Scientists have dreamed of easily patching up heart tissue in the wake of heart attacks, but there are always gotchas: for example, it's no mean feat to replicate the complex structures of real tissue. However, there may be a solution in sight. Researchers have produced a 3D-printed cell patch that can heal scarred heart tissue. The team used laser-based bioprinting to fit stem cells (based on adult human heart cells) to a matrix developed around a 3D scan of heart tissue's native proteins. When those cells grew, the matrix not only replicated the structures of regular heart tissue (down to 1 micron) but started beating in sync. And the early results are very promising.