(a) Broken chicken egg in a bowl. (b) Schematic diagram of albumen-gated IZO-based synaptic transistor with two in-plane gates. (c) Albumen film spin-coated on the ITO glass substrate (d) Ttransfer curves of the device. Reprinted with permission from Ref. [82]. Copyright 2016, Nature Publishing Group. (e) Schematic illustration of in-plane double-gate EDLT with CNF film used as the gate dielectric. A picture of the CNF hydrogel is given on the right. Reprinted with permission from Ref. [42]. Copyright 2017, John Wiley & Sons. (f) Freestanding synaptic transistors fabricated on solution-processed chitosan membranes. Reprinted with permission from Ref. [83]. Copyright 2015, John Wiley & Sons.