A tissue thickness compensator may generally comprise a biocompatible material, a first component, and a second component, wherein the first component and second component form a reaction product to expand the tissue thickness compensator. The first component may comprise a first hydrogel precursor, the second component may comprise a second hydrogel precursor, and the reaction product may comprise a hydrogel. The reaction product may be formed in vivo and/or in situ by contacting the first component and the second component. The first component and/or second component may be encapsulated and configured to release the components when ruptured. The reaction product may comprise a fluid-swellable composition. Articles of manufacture comprising the tissue thickness compensator and methods of making and using the tissue thickness compensator are also described.