Multifunctional erythromycin-loaded liposomes: a methodological optimization for enhanced mucoadhesion, antioxidant activity, and biocompatibility

In recent years, liposomes have emerged as versatile nanocarriers for the delivery of antibacterial agents, enhancing drug pharmacokinetics in an effort to overcome antibiotic resistance. This study presents a systematic, multivariate optimization of erythromycin-loaded liposomes (ERY-liposomes) coated with chitosan oligomers (CSO), aiming for drug encapsulation into nanoscale-sized particles, while promoting mucoadhesive, antioxidant, antimicrobial, and biocompatibility attributes. Critical formulation parameters including lipid-to-drug ratio, thin-film formation conditions, hydration medium and time, liposome downsizing technique, chitosan molecular weight and concentration, as well as cryoprotectant content were comprehensively optimized via multivariate analysis. Physicochemical and structural characterization was conducted using a broad array of techniques: FTIR, ¹H-NMR, DLS, STEM, AFM, XRD, and variable temperature polarized light microscopy (POM). The optimized ERY-liposomes achieved an encapsulation efficiency of 63%, a hydrodynamic diameter of 97 nm, and a low polydispersity index (PDI < 0.1), indicative of uniform size distribution. Structural analysis revealed strong intermolecular forces among ERY, CSO and the phospholipid, resulting in densely packed vesicles incorporating the drug in an amorphous state. STEM imaging displayed spherical morphology with compact cores surrounded by a rough coating, and POM indicated enhanced thermal stability. The formulation demonstrated sustained ERY release governed by diffusion and matrix erosion mechanisms, potent antibacterial activity over 24 hours, and considerable early bactericidal activity, particularly against Gram-positive strains. Additionally, ERY-liposomes displayed pronounced scavenging activity (80% radical inhibition, EC₅₀ = 0.396 mg mL^-1 ERY), and mucoadhesive properties, as well as cytocompatibility with normal human fibroblasts. These findings indicate the advanced therapeutic potential of ERY-liposomes.