2.7 Rheological properties of BMSC-laden GelMA/Gel bioinks
7 w/v% GelMA, 3 w/v% gelatin and BMSCs at the density of 1×106 per ml were mixed to prepare BMSC-laden GelMA/Gel bioinks for 3D bioprinting. The rheological properties of GelMA/Gel inks and BMSC-laden GelMA/Gel bioinks were investigated at 20 ℃ using a rheometer (MCR 302, 176 Anton Paar, Austria) equipped with a parallel plate unit with a 20 mm diameter. In accordance with the preliminary strain sweep test results, GelMA/Gel inks and BMSC-laden GelMA/Gel bioinks with or without UV crosslinking were loaded onto a parallel plate and subjected to a maximum strain (γ) of 1.0% under continuous oscillation. In the frequency sweep mode, the storage moduli (G’) and loss moduli (G”) of GelMA/Gel inks and BMSC-laden GelMA/Gel bioinks were measured in the range of 0.1 - 100 rad/s. Furthermore, the shear thinning behavior of GelMA/Gel inks and BMSC-laden GelMA/Gel bioinks was studied. The viscosity of each sample was measured over the temperature range of 15-50 ℃ at 1 s-1 shear rate. Thixotropic tests were conducted in two repeated steps by varying the shear rate. First, a low shear rate (1 s-1) was applied for 120 s. Then, a high shear rate (500 s-1) was applied for 60 s.