Why models made on desktop 3D printers cannot be used in the operating room…?

For several years, from time to time, in mainstream media we can find an article that in some hospital a surgical operation was performed, during which models printed on a 3D printer proved to be helpful. The pictures attached to the article show an anatomical model made on a typical desktop FFF 3D printer. I always ask myself the same question: how can it be…? Can anatomical models, surgical instruments or implants be made using the most popular additive method in the world – FDM / FFF? Is it enough for a given plastic to be certified? Is it possible to certify this type of 3D desktop printer? What conditions must be met to make this possible?

Let’s start with the fact that the “source” plastic in the form of granules, and the plastic in the form of the final 3D print is not the same. I mean – theoretically it can be, but in reality there are several stages along the way that make the material lose its original chemical composition and become “polluted” in its own way. The first stage of change occurs in the process of transforming the granulate into a filament. To be able to produce a filament that has a given diameter (1.75 or 2.85 / 3 mm), the plastic must go through the entire production line, which should meet certain technological conditions and be certified for medical purposes.

We already know that certification means that only one type of material should be used on a given device (in this case the production line), otherwise there is a risk of contamination. If the production line is dedicated to the processing of materials such as ABS, PLA and “once in a while” will be used for the production of, for example, biocompatible PEEK or PCL, there is a risk that the module melting the granulate and extruding it into a filament thread may cause material contamination.

Another issue is that the filament dedicated to 3D printers must have slightly different properties than granules, which are used e.g. in the injection molding process. Generally, it all comes down to what will flow through the print head of the 3D printer, how it will bond between the individual layers during the 3D printing process and how its shrinkage or final strength will look. To improve these properties, filament manufacturers use various types of chemicals, thus changing the original properties of the granulate. The changes do not have to be large and may be less than 1% – unfortunately, in the end, from the chemical point of view, the obtained material is no longer 100% identical to the granulate from which it was made.

Another, quite obvious thing is the color. There is no room for interpretation here – when we change it, we obviously interfere with its chemical composition.

Thus, the fact that a given filament was made of certified, biocompatible granules does not mean that it is itself certified and biocompatible. To obtain this status, he must pass the certification himself, which is a complex, complicated and, above all, expensive process.

Let’s assume, however, that we have such certified material. Does this mean that we can start printing elements that will have the possibility of contact with tissue? Unfortunately, to achieve this, the 3D printer itself must also be certified for this. Is this even possible with FDM / FFF 3D printers?

Let’s start from the end – the 3D printer must be certified and dedicated only to printing details from a specific, biocompatible plastic. Any change of material to another causes loss of certification. The design of the 3D printer must meet certain requirements – both the filament itself and the working chamber should be separated to prevent any type of dirt from getting into the print – dust, etc. After all, the use of any adhesive preparations may be harmful – the first layer of the print may bind with an adhesive that cannot be washed out and which will chemically contaminate the material.

If we meet all the above-mentioned requirements, the device must undergo the aforementioned certification, and with it must be certified the workshop in which the 3D printer works. From a formal point of view, even such obvious tools as pliers for removing support or tweezers should be of a certain quality or come from specific manufacturers. In short, it is a very complicated and complex process that is also extremely costly and time consuming. Sooner or later the question arises whether it can not be achieved in a much simpler and cheaper way…?

Alternatives are CNC milling, metal 3D printing or light-cured resins (e.g. in PolyJet technology). All three are much more expensive than cheap 3D printing from thermoplastics, but when we add the whole formalistic coating to it, it turns out that in total the costs are not that diverse…

Thus, answering the question posed in the second paragraph of the article: “can anatomical models, surgical instruments or implants be made in FFF technology” – they can, but from a formal point of view it is very problematic and so far completely unprofitable. However, everyone who tries to do it in a traditional way, from the point of view of the rules – break them.

Equally, you could print military aircraft components or spare parts for Formula 1 cars on cheap Chinese Anet A8 kit…