A fastener cartridge can comprise, one, a cartridge body configured to at least partially store a plurality of fasteners therein and, two, a layer of material attached to the cartridge body by a retention member. The retention member can be deactivated to release the layer from the cartridge body when a firing member is moved through the cartridge body to eject the fasteners from the cartridge body. The retention member can be deactivated at the beginning, the end, and/or at any suitable time during a firing stroke of the firing member. Certain fastener cartridges can comprise a plurality of retention members configured to releasably hold the layer to the cartridge body. In certain circumstances, the retention members can be sequentially released in order to progressively release the layer.

A fastener cartridge can comprise a cartridge body comprising fastener cavities, fasteners at least partially stored within the cartridge body, and a layer positioned over the cartridge body. The cartridge body can include a proximal end and a distal end. Similarly, the layer can include a proximal end and a distal end. The distal end of the layer can extend distally with respect to the distal end of the cartridge body. Furthermore, the layer can include a distal portion which extends distally with respect to the fastener cavities defined in the cartridge body. This distal portion can be positioned against the tissue being fastened and can flexibly support the tissue after the layer has been implanted against the tissue. The layer may include a proximal portion which extends proximally with respect to the fastener cavities which can flexibly support the tissue after the layer has been implanted.

A staple cartridge includes a plurality of staples, wherein each said staple comprises a base and a deformable leg extending from said base. The staple cartridge further includes a first region comprising a first density, a second region, and a third region comprising a density greater than said first density, wherein said third region is separable into a plurality of pieces.

A fastener cartridge can comprise a cartridge body and a layer, such as a tissue thickness compensator, for example, releasably attached to the cartridge body. The tissue thickness compensator can comprise a compressible first portion and a second support portion. The second portion can be rigid and can support the first portion when mounted thereto. The properties of the first portion and/or the second portion can be selected so as to prevent the premature deflection and release from the cartridge body. The fastener cartridge can further comprise one or more attachment portions configured to releasably hold the tissue thickness compensator to the cartridge body. The attachment portions can be configured to permit a firing member to pass therethrough. In some circumstances, the tissue thickness compensator can be configured to hold the firing member in an unfired position until a sufficient firing force has been applied to the firing member.