Described are devices, methods, and kits for controlled incremental filtration (CIF), as well as methods of designing CIF devices. For example, a method for CIF may modulate a concentration of particles of a desired size in a fluid. The fluid including the particles may be flowed along a flow path through a central channel to contact a plurality of gaps that fluidically couple the central channel to at least one adjacent side channel network. Flow resistance may be decreased along at least a portion of the flow path effective to modulate the concentration of particles. The method may include selecting the plurality of gaps to be larger than the particles. The method may include causing a consistent flow fraction fgap in the central channel to traverse each gap in the plurality of gaps and flow through the at least one side channel network along the flow path.
