But its most striking feature is that such a complex yet faithful self-assembly is achieved in conditions compatible with live-cell environments. This has allowed us to achieve the in situ self-assembly of userdefined 2D and 3D DNA origamis directly in the presence of living mammalian cells, with nanostructures forming within minutes and remaining stable for several hours. The formation and presence of DNA origamis did not perturb the cell behaviour: HEK cells maintained normal growth and viability, while hiPSCs successfully formed embryoid bodies and differentiated into well-defined human cerebral organoids. While demonstrated here with DNA origamis, this approach could be extended to other DNA assemblies, such as single-stranded titles (SST), DNA nanogrids or DNA nanotubes. However, adapting these structures may require sequence optimization to fine-tune their melting temperature (Tm). For instance, DNA nanotubes have a lower Tm than DNA origamis in similar buffer conditions. As the method was functional with common cells (HEK cell line, commercially available hiPSCs) and in different formats (conventional 2D culture, 3D organoid formation), we envisage that the in situ DNA origami assembly described here is readily applicable to other cell types and tissues.