Tissue engineering requires large amounts of cell spheroids [1-3]. Tissue spheroids have been actively used as 3D tumour models , tissue reconstruction and organ bioprinting . Spheroids of adherent cells can be formed using different processes for cell clustering where they adhere to each other rather than to a substrate. The current processes of cell spheroid production involve spinner culture, NASA rotary culture and non-adhesive surfaces , the hanging-drop culture  and 3D culturing in microwells . Although many techniques for tissue spheroids preparation have been reported, none of them are currently able to rapidly produce significant amounts of spheroids. Here we describe a simple and generic technique for high throughput generation of tissue spheroids based on encapsulation of dispersed adherent cells in a water-in-water Pickering emulsion stabilised by protein particles . The emulsion is formed from a cell suspension in an aqueous solution of dextran (DEX), which is dispersed in an aqueous solution of polyethylene oxide (PEO) containing protein particles. The cells are trapped in the DEX drops of a stable DEX/PEO emulsion which they prefer compared with the continuous PEO phase. Further addition of more concentrated PEO phase leads to osmotically driven shrinking of the DEX drops and compresses the adherent cells into tissue spheroids which are isolated by breaking the emulsion by dilution with a culture media. We demonstrate the method by using HEK293 fibroblasts and show that the cells preserve their viability in the spheroid generation process. This work will give researchers cheap and scalable technique for rapid preparation of similarly sized spheroids of adherent cells for bio-inks for 3D organ bioprinting applications and potentially for tumour models.
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