Stimulus-responsive or 'smart' polymers undergo strong conformational changes when only small changes in the environment (e. g. pH, temperature, ionic strength) occur. These changes result in phase separation from aqueous solution or order-of-magnitude changes in hydrogel size. Smart polymers are used in bioseparation and drug delivery, for the development of new biocatalysts, as biomimetic actuators, and as surfaces with switchable hydrophobic-hydrophilic properties.