A microfluidic chip has been developed coupling the advantages of the microfluidic technology and the microdialysis protein crystallization method allowing for accurate, fine-tuned and reversible control over the experimental parameters of the on chip crystallization. Microchips with 0.1 µL and 0.3 µL maximum volume of the protein reservoir have been developed for the on chip crystallization of proteins via microdialysis. Dialysis is based on the diffusion and equilibration of the precipitant molecules through a semi-permeable membrane. A small piece of regenerated cellulose dialysis membrane is embedded within two layers of the chip. The molecular weight cut off of the membrane can be chosen according to the molecular weight of the protein sample and the precipitant solution. Dialysis offers a kinetic trajectory that allows an extensive exploration of the phase diagram and it can be used in combination with temperature control to decouple nucleation from crystal growth, while a multitude of crystallization conditions can be screened with the same protein sample.Two model soluble proteins (Hen Egg White Lysozyme (HEWL) and Thaumatin from Thaumatococcus danielli) and four membrane proteins (AcrB from Escherichia coli, ShuA from Shigella dysenteriae, SERCA from Oryctolagus cuniculus and TmPPase from Thermotoga maritima) were crystallized on chip with the microdialysis method and used for room temperature in situ X-ray diffraction experiments. The background noise generated by the interaction of X-rays with the materials comprising the dialysis chip was evaluated, rendering the chips compatible with in situ X-ray data collection. Detailed electron density maps were produced for HEWL crystals at a resolution higher than 2 Å. Moreover, partial diffraction data sets were collected from numerous, small Thaumatin crystals and HEWL crystals grown on chip with the lipidic cubic phase (LCP) crystallization method, verifying the compatibility of the chip for in situ synchrotron serial X-ray crystallography (SSX). As expected, in the case of membrane protein targets, on chip crystallization was more challenging. However, the crystals of all four membrane proteins tested were produced on the dialysis chips. SERCA crystals diffracted close to 7 Å, which gives the best resolution so far acquired with membrane protein crystals on our chip.A platform (MicroCrys) has been developed to automate the on chip crystallization via microdialysis for investigating phase diagrams through chemical composition and temperature control. The platform contributes to the overall goal of optimizing and rationalizing protein crystallization. All the separate components of the platform are controlled by a custom-built LabVIEW software displaying a user-friendly graphical interface. Moreover, a commercial fluidic system (Elveflow) for mixing and circulating the crystallization solution has been incorporated in the platform. This fluidic system contributes to the automation of the on chip crystallization via microdialysis allowing the exchange of crystallization solutions in the fluidic channel of the chip. A qualitative study of the HEWL phase diagram was performed by nucleating, growing, dissolving and re-nucleating HEWL crystals on chip in different precipitant concentrations using MicroCrys and the pressure-driven fluidic system. Finally, a prototype for thermal regulation using the Peltier effect has been developed to couple the on chip microdialysis with temperature control. A LabVIEW program has been written for real-time acquisition, displaying and recording of the temperature value at the protein reservoir of the chip. Once, the thermal regulation system and the pressure-driven fluidic system will be integrated into the main software of the platform, MicroCrys will be a fully-automated, user-friendly platform for on chip crystallization experiments.