Osteoconductivity and Hydrophilicity of TiO(2) Coatings on Ti Substrates Prepared by Different Oxidizing Processes

Abstract

Various techniques for forming TiO(2) coatings on Ti have been investigated for the improvement of the osteoconductivity of Ti implants. However, it is not clear how the oxidizing process affects this osteoconductivity. In this study, TiO(2) coatings were prepared using the following three processes: anodizing in 0.1 M H(3)PO(4) or 0.1 M NaOH aqueous solution; thermal oxidation at 673 K for 2 h in air; and a two-step process of anodizing followed by thermal oxidation. The oxide coatings were evaluated using SEM, XRD, and XPS. The water contact angle on the TiO(2) coatings was measured as a surface property. The osteoconductivity of these samples was evaluated by measuring the contact ratio of formed hard tissue on the implanted samples (defined as the R(B-I) value) after 14 d implantation in rats' tibias. Anatase was formed by anodizing and rutile by thermal oxidation, but the difference in the TiO(2) crystal structure did not influence the osteoconductivity. Anodized TiO(2) coatings were hydrophilic, but thermally oxidized TiO(2) coatings were less hydrophilic than anodized TiO(2) coatings because they lacked in surface OH groups. The TiO(2) coating process using anodizing without thermal oxidation gave effective improvement of the osteoconductivity of Ti samples.

Figure 1

The surface SEM images, surface roughness Ra, and WCA of the samples prepared in this study.

Figure 2

The XRD patterns of the surface coatings on samples treated by (a) AZ treatment up to 100 V in 0.1 M H₃PO₄ aq., (b) AZ-TO treatment (anodized in H₃PO₄ aq.), (c) AZ treatment up to 80 V in 0.1 M NaOH aq., (d) AZ-TO treatment (anodized in NaOH aq.), and (e) TO treatment.

Figure 3

The (A) O1s, (B) P2p, and (C) Na1s XPS surface spectra of samples treated by (a) AZ treatment up 100 V in 0.1 M H₃PO₄ aq., (b) AZ-TO treatment (anodized in H₃PO₄ aq.), (c) AZ treatment up to 80 V in 0.1 M NaOH aq., (d) AZ-TO treatment (anodized in NaOH aq.), and (e) TO treatment.

Figure 4

Bone-implant contact ratio, R _B-I, of Ti samples in both (A) the cortical bone part and (B) the cancellous bone part. *P < 0.05.

Figure 5

Relationship between the WCA and R _B-I values in the cortical bone part. The symbols in closed circle correspond to the letters in Figure 4. Open circles represent the data for the sample anodized in various aqueous solutions, taken from previous work [26].