(679f) Evaluating Differences in the Onset of Viscoelastic Film Formation at the Air-Liquid Interface for an IgG Monoclonal Antibody and an Fc-Fusion Protein

The presence of air-liquid interfaces has been recognized to negatively impact therapeutic protein stability from bioprocessing to drug administration. As proteins are amphiphilic, they adsorb to the air-liquid interface, where they tend to partially unfold and interact, forming a viscoelastic film. In this work, a passive microrheology technique was used to evaluate how bulk protein concentration impacts film viscoelastic onset in two antibody-based biotherapeutics, an IgG monoclonal antibody (mAb) and an Fc-Fusion protein. Overall, the combination of interfacial rheology and surface activity measurements demonstrates that film development follows three stages. At the beginning, an induction period was observed, where buffer-like surface activities and viscosities were measured. Following that, a sharp increase in surface pressure and viscosity was measured, characterizing a diffusion-limited adsorption phase. Finally, as protein molecules populate the surface, both surface activity and rheology changes slow down, characterizing the rearrangement of protein molecules at the interface. For each protein modality, bulk concentration dictated the evolution of surface measurements, and whether the interface remained purely viscous or transitioned to viscoelastic film. In addition, when contrasting the two antibody types, the results suggested that film evolution relied on protein modality. Particularly, results with the Fusion protein suggested faster interfacial adsorption and resulted in the formation of a viscoelastic film at lower concentrations than the mAb studied. These findings shed light on the dynamics of protein film formation at the air-liquid interface, offering valuable insights into the stability of therapeutic proteins of different modalities.