Feedback Loop Replication in Cyborg Development

Aug. 29, 2012
The feedback loop so inherent to common industrial control applications is now playing a role in bioengineering as researchers develop a method for embedding networks of biocompatible nanoscale wires within engineered tissues.

The cyborg, a being that is both biological and artificial, has long been a subject of fascination in books and movies and became widely known through the “Terminator” movie series. And though real-world experimentation on this area has been ongoing for years, a major breakthrough has recently occurred—and at its core is the control feedback loop.

“In the body, the autonomic nervous system keeps track of pH, chemistry, oxygen and other factors, and triggers responses as needed,” explains Daniel Kohane, M.D., Ph.D. In developing bioengineered tissues, “we need to be able to mimic the kind of intrinsic feedback loops the body has evolved in order to maintain fine control at the cellular and tissue level.”

Kohane, who works in the Department of Anesthesia at Boston Children's Hospital, is working with Charles M. Lieber, Ph.D., at Harvard University, and Robert Langer, ScD, at the Massachusetts Institute of Technology on developing a bioengineered network that marks the first time electronics and tissue have been merged in 3D—allowing direct tissue sensing and potentially stimulation.

Their work was reported online on August 26 in Nature Materials.

The control feedback loop has proven to be one of the major challenges in developing bioengineered tissues that are able to sense what is going on (either chemically or electrically) within a tissue after it has been grown and/or implanted.

Using the autonomic nervous system as inspiration, the researchers built mesh-like networks of nanoscale silicon wires—about 80 nm in diameter. The networks were porous enough to allow the team to seed them with cells and encourage those cells to grow in 3D cultures.

“The current methods we have for monitoring or interacting with living systems are limited,” says Lieber. “We can use electrodes to measure activity in cells or tissue, but that damages them. With this technology, for the first time, we can work at the same scale as the unit of biological system without interrupting it. Ultimately, this is about merging tissue with electronics in a way that it becomes difficult to determine where the tissue ends and the electronics begin.”

Thus far, the team has successfully engineered tissues (heart and nerve cells) containing embedded nanoscale networks without affecting the cells' viability or activity. Via the networks, the researchers could detect electrical signals generated by cells deep within the engineered tissues, as well as measure changes in those signals in response to cardio- or neurostimulating drugs.

Future applications for this technology range from the development of hybrid bioengineered “cyborg” tissues that sense changes within the body and trigger responses (e.g., drug release, electrical stimulation) from other implanted therapeutic or diagnostic devices, to development of “lab-on-a-chip” systems using engineered tissues for screening of drug libraries.

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