The first recorded human kidney transplants started in the 1950s. Other human tissues and
organs have been successfully transplanted from either cadavers or living donors, but the
demand for an organ exceeds the current availability. What if you could 3D print a human organ?

Scientists and engineers utilize 3D bioprinting for several applications. One use of 3D bioprinting
is the potential to better examine how cells organize themselves into specific shapes and form
new tissues. How many cells would you need to print a meniscus like the one in the video?
Where would they come from? Check out this blogpost to learn more!

By printing the cells into a pre-programmed structure, the cellular response can be directly observed and measured. A
second use of 3D bioprinting enables the study of the effects of existing and new drugs on living
cells. Large arrays of printed cells can be patterned and exposed to different drug concentrations
and formulations simultaneously. A third capability of 3D bioprinting is the design and comparison
of in vitro healthy and diseased living cell and tissue models, such as cancerous tumors. The
ability to 3D bioprint living models could reduce the need for animal models, which would save
time, material and money.

In extrusion-based bioprinting (EBB), bioink is dispensed from a printing chamber out of a
printing nozzle. There are several challenges that must be addressed to bioprint fully functional
organs using EBB. Cells are the basic building blocks of life, and bioink material must be
cell-friendly and support living cells before, during and after bioprinting. Often, the bioink is
designed as a printable form of extracellular matrix, or ECM. The ECM is an interactive network
that surrounds and protects the cells. This mesh is made of proteins, polysaccharides, growth
factors and cytokines. Hydrogels can contain natural components of the ECM, such as collagen
or gelatin. An ECM can be difficult to bioprint when the processing temperature may be different
from the temperature required to achieve stable cell-laden 3D structures.

For example, think about how cold gelatin filled with pineapple chunks is prepared. To mix the
fruit inside the gelatin, it must be above room temperature, say, 25°C. Next, the warmed gelatin
filled with the pineapple chunks is placed in a cold refrigerator (4°C) to solidify the fruit-filled
gelatin. If the gelatin is significantly warmed (37°C), it liquifies and the fruit may settle. The cells
are like the pineapple chunks and may be sensitive to temperature changes. The gelatin
represents the surrounding ECM material used to protect and print the living cells. A slurry
liquid-like supportive bath can be used to help stabilize sensitive bioinks.

Although cell-laden bioink can be printed into structural shapes such as lattices, tubes and more
complex shapes such as the heart, function must complement the printed structures. If a
bioprinted structure looks like a heart, does it function like one? Watch this video showing how
researchers at Carnegie Mellon University bioprint an ECM protein into a supportive bath to make
progress towards a 3D bioprinted heart.

Despite these limitations, extrusion-based bioprinting is a unique fabrication platform enabling the
controlled deposition of bioink geometry and time. Researchers are already working on printing
interesting structures with enhanced capabilities, such as a bionic ear , and even bioprinting in
space ! Although bioprinting fully functional organs using extrusion-based bioprinting is not yet
demonstrated, the bioprinting of cellular building blocks and tissue models is already possible.
Watch this TedED lesson to better understand how the human body might respond to 3D
bioprinted implanted organs or prosthetics with embedded electronics.

References from the Dig Deeper section
Lim, M. (2019, June 11). Cells as Bioinks for 3D Bioprinting. Retrieved from
http://roosterbio.blogspot.com/2019/06/cells-as-bi...

College of Engineering, C. M. (2019, August 01). Retrieved from
https://www.youtube.com/watch?v=ivWJOVRA8CQ&featur...

Online, C. (2013, May 13). Retrieved from
https://www.youtube.com/watch?v=duusG6LBWoo&featur...

(2019, April 5). Retrieved from https://cellink.com/blog/why-are-there-bioprinters...

Academic references for additional consideration:

Ozbolat, I. T., & Hospodiuk, M. (2016). Current advances and future perspectives in
extrusion-based bioprinting. Biomaterials,76 , 321-343. doi:10.1016/j.biomaterials.2015.10.076

Hospodiuk, M., Dey, M., Sosnoski, D., & Ozbolat, I. T. (2017). The bioink: A comprehensive
review on bioprintable materials. Biotechnology Advances, 35(2), 217-239.
doi:10.1016/j.biotechadv.2016.12.006