<iframe width="560" height="315" src="https://www.youtube.com/embed/FkCzEKMhtV0" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe> See also [Wikipedia entry on microelectrodes](https://en.wikipedia.org/wiki/Microelectrode_array). #### Notes from the talk - Neurons are of the size ~20 um and 50-100 um around them there is extra cellular field potential that can be detected by electrodes - Doubling time of simultaneously recorded neurons is 6 years ![[Screenshot 2021-12-07 at 12.11.51 PM.png]] [Source](https://stevenson.lab.uconn.edu/scaling/#) ##### Three approaches to making implants - **Wire**: insulated all along except the tip. Generally tungsten or stainless steel or gold wire - **Silicon based**: microfabrication of semiconductors (silicon based) - Utah array: 2D grid of electrodes with one recording tip per shank - Michigan array: 3D grid, with multipple recording tip per shank - **Flexible, polymer based**: gold or platinum based wires coated around polyamide or parylene (that are biocompatible insulators and used in FDA approved devices). Advantage these can be microfabricated (in a fab using wafer process) and aren't stiff (so get less immune response) ![[microelectrodes.jpg]] [Source](https://go.gale.com/ps/i.do?id=GALE%7CA186517543&sid=googleScholar&v=2.1&it=r&linkaccess=abs&issn=1745834X&p=HRCA&sw=w&userGroupName=anon%7E14934525) ##### The etching process is roughly as follows ![[etching-process.jpg]] [Source](https://www.sciencedirect.com/topics/engineering/silicon-electrode) ##### Bottleneck in brain implants You can keep on increasing electrodes but powering those electrodes, processing of data received by electrodes and sending it for further actions requires microelectronics which generally becomes bulky and hence becomes a bottleneck. Microelectronics should contain: - Power supply - Neural spike detection - Amplifier (electrode currents are tiny) - Analog to digital container - Data transmission - Optional storage for debugging - Sensors like temperature, accelerometer, etc. ##### Requirements from a good implant - Able to record simultaneously from a large number of neurons spread across different brain regions - Able to reach to deeper structures of the brain (which in human brain can be up to 100 mm, while current state of the art implants only got upto 10 mm because implanting microelectrodes such deep into the brain becomes a challenge) - Minimize tissue damage while inserting - Maintain quality of recording for long period of time (as due to immune response / scarring, astrocytes surround the electrode and deteriorate the quality) - One way to prevent this scarring is to use thin and flexible microelectrodes that have less Young's modulus - Brain is highly elastic (~10 kpa) - Comparison: Silicon based electrodes: 150 gpa while polyamide / paralyene is ~5 gpa - Polyamide based electrodes have been observed to provide high quality recordings up to 1 year without any significant issue <iframe class="signup-iframe" src="https://invertedpassion.com/signup-collector" title="Signup collector"></iframe>