**1. Introduction**

Nowadays orthopaedic and dental metallic prostheses are widely used in the medical field, the most common being 316L stainless steel, Co-Cr alloys, titanium (Ti) or Ti superalloys. These metallic materials were preferred due to their good mechanical performance, adequate stiffness, non-magnetic properties and to their intrinsic property of promoting on their surface in contact with air or biological media a very thin and biologically inert oxide film (Cr2O3 in case of stainless steel and Co-Cr alloy or TiO2 for (Ti) and Ti alloys), which could act as a metallic ions diffusion barrier layer. However, due to corrosion in the aggressive biological media, this thin protective layer could easily be shattered locally and metallic ions could enter the biological environment causing adverse reactions. Allergies, bone necrosis and the accumulation of metal particles in organs were detected in some cases (C. Brown et al., 2006; C. Brown et al., 2007).

The new generation of orthopaedic and dental implants aims towards the increase of biocompatibility by replacing the biotolerated metallic surfaces with bioactive ones. For increasing the bioactivity of prostheses and implants, there were designed devices coated with biologically active materials such as hydroxyapatite, simple or doped with different metallic ions or functional groups, various calcium phosphates, and more recently, bioglasses and glass-ceramics. Therefore, considerable attention has been given to the use of implants with bioactive fixation in the past decade (L.L. Hench & J. Wilson, 2003).

The commercial solution currently applied worldwide is the orthopaedic and dental titanium implants biofunctionalized with thick (>50 μm) bioactive coatings of hydroxyapatite [HA, Ca10(PO4)6(OH)2] prepared by plasma spraying.

Although this type of implant structure proved to be successful clinically, there are still significant deficiencies hard to ignore (e.g. low mechanical strength, difficulty in controlling

Magnetron Sputtered BG Thin Films: An Alternative Biofunctionalization

well as the reactor chamber walls (Palmero et al., 2007).

and excellent uniformity on large area substrates (Wasa et al., 2004).

characterizations were employed by FTIR, GIXRD, SEM, and pull-out tests.

technological point of view.

**coating interface** 

that prevented the use of BG/Ti structures for load-bearing applications.

Approach – Peculiarities of Bioglass Sputtering and Bioactivity Behaviour 73

The implants must simultaneously satisfy requirements such as biocompatibility, strength, corrosion resistance and sometimes aesthetics. It is widely accepted that both mechanical properties and chemical composition are important factors in the preliminary physiological bond of such implants to living tissues. Low mechanical properties are the major problem

This chapter aims to introduce magnetron sputtering technique as a solid alternative for bioactive implants' functionalization, taking a new step in the research of implant-type structures based on bioactive glasses. The chapter will present our recent findings on the correlation between bioactive powder targets/RF-MS deposition parameters versus composition tailoring of BG thin films, and their mechanical and in vitro behaviour in simulated body fluids (SBF). Understanding these correlations could be important for fundamental physics, materials science and prosthetic medicine as well as from a

Radio Frequency – Magnetron Sputtering (RF-MS) deposition is nowadays one of the most popular techniques to grow thin films in research and in decorative and semiconductor industry. In this method the plasma is used as a source of energetic ions (within the energy range 10–500 eV) that are accelerated towards the cathode target. When energetic ions reach the target surface with energy above the surface binding energy (the minimum threshold is typically somewhere in the range 10–100 eV), an atom can be ejected. This way free atoms and clusters are produced by sputtering, which are subsequently deposited on a substrate as

Recently, Radio Frequency – Magnetron Sputtering (RF–MS) has emerged a promising alternative for preparing adherent bioactive glass films (G.E. Stan et al., 2009; G.E. Stan et al., 2010a, 2010b, 2010c, 2010d) due to its tailoring possibilities and due to some advantages: low pressure operation, low substrate temperature, high purity of the films, ease of automation,

In this chapter we present recent findings on the adherence and bioactivity of bioglass coatings prepared by magnetron sputtering technique. The study will indicate how features such as composition, structure, adherence and bioactivity of bioglass films can be tailored simply by altering the magnetron sputtering working conditions, proving that this less explored technique is a promising alternative for preparing implant-type coatings. Extensive multi-parametrical structural, compositional, morphological and mechanical

**2. Solutions for increasing the adherence at the titanium substrate / glass** 

It is widely accepted that the integrity of the substrate/coating interface is always critical in determining the performance and the reliability of any implant-type coating. Generally, low values of adhesion for bioglass coatings were published (Mardare et al., 2003; Goller, 2004; Peddi et al., 2008). Among the deposition techniques available for producing bioglass coatings, magnetron sputtering is the less explored. Only three papers have been published by other groups on this topic to the best of our knowledge (Mardare et al., 2003; Wolke et al., 2008; Saino et al., 2010). The main impediment in using bioglass coatings as implant

the solubility in vivo, etc.), both in the preparation of biofunctional coatings and in their long-term *in situ* functional operation (Batchelor & Chandrasekaran, 2004; Epinette et al., 2003). Albeit their biological properties are excellent, the large thickness of the HA films synthesized by plasma spray determines the susceptibility to cracking and/or delamination due to poor adherence, phenomena that will allow the diffusion of implant's metal ions into the surrounding tissues and can lead to malfunctioning of the medical device in question. To address these shortcomings, currently a variety of alternative coating methods are being studied, from wet sol-gel technology, electrophoretic deposition and pulsed laser ablation, to magnetron sputtering for producing thinner adherent films of hydroxyapatite, calcium phosphates or bioactive glasses.

Bioactive glasses or bioglasses (BG) are osteoproductive-type inorganic materials far from proving their fully operative potential yet. Since the discovery of Bioglass® (45S5) by Larry Hench (L.L. Hench & J. Wilson, 2003), many bioglass compositional systems have been proposed and proved their suitability to form a bond with the living bone tissue and enhance the osteosynthesis at the implant site due to the favourable chemical interactions with the body fluid in the tissue rehabilitation process.

The behaviour of bioactive glasses in the formation of new bone tissue depends on the chemical composition and textural properties (Saravanapavan & Hench, 2001; Sepulveda et al., 2002). Glasses of the Na2O-CaO-P2O5-SiO2 system can be either formed from the traditional melt-quenching (Wu et al., 2011) or by the modern sol-gel method (Balamurugan et al., 2007). It has also been proved that an increase in the growth rate of apatite-like layer as well as the wider bioactivity were observed depending on the compositional range used for the preparation of bioglass (Rámila & Vallet-Regí, 2001; Vallet-Regí et al., 2003). The recent progresses made on the synthesis and processing of bioglasses that allowed the formulation of new compositional systems with lower thermal expansion coefficients (CTE) and enhanced bioactivity (Agathopoulos et al., 2006; Balamurugan et al., 2007; Tulyaganov et al., 2011) reopened the issue of bioglass coatings as a viable implantologic solution for load-bearing applications.

Generally bioactive glasses and glass-ceramics have been extensively developed and investigated for non-loading applications as bone grafts, fillers or auricular implants owing to their ability to form a bond with the living bone and put into clinical use following many years of animal testing in a variety of experimental models (Hench, 1991; Ratner et al., 2004).

To the best of our knowledge there are still no commercial titanium (Ti) implants functionalized with bioactive glass (BG) coatings, due to their poor adhesion to the metallic substrate determined by their native friability and to the significant mismatch of the CTEs for the BG coating (12–17 x 10-6/°C) and Ti-based substrate (~9.2–9.6 x 10-6/°C). Pull-out adherence values higher than 40 MPa are accepted for such implant-type coatings (ASTM, 2009; FDA, 1997; ISO/DIS, 1999).

The research on implants with thick coatings made of bioglasses prepared by using an enamelling process has shown that, in time, cracks appear in the coatings, allowing metallic ions to spread inside the human body, and producing finally their delamination. Moreover, in comparison with hydroxyapatite films, the control of composition and adhesion to metallic substrates seems to be more difficult to accomplish in the case of the BG ones.

the solubility in vivo, etc.), both in the preparation of biofunctional coatings and in their long-term *in situ* functional operation (Batchelor & Chandrasekaran, 2004; Epinette et al., 2003). Albeit their biological properties are excellent, the large thickness of the HA films synthesized by plasma spray determines the susceptibility to cracking and/or delamination due to poor adherence, phenomena that will allow the diffusion of implant's metal ions into the surrounding tissues and can lead to malfunctioning of the medical device in question. To address these shortcomings, currently a variety of alternative coating methods are being studied, from wet sol-gel technology, electrophoretic deposition and pulsed laser ablation, to magnetron sputtering for producing thinner adherent films of hydroxyapatite, calcium

Bioactive glasses or bioglasses (BG) are osteoproductive-type inorganic materials far from proving their fully operative potential yet. Since the discovery of Bioglass® (45S5) by Larry Hench (L.L. Hench & J. Wilson, 2003), many bioglass compositional systems have been proposed and proved their suitability to form a bond with the living bone tissue and enhance the osteosynthesis at the implant site due to the favourable chemical interactions

The behaviour of bioactive glasses in the formation of new bone tissue depends on the chemical composition and textural properties (Saravanapavan & Hench, 2001; Sepulveda et al., 2002). Glasses of the Na2O-CaO-P2O5-SiO2 system can be either formed from the traditional melt-quenching (Wu et al., 2011) or by the modern sol-gel method (Balamurugan et al., 2007). It has also been proved that an increase in the growth rate of apatite-like layer as well as the wider bioactivity were observed depending on the compositional range used for the preparation of bioglass (Rámila & Vallet-Regí, 2001; Vallet-Regí et al., 2003). The recent progresses made on the synthesis and processing of bioglasses that allowed the formulation of new compositional systems with lower thermal expansion coefficients (CTE) and enhanced bioactivity (Agathopoulos et al., 2006; Balamurugan et al., 2007; Tulyaganov et al., 2011) reopened the issue of bioglass coatings as a viable implantologic solution for

Generally bioactive glasses and glass-ceramics have been extensively developed and investigated for non-loading applications as bone grafts, fillers or auricular implants owing to their ability to form a bond with the living bone and put into clinical use following many years of animal testing in a variety of experimental models (Hench, 1991;

To the best of our knowledge there are still no commercial titanium (Ti) implants functionalized with bioactive glass (BG) coatings, due to their poor adhesion to the metallic substrate determined by their native friability and to the significant mismatch of the CTEs for the BG coating (12–17 x 10-6/°C) and Ti-based substrate (~9.2–9.6 x 10-6/°C). Pull-out adherence values higher than 40 MPa are accepted for such implant-type coatings (ASTM,

The research on implants with thick coatings made of bioglasses prepared by using an enamelling process has shown that, in time, cracks appear in the coatings, allowing metallic ions to spread inside the human body, and producing finally their delamination. Moreover, in comparison with hydroxyapatite films, the control of composition and adhesion to metallic substrates seems to be more difficult to accomplish in the case of the BG ones.

phosphates or bioactive glasses.

load-bearing applications.

2009; FDA, 1997; ISO/DIS, 1999).

Ratner et al., 2004).

with the body fluid in the tissue rehabilitation process.

The implants must simultaneously satisfy requirements such as biocompatibility, strength, corrosion resistance and sometimes aesthetics. It is widely accepted that both mechanical properties and chemical composition are important factors in the preliminary physiological bond of such implants to living tissues. Low mechanical properties are the major problem that prevented the use of BG/Ti structures for load-bearing applications.

This chapter aims to introduce magnetron sputtering technique as a solid alternative for bioactive implants' functionalization, taking a new step in the research of implant-type structures based on bioactive glasses. The chapter will present our recent findings on the correlation between bioactive powder targets/RF-MS deposition parameters versus composition tailoring of BG thin films, and their mechanical and in vitro behaviour in simulated body fluids (SBF). Understanding these correlations could be important for fundamental physics, materials science and prosthetic medicine as well as from a technological point of view.

Radio Frequency – Magnetron Sputtering (RF-MS) deposition is nowadays one of the most popular techniques to grow thin films in research and in decorative and semiconductor industry. In this method the plasma is used as a source of energetic ions (within the energy range 10–500 eV) that are accelerated towards the cathode target. When energetic ions reach the target surface with energy above the surface binding energy (the minimum threshold is typically somewhere in the range 10–100 eV), an atom can be ejected. This way free atoms and clusters are produced by sputtering, which are subsequently deposited on a substrate as well as the reactor chamber walls (Palmero et al., 2007).

Recently, Radio Frequency – Magnetron Sputtering (RF–MS) has emerged a promising alternative for preparing adherent bioactive glass films (G.E. Stan et al., 2009; G.E. Stan et al., 2010a, 2010b, 2010c, 2010d) due to its tailoring possibilities and due to some advantages: low pressure operation, low substrate temperature, high purity of the films, ease of automation, and excellent uniformity on large area substrates (Wasa et al., 2004).

In this chapter we present recent findings on the adherence and bioactivity of bioglass coatings prepared by magnetron sputtering technique. The study will indicate how features such as composition, structure, adherence and bioactivity of bioglass films can be tailored simply by altering the magnetron sputtering working conditions, proving that this less explored technique is a promising alternative for preparing implant-type coatings. Extensive multi-parametrical structural, compositional, morphological and mechanical characterizations were employed by FTIR, GIXRD, SEM, and pull-out tests.
