The invention provides medical device for insertion into a body cavity such as the urinary bladder, and for the release of substances into the cavity. The device includes a core and an expandable balloon surrounding the core. The balloon wall is made from an elastic permeable material. When the balloon is empty, the balloon wall is stretched and applied to a surface of the core. A valve allows introductions of one or more fluids between the wall of the balloon and the surface of the core. The invention also provides a system including the device of the invention and one or more instruments for inserting the device into the body cavity or retrieving the device from the body cavity.
