Fluidic assembly at the microscale: progress and prospects

Assembly permits the integration of different materials and manufacturing processes to increase system functionality. It is an essential step in the fabrication of useful systems across size scales from buildings to molecules. However, at the microscale, traditional grasp and release assembly methods and chemically inspired self-assembly processes are less effective due to scaling effects. Many methods have been developed for improving microscale assembly. Often these methods include fluidic forces or the use a fluidic medium in order to enhance their performance. This paper reviews basic assembly theory and modeling methods. Three basic assembly strategies (tool-directed, process-directed, and part-directed) are proposed for categorizing these methods. It then summarizes progress in using fluidic forces (surface tension, viscous) and external fields (magnetic, electric, light) to aid microscale assembly. Applications of recent advances in both continuous flow and digital microfluidics in microscale assembly are also addressed.