The study investigates the impact of lipid phase structures on the efficiency of lipid nanoparticle (LNP)-mediated transfection of small interfering RNA (siRNA). Using a bottom-up rational design approach, the researchers assemble LNPs with programmable lipid phases encapsulating siRNA. Cryogenic transmission electron microscopy (cryoTEM), cryogenic electron tomography (cryoET), and small-angle X-ray scattering (SAXS) techniques are employed to characterize the lipid structures within the LNP core. The results show that inverse hexagonal structures, which are liquid crystalline in nature, enhance intracellular silencing efficiency compared to lamellar structures. The presence of inverse hexagonal phases allows for a more efficient one-step delivery mechanism, bypassing the transition from lamellar to inverse hexagonal phases upon interaction with anionic membranes. This study provides insights into the nano-bio interface and offers new avenues for the design and optimization of LNP-based RNA therapeutics.The study investigates the impact of lipid phase structures on the efficiency of lipid nanoparticle (LNP)-mediated transfection of small interfering RNA (siRNA). Using a bottom-up rational design approach, the researchers assemble LNPs with programmable lipid phases encapsulating siRNA. Cryogenic transmission electron microscopy (cryoTEM), cryogenic electron tomography (cryoET), and small-angle X-ray scattering (SAXS) techniques are employed to characterize the lipid structures within the LNP core. The results show that inverse hexagonal structures, which are liquid crystalline in nature, enhance intracellular silencing efficiency compared to lamellar structures. The presence of inverse hexagonal phases allows for a more efficient one-step delivery mechanism, bypassing the transition from lamellar to inverse hexagonal phases upon interaction with anionic membranes. This study provides insights into the nano-bio interface and offers new avenues for the design and optimization of LNP-based RNA therapeutics.