Apparatus for extracting constituents from a biological sample for concentrating a desired constituent of the biological sample, the apparatus comprising: a plurality of membrane devices, wherein each of the plurality of membrane devices comprises: a membrane having a first side, a second side, a first end and a second end, the membrane having a plurality of pores having a pore size to selectively permit one or more constituents of the biological sample to pass through the membrane from the first side to the second side while retaining other constituents of the biological sample at the first side; an input chamber having an inlet proximate to the first end and an outlet proximate to the second end, the input chamber configured at the first side of the membrane to permit (a) a tangential flow of the biological sample along a first surface of the membrane at the first side from the inlet to the outlet, and (b) a trans-membrane passing of the one or more constituents of the biological sample from the first side to the second side; an output chamber configured at a second surface of the membrane at the second side and configured to receive the one or more constituents of the biological sample that pass through the membrane ; and a pressure source coupled to the inlet of the input chamber , wherein the plurality of membrane devices are collectively configured to isolate a desired passband of constituents of the biological sample, characterized in that each membrane device further comprises an additional pressure source coupled to the outlet of the input chamber and configured to induce the tangential flow of the biological sample along the first surface of the membrane , wherein the tangential flow is a reciprocating flow. a membrane having a first side, a second side, a first end and a second end, the membrane having a plurality of pores having a pore size to selectively permit one or more constituents of the biological sample to pass through the membrane from the first side to the second side while retaining other constituents of the biological sample at the first side; an input chamber having an inlet proximate to the first end and an outlet proximate to the second end, the input chamber configured at the first side of the membrane to permit (a) a tangential flow of the biological sample along a first surface of the membrane at the first side from the inlet to the outlet, and (b) a trans-membrane passing of the one or more constituents of the biological sample from the first side to the second side; an output chamber configured at a second surface of the membrane at the second side and configured to receive the one or more constituents of the biological sample that pass through the membrane ; and a pressure source coupled to the inlet of the input chamber , wherein the plurality of membrane devices are collectively configured to isolate a desired passband of constituents of the biological sample, characterized in that each membrane device further comprises an additional pressure source coupled to the outlet of the input chamber and configured to induce the tangential flow of the biological sample along the first surface of the membrane , wherein the tangential flow is a reciprocating flow. <EOS>