Scientists at the University of Osaka in Japan have developed a new technology that should make it possible to bioprint highly complex biological structures using a greater variety of cells. Although inkjet bioprinting isn’t a new concept, there are currently limited methods for gelling the bioink droplets together once printed, and the methods that are available aren’t suitable for every cell type. The refined approach developed by the University Osaka team should be suitable for use with a greater range of cell types, make it possible to print highly complex structures. Reporting on their method in Macromolecular Rapid Communications, the Osaka University team claims the new method will enable “the use of a variety of bioinks to produce hydrogels with a wide range of characteristics.” Their published paper is entitled “Drop-On-Drop Multimaterial 3D Bioprinting Realized by Peroxidase-Mediated Cross-Linking.

The potential use of inkjet bioprinting to fabricate 3D tissues and organs in vitro is well recognized, but the bioink must exhibit specific properties. “Printing any kind of tissue structure is a complex process,” notes Shinji Sakai, Ph.D., who heads the research at Osaka University. “The bioink must have low enough viscosity to flow through the inkjet printer, but also needs to rapidly form a highly viscose gel-like structure when printed.”

Sodium alginate is currently the primary gelling agent used for inkjet bioprinting, but the component isn’t compatible with some cell types. Building on their previous work, the Osaka team’s new technology uses horseradish peroxidase (HRP) to catalyze the creation of cross-links between the polymers supporting the cells, in the presence of hydrogen peroxide (H2O2). Although H2O2 is damaging to cells, the new printing approach keeps the cells and H2O2 in separate droplets to minimize contact. “3D cell-laden hydrogels are fabricated by the sequential dropping of a bioink containing polymer(s) cross-linkable through the enzymatic reaction and H2O2 onto droplets of another bioink containing the polymer, HRP, and cells,” the authors state. Using this approach, about 95% of cells remained viable. “Our new approach meets these requirements while avoiding sodium alginate,” Dr. Sakai states. “In fact, the polymer we used offers excellent potential for tailoring the scaffold material for specific purposes.”

The authors point out that numerous polymers, such as polyscaccharide derivatives, proteins, and synthetic polymers can be cross-linked through the HRP-catalyzed reaction, and this means that “the current approach shows great promise for biofabrication of functional and structurally complex tissues.”

“Advances in induced pluripotent stem cell technologies have made it possible for us to induce stem cells to differentiate in many different ways,” adds co-author Makoto Nakamura, Ph.D. “Now we need new scaffolds so we can print and support these cells to move closer to achieving full 3D printing of functional tissues. Our new approach is highly versatile and should help all groups working to this goal.”

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