Phys. Rev. X 6, 031001 (2016)

Credit: HTTP://CREATIVECOMMONS.ORG/LICENSES/BY/3.0/

Optogenetics and lithography has been used to create concentric ring-like patterns of cells that act as optically controlled natural oscillators for electrical waves. A team of scientists from Harvard University and the Howard Hughes Medical Institute engineered a human embryonic kidney (HEK) cell line with four transgenic components — an inward rectifier potassium channel (Kir2.1), a voltage-gated sodium channel (Nav1.5), a blue light-activated channelrhodopsin (CheRiff) and a red light-excited fluorescent voltage indicator (QuasAr2). On stimulation with blue light, unidirectional electrical waves are excited in rings of 2, 3 or 4 mm diameter that were created by using soft lithography to encourage cell growth in annular patterns. These waves serve as a topological bit of information with data stored in the direction of electrical circulation. Importantly, the wave can be stopped or the direction reversed by illumination with a bar of light crossing the ring. Tests with oscillations in concentric rings indicate that these cellular ring oscillators will run stably in excess of 2 hours, and that the oscillation frequency drifts by less than 5 Hz from a value of around 2.3 Hz.