Photocrosslinked poly(γ-glutamic acid) hydrogel for 3D bioprinting

In this study, tyramine-modified poly(γ-glutamic acid) (γ-PGA/Tyr) was synthesized to fabricate a photocrosslinked γ-PGA hydrogel for 3D bioprinting. The Tyr moiety was successfully introduced into γ-PGA at different degrees of substitution (DS) ranging from 13.4 to 53.8%, as determined by 1H NMR spectroscopy. The gelation time of γ-PGA/Tyr conjugate decreased with increasing DS of Tyr in the presence of Ru2+/sodium persulfate initiators. The optimum photoinitiation conditions for the gelation of γ-PGA/Tyr conjugate at the concentration of 12 wt% and DS of 53.8% were found to be Ru2+ concentration of 0.5 mM, and sodium persulfate of 40 mM, resulting in the highest mechanical strength of the γ-PGA/Tyr hydrogel. The crosslinking density, molecular weight between crosslinks, and mesh size of the γ-PGA/Tyr hydrogel calculated using the Flory-Rehner equation agreed with the rheological and mechanical properties of the hydrogel. The cytotoxicity and proliferative ability of γ-PGA/Tyr hydrogels with a DS, 53.8% were found to be excellent through live/dead and WST-1 assay. Finally, a lattice structure of the γ-PGA/Tyr hydrogel (DS, 53.8%) blended with cellulose nanofibrils was successfully fabricated via 3D bioprinting.