Laser direct-write techniques for printing of complex materials

This article reviews recent developments in laser direct-write addition (LDW+) processes for printing complex materials. Various applications, ranging from small-scale energy storage and generation devices to tissue engineering, require the ability to deposit precise patterns of multicomponent and multiphase materials without degrading desirable properties such as porosity, homogeneity, or biological activity. Structurally complex inorganic materials for the successful fabrication of alkaline and lithium-based microbatteries, micro-ultracapacitors, and dye-sensitized micro solar cells are shown on various low-processing-temperature and flexible substrates using LDW+. In particular, the ability to deposit thick layers while maintaining pattern integrity allows devices produced in this manner to exhibit higher energy densities per unit area than can be achieved by traditional thin-film techniques. We then focus on more complex systems of living and biologically active materials. Patterns of biomaterials such as proteins, DNA, and even living cells can be printed using LDW+ with high spatial and volumetric resolution on the order of a picoliter or less, without compromising the viability of these delicate structures. These results provide for highly selective sensor arrays or cell seeding for tissue engineering. Finally, we review recent work on LDW+ of entire semiconductor circuits, showing the broad range of applications this technique enables.