Micro-/nano- thermosensitive microgels are paramount in Nanomedicine, as they support a multifunctional approach for diseases treatment (localization and simultaneous controlled drug delivery). A microgel particle with enhanced thermoresponsivity allows to controll the drug release via the temperature change of the environment sourrounding the particle. In this respect we have designed and characterized biodegradable, hydrophilic dextran-based microgel particles with thermoresponsive behaviour consisting in a volume phase transition, i.e. a particle volume reduction when the system is brought to physiological temperature. With this proposal we plan to study the dynamic behaviour of the solvent (water) strongly associated in the microgel particles around the volume phase transition using IRIS, a spectrometer we used successfully for several type of polymer based hydrogels.