Raman spectroscopic study of bioactive silica-based glasses - Hindawi

Spectroscopy 23 (2009) 227–232 DOI 10.3233/SPE-2009-0380 IOS Press

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Raman spectroscopic study of bioactive silica-based glasses: The role of the alkali/alkali earth ratio on the Non-Bridging Oxygen/Bridging Oxygen (NBO/BO) ratio Lucia Marsich a , Loredana Moimas b , Valter Sergo a,c,∗ and Chiara Schmid a,c a

DMRN University of Trieste, Trieste, Italy Inion Ltd., Tampere, Finland c Center of Excellence for Nanostructured Materials, University of Trieste, Trieste, Italy b

Abstract. Raman spectra of bioactive glasses of the Na2 O–K2 O–MgO–CaO–B2 O3 –P2 O5 –SiO2 to be used in bone reconstruction systems have been collected from samples with three different concentrations of alkali and alkali earth elements. Compositions were chosen with a constant total amount of modifiers and formers, with only minor changes among the formers. The ratio of Non-Bridging Oxygens to Bridging Oxygens (NBO/BO) has been obtained from the Raman spectra and reported as a function of the alkali/alkali earth ratio, showing a linear increase. Dissolution tests indicate also a linear dependence of the amount of Na+ , K+ and Ca++ ions leached in water on the alkali/alkali earth ratio. Consequently a calibration plot correlating the NBO/BO ratio with the amount of Na+ , K+ and Ca++ ions leached in water has been obtained, thus demonstrating the sensitivity of the method, given that the changes from one glass composition to the other are of the order of some points in percentage among the glass modifiers. Keywords: Bioglasses, Raman spectroscopy, non-bridging oxygen, dissolution test

1. Introduction It is widely known that bone grafting procedures are very frequent, and that there is a high demand for synthetic materials that can successfully sustain and promote natural bone re-growth. Various materials [1–4] have been developed for this purpose; among them, a prominent role is played by bioactive glasses, which have shown the ability to improve bone bonding due to the formation of a superficial calcium phosphate layer when these materials come in contact with biological fluids [5–9]. Historically, Hench [10] and colleagues first introduced bioactive glasses in 1969, discovering that bone could bond chemically to silica glasses containing Na2 O, CaO and P2 O5 . From a clinical perspective, numerous studies have demonstrated that bioactive glasses are not only osteoconductive but also osteoproductive [11–14], which means that they have the capability to enhance proliferation and differentiation of progenitor cells, thus accelerating bone healing. From a materials science perspective, for many years it *

Corresponding author: Valter Sergo, CENMAT – Center of Excellence for Nanostructured Materials, University of Trieste, Via Valerio 6A, I-34127 Trieste, Italy. Tel.: +39 040 5583702; Fax: +39 040 572044; E-mail: [email protected]. 0712-4813/09/$17.00 © 2009 – IOS Press and the authors. All rights reserved

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L. Marsich et al. / Raman spectroscopic study of bioactive silica-based glasses

has been difficult to process thermally melt-derived bioactive glass because of its tendency to devitrify, till it was discovered how to enlarge the working range for bioactive glasses by adding K2 O, MgO and B2 O3 [15]. Now it is possible to obtain 3-dimensional scaffolds for bone reconstruction by sintering bioactive glass fibres that have been previously spun from melt [16]. Clearly, the goal for this kind of structures is to match the dissolution rate of the bioactive glass with the growth rate of the bone. In this sense, the dissolution behavior of bioactive glasses is very important. In line with these premises, the objective of this work is (i) to measure the NBO/BO ratio as a function of the alkali/alkali earth ratio by means of a quick, non-invasive method, identified in Raman spectroscopy, and (ii) to show a correlation between the NBO/BO ratio thus obtained and the concentration of the leached alkali and alkaline earth ions, as determined on the solutions obtained after dissolution tests. 2. Materials and methods Three bioactive glasses have been investigated, with different compositions with respect to the alkali/alkali earth ratio, while the total amount of the glass formers remained constant. The absolute quantities of the alkali and alkaline earths were not very different among the three compositions, in order to assess the sensitivity of the method. Table 1 presents the composition of the three glasses. The samples were in form of fibres, produced by melt spinning [16]. Raman spectra have been acquired by a Renishaw Invia Raman Microscope; the wavelength and the power of the laser used as excitation source were 514.5 nm and 20 mW, respectively. A 50× objective has been used to focus the incident light on the sample and to collect the radiation scattered by the sample (back-scattered configuration). The acquisition time of a single spectrum was 360 seconds. At least 10 spectra were acquired for each composition, taking care to acquire the spectra from different fibres. The Raman spectra were analysed with the program Origin 7.5, fitting the vibrational bands with Asymmetric double sigmoidal function (Asym2Sig in the Origin software, OriginLab Corporation, Northampton, MA 01060, USA). The dissolution tests were conducted soaking 2 g of glass fibres (75 µm in diameter and 3 mm long) in 50 ml of deionised water at 98.0 ± 0.5◦ C for 1 hour. Hence they were actually hydrolysis tests. The solutions were filtered and then Na+ , K+ and Ca++ content were determined by acid titration (HCl 0.01 M) and by atomic absorption (Perkin-Elmer 2380 double ray); Ca++ was determined by atomic emission. 3. Results and discussion An example of the spectra for the three bioglass compositions is reported in Fig. 1. It is possible to see clearly the typical vibration bands of bioactive glasses [18]: • 560–650 cm−1 : bond-rocking vibration (the oxygen atoms move perpendicularly to the Si–O–Si plane); Table 1 Composition of the three bioglasses expressed in molar percentage Glass BG1 BG2 BG3

Na2 O 12.10 12.90 11.07

K2 O 10.10 10.90 9.08

MgO 5.00 5.00 5.00

CaO 14.80 13.20 16.85

B2 O3 0.90 0.90 0.90

P2 O 5 0.90 0.90 0.90

SiO2 56.20 56.20 56.20

Alkali 22.20 23.80 20.15

Alkali earths 19.80 18.20 21.85

Formers 58.00 58.00 58.00


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Fig. 1. Raman spectra of the three glass compositions. The spectrum of glass BG1 reports, as an example, the deconvolution in two bands of the spectral regions containing the information on Bridging Oxygen (BO) and Non-Bridging Oxygen (NBO) bands. The areas obtained from the deconvolution are used to compute the values of Table 2.

Table 2 Mean areal ratio of the bands at 940 cm−1 (NBO) and 1080 cm−1 (BO) for the three different glasses Glass BG1 BG2 BG3

−1

−1

A940 cm /A1080 cm 0.261397 0.280146 0.234893

Standard deviation 0.013619 0.016941 0.010464

• 750–800 cm−1 : bond bending vibration (the oxygen atoms move to and from the two adjacent Si atoms in the Si–O–Si plane); • 900–980 cm−1 : vibrations of Non-Bridging Oxygen (NBO) atoms; • 1000–1200 cm−1 : bond stretching vibrations (the BO’s move parallel to the Si–Si lines in the opposite direction to their Si neighbors; these are the BO vibrations). Hence, the bands of interest for the NBO/BO analysis are those at about 945 cm−1 (NBO) and 1080 cm−1 (BO); another vibrational indicator of the network disruption is given by the strong asymmetry in the shape of the BO band at 1080 cm−1 . The results of the mathematical fitting of these bands, considering the area of fitting curves as proportional to the band intensity, are reported in Table 2. Though not reported here, we observe incidentally that there are no significant frequency shifts of the bands from one composition to the other; marked frequency shifts of the vibrational bands are reported only if the SiO2 content is changed [18], whereas in our case the total SiO2 content of the three compositions is identical. The results of the dissolution, hydrolysis test are reported in Table 3; the values of Mg++ ion have not been reported because they were equal, within the experimental error, with those determined in the pure water used for the hydrolysis test. Moreover, the initial content of MgO was identical for all three compositions. The titration method does not allow distinguishing between the elements and provides directly the total (K+ + Na+ + Ca++ ) concentration. Comparing the last two columns of Table 3, it

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Table 3 Milliequivalents (± standard deviation) of K+ , Na+ and Ca++ as determined from atomic absorption (AA), atomic emission (AE) and titration with HCl 0.01 M Glass

BG1 BG2 BG3

K+ (AA) [meq/100 g glass] 3.29 ± 0.03 7.01 ± 0.13 1.67 ± 0.02

Na+ (AA) [meq/100 g glass] 5.28 ± 0.02 11.34 ± 0.06 2.51 ± 0.02

Ca++ (AE) [meq/100 g glass] 1.17 ± 0.01 0.64 ± 0.003 1.38 ± 0.01

(K+ + Na+ + Ca++ ) Total AA + AE [meq/100 g glass] 9.74 18.99 5.56

(K+ + Na+ + Ca++ ) (Titration) [meq/100 g glass] 8.85 ± 0.92 18.30 ± 0.11 5.28 ± 0.18

Fig. 2. The amount of (K+ + Na+ + Ca++ ) ions leached in water (left Y -axis) and the NBO/BO ratio (right Y -axis) vs. the alkali/alkali earth ratio in the original glass composition. The best fitting lines are traced and the pertinent R correlation parameter is reported for both sets of data points.

is immediate to recognize that the two analytical methods, acid titration and atomic absorption, give congruent results. Given that the total amount of modifiers is identical for all three compositions, the hydrolysis tests indicate a clear dependence on the alkali/alkali earth ratio (see Fig. 2). A confluence of the Raman and dissolution experiments is reported in Fig. 2. As it can be seen, both the NBO/BO ratio and the total amount of Na+ + K+ + Ca++ ions leached increase with increasing alkali/alkali earth ratio. Figure 2 shows also that (i) alkali oxides, as expected, tend to make the glass less resistant to dissolution than the alkali earth oxides and, more important, (ii) the NBO/BO ratio as derived from the Raman spectra is directly proportional to the alkali/alkali earth ratio. This latter result is new, in the sense that some studies have appeared concerning the influence of alkali modifiers on the Raman spectrum of glasses [19] and on the leaching behaviour of glasses [17,20], but none is available on the interplay between alkali and alkali earth modifiers within the same overall composition of a glass. Indeed, the double set of data of Fig. 2 hints also at the possibility of using the Raman spectra to predict quantitatively, albeit for a homogenous family of glasses, the dissolution behaviour of alkaline and alkaline earths ions, as reported in Fig. 3. It is worth emphasizing that the discriminating power the Raman analysis of the NBO/BO has been tested for three glass of almost identical compositions, differing only for few points percentage of the total content of glass modifiers.


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Fig. 3. The NBO/BO ratio in the original glass composition vs. the amount of (K+ + Na+ + Ca++ ) ions leached in water. The best fitting line is traced and the pertinent R correlation parameter is reported.

Acknowledgements This work has been partly supported by BINASP/INFRAEUR funding and partly by internal DRMN funding. References [1] P.D. Costantino and C.D. Friedman, Synthetic bone graft substitutes, Otolaryng. Clin. North Am. 27 (1994), 1037–1074. [2] T.E. Orr, P.A. Vilars, S.L. Mitchell, H.P. Hsu and M. Spector, Compressive properties of cancellous bone defects in a rabbit model treated with particles of natural bone mineral and synthetic hydroxyapatite, Biomaterials 22 (2001), 1953–1959. [3] C.G. Finkemeier, Bone-grafting and bone-graft substitutes, J. Bone Joint Surg. Am. 84-A (2002), 454–464. [4] V.J. Sammarco and L. Chang, Modern issues in bone graft substitutes and advances in bone tissue technology, Foot Ankle Clin. 7 (2002), 19–41. [5] H. Oonishi, S. Kushitami, E. Yasukawa, H. Iwaki, L.L. Hench, J. Wilson, E. Tsuji and T. Sugihara, Particulate bioglass compared with hydroxyapatite as bone graft substitute, Clin. Orthop. Rel. Res. 334 (1987), 316–325. [6] T. Kokubo, S. Ito, Z.T. Huang, T. Hayashi, S. Sakka, T. Kitsugi and T. Yamamuro, Ca, P-rich layer formed on high-strength bioactive glass-ceramic, J. Biomed. Mater. Res. 24 (1990), 331–343. [7] A.M. Gatti and D. Zaffe, A short-term behaviour of two similar active glasses used as granules in the repair of bone defects, Biomaterials 12 (1991), 497–504. [8] E.J.G. Schepers and P. Ducheyne, Bioactive glass particles of narrow size range for the treatment of oral bone defects: a 1–24 month experiment with several materials and particle sizes and size ranges, J. Oral Rehab. 24 (1997), 171–181. [9] L. Moimas, G. De Rosa, V. Sergo and C. Schmid, Bioactive porous scaffolds for tissue engineering applications: investigation on the degradation process by Raman spectroscopy and Scanning Electron Microscopy, J. Appl. Biomat. Biomech. 4(2) (2006), 102–109. [10] L.L. Hench and Ö. Andersson, in: An Introduction to Bioceramics, L.L. Hench and J. Wilson, eds, World Scientific, Singapore, 1993, Chapter 3. [11] J. Wilson and S.B. Low, Bioactive ceramics for periodontal treatment: comparative studies in Patus monkeys, J. Appl. Biomater. 3 (1992), 123–129. [12] L. Moimas, M. Biasotto, R. Di Lenarda, A. Olivo and C. Schmid, Rabbit pilot study on the resorbability of threedimensional bioactive glass fibre scaffolds, Acta Biomater. 2 (2006), 191–199. [13] P. Ducheyne and Q. Qiu, Bioactive ceramics: the effect of surface reactivity on bone formation and bone cell function, Biomaterials 20 (1999), 2287–2303.

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[14] I.D. Xynos, M.V.J. Hukkanen, J.J. Batten, L.D. Buttery, L.L. Hench and J.M. Polak, Bioglass 45S5 stimulates osteoblasts turnover and enhances bone formation in vitro: implication and applications for bone tissue engineering, Calcif. Tissue Int. 67 (2002), 321–329. [15] M. Brink, The influence of alkali and alkaline earths on the working range of bioactive glasses, J. Biomed. Mater. Res. 36 (1997), 109–117. [16] E.M. Pirhonen, L. Moimas and J. Haapanen, Porous bioactive 3-D glass fiber scaffolds for tissue engineering applications manufactured by sintering technique, Key Eng. Mater. 240–242 (2002), 237–243. [17] B.C. Bunker, Molecular mechanisms for corrosion of silica and silicate glasses, J. Non-Crystal. Solids 179 (1994), 300. [18] P. Gonzalez, J. Serra, S. Liste, S. Chiussi, B. Leon and M. Perez-Amor, Raman spectroscopy study of bioactive silica based glasses, J. Non-Crystal. Solids 320 (2003), 92. [19] S.A. Brawer and W.B. White, Raman spectroscopic investigation of the structure of silicate glasses. I. The binary alkali silicates, J. Chem. Phys. 63 (1975), 2421–2432. [20] R.W. Douglas and T.M.M. El-Shamy, Reactions of glasses with aqueous solutions, J. Am. Ceram. Soc. 50 (1967), 1–12.

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