This is a photograph of a 3-D hydrogel construct obtained through drop-on-drop multi-material bioprintinig. Credit: Osaka University
Researchers develop a finely tuned enzyme-driven crosslinking method to glue together biological ink droplets and extend the range of cell types that can be handled by inkjet bioprinting. Such printing holds strong promise for regenerative medicine, such as in use of iPS cells. Researchers refine method of making bio-ink droplets stick to each other, enabling 3D printing of highly complex biological structures with a wide variety of cell types using inkjet printers.
Before any real applications, “bioprinting” has always faced many technical challenges. Processing the bio-ink and making it stick to itself and hold the desired printed gel structure have been proving particularly difficult especially in inkjet printing. Few methods currently exist for gluing bio-ink droplets together and these do not work for every kind of cell, motivating new alternative approaches.
Lead author, Shinji Sakai says, “Printing any kind of tissue structure is a complex process. The bio-ink 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. Our new approach meets these requirements while avoiding sodium alginate. In fact, the polymer we used offers excellent potential for tailoring the scaffold material for specific purposes.”
Currently, sodium alginate is the main gelling agent used for inkjet bioprinting, but has some compatibility problems with certain cell types. The researchers’ new approach is based on hydrogelation mediated by an enzyme, horseradish peroxidase, which can create cross-links between phenyl groups of an added polymer in the presence of the oxidant hydrogen peroxide.
Although hydrogen peroxide itself can also damage cells, the researchers carefully tuned the delivery of cells and hydrogen peroxide in separate droplets to limit their contact and keep the cells alive. More than 90% of the cells were viable in biological test gels prepared in this way. A number of complex test structures could also be grown from different types of cells.
“Advances in induced pluripotent stem cell technologies have made it possible for us to induce stem cells to differentiate in many different ways,” Makoto Nakamura says. “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.”
https://www.ncbi.nlm.nih.gov/pubmed/29226501
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