Herein, we report on the development of a platform for the selective delivery of mRNA to the hard-to-transfect Activated Hepatic Stellate Cells (aHSCs), the fundamental player in the progression of liver fibrosis. Using a microfluidic device (iLiNP), we prepared a series of lipid nanoparticles (LNPs) based on a diverse library of pH-sensitive lipids. After an in-depth in vivo optimization of the LNPs, their mRNA delivery efficiency, selectivity, potency, robustness, and biosafety were confirmed. Furthermore, some mechanistic aspects of their selective delivery to aHSCs were investigated. We identified a promising lipid candidate, CL15A6, that has a high affinity to aHSCs. Tweaking the composition and physico-chemical properties of the LNPs enabled the robust and ligand-free mRNA delivery to aHSCs in vivo post intravenous administration, with a high biosafety at mRNA doses of up to 2 mg/Kg, upon either acute or chronic administrations. The mechanistic investigation suggested that CL15A6 LNPs were taken up by aHSCs via Clathrin-mediated endocytosis through the Platelet-derived growth factor receptor beta (PDGFRβ) and showed a pKa-dependent cellular uptake. The novel and scalable platform reported in this study is highly promising for clinical applications.