Shape, ligand length, and polymer flexibility all play a role in the active fractional area of a nano-carrier (AFAC). For a sphere, the AFAC is defined as (L-dB)/Dc, where L is the length of the ligand, db is the binding distance between the nanoparticle and the receptor, and Dc is the diameter of the nano-carrier. For particles with equal surface area, the ligand length, binding distance, and shape affects AFAC.