Engineering 3D neuronal networks with directional endogenous neuronal plasticity pathways
The forward engineering of the structure and function of three-dimensional millimeter to centimeter scale living Neuronal Tissue Mimics (NTMs) can advance many engineering and biomedical applications. While hydrogels and 3D printing have achieved major breakthroughs in the development of cm-scale neural tissues that mimic structural morphologies in native neural networks, controlling and programming the resulting function of these NTMs have remained elusive. In this work, using human embryonic stem cell derived optogenetic neurons, we report the in-situ formation of the NTMs on a 2-dimensional micro electrode array with an intimate electrical contact between the electrodes and the tissue. These NTMs were optimized during the differentiation phase of the cells to enrich for neuronal populations that expressed receptors responsible for activating spike-timing dependent plasticity (STDP). Using an optical stimulation regiment with millisecond temporal and micrometer spatial resolution, we were able to program the otherwise omnidirectional spontaneous firing in the NTMs to demonstrate directional firing across different shapes of the NTMs. Our work can pave the way for developing cellular based computational devices, bio-processors, and biological memories.