Scientists seeking to improve stem cell-related treatment options for heart attack survivors have engineered a patch that can better integrate stem cells into viable heart tissue. The patch features an arrangement of prickly microneedles to “communicate” between the stem cells and the injured heart, a task that has not yet been accomplished in an internal organ. When tested in rats and pigs that suffered an acute heart attack, the patch promoted healing by boosting the development of heart tissue, reducing scar size and increasing cardiac functions. These results suggest this cardiac stem cell patch may be a promising form of cardiac therapy in humans, following further tests. More than 600,000 people in the U.S. suffer a heart attack each year and 36% of survivors have an increased risk of developing heart failure in the future. Stem cell therapy has been used to improve treatment options for survivors, but so far, cardiac stem cell (CSC) retention rate has been low in many delivery routes. To overcome this hurdle, Junnan Tang and colleagues created a microneedle (MN) patch for therapeutic heart regeneration. Its biocompatible needles can penetrate the skin and serve as communication channels between the patch and the heart, feeding CSCs from the patch to the injured area for repair. In a rat model of heart attack, the researchers placed a 0.5-centimeter by 0.5-centimeter MN-CSC patch containing rat CSCs directly onto the damaged area of the rat’s heart during open heart surgery. The patch treatment reduced cardiac cell death and promoted growth of myocytes – cells found in muscle tissue of the heart – as well as the development of new heart tissue. The authors further validated their device in a pig – an animal that has similar blood flow features to humans – and this test confirmed the safety and biocompatibility of the MN-CSC patch. According to Tang et al., future work should focus on less invasive ways to deliver the patch, rather than during open heart surgery.