Single step synthesis and characterization of thermoresponsive hyaluronan hydrogels.

An efficient and scale-up ready single-step synthesis for the conjugation of thermoresponsive polymers to hyaluronic acid (HA) was established. Jeffamines(®) (JFM) and poly(N-isopropylacrylamide) (PNIPAM) were grafted to HA via direct amidation mediated by 1,1'-carbonyldiimidazole activation. The temperature-induced gelation of the semi-synthetic co-polymers was characterized by rheology as a function of the temperature and by differential scanning calorimetry (DSC). A HA-JFM conjugate with sol-gel transition in a physiologically relevant temperature range was identified. The grafting of PNIPAM resulted in the drastic change of the main rheological properties of native HA, revealing the hydrophobic non-covalent nature of the interactions between the thermoresponsive brushes in the gel state. Owing to the reversibility of these interactions and the sharpness of the transition, the HA-PNIPAM conjugates are suitable candidates for the incorporation of drugs, cells or ceramic materials for different biomedical applications.