Biomechanics of Mineralized Collagens

How mineralized collagens mechanically respond when the physiological condition of bone marrow changes is discussed. The physiological condition of bone marrow has been described in terms of varying pH conditions. The molecular-level mechanism of the pH-dependent interface interaction process between collagen molecules (TC) and hydroxyapatite (HAP) crystals in mineralized collagen fibrils is studied. It is known that TC and HAP crystals are the two major nanostructural components of mineralized collagen fibrils. These fibrils are the sub-nanostructural members of the hierarchical organization of trabecular bone. When a trabecular bone breaks, it can be anticipated that the fracture process of the mineralized fibril level might begin from the TC-HAP interface. Studies suggest that the pH condition of bone-marrow fluids varies significantly during the bone remodeling process. This study uncovers the role pH plays in TC-HAP interface adhesion using a novel constant-pH molecular dynamics simulation method. Our results suggest that the interfacial adhesion between TC and HAP can be drastically reduced if the pH of the buffer environment they are submerged in is changed from 12 to 2. A pH-dependent change in the electrostatic surface potentials of bone mineral crystals and collagen molecules is responsible for such interface energy variation. This edition first published 2013