Mechanical Properties and In Vitro Physico-chemical Reactivity of Gel-derived SiO2–Na2O–CaO–P2O5 Glass from Sand Enobong R. Essien,a* Luqman A. Adamsb and Femi O. Igbarib aDepartment of Chemical Sciences, Bells University of Technology, P.M.B 1015 Ota, Ogun, Nigeria bDepartment of Chemistry, University of Lagos, Nigeria (Received: Dec. 4, 2015; Accepted: May 11, 2016; Published Online: ???; DOI: 10.1002/jccs.201500496) In the present report, a bioactive glass was synthesized from silica sand as economic substitute to alkoxy silane reagents. Sodium metasilicate (Na2SiO3) obtained from the sand was hydrolyzed and gelled using appropriate reagents before sintering at 950 �C for 3 h to produce glass in the system SiO2–Na2O– CaO–P2O5. Compression test was conducted to investigate the mechanical strength of the glass, while im- mersion studies in simulated body fluid (SBF) was used to evaluate reactivity, bioactivity and de- gradability. Furthermore, the glass samples were characterized by scanning electron microscopy (SEM), X–ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and energy dispersive X–ray spectroscopy (EDX) to evaluate the microstructure and confirm apatite formation on the glass surface. The glass, dominated by bioactive sodium calcium silicate, Na2Ca2Si3O9 (combeite) crystals, had mechan- ical strength of 0.37 MPa and showed potentials for application as scaffold in bone repair. Keywords: Sand; Silica source; Na2Ca2Si3O9; Mechanical strength; Bioactivity; Characterization. INTRODUCTION Skeletal regeneration has continued to gain promi- nence in biomedical research due to increasing clinical de- mand for biocompatible substitute materials for repair of damaged or diseased bones as emphasis shifts from tissue replacement to regeneration.1,2 Certain inorganic materials capable of eliciting osteoinductive behaviour in the pre- sence of physiological fluids are being used to act as temporary scaffolds to facilitate complete restoration of the damaged bone. Some of these materials, which include bioactive glasses and ceramics, calcium phosphates (CaP’s) such as hydroxyapatite (HA), tricalcium phosphate (TCP), biphasic calcium phosphate (BCP) and biodegradable polymers in combination with inorganic materials as com- posites,3,4 when used as implants, undergo a process called “bioactive fixation” forming interfacial bonds to the host tissue through the formation of biologically active hydro- xyapatite (HA) layer on the surface of the implants.5 The bond thus formed at the implant-bone interface has a strength similar to bone. An ideal scaffold should be highly porous to allow for cell seeding and infiltration, tissue ingrowth and vascular- ization, as well as nutrient delivery and waste removal.3 It is generally agreed that a minimum of 100 �m intercon- nected aperture pore diameter is required by the scaffold to accomplish this function in vivo.6 A scaffold should also stimulate osteoblastic cell proliferation and differentiation in vivo while acting as a passive material during the regen- eration process.4,7 Bioactive glasses are based on a random network of silica tetrahedra containing Si–O–Si bonds. The network can be modified by the addition of network modifiers such as Ca, Na and P, which are bonded to the network via non-bridging oxygen bonds. The mechanism of bone bond- ing to bioactive glasses is due to the formation of a carbon- ate substituted hydroxyapatite layer (HCA) on the surface of the materials after immersion in body fluid.8,9 This layer is similar to the apatite layer in bone and, therefore, a strong bond can form.10 The foremost bioactive glass is the silicate-based 45S5 Bioglass� having the composition (46.1 SiO2, 24.4 Na2O, 26.9 CaO and 2.6 P2O5, in mol%),9 which was first prepared using the melting method. This Bioglass� (Perio- glas) is being used clinically to treat periodontal disease and as a bone filling material (Novabone10,11). Another im- portant use of Bioglass� implants has been in the replace- ment of damaged middle ear bones and as tooth root re- placements.12 The key compositional features that are responsible for the bioactivity of 45S5 glass are its low SiO2 content (when compared to more chemically durable silicate glasses), high Na2O and CaO content, and high CaO/P2O5 ratio.13 J. Chin. Chem. Soc. 2016, 63, 000-000 © 2016 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1 JOURNAL OF THE CHINESE CHEMICAL SOCIETYArticle * Corresponding author. Tel: +2348139447446; Email: reggiessien@gmail.com Most routes to synthesis of bioactive glasses are through the sol-gel processing method that involves the hy- drolysis of alkoxide precursors to form a sol. The sol formed undergoes polycondensation to form a silica net- work (gel). Heat treatment of the resultant gel after aging affords the glass.14,15 Several advantages of a sol-gel-de- rived glass over a melt-derived glass include; relatively lower processing temperatures,16 higher purity and homo- geneity,16 wider compositional range of up to 100% of SiO2 while maintaining bioactivity.17 Additionally, the glass dis- plays higher bioactivity and resorbability in aqueous media due to its nanometre scale textural porosity which results in a higher surface area for cation exchange, and exposure of many silanol groups to the solution to act as nucleation sites for HCA layer formation for bone bonding.18 The bonding to living bone of HCA layer occurs upon a sequence of reactions on the material surface19 followed by cellular reactions. The reactions on the glass surface can be summarized to include ion leaching/exchange, dissolu- tion of the glass network and precipitation and growth of calcium deficient carbonated apatite (HCA) surface,8,9,19 while cellular reactions include colonization, proliferation and differentiation of relevant (bone) cells.10 Mechanical competence is key for application of the scaffold material in load-bearing sites. The material should be able to act as temporary support and also match the bioresorption kinetics of the damaged site pending when a new bone is formed. A limitation in the application of bioactive glasses is their low fracture toughness. Densi- fication at high temperatures is one of the strategies to opti- mize the mechanical properties of bioactive glasses. In ad- dition, inclusion of Na2O in the composition may result in improved mechanical capability because Na2O containing bioactive glasses transform from amorphous to glass ce- ramic forming hard, yet biodegradable crystalline phase Na2Ca2Si3O9 (combeite) when sintered.20,21 Crystallinity is thought to have an adverse effect on the reactivity of the glass in physiological fluids, thus decreasing apatite forma- tion and protein adsorption profile.22 To avoid complete crystallization and its inherent effects on bioactivity of glass, a sintering protocol where the glass is partially crystallized is desirable. Large scale preparation of bioactive glasses faces a huge challenge because of high cost of alkoxysilanes such as tetramethyl orthosilicate (TMOS) and tetraethyl ortho- silicate (TEOS), which serve as precursors for SiO2 as glass network former.22-27 As a follow-up to our previous work23 we report herein the study of the mechanical and dissolu- tion behaviour in SBF of porous silicate-based quaternary bioactive glass from sand as an inexpensive substitute to alkoxysilanes. RESULTS AND DISCUSSION Comparison of chemical bonds present in the sodium metasilicate prepared from sand (SM) and commercial sodium metasilicate, Na2SiO3.9H2O (CM) The chemical bonds present in the liquid sodium metasilicate synthesized from sand (SM) and commercial sodium metasilicate, Na2SiO3.9H2O (CM) (Sigma-Ald- rich) as evaluated by FTIR, are shown in Figure 1, while the comparison of bond types present in the two samples are presented in Table 1. The spectra of both samples are similar showing the presence Qn [SiO4] silicate tetrahedra connectivity, where n is the number of bridging oxygens (BO) on the tetrahedral unit.28 The frequencies at 893, 970 and 1196 cm-1 in CM (Figure 1(a) are considered for Q0, Q1 and Q4 species respectively; while the spectra of SM (Fig- ure 1(b) shows the presence of only Q0 and Q1 at 899 and 2 www.jccs.wiley-vch.de © 2016 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim J. Chin. Chem. Soc. 2016, 63, 000-000 Article Essien et al. Fig. 1. FTIR spectra of CM (a) and SM (b) showing the frequencies of bonds present. 1001 cm-1 wavenumbers respectively.29-31 The broad band centred at 3277 cm-1 in Figure 1(a) is assigned to the stretching vibration of H2O in CM. A similar H2O stretch- ing vibration observed around 3408 cm-1 in the spectra of SM (Figure 1(b) may be the result of absorption of atmo- spheric moisture by the sample. Compression strength Compression testing carried out on the sintered sam- ple gave a force-displacement curve shown in Figure 2. There are four distinct stages: in stage I, the material main- tains a positive slope until a maximum stress is reached, then ceases temporarily due to the closing up of the micro- pores, stage II. This is followed by stage III where densi- fication of the pores occurs and the material still shows ability to bear higher loads causing the force-displacement curve to rise again.32 In stage IV the material collapses completely as more load is applied. This result is in agree- ment with the general findings on the strength value of po- rous ceramics.33 The compression strength of the bioactive glass obtained in this study was 0.37 MPa, while the poros- ity was 82%. The compression strength of spongy bone, without considering the struts, is in the range of 0.2–4 MPa, when the relative density is ~0.1.33 Interestingly, our result is within this range although closer to the lower bound and may find useful application in the repair of trabecular bone6 as well as seeding of cells in bone tissue engineering. Average pore size of glass The pore architecture and distribution of the sintered glass material was determined by porometric using SEM (Phenom ProX 800-07334). As shown in the histogram (Figure 3), the pore sizes of the glass are in the range 7-43 �m with the average pore diameter of 13 �m. Changes in the composition of SBF Figure 4 shows variation in Na, Si, Ca, and P concen- trations in the SBF solution for various periods of immer- sion of the glass. During the reaction of the glass with the solution, the structure of the glass changes as well as the chemical composition of the SBF due to accumulation of dissolution products from the glass.18 As it is observed, the concentration of Na in the solution rises rapidly from 142 mM to 343 mM after the first 4 days of soaking and contin- ues to increase slowly to 395 mM after soaking for 14 days. The variation of Si ionic concentration is similar to that of Na. The Si ionic concentration increased rapidly from 0 to 0.91 in 4 days, and reached a constant value of 1.06 mM af- ter 14 days. Ca concentration showed a steep rise for the first 7 days, increasing from 2.5 to 5.38 mM, but slowed J. Chin. Chem. Soc. 2016, 63, 000-000 © 2016 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.jccs.wiley-vch.de 3 JOURNAL OF THE CHINESE Mechanical Properties and Reactivity of Sand-based Glass CHEMICAL SOCIETY Table 1. Comparison of bonds in CM and SM Frequencies (cm-1) CM SM Assignments References 3277 3408 �as H–O–H 28 2386 2359 �H Si–O–HL O 29 1665 1655 �s H–O–H 30 1196, 970 1001 �as (X)O–Si–O(X) [X = H or Na] 30 893 899 �as O–Si–O 30 779 760 �as (H)O–Si–O(H) 30 702 652 �as (H)O–Si–O(H) 30 461 455 �s (H)O–Si–O(Na) 30 Fig. 2. Force-deflection curve of the bioactive glass sintered at 950 �C for 3 h. The compression strength was 0.37 MPa. Fig. 3. Histogram showing pore size distribution in the glass. thereafter stabilizing at 5.44 mM after 14 days. On the con- trary, the concentration of P depleted fast from 0.31 mM reaching a constant value of 0.0027 mM after soaking fo 8 days and became exhausted before reaching 14 days. pH assessment of reactivity and degradability of the glass during immersion in SBF The variation of pH value relative to soaking times in SBF of the bioactive glass is shown in Figure 5. The in- crease in pH value from 7.4 to 8.6 during the first four days is due to partial dissolution at the surface of the glass, re- leasing Na+ and Ca2+ into the solution as shown in the result obtained earlier in Figure 4. This indicates that the glass has high reactivity in biological fluid. This fact agrees with the formation mechanisms of apatite on bioactive glasses and glass ceramics, that is, in the early stages there is fast release of Na+ and Ca2+ ions from the bioactive glass into the surrounding solution followed by an interchange be- tween Ca2+ and H3O+ from the solution.34 Such inter- changes provoke an increase of the pH that favours the for- mation of apatite nuclei on the silanol groups on the glass surface.35 After this stage, there is a slow increase in pH to a saturated value of 8.8 on the 9th day. This can be explained by the release kinetics of Ca2+ ions being lower for the glass than its uptake from the SBF solution to form apatite layer on the its surface, and hence corroborates the decline in the rate of increase in concentration of Ca in the solution after 7 days of soaking, which was observed in Figure 4. The pH variation of the bioactive glass supports previous studies on pH changes of gel-derived SiO2–CaO–Na2O–P2O5 bioactive glasses in biological fluids,36 thus indicating that the material is reactive and degradable. Critical concentra- tions of ionic dissolution products from degrading bio- active glasses, such as soluble silica and calcium ions could enhance osteogenesis by regulating osteoblast prolifera- tion, differentiation, and gene expression.9 Crystallization and bioactivity of the glass Changes on the surface of the glass before and after immersion in SBF for different time periods were studied for formation of crystalline phases and transformation of the crystalline phase to HA from the data obtained from SEM, XRD, FTIR and EDX. SEM Figure 6 shows the morphology of the glass before and after immersion in SBF. As seen in Figure 6(a), after devitrification, the glass shows a porous network structure of macropores interconnected with micropores, which is in agreement with the porosity value of 82% obtained earlier from calculation using Eq. 2 and the result shown in Figure 3. The glass microstructure appears acicular shaped with associated surface roughness, and as observed, most of the pores are open with struts of average thickness, which may be due to partial crystallization. It is particularly observed that a hollow strut with microstructure walls formed in the glass, as a result of the sintering protocol adopted, which is similar in morphology to sintered bioactive glasses re- ported in previous works.32,37 One of the basic require- ments of an ideal scaffold is that it should possess an inter- connected porous structure, that is, it should be highly per- 4 www.jccs.wiley-vch.de © 2016 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim J. Chin. Chem. Soc. 2016, 63, 000-000 Article Essien et al. Fig. 5. Changes in pH of the bioactive glass from ini- tial pH = 7.4 during immersion in SBF for the first 9 days. Fig. 4. Variation of Na, Si, Ca and P in the SBF with soaking time. meable with pore diameter in the range 10-500 �m to allow for for cell seeding, tissue ingrowth and vascularisation as well as nutrient delivery and waste removal.3,38 Micro- porosity (�2–10 �m, < 50 �m) and surface roughness are required for immediate protein and cell adhesion, cell mi- gration and osteointegration.38,39 The morphology pre- sented by the glass shows properties that match these re- quirements. After immersion for 3 days in SBF, apatite began to nucleate on the surface as shown in Figure 6(b) and in- creased in colony after immersion for 7 days as observed in Figure 6(c). On the 14th day, Figure 6(d), apatite had al- most completely populated the surface of the glass, except at the middle region where the glass surface structure is still visible. XRD XRD assessment revealed that the sintering protocol led to partial crystallization32 of the glass as shown in the XRD spectrum, before transferring to SBF for immersion study (at day 0), Figure 7, which confirms the suggestion made earlier during the SEM evaluation. As seen, both an- gular location and intensity of the peaks match the standard PDF #22.1455, indicating that Na2Ca2Si3O9 was the major phase present.32 Crystallization temperature of 45S5 Bio- glass� is known to be 600 �C.36 During this heat treatment, NaNO3 and Ca(NO3)2.4H2O decompose to Na2O and CaO respectively, and combine further with SiO2 present in the composition to give Na2Ca2Si3O9. Our sintering condition was set at 950 �C for 3 h to balance mechanical competence and biodegradability of the material.40,41 There are significant changes in the XRD spectra of the glass after immersion in SBF. Following immersion for 3 days, the intensity of the Na2Ca2Si3O9 peaks decreases and apatite peak is identified at 2� 32.9. Further immersion led to increase in the number of apatite peaks, whose con- figurations matched the standard PDF file, JCPDS #9- 0432. At day 14, the Na2Ca2Si3O9 peaks had almost disap- peared, suggesting that the material is biodegradable and is in conformity with the transformation mechanism of Na2Ca2Si3O9 reported previously.42,43 Formation of HA, HCA and degradation of the material is an indication that it could be a promising candidate for application in bone re- pair. FTIR Figure 8 shows the FTIR spectra of samples im- mersed in SBF solution for 0, 3, 7 and 14 days As can be seen, the spectrum of the parent glass before soaking re- veals several peaks. The bands at 1119 and 1038 cm-1 are associated with Si�O�Si and P�O vibrational modes;44 900-964 cm-1 are related to Si�O non-bridging oxygen bonds (NBO). The bands around 797 and 475 cm-1 are at- tributed to Si�O�Si bending vibrations. The sharp peaks at 641, 617 and 567 cm-1 can be assigned to the presence of J. Chin. Chem. Soc. 2016, 63, 000-000 © 2016 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.jccs.wiley-vch.de 5 JOURNAL OF THE CHINESE Mechanical Properties and Reactivity of Sand-based Glass CHEMICAL SOCIETY Fig. 6. SEM micrographs of the glass sample sintered at 950 �C for 3 h, (a), and after immersion in SBF for (b) 3 days, (c) 7 days and (c) 14 days. All images at the same magnification. Fig. 7. XRD diffraction patterns of the sintered glass before incubation in SBF (0 day) and after incu- bation (3 – 14 days) showing growth of HA. crystalline phase in the sample,45 which supports the for- mation of Na2Ca2Si3O9 observed in the XRD result. After soaking for 3 days new peaks emerge at 573 and 1427 cm-1, which are also observable in the spectrum of the sample soaked for 7 days. The peak at 573 cm-1 is assigned to P�O bend in amorphous calcium phosphate resulting from for- mation of HA on the surface of the sample.46 The band at 1427 cm-1, which became more intense after soaking the sample in SBF for 7 days can be attributed to the presence of CO3 2-, suggesting the onset of CO3 2- into HA. After 14 days of immersion, the bands between 950-1120 cm-1 in- creased in number which may be due to re-polymerization of SiO2 to form silica rich layer on the glass surface cou- pled with incorporation of Ca2+ re-adsorbed from SBF so- lution. Additionally, the CO3 2- band becomes broader and develops a second band at 1470 cm-1, while the peak at 573 cm-1 splits into two sharp modes at 604 and 554 cm-1, which are characteristic of apatite crystalline phase46 due to formation of HCA. EDX In Figure 9 is shown the EDX spectra of the glass be- fore and after immersion in SBF. The EDX of the parent glass confirms the composition of the glass as prepared. After immersion for 3 days in SBF, the concentration of Na, Ca and Si decreased in accordance with the dissolution the- ory of bioactive glasses in physiological fluids,19,47 and consequently P increases slightly due to re-adsorption from the SBF solution, which was observed in Figure 4, to form HA on the surface of the glass. Subsequent immersions led to increase in Ca to form apatite. Additionally, it is ob- served that at day 14, the intensity of Si was low, corre- spondingly, that of Ca and P increased, indicating that apa- tite had colonized the surface of the glass to a large extent. Also, there was an appearance of C in the spectrum of the glass soaked for 14 days, which could be attributed to CO3 2- incorporation to form HCA, thus confirming the FTIR result. EXPERIMENTAL Preparation of bioactive glass from sand: The composi- tion of the sand used as source of silica is shown elsewhere.23 To prepare sodium metasilicate (Na2SiO3), the sand ranging in sizes between 159–595 �m was first obtained by passing it through a sieve, then washed thoroughly with deionized water to free it from impurities before drying at 120 �C in an oven for 3 h. There- after, 4.00 g of the sand was mixed with 3.53 g of soda ash (Na2CO3) and placed in a cavity constructed with bricks. The mixture was fused in a furnace at 1300 �C for 1 h to form Na2SiO3 (mole ratio: Na2O:SiO2 = 1:2) as shown in Eq. 1. Na2CO3 + xSiO2 � (Na2O).(SiO2)x + CO2 (x = 2) (1) The bioactive glass with composition (mol %) 46.81 SiO2, 6 www.jccs.wiley-vch.de © 2016 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim J. Chin. Chem. Soc. 2016, 63, 000-000 Article Essien et al. Fig. 8. FTIR Spectra of the glass before immersion (0 day) and after immersion for 3 – 14 days in SBF. Fig. 9. EDX spectra of the parent glass (0 day) and af- ter soaking in SBF for 3 – 14 days. A distinct peak for carbon (C) can be seen after 14 days in SBF. 24.55 Na2O, 27.38 CaO and 1.26 P2O5, were prepared by mixing the following reagents at room temperature with stirring using a magnetic stirrer in the order: 0.05M HNO3 (Riedel-DeHaën, 60%) and Na2SiO3 liquid (as-prepared from sand), NaH2PO4· 2H2O (Kermel, 99%) and Ca(NO3)2.4H2O (Loba Chemie, 99%) in the molar ratio of water to the rest of the chemicals of 20:1 to obtain the sol. Each reagent was allowed a maximum reaction time of 45 minutes before adding the next. After adding the final reagent, the mixture was stirred for 1 hour before pouring the re- sulting sol into teflon moulds and kept at room temperature for 72 h for gelation. The obtained gel was heated at 70 �C for 72 h, 130 �C for 42 h, 700 �C for 2 h and 950 �C for 3 h for aging, drying, stabilization and sintering respectively. The heating and cooling rate was maintained at 5 �C/min. Characterization: The density �glass of the glass was de- termined from the mass and dimensions of the sintered material. The porosity P was calculated by P = (1 � �glass / �solid) 100 (2) where �solid = 2.7 g/cm3 is the density of 45S5 Bioglass �.35 The microstructure and composition of the glass was as- sessed in an EVO/MAIO scanning electron microscope (SEM) equipped with energy dispersive X-ray analyzer (EDX) before and after immersion in simulated body fluid (SBF) for a maxi- mum of 14 days. Silicon substrates were sequentially cleaned with soap and deionized water, ethanol and acetone in an ultra- sonic bath and then dried in the oven at 110 �C for 15 min. The samples were thoroughly milled into fine powders and dispersed in an adequate volume of ethanol via ultrasonication for 15 min. The dispersed samples were dropped on the pre-cleaned silicon substrates, placed in an oven at 110 �C for 15 min to dry the etha- nol, and then observed at an accelerating voltage of 15 kV. Samples were characterized using X-ray diffraction (XRD) analysis after sintering and after each immersion experiment in SBF with the aim of assessing the crystallinity and the formation of hydroxyapatite (HA) crystals respectively on samples strut sur- faces. The samples were first ground to powder. Then 0.1 g of the powder was measured in a PANalytical Empyrean X-ray dif- fractometer using CuK radiation source of wavelength (�) = 0.154056 nm operated at 40 kV and 40 mA to obtain the diffrac- tion patterns in the 2� range from 5� - 90�. Fourier transform infrared (FTIR, Shimadzu 8400S), with wavenumber range of 4000-400 cm-1 employing KBr pellets op- erating in a reflectance mode with a 4 cm-1 resolution was used to monitor the nature of bonds present in the samples. Mechanical Testing: The compression strength of the sintered bioactive glass was measured using a Testometric OL11 INR (Lancashire, England) mechanical tester at crosshead speed of 0.5 mm/min. The samples were cylindrical in shape with di- mensions 15 mm in diameter and 30 mm in height. During the compression test, the load was applied until densification of the porous samples started to occur. The compression strength was determined using the relation: �c = F/ r2 (3) where �c is the compression strength, F is the applied load at fail- ure and r is the sample radius. Assessment of bioactivity in simulated body fluid: As- sessment of bioactivity was carried out by the standard in vitro procedure47 using analytical reagent-grade chemicals NaCl, NaHCO3, KCl, K2HPO4·3H2O, MgCl2·6H2O, CaCl2, trishydro- xymethyl aminomethane [Tris-buffer, (CH2OH)3CNH2], and 1M HCl with ions concentrations shown in Table 2. Samples were im- mersed in acellular SBF at concentration of 0.01 g/ml in clean plastic bottles, which had previously been washed using HCl and deionized water. The bottles were placed inside a thermostated in- cubator at a temperature of 36.5 �C while maintaining pH at 7.4. The SBF solutions were not refreshed throughout the period of immersion. The pH of the solution was checked daily for 9 days using a pH meter (Hanna, HI96107) and ion concentration of the SBF were also monitored daily throughout the period of immer- sion. Concentrations of Na and Ca were examined by atomic ab- sorption spectrophotometer (AAS) (Perkin Elmer Buck A Ana- lyst); P and Si were estimated by UV/VIS spectrophotometer (Uniscope SM 7504) at wavelengths of 400 and 815 nm respec- tively. The samples were extracted from the SBF solution after 3, 7 and 14 days respectively. The extracted samples were rinsed with deionized water and left to dry at ambient temperature in a desiccator. The formation of apatite layer on the glass surface was monitored by SEM, EDX, XRD and FTIR. CONCLUSIONS A bioactive glass of the SiO2–Na2O–CaO–P2O5 sys- tem using high silica–containing sand as economic starting material was formed by the sol-gel processing method. Af- J. Chin. Chem. Soc. 2016, 63, 000-000 © 2016 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.jccs.wiley-vch.de 7 JOURNAL OF THE CHINESE Mechanical Properties and Reactivity of Sand-based Glass CHEMICAL SOCIETY Table 2. Ion concentrations (mM) in human plasma in comparison with SBF Ion Na+ K+ Mg2+ Ca2+ Cl- HCO3 - HPO4 2- SO4 2- SBF 142.0 5.0 1.5 2.5 147.8 4.2 1.0 0.5 Human plasma 142.0 5.0 1.5 2.5 103.0 27.0 1.0 0.5 ter maintaining the sintering condition at 950 �C for 3 h, a crystalline phase, Na2Ca2Si3O9 was produced in the glass. Compression study indicated the glass has strength of 0.37 MPa that falls within the trabecular bone region, attribut- able to the Na2Ca2Si3O9 phase. Daily evaluation of the composition of the SBF revealed that the glass has a con- trolled rate of degradation in SBF, a property which could enable it serve as a temporary scaffold pending the forma- tion of a new bone. The significance of this work is that the silica sand route herein compares favourably to previously synthesized sodium–containing bioactive glasses like 45S5 Bioglass� based on TEOS. 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