A device for delivering a substance in situ in a body comprising at least one permeable expandable container having a first dimension and a second dimension and having contained therein the substance to be delivered; and at least one expandable particle comprising a swellable material contained within the container and capable of expanding when contacted with a fluid; whereby when the device is positioned in situ, bodily fluid permeates the container causing the at least one expandable particle contained therein to swell and the container to expand from the first dimension to the second dimension so that the device remains in situ for a period of time sufficient to achieve the desired delivery of the substance is provided.