Here are the steps to print a complex organ:
- First, doctors make CT or MRI scans of the desired organ.
- Next, they load the images into a computer and build a corresponding 3-D blueprint of the structure using CAD software.
- Combining this 3-D data with histological information collected from years of microscopic analysis of tissues, scientists build a slice-by-slice model of the patient's organ. Each slice accurately reflects how the unique cells and the surrounding cellular matrix fit together in three-dimensional space.
- After that, it's a matter of hitting File > Print, which sends the modeling data to the bioprinter.
- The printer outputs the organ one layer at a time, using bioink and gel to create the complex multicellular tissue and hold it in place.
- Finally, scientists remove the organ from the printer and place it in an incubator, where the cells in the bioink enjoy some warm, quiet downtime to start living and working together. For example, liver cells need to form what biologists call "tight junctions," which describes how the cell membrane of one cell fuses to the cell membrane of the adjacent cell. The time in the incubator really pays off -- a few hours in the warmth turns the bioink into living tissue capable of carrying out liver functions and surviving in a lab for up to 40 days.
The final step of this process -- making printed organ cells behave like native cells -- has been challenging. Some scientists recommend that bioprinting be done with a patient's stem cells. After being deposited in their required three-dimensional space, they would then differentiate into mature cells, with all of the instructions about how to "behave." Then, of course, there's the issue of getting blood to all of the cells in a printed organ. Currently, bioprinting doesn't offer sufficient resolutions to create tiny, single-cell-thick capillaries. But scientists have printed larger blood vessels, and as the technology improves, the next step will be fully functional replacement organs, complete with the vascularization necessary to remain alive and healthy.