Imagine a future in which a single drop of water holds a veritable army of living robots; in which people download software updates not for their computers, but for their bacteria; and in which specially programmed cells course through a person’s arteries, monitoring blood sugar concentrations and keeping an eye out for cholesterol buildups.

These scenarios still belong to the realm of science fiction—but implanting computer programs into living creatures may not be far away. In the past few years, scientists have taken the first steps towards creating a host of cellular robots that are programmed to carry out tasks such as detecting and cleaning up environmental pollutants, tracking down cancer cells in a body, and manufacturing antibiotics or molecular-scale electronic components. These researchers have imported notions of electrical engineering—digital logic, memory, and oscillators—into the realm of biology. Their plan: to create cells with computer programs hardwired into the DNA.

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