Artificial hearts only kinda-sorta behave like the real thing. They pump blood, sure, but they’re typically solid blocks of machinery that are out of place in a squishy human body. Cornell University thinks it can do better, though: its scientists have developed an artificial foam heart that imitates both the functions and shape of its fleshy counterpart. The key is a new polymer that can be poured into specific shapes, and has pores that let it pump fluids. It’s not only soft and stretchable, but more efficient — you don’t need much energy to get liquids moving.