To control the three-dimensional shape of engineered tissue, researchers grow cells on tiny, sponge-like scaffolds. These devices can be implanted into patients or used in the lab to study tissue responses to potential drugs.
A team of researchers from MIT, Harvard University and Boston Children’s Hospital has now added a new element to tissue scaffolds: electronic sensors. These sensors, made of silicon nanowires, could be used to monitor electrical activity in the tissue surrounding the scaffold, control drug release or screen drug candidates for their effects on the beating of heart tissue.
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 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.
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.