The present article covers the matters related to the raw materials used for additive manufacturing, the impact of post-processing, and the validation of manufacturing processes.
The Food and Drug Administration (FDA or the Agency), the US regulating authority in the sphere of healthcare products, has published a guidance document dedicated to technician considerations for additive manufactured medical devices. The document highlights the most important aspects related to the use of 3D printing (additive manufacturing) when creating medical devices. In particular, the guidance provides additional clarifications regarding the applicable regulatory requirements, as well as recommendations to be considered by medical device manufacturers to ensure compliance thereto. At the same time, the authority also mentions that provisions of the guidance are non-binding. Moreover, an alternative approach could be applied, provided such an approach is in line with existing legislation and has been agreed with the authority in advance.
The Agency acknowledges that the overall quality of additively manufactured medical devices depends significantly on the initial quality of the materials used since they could be subject to certain changes in the course of the manufacturing process. Hence, it is important to take measures to ensure consistency in the quality of the materials used. In particular, the authority mentions that key details should be duly documented, namely:
- The identity of the material or chemical by common name, chemical name, trade names, Chemical Abstracts Service (CAS) number, or recognized consensus material standard,
- Material supplier,
- Incoming material specifications and material certificates of analysis (COAs), with the test methods used for the COAs. Applicable materials standards and test methods (e.g. ISO or ASTM) should be referenced.
The authority additionally emphasizes that the specifications for incoming materials and test methods should be based on the additive manufacturing technology used, the intended use of the final medical product, and the information available. The particular aspects to be addressed in specifications for materials would depend on the manufacturing process for which such materials are intended to be used, as well as the nature of such materials themselves. For instance, the most important characteristics for solid materials are particle size and distribution, for fluid ones – viscosity, for polymers – composition and molecular formula, for metals and alloys – composition and purity. Specific requirements should be also applied in case of materials of animal origin or composite materials. Furthermore, the authority states that in case of changes to the materials used or their specifications, the manufacturer should assess the impact this would cause to the manufacturing process and product itself, and also duly document the results of such an assessment.
The FDA also mentions that in certain cases the materials could be reused – if they were not incorporated into the product or components thereof. At the same time, when considering the reuse of such materials, the manufacturer should consider the impact caused by external factors the material was subject to during the manufacturing process. In certain cases, this could significantly affect the characteristics of the material, so they will be different from the ones described in the respective specification. Thus, the manufacturer should justify such use of materials and describe all the aspects associated thereto in detail. Furthermore, the Agency encourages medical device manufacturers to provide additional evidence demonstrating that reusing materials would not adversely impact the safety and quality of medical devices. For instance, the manufacturer may provide details about the studies conducted to evaluate the effect of material reuse.
Another important aspect addressed in the guidance is post-processing and the impact it causes on the quality of the final product. The concept of post-processing covers all the technological processes the product is subject to once the printing process is completed. For instance, it covers the actions taken to remove residues or final machining. According to the guidance, any post-processing procedures should be duly documented. Moreover, the manufacturer should also provide a detailed enough description of the way these processes impact the safety and quality of a medical device. The authority acknowledges that to simplify the processes, some of them could be unified for the particular design or medical device. The FDA expects medical device manufacturers to assess the way post-processing could impact the quality of a final product, and also provide additional details regarding the measures taken to mitigate the potential adverse effects. The guidance also provides some examples illustrating the way such an approach should be applied. For instance, should it be identified that post-processing may impact adversely some of the important characteristics of the product, the manufacturer shall reduce such post-processing to the lowest extent possible.
According to the guidance, the quality of additively manufactured medical devices could be impacted significantly by numerous factors including, inter alia, manufacturing processes, materials or equipment used, and other aspects. For instance, even the parameters for manufacturing equipment could impact the qualify of final products. Consequently, it is vitally important for the manufacturer to identify and be aware of how each of the variables impacts the result, and how this impact could be properly mitigated. As in the case with other manufacturing technologies, if the final product cannot be fully verified, it is necessary to validate the processes to ensure consistency in the results thereof. Furthermore, the authority additionally emphasizes the importance of following the guidelines related to the Quality System regulation in terms of device validation. In particular, the Agency states that process validation must be performed to ensure and maintain quality for all devices and components built in a single build cycle, between build cycles, and between machines, where the results of a process (i.e., output specifications) cannot be fully verified by subsequent inspection and test. It is also important to mention that the software used should be subject to validation as well.
Once the process has been validated, it is important to ensure that everything related to ongoing monitoring and control is duly documented.
To assist medical device manufacturers using additive manufacturing technology in following the recommendations provided hereinabove, the FDA also outlines the main methods to be used, as well as respective parameters subject to monitoring, namely:
- In-process monitoring of parameters such as:
- Temperate at the beam focus,
- Melt pool data,
- Build-space environmental conditions,
- Power of the energy delivery system,
- Status of mechanical elements of the printing system.
- Manual or automated visual inspection with defined acceptance criteria,
- Non-destructive evaluation, and
- Test coupon evaluation.
The authority mentions that monitoring could be also applied for the processes that have not been validated. The monitoring methods themselves should be subject to validation as well.
In summary, the present FDA guidance covers the most important aspects related to the raw materials used for additive manufacturing, their reuse, and key points to be considered in this respect. The document also addresses the matters related to the validation of manufacturing processes to ensure consistency in results.
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