The present invention provides highly porous, biocompatible and biostable scaffold constructs for improving overall cell engraftment, survival, function and long-term viability. These scaffolds can provide mechanical protection to implanted cells, afford retrievability from a subject, and allow for both intra-device vascularization and a means to spatially distribute the cells within the device. The scaffold surface or material may be modified with one or more different adhesion proteins and optionally other biological factors for enhanced cell adherence and viability. Further, the scaffold surface or material may be modified with one or more agents with slow/sustained release characteristics to aid engraftment, survival, function or long-term viability. Implanted cells of the invention may be insulin-producing cells such as islets.