Cell encapsulation devices with controlled oxygen diffusion distances

Cell encapsulation devices for biological entities and/or cell populations that contain at least one biocompatible membrane composite are provided. The cell encapsulation devices mitigate or tailor the foreign body response from a host such that sufficient blood vessels are able to form at a cell impermeable surface. Additionally, the encapsulation devices have an oxygen diffusion distance that is sufficient for the survival of the encapsulated cells so that the cells are able to secrete a therapeutically useful substance. The biocompatible membrane composite is formed of a cell impermeable layer and a mitigation layer. The cell encapsulation device maintains an optimal oxygen diffusion distance through the design of the cell encapsulation device or through the use of lumen control mechanisms. Lumen control mechanisms include a reinforcing component that is also a nutrient impermeable layer, internal structural pillars, internal tensioning member(s), and/or an internal cell displacing core.