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. 2016 Feb 25;11(2):e0150081.
doi: 10.1371/journal.pone.0150081. eCollection 2016.

Apatite Formation and Biocompatibility of a Low Young's Modulus Ti-Nb-Sn Alloy Treated with Anodic Oxidation and Hot Water

Hidetatsu Tanaka  1 , Yu Mori  1 , Atsushi Noro  1 , Atsushi Kogure  1 , Masayuki Kamimura  1 , Norikazu Yamada  1 , Shuji Hanada  2 , Naoya Masahashi  2 , Eiji Itoi  1
Affiliations

Apatite Formation and Biocompatibility of a Low Young's Modulus Ti-Nb-Sn Alloy Treated with Anodic Oxidation and Hot Water

Hidetatsu Tanaka et al. PLoS One. .

Abstract

Ti-6Al-4V alloy is widely prevalent as a material for orthopaedic implants because of its good corrosion resistance and biocompatibility. However, the discrepancy in Young's modulus between metal prosthesis and human cortical bone sometimes induces clinical problems, thigh pain and bone atrophy due to stress shielding. We designed a Ti-Nb-Sn alloy with a low Young's modulus to address problems of stress disproportion. In this study, we assessed effects of anodic oxidation with or without hot water treatment on the bone-bonding characteristics of a Ti-Nb-Sn alloy. We examined surface analyses and apatite formation by SEM micrographs, XPS and XRD analyses. We also evaluated biocompatibility in experimental animal models by measuring failure loads with a pull-out test and by quantitative histomorphometric analyses. By SEM, abundant apatite formation was observed on the surface of Ti-Nb-Sn alloy discs treated with anodic oxidation and hot water after incubation in Hank's solution. A strong peak of apatite formation was detected on the surface using XRD analyses. XPS analysis revealed an increase of the H2O fraction in O 1s XPS. Results of the pull-out test showed that the failure loads of Ti-Nb-Sn alloy rods treated with anodic oxidation and hot water was greater than those of untreated rods. Quantitative histomorphometric analyses indicated that anodic oxidation and hot water treatment induced higher new bone formation around the rods. Our findings indicate that Ti-Nb-Sn alloy treated with anodic oxidation and hot water showed greater capacity for apatite formation, stronger bone bonding and higher biocompatibility for osteosynthesis. Ti-Nb-Sn alloy treated with anodic oxidation and hot water treatment is a promising material for orthopaedic implants enabling higher osteosynthesis and lower stress disproportion.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Regions of histomorphometric measurements.
(A) Radiograph of a Ti-Nb-Sn rod implanted in the distal femur of a rabbit. Locations of proximal (P) and distal (D) samples subjected to histological analyses are indicated. (B) A histological image of a Ti-Nb-Sn rod-implanted femur. Red squares indicated regions of interest for quantitative histological analyses.
Fig 2
Fig 2. SEM images of AO- and HW-treated Ti-Nb-Sn and CP-Ti discs.
Representative images of SEM micrographs of AO- and HW-treated Ti-Nb-Sn and CP-Ti discs. Numerous small spheres were observed on both substrates after HW treatment. (A) AO-treated CP-Ti; (B) AO-treated Ti-Nb-Sn; (C) AO- plus HW-treated CP-Ti; (D) AO- plus HW-treated Ti-Nb-Sn
Fig 3
Fig 3. XRD analysis for apatite formation.
XRD profiles of AO-treated and AO- plus HW-treated Ti-Nb-Sn and CP-Ti discs. After 7 days incubation in Hank’s solution, both CP-Ti and Ti-Nb-Sn alloy discs showed crystalline apatite formation.
Fig 4
Fig 4. XPS analysis of the surface of Ti-Nb-Sn.
O 1s XPS profiles of AO-treated and AO- plus HW-treated Ti-Nb-Sn. (A) AO-treated Ti-Nb-Sn; (B) AO- plus HW-treated Ti-Nb-Sn.
Fig 5
Fig 5. SEM images of apatite formation.
Representative images of SEM micrographs of Ti-Nb-Sn and CP-Ti discs after AO-treatment or AO- plus HW-treatment, followed by 7 days’ incubation in Hank’s solution. A crystalline apatite layer is observed on the surface of Ti-Nb-Sn and CP-Ti discs after AO- plus HW-treatment and incubation in Hank’s solution. (A) AO-treated CP-Ti; (B) AO-treated Ti-Nb-Sn; (C) AO- plus HW-treated CP-Ti; (D) AO- plus HW-treated Ti-Nb-Sn. (A–D) were all incubated in Hank’s solution.
Fig 6
Fig 6. SEM images of Ti-Nb-Sn rods with apatite formation and pull-out test.
Representative images of SEM micrographs of AO-treated and AO- plus HW-treated rods and the results of pull-out test of untreated and AO- plus HW-treated rods. (A) SEM images of AO-treated rod with incubation in Hank’s solution. Numerous small spheres were observed on the surface. (B) SEM images of AO- plus HW-treated rod with incubation in Hank’s solution. A crystalline apatite phase was observed. (C) Failure loads at 3 and 6 weeks after rod implantation were measured by the pull-out test. The failure loads of AO- plus HW-treated rods were significantly higher than those of untreated rods at 3 and 6 weeks. (**: p < 0.01).
Fig 7
Fig 7. Histological images of newly-formed bone.
Representative histological images of Ti-Nb-Sn alloys implanted into the femur. Newly formed bone was observed, especially in the area of the distal femur (arrows). Higher magnification images (panels E–H) of the rectangular areas (panels A–D) as visualized under a fluorescence microscope. The yellow and green fluorescence indicates tetracycline (injected before operation) and calcein (injected before death) signals, respectively. (A, E) Distal section of an AO- plus HW-treated rod; (B, F) Distal section of an untreated rod; (C, G) Proximal section of an AO- plus HW-treated rod; (D, H) Proximal section of an untreated rod.
Fig 8
Fig 8. Quantitative histomorphometric analysis of newly-formed bone.
Quantitative histomorphometric analysis of newly-formed bone around Ti-Nb-Sn alloy rods 6 weeks after implantation. Parameters from A to F indicate the results of analysing distal areas and parameters from G to L indicate results from proximal areas. BV/TV and OV/TV values in the distal area were significantly higher in AO- plus HW-treated Ti-Nb-Sn alloy rods than in untreated rods (A, C). (*: p < 0.05; n.s.: not significant).
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