Printing equipment is increasingly open – allowing materials from diverse suppliers to be used on more additive manufacturing machines. The FDA is working with manufacturers, service bureaus and material suppliers on best practices. With strong support from all corners of the industry, healthcare device designers are gaining new resources that can expand additive manufacturing’s horizons and maximize its value.

By Dane Waund, global marketing manager, Healthcare, Solvay Specialty Polymers, and Sophia Song, marketing & E-commerce manager, Business Incubation, Additive Manufacturing, Solvay Specialty Polymers

Additive manufacturing offers designers exceptional opportunities to accelerate prototyping, create custom devices, support just-in-time manufacturing (including producing parts on-site at hospitals), and reduce or eliminate traditional production costs such as the development of mold tools. However, additive manufacturing is a relatively new and fast-evolving technology. The industry is racing to develop new specialized materials, printers, design software, and other tools that can propel broader adoption of this process, with the goals of expanding the range of applications, boosting part volumes and streamlining production.

Production of medical devices, however, adds another layer of complexity to additive manufacturing, due to the many regulations and requirements that materials must meet to be used in these critical applications. They must be identified as safe, based on biocompatibility standards set forth in ISO 10993. Compliance with these standards is necessary to manage biological risk. Further, the U.S. Food and Drug Administration (FDA) recently issued official guidance on the use of additive manufacturing to produce medical devices. This report, “Technical Considerations for Additive Manufactured Medical Devices,” comprises two main sections: design and manufacturing considerations and device testing considerations.

In view of these healthcare requirements, combined with ongoing changes in additive manufacturing technology, engineers need important resources to optimize medical device designs:

–Innovative new materials that meet the specific performance and aesthetic requirements of the application and the chosen printing method. Different material forms, such as filaments for fused filament fabrication (FFF), powders for selective laser sintering (SLS), and pellets for pellet extrusion, are required.

–Cutting-edge technologies and tools, particularly software systems, which help expedite the design process—including testing and prototyping.

–Regulatory expertise and quality system certifications, data and documentation to support FDA clearance under a 510(K) or premarket approval (PMA) pathway in the United States, assessment by Notified Bodies in the European Union, and the needs of other regulatory authorities worldwide.

Specialized materials for additive manufacturing
Growing availability of advanced polymer materials in popular formats, including filaments and powders, gives designers the freedom to choose their preferred additive manufacturing method and ensures the end-use application delivers required properties and reliable performance.

Besides biocompatibility, material requirements for medical devices can include:
–High-temperature performance for sterilization
–Chemical resistance to withstand harsh disinfectants
–Impact strength for durable housings
–Abrasion resistance for drill and cutting guides
–Tensile strength for surgical tools
–Rigidity for precision in small-diameter, minimally invasive instruments
–Fatigue performance for repeated loading in structural implants
–Radio-opacity or translucency for surgical imaging

Colorability is also often needed for device function identification and better usability.
High-performance healthcare materials for additive manufacturing include two chemistries with a long history of use. Polyetheretherketone (PEEK) delivers long-term performance under repeat loading, can be repeatedly steam-sterilized due to its stability at temperatures up to 240°C (464°F), and offers exceptional chemical, wear and abrasion resistance. It is often reinforced with glass or carbon fiber for additional strength and stiffness. This combination of properties makes PEEK particularly suitable for metal replacement in surgical instrumentation.

Polyphenylsulfone (PPSU) offers best-in-class toughness and abuse resistance, which has led to its widespread use in surgical cases and trays. Chemical and hydrolysis resistance, and high-temperature capabilities are driving PPSU’s adoption for reusable surgical instruments that must be repeatedly steam sterilized. Early development work with fused filament technologies has shown a promisingly wide conversion processing window, which many attribute to PPSU’s amorphous chemistry. This polymer is translucent when additively manufactured.

Software systems for printing simulation
Current design processes for an additively manufactured device may require multiple physical prototypes for testing and modification, adding time and effort. Simulation software tools, on the other hand, allow engineers to test potential designs using different materials, identify issues and make changes digitally.

Further, integration with suppliers’ material data enables software systems to simulate and compare the printing process for a given design using different thermoplastics. For example, designers can predict mechanical performance and potential failures, and identify issues such as part warpage, anisotropic shrinkage, decohesion, residual stresses and process-induced microstructure. They can use this information to optimize additive manufacturing parameters such as print direction and infill.
Material suppliers are working with software companies to print and test polymer samples and demonstration parts to predict thermo-mechanical performance and compare it to actual results. Such collaboration offers important advantages to the customer.

The benefits of using simulation software populated with material performance data start with faster time to market for a novel device. Designers can avoid time-consuming trial and error by making design modifications digitally, based on results of the simulation. In addition to identifying potential problems, they can spot opportunities to reduce infill for lighter weight parts and shorten printing times for improved productivity. Modifying a design on-screen is fast, easy, less costly and potentially more accurate than creating and testing physical prototypes, and helps ensure the part is printed correctly the first time.

Regulatory and quality support for device clearance
Device designers can benefit significantly from regulatory and quality assistance from their material suppliers. Resources such as supplier support for an FDA Master Access File can help expedite the clearance process and strengthen the application. The following are key areas where suppliers can contribute to regulatory compliance and quality assurance.

–A robust quality management system (QMS) remains critical for medical raw materials converted for use in additive manufacturing. The ISO 13485 standard sets out requirements for a QMS specific to the medical device industry. Suppliers that adhere to this standard can demonstrate the stringency of their quality management processes.

–Validated processes are required in some supply chains for critical applications such as permanent implants. In additive manufacturing, where end products may not be able to be directly inspected or tested, regulators rely on process validation and need to understand how it is accomplished. The ability to explain validation methods can help manufacturers avoid a notice of non-compliance from the regulator.

In some cases, processes that comply with current Good Manufacturing Practice (cGMP), the main regulatory standard for ensuring pharmaceutical quality, may be required. One example is a combination product—a device that delivers a drug or biologic. The FDA has issued a rule that the constituents of a combination product retain their regulatory status (as a drug or device, for example) after they are combined, and the cGMP requirements that apply to each of the constituent parts also apply to the combination product.

The biological safety of materials used in a medical device must be demonstrated under the ISO 10993-1 standard: Biological Evaluation of Medical Devices – Part 1: Evaluation and testing within a risk management process. Commonly required testing for the biological safety of limited body contact applications, such as wearables and instrumentation, includes cytotoxicity, sensitization, intracutaneous toxicity, acute systemic toxicity and subchronic toxicity.

Additionally, more-stringent testing such as genotoxicity, bone and muscle implant tests, hemolysis and complete characterization including exhaustive extractions and risk assessment, may be needed to ensure patient safety for long-term implants or devices that communicate with the body for a prolonged period.

Biological safety tests and reference standards
More than 60% of global medical devices are still manufactured in North America. Device manufacturers should consider using material suppliers that are willing to support an FDA Master Access File for their additive manufacturing products. Material data provided by the supplier through a Master Access File can demonstrate successful testing for biocompatibility and include product formulation details to the regulator reviewing the FDA petition. This confidential access by the agency can help reduce risk in the clearance process and accelerate time to market for additively manufactured medical products.

Solvay Specialty Polymers
www.solvay.com