Traditional medical devices are solid and rigid while human bodies are soft and flexible. That mismatch in physical properties makes it hard to integrate man-made devices with the body. But that is now changing, thanks to advances in mechanical and electrical engineering, materials science, and manufacturing. This talk features some of these recent “biocompatible” devices, including a battery-free electronic “tattoo” that monitors vital signs for neonatal intensive care patients and a microfluidic sensor that helps elite athletes manage their hydration.