(a) Automatically embedded charge marks on the atoms’ surfaces in the CAD model. (b) Charged marks in the 3D printed model. (c) Paint used to color a partially negatively charged atom. (d) Wiping paint from the surfaces. (e) Charged marks remained colored after wiping the paint. (f) The heat map of electrostatic energy generated for a 3–piece chain consisting of one negatively charged side chain (GLU) and one positively charged side chain (LYS), at pH = 7, flexible via two main chain angles of θ1 and θ2; Different levels of electrostatic energy for relatively (g) medium, (h) small, and (i) large distances of the two regions in which the opposite charges are concentrated.