Abstract
In this paper, hydroxyapatite-carbon nanotube/titania (HA-CNT/TiO2) double layer coatings were successfully developed on titanium (Ti) substrates intended for biomedical applications. A TiO2 coating was firstly developed by anodization to improve bonding between HA and Ti, and then the layer of HA and CNTs was coated on the surface by the sol-gel process to improve the biocompatibility and mechanical properties of Ti. The surfaces of double layer coatings were uniform and crack-free with a thickness of about 7 μm. The bonding strength of the HA-CNT/TiO2 coating was higher than that of the pure HA and HA-CNT coatings. Additionally, in vitro cell experiments showed that CNTs promoted the adhesion of preosteoblasts on the HA-CNT/TiO2 double layer coatings. These unique surfaces combined with the osteoconductive properties of HA exhibited the excellent mechanical properties of CNTs. Therefore, the developed HA-CNT/TiO2 coatings on Ti substrates might be a promising material for bone replacement.
Highlights
Titanium (Ti) has been widely used to fabricate biomedical materials because it has excellent biocompatibility, corrosion resistance, and mechanical properties [1,2]
Because the mismatch of the thermal expansion coefficients of HA and Ti was alleviated by the addition of TiO2, resulting in the decreased residual stress in the coatings. These results proved that the oxidation of Ti substrate improved the attachment of HA to metal substrates, which was in agreement with the findings of Hautaniemi et al [23]
Failure occurred entirely at the Ti substrate/coating interface for the HA-Carbon nanotubes (CNTs) coating (Figure 7a), While some debris of the coatings remained on the surface of HA-CNT/TiO2 double layer coatings, which showed failure occurred between interlayer and topcoat (Figure 7b)
Summary
Titanium (Ti) has been widely used to fabricate biomedical materials because it has excellent biocompatibility, corrosion resistance, and mechanical properties [1,2]. In order to overcome this shortage, HA has been applied as a coating on metallic surface, which combined the high mechanical strength of the metal with the excellent biocompatibility and bioactivity of the ceramic and is suitable for implants in high load-bearing applications. Various methods have been adopted to form a TiO2 layer on the Ti substrate, such as anodization, thermal oxidation and the sol-gel process. Anodization has been applied to obtain a rough, porous TiO2 layer on the surface of Ti [13,14]. This method is attractive because the TiO2 layer can be controlled by adjusting the processing conditions. The bonding strength of the coatings and their in vitro biological properties were evaluated
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