Protein nanofibrils are one-dimensional nanomaterials with excellent mechanical strength and cytocompatibility. Like natural extracellular matrix, synthesized protein nanofibrils can be organized into 3D networks that promote cell adhesion, proliferation and differentiation, revealing irreplaceable implications in tissue engineering. We have previously reported an all-aqueous approach to fabricate robust 'fibrillosomes' by cross-linking lysozyme fibrils at the W/W interface, forming two-dimensional multilayer fibril networks. However, fibrillosomes are only stable in acidic solutions (pH= 2-4), and they collapse into solid precipitates in pH-neutral solutions. To further develop a nanofibrils-coated droplet chamber for tissue culture, here we synthesized multi-arm PEG cross-linked fibril clusters as new building blocks for stabilization of W/W emulsions in pH-neutral solution. These fibril clusters are subsequently complexed with alginate to prepare robust membrane at the W/W interface, yielding thin-shelled, inflatable and semi-permeable capsules that support long-term culture of large tumor spheroids over 200 μm.