Taking a cue from the structural complexity of trees and bones, engineers have created a way to 3D-print two types of steel in the same circular layer using two welding machines. The resulting bimetallic material proved 33% to 42% stronger than either metal alone, thanks in part to pressure caused between the metals as they cool together. The new method uses commonplace, relatively inexpensive tools, so manufacturers and repair shops could use it in the near term. With further development, it could potentially be used to make high-performance medical implants or even parts for space travel.