Hybrid hyaluronic acid (HA)/poly (N-isopropylacrylamide) [p(NiPAAm)] hydrogels undergo a volume phase transition as a function of temperature. Their swelling state depends also on the pH and on the ionic strength of the medium. We have synthesized the p(NiPAAm) chains with controlled molecular weight using RAFT polymerization method and to selectively couple them onto suitably modified HA chains using "click chemistry" approach. The final network is a hydrogel with controlled pore size able to shrink at physiological temperature and at different pH. This system is eligible for applications in drug delivery and in tissue engineering. IRIS study will address the diffusional behavior of water in the hydrogel meshes and will assess at molecular level the findings obtained at macroscopic scale.