Long-Term Implants Need To Be Stretchy

Mechanical mismatch injures neurons each time the soft tissue moves. To prevent this, microelectronic meshes should be cushioned with hydrogels or similar materials.At cortical parenchyma, just below where webbed collagen of the arachnoid layer thickens into pia, we find many immune cells called astrocytes. This is the glia limitans.Glia limitans is a gatekeeping layer, like an army posted just inside castle gates. Nothing enters vulnerable brain tissue without the astrocytes noticing.If we put something stiff into glia limitans, the surrounding tissue pulses with heartbeats. This mismatch causes fluid shear, akin to stirring a pot of water, which astrocytes interpret as an (extremely severe) infection[1].The resulting inflammatory fallout kills surrounding neurons, and leftover scar tissue electrically insulates (blinds/mutes) electrodes.We probably can't remove astrocyte cells. The immune system is important, but also astrocytes might be involved in more than "just" immunity[2].Also, astrocytes are sensing something important! An oscillating rigid probe is like raking steel velcro across your skin all day.However, immunosuppressants do help a lot and are in fact probably required for the immediate post-insertion inflammation at this sampling density. They degrade CNS[3] wound healing in some cases, but a soft implant probably isn't catastrophically injurious.For whatever inflammatory chemicals appear, we can prevent their adhesion (so they don't stick around causing more inflammation) by using zwitterionic chemistry; I'll cover this in depth later. In short, zwitterionics prefer to be coated in water molecules than amino acids, so proteins bounce off.So implants with enough surface area (>100 mjx-math { display: inline-block; text-align: left; line-height: 0; text-indent: 0; font-style: normal; font-weight: normal; font-size: 100%; font-size-adjust: none; letter-spacing: normal; border-collapse: collapse; word-wrap: normal; word-spacing: normal; white-space: nowra