Without such a network in place, the tissue created by engineers is dependent upon diffusion for the transport of nutrients and waste products. Diffusion, however, is a slow process, taking about 17 minutes to traverse a span of 200 microns, or about twice the thickness of a human hair. Increase that distance to an inch, and it takes close to four months for diffusion to occur. That length of time won't support cell growth, Ugaz notes.
"That's just a fundamental limit of this diffusion mechanism the timescale," Ugaz says. "If your aim is to manufacture artificial organs, you'll need a network that has the ability to supply all of the cells in a three-dimensional volume with nutrients while moving waste products out and keeping these processes going in a certain timescale.
"The way this is all accomplished [in nature] is with a type of branched network, similar to how a tree is naturally structured. There is a trunk, and distribution occurs throughout a large volume by branches of various lengths and thicknesses that emanate from that trunk. This allows transport to penetrate inside a large volume, until the distance between branches and stems is minimized. It's all really an issue of transport."
Framing the challenge in those terms, Ugaz began contemplating how such a complex architecture could be artificially mimicked. He was well aware of a phenomenon known as the Lichtenberg effect. Named after German physicist Georg Christoph Lichtenberg, the effect is responsible for the creation of a fractal pattern
|Contact: Victor Ugaz|
Texas A&M University