A surgically implantable and sealable delivery device that upon contact of its contents via an interface window or port therein with an organ or tissue exposes a therapeutic agent to the organ or tissue surface, allowing a controlled, selective and unidirectional diffusion of the agent into the tissue or organ. The device protects adjacent organs or tissue structures from unnecessary high levels of the delivered agent. Novel methods to deliver chemotherapeutics or bioactive agents to mammalian organs or tissues through a surgically implanted device by the way of a selective and protected diffusion mechanism are disclosed as well as method to achieve the sealing properties of the device.