From the MIT Technology Review: "Engineering heart tissue presents particularly tough problems for researchers, since the heart is an active organ ... scaffolds designed for other kinds of tissues did not have the right mechanical properties for heart tissue. Heart tissue must be flexible enough to change shape as the heart contracts, but also strong enough to withstand the intense forces generated by these contractions. ... The researchers designed the scaffold to encourage cells to align themselves in the same direction to better mimic this property of natural heart muscle tissue. Using a laser cutting technique, they created a pattern of oblong holes in the polymer; the result is a flexible, honeycomb-like structure that is stiffer in one direction than another. ... just as rowers line up in one direction to propel a boat forward, 'all the heart muscle cells in a given region have to be lined up and contracting in the same direction' in order for the heart to beat efficiently. The honeycomb-like scaffold [represents] a 'substantial jump' toward that goal ... If we had a biodegradable biomaterial, which had beating heart cells, we might be able to return function to [damaged parts] of the heart."