Development and Characterization of ZnO-Loaded Solid Lipid Nanoparticles for Oral Delivery: Physicochemical, Cytocompatibility, and Antibacterial Evaluation

Chitosan-coated solid lipid nanoparticles loaded with zinc oxide (ZnO-CS-SLNs) were developed to enhance oral zinc delivery and improve formulation performance. The nanoparticles were synthesized via a microemulsion technique and exhibited spherical morphology, an average diameter of 91.2 ± 2.8 nm, a positive zeta potential (+25 mV), and high encapsulation efficiency (90 ± 3%), quantified using ICP-OES. FTIR, DSC, and XRD analyses confirmed structural integrity and uniform ZnO distribution within the lipid matrix. FE-SEM and TEM imaging revealed homogeneous particles with no signs of aggregation. In vitro release studies conducted in simulated gastric (pH 1.2) and intestinal (pH 6.8) fluids demonstrated sustained release profiles reaching up to 93% over 24 hours, consistent with Higuchi kinetics. Cytotoxicity assays on AGS cells indicated excellent biocompatibility, with cell viability exceeding 100% across all tested concentrations. Antibacterial activity of ZnO-002 was validated against Gram-positive and Gram-negative strains using disk diffusion, MIC, and MBC assays. Accelerated stability testing over six months (40 ± 2 °C, 75 ± 5% RH) confirmed the physical and colloidal stability of the formulations. Collectively, these results support ZnO-CS-SLNs as a robust oral delivery system with multifunctional attributes and consistent in vitro performance.