Figure 2.

Existing techniques to create three-dimensional in vitro tumour models. (a) An ex vivo tumour culture based on a tumour tissue section. (b) Single tumour cells embedded in hydrogel on transwell insert is one of the earliest three-dimensional models that can also characterize invasiveness. Tumour spheroids can be prepared from dissociated cells from tumour or circulating tumour cells (CTCs) by (c) the spinning mask method, (d) NASA microgravity apparatus, (e) the hanging drop method, (f) the liquid overlay method, (g) magnetic levitation after cells are incubated with magnetic nanoparticles, (h) bio-orthogonal chemistry and (i) microfluidic methods such as flow focusing, droplet microfluidics and digital microfluidics. Alternative to spheroids, three-dimensional tumour models can be fabricated by seeding cells in artificial three-dimensional matrices. (j) Cancer cells can be seeded in fabricated scaffolds. (k) Cell-embedded bioink can be printed as building blocks for tissues. (l) Microfluidics–microvascular model uses a microdevice to model a multiple tissue-type microenvironment. Adapted from [28,29].