It has been discovered recently that a range of proteins exist in the cell as liquid-like condensates and these condensates carry out essential biological functions in many systems, such as, signaling pathway, embryogenesis and RNA processing in their liquid state. It has been shown that a further liquid-to-solid transition (LST) of these condensates can lead to aberrant biology resulting cell malfunction. Thus, the kinetics and dynamics of protein phase behavior are at the heart of the onset and development of pathological protein aggregation. The previous studies have focused on the fundamentals of liquid-liquid phase separation (LLPS) of intrinsically disordered proteins in complex biological systems. However, the nucleation of pathological protein aggregates during the LST governed by physical factors remains unexplored. The present studies demonstrated that a range of biomolecular condensates can undergo a LST driven by shear force, forming beta-sheet rich nanofibrils. Moreover, an approach combining microfabrication, infrared spectroscopy and fluorescence detection was developed to map out the changes in the mechanical properties, secondary structures and thermodynamic stability of FUS (Fused in Sarcoma) condensates undergoing the LST as a function of time. These studies explored the role of physical force in the protein aberrant aggregation and characterized the protein phase behavior from a biophysical point of view.