Rheological and adhesive properties of new thermoresponsive hyperbranched poly[ethylene oxide-b-propylene oxide-b-ethylene oxide]

Hydrogels are promising platforms for drug delivery, primarily due to the fact that many desirable physicochemical properties can be simultaneously conferred to such systems. In this respect thermoresponsive hydrogels are of interest. The adhesive and rheological properties of new hydrophilic thermoresponsive polymers are based on hyperbranched block copolymers of ethylene oxide and propylene oxide, EG35 and EG 40. EG 40 is constituted by the polycondensation of dihydroxytelechelic POE-PPO-POE triblocks linked together via carbanate, urea, allophanate and biuret bridges. The structure of EG35 is similar to EG40 if one accepts that EG35 exhibits acidic pendant groups. Oscillation stress sweep and creep recovery tests showed that EG35 and EG40 hydrogels were characterized by a remarkable elasticity. Temperature sweep tests and studies of the variation of viscosity at increasing temperatures have also proved the thermogelling character of these hydrogels. The gelling temperature was in the range of 30-37 °C. Furthermore, the adhesiveness of these hydrogels was shown to depend simultaneously on the intensity of the interfacial interactions developed between the hydrogel and the adhesion substrate, and the mechanical behavior of the hydrogel under mechanical solicitation. The mucoadhesion of the two hydrogels depended strongly on the temperature. Very interestingly, at 37 °C, thus over the gelling temperature, they exhibited considerable mucoadhesivity on rat intestinal mucosa compared to Carbopol 974P hydrogels, which were used as a positive control for mucoadhesion. These data suggested that EG35 and EG40 could be promising polymers for pharmaceutical applications, and particularly EG35, which had a considerable adhesiveness and a remarkable elasticity compared to Carbopol 974P.