Molecular Dynamic Simulations of Interactions between Non-collagenous Proteins and Hydroxyapatite Crystal in Bone
Inside the bone, lamellae is a sheet-like structure that represents the major ultrastructural features of bone. Previous studies suggest that lamellae are comprised of mineralized collagen fibrils embedded in an extrafibrillar matrix, which consists of carbonated apatite (or hydroxyapatite) crystals and non-collagenous proteins (NCPs). NCPs in bone are a heterogeneous group of matrix proteins dispersed throughout the bone matrix. NCP at nanoscale interfaces in bone is less than 2-3 % by weight still contributes more than 30 % in fracture toughness. Particularity, the amalgamation of various NCP acts as a naturally occurring glue to interact with minerals to form strong bonds in the interface. Therefore, the mechanism of the interfacial interaction between the mineral matrix and NCPs greatly contributes to the mechanical behavior of bone. However, the mechanistic understanding of the interfacial interactions at the atomic level is still lacking. In this thesis, using all-atom molecular dynamics simulation, we studied the interactions between minerals and two important types of NCP: Osteocalcin and Osteopontin. We identified the key interaction sites on the proteins and calculated the bonding strength in both normal and shear loading modes. In addition, we also explored the structure of another important type of NCP: Glycosaminoglycans(GAGs) which are part of proteoglycans and could absorb an enormous amount of water, thus greatly influence the interfacial strength.