On arriving at the tumor site, the PEG chain was cleaved off by MMP-2, and thus liberated the RGD motif for active targeting of integrin-positive tumor cells.490 Recently, Xue et al. developed an amorphous calcium carbonate (ACC)-based nanocarrier, which was simultaneously functionalized with folate and MMP2-sheddable PEG. Here, MMP2 is linked to neoplasm.