Systems and methods of microfluidic membraneless exchange using filtration of extraction outlet streams

A method for purifying blood, comprising:

• separating macromolecular blood components from whole blood from a patient's blood stream using a microporous filter, the separating including flowing the whole blood through a microfluidic channel in which the microporous filter is configured to form a portion of a wall of the microfluidic channel such that crossflow exists across the wall creating a shear rate sufficient to sweep blood cells from the surface of the microporous filter;
• wherein the microporous filter has a regular array of pores whose diameters are less than 800 nm, each pore defining non-serpentine, non-branching channels;
• wherein the microfluidic channel has a depth across the direction of flow which is between 75 and 300 microns, and a width, perpendicular to the depth, that is at least ten times the depth;
• ultrafiltering the blood components and returning ultrafiltered blood components to the patient minus some water and micromolecular components passed by an ultrafilter used for said ultrafiltering.