The invention relates to silk or other materials formed to have predetermined contraction/relaxation characteristics, wherein the contraction/relaxation characteristics are initiated by exposure thereof to predetermined humidity characteristics in the adjacent atmosphere. The materials may comprise a single silk fiber, a bundle of fibers of a predetermined size or diameter, a meshwork of fibers forming a predetermined configuration such as one or more sheets, bundles or other bodies. In this manner, the material can be scaled across a size range of any desired magnitude to produce predetermined force and/or displacement characteristics in association therewith.