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Synthesis and characterization of strontium and chlorine co-doped tricalcium phosphate
Materials Letters 248 (2019) 69–72
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Synthesis and characterization of strontium and chlorine co-doped tricalcium phosphate Serap Gungor Koc Department of Mechanical Engineering, Van Yuzuncu Yil University, 65080 Van, Turkey
a r t i c l e
i n f o
Article history: Received 16 October 2018 Received in revised form 16 March 2019 Accepted 30 March 2019 Available online 1 April 2019 Keywords: Biomaterials Bioceramics Ceramics Chlorine Strontium and tri-calcium phosphate
a b s t r a c t The strontium (Sr2+) and chlorine (Cl ) substituted tricalcium phosphate (TCP) were synthesized via aqueous precipitation method. To understand the effect of the Sr2+ and Cl doping on mechanical properties of tricalcium phosphate (TCP) ceramics, dense TCP compacts of different compositions were prepared and sintered at 1100 °C for 1 h. X-ray diffraction of sintered samples revealed that dopants turn into b-TCP to HA phase transformation during sintering. The binary combination and amount of codopants significantly affect the microstructure. The microhardness of the samples increased with increasing of the Sr2+ and Cl ion concentrations. Cl ion addition, 2.5–10 mol% affect micro hardness results negatively. A comparison between samples were carried out and differences were considered statistically significant at p < 0.05 (standard deviation: 1.2296 GPa). Ó 2019 Elsevier B.V. All rights reserved.
1. Introduction Calcium phosphates (CaP) are used frequently in medical applications due to their high biocompatibility in the human body [1]. TCP is one of the CaP’s which has demonstrated excellent biodegradability and biocompatibility [2,3]. When these materials are implanted in vivo, the results showed non-toxic, antigenically inactive, not inducing cancer and bonding directly to bone without any intervening connective tissue layer [3]. Recently, the chemical alteration of TCP with various ions is common considering that main components of bone are consist of different elements. Within this scope, studies of strontium (Sr+2) and chlorine (Cl ) doped TCP hasn’t been stated previously [4]. Strontium, as bone seekingelement, stimulates bone formation by osteoblasts and inhibits bone resorption by osteoclasts. Results after treatment with strontium containing drugs has been revealed that to increase bone mass and strength. Moreover, they have promising properties on the implant fixations and osseointegration, increasing the volume and microarchitecture of the bone tissue development around implants [5]. Ionic substitutions will affect the thermal stability, the crystal structure, the crystallinity, surface morphology, grain size and the solubility of the apatites. When two or more ions are substituted together, their multiple-effect results would be more complicated than single ions due to the dopant ions affect the atomic structure of TCP. Bivalent ions substituted in TCP lead to no charge imbalance in the apatite lattice. Substitutions of Ca2+ ions by other E-mail address: [email protected] https://doi.org/10.1016/j.matlet.2019.03.136 0167-577X/Ó 2019 Elsevier B.V. All rights reserved.
cations resulted in contraction or expansion of the lattice parameters [6]. Monovalent anions (Cl ) replaced OH anions in the anion channel without charge imbalance [7]. Sr2+, member of alkaline earth element, can be easily doped into the CaP structure. Studies revealed that bigger Sr2+ cations substituted in the Ca (II) site in the CaP structure [8]. As a biomaterial, pure chloroapatites have disadvantages due to replacement of the hydroxyl groups by chloride ions which trigger the acidity of the environment. Cl co-doped HA materials were synthesized using combustion method, demonstrated that the a-axis parameter of the Cl doped samples increased gradually with the increase in Cl concentration. Pure chloropatite cannot be a suitable for biomaterials because chlorine ions will increase the acidity of the environment. Chloride doped HA is more suitable for biomedical applications due to the naturel bone consist of 0.13 wt% chlorine (pure chloropatite: 6.8 wt% chlorine) [6]. When chlorine incorporated into the lattice parameters, a-axis parameter of the Cl doped samples increased gradually with the increase in Cl concentration [9]. From the point of microstructure, Cl substitution in HA resulted in the expansion of the c-axis and the unit cell volume [10]. Considering the significance of the strontium and chlorine as essential elements, the purpose of the present study was to produce a series of TCP samples co-doped with strontium and chlorine ions. In this study we have tried to prepare strontium and chlorine co-substituted TCP through aqueous precipitation method. To investigate the effect of the binary combinations of these dopants, and their characterizations were carried out using scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques.
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2. Material and methods Pure TCP and TCP-strontium and chlorine composites were synthesized by an aqueous precipitation method [11]. Calcium nitrate tetrahydrate (Ca(NO3)24H2O), di-ammonium hydrogen phosphate ((NH4)2HPO4), strontium nitrate (Sr(NO3)2) and calcium chloride (CaCl22 H2O) (Merck) were used as starting reagents. To prepare the pure and doped samples calcium nitrate tetrahydrate (Ca(NO3)24H2O) and di-ammonium hydrogen phosphate ((NH4)2HPO4) were added into distilled water to prepare the solutions with a certain molar ratio. These two powders were dissolved separately in distilled water with Ca/P ratio of 1.50. Ammonia (NH4OH) was added into (NH4)2HPO4 solution after previous solutions were stirred for 1 h. NH4OH was added to these both solutions to bring pH level to 11–12. Different from pure TCP, Sr(NO3)2) and CaCl22 H2O were added at the same time into the solution in a drop wise manner after stirring for 10 min. The final mixture was heated until boiling to increase the reaction. After boiling, the mixture was left for stirring for 24 h. After 1 day of aging, solution was filtered to
obtain a wet cake. The wet cake was dried in an oven at 200 °C to remove the excess water and ammonia. The precipitated and dried TCP’s were crushed with an agate mortar and pestle and the resulting powders and bulks were sintered at 1100 °C in for 1 h. Densities of the sintered materials were obtained by Archimedes method [11]. Phases present in the samples were investigated by XRD using a Rigaku DMAX 2200 machine. XRD was performed on the samples with a Cu-Ka radiation at 40 kV/40 mA and samples were scanned from 10° to 80° in 2h with a scanning step size of 2.0°/min. International Centre for Diffraction Data (ICDD) files were used for comparison with the positions of diffracted planes taken from XRD results. Presence of phases in pure and doped TCPs was calculated by using relative intensity measurements of diffracted planes. Grain size and morphology of the prepared samples were determined by SEM (QUANTA 400F Field Emission) at a voltage of 20 kV. Before to the SEM analysis, the samples were coated with gold and palladium. Micro-hardness of the samples was obtained by a Vickers micro-hardness tester.
Fig. 1. XRD patterns of a) pure TCP, b) 1–10 mol%Sr_1 mol%Cl_TCP, c) 2.5 mol%Sr_2.5–10 mol%Cl_TCP.
S. Gungor Koc / Materials Letters 248 (2019) 69–72
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Fig. 2. SEM images showing the microstructure of a) pure TCP, b) 1 mol%Sr_1 mol%Cl_TCP, c) 2.5 mol%Sr_1 mol%Cl_TCP, d) 5 mol%Sr_1 mol%Cl_TCP, e) 10 mol%Sr_1 mol% Cl_TCP f) 2.5 mol%Sr_2.5 mol%Cl_TCP, g) 2.5 mol%Sr_5 mol%Cl_TCP, h) 2.5 mol%Sr_10 mol%Cl_TCP.
3. Results and discussion As shown by the XRD patterns given in Fig. 1, the primary phase for the powders sintered at 1100 °C was b-TCP (JCPDS: 9-169). There were formation of a-TCP and HA. This indicated that the powder undergoes a phase transformation during sintering and 1100 °C. The reason for that is substitution of chlorine in calcium-deficient apatites tend to form biphasic mixtures after calcinations, and the ratio of the ions in the mixtures were dependent on the lack of calcium in the precursors that were used [10]. Higher Sr2+ concentration helped to stabilize b-TCP phase together with low crystallinity. Previous studies demonstrated that strontium substitution for calcium in HA structures affected the length of crystalline domains [12]. In agreement with those data, also in TCP, patterns in Fig. 1b revealed a slight broading of the diffraction peak, consistent with a shortening of the crystalline domain (5 mol %Sr_1 mol%C_TCP), where strontium concentration was increased. Additionally, a-TCP phase almost disappeared in the samples 10 mol%Sr_1 mol%Cl_TCP. From Fig. 1c, with increasing the Cl concentration crystallinity increased. The phase formation of TCP during high temperature calcination may be promoted by the decomposition of hydroxyl groups. With increasing Cl amounts b-TCP phase transformed totally to HA phase. The main phase was HA for 2.5 mol%Sr_10 mol%Cl_TCP sample. The density of the sintered samples tended to increase according to Sr2+ and Cl dopant concentration. The maximum density was achieved for 1 mol%Sr_1 mol%Cl_TCP (3.1268 g/cm3). The increase in density can be attributed to the increased sintering kinetics caused by the Sr2+, Cl ions doping. SEM images in Fig. 2 shows that apatite was present as aggregates, rough and its particles demonstrated different shapes as short columns, thick-like plates. In the samples 2.5 mol%Sr_1 mol %Cl_TCP and 5 mol%Sr_1 mol%Cl_TCP the grains were in regular and isotropic shape and showed a bimodal distribution in size. Moreover, the grain boundaries were observed clearly. However,
the pure TCP, 1 mol%Sr_1 mol%Cl_TCP, 10 mol%Sr_1 mol%Cl_TCP, 2.5 mol%Sr_2.5 mol%Cl_TCP, 2.5 mol%Sr_5 mol%Cl_TCP, 2.5 mol% Sr_10 mol%Cl_TCP had a quite different morphology as shown in Fig. 2(a), (b), (e)–(h). Compared to samples 2.5 mol%Sr_1 mol% Cl_TCP and 5 mol%Sr_1 mol%Cl_TCP, the grains were irregular in shape and the grain boundaries of the samples were not clear. Except 2.5 mol%Sr_1 mol%Cl_TCP and 5 mol%Sr_1 molCl_TCP samples, they had a lot of porosity in their structure. It has been proved that the incorporation of Sr2+ and porosities will affect the mechanical properties. Differently from this, porous structure of the samples will be advantage to mimic the pore size of the spongy bone for use as bone substitutes and drug delivery systems. The Vickers hardness of the sintered samples was tested by indentation at a load of 1.96 N, as shown in Fig. 3. Compared to the pure TCP, there was depreciation observed at 1 mol%Sr_1 mol
Fig. 3. Vickers hardness of the Sr2+ and Cl doped TCP ceramics after sintered at 1100 °C for 1 h in air.
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S. Gungor Koc / Materials Letters 248 (2019) 69–72
%Cl_TCP and 2.5 mol%Sr_1 mol%Cl_TCP samples (5.551 GPa, 5.168 GPa). This seems to be correlated with TCP formation. When Sr2+ amount increased there was a slight decrease were observed (where Cl amount 1%). Increased Cl amounts resulted in sharp decrease in the microhardness values.
Acknowledgement This work was supported by the Van Yuzuncu Yil University, _ BAP (Grant No: 2014-MIM-B152). References
4. Conclusions Sr2+ and Cl substituted TCP samples, with varying Sr2+, Cl contents, were synthesized by aqueous precipitation method. Upon sintering and doping, a phase formation from b-TCP, a-TCP to HA occurred in the Sr2+, Cl containing samples. This was attributed to a reduction in lattice ideality due to substitution of Sr2+ for Ca. b-TCP remained the major phase in the biphasic mixtures with Sr2+ and Cl contents. The stabilizing effect of Sr2+ on the b-TCP structure inhibited the formation a-TCP during sintering when Sr2+ was introduced. The binary combination and amount of codopants significantly affect the microstructure. The Ca-deficiency occurs related to the co-doping process and increases with increasing amount of the dopants. This study provides the effect of Sr2+ and Cl substitution on the phase transformation and crystal structure of apatite. The effective partial substitution of Sr2+, Cl in TCP (1 mol%Sr_1 mol%Cl_TCP and 2.5 mol%Sr_5 mol%Cl_TCP) makes these materials promising candidates for bone repair and coating elements for implants. The microstructural properties of Sr2+ and Cl co-substituted TCP should be further investigated by optimizing the substitution degrees of both Sr2+ and Cl ions. Conflict of interest None.
[1] F.H. Albee, Studies in bone growth triple calcium phosphate as a stimulus to osteogenesis, Ann. Surg. 71 (1920) 32. [2] X. Yang, Z. Wang, J. Mater. Chem. 8 (1998) 2233–2237. [3] M. Epple, K. Ganesan, R. Heumann, J. Klesing, A. Kovtun, S. Neumann, V. Sokolova, J. Mater. Chem. 20 (2010) 18–23. [4] L. Obadia, P. Deniard, B. Alonso, T. Rovillon, S. Jobic, J. Guicheux, et al., Effect of sodium doping in b-tricalcium phosphate on its structure and properties, Chem. Mater. 18 (2006) 1425–1433. [5] L. Maimoun, T.C. Brennan, I. Badoud, V. Dubois-Ferriere, R. Rizzoli, P. Ammann, Strontium ranelate improves implant osseointegration, Bone 46 (2010) 1436– 1441. [6] J.A. Weatherell, C. Robinson, The inorganic composition of teeth, in: I. Zipkin (Ed.), Biological Mineralization, John Wiley, NY, USA, 1973, pp. 43–74. [7] M. Supova, Substituted hydroxyapatites for biomedical applications: a review, Ceram. Int. 41 (2015) 9203–9923. [8] S. Gomes, J.M. Nedelec, E. Jallot, D. Sheptyakov, G. Renaudin, Unexpected mechanism of Zn2+ insertion in calcium phosphate bioceramics, Chem. Mater. 23 (2011) 3072–3085. [9] J. Zhao, X. Dong, M. Bian, et al., Solution combustion method for synthesis of nanostructured hydroxyapatite, fluorapatite and chlorapatite, Appl. Surf. Sci. (2014) 1026–1033. [10] S. Kannan, J.H.G. Rocha, J.M.F. Ferreira, Synthesis of hydroxychlorapatites solid solutions, Mater. Lett. 60 (2006) 864–868. [11] Q. Song, C. Wang, S. Wen, Effects of doping on crystal and grain boundary in human enamel, Mater. Sci. Eng. A 297 (2001) 272–280. [12] A. Bigi, E. Boanini, C. Capuccini, M. Gazzano, Strontium-substituted hydroxyapatite nanocrystals, Inorg. Chim. Acta 360 (2007) 1009–1016.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Synthesis and characterization of strontium and chlorine co-doped tricalcium phosphate Serap Gungor Koc Department of Mechanical Engineering, Van Yuzuncu Yil University, 65080 Van, Turkey
a r t i c l e
i n f o
Article history: Received 16 October 2018 Received in revised form 16 March 2019 Accepted 30 March 2019 Available online 1 April 2019 Keywords: Biomaterials Bioceramics Ceramics Chlorine Strontium and tri-calcium phosphate
a b s t r a c t The strontium (Sr2+) and chlorine (Cl ) substituted tricalcium phosphate (TCP) were synthesized via aqueous precipitation method. To understand the effect of the Sr2+ and Cl doping on mechanical properties of tricalcium phosphate (TCP) ceramics, dense TCP compacts of different compositions were prepared and sintered at 1100 °C for 1 h. X-ray diffraction of sintered samples revealed that dopants turn into b-TCP to HA phase transformation during sintering. The binary combination and amount of codopants significantly affect the microstructure. The microhardness of the samples increased with increasing of the Sr2+ and Cl ion concentrations. Cl ion addition, 2.5–10 mol% affect micro hardness results negatively. A comparison between samples were carried out and differences were considered statistically significant at p < 0.05 (standard deviation: 1.2296 GPa). Ó 2019 Elsevier B.V. All rights reserved.
1. Introduction Calcium phosphates (CaP) are used frequently in medical applications due to their high biocompatibility in the human body [1]. TCP is one of the CaP’s which has demonstrated excellent biodegradability and biocompatibility [2,3]. When these materials are implanted in vivo, the results showed non-toxic, antigenically inactive, not inducing cancer and bonding directly to bone without any intervening connective tissue layer [3]. Recently, the chemical alteration of TCP with various ions is common considering that main components of bone are consist of different elements. Within this scope, studies of strontium (Sr+2) and chlorine (Cl ) doped TCP hasn’t been stated previously [4]. Strontium, as bone seekingelement, stimulates bone formation by osteoblasts and inhibits bone resorption by osteoclasts. Results after treatment with strontium containing drugs has been revealed that to increase bone mass and strength. Moreover, they have promising properties on the implant fixations and osseointegration, increasing the volume and microarchitecture of the bone tissue development around implants [5]. Ionic substitutions will affect the thermal stability, the crystal structure, the crystallinity, surface morphology, grain size and the solubility of the apatites. When two or more ions are substituted together, their multiple-effect results would be more complicated than single ions due to the dopant ions affect the atomic structure of TCP. Bivalent ions substituted in TCP lead to no charge imbalance in the apatite lattice. Substitutions of Ca2+ ions by other E-mail address: [email protected] https://doi.org/10.1016/j.matlet.2019.03.136 0167-577X/Ó 2019 Elsevier B.V. All rights reserved.
cations resulted in contraction or expansion of the lattice parameters [6]. Monovalent anions (Cl ) replaced OH anions in the anion channel without charge imbalance [7]. Sr2+, member of alkaline earth element, can be easily doped into the CaP structure. Studies revealed that bigger Sr2+ cations substituted in the Ca (II) site in the CaP structure [8]. As a biomaterial, pure chloroapatites have disadvantages due to replacement of the hydroxyl groups by chloride ions which trigger the acidity of the environment. Cl co-doped HA materials were synthesized using combustion method, demonstrated that the a-axis parameter of the Cl doped samples increased gradually with the increase in Cl concentration. Pure chloropatite cannot be a suitable for biomaterials because chlorine ions will increase the acidity of the environment. Chloride doped HA is more suitable for biomedical applications due to the naturel bone consist of 0.13 wt% chlorine (pure chloropatite: 6.8 wt% chlorine) [6]. When chlorine incorporated into the lattice parameters, a-axis parameter of the Cl doped samples increased gradually with the increase in Cl concentration [9]. From the point of microstructure, Cl substitution in HA resulted in the expansion of the c-axis and the unit cell volume [10]. Considering the significance of the strontium and chlorine as essential elements, the purpose of the present study was to produce a series of TCP samples co-doped with strontium and chlorine ions. In this study we have tried to prepare strontium and chlorine co-substituted TCP through aqueous precipitation method. To investigate the effect of the binary combinations of these dopants, and their characterizations were carried out using scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques.
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2. Material and methods Pure TCP and TCP-strontium and chlorine composites were synthesized by an aqueous precipitation method [11]. Calcium nitrate tetrahydrate (Ca(NO3)24H2O), di-ammonium hydrogen phosphate ((NH4)2HPO4), strontium nitrate (Sr(NO3)2) and calcium chloride (CaCl22 H2O) (Merck) were used as starting reagents. To prepare the pure and doped samples calcium nitrate tetrahydrate (Ca(NO3)24H2O) and di-ammonium hydrogen phosphate ((NH4)2HPO4) were added into distilled water to prepare the solutions with a certain molar ratio. These two powders were dissolved separately in distilled water with Ca/P ratio of 1.50. Ammonia (NH4OH) was added into (NH4)2HPO4 solution after previous solutions were stirred for 1 h. NH4OH was added to these both solutions to bring pH level to 11–12. Different from pure TCP, Sr(NO3)2) and CaCl22 H2O were added at the same time into the solution in a drop wise manner after stirring for 10 min. The final mixture was heated until boiling to increase the reaction. After boiling, the mixture was left for stirring for 24 h. After 1 day of aging, solution was filtered to
obtain a wet cake. The wet cake was dried in an oven at 200 °C to remove the excess water and ammonia. The precipitated and dried TCP’s were crushed with an agate mortar and pestle and the resulting powders and bulks were sintered at 1100 °C in for 1 h. Densities of the sintered materials were obtained by Archimedes method [11]. Phases present in the samples were investigated by XRD using a Rigaku DMAX 2200 machine. XRD was performed on the samples with a Cu-Ka radiation at 40 kV/40 mA and samples were scanned from 10° to 80° in 2h with a scanning step size of 2.0°/min. International Centre for Diffraction Data (ICDD) files were used for comparison with the positions of diffracted planes taken from XRD results. Presence of phases in pure and doped TCPs was calculated by using relative intensity measurements of diffracted planes. Grain size and morphology of the prepared samples were determined by SEM (QUANTA 400F Field Emission) at a voltage of 20 kV. Before to the SEM analysis, the samples were coated with gold and palladium. Micro-hardness of the samples was obtained by a Vickers micro-hardness tester.
Fig. 1. XRD patterns of a) pure TCP, b) 1–10 mol%Sr_1 mol%Cl_TCP, c) 2.5 mol%Sr_2.5–10 mol%Cl_TCP.
S. Gungor Koc / Materials Letters 248 (2019) 69–72
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Fig. 2. SEM images showing the microstructure of a) pure TCP, b) 1 mol%Sr_1 mol%Cl_TCP, c) 2.5 mol%Sr_1 mol%Cl_TCP, d) 5 mol%Sr_1 mol%Cl_TCP, e) 10 mol%Sr_1 mol% Cl_TCP f) 2.5 mol%Sr_2.5 mol%Cl_TCP, g) 2.5 mol%Sr_5 mol%Cl_TCP, h) 2.5 mol%Sr_10 mol%Cl_TCP.
3. Results and discussion As shown by the XRD patterns given in Fig. 1, the primary phase for the powders sintered at 1100 °C was b-TCP (JCPDS: 9-169). There were formation of a-TCP and HA. This indicated that the powder undergoes a phase transformation during sintering and 1100 °C. The reason for that is substitution of chlorine in calcium-deficient apatites tend to form biphasic mixtures after calcinations, and the ratio of the ions in the mixtures were dependent on the lack of calcium in the precursors that were used [10]. Higher Sr2+ concentration helped to stabilize b-TCP phase together with low crystallinity. Previous studies demonstrated that strontium substitution for calcium in HA structures affected the length of crystalline domains [12]. In agreement with those data, also in TCP, patterns in Fig. 1b revealed a slight broading of the diffraction peak, consistent with a shortening of the crystalline domain (5 mol %Sr_1 mol%C_TCP), where strontium concentration was increased. Additionally, a-TCP phase almost disappeared in the samples 10 mol%Sr_1 mol%Cl_TCP. From Fig. 1c, with increasing the Cl concentration crystallinity increased. The phase formation of TCP during high temperature calcination may be promoted by the decomposition of hydroxyl groups. With increasing Cl amounts b-TCP phase transformed totally to HA phase. The main phase was HA for 2.5 mol%Sr_10 mol%Cl_TCP sample. The density of the sintered samples tended to increase according to Sr2+ and Cl dopant concentration. The maximum density was achieved for 1 mol%Sr_1 mol%Cl_TCP (3.1268 g/cm3). The increase in density can be attributed to the increased sintering kinetics caused by the Sr2+, Cl ions doping. SEM images in Fig. 2 shows that apatite was present as aggregates, rough and its particles demonstrated different shapes as short columns, thick-like plates. In the samples 2.5 mol%Sr_1 mol %Cl_TCP and 5 mol%Sr_1 mol%Cl_TCP the grains were in regular and isotropic shape and showed a bimodal distribution in size. Moreover, the grain boundaries were observed clearly. However,
the pure TCP, 1 mol%Sr_1 mol%Cl_TCP, 10 mol%Sr_1 mol%Cl_TCP, 2.5 mol%Sr_2.5 mol%Cl_TCP, 2.5 mol%Sr_5 mol%Cl_TCP, 2.5 mol% Sr_10 mol%Cl_TCP had a quite different morphology as shown in Fig. 2(a), (b), (e)–(h). Compared to samples 2.5 mol%Sr_1 mol% Cl_TCP and 5 mol%Sr_1 mol%Cl_TCP, the grains were irregular in shape and the grain boundaries of the samples were not clear. Except 2.5 mol%Sr_1 mol%Cl_TCP and 5 mol%Sr_1 molCl_TCP samples, they had a lot of porosity in their structure. It has been proved that the incorporation of Sr2+ and porosities will affect the mechanical properties. Differently from this, porous structure of the samples will be advantage to mimic the pore size of the spongy bone for use as bone substitutes and drug delivery systems. The Vickers hardness of the sintered samples was tested by indentation at a load of 1.96 N, as shown in Fig. 3. Compared to the pure TCP, there was depreciation observed at 1 mol%Sr_1 mol
Fig. 3. Vickers hardness of the Sr2+ and Cl doped TCP ceramics after sintered at 1100 °C for 1 h in air.
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S. Gungor Koc / Materials Letters 248 (2019) 69–72
%Cl_TCP and 2.5 mol%Sr_1 mol%Cl_TCP samples (5.551 GPa, 5.168 GPa). This seems to be correlated with TCP formation. When Sr2+ amount increased there was a slight decrease were observed (where Cl amount 1%). Increased Cl amounts resulted in sharp decrease in the microhardness values.
Acknowledgement This work was supported by the Van Yuzuncu Yil University, _ BAP (Grant No: 2014-MIM-B152). References
4. Conclusions Sr2+ and Cl substituted TCP samples, with varying Sr2+, Cl contents, were synthesized by aqueous precipitation method. Upon sintering and doping, a phase formation from b-TCP, a-TCP to HA occurred in the Sr2+, Cl containing samples. This was attributed to a reduction in lattice ideality due to substitution of Sr2+ for Ca. b-TCP remained the major phase in the biphasic mixtures with Sr2+ and Cl contents. The stabilizing effect of Sr2+ on the b-TCP structure inhibited the formation a-TCP during sintering when Sr2+ was introduced. The binary combination and amount of codopants significantly affect the microstructure. The Ca-deficiency occurs related to the co-doping process and increases with increasing amount of the dopants. This study provides the effect of Sr2+ and Cl substitution on the phase transformation and crystal structure of apatite. The effective partial substitution of Sr2+, Cl in TCP (1 mol%Sr_1 mol%Cl_TCP and 2.5 mol%Sr_5 mol%Cl_TCP) makes these materials promising candidates for bone repair and coating elements for implants. The microstructural properties of Sr2+ and Cl co-substituted TCP should be further investigated by optimizing the substitution degrees of both Sr2+ and Cl ions. Conflict of interest None.
[1] F.H. Albee, Studies in bone growth triple calcium phosphate as a stimulus to osteogenesis, Ann. Surg. 71 (1920) 32. [2] X. Yang, Z. Wang, J. Mater. Chem. 8 (1998) 2233–2237. [3] M. Epple, K. Ganesan, R. Heumann, J. Klesing, A. Kovtun, S. Neumann, V. Sokolova, J. Mater. Chem. 20 (2010) 18–23. [4] L. Obadia, P. Deniard, B. Alonso, T. Rovillon, S. Jobic, J. Guicheux, et al., Effect of sodium doping in b-tricalcium phosphate on its structure and properties, Chem. Mater. 18 (2006) 1425–1433. [5] L. Maimoun, T.C. Brennan, I. Badoud, V. Dubois-Ferriere, R. Rizzoli, P. Ammann, Strontium ranelate improves implant osseointegration, Bone 46 (2010) 1436– 1441. [6] J.A. Weatherell, C. Robinson, The inorganic composition of teeth, in: I. Zipkin (Ed.), Biological Mineralization, John Wiley, NY, USA, 1973, pp. 43–74. [7] M. Supova, Substituted hydroxyapatites for biomedical applications: a review, Ceram. Int. 41 (2015) 9203–9923. [8] S. Gomes, J.M. Nedelec, E. Jallot, D. Sheptyakov, G. Renaudin, Unexpected mechanism of Zn2+ insertion in calcium phosphate bioceramics, Chem. Mater. 23 (2011) 3072–3085. [9] J. Zhao, X. Dong, M. Bian, et al., Solution combustion method for synthesis of nanostructured hydroxyapatite, fluorapatite and chlorapatite, Appl. Surf. Sci. (2014) 1026–1033. [10] S. Kannan, J.H.G. Rocha, J.M.F. Ferreira, Synthesis of hydroxychlorapatites solid solutions, Mater. Lett. 60 (2006) 864–868. [11] Q. Song, C. Wang, S. Wen, Effects of doping on crystal and grain boundary in human enamel, Mater. Sci. Eng. A 297 (2001) 272–280. [12] A. Bigi, E. Boanini, C. Capuccini, M. Gazzano, Strontium-substituted hydroxyapatite nanocrystals, Inorg. Chim. Acta 360 (2007) 1009–1016.