A multi-scaled hybrid orthopedic implant: Bone ECM-shaped Sr-HA nanofibers on the microporous walls of a macroporous titanium scaffold

We report here, for the first time, a novel multi-scaled hybrid orthopedic implant material consisting of a macroporous Ti scaffold, whose macropores' walls have a microporous titania layer which is fully covered with nanofibers of Sr-doped hydroxyapatite (Sr-HA). The microporous titania layer is formed on and within the Ti scaffold by micro-arc oxidation, which firmly binds to the Ti substrate and contains Ca^{2 +}, Sr^{2 +} and PO ₄^{3 -} ions. It is then hydrothermally treated to form Sr-HA nanofibers. During the hydrothermal treatment, Sr-HA nanoprisms nucleate from Ca_0.5Sr_0.5TiO₃ pre-formed on the TiO ₂ and grow in length to nanofibers at the expense of Ca ^{2 +}, Sr^{2 +} and PO₄^{3 -} ions that migrate from the TiO₂. These Sr-HA nanofibers construct a network structure similar to the hierarchical organization of bone extracellular matrix (ECM), and the resulting nanofibrous surface displays a firm adhesion to substrate, superhydrophilicity and apatite-inducing ability. The induced apatite prefers to nucleate on the basal-faceted surfaces of Sr-HA nanofibers. The nanofiber-walled scaffold has a great potential for load-bearing orthotopic use.