Mechanistic Insights and Characteristics of Levofloxacin HCl-Loaded Solvent Exchange-Triggered Myristic-Based In Situ Forming Matrix

Abstract A solvent exchange–triggered myristic acid (MYR)-based in situ forming matrix (ISM) incorporating levofloxacin hydrochloride (Lf) was developed as a controlled drug release system for localized periodontal therapy. The formulation, composed of MYR dissolved in N-methyl-2-pyrrolidone (NMP) with optional triacetin (TRI), undergoes aqueous-induced phase inversion to form a crystalline laminar matrix. Physicochemical evaluation demonstrated low injection force (<1.2 N), tunable viscosity, and density-driven buoyancy behavior, while water tolerance and interfacial studies confirmed that TRI retarded solvent exchange and delayed matrix crystallization. Differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD) supported the retention of MYR crystallinity after matrix formation. Cross-sectional and SEM analyses revealed progressive matrix densification and increasing structural tortuosity over time, explaining the transition from initial burst release to sustained diffusion-controlled drug release. In vitro drug release exhibited dose-dependent and matrix-modulated behavior (0.25–1.5% w/w), with higher MYR content restricting diffusion and higher Lf loading enhancing concentration gradients. The controlled release characteristics directly translated into antimicrobial performance. Antimicrobial studies against Staphylococcus aureus, MRSA, Porphyromonas gingivalis, and Aggregatibacter actinomycetemcomitans demonstrated intrinsic solvent contribution, clear dose-dependent inhibition, and sustained activity for up to 7 days. Cytotoxicity evaluation in human dermal fibroblasts showed >80% cell viability in the MTT assay and >90% viable cells in the Annexin V/PI assay, with no significant increase in apoptosis under the tested conditions. Under a clinically realistic loading constraint of 1.0 mg formulation per periodontal pocket, theoretical drug concentrations (5–30 μg/mL) exceeded MIC values for key pathogens. Computational analyses further supported diffusion retardation and MYR–Lf interaction as molecular mechanisms underlying sustained release. Collectively, the MYR-based ISM platform enables tunable and sustained antimicrobial delivery through crystallization-driven matrix formation and controlled solvent exchange.