Highlights  Cell spheroids are spherical aggregates best mimicking the tissue microenvironment.  Spheroid culture better recapitulates the in-vivo condition in microfluidic chips.  Microfluidics provides rapid spheroid formation with size uniformity and control.  These chips contain microwells, microstructures, droplet generators, etc.  To fabricate such chips, some design considerations must be taken into account.

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Three-dimensional (3D) cell culture systems can be regarded as suitable platforms to bridge the huge gap between animal studies and two-dimensional (2D) monolayer cell culture to study chronic diseases such as cancer. In particular, the preclinical platforms for multicellular spheroid formation and culture can be regarded as ideal in vitro tumour models. The complex tumour microenvironment such as hypoxic region and necrotic core can be recapitulated in 3D spheroid configuration. Cells aggregated in spheroid structures can better illustrate the performance of anti-cancer drugs as well. Various methods have been proposed so far to create such 3D spheroid aggregations. Both conventional techniques and microfluidic methods can be used for generation of multicellular spheroids. In this review paper, we first discuss various spheroid formation phases. Then, the conventional spheroid formation techniques such as bioreactor flasks, liquid overlay and hanging droplet technique are explained. Next, a particular topic of the hydrogel in spheroid formation and culture is explored. This topic has received less attention in the literature. Hydrogels entail some advantages to the spheroid formation and culture such as size uniformity, the formation of porous spheroids or hetero-spheroids as well as chemosensitivity and invasion assays and protecting from shear stress. Finally, microfluidic methods for spheroid formation and culture are briefly reviewed.

Three-dimensional (3D) cell culture systems can be regarded as suitable platforms to 11 bridge the huge gap between animal studies and two-dimensional (2D) monolayer cell culture to 12 study chronic diseases such as cancer. In particular, the preclinical platforms for multicellular