Study of HVOF-sprayed hydroxyapatite/titania graded coatings under in-vitro conditions

Abstract

The present study concentrates on the bioactive behavior of HVOF-sprayed HAp/TiO2 graded coatings on a Ti-6Al-4V alloy. In-vitro bioactivity was evaluated by immersing graded coating samples in Hank’s solution at body temperature up to 28 days. Natural in-vitro bioactivity of the graded coatings was compared with in-vitro electrochemical analysis also performed for 28 days. Potentiodynamic polarization, open circuit potential, linear polarization resistance, and electrochemical impedance spectroscopy measurements in Hank’s solution, at body temperature, were performed to study the interaction of the HVOF-sprayed HAp/TiO2 graded coating with the simulated body fluid. Electrochemical in-vitro data of graded coatings were compared with those from an uncoated Ti-6Al-4V alloy. Graded coatings presented a rapid interaction with simulated body fluid during the first 4 days of immersion. The interaction between HAp/TiO2 graded coating and simulated body fluid led to the formation of a bone like-apatite layer on the top surface of the graded coating. This layer was not observed on the surface of the Ti-6Al-4V alloy. The growing kinetics of the apatite layer on the top surface of the graded coatings varied on time and provided useful information for future in-vivo studies focused on studying medical healing times. From a bioactive standpoint, the present study shows the advantages that a HVOF-sprayed HAp-based coating architecture has over an un-coated Ti-6Al-4V alloy, and how it represents a step forward in the development of bioactive coatings for implant technology.

Keywords

• Graded coating
• In-vitro behavior
• Hydroxyapatite
• Electrochemistry
• Thermal spray