Orthoses and Prostheses from Bio-Based Polymers
Bio-Based Knee Prosthesis Withstands a Fatigue Test to ISO 10328
In a research project, the Fraunhofer Institute for Manufacturing Engineering and Automation (IPA) and the companies Tecnaro GmbH, Ilsfeld, Germany, and Dambeck GmbH, Kempten, Germany, investigated orthotic and prosthetic devices of bio-based materials. They developed suitable biopolymer compounds, producing functional models, which they tested. The bio-based knee prosthesis successfully withstood the fatigue test according to ISO 10328. The 3D printing of prostheses and biomaterials also proved highly promising.
Tecnaro’s task was to select suitable biopolymers, natural fibers and additives in order to develop new compounds. The biopolymer manufacturer attached particular importance to good processability during sheet extrusion, permitting subsequent industrial production. The materials chosen were then used by the Fraunhofer IPA and the orthotic device manufacturer Dambeck to produce orthotic and prosthetic devices, which were subject to various tests. The injection molding of a so-called all-terrain knee prosthesis (AT-knee) was particularly promising. A version made from conventional plastics is already commercially available. The researchers manufactured two bio-based versions made from compounds containing 72% and 100% bio-based polymer respectively, and tested them successfully according to ISO 10328 in a fatigue test with 3 million load cycles.
Imitating the Body Shape by 3D Printing
An important milestone in the project was 3D printing. IPA used this process to produce a Niagara foot prosthesis, including a so-called cosmetic cover (imitation of the body shape). The soft bioplastic required for this had also been developed for this purpose as part of the project. Within the scope of the project, it was no longer possible to perform mechanical tests on the 3D printed model, however the researchers regarded this method as particularly interesting.
As a result of the project, many new bio-based materials are now available, including grades that are transparent, heat-stable, almost splinter-free or can be processed by 3D printing. Particularly high-modulus materials for applications requiring high dimensional stability and particularly soft materials that, according to the researchers are also suitable for children’s toys, have been developed. All the compounds have good melting behavior; the viscosities can be adjusted to values that are typical for polymer melts. They were also tested for safety in contact with the human body. The materials developed thus met all the prerequisites for series production of orthotic and prosthetic components or other new products. The project partners will be pleased to provide material samples to interested parties.
The project was sponsored by the Federal Ministry of Food and Agriculture (BMEI), via the project sponsor Agency for Renewable Resources (FNR). The final report is available under the grant numbers 22022012, 22016014 and 22015914.