Handheld Co-Axial Bioprinting: Application to in situ surgical cartilage repair

Abstract

Three-dimensional (3D) bioprinting is driving major innovations in the area of cartilage tissue engineering. Extrusion-based 3D bioprinting necessitates a phase change from a liquid bioink to a semi-solid crosslinked network achieved by a photo-initiated free radical polymerization reaction that is known to be cytotoxic. Therefore, the choice of the photocuring conditions has to be carefully addressed to generate a structure stiff enough to withstand the forces phisiologically applied on articular cartilage, while ensuring adequate cell survival for functional chondral repair. We recently developed a handheld 3D printer called “Biopen”. To progress towards translating this freeform biofabrication tool into clinical practice, we aimed to define the ideal bioprinting conditions that would deliver a scaffold with high cell viability and structural stiffness relevant for chondral repair. To fulfill those criteria, free radical cytotoxicity was confined by a co-axial Core/Shell separation. This system allowed the generation of Core/Shell GelMa/HAMa bioscaffolds with stiffness of 200KPa, achieved after only 10 seconds of exposure to 700 mW/cm2 of 365 nm UV-A, containing >90% viable stem cells that retained proliferative capacity. Overall, the Core/Shell handheld 3D bioprinting strategy enabled rapid generation of high modulus bioscaffolds with high cell viability, with potential for in situ surgical cartilage engineering.

Human articular cartilage repair: Sources and detection of cytotoxicity and genotoxicity in photo-crosslinkable hydrogel bioscaffolds

“…Fedorovich et al demonstrated that the combination of UV light with Irgacure 2959 resulted in the highest cytotoxicity compared with the two modalities alone . Similar results were generated with LAP and RB indicating that the PI toxicity is drastically exacerbated by photoactivation …”

“…In cartilage tissue engineering, the coaxial method was found to be superior to the monoaxial configuration where cells are embedded throughout the hydrogel and exposed to the toxic photoinitiation process triggered by a fast high irradiance exposure to UV light. In Duchi et al, the cytotoxicity of bioprinted hADSCs upon 10 second irradiation with 365 nm at 700 mW/cm 2 was found to be negligible, when cells were segregated from the PI, and the viability of UV only irradiated cells was comparable to the nonirradiated control group throughout 7 days . Moreover, high levels of cell survival immediately after printing and crosslinking with an increase in cell number 10 days following extrusion.…”

“…A comparative study between three PIs, Irgacure 2959 (2‐hydroxy‐4′‐(2‐hydroxyethoxy)‐2‐methylpropiophenone), Irgacure 184 (1‐hydroxy‐cyclohexyl‐phenyl‐ketone), and Irgacure 651 (2,2‐dimethoxy‐1,2‐diphenylethan‐1‐one), found that Irgacure 651, the most nonpolar molecule of the PIs, exhibited the highest cytotoxicity whereas Irgacure 2959, which has a relatively polar structure, was the least toxic . Several studies have analyzed the individual effects of the different components of the photo‐crosslinking process on cell viability in 2D by exposing cells to UV irradiation, PI alone, and PI with UV irradiation . Table summarizes the intrinsic toxicity of different PI molecules.…”

“…is p > 0.05. Source : Used with permission ( http://creativecommons.org/licenses/by/4.0/) from Duchi et al…”

“…Nevertheless, the increased efficiency of LAP suggests that shorter light exposure times can yield sufficiently crosslinked hydrogels hence, the reduced viability observed at longer exposure times does not necessarily have a practical implication. Indeed, a short 10 second exposure time of LAP to UV light (365 nm, 700 mW/cm 2 ) produces hardened GelMa‐HAMa scaffolds suitable for cartilage tissue regeneration whereas identical concentrations of other PIs such as Irgacure 2959 and VA‐086 did not achieve the same stiffness even after 2 minutes …”