Therapeutic protein powders can be prepared by spray-drying. This process is known to result in solid particles of relatively narrow size distribution and high yield and purity [1], [2]. Additionally, the spray-drying process is rapid, semi-continuous, cost-effective, reproducible and scalable. The process transforms a liquid into dry particles by atomising the liquid feed in a hot drying gas stream [3]. One of the main advantages of spray-drying is that a wide range of formulations, including heat-sensitive materials, can be dried using this technique since the droplet surface will retain the wet-bulb temperature rather than the temperature of the hot drying gas, provided evaporation is taking place at the droplet surface. By the time the evaporation at the droplet/particle surface stops, the drying gas will already have cooled down, thus limiting the heat exposure of the formulation components to the relatively high inlet gas temperatures, and, in combination with the short process duration, making spray-drying a feasible process for heat-sensitive materials, including proteins [1], [2], [3]. While spray-drying is a well established process for small molecules, the additional challenge of ensuring protein stability of the dried product during storage currently limits its use for biopharmaceutical products [2], [4]. A major concern during the spray-drying process is the entire or partial unfolding of proteins due to their high susceptibility to migrate to the air-liquid interfaces where the surface energies can cause the protein to expose hydrophobic regions, resulting in facilitated protein-protein interactions and ultimately aggregation [5]. In order to prevent such undesired aggregation non-ionic surfactants, for example polysorbate, are often used to prevent accumulation of protein at the air-liquid interface, as these small and more mobile surfactants will preferentially position themselves at the interfaces [6]. To put more generally, the excipients of a formulation are vital in providing stability to the protein by maintaining its native conformation during the spray-drying process.