now of the process and the processable materials. AM is considered by some manufacturers to be suitable for orthopedic implant design and manufacturing since it allows for the building of very complex structures in a short time. Consequently, AM can lead to multiple design iterations without even delaying the overall design control process. Many of the current orthopedic implant designs also include complex anatomical structures facilitated through AM. Such design complexity cannot only be observed on the surface area but also in the inside mechanics, where subtractive technologies cannot reach.

Every manufacturing process has, besides its benefits, certain limitations and challenges. For AM, it is reported that post-processing must be considered on a high scale. Another limitation is the medical application of the orthopedic implant, where the necessary solidity cannot be achieved through AM, if the process is controlled inadequately. Whereas those aspects seem to be manageable, there are other challenges—for example, difficult or sometimes impossible cleaning or sterilization of complex structures. One of the biggest challenges currently faced is the profound knowledge on how to ensure process controls and quality assurance in AM. Combined with the requirements set in the MDR, the emphasis on process control within the manufacturing steps becomes more relevant and the challenges with AM technology for medical devices clearly emerge.

Process Control Challenges & Solutions
Under the MDR, medical device manufacturers must comply with the “General Safety and Performance Requirements” (GSPR) set out in Annex I. Chapter II of this annex comprises requirements regarding the design and manufacture of medical devices. Clause 10.1. (a) concerns the choice of materials and substances, and 10.1 (d) addresses the impact of processes on material properties. With respect to AM, these requirements point toward the understanding of what happens to the material through this manufacturing process. Basically, as the ground material is powder—if a powder-bed-fusion (PBF) technology is used—its characteristics are critical. Depending on the medical application, the material can range from metal alloys (e.g., acetabular cups, spinal cages, dental implants) to plastics (e.g., dental splints, cranial implants). For medical device manufacturers, it is of significant importance to not only utilize the appropriate powder, but also to ensure the consistency of the powder quality. To build a component with PBF technology, a laser beam or electron beam is used to melt the powder material. Possible challenges in this stage could be the vaporization of the material and its reaction with the laser. This process may result in different material properties at different layers of the manufactured device. Key questions to answer for a medical device manufacturer include how to validate and sample such devices during the manufacturing process.

To solve these challenges by solely investigating the manufacturing process of building the device layer by layer in a robust way would not be enough. It is essential to look at the entire AM workflow and address the potential risks known from similar well-established manufacturing processes. A definition for the workflow can be found in the state-of-the-art normative document DIN SPEC 17071, which is currently in the transition phase into the international ISO/ASTM 52920-2 standard. This includes the design, feedstock (e.g., powder) management, machine-specific pre- and post-processing, and the technology-specific part post-processing. Along the AM workflow, the following solution approaches attempt to shed some light on validation, risk minimization, and AM-conform quality assurance.

• Clear traceability of all relevant data and part properties. This can include the 3D CAD -file; build preparation data (e.g., positioning, support structures, slicing data); documentation of the used process parameters (e.g., laser power or build chamber temperature); process monitoring data (e.g., oxygen-content in build chamber, melt pool); or archiving and documentation of test samples, checklists, work instructions, and route cards.
• Personnel must be trained to ensure a high quality and functional production. In the field of AM, this means all roles have a concept of AM-relevant risk assessment, quality management and assurance, validation, and applicable standards. Furthermore, the AM engineer needs to have profound knowledge in the areas of materials, technology capabilities, and AM compatible design. Other necessary roles include the AM machine operator with knowledge how to set-up an AM machine to minimize the risks of contamination. Also, the AM quality manager with knowledge about the state-of-the-art standards, health and safety aspects, and quality assurance technological pitfalls in AM.
• All machines in the AM-workflow must be validated according the product and manufacturing process risks for the intended purpose. For the AM system, this IQ/OQ/PQ (installation, operational, and performance qualification) can be a challenging task when every AM machine functions differently and there is no approved quality seal. Different standards and guidelines were already published but most only scratch the surface of this topic. The next advance is the standard ISO/ASTM PWI 52930, which will be published in 2021. This standard has an integral approach on qualification and validation of PBF and defines a clear recommendation of activities and responsibilities of users and machine providers.
• The feedstock management is also a critical process for the quality of the printed device. Key factors that influence quality are the incoming feedstock batch control, the consistency of the material properties during storage, processing and handling, and the reproducible and contamination-free feedstock management.

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Dr. Max Singh is the global director of the Orthopedic Focus Team at TÜV SÜD Product Service GmbH. Prior to this role, he spent about 15 years in the medical device industry, mainly working in the orthopedic, ENT, and CMF sectors. He held several positions in R&D, where he was in charge of designing active and non-active medical devices for knee, hip, trauma, and spine surgery. He also has experience in computer-assisted surgery and surgical robotics. Besides R&D, he was also responsible for product management and marketing of large amounts of product portfolios. Through global launch activities, he was exposed to the international regulatory requirements in the medical device industry.

Simon Schlagintweit has been working in TÜV SÜD’s AM team since 2018. His functions include auditing AM companies to ensure state-of-the art quality assurance and developing AM-specific services for the medical sector. Before joining TÜV SÜD, he received his Master’s degree in materials science from RWTH Aachen University. He gained experience in AM in scientific work (Fraunhofer ILT and iwb TUM) and at the Fraunhofer IGCV (research assistant).

Gregor Reischle is the head of AM at TÜV SÜD. In addition to establishing 3D printing technologies in production, he is passionate about quality assurance in practice and lean entrepreneurship. He is leading the AM Team of 20 professionals, presently developing and establishing the services required to enable additive manufacturers to overcome their current limitations and launch series production in regulated industries.