Because adult heart cells have almost no capacity for replication, muscle damage caused by a heart attack is largely irreparable, causing life-long heart weakness. Certain microRNAs – small, gene-regulatory molecules – have been shown to encourage heart cell replication and improve heart function in mice. But because RNAs degrade rapidly after injection, repeated treatments are necessary for them to be effective. To sustain microRNA activity for longer, scientists have now engineered a novel microRNA-containing hydrogel (a mix of polymers and water) that acts like a liquid as it passes through the syringe needle, but returns to a firm gel state once injected into the heart. As such, the microRNAs are stuck in place, protected by the gel and are released slowly as the gel degrades. Indeed, a single injection has been show to sustain heart cell replication (red dots) in mice for two weeks and improve heart function within a month.
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