Electronic sensors monitor 3D medical tissues
Until now, the only cellular platforms that incorporated electronic sensors consisted of flat layers of cells grown on planar metal electrodes or transistors. Those two-dimensional systems do not accurately replicate natural tissue, so the research team set out to design a 3-D scaffold that could monitor electrical activity, allowing them to see how cells inside the structure would respond to specific drugs.
The researchers built their new scaffold out of epoxy, a nontoxic material that can take on a porous, 3-D structure. Silicon nanowires embedded in the scaffold carry electrical signals to and from cells grown within the structure.
"The scaffold is not just a mechanical support for cells, it contains multiple sensors. We seed cells into the scaffold and eventually it becomes a 3-D engineered tissue," says Bozhi Tian, a former postdoc at MIT and Children’s Hospital.
The team chose silicon nanowires for electronic sensors because they are small, stable, can be safely implanted into living tissue and are more electrically sensitive than metal electrodes. The nanowires, which range in diameter from 30 to 80 nanometers (about 1,000 times smaller than a human hair), can detect less than one-thousandth of a watt, which is the level of electricity that might be seen in a cell.
In the Nature Materials study, the researchers used their scaffolds to grow cardiac, neural and muscle tissue. Using the engineered cardiac tissue, the researchers were able to monitor cells’ response to noradrenalin, a stimulant that typically increases heart rate.
A 3-D reconstructed confocal fluorescence micrograph of a tissue scaffold. Source: Charles M. Lieber and Daniel S. Kohane.
Gordana Vunjak-Novakovic, a professor of biomedical engineering at Columbia University, says the work could help address a great need to engineer cells that respond to electrical stimuli, which may advance the treatment of cardiac and neurological disease.
The team also grew blood vessels with embedded electronic sensors and showed that they could be used to measure pH changes within and outside the vessels. Such implantable devices could allow doctors to monitor inflammation or other biochemical events in patients who receive the implants. Ultimately, the researchers would like to engineer tissues that can not only sense an electrical or chemical event, but also respond to it appropriately — for example, by releasing a drug. The team is now further studying the mechanical properties of the scaffolds and making plans to test them in animals.