Harvard bioengineers designed ultrathin, flexible mesh microelectrode arrays that integrate seamlessly into the developing neural plate of tadpole embryos. This innovative implant expands naturally with the brain’s morphological changes, allowing stable, high-resolution single-neuron electrophysiology longitudinally during embryogenesis. Such soft bioelectronics overcome previous limitations imposed by brain development dynamics, opening new avenues to study neurodevelopmental disorders and neural circuit formation at earliest stages.