Trimethyl chitosan (TMC)-coated alginate/dextran sulfate (ADS) nanoparticles were developed as mucoadhesive nanocarriers for oral insulin delivery using a Quality-by-Design strategy. In a first screening step, a two-level factorial design was applied to evaluate the influence of ADS concentration, TMC concentration, insulin concentration, and poloxamer® concentration on particle size and encapsulation efficiency. The screening design identified the ADS-TMC pair as the main formulation parameter for particle size, while TMC and poloxamer® were the most influential factors for encapsulation efficiency. In a second step, formulation optimization was performed using a three-factor, three-level Box–Behnken design in which ADS concentration, TMC concentration, and the degree of quaternization (DQ) of TMC were investigated as critical material attributes. Particle size, zeta potential, and in vitro mucoadhesion were selected as critical quality attributes. Across the Box–Behnken design, the experimental formulations showed particle sizes ranging from 316 to 1340 nm, zeta potentials between +17 and +39 mV, and mucin-binding values from 7 to 87%. Numerical optimization by Design-Expert® desirability analysis identified an optimal formulation composed of 0.096% (w/v) ADS and 0.700% (w/v) TMC with 60% DQ. The model predicted a particle size of 316.24 nm, a zeta potential of +38.43 mV, and an in vitro mucoadhesion of 87.14%. Experimental confirmation yielded values of 330.79 nm, +37.09 mV, and 84.61%, respectively, with prediction errors below 5% for all responses. In simulated gastric medium, partial insulin leakage was observed during the first 120 min, whereas cumulative insulin release reached 54% after 5 h in simulated intestinal medium. These results demonstrate the usefulness of a QbD framework combined with desirability-based optimization for defining robust formulation conditions for mucoadhesive TMC-coated ADS nanoparticles intended for oral insulin delivery.
Pessoa et al. (2026) studied this question.