Fig. 2

a Structure of MCTs, which is organized in three main layers, including a proliferative outer layer, quiescent inner layer, and necrotic core. MCTs have a gradient in oxygen, carbon dioxide, and nutrient content similar to in vivo solid tumors. b MCTs formation process. Cells initially aggregate by loose bonds between integrin and ECM and then form close contact through N-cadherin-to-E-cadherin interactions. c MCTs culture methods which are categorized in two groups—scaffold-based and scaffold-free cell culture methods. Several techniques are developed in each group