“…and hydrogels [ 29 , 30 , 31 , 32 ]. Examined fillers include 0-dimensional “spheres” (carbon black [ 33 , 34 , 35 ], metal-oxide nanoparticles [ 36 , 37 , 38 , 39 , 40 , 41 ], quantum dots [ 42 , 43 , 44 , 45 ] et cetera), 1-dimensional “fibers” (carbon nanotubes [ 46 , 47 , 48 , 49 , 50 ], carbon nanofibers [ 51 , 52 , 53 , 54 ], carbon fibers [ 55 , 56 , 57 ]) and 2-dimensional “flakes” (graphene [ 58 , 59 , 60 , 61 ], graphene oxide [ 62 , 63 , 64 , 65 ], graphite nanoflakes etc.).…”