Design and physicochemical characterization of novel hybrid SLN-liposome nanocarriers for the smart co-delivery of two antitubercular drugs

In the present work a novel hybrid system for the delivery of two first-line antitubercular drugs, rifampicin (RIF) and isoniazid (INH), was designed. In order to control the release of the drugs and improve the efficiency of conventional carriers, like liposomes or solid lipid nanoparticles (SLNs), the new systems were developed by embedding SLNs into lecithin-based liposomes through the reverse-phase evaporation method. The hybrid system was characterized and compared to SLNs and liposomes in terms of size, encapsulation efficiency, morphology, and drug release. Detailed structural data and further evidence of the successful formation of the hybrid nanoparticles were obtained by applying small-angle neutron scattering (SANS). The hybrid system displayed a particle size comparable to liposomes and a high encapsulation efficiency. Morphological results obtained by atomic force microscopy (AFM) highlighted the possible presence of SLNs into the phospholipid bilayer; this hypothesis was supported by the slower in vitro release of the hydrophilic drug INH compared to liposomes and SLNs. Moreover, scattering differences of the inner core of the nanoparticles, evidenced in the SANS analysis, further corroborated the successful formation of the hybrid carrier. These novel systems were able to release their content as expected from an efficient dosage form in a perspective of an inhaled administration, improving the stability and the drug release profile with respect to plain liposomes. The physicochemical characterization of our systems opens new avenues towards a better understanding of the formulation of vesicles encapsulating SLNs.