The Steinberg model has been used to drive computer simulations and, most recently, to print tubular structures resembling blood vessels. In 2005, Gabor Forgacs at the University of Missouri in Columbia and colleagues used spherical aggregates of ovary cells from Chinese hamsters, composed of hundreds of the same type of cell. When the cell spheres were printed in a ring formation and stacked on top of one another, they fused together within 24 hours. Forgacs also showed that when two types of cell spheres were used, they separated from each other and formed a tube with two different layers.
In a paper in Physical Review Letters, Forgacs explained that these tubes are precursors to the formation of more complicated structures, such as thick blood vessels, which are composed of two types of cells: endothelial cells line the interior wall and smooth muscle cells are on the exterior.
Understanding what printing process produces the best blood vessels is important for tissue engineering as a whole, says Vladimir Mironov, developmental biologist at the Medical University of South Carolina, who collaborates with Forgacs and Newman. If an organ is printed without a viable vascular system, Mironov says, there is no way to supply nutrients to the tissue, and it will die.
Newman and his colleagues are using animal cells such as chicken cells right now; but their goal is to do the experiments with human cells. “As a scientific tool on animal models, the late-state embryo cells are very desirable experimental models because they will teach us about all sorts of properties of tissues,” he says. One problem, of course, is that human embryonic cells are difficult to obtain and controversial to use, especially embryonic stem cells. But Newman thinks they’ll eventually be able to use less controversial adult stem cells.
Ultimately, for human organ printing, Newman believes that researchers will most likely turn to adult stem cells – cells taken from mature tissue with limited ability to become a specialized cell type -– because they have recently shown promise as an alternative to embryonic stem cells, and they are less controversial. But at the same time that biologists are smoothing out the details of the genetic contribution to development, biophysicists are figuring out the basics of self-assembly in cells. This combined effort could be the ticket to organs on demand.
Home page image courtesy of Vladimir Mironov and Gabor Forgacs.