Innovative evaluation of topical simvastatin using 3D printed Franz-type cells and rheological testing

Simvastatin (SIM), a commonly used lipid-lowering drug, exhibits pleiotropic effects with potential for dermatological applications. This study aimed to analyze the <i>in vitro</i> release and rheological properties of SIM from three extemporaneously prepared topical formulations. Formulations were prepared from commercially available SIM tablets. A structured risk assessment confirmed the low-risk profile of these preparations. SIM content and dissolution profiles were evaluated using high-performance liquid chromatography (HPLC). <i>In vitro</i> release testing was conducted using vertical diffusion cells fabricated by using fused deposition modeling (FDM) technology of 3D printing with polylactic acid (PLA). The cream demonstrated the most favorable release characteristics, while the ointment exhibited the greatest resistance to rheological alteration following incorporation of powdered tablets. The 3D-printed diffusion cells ensured reproducibility and adaptability for topical product evaluation. Thixotropy was observed in all tested formulations. Overall, elastic behavior dominated, and the effect of tablet powder on viscosity and structure varied depending on the formulation base. Formulation type significantly influenced SIM release and rheological properties. The findings highlight the utility of low-cost 3D-printed diffusion systems in preclinical topical research and support further translational development of repurposed SIM formulations for skin-related indications.