Figure 2.

Common techniques used to generate 3D spheroids. Hanging drop methods: Either a suspension of cells is deposited on a petri dish lid which is inverted over a petri dish (A), or in a well and passes through a micro-well to form a drop (B). Scaffold-based methods: Either cells are seeded on a hydrogel-coated petri dish (C) or they are embedded in the hydrogel and seeded in a petri dish (D). Low-adhesion/non-adherent surfaces: Cells are seeded in low-adhesion wells to form one spheroid per well (E) or on non-adherent surface coated with a hydrophobic substance to prevent cells from spreading (F). Suspension culture methods: Cells are placed in spinner flasks (G) or in bioreactor (H) and put under dynamic culture conditions. Magnetic levitation: Cells are first prepared with magnetic beads and then placed in low-adhesion plates with a magnet on the lid (I). Figure produced with Biorender.com.