Mechanical properties and in vitro biocompatibility evaluation of TiN/TiO2 coated Ti6Al4V alloy

Abstract Production of a mechanical matched and bioactive bone substitute is important for biomedical application in bone defects repair. In this paper, as-received (AR) and solution treated (ST) Ti6Al4V was coated with PVD deposited TiN/TiO2 films. The microstructure, phase composition, adhesion, and hardness of the bioactive coatings were characterized. Except near stoichiometric (2 0 0) and (2 2 0) textured TiN phase, XRD analysis revealed that the superficial TiO2 consisted of rutile and anatase with ratio 71%-29% and 85%-15% on the surface of AR and ST samples, respectively. With SEM cross-section micrographs it was measured that the thickness of the nitride and oxide was 3.3 and 0.5 μm, respectively. The scratch test showed that the coating deposited on the treated substrate exhibited an ability to higher critical load (72.0 ± 3.16 N) as opposed to that on AR substrate (43.4 ± 1.42 N). The coating deposited on the ST substrate had higher nanohardness and elastic modulus (5.33 GPa and 145.70 GPa, respectively) than that on AR alloy (2.73 GPa and 37.70 GPa, respectively). Cell adhesion, viability, and bone mineralization of osteoblast cells were determined using adsorption, MTT assay, and microscopy. The coated samples displayed better cell attachment and cytocompatibility with no negative effects on MG63 cells. Increased cell viability by almost 100% was seen after 24 h on both coated samples relative to the bare AR alloy. After 31 days, the mineralized areas at coated ST surface were almost twice higher as opposed to the coated AR samples because of the different surface characteristics and oxide composition.