Date of Completion


Embargo Period



Protein aggregation, silicone oil, protein-silicone oil interactions, interfacial protein adsorption, protein denaturation, interfacial viscoelasticity, quartz crystal microbalance, prefilled syringes

Major Advisor

Devendra S. Kalonia

Associate Advisor

Michael J. Pikal

Associate Advisor

Robin H. Bogner

Associate Advisor

Kevin M. Maloney

Field of Study

Pharmaceutical Science


Doctor of Philosophy

Open Access

Open Access


Silicone oil, a lubricant in pharmaceutical containers, has been implicated as a risk factor for protein formulations because of its tendency to cause protein aggregation and/or particulate generation. Due to a lack of published data in this area, it is not clear as to what extent this risk can be generalized across protein pharmaceuticals. A fundamental understanding of the factors that influence protein-silicone oil interactions can help in better understanding the implied risks to drug product stability. The technique of quartz crystal microbalance with silicone coated quartz crystals, mimicking the lubricated syringe surface, was used for the studies. The frequency (F) and resistance (R) signals were measured to determine the mass adsorbed and property of adsorbed layer, respectively. The effect of processing parameters on the physical stability of silicone oil coating against leaching was studied. The application of an optimized silicone amount and using silicone of higher viscosity significantly improved the coating stability. Adsorption studies for a Fc-fusion protein as a function of solution pH (3.0-9.0) at 10 and 150 mM ionic strength indicated the role of both electrostatic and hydrophobic forces in governing protein adsorption at silicone oil/water interface. The adsorption of the protein caused a small change in the R value, and was irreversible to a significant extent. This rigidity suggested strong protein-silicone oil interactions, potentially resulting from the protein denaturation at the hydrophobic interface. The inability of the nonionic surfactants to displace the adsorbed protein, when studied in sequential mode, supported this argument. However, surfactants were effective in reducing the interfacial protein adsorption when present as pre-adsorbed species. The total mass adsorbed at silicone oil/water interface from a mixture of protein and surfactant implied the absence of surfactant binding to protein as a mechanism in affecting the interfacial protein adsorption. The lack of any measurable binding between protein and surfactant in the bulk, using dynamic surface tension studies, supported this hypothesis. The overall results demonstrated that controlling the variables related to silicone oil is important to reduce the free silicone oil in a formulation, and how favorable solution conditions could be chosen to minimize the protein-silicone oil interactions.