Two recent review articles touched upon interesting and current musculoskeletal tissue engineering applications utilizing carbon nanotube-based biomaterials as an innovative approach to restore injured bone or cartilage tissue. In the first review entitled “Carbon nanotube-based biomaterials for orthopedic applications” by Aoki and coworkers, the safety of carbon nanotubes in in vitro and in vivo studies was reviewed in detail. Indeed, the safety and efficacy of all regenerative medicine applications is to be rigorously inspected and verified before translation into the clinics. The cytotoxicity of multi-walled carbon nanotubes (MWCNTs) was found to be connected to the amount of MWCNT uptake as well as on cell type. For human bronchial epithelial cells, inflammatory cytokine levels increased with the higher MWCNT dispersion concentrations of those tested at 1, 10, and 50 μg mL−1 although the different dispersants also had an effect on the cells. However, the respitory system’s hazardous exposure to carbon nanotubes (CNTs) is practically limited to the work safety of CNT-based material production processes. For musculoskeletal tissue engineering applications including bone and cartilage tissue, the CNT negative surface charge has been linked to accumulation of Ca ions and thus increased bone matrix mineralization promoting bone formation. For cartilage, degenerative processes of osteoarthritis could be stalled or potentially reversed with CNT-containing nanobiomaterials. In alginate hydrogel culture with embedded CNTs, the chondrogenic differentiation of human adipose stem cells was enhanced compared to CNT-free control condition. For damaged cartilage, the chondrocyte extracellular matrix production was increased within CNT-loaded agarose hydrogel.
In the second recently published review article entitled “Utilization of Carbon Nanotubes in Manufacturing of 3D Cartilage and Bone Scaffolds” by Szymanski and coworkers, the cytotoxicity of CNT-based biomaterials was reported to be related to a significantly increased dose or presence of unpurified residual iron catalyst. Increased cytotoxicity was connected to CNT size with a length of over 6 µm and mild cytotoxicity was found for CNTs of diameter between 15 and 40 nm. However, the size dependent effects were diminished by CNT functionalization with carboxyl or amine groups which promote protein adsorption for an enhanced biological response and decrease of inflammation reaction. Interestingly, various cytotoxicity analyses yielded different results and therefore the testing methods require further development for more reliable and repeatable results in the future.
Aoki K, Ogihara N, Tanaka M, Haniu H, Saito N. Carbon nanotube-based biomaterials for orthopaedic applications. J Mater Chem B. 2020 Sep 16.
Szymański T, Mieloch AA, Richter M, Trzeciak T, Florek E, Rybka JD, Giersig M. Utilization of Carbon Nanotubes in Manufacturing of 3D Cartilage and Bone Scaffolds. Materials (Basel). 2020 Sep 11;13(18).