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Contents lists available at SciVerse ScienceDirect

Chemical Engineering Research and Design

j ourna l h omepage: www.elsev ier .com/ locate /cherd

ynthesis, characterization and bioactivity of bioglasses inhe Na2O–CaO–P2O5–SiO2 system prepared via sol gelrocessing

émy Catteauxa,∗, Isabelle Grattepanche-Lebecqa, Francoise Désangloisa,eng Chaib, Jean-Christophe Horneza, Stuart Hampshire c, Claudine Follet-Houttemanea

Laboratoire des Matériaux Céramiques et Procédés Associés EA2443, Université de Valenciennes et du Hainaut-Cambrésis, BâtimentECMA, Zl du champ de l’Abbesse, 59600 Maubeuge, FranceINSERM U1008, Laboratory of Biomaterial Research, Faculté de Médecine et de Pharmacie, Université Lille Nord De France, F-59000ille, FranceMaterials and Surface Science Institute, University of Limerick, Limerick, Ireland

a b s t r a c t

Different kinds of bioactive materials are used as bone substitutes. In particular, bioglasses containing Si, Ca, Na and P,

bind to host tissues with a stable chemical bond. The phenomenon of bioactivity is associated with the formation of a

crystallized hydroxycarbonated apatite (HCA) layer on the bioglass surface, when soaked in a simulated physiological

fluid. This layer is similar to the mineral phase of bone.

Synthesized bioglasses have been obtained using organic modifiers instead of mineral modifiers, which are the

usual precursors for sol–gel synthesis.

First, a slightly soluble ternary glass, containing 48% CaO, 5% P2O5 and 47% SiO2, referred to as Si47P5T, was

prepared.

Then, some sodium oxide has been added to obtain a more bioactive quaternary bioglass, containing 21.5% Na2O,

26.5% CaO, 5% P2O5 and 47% SiO2 which is referred to as Si47P5Q.

Physicochemical properties of both bioglasses have been studied. Bioactivity in a simulated body fluid (SBF) and

cytotoxicity tests have complemented the study.

© 2013 The Institution of Chemical Engineers. All rights reserved.

Keywords: Bone substitute; Bioglass; Sol–gel; Hydroxyapatite; Simulated body fluid; Cytotoxicity

2004; Chen et al., 2012). For example, the use of mineral precur-

. Introduction

ioglasses are reactive materials that can be integrated intohe body. Bioactivity is a phenomenon whereby a hydroxy-arbonated apatite (HCA) layer, similar to the mineral phasef bone, forms on the bioglass surface when soaked in vivo

n the body or in vitro in a simulated physiological fluid. Itnsures a strong chemical bond with living tissue and a stablettachment of the implant (Hench, 1991, 1998).

The sol–gel method is used to synthesize bioglassesecause it offers many advantages in comparison with

Please cite this article in press as: Catteaux, R., et al., Synthesis, characsystem prepared via sol gel processing. Chem. Eng. Res. Des. (2013), http:/

he traditional fusion-quenching process. It involves “soft

∗ Corresponding author. Tel.: +33 0327531660; fax: +33 0327531667.E-mail address: remy.catteaux@univ-valenciennes.fr (R. Catteaux).Received 10 October 2012; Received in revised form 3 May 2013; Accep

263-8762/$ – see front matter © 2013 The Institution of Chemical Engittp://dx.doi.org/10.1016/j.cherd.2013.05.017

chemistry”, which preforms the glass network during gelformation and gives a stabilized glass at lower temperaturesthan for conventional melting. Bioglasses prepared by thesol–gel method have a higher reactive surface, allowinga better nucleation of the HCA during the soaking of thematerial in vitro or in vivo (Arcos and Vallet-Regí, 2010).

Various studies on sol–gel inverted bioglasses, with highcontents of modifiers (sodium and calcium), have shown thatthe use of mineral precursors such as nitrates or carbonatesdoes not lead to totally amorphous bioglasses (Catauro et al.,

terization and bioactivity of bioglasses in the Na2O–CaO–P2O5–SiO2

/dx.doi.org/10.1016/j.cherd.2013.05.017

ted 27 May 2013

sors to introduce sodium into sol–gel bioglasses often results

neers. All rights reserved.

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Table 1 – Chemical compositions of the prepared bioglasses (mol%).

Sample Method Composition

Si47C HCl catalyst 21.5%Na2O–26.5%CaO–5%P2O5–47%SiO2

Si47N HNO3 catalyst 21.5%Na2O–26.5%CaO–5%P2O5–47%SiO2

Si47P5T Organic 48%CaO–5%P2O5–47%SiO2

Si47P5Q Organic 21.5%Na2O–26.5%CaO–5%P2O5–47%SiO2

Si47M Melting

in the formation of a glass-ceramic during the final thermoly-sis (Chen and Thouas, 2011). In the sol–gel process of bioglassformation, the replacement of mineral precursors by organictypes presents several advantages. It maintains a fully amor-phous glass and retains good mechanical strength during heattreatments (Carturan and Guglielmi, 1988; Pereira et al., 1994).Another advantage is that the glass obtained with organic pre-cursors is in a bulk form instead of a powder with mineralprecursors.

Glass formers are chosen based on previous studies in thefield of sol–gel bioglasses (Cacciotti et al., 2012). Silicon alkox-ide (tetraethylorthosilicate, TEOS) and phosphorus alkoxide(triethylphosphate, TEP) are used to introduce, respectively,silicon and phosphorus into the composition. These alkox-ides have the ability to hydrolyse and to condense quite easilyin the presence of water and a catalyst, forming a perfectlyamorphous gel, which is essential to obtain good bioactivity(Duée, 2007; Lebecq et al., 2007). The use of alkoxide salts tointroduce calcium into the compositions provides good resultsfor the preparation of ternary glasses based on Si, Ca and P.Sodium is however necessary to improve the reactivity of bio-glasses (Arcos and Vallet-Regí, 2010). To obtain a quaternarybioglass, containing sodium, sodium acetate can be consid-ered (Yasumori et al., 1986).

In the current work, it was decided to use a new processfor sol–gel synthesis which is totally organic with an acid cata-lyst. First, the choice of the studied compositions is explained.Then, the paper summarizes the sol–gel process and the treat-ment to obtain a glass. A comparison is made between theglasses obtained by the sol–gel process and the classical melt-ing method. The bioactivity of the glasses has been evaluatedby soaking them in simulated body fluid (SBF) (Siqueira et al.,2011). The changes at the glass surface as a function of soak-ing time in the SBF was analysed by infrared spectroscopy. Thecytotoxicity has also been studied with L132 epithelial cell lineto assess the ability of the bioglasses for bone reconstruction.Cytotoxicity tests based on different concentrations of bio-glass powders in a cell growth environment have completedthe study.

2. Materials and methods

2.1. Synthesis of glasses

2.1.1. Selection of compositionsThe compositions were chosen based on previous studies(Lebecq et al., 2007; Duée et al., 2009). Initially, an invertedternary bioglass in the CaO–P2O5–SiO2 system, referred toas Si47P5T is obtained by an organic sol–gel process. It con-tains 48% CaO, 5% P2O5 and 47% SiO2 (mol%). It cannot besynthesized by the traditional melting method because itscomposition does not contain sodium oxide, which is a flux.

Then, a second inverted glass is prepared in the

Please cite this article in press as: Catteaux, R., et al., Synthesis, characsystem prepared via sol gel processing. Chem. Eng. Res. Des. (2013), http:/

Na2O–CaO–P2O5–SiO2 system by replacing a part of the cal-cium of the ternary glass by sodium. It contains 21.5% Na2O,

21.5%Na2O–26.5%CaO–5%P2O5–47%SiO2

26.5% CaO, 5% P2O5 and 47% SiO2 (mol%). In order to knowif the preparation of this quaternary glass, poor in silica andrich in sodium oxide, can be effected using the sol–gel pro-cess, three syntheses have been considered. The first glass isprepared using calcium and sodium nitrates and the catalystis nitric acid (Saravanapavan et al., 2004) and is referred to asSi47N. In the second synthesis, the nitric acid is replaced byhydrochloric acid (Laczka et al., 2000) and this glass is referredto as Si47C. Finally, in the third synthesis, organic precursorshave been used to introduce modifiers and the glass is referredto as Si47P5Q. In these glasses, the sodium has been carefullyadded to avoid problems of crystallization.

The properties of the quaternary glasses obtained bysol–gel route were compared with quaternary glasses of thesame composition prepared by melting (Si47M).

Table 1 summarizes the chemical compositions of preparedglasses (mol%).

2.1.2. Synthesis by sol–gel route using mineral modifiersThe quaternary glasses, referred to as Si47N and Si47C, are pre-pared by sol–gel route. The formers are tetraethylorthosilicate(TEOS, Si(OCH2H5)4, Sigma Aldrich 99.9%) and triethylphos-phate (TEP, (C2H5)3PO4, Sigma Aldrich, 98%). The mineralmodifiers are calcium nitrate (Ca(NO3)2, Sigma Aldrich, 99.9%)and sodium nitrate (NaNO3, Sigma Aldrich, 99.9%).

To prepare the Si47C material, a solution of HCl 1 mol L−1

is used to initiate the hydrolysis and condensation reactions.The synthesis of the Si47N material is catalysed by addition ofa solution of HNO3 1 mol L−1 instead of HCl.

Both glasses have been prepared by means of the followingsteps:

The raw materials are weighed in stoichiometric propor-tions. Firstly, the formers TEOS and TEP are mixed for 20 minin a teflon beaker with 10 ml of ethanol. Secondly, the modi-fiers Ca(NO3)2 and NaNO3 are mixed for 20 min in 30 ml of acidsolution (HNO3 or HCl). Then, the modifiers are added to theformers and the sol is stirred at room temperature for 20 min.A heat treatment at 50 ◦C allows the removal of excess of sol-vents (water and ethanol). After about 1 h, heating is stopped,and the gel starts to form.

It is stabilized at room temperature for 24 h and is dried inan oven at 130 ◦C. Finally, the glass is obtained by heating thegel between the transition and crystallization temperatures.

2.1.3. Synthesis by sol–gel route using organic compoundsThe organic synthesis consists of the hydrolysis andpolycondensation of a mixture of tetraethylorthosilicate(TEOS, Si(OCH2H5)4, Sigma Aldrich 99.9%), dimethoxycalcium(Ca(OCH3)2, Sigma Aldrich, 98%), sodium acetate (CH3COONa,Sigma Aldrich, 99.9%) and triethylphosphate (TEP, (C2H5)3PO4,Sigma Aldrich, 98%). The catalyst is acetic acid (CH3COOH,Sigma Aldrich, 99%).

The raw materials are weighed in stoichiometric propor-

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tions. Fig. 1 summarizes the different steps of sol and gelpreparation.

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The gels are then dried at 130 ◦C for 24 h. The last syn-hesis step is the ageing of the gel in order to obtain thelass. This ageing is done in a Nabertherm electric furnaceith a heating rate of 1 ◦C/min from room temperature to

00 ◦C for the ternary glass and 700 ◦C for the quaternaryomposition. These temperatures have been chosen basedn the thermal analysis performed on the gels. By means ofhis process, the ternary compound, referred to as Si47P5Tnd the quaternary compound referred to as Si47P5Q arerepared.

.1.4. Glass synthesis by meltinghe quaternary glass referred to as Si47M is prepared using

he following precursors: quartz (SiO2, Merck, 99.9%), calciumarbonate (CaCO3, Prolabo, 99.9%), sodium carbonate (Na2CO3,erck, 99%) and Graham’s salt ((NaPO3)n, Merck, 99%). The

owders are mixed and ground in an agate mortar and placedn a platinum crucible. They are first heated from room tem-erature to 800 ◦C at a heating rate of 200 ◦C/h which allowshe removal of carbonates. The crucibles are then heated up to400 ◦C (at 5 ◦C/min) and maintained at this temperature for

h in order to obtain a homogeneous melt. The liquid is thenuenched on a steel plate at room temperature to form theolid glass.

.2. Physical analysis

hermogravimetry (TGA) and differential thermal analysisDTA) are coupled to determine the thermal behaviour of gelsnd bioglasses. They are performed using a Setaram SetsysG16, with a temperature range from 25 to 1200 ◦C and a heat-

ng rate of 0.5 ◦C/min.X-ray diffraction (XRD) analysis is performed over a range of

� between 20◦ and 80◦, using an X-ray diffractometer (PanAn-lytical X’Pert Pro).

Infrared spectra are obtained over a range of wavenum-er from 400 to 1400 cm−1, with a Fourier transform infrared

FTIR) device (JASCO FT/IR 460 Plus). The assignment ofnfrared bands is made in accordance with previously pub-

Please cite this article in press as: Catteaux, R., et al., Synthesis, characsystem prepared via sol gel processing. Chem. Eng. Res. Des. (2013), http:/

ished results (Lebecq et al., 2007; Duée et al., 2009; Cacciottit al., 2012).

nic sol–gel process.

2.3. Assessment of in vitro bioactivity

The glasses are first crushed in an agate mortar and the pow-ders compacted and pelletized using a hydraulic press in orderto obtain 10 mm diameter cylinders. They are embedded inan epoxy resin keeping only one face of area 0.785 cm2 freeto react. This preparation provides the same reaction surfacearea (S) for all samples.

They are then rinsed with acetone and soaked for var-ious times in 60 ml of SBF (Kokubo et al., 1990) at 37 ◦Cusing a thermostatic bath. The SBF is buffered at 7.4 pHwith tris(hydroxymethyl)aminomethane. The surface to vol-ume ratio S/V is 0.013 cm−1.

Only static in vitro tests have been performed (Kokuboet al., 1990) since the aim of these tests is simply to comparethe bioactivity of the glasses, in order to know if there is adifference between glasses prepared by different routes.

The samples are then removed from the SBF, rinsed withdeionized water and air dried. Two kinds of analysis areperformed on samples which have undergone the same treat-ment.

In the first case, the glass surface is removed by polishingand analysed with Fourier Transform Infrared Spectroscopy.The different reaction steps can thus be detected. It is espe-cially the presence of HCA which is finally formed afterdifferent soaking times in SBF. It is also possible to observethe silica gel layer which precedes the formation of the amor-phous CaP layer that finally crystallizes to HCA.

The second type of analysis is characterization of thesamples after soaking in SBF by means of scanning elec-tron microscopy coupled with energy dispersive spectroscopy(SEM-EDS Hitachi S-3500N). The bulk glasses and the resin aretransversally cut to show the depth of reaction. The proportionof different constituents, in particular the Ca/P molar ratio,and thickness of the surface layers for various different timesare measured by this SEM-EDS technique.

2.4. Cytotoxicity

Cytotoxicity tests consist of viability tests which evalu-ate the relative plating efficiency (RPE) and subsequently

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the 50% lethal concentration LC50 (or RPE 50) by meansof colony-forming assay with epithelial cell line (L132

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Fig. 2 – X-ray diffractograms of quaternary compositions Si47M, Si47N, Si47C and Si47P5Q following different heat

Fig. 3 – Thermal analysis of the gel associated with thequaternary glass Si47P5Q.

treatments.

cells) (Frazier and Andrews, 1979; Puck and Markus,1995).

According to the International and European Standards(ISO10993-5/EN30993-5), the L132 epithelial cell line is selectedfor its good reproducibility and cloning efficiency (about 37%)(Hornez et al., 2002). In minimum essential medium (MEM)supplemented with 10% foetal calf serum (FCS), the L132cells are continuously exposed to gradually increasing con-centrations (0, 25, 50, 100, 200, 400 mg L−1) of bioglass powder(20 mm diameter granules) without renewal of the growthenvironment during the experiments. After a 9-day cultureperiod, the environment is removed and the colonies arestained with violet crystal. The number of colonies is thencounted under a binocular microscope. At least six repeatedexperiments are performed, in triplicate for each concentra-tion group. Results are expressed as mean values ± SD withrespect to the control (environment without glass powder,100%). Nickel powder is also tested as a positive control forcomparison.

3. Results

3.1. Physicochemical analysis

Fig. 2 shows the X-ray diffraction analysis of the four quater-nary glasses.

The X-ray diffractogram of the Si47M glass, prepared bymelting, shows that it is perfectly amorphous.

The Si47N and Si47C glasses have been prepared withmineral precursors by the sol–gel process. The X-ray diffrac-tograms of their gels at 130 ◦C show an early crystallizationin the amorphous phase. XRD of the dried gel of Si47N showsthe coexistence of several phases, which makes the identifi-cation of the individual crystallized phases difficult. The gelSi47C clearly contains some sodium chloride, NaCl (JCPDS No.5/628). The use of mineral precursors does not seem adaptedto prepare bioglasses.

In contrast, the diffractogram of Si47P5Q at 130 ◦C showsthat the gel, prepared by organic sol–gel route, is perfectlyamorphous. Its ageing at 700 ◦C gives an amorphous glasswhich presents the same diffractogram as Si14M. For this com-position, a totally amorphous glass can be prepared by an

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organic sol–gel process as well as by melting. At 800 ◦C, wollas-tonite (Na2Ca3Si6O18 JCPDS no. 27/88) appears as a crystalline

phase. Therefore, to keep the composition amorphous, the gelheat treatment must not exceed 700 ◦C.

For Si47P5T, the same changes occur as for Si47P5Q andcrystallization first appears at 800 ◦C.

Fig. 3 shows the thermal analysis of the gel associated withthe quaternary glass Si47P5Q, dried at 130 ◦C. The TGA ther-mogram shows that most of the weight losses occur betweenroom temperature and 800 ◦C, due to the evolution of solvents.The DTA thermogram gives the characteristic temperaturesof the same quaternary gel. The peaks between 200 ◦C and400 ◦C are attributed to the loss of water and alcohol from theraw materials. The glass transition temperature, Tg, is around750 ◦C. The crystallization temperature, Tc, is about 875 ◦C.These results indicate that it is possible to heat the gel below875 ◦C to obtain the glass Si47P5Q.

The TGA and DTA thermograms of the ternary gel aresimilar. To obtain the glass Si47P5 T, the gel must be heatedbetween 750 and 850 ◦C.

The difference in the crystallization temperatures,obtained by DTA and X-ray diffraction comes from themodification of the heating rate.

Fig. 4 shows the spectra obtained by IR spectroscopy for (1)Si47P5T gel, dried at 130 ◦C and aged at 800 ◦C, (2) Si47P5Q gel,dried at 130 ◦C and aged at 700 ◦C, and (3) Si47M, which is thesame quaternary composition prepared by melting.

The intensification of the � Si O 2 NBO (non bridging oxy-gen) band, at 915 cm−1, and the broadening of the ı Si O Siband at 475 cm−1, shows that the thermal treatment of the gel

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at 800 ◦C for the ternary material and 700 ◦C for the quater-nary material gives a glass. The IR spectrum of the quaternary

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Fig. 4 – Infrared spectra of Si47P5T and Si47P5Q sol–gelg

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lasses and IR spectra of Si47M glass obtained by melting.

lass Si47P5Q corresponds to that of the same composition,btained by melting at 1400 ◦C.

This analysis confirms that it is possible to prepare auaternary glass by the organic sol–gel route at a lower tem-erature than by melting.

It is impossible to prepare the ternary glass by meltingecause of the high melting temperature and this shows alsohat the organic sol–gel route is more practical.

.2. Bioactivity

.2.1. In vitro testsig. 5 shows the changes in the Infrared spectra of the surfacef the bioglass Si47P5Q after different soaking times in SBF:

h, 2 h, 3 h, 10 h, 1 day and 10 days.After 1 h of soaking in SBF, the glass network hydrolysis

egins. It is seen on the spectrum with the appearance ofhe asymmetrical stretching vibration band of �as Si O 4 BObridging oxygen) intra-tetrahedra at 1080 cm−1 and the reduc-ion of the stretching vibration of Si O 2 NBO at 926 cm−1.his is due to the dissolution of the glass by formation ofi OH groups which have the ability to recondense to form

silica gel. This is characterized by the symmetric stretch-ng vibration band of �s Si O tetra at 794 cm−1. There is also

narrowing of the bending band ı Si O Si at 459 cm−1 andhe presence of the stretching vibration band of Si OH (�i OH) at 952 cm−1, confirming the existence of the silicael. The amorphous CaP layer also grows and its formationan be observed by the presence of the stretching vibrationand of P O (� P O) at 1227 cm−1 and the bending vibrationand of PO4 antisymmetric O P O (ıas O P O amorphous) at85 cm−1.

After 3 h of soaking, the spectrum shows the elongatedibration band of carbonates (� C O) at 878 cm−1 and the twoending vibration bands of crystallized PO4 groups (ı O P O)t 556 cm−1 and 603 cm−1 of crystallized HCA.

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After 10 h, 1 day and 10 days, the apatite phase growthontinues.

This glass, which develops an HCA layer on its surface,is bioactive. It is similar to that of glass of the same com-position prepared by melting. The Si47P5T exhibits the samecharacteristic bands but at longer soaking times (1 day for theappearance of HCA layer). The ternary glass is less bioactivethan the quaternary glass. The presence of sodium promotesa bidimensional inverted glass, which makes it more soluble,and also, more bioactive.

The glasses obtained by the organic sol–gel route have thesame bioactivity as bioglasses of the same composition pre-pared by melting.

3.2.2. Characterization of the bioglasses after soakingThe compositions of the deposited layers on Si47P5Q werestudied after 10 days of soaking in SBF. This time was chosenbecause the glass exhibits a well-developed crystalline HCAlayer.

Fig. 6 illustrates the compositional profile of the reactedbulk glass with the layer. Five regions can be observed fromthe glass to its surface (from left to right).

In the left part, the presence of Si, Ca, Na, P and O is char-acteristic of the bulk bioglass composition. The second regionexhibits a high Si content, which confirms the presence of asilica gel layer. The third zone shows a decrease of Si, and anincrease of Ca and P content. These variations correspond to amixed silica and calcium phosphate layer. The fourth zone is

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rich in Ca and P, which corresponds to the HCA layer. Finally,

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Fig. 6 – Compositional profile of the Si47P5Q transversal cutafter 10 days in SBF.

Table 2 – Atomic compositions of the surface layers ofSi47P5Q glass after 10 days soaking in SBF.

Atoms O Na Si P Ca

Point 1 59.12 14.21 14.97 3.35 8.13Point 2 58.88 14.11 15.15 3.40 8.88Point 3 58.76 14.41 14.99 3.33 8.59Point 4 64.95 4.98 20.38 3.95 5.72Point 5 64.24 5.05 19.03 4.10 7.74Point 6 64.22 4.97 18.04 4.32 8.57Point 7 63.27 5.06 6.22 9.83 15.64Point 8 63.71 5.47 5.58 9.75 15.79Point 9 63.77 4.61 5.34 10.03 16.05Before soaking 57.92 14.63 15.98 3.39 9.01

Fig. 7 – Transverse profile of Si47P5Q after 10 days soakingin SBF.

Fig. 8 – L132 viability tests on Si47P5Q and Si47M.

ions decreases the viability to around 80%.

the last layer is the coating resin, which has been added at thesurface to allow the sample to be cut.

To specify layer compositions, a SEM-EDS study was madealong the profile lines. Table 2 gives the atomic compositionof each layer. The different points are represented in Fig. 6.

Examination of several points on the glass surface aftersoaking (points 1–3) shows that the composition is quite sim-ilar to the glass before soaking. In the silica rich layer (points4–6), the amount of Si is larger and the contents of Na, Ca and Pare lower than those of the initial glass. Observation of points7–9 confirms a homogeneous composition. The Ca:P ratio isequal to 1.6 which is less than 1.67, the stoichiometric ratio inhydroxyapatite Ca10(PO4)6(OH)2. The CaP layer corresponds toa non-stoichiometric hydroxyapatite, containing carbonates,as in the mineral phase of natural bone.

The different points corresponding to the reaction zones,are shown in Fig. 7. The HCA layer thickness is about 20 �m.

The composition and the thickness of the HCA layer aresimilar for both Si47P5Q, prepared by the organic sol–gelmethod and Si47M, obtained by melting.

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3.2.3. CytotoxicityFig. 8 shows the results of viability tests, performed on sam-ples of Si47P5Q, Si47M and nickel powder as a function ofpowder concentration. The percentage of viability is deter-mined by the ratio between the number of surviving L132 cellsin the medium exposed to the powder sample and the num-ber of surviving cells in a control medium. LC 50 correspondsto the death of 50% of the cells. The number of introducedcells is the same in all the samples and the control. It is nec-essary to compare with the control because the survival ratiois never really 100%. Indeed, the cells are stressed during thesubculture, which leads to the death of a small fraction.

A compound will be considered cytotoxic if its additioninto the culture medium increases the cell death as the com-pound concentration increases. In the present case, bioglassesSi47P5Q and Si47M do not show this behaviour. With a concen-tration of 400 mg L−1, the average survival of L132 cells is 83%for Si47P5Q and 72% for Si47M. Thus, neither of the glasses arecytotoxic.

It is interesting to note that both bioglasses show a highersurvival ratio than 100% at low concentrations (112% forSi47P5Q and 105% for Si47M with 25 ml L−1). This result showsthat the bioglasses improve growth conditions for cells whichmight reduce the stress on the L132 cells. The sol–gel bioglassSi47P5Q shows this effect at lower concentrations (from 0 to120 mg L−1) than the Si47M glass (from 50 to 220 mg L−1). Thismay be explained by a higher reactivity of the sol–gel glass,which has a higher solubility than its counterpart obtainedby fusion. At higher concentrations, the increasing release of

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. Conclusions

rganic sol–gel synthesis is a good alternative to the tradi-ional synthesis of bioglasses by melting and quenching. It ishus possible to obtain glasses with a heat treatment signifi-antly lower than those achieved by melting. Moreover, thisechnique allows the preparation of glasses with composi-ions that cannot be synthesized by melting. Two glasses, aernary composition containing 48% CaO, 5% P2O5 and 47%iO2 (Si47P5T, mol%) and a quaternary composition contain-

ng 21.5% Na2O, 26.5% CaO, 5% P2O5 and 47% SiO2 (Si47P5Q,ol%) have been prepared by an organic sol–gel route. In vitro

ests, by soaking in SBF at 37 ◦C, show that they are as bioactives their counterparts synthesized by the traditional meltingethod. Cytotoxicity tests show that they are not cytotoxic.

ecause of the gel step and ageing at quite low temperatures,hey can be used as coatings for various substrates, which isot possible with glasses prepared by melting.

eferences

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