Force-controlled release of small molecules offers great promise for the delivery of drugs and the release of healing or reporting agents in a medical or materials context. However, the systems described so far are limited in the diversity and/or quantity of the molecules released per stretching event. This is due to the difficulty in iteratively activating scissile mechanophores, as the actuating polymers will dissociate after the first activation.
Fig. 1: Elongation of the rotaxane actuator leads to the sequential release of the cargo units placed on the axle as they are pushed by the macrocycle., able to release up to five cargo units per chain. The rotaxane is built around a pillararene macrocycle, which can trigger the release of macrocycle threaded onto a C12 alkyl chain, extended on one side with a poly polymer and on the other side with the cargo-bearing oligomer .
The bulk activation of one-, three- or five-cargo rotaxanes was performed by compressing a small sample of polymers, a substantial amount of cargo release was observed in these entangled networks . The bulk activation contrasts with the solution experiments by the lower proportion of rotaxanes releasing their entire cargo load; that is to say, fewer macrocycles can reach the end of their cargo compartment.
Extended Data Fig. 1 Cartoon depiction of the force-controlled release of cargo molecules by a rotaxane actuator. Upon elongation of the rotaxane, by the intermediary of the polymer chains , the macrocycle is pulled along the cargo compartment until it reaches the first cargo molecule , which acts as a barrier as the macrocycle is unable to pass this steric obstacle without its detachment. Pulling the macrocycle further eventually triggers the release of the first cargo unit.