Biologists Grow Living Circuits

PORTLAND, Ore. -- Genetic engineering takes cells and alters their genes so they perform functions different from what nature originally intended. A new trend uses circuitry to re-engineer the cell. These biological circuits "wire" naturally occurring cells into a circuit that performs a new function, such as filling in for the dopamine-generating cells destroyed by Parkinson's disease.

"Our ultimate goal, many years from now, is complex medical applications, such as injection of a circuit into the bloodstream that looks for cancer cells and, when it finds one, injects a drug," Domitilla Del Vecchio, a professor at MIT, told EE Times. "Such a circuit would need a sensor, a computer, and an actuation component to inject the drug, and those are the kinds of components we are working on today."

Yeast cells (middle) are wired together like electronic components, but they communicate, not with electrical wires, but with chemicals that only plug into cells with the proper receptor. (Image: MIT)

Other possible applications include synthetic biological circuits that measure glucose levels constantly for diabetic patients and then automatically release insulin when it is needed.

The design process for such biocircuitry is slow and arduous compared with designing electronic circuits. For one thing, the researchers are not using nerves for communication. Instead, they use the normal communication method inside a natural cell, with the "output" secreting a chemical that only affects the "input" cells that have receptors tailored to be activated by that particular chemical.

The second big slowdown is the mathematics used to model the desired circuits. The researchers cannot use simple R-L-C equations like Ohm's Law. They must use the tedious mathematics of differential equations. "Biological circuits are very nonlinear, so we have to use differential equations to model them," Del Vecchio said.

Nevertheless, the payoff will make the effort worth it, since many maladies seem immune to solution by a simple symptom-treating drug. They require a complex cure that actively senses, computes, and responds. The best way to do that, according to MIT researchers, is to create cells that perform those functions internally, rather than trying to wire together an artificial neural network, as so many others have attempted.

Left to right: Ron Weiss, professor of biological engineering; Domitilla Del Vecchio, associate professor of mechanical engineering; and Deepak Mishra, MIT graduate student in biological engineering. (Image: MIT/Brian Teague)

"Besides nerve cells, there are many types of circuitry in biological systems, such as genetic circuitry that controls the expression of genes and the cells that controls the time keeping of the organism, such as when to get up in the morning," Del Vecchio said.

So far, most of the research group's circuits have been designed to sense something, using either yeast cells (in the illustration above) or bacteria cells. "Bacteria cells are much easier to work with, because they don't have a nucleus to deal with."

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Biologists Grow Living Circuits