A recent study at Harvard, published in the journal Science, found that mechanical factors play a significant role in tissue development. Learning these factors that contribute to the natural formation of tissues will not only improve our understanding of tissues, it will also improve our ability to engineer tissues in the future and improve our ability to discern developmental problems.
The walls lining the intestines are not smooth. They are covered with many tiny, finger-like protrusions, or villi, yielding a high surface area for high nutrient absorption. These villi are present in many different animals including humans, chickens, and mice. This study follows the chick’s gut from earlier embryonic stages through the gut formation.
In the beginning of gut formation, the intestine is a smooth, cylindrical tube. As the embryo matures, a outer layer of smooth muscle binds the inner regions. The inner region continues to expand, but the outer region restricts it causing the inner tube to buckle and bend back over on itself. As the embryo continues to grow, the outer layer is enhanced and strengthened, causing the inners layers to make smaller and tighter folds, eventually yielding the villi. This paper shows that without the outer muscle layer, the inner layer will continue to grow, but rather than forming villi, it just ends up with a larger circumference.
This study goes on to show that across different animals (xenopus, chick, and mouse), while the time scales and intermediate steps may vary, the constraints from the outer loop cause the buckling of the inner layer into the villi.
This research establishes that in natural formation of specific tissues—and consequently engineered tissues—mechanical factors must not be ignored.
Charli Dawidczyk is a PhD candidate in Materials Science and Engineering working in Peter Searson’s research group.