A surgical stapling system comprising: a staple cartridge; an adjunct (1530, 1630, 1830) configured for use with the stapler cartridge, wherein the adjunct comprises: (a) a tissue-effecting portion comprising a first material; and (b) at least one movable attachment feature (1540a, 1540b, 1640, 1840) coupled to the tissue-effecting portion and comprising a second material different from the first material, wherein the at least one movable attachment feature (1540a, 1540b, 1640, 1840) is configured to releasably attach the tissue-effecting portion to a stapling surface of the staple cartridge, wherein the tissue-effecting portion is configured to contact tissue clamped by an end effector during closure thereof, wherein the tissue-effecting portion is further configured to be pierced and captured by staples ejected from the end effector into the clamped tissue and thereby reinforce the engagement between the ejected staples and the clamped tissue, wherein the at least one movable attachment feature (1540a, 1540b, 1640, 1840) is configured to transition between a first state in which the at least one movable attachment feature attaches the tissue-effecting portion to the stapling surface and a second state in which the at least one movable attachment feature releases the tissue-effecting portion from the stapling surface, the at least one attachment feature (1540a, 1540b, 1640, 1840) of the adjunct is aligned with a respective recess of the staple cartridge (1520, 1606, 1820) and characterised in that the second material includes a moisture-sensitive polymeric shape memory material. a staple cartridge; an adjunct (1530, 1630, 1830) configured for use with the stapler cartridge, wherein the adjunct comprises: (a) a tissue-effecting portion comprising a first material; and (b) at least one movable attachment feature (1540a, 1540b, 1640, 1840) coupled to the tissue-effecting portion and comprising a second material different from the first material, wherein the at least one movable attachment feature (1540a, 1540b, 1640, 1840) is configured to releasably attach the tissue-effecting portion to a stapling surface of the staple cartridge, (a) a tissue-effecting portion comprising a first material; and (b) at least one movable attachment feature (1540a, 1540b, 1640, 1840) coupled to the tissue-effecting portion and comprising a second material different from the first material, wherein the at least one movable attachment feature (1540a, 1540b, 1640, 1840) is configured to releasably attach the tissue-effecting portion to a stapling surface of the staple cartridge, wherein the tissue-effecting portion is configured to contact tissue clamped by an end effector during closure thereof, wherein the tissue-effecting portion is further configured to be pierced and captured by staples ejected from the end effector into the clamped tissue and thereby reinforce the engagement between the ejected staples and the clamped tissue, wherein the at least one movable attachment feature (1540a, 1540b, 1640, 1840) is configured to transition between a first state in which the at least one movable attachment feature attaches the tissue-effecting portion to the stapling surface and a second state in which the at least one movable attachment feature releases the tissue-effecting portion from the stapling surface, the at least one attachment feature (1540a, 1540b, 1640, 1840) of the adjunct is aligned with a respective recess of the staple cartridge (1520, 1606, 1820) and characterised in that the second material includes a moisture-sensitive polymeric shape memory material.