Purpose <p>Mechanical, interfacial, and shear stresses encountered during development, manufacturing and transportation of biologics can compromise monoclonal antibody (mAb) stability. However, most scale-down shaking models often depend solely on orbital agitation and overlook the effect of the solid–liquid interface. To study this gap, stress conditions were applied to simulate early-stage product development and real-world transportation in this work.</p> Methodology <p>Accordingly, the aggregation profiles of Cetuximab and Tocilizumab formulations, with and without polysorbate 80 (PS80), were systematically compared after applying horizontal and orbital shaking. Protein aggregation was assessed using orthogonal techniques such as size-exclusion chromatography, dynamic light scattering, flow imaging microscopy, ultraviolet–visible spectroscopy, and visual inspection.</p> Results <p>Horizontal shaking more effectively revealed Cetuximab’s susceptibility to aggregation under mechanical and interfacial stress whereas orbital shaking conditions were not as discriminative. Furthermore, to explore the effect of vial surface chemistry on subsequent protein aggregation, Cetuximab was subjected to horizontal shaking stress using both untreated and silanized glass vials. Interestingly, hydrophobic silanized vials without surfactant resulted in increased Cetuximab aggregation compared to untreated vials. In contrast, Cetuximab with PS80 showed fewer aggregates in silanized vials than in glass vials.</p> Conclusion <p>These results underscore the value of selecting right-for-purpose agitation models and highlight the need to explore the triple interface for improving stress screening in drug product development.</p>