The article provides an overview of the most important aspects to be considered for the impact the software could cause on the additive manufacturing process.
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 technical considerations for additive manufactured medical devices. The document provides an overview of regulatory requirements such products are subject to and also highlights the most important aspects to be considered by medical device manufacturers and other parties involved due to the specific nature of such devices. The scope of the guidance covers, inter alia, the aspects related to software workflow, providing additional details about file format conversion, the process for turning digital device design to physical devices, as well as validation and automation of software processes.
File Format Conversions
The authority acknowledges that the additive manufacturing process itself usually requires the use of several software products that could be developed by different software developers. Hence, it is important to ensure they are compatible with each other, especially in terms of standards used. Moreover, it is important to ensure that the product specifications are interpreted by all software products in the same way. Thus, the authority encourages medical device manufacturers to implement and apply the appropriate procedures to ensure that the final product operates as intended in terms of software used. Furthermore, in case of significant changes to the product (e.g., changes to the software used), revalidation could be required.
The FDA also mentions that the files containing information about medical devices to be printed should be created and kept in a format ensuring access to the information when necessary. In particular, medical device manufacturers can use the Additive Manufacturing File Format (AMF) as described in the ISO/ASTM 52915 Standard specification for additive manufacturing file format (AMF). Such files should contain information about the objects to be created.
Digital Device Design to Physical Device
The guidance further describes the way the design turns into a physical medical device. In this regard, the authority mentions that additional preparatory procedures should be performed with the help of the appropriate software. According to the guidance, these processes include the following steps:
- Build volume placement;
- Addition of support material;
- Slicing; and
- Creating build paths.
The first step covers the measures to be taken to ensure consistency in the quality of medical devices to be created with the use of additive manufacturing technology. In particular, the authority mentions that placement, orientation, and packing density of devices or components within the build volume may be integral to an individual device or component quality; while the distance between each device or component, and whether they are identical or different designs, can affect the material properties, surface finish and ease of post-processing. Hence, the abovementioned factors should be considered by medical device manufacturers as they could impact the quality of a medical device and its overall performance. Due to the specific nature of the additive manufacturing process, special software should be used to ensure the product is oriented properly in the course of manufacturing (printing).
The second step applies to additive manufacturing technologies based on a layer-by-layer approach. In such cases, temporary support structures are needed. The choice of a particular support structure to be used depends on the additive manufacturing technology employed. Hence, to ensure the proper quality of a final product, the manufacturer should assess the impact additional support structures would have. At the same time, the manufacturers should also pay attention to the way these support structures are removed. As described in the guidance, this could be done either physically, or by chemical means. In this regard, it is important to ensure no residues are remaining after removal, as this could affect the safety or performance of a medical device. As it is mentioned by the FDA, the complete description of the support material geometry and the removal process method should be included in the Device Master Record (DMR).
The third step refers to the way the layer-by-layer manufacturing method should be used when creating medical devices via 3D printing. In particular, the manufacturer shall determine the proper thickness of a layer, which will be based on a specification of the equipment and software employed, as well as the materials used. All these aspects should be considered carefully by the manufacturer, while the decision taken for the layer thickness should be duly justified and documented.
The fourth step describes the approach to be applied about build path, which is the path traced by the energy or material delivery system (e.g, laser or extruder) since this can significantly impact the overall quality of an additive manufactured medical device. For instance, in certain cases, the time to cool or harden for different sides of the same product could be different. Hence, the authority encourages medical device manufacturers to assess rigorously the way the build path would impact the internal structure of the product. Moreover, consistency in the build path should be followed for all components of the device. The scope of factors to be considered shall include, inter alia, technical characteristics and specifications of machines used for 3D printing.
The authority further emphasizes the importance of proper calibration of the equipment used, as this also impacts the quality of final products. When performing calibration, environmental conditions should be considered as well, since they can affect the way the equipment operates. In particular, the FDA mentions that for machines without a self-contained, well-controlled build volume, the ambient temperature, atmospheric composition, and flow patterns can impact solidification/polymerization rate, layer bonding, and the final mechanical properties of the component. The particular set of parameters to be used would depend on the machine itself, the use environment, and the medical device component manufacturing. The medical device manufacturer shall duly document parameters used, and such information should be kept for further use.
Validating and Automating Software Process
According to the guidance, should the medical device manufacturer decide to implement a workflow intended to automate several steps, the recommendations provided in the FDA Guidance on “General Principles of Software Validation” should be followed?
In summary, the present FDA guidance provides additional clarifications about the most important aspects to be considered concerning the software used in the additive manufacturing process. The Agency outlines the main factors that could impact the quality and safety of the final product and describes the approach to be applied when developing the processes.
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