**4. The importance of nano-coatings for bone implant materials**

Surface modification is a process that changes the composition, microstructure and mor‐ phology of a surface layer while maintaining the mechanical properties of the material. The aim of surface modification is to improve the bioactivity of the biomaterials so that the bio‐ materials demonstrate a higher apatite inducing ability that, in turn, leads to rapid osseoin‐ tegration. After surface treatment, it is expected that the implant's surface will form an active apatite layer. The role of the thin apatite layer is to be a bonding interface to stimulate bone apatite and collagen production [15-16]. It is suggested that altering the nanostruc‐ tured surface morphology influences the apatite inducing ability and improves osteoblast adhesion and differentiation [17].

fluid of a similar ion concentration and pH value to human blood plasma. In addition to en‐ hancing titanium bioactivity, HA-titania coating is expected to increase the bonding strength and corrosion resistance. The surface morphology and microstructure of HA and titania coating before and after being immersed in SBF are presented in Figure 1 (a)-(d). It can be seen that the coating is dense, uniform and without cracks. Wen *et al.* also reported that after

Sputtered Hydroxyapatite Nanocoatings on Novel Titanium Alloys for Biomedical Applications

http://dx.doi.org/10.5772/54263

27

**Figure 1.** SEM micrographs of the surface morphology of HA/TiO2 films after soaking in SBF for (a) 0 day, (b) 1 day, (c)

Electrodeposition is a coating method applied to the fabrication of computer chips and mag‐ netic data storage. Recently, that has been rising interest in electrochemical deposition for

Lopez-Heredia *et al.* [23] coated calcium phosphate onto porous titanium using the electro‐ deposition method. In the process, Ti, platinum mesh, and supersaturated calcium phos‐ phate solution were used as the cathode, electrode and electrolyte, respectively. The ratio of Ca/P in the calcium phosphate coating was 1.65 and the coating thickness was 25 µm. The calcium phosphate coating was homogenous and covered the entire Ti surface. Moreover,

tissue engineering applications due to its ability to coat complex 3D components.

soaking in SBF, HA granules grow gradually.

8 days, and (d) 15 days

**5.2. Electrodeposition of materials**

### **4.1. Calcium phosphate coatings**

Calcium phosphate is a synthetic ceramic that has been proven to support bone apposition and to enhance the osteoconduction of the bone. Calcium phosphate ceramics for bone tis‐ sue applications include tricalcium phosphate (TCP), octocalcium phosphate (OCP), hydrox‐ yapatite (Ca10(PO4)6(OH)2, HA), and biphasic calcium phosphate (BCP) [18]. These ceramics accelerate the healing process and have been widely used in conjunction with metallic mate‐ rial as a bioactive coating material. The ratio of Ca/P in calcium phosphate should resemble the biological apatite mineral of bone (*i*.*e*., 1.50-1.69). Calcium phosphate has the natural fa‐ cility to bond directly to bone.

#### **4.2. Nano-hydroxyapatite coatings**

Hydroxyapatite demonstrates the best bioactivity amongst all the forms of calcium phos‐ phate. Hydroxyapatite (HA) exhibits functionality in promoting osteoblast adhesion, migra‐ tion, differentiation and proliferation; all of which are essential for bone regeneration. HA also has the ability to bond directly onto bone. The bioactivity of HA has made this ceramic the favourite for implant applications. HA nanoparticles may also induce cancer cell apopto‐ sis [19]. The crystalline form of HA exhibits biointegration and prevents formation of ad‐ verse fibrous tissue. It is a more desirable coating than amorphous HA due to its ability to provide a better substrate for a different cell line [20]. Amorphous HA tends to dissolve in human fluid more easily and leads to loosening of the implant. Nanocrystalline HA is more favourable than microcrystalline HA because of its structural similarity with apatite [21].
