“…Solution viscosity is a critical attribute for the development of high-concentration protein formulations, as an elevated viscosity (>30 cP) can significantly impact the pressure and flow in various unit operations such as filtration, ultrafiltration-diafiltration, and filling, 95 , 96 as well as limit the development of devices for drug administration (e.g., auto-injectors and pre-filled syringes). 186 From a physicochemical standpoint, it has been proposed that the presence of transient protein clusters is the root cause of high viscosity in protein solutions, which is in turn driven by protein–protein interactions. 187 , 188 As such, understanding the relationships between interactions, solution structure and solution rheology is key for establishing appropriate formulation strategies to achieve a suitable viscosity in high-concentration biotherapeutics.…”