Figure 1. A three-dimensional model of the Han sphere (Han et al. 2011).
In our search for a robust and elegant design, we were inspired by the origami sphere that Dongran Han et al. demonstrated in their 2011 Science paper "DNA Origami with Complex Curvatures in Three-Dimensional Space". The spherical design appealed to us because of its efficient use of DNA and lack of weak points--that is, instead of having edges, it only has two holes at each pole, minimizing spots where cargo can leak out. We imagined that we would be able to change the design of the Han sphere to make it an openable and closable container.
The design principles for an origami sphere (and other 3D origami with complex curvatures) employed by Han et al. are the following (see Figure 1):
- Multi-planar arrangement of parallel double helices with in-plane curvature of helices into rings, and
- Curvature across planes caused by different ring sizes and greater distance between crossovers in larger rings than in smaller rings.
Figure 2. A two-dimensional, caDNAno representation of the Han sphere.
Ultimately, the Han sphere is comprised of 24 parallel rings of helices (12 rings in each hemisphere) and is 6626 bases long.
To adapt the Han sphere to our purposes, we first had to generate a caDNAno file from diagrams provided in Han et al.'s supplementary materials. We succeeded in reconstructing the Han sphere down to the base and matched all staple strands generated by caDNAno to staple strands used by Han et al. The final caDNAno file can be found here:
Media:Sphere_match.json (see Figure 2).
Here is a list of staple sequences: