In order to grow the blood vessels, the scientists, who recently published their results in the scientific journal Neuro Report, coated the tiny single millimeter long brains with endothelial cells, specialized blood vessel cells. These coated mini-brains were then implanted in mice for two weeks.
During the time the brains spent inside test tubes and then inside the mice, they were able to grow blood vessels and capillaries from the endothelial cells. The blood vessel network also grew deep into the organoid, and both the lab-grown brains and the blood vessels were developed using the same patient's cells.
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This marks the first time mini-brains have been vascularized, or able to sprout their own blood vessels. Previous attempts resulted in mouse blood cells entering the organoids.
"The whole idea with these organoids is to one day be able to develop a brain structure the patient has lost made with the patient's own cells," University of Calfiornia-Davis vascular neurosurgeon Ben Waldau, who was involved with the research, told Wired. "We see the injuries still there on the CT scans, but there's nothing we can do. So many of them are left behind with permanent neural deficits—paralysis, numbness, weakness—even after surgery and physical therapy."
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Waldau added that his team developed the idea for the experiment by treating a rare disorder called Moyamoya disease, a condition that involves blocked arteries at the bases of the brain, which keeps blood from reaching the organ.
"We sometimes lay a patient's own artery on top of the brain to get the blood vessels to start growing in," Waldau said. "When we replicated that process on a miniaturized scale we saw these vessels self-assemble."
The researchers hope that these results will help them develop a treatment to someday cure stroke victims as well.
At the same time, the mini-brains still have a long way to go before they reach a level similar to a mature human. At this point, the goal is to reach the tissue organization found in the second trimester of pregnancy.
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"The fact that I can look out at the world and see it as spatially organized—left, right, near, far— is all due to the organization of my cortex that reflects the regularity of the world," Koch said. "There's nothing like that in these organoids yet."