Responsive by design: self-assembled polymer systems from structure to function in medicine

Stimuli-responsive polymer assemblies possess numerous advantages for medicine because they combine the synthetic versatility of macromolecules with the specific functions of self-organized soft matter. However, the biomedical performance of these materials cannot be fully understood solely from the change in properties of the stimulus-responsive component as a response to an external trigger. The decisive variables are structural: morphology, aggregation number, membrane or core mobility, interparticle ordering, concentration-dependent phase behavior, and the kinetics with which assemblies form, exchange chains, reorganize, or disassemble. In this feature article, we view the field through a structure-to-function lens, in which pH, temperature, redox or reactive oxygen species, ionic strength, and related inputs are treated as regulators of supramolecular state rather than simple 'on-off' switches. The focus spans responsive nanomedicines and theranostic systems, the physical chemistry of block copolymer micelles and polymersomes, and the concentration-dependent rheology and ordering of medically relevant assemblies. We show in this review how progress in responsive polymer medicine increasingly depends on understanding interference among triggers, non-equilibrium self-assembly, and characterization under realistic formulation and biological conditions.