(A) SAM structure including a 5’ cap, 5’ untranslated region (UTR), non-structural protein genes 1–4 from alphavirus, GOI, 3’ UTR, and PolyA tail. (B) Generalized structure of PBAE polymer, naming scheme for 4-component polymer and cartoon of assembled nanoparticle with PEG-lipid (C) DLS measurement of polymeric nanoparticles with and without SAM. (D) TEM microscopy of SAM nanoparticles. (E) Effect of PEG-lipid inclusion on NP diameter, polydispersity and zeta potential. (F) Physiochemical properties and encapsulation efficiency of the two lead nanoparticle structures (mean ± SD of three measurements).