A dual-layer coaxial hollow fiber (DLHF) bioreactor for cell immobilization developed to overcome nutrients transport limitation is presented. Cells were contained in the annular space between two coaxial hollow fibers, and nutrients were supplied by a forced convective transport from the shell side through the annular space to the lumen side. With judicious selection of the membrane materials, a low operating transmembrane pressure of 50 kPa, and using E coli as the model organism, a high cell density of 10(11) cells/mL annular space volume and a high cell viability of (up to 80%) were obtained. (c) 2005 Elsevier Ltd. All rights reserved.