Effect of changes in tropocollagen residue sequence and hydroxyapatite mineral texture on the strength of ideal nanoscale tropocollagen-hydroxyapatite biomaterials.

Changes in mineral texture (e.g. hydroxyapatite (HAP) or aragonite) and polypeptide (e.g. tropocollagen (TC)) residue sequence are characteristic features of a disease known as osteogenesis imperfecta (OI). In OI, different possibilities of changes in polypeptide residue sequence as well as changes in polypeptide helix replacement (e.g. 3 alpha1 chains instead of 2 alpha1 and 1 alpha2 chain in OI murine) exist. The cross section of the HAP crystals could be needle like or plate like. Such texture and residue sequence related changes can significantly affect the material strength at the nanoscale. In this work, a mechanistic understanding of such factors in determining strength of nanoscale TC-HAP biomaterials is presented using three dimensional molecular dynamics (MD) simulations. Analyses point out that the peak interfacial strength for failure is the highest for supercells with plate shaped HAP crystals. TC molecules with higher number of side chain functional groups impart higher strength to the TC-HAP biomaterials at the nanoscale. Overall, HAP crystal shape variation, the direction of applied loading with respect to the relative TC-HAP orientation, and the number of side chain functional groups in TC molecules are the factor that affect TC-HAP biomaterial strength in a significant manner.