For the past several years, Nenad Bursac has been trying to make muscles from scratch. A biological engineer at Duke, Bursac came close in 2015, when his lab became the first to grow functional human skeletal muscle in culture. "Functional" being the operative word. Like the muscle fibers in, say, your bicep, the tissues could contract and generate forces in response to things like electrical pulses and shots of chemicals.

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