Embedding a controlled layer of hydroxyapatite on a Ti- 6 Al- 4 V substrate in superplastic condition

The scientific research in the biomedical sector has underlined the importance of going beyond the basic requirements of the biomaterials, i.e., to be bioinert and avoid the occurrence of any adverse effects once in contact with a biological environment. In fact, the next generation of biomaterials must ensure anti-bacterial and bioactive properties to, for example, accelerate the bone regrowth. Therefore, the activation of a bioinert surface implies an additional step that is generally carried out after the manufacturing process. In the present work, an alternative route is investigated and is based on the mechanical deposition of hydroxyapatite (HA) particles on a Ti- 6 Al- 4 V ELI by applying a compressive load in superplastic conditions. Embedding tests were experimentally carried out using a designed equipment interfaced with a universal Instron testing machine. The applied load and the holding time were changed over three levels according to a full factorial plan and adopting a HA powder with a controlled particles size ranging from 80 to 150 μm. Post-embedding properties were initially analyzed via optical microscopy and further deepened via scanning electron microscopy (SEM). It was demonstrated that high level of the applied load combined with prolonged holding time led to the embedding of an 18 μm uniformly thick layer of HA. The scratch tests proved that embedding in superplastic conditions could ensure a level of adhesion strength comparable to other deposition techniques.