One of the key challenges for nucleic acid therapeutics is their delivery into cells. The embedding of nucleic acids in liposomal nanoparticles is often chosen for this purpose - a proven approach, which, however, still leaves open wishes with regard to uptake efficiency and cell/tissue specificity. WP4 applies defined test systems in which molecular libraries of carrier sequences or chemical modifications are iteratively investigated and developed for different applications (siRNA, mRNA, different organs and application routes).