When raising a building, construction workers first create a scaffold, a rough framework that mimics the structure of the completed project. As it turns out, biological engineers do the same thing when they develop technology that will enable people to repair their own damaged hearts. This week in Nature Materials, Lisa E. Freed and George C. Engelmayr, Jr. of Harvard-MIT Health Sciences and Technology describe the "accordion-like honeycombs" they've designed that can fight the effects of heart attacks or congenital heart defects — and they present an eerie video of the pulsing, beating tissues in action.Using laser microfabrication techniques, Freed and Engelmayr created a scaffold out of an elastic polymer called poly(glycerol sebacate) (PGS). Though there have been previous attempts to rebuild heart tissue in this way, their new approach has three key advantages that make it the best bet so far for broken hearts. First, they can control the stiffness of the PGS structure to match the mechanical properties of actual heart tissue. In addition, by exciting the tissue with electrical fields, they can encourage the growth of the scaffold in any direction they want. Plus, Freed and Engelmayr found that their PGS structure conformed naturally to the desired alignment of healthy cardiac cells — "the scaffold itself has an intrinsic ability to guide the orientation of cultured heart cells," says Freed. And as an added bonus, their growing structure looks really ridiculously cool: Mending broken hearts with tissue engineering [MIT] Accordion-like honeycombs for tissue engineering of cardiac anisotropy [Nature Materials] Image by G.C. Engelmayr, Jr. of MIT. Video courtesy of Macmillan Publishers Ltd.: Nature Materials, advance online publication, 02 November 2008 (doi: 10.1038/nmat2316).