Collagen-alginate as bioink for three-dimensional (3D) cell printing based cartilage tissue engineering

Articular cartilage repair is still a huge challenge for researchers and clinicians. 3D bioprinting could be an innovative technology for cartilage tissue engineering. In this study, we used collagen type I (COL) or agarose (AG) mixed with sodium alginate (SA) to serve as 3D bioprinting bioinks and incorporated chondrocytes to construct in vitro 3D printed cartilage tissue. Swelling ratio, mechanical properties, scanning electron microscopy (SEM), cell viability and cytoskeleton, biochemistry analysis and quantitative real-time polymerase chain reaction (qRT-PCR) were performed to investigate the function of different bioinks in 3D printing cartilage tissue engineering applications. The results showed that the mechanical strength was improved in both SA/COL and SA/AG groups compared to SA alone. Besides, the addition of COL or AG has little impact on gelling behavior, demonstrating the advantage as bioinks for 3D printing. Among the three scaffolds, SA/COL could distinctly facilitated cell adhesion, accelerated cell proliferation and enhanced the expression of cartilage specific genes such as Acan, Col2al and Sox9 than the other two groups. Lower expression of Col1a1, the fibrocartilage marker, was present in SA/COL group than that in both of SA and SA/AG groups. The results indicated that SA/COL effectively suppressed dedifferentiation of chondrocytes and preserved the phenotype. In summary, 3D bioprinted SA/COL with favorable mechanical strength and biological functionality is promising in cartilage tissue engineering.