Use of Standard Files for Additive Manufacturing in Healthcare

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(Translated from Portuguese)

It’s a Long story.

Information storage and distribution is something old, started with memory recap and speeches, passed by stone sculpting, handwriting, was highly improved by Gutenberg and now relies on computer files and the “cloud”. On additive, the information had been transferred mostly by “Standard Tessellation Language” –. STL computer files.

Created to take the geometry from CAD to the stereolithography machine it is a simple way to give shape to the computer information by making a huge list of point coordinates.

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Figure 1- Segmented CT SCAN of my back – STL format

   

What is the AMF format?

But nowadays, with the wonders of “additive machines”, we need more information than geometry to be able to define a part. We need to define color, material, quantities, geometry, textures, design, authorship, intellectual property information to more precisely define additive manufactured parts. 

One initiative to improve information transfer in additive manufacturing is ISO/ASTM52915 – 16 Standard Specification for Additive Manufacturing File Format (AMF) Version 1.1. ISO and ASTM have a special joint development initiative for additive manufacturing, with a joined committee ASTM/F42 and ISO/TC261. This committee manages how information is transferred, stored and used by the community either for industrial or medical purposes.

The format not only defines the geometry by points and triangles, but also permits a new shape of facet called “curved” where the edges of the “triangle” are interpolated curves. This can be challenging, but it is one step closer to define real world shapes.

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Figure 2 – Courtesy ISO/ ASTM 52915-16

The format also includes definition for colors in RGB standard,  for part surface in 2D and 3D textures, and even for materials, which are all new information compared to STL .  This is a huge advance in communication for AM.

As manufacturing information, AMF can pass build positions, quantities, arrays, and others. This has great potential not only in communication but also in file sizes since AMF is XML standardized so it can be compressed via ZIP format.  Using a single shape, we can define a fulfilled building volume in a much smaller file.   

Object definition can contain metadata, which is the space for other information like in CAD files. It can include information about ownership, part ID, object description, producer, tolerances, or how it was scanned or constructed plus two physical properties, elastic modulus and Poisson ratio. Containing these additional information represents a significant improvement in the quality of communication in comparison to an STL file. With more information inside a single file, it can be used directly by the systems to build a much more well-defined part or object.

Future Ahead

A lot of information relevant to the final object and its built process are not yet covered by the standard yet, perhaps omitted to simplify the initial adoption. But some are already in discussion to be added (by ISO/ASTM committee), including information such as critical dimensional and geometrical tolerancing , equation defined geometries , Boolean operations,  surface roughness ( very important on fatigue properties and also in the medical use ) , definition for the type and geometry of particular processes supports , voxel representations (something that may open a completely new technology inside this already new technology) , IP locks and watermarking , surface patterns related to tactile and coatings, and more .

Why Make Sense?

In a broader sense,  it’s easy to understand the beauty of having a common information container.  

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Figure 3 – Courtesy Pesquisa Fapesp Magazine

Having all this info is very important down the line when, for example, building a biomodel. It’s important to have a real representation of the anatomy. It should include the texture, the hardness of the material, the feeling in the surgeon hands, the right resistance to the scapel cuts or the tension on the vascular models (for example, that will compress the stent being tested).  Manufacturing implants or surgical guides needs to be done right in the shape, quantity, and material. We cannot waste expensive titanium alloy we are using, so it is important to automate the quantities and shape checking. It is also important for the implant to match the physical attributes tailored for the part and its effects against the bony structure and encourage osteointegration. FDA already realized this and included a recommendation about .AMF inside the “Technical Considerations for Additive Manufactured Medical Devices ; Guidance for Industry and Food and Drug Administration Staff” issued last year.

The community didn’t embrace this format yet due to lack of awareness and discordance on how geometry had been defined among other debates. Other formats like the 3MF for lattices and new formats are coming out, and the constant technology advances are bringing benefits to the additive world. 

In conclusion, on medical or industrial processes, consistency is mandatory, so the more information a file can include, the better the process you get and the less you need to depend on people decision or actions. Consequentially, more information results in more automation, more accuracy, more repeatability, and higher quality.  These factors lead to better life for consumers or patients, independently of what market you are in.

About the Author:

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Fabio Sant’Ana has Precision Mechanics degree and Business Administration Bachelor’s , born and raised in São Paulo he has 25 years experience in helping companies to aquire and take full advantage of 3d Machining and Additive Manufacturing Equipment . Entrepreneur and knowledge avid is member of stardarts organizations ASTM F42 Additive Manufacturing , ABNT CEE-261 Manufatura Aditiva e ABNT CB-26 Odonto-Médico-Hospitalar . CAD/CAM , Surface Modelling and EBM specialist he is passionate in connect people and companies to the right tools to accomplish the mission.

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