A 3D model of the University of Alberta scientists’ 3D bioprinted nose-shaped tissue implant. Image via the FASEB journal.
Investigating new polymers
For their study, the University of Coimbra researchers sought to explore new polymers suitable for producing 3D printed cartilaginous tissue that could potentially serve as total cartilage replacements.
The team studied PA12, which has been deployed for similar biomedical applications in the past, and a new filament, FOMM, which they say has not yet been investigated as a potential material for creating cartilage via additive manufacturing.
Typically, the two most common approaches for cartilage replacement and repair are total replacement, usually with cobalt–chrome (CoCr) or ultrahigh molecular weight polyethylene (UHMWPE)-based structures, or through scaffold implantation. However, even though CoCr is considered biocompatible and non-degradable, its stiffness leads to the mechanical shielding of the bone due to mechanical loading. Meanwhile, although UHMWPE presents mechanical properties similar to those of native cartilage, it can be structurally unstable under loading.
For repair and regeneration, biomedical scaffolds are beneficial as they can provide a 3D framework to enable cell proliferation, with the most common natural materials used being that of collagen, agarose, chitosan, fibrin, and alginate. Synthetic polymers currently used for this purpose tend to include PEG, PLA, PVA, and PU.
To date, though, approaches with each of these materials leveraging 3D printing has been directed at a specific type of cartilage and local implantation, which can impair the standardization of the structure going forwards.
The Coimbra researchers decided, therefore, to focus on FOMM for 3D printing structures for cartilage repair. FOMM is composed of PVA and TPU, both which have been previously deployed for cartilage-related applications. They used PA12 as a control material due to its excellent impact resistance at low temperatures, low water absorption, resistance to stress cracking, and fatigue under high-frequency cyclical loading conditions. The material has also previously been used for cartilage applications.