Polymer-incorporated liposomes were prepared from preformed liposomes and a cholesterol-functionalized poly(acrylic acid) additive via a simple drop-in procedure. These modified liposomes possess surface-active carboxylate groups that can be cross-linked with telechelic 2,2'-(ethylenedioxy)bis(ethylamine) linkers, resulting in polymer-caged liposomes (PCLs) that are highly stable and have tunable pH-sensitive responses.