Optimization of Chitosan-Coated Niosomes Encapsulating Doxycycline Hyclate for pH-Responsive Drug Release

In this work, nanometric niosomes (158 ± 38 nm) presenting a narrow size distribution were obtained by a supercritical CO2-assisted process, operated at 100 bar and 40 °C. The chitosan coating of these nanovesicles was performed by testing different concentrations of chitosan (from 0.05 to 0.20 mg/mL) and acetic acid (from 0.05 to 0.20% v/v) to obtain pH-responsive chitosomes. Optimal concentrations were found equal to 0.10 mg/mL and 0.05% v/v for chitosan and acetic acid, respectively. Doxycycline hyclate, an active compound presenting antibacterial and antitumoral properties, was loaded in it, reaching an encapsulation efficiency of 83 ± 3.0%. In vitro release tests were carried out using different release media to simulate gastric, small intestine, and colonic conditions. Chitosomes showed a low drug release in gastric conditions (24.81%), whereas a 48% doxycycline release was reached in the colonic simulating medium, making chitosomes promising candidates for colonic disease treatment.