Advancing injection force modeling and viscosity-dependent injectability evaluation for prefilled syringes

The development of PFS requires a detailed understanding of the forces occurring during the drug administration process and patient's capability. This research describes an advanced mathematic injection force model that consisting hydrodynamic force and friction force. The hydrodynamic force follows the basic law of Hagen-Poiseuille but refines the modeling approach by delving into specific properties of drug viscosity (Newtonian and Shear-thinning) and syringe shape constant, while the friction force was accounted from empty barrel injection force. Additionally, we take actual temperature of injection into consideration, providing more accurate predication. The results show that the derivation of the needle dimension constant and the rheological behavior of the protein solutions are critical parameters. Also, the counter pressure generated by the tissue has been considered in actual administration to address the issue of the inaccuracies of current injection force evaluation preformed in air, especially when the viscosity of the injected drug solution is below 9.0 cP (injecting with 1 mL L PFS staked with 29G ½ inch needle). Human factor studies on patients' capability against medication viscosity filled the gap in design space of PFS drug product and available viscosity data in very early phase.