- Email: [email protected]
Fabrication and characterization of bioactive glass-ceramic using soda–lime–silica waste glass
Materials Science and Engineering C 37 (2014) 399–404
Contents lists available at ScienceDirect
Materials Science and Engineering C journal homepage: www.elsevier.com/locate/msec
Fabrication and characterization of bioactive glass-ceramic using soda–lime–silica waste glass Mojtaba Abbasi, Babak Hashemi ⁎ Department of Materials Science and Engineering, School of Engineering, Shiraz University, Zand Street, Shiraz, Iran
a r t i c l e
i n f o
Article history: Received 2 November 2013 Received in revised form 18 December 2013 Accepted 19 January 2014 Available online 24 January 2014 Keyword: Solid-state reaction Bioactive glass-ceramic Soda–lime–silica waste glass Biomedical applications
a b s t r a c t Soda–lime–silica waste glass was used to synthesize a bioactive glass-ceramic through solid-state reactions. In comparison with the conventional route, that is, the melt-quenching and subsequent heat treatment, the present work is an economical technique. Structural and thermal properties of the samples were examined by X-ray diffraction (XRD) and differential thermal analysis (DTA). The in vitro test was utilized to assess the bioactivity level of the samples by Hanks' solution as simulated body fluid (SBF). Bioactivity assessment by atomic absorption spectroscopy (AAS) and scanning electron microscopy (SEM) was revealed that the samples with smaller amount of crystalline phase had a higher level of bioactivity. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Biomaterials have recently been improved for new medical applications [1,2]. A biomaterial is described by the Clemson University Advisory Board for Biomaterials as “a systematically and pharmacologically inert substance designed for implantation within or incorporation with living systems” [3]. Bioactive materials, such as Bioglass®, apatite–wollastonite (A–W) glass-ceramic and tricalcium phosphate [4–7] are a specific group of biomaterials, which attach directly to bone tissue through formation of a biologically active hydroxycarbonate apatite (HCA) layer. This layer, chemically and structurally, corresponds to the bone mineral phases, which allow interfacial bonding [8]. For bioactive glasses, bone bonding was first observed for certain compositional range containing SiO2, Na2O, CaO and P2O5 [9]. There were three main compositional features for these bioglasses: i) SiO2 less than 60 mol%; ii) high amount of Na2O and CaO; and iii) a high CaO/P2O5 ratio which distinguish them from the traditional soda–lime–silica glasses. These compositional features cause the surface to be highly reactive when exposed to an aqueous medium [10]. Among these bone bonding materials, 45S5 bioactive glass (Bioglass®) is the most widely studied system, which consists of 45 wt.% SiO 2, 24.5 wt.% CaO, 24.5 wt.% Na 2O and 6 wt.% P2O5 [11]. One of the major characteristics of this bioactive glass is its highly reactive surface when immersed in human plasma or a similar solution. It has been found that a partial dissolution of the bioactive glass surface takes place, resulting in the formation of a silica-rich gel layer and,
⁎ Corresponding author. Tel.: +98 7116133399; fax: +98 7112307293. E-mail address: [email protected] (B. Hashemi). 0928-4931/$ – see front matter © 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.msec.2014.01.031
subsequently the precipitation of a calcium phosphate layer on the bioactive material occurs [12–14]. Poor mechanical strength of bioactive glasses is a main drawback restricting their application as load-bearing implants. To improve mechanical properties, methods such as the transformation of bioactive glasses into glass-ceramics are used. In this technique, the glasses are exposed to heat treatments which may influence not only the material microstructure and hence their mechanical properties, but also their biological activity [15]. Li et al. [16] and Peitl et al. [17] investigated the effect of the amount of crystalline phase on the bioactivity level of glass-ceramics. Based on Li research, the crystalline phase suppresses the formation of HCA layer on the surface of the bioglass ceramic after being immersed in simulated body fluid while, Peitl stated that the crystalline phase only delays the onset time for formation of HCA layer. Arstila et al. [18] studied the parameters affecting the crystallization of the Bioglass® 45S5 and the influence of the thermal treatment on the bioglass properties [19]. In another research, ElBatal et al. [1] studied the effect of the transition metal oxides on the properties of bioglasses and its derived glassceramics. Siqueira and Zanotto [20] provided a report on the production of the bioactive soda–lime–silicate containing phosphorous in solid solution using solid-state reaction. In this research, the synthesis of bioactive glass-ceramic was carried out by the solid-state reaction method, which is different from meltquenching and subsequent heat treatment, which is the conventional method to obtain glass-ceramics. To the best of our knowledge, this was the first time that soda–lime–silica waste glass was used as the main raw material. For this purpose, the calculated amounts of calcium carbonate, sodium carbonate and phosphorus pentoxide were added to waste glass powder and the resultant mixture was calcined at suitable temperature in order to obtain a bioactive glass-ceramic with 45S5
400
M. Abbasi, B. Hashemi / Materials Science and Engineering C 37 (2014) 399–404
Table 1 XRF analysis of the soda–lime–silica glass.
Table 3 Composition of the Hanks' solution.
Oxide
wt.%
Std. err.
Components
Concentration (g/l)
SiO2 Na2O CaO MgO Al2O3 K2O
72.4 12.1 8.7 4.1 1.30 1.60
0.2 0.2 0.1 0.1 0.05 0.06
CaCl2 KCl KH2PO4 MgCl2·6H20 MgSO4·7H2O NaCl NaHCO3 Na2HPO4
0.14 0.40 0.06 0.10 0.10 8.00 0.35 0.048
bioactive glass composition [11]. In addition, Hanks' solution was utilized to evaluate the bioactivity level of different heat-treated samples. HCA layer on the surface of the immersed samples was investigated by a scanning electron microscope (Type VEGA-TESCAN-LMU) equipped with X-ray energy dispersive spectroscopy.
2. Materials and methods The samples were prepared from reagent-grade powders: calcium carbonate (CaCO3, Merck, ≥ 99%), sodium carbonate (Na2CO3, Merck, ≥99.5%), phosphorus pentoxide (P2O5, Dae-Jung Chemical & Metal Co, ≥97%) and soda–lime–silica glass powder. A white glass powder was obtained after the glass cullets were milled in a ball mill with stainless steel balls. The XRF (type ARL 8410) analysis of soda–lime–silica glass is summarized in Table 1. With the addition of proper amounts of CaCO3, Na2CO3 and P2O5 to the glass powder, its composition was modified according to Bioglass® 45S5 composition. The homogenization and grinding of the batch mix were achieved in an attritor mill in isopropyl alcohol for 2 h using zirconia balls (BPR 20:1) as grinding media. After drying and sieving, the powder (named as BGC) was compacted into disks (10 × 2 mm) by isostatic pressing. To achieve glass-ceramics with various percentages of crystalline phases, different heat treatments were performed on the samples in air in a box furnace, with a heating rate of 5 °C/min. These data are summarized in Table 2. The thermal behavior of the pulverized BGC sample was examined by DTA/TG (PLSTA 1640) with Al2O3 powder as the standard material. A uniform heating rate of 10 °C/min was adopted up to 1000 °C. XRD was performed to identify the crystalline phases formed in the thermally treated glasses using a Bruker D8 Advance X-ray diffractometer with Cu Kα radiation equipped with “X'Pert HighScore” software. The IR reflection spectra of the samples in the range of 4000–400 cm−1 were determined using a Bruker Vector 22 FTIR spectrometer. The bioactivity test was conducted according to Kokubo and Takadama [21]. Prepared glass-ceramic samples were immersed in Hanks' solution. The required amount of Hanks' solution for each sample was calculated by the following Eq. Vs ¼ Sa =10
ð1Þ
where Vs is the volume of the solution (ml) and Sa is the apparent surface area of the sample (mm2). In this research, the volume of Hanks' solution was greater than the calculated Vs because the prepared samples were porous. The composition of Hanks' solution is shown in Table 3. All the samples were suspended in polyethylene containers and incubated at 37 °C for 1, 3, 7 and 30 day(s) in Hanks' solution. The immersed samples were removed from the solution, washed with distilled water and dried at room temperature. The concentration of the Ca2+ ion in Hanks' solution after soaking was examined by atomic absorption spectroscopy (Type Philips, PU0100X). The formation of the
3. Results and discussion 3.1. Thermal analysis Before DTA/TG analysis, an XRD analysis of the BGC sample was conducted (Fig. 1). In this pattern, the peaks correspond to Na2CO3 and CaCO3 and those related to P2O5 are not observed. This could be due to the dissolution of P2O5 in the glass phase during milling. Fig. 2 demonstrates the DTA/TG analysis of the BGC powder. It is clear that there are two endothermic peaks at temperatures between 80 and 100 °C. These peaks are related to the evaporation of the physically adsorbed water and organic impurities. An exothermic peak is observed at 320 °C due to the phase transformation of Na2CO3 [22]. There are two overlapped peaks, namely endothermic and exothermic ones at temperatures between 670 and 690 °C with a decrease in weight corresponding to the TG curve. In order to determine the nature of these peaks, a BGC sample was heated at 700 °C for 3 h and then analyzed by XRD as shown in Fig. 3. The absence of the CaCO3 peaks and the corresponding weight loss in the TG curve show decomposition of CaCO3 and release of CO2 from the system at a temperature of about 670 °C. The peaks in this figure show the presence of sodium–calcium–silicate (Ca2Na2Si3O9) and sodium–calcium–phosphate phases (CaNaPO4). Arstila et al. [18] divided the silicate-based bioglasses into two groups: 1) the glasses with the transition temperatures of about 500 °C and the onset of crystallization at below 750 °C; and 2) the glasses with transition temperatures between 550 and 600 °C and the onset of crystallization at about 900 °C. The group 1 glasses form the sodium– calcium–silicate phase, whereas the glasses related to group 2 form wollastonite. Therefore, the heated sample of this work belongs to the first group and the temperature 690 °C refers to the crystallization temperature of new phases.
Table 2 Heat treatment conditions of the samples. Sample no.
Temperature (°C)
Time (h)
BGC1 BGC2 BGC3 BGC4
950 900 900 850
3 6 3 3
Fig. 1. XRD pattern of the BGC sample.
M. Abbasi, B. Hashemi / Materials Science and Engineering C 37 (2014) 399–404
401
Fig. 2. DTA/TG analysis curves for the BGC sample.
3.2. XRD measurements Fig. 4 illustrates the XRD analysis of the glass-ceramics. It is obvious that all samples have sodium–calcium–silicate and sodium–calcium– phosphate crystalline phases. It is evident from XRD patterns that an increase in the temperature resulted in an increase in the amount of crystalline phase. In Fig. 4(d) there is a halo around 2θ = 30°, which indicates the existence of the residual glassy phases in this sample, which vanished as the temperature increased. In addition, as the temperature increased, the peaks became sharper and their intensity increased. Actually, the behavior of the phosphorus in the crystallization of the phosphate phase in the silicate glasses is a controversial issue. The phosphorus ions can replace the silicon ions at the glass tetrahedral sites. However, according to the McMillan [23] the double oxygen bond (P_O) can be formed in the glass phase and it is suitable for forming the phosphate phase in the silicate network. Hence, the tendency toward the crystallization of the phosphate phase increases. Peitl et al. [24] stated that a thermal treatment in normal condition is not sufficient to form a calcium–phosphate phase (an apatite-like phase). They also stated that under these conditions phosphorus ions remain in the form of solid solution in the sodium–calcium–silicate phase and that a drastic heat treatment (long time and high temperature) is required to crystallize an apatite-like phase. Siqueira and Zanotto [20] also synthesized Na2Ca2Si3O9 containing phosphorus in solid solution using the solid-state reaction (950 °C/480 min). They attributed the changes observed in the FTIR spectrum to the formation of NaCaPO4, which did not exist in the XRD pattern.
Fig. 3. XRD pattern of the BGC sample heated at 700 °C.
Fig. 4. XRD patterns of the a) BGC1 sample, b) BGC2 sample, c) BGC3 sample and d) BGC4 sample.
3.3. FTIR spectroscopy The FTIR analyses of the heat-treated samples are shown in Fig. 5. It is clear that the spectra of all samples are similar. According to the literature, the peaks near wave numbers 530, 575 and 620 cm− 1 were assigned to a calcium phosphate or an apatite-like phase. Furthermore, there was a peak at 1040 cm−1, which was related to the stretching PO4 vibration [25]. The peaks at 450, 930 and 1080 cm−1 were attributed to the Si\O\Si vibration. These peaks were related to the bond stretching in amorphous silica, the stretching of non-bridging oxygen atoms and the asymmetric stretching of bridging oxygen atoms within the tetrahedral site, respectively [1]. In the 1000–1100 cm−1 region the asymmetric vibration Si\O\Si is very strong due to the overlap of the stretching PO4 vibrational peaks [10,25]. The results obtained from XRD and FTIR experiments indicated that sodium–calcium–phosphate and sodium– calcium–silicate phases crystallized in all the samples by a one-step thermal treatment. 3.4. Bioactivity Fig. 6 exhibits the Ca2+ concentration changes in Hanks' solution. According to the Hench model [9] that was proposed for the reaction on the surface of the bioactive material, at first the concentrations of the Ca2+, Na+, Si4+ and P5+ ions increase in the solution. Afterward the Ca2+ and P5+ ions move to the surface of the material and a CaO– P2O5-rich amorphous layer is formed upon the SiO2-rich layer. Therefore, concentrations of Ca2+ and P5+ ions decrease in the solution. At last the crystallization occurs, leading to the formation of an HCA layer. From Fig. 6 and in accordance with the Hench model, an HCA
Fig. 5. FTIR spectrum of the BGC1, BGC2, BGC3 and BGC4 samples.
402
M. Abbasi, B. Hashemi / Materials Science and Engineering C 37 (2014) 399–404
Fig. 6. Ca2+ ion concentration in Hanks' solution for BGC1, BGC2, BGC3 and BGC4 samples versus time.
layer must not be formed on the BGC1 sample since the concentration of the Ca2+ ion in the solution has only an increasing trend. Fig. 7(a) demonstrates the SEM image of the BGC1 sample after immersion in Hanks'
solution for 1 month. According to this figure, no layer has been formed on this sample. The EDS analysis shows that the Ca/P ratio of this sample is 1.96 (Fig. 8(a)), while this ratio for an ideal hydroxyapatite is 1.67 [26]. It should be noted that the dimension of the y-axis in Fig. 8 is cps/ev. Fig. 6 reveals that the BGC2 and BGC3 samples have similar behaviors. In both of these samples the Ca2+ ion concentration increased for 1 week and then the Ca2+ ion was absorbed slightly into the surface. Fig. 7(b) shows the SEM image of the BGC2 sample after having been soaked in the solution for 1 month. There was no perceptible change on the surface of this sample. The Ca/P ratio for BGC2 and BGC3 samples was equal to 2.00 (Fig. 8(b)), confirming that the apatite layer has not been formed. The concentration variation of the Ca2+ ion for the BGC4 sample (Fig. 6) indicated that this sample had a good level of bioactivity because the calcium ions were absorbed into the surface after being immersed in the solution for 3 days. Fig. 7(c), (d) and (e) demonstrates the SEM images of the BGC4 sample, which were taken before soaking and after 7 and 30 days of soaking in the solution, respectively. The formation of a phase with a spherical morphology was observed after 1 week (Fig. 7(d)). This phase was homogenized further after 1 month (Fig. 7(e)). Fig. 7(f) shows the cross-sectional image of the BGC4 sample. In this figure, the formation of the HCA layer on the
Fig. 7. SEM images of a) the BGC1 sample after 1 month of immersion, b) the BGC2 sample after 1 month of immersion, c) the BGC4 sample before immersion, d) the BGC4 after 7 days of immersion, e) the BGC4 after 30 days of immersion and f) cross section of the BGC4 after 1 month of immersion.
M. Abbasi, B. Hashemi / Materials Science and Engineering C 37 (2014) 399–404
surface is observed clearly. In addition, the EDS analysis indicated that the Ca/P ratio was equal to 1.64 (Fig. 8(e) and (f)). Results show that the heat treatment conditions were effective in the formation of an HCA layer and in comparison with other researches; this could be due to the amounts of crystalline phases in the samples. Li et al. [16] showed that crystallization could prevent the bioactivity of the Bioglass®. They observed that an HCA layer was formed in the simulated body fluid (SBF) only when the glass-ceramic contained more than 90% amorphous phase. However, Peitl et al. [17] showed that the crystallization in the Bioglass® 45S5 did not prevent the formation of the HCA layer, even though the amount of crystalline phase was 100%. They stated that by increasing the amount of the crystalline phase the onset time of the HCA layer formation increased. In addition, they showed that the state of the phosphorus ions affect the bioactivity. The glass-ceramics containing a crystalline apatite-phase are much less bioactive than the materials containing phosphorus in solid solution. Nevertheless, in this research the phosphorus ion state did not have any effect on the bioactivity because the entire samples contain the crystalline sodium–calcium–phosphate phase and their bioactivity levels were different only due to the difference in the thermal treatment conditions of the samples. It should be noted that not only the amorphous phase content can promote bioactivity, but also the amount of Si\OH nuclei on the surface of bioactive glass-ceramic is other possible factor which influences HCA layer formation [27].
403
4. Conclusions A review of the literature shows that for the first time a bioactive glass-ceramic was synthesized using soda–lime–silica waste glass by the solid-state reaction method rather than conventional melt-quenching one. The results of DTA and XRD analyses revealed that at temperature about 690 °C two crystalline phases, sodium–calcium–silicate and sodium–calcium–phosphate phases, were formed. The in vitro bioactivity test showed that, first, the amount of crystalline phase influenced the bioactivity level. The samples with a smaller amount of the crystalline phase had a higher bioactivity level. Second, the crystalline apatite-like phase did not suppress the bioactivity. The BGC4 sample with the lowest amount of crystalline phase, showed the highest bioactivity. The onset time of the HCA layer formation on the BGC4 sample was 7 days which completed and homogenized within 30 days.
References [1] F.H. ElBatal, G.T. El-Bassyouni, Silicon 3 (2011) 185–197. [2] M. Talha, C.K. Behera, O.P. Sinha, Mater. Sci. Eng. C 33 (2013) 3563–3575. [3] J.Y. Wong, J.D. Bronzino, Introduction, in: J.Y. Wong, J.D. Bronzino (Eds.), Biomaterials, CRC Press, New York, 2007. [4] M. Magallanes-Perdomo, S. Meille, J.M. Chenal, E. Pacard, J. Chevalier, J. Eur. Ceram. Soc. 32 (2012) 2765–2775. [5] L. Tan, X. Yu, P. Wan, K. Yang, J. Mater. Sci. Technol. 29 (2013) 503–513.
Fig. 8. EDS analysis of the surface of the samples. a) The BGC1 sample after 1 month of immersion, b) the BGC2 sample after 1 month of immersion, c) the BGC4 after 7 days of immersion, d) the BGC4 after 30 days of immersion, e) the HCA layer which is formed on top of the BGC4 sample in cross section image and f) the BGC4 sample in cross-section image.
404
M. Abbasi, B. Hashemi / Materials Science and Engineering C 37 (2014) 399–404
[6] C. Zou, K. Cheng, W. Weng, C. Song, P. Du, G. Shen, G. Han, J. Alloys Compd. 509 (2011) 6852–6858. [7] M. Kamitakahara, C. Ohtsuki, H. Inada, M. Tanihara, T. Miyazaki, Acta Biomater. 2 (2006) 467–471. [8] P.N. De Aza, A.H. De Aza, P. Pena, S. De Aza, Bol. Soc. Esp. Ceram. 46 (2007) 45–55. [9] L.L. Hench, R.J. Splinter, W.C. Allen, T.K. Greenlee Jr., J. Biomed. Mater. Res. Symp. 2 (1971) 117–141. [10] H.A. ElBatal, M.A. Azooz, E.M.A. Khalil, A. Soltan Monem, Y.M. Hamdy, Mat. Chem. Phys. 80 (2003) 599–609. [11] L.L. Hench, J. Mater. Sci. Mater. Med. 17 (2006) 967–978. [12] L.L. Hench, J. Am. Ceram. Soc. 81 (1998) 1705–1728. [13] D.C. Chepper, J.E. Gough, P.M. Embanga, I. Notingher, L.L. Hench, M.M. Hall, J. Mater. Sci. Mater. Med. 15 (2004) 803. [14] H.A. ElBatal, E.M.A. Khalil, Y.M. Hamdy, Ceram. Int. 35 (2009) 1195–1204.
[15] L. Lefebvre, J. Chevalier, L. Gremillard, R. Zenati, G. Thollet, D. Bernache-Assolant, A. Govin, Acta Mater. 55 (2007) 3305–3313. [16] P. Li, F. Zhang, T. Kokubo, J. Mater. Sci. Mater. Med. 3 (1992) 452. [17] O. Peitl, G.P. LaTorre, L.L. Hench, J. Biomed. Mater. Res. 30 (1996) 509–514. [18] H. Arstila, E. Vedel, L. Hupa, M. Hupa, J. Eur. Ceram. Soc. 27 (2007) 1543–1546. [19] H. Arstila, L. Hupa, K.H. Karlsson, M. Hupa, J. Non-Cryst. Solids 354 (2008) 722–728. [20] R.L. Siqueira, E.D. Zanotto, Mater. Sci. Eng. C 31 (2011) 1791–1799. [21] T. Kokubo, H. Takadama, Biomaterials 27 (2006) 2907–2915. [22] A. Arakcheeva, G. Chapuis, Acta Cryst. B 61 (2005) 601–607. [23] P.W. McMillan, Glass-ceramics, 2nd ed. Academic Press, London, 1979. [24] O. Peitl, E.D. Zanotto, L.L. Hench, J. Non-Cryst. Solids 292 (2001) 115–126. [25] X. Chatzistavroa, T. Zorba, E. Kontonasaki, K. Chrissafis, P. Koidis, K.M. Paraskevopoulos, Phys. Stat. Sol. (a) 201 (2004) 944–951. [26] K. Ishikawa, P. Ducheyne, S. Radin, J. Mater. Sci. Mater. Med. 4 (1993) 165–168. [27] J.R. Jones, T.F. Kemp, M.E. Smith, Key Eng. Maer. 309–311 (2006) 1031–1034.
Contents lists available at ScienceDirect
Materials Science and Engineering C journal homepage: www.elsevier.com/locate/msec
Fabrication and characterization of bioactive glass-ceramic using soda–lime–silica waste glass Mojtaba Abbasi, Babak Hashemi ⁎ Department of Materials Science and Engineering, School of Engineering, Shiraz University, Zand Street, Shiraz, Iran
a r t i c l e
i n f o
Article history: Received 2 November 2013 Received in revised form 18 December 2013 Accepted 19 January 2014 Available online 24 January 2014 Keyword: Solid-state reaction Bioactive glass-ceramic Soda–lime–silica waste glass Biomedical applications
a b s t r a c t Soda–lime–silica waste glass was used to synthesize a bioactive glass-ceramic through solid-state reactions. In comparison with the conventional route, that is, the melt-quenching and subsequent heat treatment, the present work is an economical technique. Structural and thermal properties of the samples were examined by X-ray diffraction (XRD) and differential thermal analysis (DTA). The in vitro test was utilized to assess the bioactivity level of the samples by Hanks' solution as simulated body fluid (SBF). Bioactivity assessment by atomic absorption spectroscopy (AAS) and scanning electron microscopy (SEM) was revealed that the samples with smaller amount of crystalline phase had a higher level of bioactivity. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Biomaterials have recently been improved for new medical applications [1,2]. A biomaterial is described by the Clemson University Advisory Board for Biomaterials as “a systematically and pharmacologically inert substance designed for implantation within or incorporation with living systems” [3]. Bioactive materials, such as Bioglass®, apatite–wollastonite (A–W) glass-ceramic and tricalcium phosphate [4–7] are a specific group of biomaterials, which attach directly to bone tissue through formation of a biologically active hydroxycarbonate apatite (HCA) layer. This layer, chemically and structurally, corresponds to the bone mineral phases, which allow interfacial bonding [8]. For bioactive glasses, bone bonding was first observed for certain compositional range containing SiO2, Na2O, CaO and P2O5 [9]. There were three main compositional features for these bioglasses: i) SiO2 less than 60 mol%; ii) high amount of Na2O and CaO; and iii) a high CaO/P2O5 ratio which distinguish them from the traditional soda–lime–silica glasses. These compositional features cause the surface to be highly reactive when exposed to an aqueous medium [10]. Among these bone bonding materials, 45S5 bioactive glass (Bioglass®) is the most widely studied system, which consists of 45 wt.% SiO 2, 24.5 wt.% CaO, 24.5 wt.% Na 2O and 6 wt.% P2O5 [11]. One of the major characteristics of this bioactive glass is its highly reactive surface when immersed in human plasma or a similar solution. It has been found that a partial dissolution of the bioactive glass surface takes place, resulting in the formation of a silica-rich gel layer and,
⁎ Corresponding author. Tel.: +98 7116133399; fax: +98 7112307293. E-mail address: [email protected] (B. Hashemi). 0928-4931/$ – see front matter © 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.msec.2014.01.031
subsequently the precipitation of a calcium phosphate layer on the bioactive material occurs [12–14]. Poor mechanical strength of bioactive glasses is a main drawback restricting their application as load-bearing implants. To improve mechanical properties, methods such as the transformation of bioactive glasses into glass-ceramics are used. In this technique, the glasses are exposed to heat treatments which may influence not only the material microstructure and hence their mechanical properties, but also their biological activity [15]. Li et al. [16] and Peitl et al. [17] investigated the effect of the amount of crystalline phase on the bioactivity level of glass-ceramics. Based on Li research, the crystalline phase suppresses the formation of HCA layer on the surface of the bioglass ceramic after being immersed in simulated body fluid while, Peitl stated that the crystalline phase only delays the onset time for formation of HCA layer. Arstila et al. [18] studied the parameters affecting the crystallization of the Bioglass® 45S5 and the influence of the thermal treatment on the bioglass properties [19]. In another research, ElBatal et al. [1] studied the effect of the transition metal oxides on the properties of bioglasses and its derived glassceramics. Siqueira and Zanotto [20] provided a report on the production of the bioactive soda–lime–silicate containing phosphorous in solid solution using solid-state reaction. In this research, the synthesis of bioactive glass-ceramic was carried out by the solid-state reaction method, which is different from meltquenching and subsequent heat treatment, which is the conventional method to obtain glass-ceramics. To the best of our knowledge, this was the first time that soda–lime–silica waste glass was used as the main raw material. For this purpose, the calculated amounts of calcium carbonate, sodium carbonate and phosphorus pentoxide were added to waste glass powder and the resultant mixture was calcined at suitable temperature in order to obtain a bioactive glass-ceramic with 45S5
400
M. Abbasi, B. Hashemi / Materials Science and Engineering C 37 (2014) 399–404
Table 1 XRF analysis of the soda–lime–silica glass.
Table 3 Composition of the Hanks' solution.
Oxide
wt.%
Std. err.
Components
Concentration (g/l)
SiO2 Na2O CaO MgO Al2O3 K2O
72.4 12.1 8.7 4.1 1.30 1.60
0.2 0.2 0.1 0.1 0.05 0.06
CaCl2 KCl KH2PO4 MgCl2·6H20 MgSO4·7H2O NaCl NaHCO3 Na2HPO4
0.14 0.40 0.06 0.10 0.10 8.00 0.35 0.048
bioactive glass composition [11]. In addition, Hanks' solution was utilized to evaluate the bioactivity level of different heat-treated samples. HCA layer on the surface of the immersed samples was investigated by a scanning electron microscope (Type VEGA-TESCAN-LMU) equipped with X-ray energy dispersive spectroscopy.
2. Materials and methods The samples were prepared from reagent-grade powders: calcium carbonate (CaCO3, Merck, ≥ 99%), sodium carbonate (Na2CO3, Merck, ≥99.5%), phosphorus pentoxide (P2O5, Dae-Jung Chemical & Metal Co, ≥97%) and soda–lime–silica glass powder. A white glass powder was obtained after the glass cullets were milled in a ball mill with stainless steel balls. The XRF (type ARL 8410) analysis of soda–lime–silica glass is summarized in Table 1. With the addition of proper amounts of CaCO3, Na2CO3 and P2O5 to the glass powder, its composition was modified according to Bioglass® 45S5 composition. The homogenization and grinding of the batch mix were achieved in an attritor mill in isopropyl alcohol for 2 h using zirconia balls (BPR 20:1) as grinding media. After drying and sieving, the powder (named as BGC) was compacted into disks (10 × 2 mm) by isostatic pressing. To achieve glass-ceramics with various percentages of crystalline phases, different heat treatments were performed on the samples in air in a box furnace, with a heating rate of 5 °C/min. These data are summarized in Table 2. The thermal behavior of the pulverized BGC sample was examined by DTA/TG (PLSTA 1640) with Al2O3 powder as the standard material. A uniform heating rate of 10 °C/min was adopted up to 1000 °C. XRD was performed to identify the crystalline phases formed in the thermally treated glasses using a Bruker D8 Advance X-ray diffractometer with Cu Kα radiation equipped with “X'Pert HighScore” software. The IR reflection spectra of the samples in the range of 4000–400 cm−1 were determined using a Bruker Vector 22 FTIR spectrometer. The bioactivity test was conducted according to Kokubo and Takadama [21]. Prepared glass-ceramic samples were immersed in Hanks' solution. The required amount of Hanks' solution for each sample was calculated by the following Eq. Vs ¼ Sa =10
ð1Þ
where Vs is the volume of the solution (ml) and Sa is the apparent surface area of the sample (mm2). In this research, the volume of Hanks' solution was greater than the calculated Vs because the prepared samples were porous. The composition of Hanks' solution is shown in Table 3. All the samples were suspended in polyethylene containers and incubated at 37 °C for 1, 3, 7 and 30 day(s) in Hanks' solution. The immersed samples were removed from the solution, washed with distilled water and dried at room temperature. The concentration of the Ca2+ ion in Hanks' solution after soaking was examined by atomic absorption spectroscopy (Type Philips, PU0100X). The formation of the
3. Results and discussion 3.1. Thermal analysis Before DTA/TG analysis, an XRD analysis of the BGC sample was conducted (Fig. 1). In this pattern, the peaks correspond to Na2CO3 and CaCO3 and those related to P2O5 are not observed. This could be due to the dissolution of P2O5 in the glass phase during milling. Fig. 2 demonstrates the DTA/TG analysis of the BGC powder. It is clear that there are two endothermic peaks at temperatures between 80 and 100 °C. These peaks are related to the evaporation of the physically adsorbed water and organic impurities. An exothermic peak is observed at 320 °C due to the phase transformation of Na2CO3 [22]. There are two overlapped peaks, namely endothermic and exothermic ones at temperatures between 670 and 690 °C with a decrease in weight corresponding to the TG curve. In order to determine the nature of these peaks, a BGC sample was heated at 700 °C for 3 h and then analyzed by XRD as shown in Fig. 3. The absence of the CaCO3 peaks and the corresponding weight loss in the TG curve show decomposition of CaCO3 and release of CO2 from the system at a temperature of about 670 °C. The peaks in this figure show the presence of sodium–calcium–silicate (Ca2Na2Si3O9) and sodium–calcium–phosphate phases (CaNaPO4). Arstila et al. [18] divided the silicate-based bioglasses into two groups: 1) the glasses with the transition temperatures of about 500 °C and the onset of crystallization at below 750 °C; and 2) the glasses with transition temperatures between 550 and 600 °C and the onset of crystallization at about 900 °C. The group 1 glasses form the sodium– calcium–silicate phase, whereas the glasses related to group 2 form wollastonite. Therefore, the heated sample of this work belongs to the first group and the temperature 690 °C refers to the crystallization temperature of new phases.
Table 2 Heat treatment conditions of the samples. Sample no.
Temperature (°C)
Time (h)
BGC1 BGC2 BGC3 BGC4
950 900 900 850
3 6 3 3
Fig. 1. XRD pattern of the BGC sample.
M. Abbasi, B. Hashemi / Materials Science and Engineering C 37 (2014) 399–404
401
Fig. 2. DTA/TG analysis curves for the BGC sample.
3.2. XRD measurements Fig. 4 illustrates the XRD analysis of the glass-ceramics. It is obvious that all samples have sodium–calcium–silicate and sodium–calcium– phosphate crystalline phases. It is evident from XRD patterns that an increase in the temperature resulted in an increase in the amount of crystalline phase. In Fig. 4(d) there is a halo around 2θ = 30°, which indicates the existence of the residual glassy phases in this sample, which vanished as the temperature increased. In addition, as the temperature increased, the peaks became sharper and their intensity increased. Actually, the behavior of the phosphorus in the crystallization of the phosphate phase in the silicate glasses is a controversial issue. The phosphorus ions can replace the silicon ions at the glass tetrahedral sites. However, according to the McMillan [23] the double oxygen bond (P_O) can be formed in the glass phase and it is suitable for forming the phosphate phase in the silicate network. Hence, the tendency toward the crystallization of the phosphate phase increases. Peitl et al. [24] stated that a thermal treatment in normal condition is not sufficient to form a calcium–phosphate phase (an apatite-like phase). They also stated that under these conditions phosphorus ions remain in the form of solid solution in the sodium–calcium–silicate phase and that a drastic heat treatment (long time and high temperature) is required to crystallize an apatite-like phase. Siqueira and Zanotto [20] also synthesized Na2Ca2Si3O9 containing phosphorus in solid solution using the solid-state reaction (950 °C/480 min). They attributed the changes observed in the FTIR spectrum to the formation of NaCaPO4, which did not exist in the XRD pattern.
Fig. 3. XRD pattern of the BGC sample heated at 700 °C.
Fig. 4. XRD patterns of the a) BGC1 sample, b) BGC2 sample, c) BGC3 sample and d) BGC4 sample.
3.3. FTIR spectroscopy The FTIR analyses of the heat-treated samples are shown in Fig. 5. It is clear that the spectra of all samples are similar. According to the literature, the peaks near wave numbers 530, 575 and 620 cm− 1 were assigned to a calcium phosphate or an apatite-like phase. Furthermore, there was a peak at 1040 cm−1, which was related to the stretching PO4 vibration [25]. The peaks at 450, 930 and 1080 cm−1 were attributed to the Si\O\Si vibration. These peaks were related to the bond stretching in amorphous silica, the stretching of non-bridging oxygen atoms and the asymmetric stretching of bridging oxygen atoms within the tetrahedral site, respectively [1]. In the 1000–1100 cm−1 region the asymmetric vibration Si\O\Si is very strong due to the overlap of the stretching PO4 vibrational peaks [10,25]. The results obtained from XRD and FTIR experiments indicated that sodium–calcium–phosphate and sodium– calcium–silicate phases crystallized in all the samples by a one-step thermal treatment. 3.4. Bioactivity Fig. 6 exhibits the Ca2+ concentration changes in Hanks' solution. According to the Hench model [9] that was proposed for the reaction on the surface of the bioactive material, at first the concentrations of the Ca2+, Na+, Si4+ and P5+ ions increase in the solution. Afterward the Ca2+ and P5+ ions move to the surface of the material and a CaO– P2O5-rich amorphous layer is formed upon the SiO2-rich layer. Therefore, concentrations of Ca2+ and P5+ ions decrease in the solution. At last the crystallization occurs, leading to the formation of an HCA layer. From Fig. 6 and in accordance with the Hench model, an HCA
Fig. 5. FTIR spectrum of the BGC1, BGC2, BGC3 and BGC4 samples.
402
M. Abbasi, B. Hashemi / Materials Science and Engineering C 37 (2014) 399–404
Fig. 6. Ca2+ ion concentration in Hanks' solution for BGC1, BGC2, BGC3 and BGC4 samples versus time.
layer must not be formed on the BGC1 sample since the concentration of the Ca2+ ion in the solution has only an increasing trend. Fig. 7(a) demonstrates the SEM image of the BGC1 sample after immersion in Hanks'
solution for 1 month. According to this figure, no layer has been formed on this sample. The EDS analysis shows that the Ca/P ratio of this sample is 1.96 (Fig. 8(a)), while this ratio for an ideal hydroxyapatite is 1.67 [26]. It should be noted that the dimension of the y-axis in Fig. 8 is cps/ev. Fig. 6 reveals that the BGC2 and BGC3 samples have similar behaviors. In both of these samples the Ca2+ ion concentration increased for 1 week and then the Ca2+ ion was absorbed slightly into the surface. Fig. 7(b) shows the SEM image of the BGC2 sample after having been soaked in the solution for 1 month. There was no perceptible change on the surface of this sample. The Ca/P ratio for BGC2 and BGC3 samples was equal to 2.00 (Fig. 8(b)), confirming that the apatite layer has not been formed. The concentration variation of the Ca2+ ion for the BGC4 sample (Fig. 6) indicated that this sample had a good level of bioactivity because the calcium ions were absorbed into the surface after being immersed in the solution for 3 days. Fig. 7(c), (d) and (e) demonstrates the SEM images of the BGC4 sample, which were taken before soaking and after 7 and 30 days of soaking in the solution, respectively. The formation of a phase with a spherical morphology was observed after 1 week (Fig. 7(d)). This phase was homogenized further after 1 month (Fig. 7(e)). Fig. 7(f) shows the cross-sectional image of the BGC4 sample. In this figure, the formation of the HCA layer on the
Fig. 7. SEM images of a) the BGC1 sample after 1 month of immersion, b) the BGC2 sample after 1 month of immersion, c) the BGC4 sample before immersion, d) the BGC4 after 7 days of immersion, e) the BGC4 after 30 days of immersion and f) cross section of the BGC4 after 1 month of immersion.
M. Abbasi, B. Hashemi / Materials Science and Engineering C 37 (2014) 399–404
surface is observed clearly. In addition, the EDS analysis indicated that the Ca/P ratio was equal to 1.64 (Fig. 8(e) and (f)). Results show that the heat treatment conditions were effective in the formation of an HCA layer and in comparison with other researches; this could be due to the amounts of crystalline phases in the samples. Li et al. [16] showed that crystallization could prevent the bioactivity of the Bioglass®. They observed that an HCA layer was formed in the simulated body fluid (SBF) only when the glass-ceramic contained more than 90% amorphous phase. However, Peitl et al. [17] showed that the crystallization in the Bioglass® 45S5 did not prevent the formation of the HCA layer, even though the amount of crystalline phase was 100%. They stated that by increasing the amount of the crystalline phase the onset time of the HCA layer formation increased. In addition, they showed that the state of the phosphorus ions affect the bioactivity. The glass-ceramics containing a crystalline apatite-phase are much less bioactive than the materials containing phosphorus in solid solution. Nevertheless, in this research the phosphorus ion state did not have any effect on the bioactivity because the entire samples contain the crystalline sodium–calcium–phosphate phase and their bioactivity levels were different only due to the difference in the thermal treatment conditions of the samples. It should be noted that not only the amorphous phase content can promote bioactivity, but also the amount of Si\OH nuclei on the surface of bioactive glass-ceramic is other possible factor which influences HCA layer formation [27].
403
4. Conclusions A review of the literature shows that for the first time a bioactive glass-ceramic was synthesized using soda–lime–silica waste glass by the solid-state reaction method rather than conventional melt-quenching one. The results of DTA and XRD analyses revealed that at temperature about 690 °C two crystalline phases, sodium–calcium–silicate and sodium–calcium–phosphate phases, were formed. The in vitro bioactivity test showed that, first, the amount of crystalline phase influenced the bioactivity level. The samples with a smaller amount of the crystalline phase had a higher bioactivity level. Second, the crystalline apatite-like phase did not suppress the bioactivity. The BGC4 sample with the lowest amount of crystalline phase, showed the highest bioactivity. The onset time of the HCA layer formation on the BGC4 sample was 7 days which completed and homogenized within 30 days.
References [1] F.H. ElBatal, G.T. El-Bassyouni, Silicon 3 (2011) 185–197. [2] M. Talha, C.K. Behera, O.P. Sinha, Mater. Sci. Eng. C 33 (2013) 3563–3575. [3] J.Y. Wong, J.D. Bronzino, Introduction, in: J.Y. Wong, J.D. Bronzino (Eds.), Biomaterials, CRC Press, New York, 2007. [4] M. Magallanes-Perdomo, S. Meille, J.M. Chenal, E. Pacard, J. Chevalier, J. Eur. Ceram. Soc. 32 (2012) 2765–2775. [5] L. Tan, X. Yu, P. Wan, K. Yang, J. Mater. Sci. Technol. 29 (2013) 503–513.
Fig. 8. EDS analysis of the surface of the samples. a) The BGC1 sample after 1 month of immersion, b) the BGC2 sample after 1 month of immersion, c) the BGC4 after 7 days of immersion, d) the BGC4 after 30 days of immersion, e) the HCA layer which is formed on top of the BGC4 sample in cross section image and f) the BGC4 sample in cross-section image.
404
M. Abbasi, B. Hashemi / Materials Science and Engineering C 37 (2014) 399–404
[6] C. Zou, K. Cheng, W. Weng, C. Song, P. Du, G. Shen, G. Han, J. Alloys Compd. 509 (2011) 6852–6858. [7] M. Kamitakahara, C. Ohtsuki, H. Inada, M. Tanihara, T. Miyazaki, Acta Biomater. 2 (2006) 467–471. [8] P.N. De Aza, A.H. De Aza, P. Pena, S. De Aza, Bol. Soc. Esp. Ceram. 46 (2007) 45–55. [9] L.L. Hench, R.J. Splinter, W.C. Allen, T.K. Greenlee Jr., J. Biomed. Mater. Res. Symp. 2 (1971) 117–141. [10] H.A. ElBatal, M.A. Azooz, E.M.A. Khalil, A. Soltan Monem, Y.M. Hamdy, Mat. Chem. Phys. 80 (2003) 599–609. [11] L.L. Hench, J. Mater. Sci. Mater. Med. 17 (2006) 967–978. [12] L.L. Hench, J. Am. Ceram. Soc. 81 (1998) 1705–1728. [13] D.C. Chepper, J.E. Gough, P.M. Embanga, I. Notingher, L.L. Hench, M.M. Hall, J. Mater. Sci. Mater. Med. 15 (2004) 803. [14] H.A. ElBatal, E.M.A. Khalil, Y.M. Hamdy, Ceram. Int. 35 (2009) 1195–1204.
[15] L. Lefebvre, J. Chevalier, L. Gremillard, R. Zenati, G. Thollet, D. Bernache-Assolant, A. Govin, Acta Mater. 55 (2007) 3305–3313. [16] P. Li, F. Zhang, T. Kokubo, J. Mater. Sci. Mater. Med. 3 (1992) 452. [17] O. Peitl, G.P. LaTorre, L.L. Hench, J. Biomed. Mater. Res. 30 (1996) 509–514. [18] H. Arstila, E. Vedel, L. Hupa, M. Hupa, J. Eur. Ceram. Soc. 27 (2007) 1543–1546. [19] H. Arstila, L. Hupa, K.H. Karlsson, M. Hupa, J. Non-Cryst. Solids 354 (2008) 722–728. [20] R.L. Siqueira, E.D. Zanotto, Mater. Sci. Eng. C 31 (2011) 1791–1799. [21] T. Kokubo, H. Takadama, Biomaterials 27 (2006) 2907–2915. [22] A. Arakcheeva, G. Chapuis, Acta Cryst. B 61 (2005) 601–607. [23] P.W. McMillan, Glass-ceramics, 2nd ed. Academic Press, London, 1979. [24] O. Peitl, E.D. Zanotto, L.L. Hench, J. Non-Cryst. Solids 292 (2001) 115–126. [25] X. Chatzistavroa, T. Zorba, E. Kontonasaki, K. Chrissafis, P. Koidis, K.M. Paraskevopoulos, Phys. Stat. Sol. (a) 201 (2004) 944–951. [26] K. Ishikawa, P. Ducheyne, S. Radin, J. Mater. Sci. Mater. Med. 4 (1993) 165–168. [27] J.R. Jones, T.F. Kemp, M.E. Smith, Key Eng. Maer. 309–311 (2006) 1031–1034.