Additive manufacturing of medical devices and implants has been seeing increased industry adoption and is expected to become common place in modern medicine within the next decade. Numerous applications for 3D printing in medicine already exist and patients have already begun receiving the benefits of additive manufacturing post-surgery.
Similar to any implant or medical device, those created from additive manufacturing require strenuous FDA evaluation and clearance prior to clinical trials and surgeon use. Because additive manufacturing is significantly more advanced than traditional methods of manufacturing, the FDA is working to develop a comprehensive regulatory pathway that ensure the safety of 3D printed devices and implants. This white paper will focus on FDA recommendations for manufacturers when testing devices or implants created from additive manufacturing.
When submitting a premarket submission to the FDA with a device made from additive manufacturing, the FDA provides guidelines on pertinent information to include in the device description portion of the submission. The manufacturer should describe the type of additive manufacturing technique being utilized for the production of the device such as filament deposition, stereolithography, selective laser sintering, or selective laser melting. As additive manufacturing affords the ability to create implants and devices in a multitude of sizes and shapes (beyond the classic small, medium, and large) and virtually endless complexity, a range of allowable values for each dimension should be clearly indicated. Additionally, the manufacturer should outline any features that are intended to be altered to match a patient’s specific anatomy and the expected range of sizes for these specific design elements. The FDA also recommends that manufacturers clearly and thoroughly describe critical features of the device that are unique to additive manufacturing such as porous scaffolding and mesh structures, including the proposed thickness and location of these elements. Technical drawings included in the device description should clearly indicate which components of a device are created from additive manufacturing if multiple modalities are employed.
Mechanical testing for a device created from additive manufacturing should be conducted in a similar manner as if the same device was created with traditional manufacturing techniques. The specific types of mechanical testing carried out vary between devices and the intended use although testing modalities may include ultimate strength, yield strength, fatigue, abrasive wear, viscoelasticity, and modulus.
As with other devices, testing should always be carried out on the final finished device; for additive manufacturing, this is a device where removal of all support structures, cleaning, and sterilization have been performed. As multiple sizes can be created, the manufacturer must provide rationale as to why the size of the test implant was selected.
The FDA also recommends testing the “worst-case scenario;” an implant with worst case combination of design elements (size, holes, supports, location of porous regions) also be created and tested for each performance domain.
Manufacturers must also consider the build orientation and location within the build volume—two factors that are unique to additive manufacturing. The build orientation of the device must be specified, and if multiple orientations are going to be used for manufacturing, performance testing must be carried out on each orientation. As with build orientation, the location within the build volume may also have an impact on the mechanical properties of the final device. For example, variability in print quality may exist for the center versus the edge of a print bed. To aid in testing different build orientations and locations in the build volume, the FDA allows for the use of a “test coupon.” The test coupon is an engineered structure with similar design elements to that of a final implant that can be printed in different orientations and in different areas of the print volume to allow for determination of best and worst-case scenarios. The test coupon should undergo similar testing as the final device. It is the manufacturer’s duty to provide justification to the type of coupon used and its appropriateness to representing the final device.
The FDA recommends that manufacturers specify the device dimension and tolerances expected for additive manufacturing. To ensure consistency in dimensional accuracy, dimensional measures should be performed on multiple samples from multiple build cycles.
Additive manufacturing is unique in that final device material is a result of altered starting material—such as changing from a powder to a solid—during production. There should be a clear description of all material changes that occur during the manufacturing process. The composition of the final product should be documented. All starting materials should be identified, including the source and purity of each material. Manufacturers should include the material safety data sheet (MSDS), certificate of analysis, and chemical abstract service (CAS) number for each material used in the submission. Additional testing of certain polymers may be required to ensure that no hazardous chemicals are formed during the change in material form, such as during melting of a polymer.
For devices created from metal or ceramic, the FDA recommends that the manufacturer characterize the microstructure, providing details about grain size, orientation, and phase composition. Alternatively, for devices made from polymers, the degree of crosslinking and curing should be evaluated to ensure the device meets required specifications, although the FDA does not provide details regarding specific tests or reporting for this.
Support Removal and Post Processing
One of the greatest benefits of additive manufacturing is the ability to create complex geometries, porous surfaces, and intricate lattices. In order to create these complex structures during manufacturing, temporary support structures are often necessary and require removal during the post processing stage. The FDA requires manufacturers to maintain procedures and guidelines for the removal of support structures and ensure that they do not ultimately affect the integrity of the final device. The final device provided to the end user must be free of all excess material and support structures and this step must be outlined and clearly stated in the premarket submission to the FDA. The FDA requires the final finished device be free of all support structures to undergo validation of the sterilization process.
As additive manufacturing becomes more widely adopted in the medical industry, the FDA is taking early steps to provide manufacturers with guidelines specific to this production process. Requirements may change over time as processes improve and change. Always obtain the latest requirements from the FDA directly for the most accurate information.