Implantable drug delivery devices are an emerging technology and a promising alternative for controlled drug release applications. Their development has progressed considerably in recent years and affects the work of many research centers all over the world. Nowadays, efforts are converging in the realization of continuously tunable drug delivery systems able to operate independently of constant external activation. In many of these systems, drug release is controlled via concentration-based diffusion through nanofluidic membranes that regulate the delivery of drug compounds from an implantable reservoir. Such systems are suitable for many different applications in the biomedical field, especially in the management of chronic diseases where continuous ad hoc monitoring and rapid adjustment of drug doses are needed.