Fig. 1. Mechanism of CAPAC platform: (1) Tz-modified biopolymer is locally injected at the pathological site. (2) A TCO-modified drug (protodrug) is infused systemically. (3) The protodrug is captured by the biopolymer at the desired site through a rapid covalent reaction between Tz and TCO moieties, followed by (4) chemical rearrangement to release active drug.