**1. Introduction**

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20 Titanium Alloys - Advances in Properties Control

Nat Mater. 2009;8:457-70.

Titanium and titanium alloys have been extensively studied for many applications in the area of bone tissue engineering. It was believed that the excellent properties of titanium al‐ loys, e.g. lightweight, excellent corrosion resistance, high mechanical strength and low elas‐ tic modulus compared to other metallic biomaterials such as stainless steels and Cr-Co alloys, would provide enhanced stability for load-bearing implants. However, they usually lack sufficient osseointegration for implant longevity, and their biocompatibility is also an important concern in these applications due to the potential adverse reactions of metallic ions with the surrounding tissues once these metallic ions are released from the implant sur‐ faces. One approach for consideration to improve the healing process is the application of a hydroxyapatite nanocoating onto the surface of biomedical devices and implants. Hydrox‐ yapatite, with its excellent biocompatibility, and similar chemistry and structure to the min‐ eral component of bone, provides a bioactive surface for direct bone formation and apposition with adjacent hard tissues. The deposition of a SiO2 interlayer between the im‐ plant surface and the hydroxyapatite nanocoating is necessary to further improve the bio‐ compatibility of metal implants, as SiO2 has its own excellent compatibility with living tissues, and high chemical inertness, which lead to enhanced osteointegrative and functional properties of the system as a whole.

Therefore, SiO2 and hydroxyapatite nanocoatings were deposited onto titanium alloys using electron beam evaporation and magnetron sputtering techniques, respectively, with differ‐ ent process parameters to optimize the deposition conditions and so achieve desired proper‐ ties. Surface characteristics are essential due to their role in enhancing osseointegration. Surface morphology and microstructure were observed using a scanning electron micro‐

© 2013 Mediaswanti et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Mediaswanti et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

scope (SEM) and elemental analysis was performed by the energy dispersive X-ray spectro‐ scopy method (EDS). The crystal structure was examined using X-ray diffractometer (XRD) to identify the phase components, while nanocoating thickness was measured using profil‐ ometer.

small spaces between its cellular and extracellular matrix. There are two types of osseous tis‐ sue on the basis of the size and distribution of these spaces: compact bone tissue and spongy bone tissue. About 80 wt.% of the human skeleton is compact bone tissue. Compact bone consists of a packed osteon within the Haversian architecture. Each osteon consists of a cen‐ tral Haversian canal, concentric lamellae, lacunae, osteocytes, and canaliculi. Spongy bone, also termed as trabecular bone, exhibits a porous structure with porosity ranging from 50-90 wt.% and consists of an integrate lamellae network. The role of trabeculae is to support and

Sputtered Hydroxyapatite Nanocoatings on Novel Titanium Alloys for Biomedical Applications

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

23

Bone structure contains macro, micro and nanoscale pores with different functions and char‐ acteristics. Macro-scale porosity gives rise to mechanical anisotropy. Micro-scale porosity provides sufficient vascularisation and cell migration, while nanoscale features act as a

Bone mechanics is determined mainly by the bone structure. Compact bone is stiffer and stronger than cancellous bone. The mechanical properties of human bone are listed in Table 1 [2]. The elastic modulus of human bone is approximately 0.05-2 GPa for cancellous bone and 7-30 GPa for compact bone [2]. It should be kept in mind that "elastic modulus" is not

**Mechanical Properties Human Haversian (MPa)**

The history of implants started with the applications of autograph, allograph, and artificial de‐ vice techniques [3]. Autographs utilized tissues from other parts of the patient's body, whilst allograft techniques used tissue from a donor. However, both techniques had drawbacks in application. The autograph method was limited only to nose bone and finger junctions [3]. Moreover, there were adverse side effects, such as infections and pain at the implant area. The allograft technique required a compatible donor that matched the patient's body system, which was usually difficult to find. There was always the potential risk of infections and dis‐ ease transmission from the donor to the recipient's body. Artificial grafts employed artificial materials, now known as biomaterials. The advantages of using artificial device grafts include (i) lower risk for any transmission of disease, (ii) a reduced risk of infections, and (iii) the avail‐ ability of many biomaterials for potential use as scaffolds. Therefore, ongoing studies aim to

Tensile strength 158 Tensile yield stress 128 Compressive strength 213 Compressive yield stress 180 Shear strength 71

an exact description for bone properties since they are anisotropic and viscoelastic.

protect the red bone marrow [2].

framework for cell and mineral binding [2].

**Table 1.** Mechanical properties of human haversian [2]

develop a new generation of biomaterials for bone implants.

**2.2. Bone implant**

This chapter is divided into five major parts. First is an overview of bone and bone implants, including their structure and mechanical properties. The second part highlights the impor‐ tance of nanocoatings for bone implants longevity. Various coatings and surface modifica‐ tion techniques of titanium and its alloys are also elucidated. The advantages and drawbacks of each technique are reviewed. The last part focuses on the study of sputtered hydroxyapatite and SiO2 nanocoatings on titanium. A thorough discussion of the results is presented.
