Optimization of a floating poloxamer 407-based hydrogel using the Box-Behnken design: in vitro characterization and in vivo buoyancy evaluation for intravesical instillation.

Intravesical instillation of a poloxamer 407 (PLX)-based hydrogel offers advantages such as thermo-sensitivity and sol-to-gel transition, but its utility is limited by urinary obstruction and insufficient bladder residence time. To overcome these obstacles, a floating PLX-hydrogel (FPH) was developed using sodium bicarbonate (BC) as a floating agent and hyaluronic acid (HA) as a gel strength modulator. The FPH composition was optimized using the Box-Behnken design with three independent variables: X [PLX concentration, 23.91%], X [BC concentration, 5.15%], and X [HA concentration, 3.49%]. The quadratic model was the best fit (desirability function, 0.623), resulting in response parameters of Y [floating time, 53.7 s], Y [gelation temperature gap, 20.3°C], and Y [duration time of gel, 396.7 min]. Rheological observations revealed the mechanical rigidity (storage modulus > loss modulus at elevated temperature) of the optimized FPH (phase transition temperature, 15.08°C). Gel erosion and drug release studies were performed using the gravimetric method; the remaining FPH fraction decreased exponentially with time, and gemcitabine release was biphasic and surface erosion-controlled. In vivo buoyancy was evaluated in rats using ultrasonography; these results were similar to those of the in vitro floating behavior. Thus, optimized FPH for intravesical instillation is a prospective option for bladder cancer treatment.