Direct writing in three dimensions

The ability to pattern materials in three dimensions is critical for several emerging technologies, including photonics, microfluidics, microelectromechanical systems, and biomaterials. Direct-write assembly allows one to design and rapidly fabricate materials in complex three-dimensional shapes without the need for expensive tooling, dies, or lithographic masks. Here, recent advances in ink and laser writing techniques are reviewed with an emphasis on the push toward finer feature sizes. Opportunities and challenges associated with direct-write assembly are also highlighted.