Water-in-water (W/W) emulsions are droplets derived from spontaneous liquidliquid phase separation of a macromolecular solution. In biology, membraneless organelles and nuclear bodies are representative W/W emulsions, and they serve as liquid chambers to compartmentalize biomolecules and coordinate their cellular functions. Bioactive molecules and cells largely preserve their native structures and biological functions in the all-aqueous environment. Consequently, W/W emulsions are more advantageous over traditional water/oil emulsions for processing of biomolecules, and they are increasingly exploited as liquid scaffolding for patterning of cells, culture of organoids and printing of tissues. W/W interface are highly permeable to oxygen, nutrients, metabolic waste, and even living cells. To confine cells within the predesigned liquid chambers or patterns, hydrogel precursors are frequently mixed with the cell-laden droplet phase, and the subsequent gelation of the precursor immobilize cells into the hydrogel. However, the hydrogel matrix, if not degraded timely, will retard the perfusion of nutrients and fusion of cell aggregates for tissue culture. An alternative hydrogel-free cell-culture strategy is to building a semi-permeable membrane at the W/W interface that blocks the undesired migration of cells. Nutrients and metabolic wastes could still diffuse across the semi-permeable membrane to support long term culture of cells, spheroids and organoids. To form semi-permeable membranes, polymers and colloidal particles can be used as building blocks for membrane formation at the W/W interface. However, interfacial tension of W/W emulsion is several orders of magnitude lower than water/oil emulsion, leading to the weak adsorption energy and low coverage ratio of colloidal particles at the W/W interface. Consequently, microcapsules and membranes formed at the W/W interface often yields low mechanical strength. To optimize the colloidal adsorption and their stacking at the W/W interface, colloids with different shapes and surface wetting properties have been explored for stabilization of W/W emulsions. However, it is difficult to achieve simultaneously suitable mechanical strength and membrane permeability for tissue culture. The feasibility to fabricate robust and semi-permeable capsules at the W/W interface will provide new solutions to control spatial configuration of tissues, without sacrificing their interior permeability.