CMC/Gel/GO 3D-printed cardiac patches: GO and CMC improve flexibility and promote H9C2 cell proliferation, while EDC/NHS enhances stability

In this research, carboxymethyl cellulose (CMC)/gelatin (Gel)/graphene oxide (GO)-based scaffolds were produced by using extrusion-based 3D printing for cardiac tissue regeneration. Rheological studies were conducted to evaluate the printability of CMC/Gel/GO inks, which revealed that CMC increased viscosity and enhanced printability. The 3D-printed cardiac patches were crosslinked with N-(3-dimethylaminopropyl)-n'-ethylcarbodiimide hydrochloride (EDC)/N-hydroxysuccinimide (NHS) (100:20 mM, 50:10 mM, 25:5 mM) and then characterized by mechanical analysis, electrical conductivity testing, contact angle measurements and degradation studies. Subsequently, cell culture studies were conducted to evaluate the viability of H9C2 cardiomyoblast cells by using the Alamar Blue assay and fluorescence imaging. A high concentration of EDC/NHS (100:20 mM) led to the stability of the patches; however, it drastically reduced the flexibility of the scaffolds. Conversely, a concentration of 25:5 mM resulted in flexible but unstable scaffolds in phosphate buffer saline solution. The suitable EDC/NHS concentration was found to be 50:10 mM, as it produced flexible, stable, and stiff cardiac scaffolds with high ultimate tensile strength. Mechanical characterization revealed that % strain at break of C15/G7.5/GO1 exhibited a remarkable increase of 61.03% compared to C15/G7.5 samples. The improvement of flexibility was attributed to the hydrogen bonding between CMC, Gel and GO. The electrical conductivity of 3D printed CMC/Gel/GO cardiac patches was 7.0 × 10^-3S cm^-1, demonstrating suitability for mimicking the desired electrical conductivity of human myocardium. The incorporation of 1 wt% of GO and addition of CMC concentration from 7.5 wt% to 15 wt% significantly enhanced relative % cell viability. Overall, although this research is at its infancy, CMC/Gel/GO cardiac patches have potential to improve the physiological function of cardiac tissue.