Wang tile

They used an exhaustive computer search to prove that 10 tiles or 3 colors are insufficient to force aperiodicity.

[8] This set, shown above in the title image, can be examined more closely at File: Wang 11 tiles.svg.

Wang tiles can be generalized in various ways, all of which are also undecidable in the above sense.

Culik and Kari have demonstrated aperiodic sets of Wang cubes.

[10] Mittal et al. have shown that these tiles can also be composed of peptide nucleic acid (PNA), a stable artificial mimic of DNA.

[11] Wang tiles have been used for procedural synthesis of textures, heightfields, and other large and nonrepeating bi-dimensional data sets; a small set of precomputed or hand-made source tiles can be assembled very cheaply without too obvious repetitions and periodicity.

[17] The short story "Wang's Carpets", later expanded to the novel Diaspora, by Greg Egan, postulates a universe, complete with resident organisms and intelligent beings, embodied as Wang tiles implemented by patterns of complex molecules.