Cell retention device

A filter comprising:

• an elongated element having a plurality of longitudinal segments, each having a plurality of axial ribs circumferentially distributed around an exterior portion thereof, the axial ribs having radial peaks and radial recessions therebetween, the elongated element being substantially nonporous, and adjacent longitudinal segments of the plurality of longitudinal segments are sealably fitted together in a stacked sequence;
• a membrane filter medium wrapped as a planar sheet around the exterior portion of the elongated element and in contact with the elongated element at only the radial peaks of the axial ribs, thereby forming a plurality of axial voids between the radial recessions and the membrane filter medium;
• a central channel extending axially through at least a portion of the elongated element and terminating in an outlet;
• and
• at least one radial channel fluidically coupling the axial voids to the central channel, whereby negative pressure at the outlet propagates through the axial voids to the membrane filter medium,
• wherein the plurality of axial ribs is interrupted by one or more annular regions between adjacent longitudinal segments of the plurality of longitudinal segments, the one or more annular regions radially recessed relative to the radial recessions of the plurality of axial ribs.