 The area covered by the colloids can be changed by modifying the ionic strength of the colloid solution.This technique is able to create large patterned surface areas, which is necessary for tissue engineering applications.Chemical etching involves soaking the material surface in an etchant such as hydrofluoric acid (HF) or sodium hydroxide (NaOH) until the surface is etched away to a desired roughness as created by pits and protrusions on the nanometer scale.