Oligopeptide-modified pBAEs-derived polyplexes were prepared according to previous published procedures. First polymer stock solutions were prepared by dissolving the corresponding pBAEs in DMSO at 100 mg/mL. Next, polyplexes were prepared by mixing equal volumes of nucleic acid (0.5 mg/mL) and polymer (12.5 mg/mL) in a NaOAc buffer solution (pH = 5.2, 12.5 mM) at 25:1 w/w ratio. The nucleic acid was added over the polymer solution and mixed by pipetting, followed by a 30 min incubation at 25ºC to allow the uniform formation of nanoparticles. This mixture was added to an equal volume of Milli-Q water for the nanoprecipitation of the particles. Thereafter, another volume equal volume of a solution of HEPES (20 mM) + 4 wt% sucrose was added as cryoprotector.