Immobilization on membranes is going one step further in the direction of process intensification, as it implies fixing the enzyme on a material that is itself functional in the sense that it is able to perform tailored compounds separation. As in the previous section, the membrane can be used to remove products during reaction, to inject reagents in a controlled way, etc. In some cases, the membrane itself can also be chemo-catalytically active. However, prior to enzyme immobilization on a membrane, the membrane surface often needs to be functionalized or chemically modified. Indeed, appropriate membrane materials which are directly amenable to enzyme immobilization are very rare 8 .