Effect of TiO2 addition on adhesion and biological behavior of BCP-TiO2 composite films deposited by magnetron sputtering

The present investigation focuses on the deposition of biphasic calcium phosphate (BCP) and titania (TiO₂) composite films on Ti-6Al-4V substrates using radio frequency (RF) magnetron sputtering. Three different compositions such as 100% BCP, 25% TiO₂-75% BCP and 50% TiO₂-50% BCP films were fabricated, and the physical, mechanical and biological behaviors of the films were analyzed. Post deposition, the films were annealed at 700 °C for 2 h to induce the crystallinity and to study its effect on different properties. The wettability was found to be 95°(±3°) for 100% BCP, 73°(±2°) for 25% TiO₂-75% BCP and 35°(±1°) for 50% TiO₂-50% BCP films, indicating improvement in wettability with an increase of TiO₂ weight percent in the composite films. The value of critical load (L_c2) for 100 BCP film improved from 8.7 N to 14.8 N (25 TiO₂-BCP) and >19 N (50 TiO₂-BCP film), indicating improvement in bonding strength with TiO₂ addition. The fetal bovine serum (FBS) adsorption decreased from 7.11 ± 0.25 to 4.42 ± 0.17 μg/cm² with TiO₂ weight percent from 0 to 50%. Cell adhesion and proliferation significantly improved in 100% BCP, 25% TiO₂-75% BCP and 50% TiO₂-50% BCP films as compared to uncoated Ti-6Al-4V. The maximum cell proliferation was found on the surface of 50% TiO₂-50% BCP film (210.1 ± 6.5%) after 6 days of incubation. However, after annealing all the films exhibited less cell adhesion and cytocompatibility presumably due to change in composition. Globular apatite structure was observed on all modified surfaces after 7 days immersion in simulated body fluid (SBF); however, the growth rate was higher for 50 TiO₂-BCP films. All these results revealed that the addition of TiO₂ in BCP film (without annealing) is advantageous for improving the bonding strength as well as the bioactivity of implants, which can be used for long-term dental and orthopedic applications.

Mechano-tribological properties and in vitro bioactivity of biphasic calcium phosphate coating on Ti-6Al-4V

Biphasic calcium phosphate (BCP) consists of hydroxyapatite (HA) and beta-tricalcium phosphate (β-TCP). BCP is mainly used in artificial tooth and bone implants due to higher protein adsorption and osteoinductivity compared to HA alone. Although, many studies have been investigated on radio frequency (RF) magnetron sputtering of HA on Ti and its alloy, however, limited studies are available on BCP coating by this process and its bioactivity and adhesion behavior. Thus, in order to obtain a better understanding and applications of BCP films, RF magnetron sputtering is used to deposit BCP films on Ti-6Al-4V in the present study. The effect of film thickness on wettability, mechanical properties and in vitro bioactivity at a particular set of sputtering parameters are investigated. BCP film thickness of 400 nm, 700 nm and 1000 nm are obtained when sputtered for 4 h, 6 h and 8 h, respectively. Although the phase compositions are almost same for all films, the surface roughness values varies around 112-153 nm with rise in film thickness. This in turn enhances hydrophilicity in accordance to Wenzel relation as the contact angle decreases from 89.6 ± 2° to 61.2 ± 2°. It is found that the 1000 nm film possess highest micro-hardness and surface scratch resistance. No cracking of film up to scratch load of 2.3 N and no significant delamination up to load of 7.8 N are observed, indicating very good adhesion between BCP films and Ti-6Al-4V substrate. There is a great improvement in wt% apatite layer formation on all films when dipped in simulated body fluid (SBF) for 14 days. Among these, 1000 nm sputtered film results the highest increase in wt% apatite layer from 44.87% to 86.7%. The apatite layer possess small globular as well as elliptical structure are nucleated and grew on all the BCP films. Thus, sputtering of BCP films improves wettability, mechanical properties as well as bioactivity of Ti-6Al-4V, which can be applied for orthopedic implants.