In conclusion, we develop an all-aqueous microfluidic approach to fabricate robust protein capsules by using fibril clusters adsorbed at the water/water interface. We show that fibril cluster better stabilize W/W emulsion than simple fibrils, and robust capsules can be prepared by complexing the fibril cluster and alginate at the W/W interface. This mild approach enables encapsulation of living cells and culture of large tumor spheroids in vitro, with great potentials to be used for cancer drug screening or 3D printing of living tissue in hydrogel-free all-aqueous multiphase environment.