When Feinberg removes the newly grown tissue from the incubator, it and the film of silicone it’s printed on are immobilized by the rigid glass coverslip. But as they cool, a temperature-sensitive glue that holds the silicone to the glass begins to dissolve. Feinberg has just a few minutes to cut out shapes before the silicone and tissue float free. Once they do, the heart tissue can contract, making the film to which it’s anchored start bending and twisting.
So far Feinberg has made rudimentary pumps, twisting actuators, pincers, a device that slowly swims, and another that walks along the bottom of a petri dish. A long rectangular strip, cut from the film so that the lines of cells run along its length, curls up with each contraction. Another rectangle, cut at a slight angle to the cells, coils up into a corkscrew. The narrow “tail” of a triangular piece propels the shape through the solution. The behavior of these devices can be controlled like that of a natural heart: with a pacemaker. Feinberg hooks electrical leads to the small dish holding the devices. Low-voltage bursts of electricity travel through the solution, signaling the muscle to contract.
Muscles on Drugs
A practical way to measure the effect of drugs on heart tissue is to determine how strongly treated tissue can contract. Thus, the device likely to be most useful in the short term is also one of the simplest: a long rectangular strip of tissue that bends slightly with each pulse of electricity. These devices could be used both to screen drugs meant to act on the heart and to identify drugs that may adversely affect the heart.
Because the mechanical properties of silicone are well known, it’s possible to determine exactly how much force the heart tissue is exerting by measuring how much the strip bends. If a change is observed in the amount of force the cells can exert, it’s a sign that a drug is having an effect. Parker envisions a testing system of small wells, each containing a strip of silicone and heart muscle. Such a system could be used to measure the effects of different compounds, or different concentrations of the same compound, on the heart tissue’s ability to function. The system could even be automated; Feinberg has already developed software that analyzes video of the strips and calculates changes in the amount of force the tissue exerts.
So far, the researchers have used only rat cells. Eventually, they hope to make screening tools with human cells, perhaps by first growing stem cells and then coaxing them to develop into heart cells. They also hope to make similar systems with muscle cells that line blood vessels–to test hypertension drugs, for example. For other applications, the devices will have to be made either smaller (for implantable robots) or larger (for patches that help heal damaged hearts).
Ultimately, the key to the technology may be its simplicity, which could make it easy to adapt to a range of applications. As Parker says, “We have dummy-proofed this technology so that it is easy to learn, easy to do, and eventually, easy to deploy in the clinic.”