A new circular-shape microfluidic network for generating gradients of multiple substances -design, demonstration and application

•An original concentration gradient generator for investigating drug synergy.•Generating spatially and temporally stable concentration gradients with a high degree of control over shapes of gradients.•Able to generate gradients of three or more substances with high flexibility in structure modification.•Assaying the sensitivities of cells to single and combined anti-cancer drugs in parallel with ease in this microfluidic chip.