The fluid dynamics of flow through microscale lattice structures is characterized for different unit cell sizes, flow angles, and flow rates. The structures consist of an octahedral-type periodic unit cell, which is formed from an interconnected pattern of self-propagating photopolymer wave guides. The periodic unit cell of each sample has a node-to-node spacing between 800 and 2400 pm and a truss member diameter between 148 and 277 pm. Water is directed through the microscale lattice structures, and the resulting pressure drop is investigated for two different flow angles and superficial flow rates between 0.5 and 4.8 L/min. Finite element analysis is used to determine pressure drop in the laminar flow regime. The results are used to develop a correlation describing friction factor as a function of flow direction, geometric characteristics, and Reynolds number. This work enables control of the fluid dynamics in microarchitected multifunctional truss materials through design and superficial flow angle. (C) 2010 American Institute of Chemical Engineers AIChE J, 57: 2636-2646, 2011