CIEMAT 1 article published in JoVE Bioengineering Generation of a Simplified Three-Dimensional Skin-on-a-chip Model in a Micromachined Microfluidic Platform Ignacio Risueño1, Leticia Valencia1, Miguel Holgado2, Jose L. Jorcano3, Diego Velasco1,4 1Department of Bioengineering and Aerospace Engineering, Universidad Carlos III de Madrid (UC3M), 2Group of Optics, Photonics and Biophotonics (GOFB). Center for Biomedical Technology, Universidad Politécnica de Madrid, 3Division of Epithelial Biomedicine, CIEMAT, 4Instituto de Investigación Sanitaria Gregorio Marañón Here, we present a protocol to generate a three-dimensional simplified and undifferentiated skin model using a micromachined microfluidic platform. A parallel flow approach allows the in situ deposition of a dermal compartment for the seeding of epithelial cells on top, all controlled by syringe pumps.