Molecular interactions of degradable and non-degradable polymers with hydroxyapatite influence mechanics of polymer-hydroxyapatite nanocomposite biomaterials

Implant materials composed of hard and soft phases (composite materials) have shown much promise for total bone replacement. Interfacial interactions between the components in these composite biomaterials affect the overall mechanical response. Here, the role of interfacial interactions on the load deformation behaviour of soft phase (polymer) have been analysed using constant velocity Steered Molecular Dynamics (v-SMD). From v-SMD simulations, it has been observed that the stiffness of polymers changes significantly when these polymers interact with the hydroxyapatite (HAP) surface. It appears that the reasons for the altered stiffness are different for non-degradable and calcium binding polymers such as polyacrylic acid (PAAc) and degradable and non-calcium binding polymers such as polycapralactone (PCL). These results indicate that mineral proximity affects the mechanical response of both polymers but differently so. The role of different pulling velocities on the load-deformation behaviour of polymers is also analysed. The pulling velocity appears to have a marginal effect on stiffness of the polymers.