  We developed a new mechanical model for determining the compression and shear
mechanical behavior of four different hemoglobin structures. Previous studies
on hemoglobin structures have focused primarily on overall mechanical behavior;
however, this study investigates the mechanical behavior of hemoglobin, a major
constituent of red blood cells (RBCs), using steered molecular dynamics (SMD)
simulations to obtain anisotropic mechanical behavior under compression and
shear loading conditions. Four different configurations of hemoglobin molecules
were considered: deoxyhemoglobin (deoxyHb), oxyhemoglobin (HbO2),
carboxyhemoglobin (HbCO), and glycated hemoglobin (HbA1C). The SMD simulations
were performed on the hemoglobin variants to estimate their unidirectional
stiffness and shear stiffness. Although hemoglobin is structurally denoted as a
globular protein due to its spherical shape and secondary structure, our
simulation results show a significant variation in the mechanical strength in
different directions (anisotropy) and also a strength variation among the four
different hemoglobin configurations studied. The glycated hemoglobin molecule
possesses an overall higher compressive mechanical stiffness and shear
stiffness when compared to deoxyhemoglobin, oxyhemoglobin, and
carboxyhemoglobin molecules. Further results from the models indicate that the
hemoglobin structures studied possess a soft outer shell and a stiff core based
on stiffness.
