CXCR4 and cancer: Given that chemokine CXCL12 promotes CXCR4-dependent chemotaxis of cancer cells (MDA-MB-231), a compartmentalized microfluidic system that consists of two layers of PDMS channels separated by a semi-permeable membrane was developed to study CXCR4-dependent chemotaxis of cancer cells (MDA-MB-231) towards a CXCL12-producing source (Figure 5A) [60].