Measurement of the sol–gel transition temperatures (Tsol–gel) of the prepared in situ gelling systems

The temperature at which the prepared mucoadhesive thermosensitive in situ gels with different combinations of P407, P188 and the mucoadhesive agent turn into gel (Tsol–gel) was measured using the method described by several authors^{17, 25, 26}. This was done to select the most appropriate combination of P407, P188 and the mucoadhesive agent that can be used for incorporating the DMH loaded PEVs. This was performed by taking a 2 ml aliquot of each formulation in a test tube which was then sealed by a parafilm and placed in a thermostatically controlled water bath (Thermo Haake model SWB25, USA). The temperature of the water bath was adjusted at 20 °C and then gradually increased in increments of 3 °C (0.5 °C in the region of the sol-gel temperature). The formulae were allowed to equilibrate at each new temperature for 2 minutes. Then the gelation temperature was determined when the meniscus remain immobile by tilting the test tube 90°.