2.4.3. Mechanical testing of carrageenan-based bioink
Mechanical testing was performed by considering the guidelines and standards for elastomers and plastics in tensile measurements (ASTM D412-06a, ASTM D638-14, ISO 37, ISO 527-1,2) as well as the standards for biomedical and regenerative medicine (ASTM F2064-14, ASTM F2900-11, and ASTM F2150-13) relevant for mechanical testing. Bioinks were printed in sheet shape (4-cm length, 1-cm width, and 1.5-mm height) to prevent printing-related stress localisation and inaccurate sample sizes. The sheets were kept in culture medium for 24 h for uniform swelling, and dumb-bell specimens were stamped according to the ISO 527-2-5B standard. The cast bioink sheets (bulk) were similarly stamped. Tension testing was performed using a custom-made testing device with uniaxial hydraulic actuators equipped with 100 N load cells. Custom-made titanium clamps equipped with sandpaper were used for specimen fixation. The tensile specimens were clamped to the retracting probes without preloading, and the stress-strain curves were recorded after a 0.005–0.01 N pre-force was reached.