NANOTUBULAR TITANIUM OXIDE LAYERS FOR ENHANCEMENT OF BONE-IMPLANT BONDING AND BIOACTIVITY

Titanium and titanium alloys are frequently used in orthopaedic implants in load bearing situations because they possess favourable properties, such as a good ductility, tensile and fatigue strength, modulus of elasticity matching that of bones, low weight, and good biocompatibility. The drawback of Ti implants is their poor osseointegration and osteoconductive properties. The present paper describes the techniques to improve the bioactivity of titanium and enhance the bone-implant bonding ability by the electrochemical anodization to fabricate titania nanotube arrays (TiO₂). The naturally formed oxide layer has bio-inert character and does not readily form a strong interface with surrounding tissue. It has been proved that osseointegration of titanium implants can be improved by rough surfaces of Ti implants [1,2]. The nanotubular surface enhances adhesion, growth and differentiation of the cells. The nanotubular arrays increase the roughness of titanium implants on the nanoscale, providing the surface similar to that of a human bone. Bone-forming cells tend to adhere to the surfaces that are similar to natural bone both in chemistry and roughness. Nanotubular layers provide a high surface-to-volume ratio with controllable dimensions which are able to differentiation of mesenchymal stem cells into osteoblastic cells. Moreover, the anodized nanotubular arrays on titanium surface can be used as reservoirs for drugs (anti-inflammatory, and improving bone-growth) with prolonged drug release ability. Also, there is possibility to further enhance bioactivity of titanium implant with nanotubular surface by hydroxyapatite deposition into the titania nanotubes which further promotes bone ingrowth. The application of nanotubular structures of oxide layers can be optimized taking into consideration some important parameters as osseointegration rate and interface strength determined by nanotube mean size and length.

The paper critically reviews so far investigations focused on nanooxidation of titanium and titanium alloys. The numerical model of nanotubular arrays with the use of Finite Element Method (FEM) is proposed for an assessment of the load transfer and stress distribution under applied loading which could be a critical factor when considering the described application of nanotubes.