**3.4 Animal experimental and histological evaluation**

Bone responses of Ti implant and CA sprayed on Ti implants, **A'** and **B'**, were evaluated after implantation into a femoral bone defect in rats [43]. After implantation at 2 weeks, differences in the histopathological appearances of cortical bone formation around the implants revealed new bone formation in all implants (**Figure 10**).

**Figure 10.** *Histological appearances of Ti,* **A'** *and* **B',** *2 weeks after implantation.*

*Fabrication of Apatite Films on Ti Substrates of Simple and Complicated Shapes by Using Stable… DOI: http://dx.doi.org/10.5772/intechopen.80409*


**Table 5.**

*Measured BIC in cortical bone and bone marrow part of implant specimens.*


**Table 6.**

*Measurement push-in loads of implant.*

Haversian canals were observed in **A'** and **B'**, but not in Ti. The bone marrow demonstrated more distinct differences in new bone formation between Ti- and CA-coated specimens. Greater amounts of new bone formation were observed for **A'** and **B'** than for Ti inside the bone marrow. Newly formed bone in bone marrow was trabecular bone, and a part of new bone was formed close to implant materials, **A'** and **B'**.

There were no significant differences in BIC (bone-to-implant contact) in the cortical bone among the three different implants 2 weeks after implantation (p > 0.05; **Table 5**). However, 4 weeks after implantation, **A'** and **B'** showed significantly higher BIC than Ti, and BIC was the highest in **B'** (p < 0.05). Indeed, BIC was significantly higher for **A'** and **B'** at 4 weeks post-implantation than that at 2 weeks (p < 0.05). In the bone marrow, **A'** showed significantly higher BIC than Ti and **B'** at 2 weeks after implantation. At 4 weeks after implantation, BIC of **A'** and **B'** was significantly higher than Ti (p < 0.05). No significant differences existed between **A'** and **B'** (p > 0.05). BICs of 4 weeks post-implantation were significantly higher than those of 2 weeks for **A'** and **B'** (p < 0.05).

CA-coating specimens **A'** and **B'** provided significantly greater amounts of BIC in cortical bone and bone marrow than Ti alone. **B'** was more effective in increasing BIC than **A'**. It is well known that rougher surfaces provide faster and more bone formation [44]. However, the surface roughness did not contribute to an increase of BIC. Mochizuki et al. [40] previously evaluated the attachment, proliferation, and differentiation of osteoblast-like cells on CA-coated Ti. They found that initial attachments of osteoblast-like cells increased due to CA coating and no difference was observed between **A'** and **B'**. On the contrary, cell differentiation was enhanced more on **B'** than on **A'**. They speculated that reduced border heights in the network structure of **B'** were preferred for the spreading of the osteoblast-like cells, and as a result, mineralization would be more accelerated with **B'**. Therefore, higher BIC in the cortical part was obtained for **B'** in the present animal experiments.

The bonding ability of CA-sprayed implant into the bone was examined by push-in tests. **A'** and **B'** showed significantly higher push-in loads than Ti (p < 0.05), and there were no significant differences between **A'** and **B'** (p > 0.05; **Table 6**). A push-in test was performed to evaluate the bonding between the implant and surrounding bone. Both CA-coating implants produced tighter bonding to the bone than Ti. Surface roughness did not influence the values in push-in

tests. Lin et al. [45] also reported that surface modification with hydroxyapatite nanoparticles increased the push-in values 2 weeks after implantation into the femur of rats. In the present study, we only monitored the peaks at the loaddisplacement curve. Studies for the failure mode during the push-in test will be necessary to analyze the bonding of CA films to Ti.
