An end effector for use with a surgical instrument, said end effector comprising: a staple cartridge, comprising: a cartridge body; a plurality of staples; a longitudinal slot extending longitudinally along a length of said cartridge body, said longitudinal slot comprising a first side and a second side opposite said first side; and a cutting member slidably movable along said longitudinal slot; and an implantable assembly, comprising: a first layer; and a second layer, comprising: a first portion; and a second portion spaced apart from said first portion, wherein said first layer is attached to said first portion and said second portion, characterised in that said first portion and said second portion define a gap therebetween, and wherein said first layer is configured to bridge said gap, and wherein said first layer is comprised of a first material, and wherein said second layer is comprised of a second material different than said first material; wherein said implantable assembly can be positioned on the cartridge body such that said first portion is positioned on the cartridge body on a first side of the longitudinal slot, and said second portion is positioned on the cartridge body on a second side, opposite the first side, of the longitudinal slot; and wherein the cutting member is configured so that its movement along the longitudinal slot causes it to move through the gap of the implantable assembly to transect the first layer and thereby separate the first portion and the second portion of the second layer. a staple cartridge, comprising: a cartridge body; a plurality of staples; a longitudinal slot extending longitudinally along a length of said cartridge body, said longitudinal slot comprising a first side and a second side opposite said first side; and a cutting member slidably movable along said longitudinal slot; and a cartridge body; a plurality of staples; a longitudinal slot extending longitudinally along a length of said cartridge body, said longitudinal slot comprising a first side and a second side opposite said first side; and a cutting member slidably movable along said longitudinal slot; and an implantable assembly, comprising: a first layer; and a second layer, comprising: a first portion; and a second portion spaced apart from said first portion, wherein said first layer is attached to said first portion and said second portion, characterised in that said first portion and said second portion define a gap therebetween, and wherein said first layer is configured to bridge said gap, and wherein said first layer is comprised of a first material, and wherein said second layer is comprised of a second material different than said first material; a first layer; and a second layer, comprising: a first portion; and a second portion spaced apart from said first portion, wherein said first layer is attached to said first portion and said second portion, characterised in that said first portion and said second portion define a gap therebetween, and wherein said first layer is configured to bridge said gap, and wherein said first layer is comprised of a first material, and wherein said second layer is comprised of a second material different than said first material; a first portion; and a second portion spaced apart from said first portion, wherein said first layer is attached to said first portion and said second portion, characterised in that said first portion and said second portion define a gap therebetween, and wherein said first layer is configured to bridge said gap, and wherein said first layer is comprised of a first material, and wherein said second layer is comprised of a second material different than said first material; wherein said implantable assembly can be positioned on the cartridge body such that said first portion is positioned on the cartridge body on a first side of the longitudinal slot, and said second portion is positioned on the cartridge body on a second side, opposite the first side, of the longitudinal slot; and wherein the cutting member is configured so that its movement along the longitudinal slot causes it to move through the gap of the implantable assembly to transect the first layer and thereby separate the first portion and the second portion of the second layer.