**1. Introduction**

356 Biomaterials – Physics and Chemistry

Ekworapoj P, Sidhu SK, McCabe JF (2007) Effect of different power parameters of Er, Cr:

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Calcium phosphates constitute an important family of biomaterials resembling the part of calcified tissues. This study is based on calcium phosphate such as hydroxyapatite (Ca10(PO4)6(OH)2, Hap), fluorapatite (Ca10(PO4)6F2, Fap) and tricalcium phosphate (Ca3(PO4)2, TCP) phases because their chemical composition is similar to that of bone mineral (Hench, 1991; Legeros, 1993; Uwe et al.,1993; Elliott, 1994; Landi et al., 2000; Varma et al., 2001; Destainville et al., 2003; Wang et al., 2004; Ben Ayed et al., 2000, 2001a, b; 2006a, b; 2007; 2008a, b; Bouslama et al., 2009; Chaari et al., 2009). The most frequent is β-TCP because it is resorbable and osteoinductive (Gaasbeek et al., 2005; Steffen et al., 2001). β-TCP is resorbed in vivo by osteoclasts and replaced by new bone (Schilling et al., 2004). The tricalcium phosphate has been used clinically to repair bone defects for many years. However, mechanical properties of calcium phosphates are generally inadequate for many load-carrying applications. The tricalcium phosphate has a low density decreasing the mechanical properties. But, the efficiency of bi-phasic calcium phosphate (BCP) has been fully importantly efficiency its clinical efficacy to combat the chronic osteomyelitis in the long term. To our knowledge, if it is possible to vary the composition of bioceramic materials (composed of Hap and -TCP) with its inherent porosity, it could be a solution owing to the faster resorption of this BCP together with the sustained release of the antibiotic.

In the literature Hap, -TCP or the combination of both (Hap/TCP) was the most commonly used synthetic augments in high tibial osteotomy (Haell et al., 2005; Koshino et al., 2003; Gaasbeek et al., 2005; Van Hemert et al., 2004; Gutierres et al., 2007). The use of bone cement as a temporary spacer for bone defects has been described, but secondary biological reconstruction was performed after cement removal (DeSilva et al., 2007). However, permanent acrylic bone cement has been used as an interface in the postero-medial part of high tibial osteotomy to maintain the opening angle and good results have been achieved (Hernigou et al., 2001). However, due to the different biomechanical features between bone and bone cement and missing bony remodelling and incorporation, the use of bone cement as a permanent spacer was not recommended, if one aims to achieve biological regeneration. Recently, Jensen and colleagues described that rapid resorption of -TCP might impair the regenerative ability of local bone, especially in the initial stage of bone healing (Jensen et al.,

Elaboration and Characterization of Calcium Phosphate

**2. Materials and methods** 

using KBr.

2001b):

Biomaterial for Biomedical Applications 359

In this study the main used materials are commercial tricalcium phosphate (Fluka) and synthesized fluorapatite. The Fap powder was synthesized by the precipitation method (Ben Ayed et al., 2000). A calcium nitrate (Ca(NO3).4H2O, Merck) solution was slowly added to a boiling solution containing diammonium hydrogenophosphate ((NH4)2HPO4, Merck) and ammonium fluorine (NH4F, Merck), with continuous magnetic stirring. During the reaction, pH was adjusted to the same level (pH 8-9) by adding ammonia. The obtained precipitate

Estimated quantities of each powder (β-TCP and Fap) were milled with absolute ethanol and treated by ultra-sound machine for 15 min. The milled powder was dried at 120°C in a steam room to remove the ethanol and produce a finely divided powder. Powder mixtures were moulded in a metal mould and uniaxially pressed at 150 MPa to form cylindrical compacts with a diameter of 20 mm and a thickness of about 6 mm. The green bodies were sintered without any applied pressure or air at various temperatures (between 1100°C and 1450°C). The heating rate was 10°C min-1. The green compacts were sintered in a vertical resistance furnace (Pyrox 2408). The relative densities of the sintered bodies were calculated by the dimensions and weight. The relative error of densification value was about 1%. The received powder was analyzed by using X-ray diffraction (XRD). The X-rays have used the Seifert XRD 3000 TT diffractometer. The X radiance was produced by using CuK<sup>α</sup> radiation (λ = 1.54056 Å). The crystalline phases were identified from powder diffraction

The samples were also submitted to infrared spectrometric analysis (Perkin-Elmer 783)

Linear shrinkage was determined by dilatometry (Setaram TMA 92 dilatometer). The

Differential thermal analysis (DTA) was carried out using about 30 mg of powder (DTA-TG,

The 31P magic angle spinning nuclear magnetic resonance (31P MAS NMR) spectra were run on a Brucker 300WB spectrometer. The 31P observational frequency was 121.49 MHz with 3.0 µs pulse duration, spin speed 8000 Hz and delay 5 s with 2048 scans. 31P shift is given in

The microstructure of the sintered compacts was investigated by scanning electron microscope (Philips XL 30) on fractured sample surfaces. Because calcium phosphates are insulating biomaterial, the sample was coated with gold for more electronic conduction. The particle size dimension of the powder was measured by means of Micromeritics Sedigraph 5000. The specific surface area (SSA) was measured by the BET method using azotes (N2) as an adsorption gas (ASAP 2010) (Brunauer et al., 1938). The main particle size (D BET) was calculated by assuming that the primary particles are spherical (Ben Ayed et al.,

> <sup>6</sup> *DBET s*

Where ρ is the theoretical density of β-TCP (3.07 g.cm-3) or Fap (3.19 g.cm-3) and s is the SSA. The Brazilian test was officially considered by the International Society for Rock Mechanics (ISRM) as a method for determining the tensile strength of rock materials (ISRM, 1978). The Brazilian test was also standardised by the American Society for testing materials (ASTM) to

(1)

was filtered and washed with deionised water; it was then dried at 70°C for 12h.

files (PDF) of the International Center for Diffraction Data (ICDD).

Setaram Model). The heating rate was 10°C min-1.

parts per million (ppm) referenced to 85 wt% H3PO4.

heating and cooling rates were 10°C min-1 and 20°C min-1, respectively.

2006). The microstructure of the used -TCP has important influence on the osteogenic effects (Okuda et al., 2007). This has recently been confirmed by Fellah and colleagues (Fellah et al., 2008). They show that the Hap/TCP with different micropores was evaluated in a goat critical-defect model.

Several research studies dealt with the question where and how to perform the osteotomy and which fixation material is most beneficial (Brouwer et al., 2006; Agneskirchner et al., 2006). Aryee et al. demonstrate histologically and radiologically that the complete rebuilding of lamelliform bone in patients without synthetic augmentation, whilst bony in growth into the Hap/TCP wedge of augmented osteotomies just slowly progressed (Aryee et al., 2008). In contrast to diminished osteotomies, there was no advantage in using Hap/TCP wedges or the combination of Hap/TCP wedges and platelet rich plasma (PRP) as supporting material after 12 months. In cases where augmentation is performed, either autologous spongious iliac bone graft or an Hap/TCP wedge of appropriate size was inserted into the osteotomy opening and pushed laterally until it is firmly aligned to the tibial bone. The Hap/TCP wedge utilised by us consists of 60% micro–macroporous biphasic Hap and 40% -TCP. The average total porosity is 65–75%, whilst two different sizes of porosity are found within this material. The microporous part consists of pores with a diameter less than 10µm. The macroporous part consists of pores with a diameter between 300µm and 600µm (same as autograft macropores).

As a result of limited autologous bone availability and to minimise the problem of donorsite morbidity, many efforts have been made to find adequate supporting material for augmentation after osteotomy (Bauer et al., 2000; De Long et al, 2007). In this context, we chose biomaterials on base of calcium phosphates as solution for the biomedical applications. Thus, β-TCP or Hap-TCP combination has been clinically used to repair bone defects for many years (Elliott, 1994). Whereas, β-TCP or Hap-TCP have poor mechanical properties (Elliott, 1994; Wang et al., 2004). The usage at high load bearing conditions was restricted due to its brittleness, poor fatigue resistance and strength. Hence, there was a need for improving the mechanical properties of these materials by suitable biomaterials for clinical applications. We offer the study of the mixtures of tricalcium phosphate (β-TCP) and synthetic Fap in order to obtain a bioceramic with better mechanical properties than Hap-TCP combination or β-TCP as separately used. In fact, Fap is an attractive material due to its similarity in structure and bone composition in addition to the benefit of fluorine release (Elliott, 1994; Ben Ayed et al., 2001a). In Vitro studies we have shown that Fap is biocompatible (Elliott, 1994). It also has better stability and provides fluorine release at a controlled rate to ensure the formation of a mechanically and functionally strong bone (Elliott, 1994; Ben Ayed et al., 2006b).

Most studies have been devoted to the knowledge of the mechanical properties and biomedical applications of TCP-Hap (Elliott, 1994; Landi et al., 2000; Gutierres et al., 2007). On the contrary little work has been devoted to the sintering, mechanical properties and clinical applications of TCP-Fap (Ben Ayed et al., 2007). So, the aim of this study is to prepare a biphasic calcium phosphates composites (tricalcium phosphate and fluorapatite) at various temperatures (between 1100°C and 1450°C) with different percentages of fluorine (0.5 wt %; 0.75 wt %; 1 wt %; 1.25 wt % and 1.5 wt % respectively, to the mass Fap percentage: 13.26 wt %; 19.9 wt %; 26.52 wt %; 33.16 wt % and 40 wt %). It also aims to characterize the resulting composites with density, mechanical resistance, infrared spectroscopy, X-ray diffraction, nuclear magnetic resonance (31P) and scanning electron microscopy measurements.
