Fig. 2.

Logical design of tile sets and ribbons grown from example seeds. (A) Variable-Width tile set. Tiles are grouped into blocks to emphasize logical relations, but crystals grow by addition of individual tiles. Dot color and number together indicate the logic of sticky-end hybridization, with complementary sticky-ends marked by an asterisk. (B) Additional tiles for the Copy tile set. Inset shows how correct copying of information at bit boundaries depends on preferred attachment of tiles matching two sticky ends over tiles matching just one. (C) Binary Counter tile set. The 4 tiles in the COUNT layers of the “Carry Bit 1-Block” and “Carry Bit 0-Block” are added to the Copy tile set, and the gray double tile is replaced by the beige one, whose sticky end provides the initial carry bit for each new COUNT layer. (Four tiles of the Copy tile set are repeated in the Carry Bit Blocks.) White dots mark tiles receiving a carry bit. Inset indicates the logic for the COUNT layers in the example 10011 + 1 = 10100. Each rectangle indicates the logic encoded by a pair of COUNT layer tiles; arrows indicate input and output. Sequences and diagrams for all tiles and strands are in Figs. S1–S4 and the SI Appendix; details for seeds are in Figs. S5 and S6.