Ask AI: Propose a step-by-step approach to design a vascularised cancer spheroid in vitro model.

1. Obtain primary cancer cell lines from a tissue culture facility. 2. Establish the cell line in a three-dimensional (3D) hydrogel scaffold. 3. Provide a suitable vascularised environment by culturing endothelial cells and/or purified proteins such as vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF), and tumour necrosis factor (TNF) in the hydrogel. 4. Monitor and ensure the ecologically and physiologically balanced environment by controlling oxygen and nutrient delivery in the hydrogel. 5. Allow the cells to self-organise into a spheroidal structure by culturing the cells in low-adhesive microplates. 6. Incubate the spheroids in a nutrient-enriched culture medium for 2–4 weeks for the cells and blood vessels to mature. 7. Test and validate the model by conducting appropriate biochemical, genetic and functional assays.