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Human skin is a special material: It needs to be flexible, so that it doesn't crack every time a user clenches his fist. It needs to be sensitive to stimuli like touch and pressure—which are measured as electrical signals, so it needs to conduct electricity. Crucially, if it's to survive the wear and tear it's put through every day, it needs to be able to repair itself. Now, researchers in California may have designed a synthetic version—a flexible, electrically conductive, self-healing polymer.