In the first part of the blog, we covered 3D printing manufacturing techniques. The second part focuses on the right materials, associated regulations, and the use of workpieces made using additive manufacturing. Finally, we briefly discuss bio-3D printing, using a regional example.
Material selection according to standard
Consideration of the material-specific USP class (“United States Pharmacopeia”) or a classification according to DIN-EN-ISO-10993 is of great importance, especially in the case of prolonged skin or mucous membrane contact.
The USP classes define the requirements for materials that come into contact with the human body and categorize them according to their biological reactivity and toxicity.
DIN EN ISO 10993 further expands this definition to include medical devices without direct body contact. Physical and chemical measurements are also included in the assessments. However, this more holistic approach also results in significantly more effort. For a more detailed overview, it's worth taking a quick look at the DIN standard for assessing biocompatibility (Wikipedia/Beuth Verlag).
Generally, there are various materials to choose from depending on the manufacturing process used. For example, the FDM printing spectrum ranges from PLA and PET(G) to PA, PP, or PC plastics, with or without glass and carbon fiber reinforcement. Depending on the material manufacturer, these materials are also available with FDA approval.
For SLA printers, Formlabs, for example, also creates ISO 13485 and FDA-compliant materials for printing body-hugging applications.
In the field of SLS printing, a variant of nylon (e.g., PA6, PA11, or PA12) is typically found. However, PP or TPU can also be chosen as a flexible alternative.
Field of application: medical device
Patient-specific manufacturing using the example of maxillofacial surgery
The conventional procedure of taking a dental impression and then pouring it can be replaced by the use of image data generated with a desktop 3D scanner or even data from a CT/MRI scan. This allows a 3D model of the oral cavity to be created, which serves as the basis for the fabrication of a custom-fit aligner or retainer.
The advantages of digital impression taking over traditional impression taking are numerous. The procedure is more comfortable for the patient. Adjustment is performed via a digital system, thus opening up significant potential for automation. Further processing of the model, the automatic creation of a detailed treatment plan, and adaptation to the current situation may also be easier on a digital platform.
Implants, orthoses, drilling templates, aids for the plastic illustration of difficult surgical procedures, splints, surgical instruments, dentures and much more can be manufactured according to the same model, thus facilitating the entire course of therapy, both for the patient and for the treating staff.
The adaptability to individual patients enables a range of applications that is unparalleled. To provide each patient with the best possible treatment in the future, it makes sense to utilize this technology comprehensively.
Local and rapid production
The mobile use of modern FDM and SLA printing systems, for example, and their straightforward operation, makes it relatively easy to set up a 3D printing lab in individual supply centers and produce important items and consumables on-site and in line with demand. This contributes to significantly reducing transportation and storage costs. Furthermore, it drastically reduces sometimes lengthy procurement times and the resulting costs, not to mention the benefit of the increased agility this provides. The coronavirus pandemic provides a prominent example of how important it can be to be able to respond quickly to a surge in demand.
The Bundeswehr Hospital in Hamburg also operates according to this principle. There, an open workshop called "OpenLab MedTec" is operated to develop cost-effective alternatives and optimized patient care strategies directly on-site and in close collaboration with physicians.
Regulatory hurdles in Germany & EU
The regulatory landscape for additive manufacturing, especially in medical technology, is not yet particularly well developed, as it is a relatively new concept.
3D printed aids are most likely to be found under the “custom-made product” referred to in Article 2 Annex XIII of the Medical Device Regulation (EU) 2017/745 (MDR), as they are most likely to be personalized medical devices.
‘[The term] “custom-made product” means a device specially manufactured in accordance with a written prescription issued by a person qualified to issue prescriptions under national law, who determines on his or her own responsibility the precise design and characteristics of the device intended for a single patient in order to meet exclusively his or her individual condition and needs.
However, mass-produced products which must be adapted to meet the specific requirements of a professional user and products which are mass-produced using industrial processes in accordance with the written instructions of an authorised person shall not be considered as custom-made products.” – MDR Art.2 Annex XIII
However, it also emerges that a custom-made product can only be considered a product after it has been specified in writing by an “authorised person” with appropriate qualifications, who defines the characteristics and adapts them specifically to a patient.
This largely does not apply to products from a 3D printing laboratory. Furthermore, industrially manufactured products are categorically excluded and should therefore be treated as completely normal medical devices.
Since workpieces resulting from 3D printing vary too much in their properties and can hardly be compared to traditionally manufactured objects, there is a significant need to catch up in this area. Likewise, the FDA regulations do not yet provide a clear guideline for dealing with additive manufacturing in medical technology; these are currently being developed.
For more information on the topic of the FDA's articles on 3D printing: https://www.fda.gov/medical-devices/products-and-medical-procedures/3d-printing-medical-devices
All in all, no satisfactory guidelines can yet be found in the standards. Manufacturers of additively manufactured solutions should ideally pay close attention to locally applicable safety standards in order to make 3D printed products useful and safe for patients and users.
Future Outlook: Bio-3D Printing
The current range of applications for this technology is already enormous, but it also holds enormous future potential. Aside from better integration of this technology into the daily routines of many doctors and medical staff, there are many other fields in which the technology can be integrated. For example, there is the field of bio-3D printing/tissue engineering, which also offers great potential.
Among other things, the University Hospital in Erlangen under the direction of Prof. Dr. Felix Engel researched a method (Laboratory questions), to form heart muscle cells into contracting constructs using a special 3D printer. This works similarly to an FDM printer. However, it uses a viscous "bio-ink" that contains the necessary structural elements and the heart muscle cells. The print is then placed in a support bath where the bio-ink can harden.
After just a few days, the first contractions of the tissue can be observed. The proposed technique aims to replace dead areas of the heart and thus achieve a "healing." In the future, it may be possible to create an entire heart in this way.
It is expected that this technology can also be applied to other cell types, such as cartilage and other slow-healing tissue types. This would allow these tissues to be replaced biologically. In the long term, this could replace metal and plastic implants, thus creating a natural and body-friendly alternative. Furthermore, the associated problems of bone loss due to shifting loads and the often necessary administration of immunosuppressants could be prevented.