Scholarly article on topic 'Magnesium incorporated hydroxyapatite: Synthesis and structural properties characterization'

Magnesium incorporated hydroxyapatite: Synthesis and structural properties characterization Academic research paper on "Nano-technology"

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{"A. Powder" / "A. Chemical preparation" / "D. Apatite" / "E. Biomedical applications" / "Magnesium substitution"}

Abstract of research paper on Nano-technology, author of scientific article — Arghavan Farzadi, Farhad Bakhshi, Mehran Solati-Hashjin, Mitra Asadi-Eydivand, Noor Azuan abu Osman

Abstract Synthetic hydroxyapatites are widely used in bone tissue engineering because of their similar composition with the inorganic phase of hard tissues. Biological apatites, however, are calcium-deficient apatites with many di- and tri-valent ion substitutions. In this study, stoichiometric hydroxyapatite (HA) powders were prepared by wet-chemical precipitation method, and the effect of Mg incorporation on the resulting solid solution was investigated. X-ray diffraction (XRD) analysis confirmed that the substitution of Mg for Ca in apatite lattice resulted in a slight increase in a lattice and more emphasized decrease in c lattice parameters: 0.0966% and 0.2964%, respectively. The results indicated an increase in the d-spacing of Mg-doped HA (MHA). Scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM–EDX) analysis showed that the Mg, C, and O elements were evenly distributed. Transmission electron microscopy (TEM) analysis revealed that incorporation of Mg did not significantly alter the size of the precipitated crystals. Although XRD patterns suggested smaller crystallite size, such a result was still consistent with TEM results, wherein change in size was not significant in Mg-doped HA (MHA) in comparison to HA. Moreover, the incorporation of impurity ions into the HA lattice did not alter the high-temperature phase stability often required for processing. The comparison of HA and MHA samples before and after heat treatment showed that the apatite structure did not decompose or undergo any phase transformation at high temperatures. A proportion of the Mg added did not substitute into the HA lattice. The Mg(OH)2 phase, as observed in the XRD pattern of the Mg-added sample, was a second phase that was easily washed by a citrate solution. In both HA and MHA samples, the calcium phosphate phase remained as a single-phase hexagonal calcium hydroxyapatite before and after heat treatment.

Academic research paper on topic "Magnesium incorporated hydroxyapatite: Synthesis and structural properties characterization"

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Ceramics International 40 (2014) 6021-6029

CERAMICS

INTERNATIONAL

www.elsevier.com/locate/ceramint

Magnesium incorporated hydroxyapatite: Synthesis and structural

properties characterization $

Arghavan Farzadia, Farhad Bakhshib, Mehran Solati-Hashjina,b *, Mitra Asadi-Eydivanda,

Noor Azuan abu Osmana

aDepartment of Biomedical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia hBiomaterials Center of Excellence, Amirkabir University of Technology, 15914 Tehran, Iran

Received 1 August 2013; received in revised form 6 November 2013; accepted 9 November 2013 Available online 26 November 2013

Abstract

Synthetic hydroxyapatites are widely used in bone tissue engineering because of their similar composition with the inorganic phase of hard tissues. Biological apatites, however, are calcium-deficient apatites with many di- and tri-valent ion substitutions. In this study, stoichiometric hydroxyapatite (HA) powders were prepared by wet-chemical precipitation method, and the effect of Mg incorporation on the resulting solid solution was investigated. X-ray diffraction (XRD) analysis confirmed that the substitution of Mg for Ca in apatite lattice resulted in a slight increase in a lattice and more emphasized decrease in c lattice parameters: 0.0966% and 0.2964%, respectively. The results indicated an increase in the d-spacing of Mg-doped HA (MHA). Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) analysis showed that the Mg, C, and O elements were evenly distributed. Transmission electron microscopy (TEM) analysis revealed that incorporation of Mg did not significantly alter the size of the precipitated crystals. Although XRD patterns suggested smaller crystallite size, such a result was still consistent with TEM results, wherein change in size was not significant in Mg-doped HA (MHA) in comparison to HA. Moreover, the incorporation of impurity ions into the HA lattice did not alter the high-temperature phase stability often required for processing. The comparison of HA and MHA samples before and after heat treatment showed that the apatite structure did not decompose or undergo any phase transformation at high temperatures. A proportion of the Mg added did not substitute into the HA lattice. The Mg(OH)2 phase, as observed in the XRD pattern of the Mg-added sample, was a second phase that was easily washed by a citrate solution. In both HA and MHA samples, the calcium phosphate phase remained as a single-phase hexagonal calcium hydroxyapatite before and after heat treatment. © 2013 The Authors. Published by Elsevier Ltd. All rights reserved.

Keywords: A. Powder; A. Chemical preparation; D. Apatite; E. Biomedical applications; Magnesium substitution

1. Introduction

Among all calcium phosphate bioceramics, hydroxyapatite (HA), Ca10(PO4)6(OH)2, is the most extensively used biocompatible ceramic materials for bone tissue engineering, as its chemical composition is similar to the bone mineral phase

*This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-No Derivative Works License, which permits non-commercial use, distribution, and reproduction in any medium, provided the original author and source are credited.

nCorresponding author at: Department of Biomedical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia. Tel.: + 60 37 9674446.

E-mail address: mehran@um.edu.my (M. Solati-Hashjin).

[1-5]. Biological apatites are nonstoichiometric nanocrystal-line carbonated HAs (CHA). Therefore, synthetic HA ceramics are doped with small amounts of additives (e.g., Mg2 +, Zn2 +, F_, Mn2 +, and CO2_ ions). Although the substitution does not intensely change the crystallographic properties of HA, it affects the biological and mechanical properties [6-13]. An ionocovalent structural model of the apatite family shows a structure that can accept both cationic and anionic substituents. These substitutions induce modifications in lattice parameters and crystallinity, which substantially influence the solubility of HA at physiological conditions without generating significant changes in the hexagonal system of apatite [14-19].

One of the elements associated with biological apatites is magnesium. Mg incorporation into HA stimulates osteoblast

0272-8842/$- see front matter © 2013 The Authors. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ceramint.2013.11.051

proliferation. Mg acts similar to a growth factor during the early stages of osteogenesis and promotes bone formation [19]. Typical concentrations of carbonate and Mg ions in human bone are 5.8 and 0.55 wt%, respectively [7,18]. Although the extent of these elemental substitutions is minimal, they are important for biological activity and interaction between bone mineral and calcium-phosphate-based implant materials by influencing crystal growth, dissolution rate, solubility, surface chemistry and charge, morphology, and the mechanical properties [6,7,9,14,20-22].

By substitution of a smaller Mg ion for a larger Ca ion, additional structural changes may be required to prevent destabilization/decomposition of the structure during heat treatment process. This can be achieved by co-substitution of a second ion, such as CO3 " to the HA structure [23,18].

The incorporation of Mg ions within the HA structure is essential for developing artificial bone substitutes. This study aims to investigate the synthesis of stoichiometric HA via a wet-chemical precipitation method, and the effect of Mg incorporation on the structure of the resulting Mg-HA solid solution. Various analytical techniques have been employed to study the phase, crystallinity, crystal size, and crystal lattice structure of the Mg-doped HA (MHA) samples.

2. Materials and methods

2.1. Sample preparation

Pure and doped nanocrystalline HA powders were synthesized based on a wet chemical method [6,15,24]. Diammonium hydrogen phosphate [(NHhHPOJ (Prolabo Merck eurolab no. 21 309.293), calcium nitrate tetrahydrate [Ca(NO3)2 • 4H2O] (Prolabo Merck eurolab no. 22 384.298), and magnesium chloride hexahydrate [MgCl2 • 6HO] (Merck no. 105833) were applied as sources of P, Ca, and Mg ions, respectively.

Stoichiometric HA was prepared as a control via a classic precipitation method by dropping 0.29 M aqueous phosphate solution into 0.30 M calcium salt solution for 3 h, while constantly stirring. The starting Ca/P molar ratio was equal to the stoichiometric value of HA (1.67). NaOH (Merck no. 105833) solution was used to control the pH of the solution mixture at 11 during the process. The resulting suspension was aged for 24 h at room temperature, centrifuged, dried in an oven at 70 °C overnight, and calcined at 900 °C in air for 1 h.

Mg-doped HA was prepared by drop-wise addition of an aqueous diammonium hydrogen phosphate solution into a basic solution consisting of magnesium chloride hexahydrate

Wavcnumbcr c

Fig. 1. XRD (a) and FTIR (b) patterns of the as-prepared HA powders.

Wavenumber c

Fig. 2. XRD (a) and FTIR (b) patterns of the calcined HA powders.

and calcium nitrate tetrahydrate with Mg/Ca molar ratio of 0.18 for 3 h. The pH of the suspension was adjusted to 11, and stirred for 24 h. The resulting precipitates were centrifuged and washed three times using distilled water. All samples were dried at 70 °C overnight, calcined at 900 °C for 1 h, and then stored for further analysis.

2.2. Sample characterization

Phase analyses, crystallinity, crystallite size, and lattice parameters of powders were determined by X-ray diffraction (XRD) (Bruker Analytical X-ray Systems, Cu-Ka radiation, 40 kV, 30 mA, and 0.02° s "1 step scan). The XRD patterns of the samples (Figs. 1-5) were obtained by using OriginLab OriginPro v9.0 SR2 and PeakFit v.4.12 softwares.

The lattice parameters of HA (before and after calcination) and MHA (before and after calcination) were calculated by Rietveld structure refinement of XRD data from each sample. The degree of crystallinity, corresponding to the crystalline HA, MHA, and calcined phases, were evaluated by Eq. (1), where I300 is the intensity of (300) reflection and Vn2/300 is the intensity of the hollow between (112) and (300) reflections, which completely disappears in noncrystalline

samples. Broadening of a diffraction peak can be related to crystallite size, which may be smaller or equal to the grain size, through Scherrer's equation shown in Eq. (2), where A is the wavelength (CuKa), t is the full width at half-maximum of the HA (211) line, and 0 is the diffraction angle. The (002), (310), and (222) HA peaks were chosen for the analysis of Bragg line broadening [1,25]:

XC — 1 ~(V112/300/I300)

0.9A t cos (0)

Fourier transform infrared spectroscopy (FTIR) (Equinox 55 Bruker) was performed to evaluate the functional groups and chemical composition of the specimens and quantify the effect of Mg substitution on the different functional groups, such as hydroxyl and phosphate [26]. FTIR pellets of powdered samples were mixed with KBr and the spectra was obtained over the 400-4000 cm_ 1 region. Scanning electron microscopic-energy dispersive X-ray spectroscopy (SEM-EDX) analysis (Tescan Vega 2XMU) was used for morphological observations. Before examination, samples were coated with a thin gold film by sputtering using low deposition rate.

Wavcnumhcr cm"

Fig. 3. XRD (a) and FTIR (b) patterns of Mg-substituted HA powders.

10 20 30 40 SO 60 70 60 4000 3600 3000 2600 2000 1500 1000 500

2-Theta YVavenumber cm"1

Fig. 4. XRD (a) and FTIR (b) patterns of washed Mg-substituted HA powders (washed MHA).

VVavenumber c

Fig. 5. XRD (a) and FTIR (b) patterns of calcined MHA powders.

In addition, MgHA crystals were observed with a Philips EM 208S transmission electron microscope at 100 keV. Samples for TEM were prepared by spreading a drop of nanoparticles solution in ethanol (~ 5 mg/mL) onto standard coated copper grid.

3. Result and discussion

The HA peaks were indexed according to the standard pattern (JCPDS 09-0432), as shown in Figs. 1a and 2a. Stoichiometric HA powders exhibited sharp diffraction peaks, indicating high crystallinity of the structure. No impurity phase was identified by XRD.

As shown in Figs. 1(b)-5(b), all FTIR spectra illustrated an OH" band at 3569 cm"1 and PO4" bands at 472, 565, 603, and 1032 cm_ 1 associated with HA. The sharp peak (1637 cm_and broad bands for adsorbed water (30003500 cm_are the evidence of water absorption due to the high specific surface area that precipitated powders usually have. The CO^- groups, that can substitute both PO3 and OH_ ions in the HA structure appeared as 1461, 1423, and 875 cm_ 1 wave numbers. The calcined HA powders exhibited FTIR patterns similar to that of untreated sample, as shown in Fig. 2b. Moreover, the peaks related to absorbed water and carbonates disappeared after heat treatment which means the carbonate is not incorporated in the lattice of HA.

Although Fig. 3a indicates the presence of HA phase in the Mg-substituted sample, the intensity of HA peaks were decreased. This suggests the decrease of crystallinity with reducing grain growth because of Mg ion substitution. Diffractogram of the sample showed additional peaks in the XRD pattern, which were corresponded to Mg(OH)2. As shown in Fig. 3b, the peak marked with "•" at 3698 cm_ 1 was observed in the Mg-doped HA sample. This peak corresponds to the stretching mode of hydroxyl groups that appears when combined with magnesium [27-31], demonstrating the presence of Mg+ 2 in the apatite structure.

The Mg-added sample contained unreacted Mg(OH)2. This was subjected to a washing treatment at room temperature by

Table 1

Lattice parameters of stoichiometric HA powders according to JCPDS no. 09-0432.

20 d (A°) h k l a (A°) c (A°)

(for Sto-HA)

18.7850 4.7200 1 1 0 9.4400

21.8190 4.0700 2 0 0 9.3993

25.8790 3.4400 0 0 2 6.8800

28.9660 3.0800 2 1 0 9.4096

32.9020 2.7200 3 0 0 9.4224

39.8180 2.2620 3 1 0 9.4175

44.3690 2.0400 4 0 0 9.4224

48.6230 1.8710 3 2 0 9.4172

51.2830 1.7800 4 1 0 9.4189

53.1430 1.7220 0 0 4 6.8880

59.9380 1.5420 4 2 0 9.4218

63.4430 1.4650 5 1 0 9.4186

Average 6.8849.4185

using 0.2 M (4.2028 g) ammonium citrate aqueous solutions (pH 9) for further characterization and elimination of non-apatitic secondary phase to ensure that measurements are only associated to the effect of magnesium incorporated to the HA lattice and not to the possible impurity Mg(OH)2 second phase [32].

Fig. 4a shows the XRD patterns of washed Mg HA powders (washed MHA). Mg(OH)2 disappeared, and no other calcium phosphate peaks were observed. Moreover, according to Fig. 4 (b), the peak corresponding to the Mg-hydroxyl band disappeared, indicating that Mg was removed from the structure. This result is consistent with the XRD pattern of the washed MHA. However, the acidic composition can destroy the stoichiometric and enhance the nonstoichiometric apatite nanostructure, thereby resulting in changes in HA characteristics, such as the degree of crystallinity, morphology, lattice parameters, and stability of the HA structure, and ultimately influence the biological response in actual applications. Thus, in this study, MHA is referred to as the as-prepared Mg HA.

Table 2

Lattice parameters of as-prepared synthesized HA powders.

20 d (A°) (for Sto-HA) h k l d (A1) (from graph) a (A°) c (A°) Ad (A°)

18.7850 4.7200 1 1 0 4.6671 9.33428 0.05286

21.8190 4.0700 2 0 0 4.0370 9.32310 0.03298

25.8790 3.4400 0 0 2 3.4399 6.87982 0.00009

28.9660 3.0800 2 1 0 3.0765 9.39892 0.00348

32.9020 2.7200 3 0 0 2.7218 9.42859 0.00180

39.8180 2.2620 3 1 0 2.2729 9.46296 0.01093

44.3690 2.0400 4 0 0 2.0378 9.41229 0.00218

48.6230 1.8710 3 2 0 1.8748 9.43614 0.00377

51.2830 1.7800 4 1 0 1.7815 9.42655 0.00145

53.1430 1.7220 0 0 4 1.7209 6.88376 0.00106

59.9380 1.5420 4 2 0 1.5397 9.40754 0.00233

63.4430 1.4650 5 1 0 1.4577 9.37164

0.00731

Average 9.41808 6.88179 0.00344

Table 3

Lattice parameters of calcined synthesized HA powders.

20 d (A°) (for Sto-HA) h k L d (A°) (from graph) a (A°) c (A°) Ad (A°)

21.8190

25.8790

28.9660

32.9020

39.8180

0.0000

Average

4.0700 3.4400 3.0800 2.7200 2.2620

4.0773 3.4425 3.0765 2.7186 2.2620

9.4161

9.4175 9.4173

9.4179

6.8850

6.8850

0.0073 0.0025 0.0035 0.0014

0.0019

Table 4

Lattice parameters of as-prepared synthesized MHA powders.

20 d (A1) (for Sto-HA) h k l d (A1) (from graph) a (A°) c (A°) Ad (A°)

18.7850 4.7200 1 1 0 4.7413 9.4827 0.0213

21.8190 4.0700 2 0 0 4.0810 9.4247 0.0110

25.8790 3.4400 0 0 2 3.4347 6.8694 0.0053

28.9660 3.0800 2 1 0 4.0869 9.4308 0.0069

32.9020 2.7200 3 0 0 2.7266 9.4454 0.0066

39.8180 2.2620 3 1 0 2.2707 9.4538 0.0087

44.3690 2.0400 4 0 0 2.0457 9.4486 0.0057

48.6230 1.8710 3 2 0 1.8733 9.4288 0.0023

51.2830 1.7800 4 1 0 1.7731 9.3822 0.0069

53.1430 1.7220 0 0 4 1.7134 6.8535 0.0086

59.9380 1.5420 4 2 0 1.5411 9.4161 0.0009

63.4430 1.4650 5 1 0 1.4557 9.3585

0.0093

Average 9.4272 6.8614 0.0061

Fig. 5a shows the XRD patterns of the MHA powders after heat treatment. The calcined powders showed a decrease in the peak width and more intense peaks with a slightly right shift in peak position compared with the as-prepared sample related to the Mg substitution. Moreover, the MgO peak is related to the calcination of the Mg(OH)2 phase. The carbonate peak disappeared and the hydroxyl group peak was clearly identified, indicating the removal of Mg (Figs. 3b and 5b).

Some of the substituted Mg + 2 were possibly integrated into the apatite lattice, whereas some were adsorbed on the surface of apatite crystals or present in other secondary phases. For some ions, only a small amount was incorporated in the apatite lattice, and the substitutions were limited [33]. The position of Mg in the HA lattice is not clearly known. Mg can occupy one of the two crystallographic calcium sites or both, referred to as Ca(I) and Ca(II), which present different local environments.

Table 5

Lattice parameters of calcined synthesized MHA powders.

20 d (A°) (for Sto-HA) h k l d (A°) (from graph) a (A°) c (A°) Ad (A°;

18.7850 4.7200 1 1 0 4.7064 9.4128 0.0136

21.8190 2.0700 2 0 0 4.0773 9.4161 0.0073

25.8790 3.4400 0 0 2 3.4425 6.8850 0.0025

28.9660 3.0800 2 1 0 3.0849 9.4244 0.0048

32.9020 2.7200 3 0 0 2.7186 9.4175 0.0014

39.8180 2.2620 3 1 0 2.2620 9.4173 0.0000

44.3690 2.0400 4 0 0 2.0396 9.4203 0.0004

48.6230 1.8710 3 2 0 1.8719 9.4215 0.0009

51.2830 1.7800 4 1 0 1.7808 9.4231 0.0008

53.1430 1.7220 0 0 4 1.7209 6.8838 0.0011

59.9380 1.5420 4 2 0 1.5425 9.4247 0.0005

63.4430 1.4650 5 1 0 1.4722 9.4647

0.0072

Average 9.4242 6.8844 0.0020

Table 6

Lattice parameters of synthesized samples and standard HA (JCPDS 09-0432).

Samples a (A°) c (A°) Ad (A°)

Standard HA(JCPDS no. 0 9-0432)9.41856.8840.0000

HA 9.4181 6.8818 0.0034

MHA 9.4272 6.8614 0.0061

Calcined HA 9.417 6.885 0.0019

Calcined MHA 9.4242 6.8844 0.0020

Table 7

The degree of crystallinity of synthesized powders.

Type of powder 20° Variable Intensity (counts) Crystallinity

32.88 I300 31.993 Xc %

HA 0.4688 46.88

32.56 V112/300 16.996

Calcined HA 32.92 I300 136.97 0.9781 97.81

32.6 V112/300 2.9993

MHA 32.82 I300 48.989 0.3878 38.78

32.66 V112/300 29.993

Calcined MHA 32.92 I300 128.97 0.969 96.9

32.62 V112/300 3.9991

Table 8

Crystallite size of synthesized powders.

Sample Crystallite size (nm)

00 2 310 22 2 Average

HA 40.756 46.911 48.065 45.244

Calcined HA 37.05 60.352 - 48.701

MHA 23.976 52.785 39.355 38.706

Calciend MHA 40.755 35.205 39.335 38.432

Some authors have proposed that Mg enters the Ca(II) site, whereas others in the Ca(I) site [18].

The lattice parameters of all samples are shown in Tables 1-5. Moreover, as shown in Table 6, the averages of calculated

Fig. 6. TEM images of samples: (a) HA and (b) MHA.

parameters were compared to the lattice parameters of standard HA (JCPDS no. 09-0432). The XRD and FTIR analyses of washed Mg HA showed that the powders contained apatitic structure without any calcium phosphate secondary phase; thus, these changes in apatite lattice parameters and structure is related to Mg incorporation into the apatite structure.

According to Table 6, substitution of Mg can reduce the c lattice constant of stoichiometric HA (0.33%) [34,35]. Consequently, the effect of Mg substitution on the c lattice parameters is about three times greater than its effect on a lattice constant. In terms of biological issues, the change of c constant is more effective because HA is grown primarily in the c direction [36].

Therefore, Mg is expected to have a significant effect on HA growth. Table 8 indicates an increase in d-spacings of purified Mg-substituted HA. Mg is expected to be slightly smaller than Ca, which may result in stresses and changing d-spacing in the HA structure.

The a lattice constant of Mg-substituted apatite increased in both calcined and uncalcined samples; while in the as-prepared HA the a lattice constant is almost the same as that of stoichiometric HA. Hence, substitution of Mg resulted in small change (~ 0.1%) in apatite structure, and the value of changes in a constant decreased in calcined samples which is in agreement with previous studies [37].

Table 7 shows the degree of crystallinity of synthesized powders, which was increased after heat treatment. Moreover, Mg substitution reduced the degree of crystallinity of HA powders, as reported by Landi et al. [25]. This supports the fact that incorporation of Mg into the HA structure does not encourage the crystallization of hydroxyapatite.

As shown in Table 8, these results clearly indicate that the average crystallite size of HA decreased because of Mg substitution which acted as a growth inhibitor. The TEM micrographs of the HA and MHA samples are illustrated in Fig. 6. The images show that both HA and MHA crystals exhibit elongated nanorod morphology with an aspect ratio approximately equal to 10:1. Although the MHA crystals seem to be a bit smaller than HA crystals, no significant difference in crystallite size of two samples was revealed. Furthermore, TEM reveals that the actual size of the precipitated crystals (30-100 nm in length and 10-20 nm in width) are different from those calculated as an average based on XRD results (Table 8). This difference could be attributed to the fact that a given particle observed by TEM could be the result of the aggregation of several small particles, which the XRD analysis does differentiate. Furthermore, feature size in microstructure strongly depends on several factors such as kinematic and dynamic conditions, and could be different from the actual size due a number of reasons.

SEM images of samples are shown in Fig. 7. Numerous agglomerations of small spherical particles in nanometric scale between 70 nm and 130 nm were observed, which were larger than those approximated by the Scherrer equation (Table 8).

This difference in particle size is consistent with carbonate substitution in the HA structure. Moreover, planes containing the carbonate groups would be closer to Mg cations (smaller) than to Ca cations (larger) [38]. Thus, particle size in Mg carbonate HA was smaller than carbonate HA particle size, suggesting that to some extent Mg inhibits grain growth in HA.

Fig. 8 shows the SEM-EDX results of MHA sample. The EDX results clearly show the presence of Mg and C, as well as calcium, phosphorous, and oxygen in the structure. These results were consistent with XRD and FTIR results.

The line-scan EDX analysis of MHA is shown in Fig. 9. The even distribution of magnesium and carbonate ions can be seen clearly. Fig. 10 shows the elemental distribution maps (dot maps) of Mg-substituted HA powders. Uniform distribution of Mg and C as trace elements in the HA structure were observed, which is consistent with the line-scan EDX results.

Fig. 7. SEM micrographs of samples: (a) HA and (b) MHA.

Fig. 8. SEM-EDX result of MHA powders.

4. Conclusion

Stoichiometric HA powders were prepared by wet chemical method at room temperature. Magnesium ions were successfully incorporated in the HA structure. Mg was uniformly distributed in the HA lattice between Ca sites in bulk and surface of HA crystals. The effect of Mg incorporation on HA structure was studied on lattice constants, the degree of crystallinity, and the crystal size. Mg substitution decreased the c lattice parameter and slightly increased the a lattice parameter. In addition, the degree of crystallinity and the size of crystals of the doped HA samples decreased due to the incorporation of Mg ions into the host lattice. The presence of impurity ions in the HA host lattice did not alter the high-temperature phase stability of hydroxyapatite that is often a

Fig. 9. Line-scan EDX result of MHA powders over a 10 mm length of samples.

requirement for ceramic processing. In both HA and MHA samples, the calcium phosphate phase remained as a singlephase hexagonal calcium hydroxyapatite before and after heat treatment.

Acknowledgment

This study was supported by High Impact Research UM/ MOHE/HIR Project no. D000010-16001.

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