Surface Tension and Self-association Properties of Aqueous Polysorbate 20 HP and 80 HP Solutions: Insights into Protein Stabilisation Mechanisms

Abstract

Polysorbates 20 and 80 are the most used surfactants for the development of parenteral protein formulations, because of their beneficial safety and stabilisation profile. Although, showing excellent stabilisation properties, the stabilisation mechanism(s) of these surfactants for aqueous protein formulations are still unclear. Different stabilisation models have been discussed in the literature, among them the possible formation of protein-surfactant micelle complexes. This study focusses on the determination of the self-association properties of compendial grade polysorbate 20 HP (PS 20 HP) and polysorbate 80 HP (PS 80 HP) with regard to the formed micelle size (by dynamic light scattering, DLS), the concentration upon which the surfactant molecules self-associate (cmr, critical micelle concentration range) to form micelles, and the related surface tension. Surface tension and micelle size were determined as a function of temperature, as well as composition of the formulation (presence of a buffer salt and influence of ionic strength). The critical micelle concentration range values (cmr) at 25 °C are between 15–75 μM for PS 20 HP, but considerably lower for PS 80 HP with 7–16 μM, depending only slightly on the formulation composition. With increasing temperature, the cmr decreases slightly. PS 80 HP forms larger micelles (Rh = 4.5 nm) compared with PS 20 HP (Rh = 3.5 nm) (25 °C). The temperature dependency of the micelle size is more pronounced for PS 80 HP. Based on these results, the suggested stabilisation mechanism, especially for antibody formulations, by the formation of antibody-polysorbate micelle complexes, is critically discussed, and the current study shows that this stabilisation mechanism is not likely, for commonly used monoclonal antibody formulations.