“…As for the material composition, both natural and synthetic materials have been employed to mimic the brain extracellular matrix (ECM). Natural polymers used for this purpose include collagen, gelatin, hyaluronic acid, agarose, alginate, fibrin, and chitosan [ 257 , [310] , [311] , [312] ]. The synthetic materials include polycaprolactone, poly- l -Lactic acid, poly-D, L-lactic-co-glycolic acid, and conductive polymers such as polypyrrole (PPy) [ [285] , [310] , [311] , [312] ].…”