L. Mahadevan and Harvard colleagues have used 3D printing to replicate a folding human brain. The goal is to understand how brain folds are related to disease. While many molecular processes determine cellular events, the study shows that what ultimately causes the brain to fold is a mechanical instability associated with buckling.
A 3D gel model of a smooth fetal brain was created based on MRI images. To mimic cortical expansion, the gel brain was immersed in a solvent that is absorbed by the outer layer, causing it to swell relative to the deeper regions. The resulting compression led to the formation of folds similar in size and shape to real brains.
In humans, folding begins in fetal brains at the 20th week of gestation, and is completed at a year and a half. The number, size, shape and position of neuronal cells during brain growth lead to the expansion of the cortex (gray matter), relative to the underlying white matter. The scientists said that this puts the cortex under compression, leading to a mechanical instability that causes it to crease locally. They believe that if a part of the brain does not grow properly, or if the global geometry is disrupted, the major folds may not be in the right place, which may cause dysfunction.
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