New 92S6 mesoporous glass: Influence of surfactant

carbon chain length on the structure, pore morphology

and bioactivity

Nouha Letaıef, Anita Lucas-Girot, Hassane Oudadesse, Rachida Dorbez-Sridi

To cite this version:

Nouha Letaıef, Anita Lucas-Girot, Hassane Oudadesse, Rachida Dorbez-Sridi. New 92S6mesoporous glass: Influence of surfactant carbon chain length on the structure, pore mor-phology and bioactivity. Materials Research Bulletin, Elsevier, 2014, Epub ahead of print.<10.1016/j.materresbull.2014.08.048>. <hal-01072536>

HAL Id: hal-01072536

https://hal.archives-ouvertes.fr/hal-01072536

Submitted on 8 Oct 2014

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1

New 92S6 mesoporous glass: Influence of surfactant carbon chain length on

the structure, pore morphology and bioactivity

N. Letaiefa,b, A. Lucas-Girota, H. Oudadessea, R. Dorbez-Sridib

aChimie du Solide et Matériaux, UMR 6226 CNRS / Université de Rennes 1, Institut des Sciences Chimiques de Rennes, Campus de Beaulieu, Avenue du Général Leclerc, 35042 Rennes Cedex, France. bLaboratoire de Physico-Chimie des Matériaux, Département de Physique, Faculté des Sciences de Monastir, Avenue de l’environnement, 5019 Monastir, Tunisie. Corresponding author(s): nouha_lf@yahoo.fr, Téléphone: +33 7 53 76 20 22

Graphical abstract

Abstract:

The main objective of the present work was to investigate the effect of surfactant chain length

on the structure, porosity and bioactivity of 92S6 (92% SiO2, 6% CaO, and 2% P2O5 mol %)

mesoporous sol-gel glasses. The aim was to provide a basis for controlling the porosity of the

glass to obtain a control of bioactive behavior.

A series of mesoporous bioactive glasses were synthesized using three different surfactants

(C10H20BrN, C19H42BrN, C22H48BrN).

Surfactant type dependence on the textural properties, particularly porosity and bioactivity

were studied.

Results indicate that bioactivity factors were improved by a short surfactant carbon length.

Keywords: A. amorphous materials, B. sol-gel chemistry, C. X-ray diffraction, C. electron

microscopy, A. glasses.

1. Introduction

Various kind of bioactive materials like hydroxyapatite, bioglasses, bioglass-ceramics and

calcium phosphate ceramics have attracted a strong interest of research over the last decades

ACCEPTED MANUSCRIP

T

was to investigatewas to investigate the the effect of surfactant chain lengtheffect of surfactant chain length

92S6 ((92% SiO92% SiO

was to provide a basis for controlling the was to provide a basis for controlling the

bioactive behaviorbioactive behavior.

A series of mesoporous bioactive glasses were synthesized using three different surfactants A series of mesoporous bioactive glasses were synthesized using three different surfactants

BrN, CBrN, C2222HH48BrN)BrN)

dependence on the textural propertiesdependence on the textural properties

Results indicate that bioactivity factors were improved by a short surfactant carbon length.Results indicate that bioactivity factors were improved by a short surfactant carbon length.

KeywordsKeywords: A.A.

microscopymicroscopy

2

and have shown significant potential in biomedical research field. These glasses facilitate

bone integration of the implant [1], they are also intended to replace bone through a bone

defect area in the human skeleton [2, 3]. The bioactive behavior of these glasses, which is

identified as capability of bone bonding, is attributed to the formation of an apatite-like layer,

whose composition and structure are equivalent to the mineral phase in bone [4].

Two methods were suggested for the preparation of bioactive glasses: melting and sol-gel

methods. Sol-gel process enables to obtain a wide range of compositions with high purity,

homogeneity and production of various shapes; such as monoliths, powders or fibers [5].

Additionally, it is well established that sol-gel glasses have higher ability to induce

hydroxyapatite formation than melt derived glasses [6]. Sol-gel technique has many

advantages with respect to the control of material’s surface chemistry which is directly related

to the bioactive behavior [6]. The major differences in surface between sol-gel and melt

derived glasses are: (i) sol-gel glass has a higher specific surface area ii) sol-gel glass has a

larger pore volume on the surface; and (iii) sol-gel glass has a larger concentration of silanols

groups (Si-OH) on the surface [1]. All these surface chemistry and textural properties induce

better bioactive behavior than conventional melt-derived glass.

In the last couple of decades, there has been some interest in porous glasses in applications

where bone ingrowth is needed or as coatings in applications such as implants, where a good

bone–implant interface is required [7,8]. Porous biomaterials have been produced by several

techniques such as the use of polymeric sponge, foaming processes and techniques using

organic surfactants such as n-hexadecyltrimethylammonium bromide CTAB [7].

The porous structure is induced by the condensation of silica around supramolecular

surfactant aggregates acting as a structure-directing agent, and the pores are formed upon

removal of the surfactant from the matrix by calcination [9]. One of the advantages with

templated mesoporous materials is that they exhibit a narrow pore size distribution in

homogeneity and production of various shapes; such as monoliths, powders or fibers [5]. homogeneity and production of various shapes; such as monoliths, powders or fibers [5].

glasses have higher ability to induce glasses have higher ability to induce

]. S]. Solol--gel techniqugel techniqu

advantages with respect to the control of material’s surface advantages with respect to the control of material’s surface chemistry which is directly relatedchemistry which is directly related

differences in surfacedifferences in surface

glass has a higher specific surface area ii) glass has a higher specific surface area ii)

larger pore volume on the surface; and (iii) larger pore volume on the surface; and (iii) solsol--gel gel glass has a larger concentration of silanols glass has a larger concentration of silanols

on the surface [1]. All these surface chemistry on the surface [1]. All these surface chemistry

better bioactive behavior than conventional meltbetter bioactive behavior than conventional melt

In the last couple of decades, there has been some interest in porous glassIn the last couple of decades, there has been some interest in porous glass

ne ingrowth is needed or as coatings in applications such as implants, where a good ne ingrowth is needed or as coatings in applications such as implants, where a good

implant interface implant interface is required [7,8]. Porous biomaterials have been produced by several

techniques such as the use of polymeric sponge, foaming processes and techniquestechniques such as the use of polymeric sponge, foaming processes and techniques

organic organic surfactantssurfactants

The porous structure is induced by the condensation of silica around supramolecular The porous structure is induced by the condensation of silica around supramolecular

3

combination with a high pore volume. The resulting amorphous material is biocompatible [9].

It’s well known that a bioactive material is one that elicits a specific biological response at the

material interface and allows the attachment to the tissue, such as soft tissue and bone [2].

When bioactive materials are implanted in human body, their interface is transformed to a

calcium phosphate phase (apatite phase) through of series of surface reactions including ion

exchange and dissolution-precipitation reactions denoted as “bioactive process” [3].

Subsequently, the implants were integrated to living bone [5]. This mechanism does not

depend on the presence of living tissues and occur even when the glasses are soaked in

simulated body fluids. In vivo studies revealed that bioactive glasses show no local or

systemic toxicity, no inflammation, and bond to tissues without encapsulation by fibrous layer

[5].

For bioactive glasses, variables such as chemical composition, structure, surface morphology,

and synthesis conditions, such as temperature, pH, and reactant ratios, are influent parameters

on the bioactivity [6, 10-15]. All these factors must be taken into account when applying this

synthesis route to biomaterials, as the bioactive process is a surface process and the response

of the living tissue will be ruled by the surface characteristics of the implant [16, 17].

The objective of this paper is to report the preparation of mesoporous glasses in the system

SiO2-CaO-P2O5 (92% SiO2, 6% CaO, and 2% P2O5 mol %), named 92S6, through sol-gel

route. In order to analyze changes in 92S6 textural properties, synthesized using different

carbon-chain-length, and in order to estimate the values of parameters describing the

properties of pore structure, X-ray diffraction studies and nitrogen adsorption isotherms were

used. In vitro bioactivity of glasses was investigated to analyze its feasibility as biomaterial.

2. Experimental method

2.1. Preparation of mesoporous bioactive glass samples (92S6)

2.1.1. Reactants

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Twhen the glasses when the glasses are soaked are soaked

revealed that bioactive glasses show no local or revealed that bioactive glasses show no local or

o tissues without encapsulation byo tissues without encapsulation by

For bioactive glasses, variables such as chemical composition, structure, surface morphology, For bioactive glasses, variables such as chemical composition, structure, surface morphology,

pHpH, and reactant ratios, are , and reactant ratios, are

All these factors must be taken intAll these factors must be taken int

synthesis route to biomaterials, as the bioactive process is a surface process and the response synthesis route to biomaterials, as the bioactive process is a surface process and the response

of the living tissue will be ruled by the surface characteristics of the implant [16, 17].of the living tissue will be ruled by the surface characteristics of the implant [16, 17].

The objective of this paper is to reportThe objective of this paper is to report

92% SiO92% SiO22, 6% CaO, and 2% P, 6% CaO, and 2% P

In order to analyzeIn order to analyze

chainchain-lengthlength

properties of pore structure, Xproperties of pore structure, X

used. used. In vitroIn vitro

4

Tetraethyl orthosilicate (TEOS) (99%; Aldrich, France) was used as a silica source, Triethyl

phosphate (TEP) (99.8%; Aldrich, France) was used as source of phosphorous, calcium carbonate

CaCO3 (> 98.5%; Merck, France) was used as source of calcium. C10H20BrN (97%; Alfa Aesar,

Germany), C19H42BrN (98%; Alfa Aesar, Germany) and C22H48BrN surfactants (80%; Alfa Aesar,

Germany) were used as a structure-directing agent. Water was used as solvent. All materials were used

as received without further purification.

2.1.2. Synthesis procedure

Samples were prepared by the sol–gel process. The synthesis was carried out according to the

modified Stöber’s method described for synthesis of monodisperse silica spheres MCM-41

[18]. In the first step, the solution was prepared as follows: 2.5 g of commercial surfactant

(C10H20BrN, C19H42BrN, C22H48BrN) was dissolved in 50 mL of deionized water and mixed

with 75 mL of absolute ethanol, at room temperature. 3.6 g of TEOS is further added to this

solution and kept under strong stirring for one hour. Under stirring, 0.16 g of TEP and an

acidic CaCO3 solution were added. In the second step, the mixture was stirred for 24 hours at

20°C. Finally 18.53 mL of aqueous ammonia solution (25% wt, Fluka, France) was added to

this clear solution and stirred for 15 min. At the end of the addition of aqueous ammonia

solution, the gel formation immediately began. The white precipitate was isolated by filtration

and washed several times with water and ethanol until neutral pH was reached.

2.1.3. Calcination

The samples were dried at 90°C overnight. The surfactant was removed by calcination,

treating the dried gel at 650°C for 6h. The resulting bioactive glass was crushed and sieved to

select grain size less than 63 µm. Samples were then characterized.

Materials are named as 92S6-C7, 92S6-C16 and 92S6-C19 according to the number of

carbons of the surfactant tail.

2.2. Samples characterization

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Tgel process. The synthesis was carried out according to the gel process. The synthesis was carried out according to the

method described for synthesis of monodisperse silica spheres MCMmethod described for synthesis of monodisperse silica spheres MCM

[18]. In the first step, the solution was prepared as follows: 2.5 g of commercial surfactant [18]. In the first step, the solution was prepared as follows: 2.5 g of commercial surfactant

was dissolved in 50 mLwas dissolved in 50 mL of deionized water and mixed of deionized water and mixed

of absolute ethanol, at room temperature. 3.6 g of TEOS is further added to this of absolute ethanol, at room temperature. 3.6 g of TEOS is further added to this

solution and kept under strong stirring for one hour. Under stirring, 0.16 g of TEP and solution and kept under strong stirring for one hour. Under stirring, 0.16 g of TEP and

solution were added. In the sesolution were added. In the second step, the mixture was stirred for 24 hours at cond step, the mixture was stirred for 24 hours at

of aqueous ammonia solution (25% wt, Fluka, France) was added to of aqueous ammonia solution (25% wt, Fluka, France) was added to

this clear solution and stirred for 15 min. At the end of the addition of aqueous ammonia this clear solution and stirred for 15 min. At the end of the addition of aqueous ammonia

solution, the gel formationsolution, the gel formation immediately began. The white precipitate was isolated by filtration immediately began. The white precipitate was isolated by filtration

and washed several times with water and ethanol until neutral pH was reached. and washed several times with water and ethanol until neutral pH was reached.

2.1.3. Calcination2.1.3. Calcination

The samples were dried at 90°C overnight. The surfactant was removed by calcination, The samples were dried at 90°C overnight. The surfactant was removed by calcination,

treating the dried gel at 650°C for 6h. The resulting bioactive glass was crushed and sieved to ting the dried gel at 650°C for 6h. The resulting bioactive glass was crushed and sieved to trea

select select grain size less than 63grain size less than 63

5

The wide angle X-ray diffraction (WAXRD) patterns of the samples were recorded on a

Bruker AXS diffractometer with monochromatized CuKα radiation (λ=1.5406Å), operating at

40 kV, 40 mA, with 0.02° step size and a counting time 300 ms per step, over a range of 5° <

2θ < 80° , at room temperature.

Scanning electron microscopy (SEM) was performed on a JEOL-JSM-6301F instrument.

Specific surface area and pore size distribution of the materials were determined by nitrogen

N2 adsorption-desorption using a Micromeritics ASAP-2010. Both the adsorption and

desorption branches of the isotherms were analyzed. From these data the specific surface area

and the pore size distribution of the samples were calculated. The pore size distribution was

determined using the BJH method (desorption) [19].

2.3. In vitro bioactivity test

The HAP-forming ability of the glass powder was analyzed by immersing the samples in

simulated body fluid (SBF) for various periods of time. Each specimen was immersed in SBF

solution at 37 ± 0.5 °C, for 7, 15, 21 and 30 days. This solution has ion concentrations and pH

nearly equal to those of human blood plasma. The glass specimen before soaking in SBF is

termed as zero days’ specimen. The SBF was prepared by dissolving reagent-grade NaCl;

KCl; NaHCO3; MgCl2, 6 H2O; CaCl2 and KH2PO4, 3 H2O in deionized water. The solution

was buffered at pH=7.4 with Tris–(hydroxymethyl)-aminomethane ((CH2OH)3CNH3) and

hydrochloric acid according to Kokubo’s protocol [20]. A solid to liquid ratio of 1 mg/2 ml

was maintained for all immersions, and the SBF solutions were not renewed during the

experiments.

The samples were removed from the incubator, rinsed with deionized water and left to dry at

ambient temperature overnight. ICP–OES was used to analyze the ionic composition of SBF

after immersion of the glass samples.

3. Results and discussion

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Tdesorption branches of the isotherms were analyzed. From these data the specific surface area desorption branches of the isotherms were analyzed. From these data the specific surface area

and the pore size distribution of the samples were calculated. The pore size distrand the pore size distribution of the samples were calculated. The pore size distr

glass powder was analyzed by immersing the samples in glass powder was analyzed by immersing the samples in

simulated body fluid (SBF) for various periods of time. Each specimen was immsimulated body fluid (SBF) for various periods of time. Each specimen was imm

at 37 ± 0.5 °C, for 7, 15, 21 and 30 days. This solution has ion concentratat 37 ± 0.5 °C, for 7, 15, 21 and 30 days. This solution has ion concentrat

of human blood plasma. The glass specimenof human blood plasma. The glass specimen

termed as zero days’ specimen. The SBF was prepatermed as zero days’ specimen. The SBF was prepa

6 H6 H22O; CaClO; CaCl

at pH=at pH=7.4 with Tris7.4 with Tris

hydrochloric acid hydrochloric acid according to Kokubo’s protocol [20]. according to Kokubo’s protocol [20].

was maintained for all immersions, and the was maintained for all immersions, and the

experiments.experiments.

The samples were removed froThe samples were removed fro

6

3.1. Glasses Characterization

3.1.1. Small and Wide X-ray diffraction

Fig. 1 shows similar Small Angle X-ray diffraction (SAXRD) patterns of the bioactive glasses

with the same chemical composition prepared with different cationic surfactants. It can be

observed that there is no diffraction peaks appearing on the pattern of the samples prepared

with C7, C16 and C19 surfactants, which suggests that for these samples there is no periodic

arrangement of the mesopores.

The powder wide-angle XRD patterns for all samples are shown in Fig. 2. They all exhibit X-

Ray diffraction data characteristic of amorphous materials with no evidence of crystalline

phases.

3.1.2. BET analysis

Nitrogen isotherms of calcined 92S6-C7, 92S6-C16 and 92S6-C19 are shown in Fig. 3. All

samples exhibited isotherms of type IV based on the IUPAC classification.

92S6-C7 and 92S6-C16 glasses exhibited hysteresis loops of H3 type, and for 92S6-C19

glass, it exhibited a H4 type which is associated with the presence of mesopores. Table 1

summarizes the different pore sizes, specific areas and pore volumes in samples. Synthesized

glasses show specific surface area (SBET) in the range of 88 to 248 m2.g-1. It shows that the use

of different surfactants has a significant influence on glass specific area. On the other hand, a

decrease of pore volume (Vp) is observed, the value is declined from 0.28 cm3/g to 0.13 cm3/g

with increasing the number of surfactant carbons. The N2 adsorption experiments revealed

that these materials have an average pore size varying from 2.6 nm to 8.24 nm.

As we know, during the sol-gel process the alkoxysilane precursors react easily with water,

the hydrolyzed species link together in condensation reactions and form a polymeric network,

especially for the tetraethylorthosilicate TEOS. A similar study on the effect of surfactant

chain length on the pore diameter of metal oxide-surfactant composite showed that the pore

ACCEPTED MANUSCRIP

T. They all exhibit X. They all exhibit X

data characteristic of amorphous materials with no evidence of data characteristic of amorphous materials with no evidence of

and 92S6and 92S6--C

based on the IUPAC classification.based on the IUPAC classification.

glasses exhibited hysteresis loops of H3 typeglasses exhibited hysteresis loops of H3 type

glass, it exhibited a H4 type which is associated with the presence of mesopores.glass, it exhibited a H4 type which is associated with the presence of mesopores.

summarizes the different pore sizes, specific areas and pore volumes in samples. Synthesized summarizes the different pore sizes, specific areas and pore volumes in samples. Synthesized

show specific surface area (Sshow specific surface area (S

of different surfactants has a significantof different surfactants has a significant

decrease of pore volume (Vp) is observed, the value is declined fromdecrease of pore volume (Vp) is observed, the value is declined from

with increasing the number of surfactant carbons. The Nwith increasing the number of surfactant carbons. The N

that these materials havethat these materials have

As we knAs we kn

7

size of the synthesized composite is assigned by changing the length of the surfactant tail. For

example, in the series CnTMABr, n = 7, 10, 12, 14, 16, 19, the pore size of the as-synthesized

material increases about 2.25 Å for each increase of one carbon in the surfactant [21, 22].

The explanation for the nature of hysteresis may be that the length of carbon chains plays an

important role in the formation of the mesoporous structure [23], and the pore diameter is

mainly influenced by the carbon chain length.

These results are associated to the mechanism of formation of these glasses. For example,

cetyltrimethylammonium bromide (C16TMABr) in water will form spherical micelles [24]. In

the surfactant molecule, the polar hydrophilic head groups form the outer surface, which is in

contact with the aqueous phase, and the apolar hydrophobic tails (hydrocarbon chain) point

toward the center [25]. So the pore diameter depends critically on the size of hydrophobic

groups in the surfactant. When we increase the number of carbons, the hydrophobic part of

the surfactant will be composed by a large tail; which results in an increase of pore diameter.

So, the increase of the number of carbons results in an increase of pore diameter in glasses

prepared with different surfactants.

The P/P0 values after inflection point, ranging from 0.40 to 0.95, confirm the mesoporous

characteristic, and the mesopores filling occurs in a slightly larger range of P/P0 values, in

that the step in the isotherms appears less pronounced. This suggests a lower homogeneity of

pore size [26]. Capillary condensation pressure increases as a function of carbons number

(Fig. 3). This result confirms that the pore size of glasses can be tailored by a modification of

the surfactant.

3.1.3. Fourier Transform Infrared Spectroscopy (FTIR)

Fig. 4 reports the FTIR spectra, in the 400-2000 cm-1 spectral range, of the 92S6-C7, 92S6-

C16 and 92S6-C19 powder surfaces, before soaking in the SBF solution. 92S6-C7 shows the

characteristic absorption bands of the silicate vibrations: 465, 807, 1060 cm-1 assigned to Si-

ACCEPTED MANUSCRIP

TTMABr) in water will form spherical micelles [24].TMABr) in water will form spherical micelles [24].

the surfactant molecule, the polar hydrophilic head groups form the outer surface, which is in the surfactant molecule, the polar hydrophilic head groups form the outer surface, which is in

contact with the aqueous phase, and the apolar hydrophobic tails (hydrocarbon chain) point contact with the aqueous phase, and the apolar hydrophobic tails (hydrocarbon chain) point

depends critically ondepends critically on the size of hydrophobic the size of hydrophobic

groups in the surfactant. When we increase the number of carbons, the hydrophobic part of groups in the surfactant. When we increase the number of carbons, the hydrophobic part of

; which results in an increase of pore diameter. ; which results in an increase of pore diameter.

increase of the number of carbons resincrease of the number of carbons results in an increase of pore diameter in glasses ults in an increase of pore diameter in glasses

values after inflection point, ranging from 0.40 to 0.95, confirmvalues after inflection point, ranging from 0.40 to 0.95, confirm

characteristic, and the mesopores filling occurs in a slightly larger range ofcharacteristic, and the mesopores filling occurs in a slightly larger range of

step in the isotherms appears less pronounced. This suggests a lower homogeneity of step in the isotherms appears less pronounced. This suggests a lower homogeneity of

pore size [26].pore size [26]. CCapillary condensation pressure increases as a function of carbons numberapillary condensation pressure increases as a function of carbons number

)). This. This result result

the surfactant.the surfactant.

3.1.3. Fourier Transform Infrared Spectroscopy (FTIR)3.1.3. Fourier Transform Infrared Spectroscopy (FTIR)

8

O-Si bending mode, Si-O-Si symmetric stretching mode of bridging oxygen atoms between

tetrahedrons and Si-O-Si asymmetric stretching of bridging oxygen atoms within the

tetrahedron, respectively [2]. The band located at 606 cm-1 is attributed to P-O bending band

of PO43- group in crystal [2]. A weak band appearing as shoulder at 973 cm-1 may be related

to P-O stretching vibrations in tetracalcium phosphate [27]. The band observed at 1238 cm-1 is

related to the presence of PO43- groups in the glass structure. For glasses with low content of

P2O5, phosphorous is not considered as a glass former like silicon, but phosphorous is present

in the glass structure as PO43- ions like a glass modifier [28]. The peaks at 1421 and 1491 cm-1

are assigned to C-O vibrations in carbonate CO32- group. The band at 673 cm-1 is due to the

presence of some adsorbed CO2 at the glass surface [29]. The band around 1628 cm-1 is the

deformation mode of O-H-O group attributed to the adsorbed water molecules [30].

Comparatively to 92S6-C7 glass, 92S6-C16 and 92S6-C19 glasses include all above

mentioned bands.

In all case the glasses were synthesized using sol-gel method without changing composition.

If the composition or the synthesis mode (melting versus sol-gel) change, some differences in

the position of vibrations for SiO4 tetrahedrons are observed [28, 31]. This phenomenon is not

observed here and the glass structure is not surfactant-dependent.

3.2. Bioactivity assays

3.2.1. Chemical reactivity investigation

The formation of a biologically equivalent apatite surface, a common characteristic of

bioactive materials, can be reproduced in vitro by immersion experiments using a simulated

physiologic fluid (SBF) that mimics the typical ion concentrations in body fluid. We present

results of ICP-OES analyses performed on solutions in contact, for different periods, with

glasses synthesized using three different surfactants. Fig. 5 shows the evolutions of silicon,

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

TThe peaks at 1421 and 1491 cm

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Tgroup. The band at 673 cm 1 is due to the

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T]. The band around 1628 cm

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TO group attributed to the adsorbed water molecules

ACCEPTED MANUSCRIP

T

C16 and 92S6-C19

ACCEPTED MANUSCRIP

T

In all case the glasses were synthesized using solIn all case the glasses were synthesized using sol-gel method without changing composition. gel method without changing composition.

If the composition or the synthesis mode (melting versus solIf the composition or the synthesis mode (melting versus sol

the position of vibrations for SiOthe position of vibrations for SiO4 tetrahetetrahedrons are observed [drons are observed [

observed here and the glass structure is not surfactantobserved here and the glass structure is not surfactant

3.2. Bioactivity assays3.2. Bioactivity assays

mical reactivity investigationmical reactivity investigation

ormation of a biologically equivalent apatite surface, a common characteristic of ormation of a biologically equivalent apatite surface, a common characteristic of

bioactive materials, can be repbioactive materials, can be rep

physiologic fluidphysiologic fluid

9

calcium and phosphorous ionic concentrations, with the soaking time in SBF, for 92S6-C7,

92S6-C16 and 92S6-C19.

As it can be observed, in all cases, variation of Si concentration in the solution was similar for

the three samples: an increase up to 57.3 during the first 7 days of immersion and then no

significant change. Similarly, variation of Ca and P concentration in SBF followed the same

tendency for the three glasses. However, these evolutions were different for each glass. For

92S6-C19, Ca and P concentrations reached a maximum after 15 days of soaking in SBF and

gradually decreased up to 30 days, while for 92S6-C16 and 92S6-C7 Ca and P concentrations

show an increase the first 7 days of soaking, followed by a decrease in concentration. These

observations highlight ionic exchanges between the surface material and the surrounding

medium, which lead to the formation of the apatite layer. According to Hench, these changes

in ionic concentrations demonstrated the dissolution/precipitation process: [32] a hydrated

silica layer formed at the surface of bioactive glass prior to the deposition of HA, and these

silanol groups (Si-OH) could be specific sites for apatite nucleation. The variations of Ca

concentration can be explained by Ca2+ ions release from the glass network, and the

consecutive apatite layer formation that causes the Ca concentration decrease in SBF.

92S6-C7 and 92S6-C16 glasses have been shown to nucleate hydroxyapatite layer more

rapidely than 92S6-C19 glass. This was mainly attributed to the larger surface areas afforded

by glasses synthesized with C7TMABr and C16TMABr surfactants.

3.2.2. XRD results

Fig.6 shows XRD pattern of 92S6 glasses synthesized at C7, C16 or C19 surfactants before

and after contact with SBF for different soaking times at 37°C. For comparison, X-ray

diffraction data of a crystallized hydroxyapatite (HA) Ca10(PO4)6(OH)2 (Alfa, Germany) are

also presented.

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

TC7 Ca and P concentrations C7 Ca and P concentrations

show an increase the first 7 days of soaking, followed by a decrease in concentration. These show an increase the first 7 days of soaking, followed by a decrease in concentration. These

observations highlight ionic exchanges between the surface material and the surrounding observations highlight ionic exchanges between the surface material and the surrounding

n of the apatite layer. According to Hench, these changes n of the apatite layer. According to Hench, these changes

in ionic concentrations demonstrated the dissolution/precipitation process: in ionic concentrations demonstrated the dissolution/precipitation process:

silica layer formed at the surface of bioactive glass prior to the deposition of HA, and these silica layer formed at the surface of bioactive glass prior to the deposition of HA, and these

OH) could be specific sites for OH) could be specific sites for apatite nucleation. The variationapatite nucleation. The variation

can be explained by Cacan be explained by Ca2+2+ ions releaseions release

ayer formation thatayer formation that causecause

6 glasses haveglasses have

-C19 glassC19 glass. T. T

by glasses synthesized with Cby glasses synthesized with C

3.2.2. XRD results 3.2.2. XRD results

ACCEPTED MANUSCRIP

T

6 shows XRD pattern of 92S6 glasses synthesized at C7, C16 or C19 surfactants before

ACCEPTED MANUSCRIP

T

and after contact with SBF for different soaking times at 37°C. For comparison, X

10

For 92S6-C19, X-ray diffraction data (Fig. 6c) show no diffraction peak up to 15 days,

suggesting no new phase crystallization at the glass surface during this period. After 21 days,

we observe two characteristic peaks of HA at 25.85° and 32.02°. After 30 days of soaking in

SBF, these two peaks become evident, confirming the formation of a crystalline apatite.

According to XRD results for 92S6-C16 glass (Fig. 6b), no crystalline phase was formed at

the glass surface before 15 days. After 15 days, we observe two characteristic peaks of HA at

25.98° and 31.73°. The intensity of diffraction peaks increased with time up to 30 days.

For 92S6-C7 glass, after 15 days of soaking in the SBF, the XRD diagram (Fig. 6a) reveals

the presence of two diffraction peaks located at 25.90° and 31.99°, corresponding respectively

to the (002) and (211) reflection of apatite phase: Ca10(PO4)6(OH)2 [33]. This phase increased

for 21 and 30 days soaked glasses. After 30 days in SBF, the 92S6-C7 glass pattern shows

well-characterized peaks of pure HA.

On the other hand, XRD results indicate that the glass prepared with C7TMABr is more

reactive and bioactive than that prepared with C16TMABr and C19TMABr. This result is in

good agreement with will be SEM results. This is related to the increase of the nucleation rate.

3.2.3. Scanning Electron Microscopy

The samples synthesized with different surfactants were examined with the Scanning Electron

Microscopy in order to determine the particles shape.

Fig. 7a, 7c, 7e show the micrographs of the 92S6-C7, 92S6-C16 and 92S6-C19 samples,

respectively, before soaking in SBF. The morphological structure result in the formation of

spherical mesoporous particles exhibiting a dense and smooth appearance (high coalescence

degree), whatever the length of the surfactant tail. It seems that the presence of the cationic

surfactant in the reaction favors the formation of spherical particles.

The formation of hydroxyapatite deposition on the glasses surfaces after immersion in SBF

was also observed by SEM.

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TC7 glass, after 15 days of soaking in the SBF, the XRD diagram (Fig.

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Tof two diffraction peaks located at 25.90° and 31.99°, corresponding respectively

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T(OH)2 [33]. This phase increased

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Tfor 21 and 30 days soaked glasses. After 30 days in SBF, the 92S6

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On the other hand, XRD results indicate that the glass prepared with C

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reactive and bioactive than that prepared with C16TMABr and C

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results. This is related to the increase of the nucleation rate

. Scanning Electron Microscopy. Scanning Electron Microscopy

The samples synthesized with different surfactants were examined with the Scanning Electron The samples synthesized with different surfactants were examined with the Scanning Electron

Microscopy in order to determine the particles shape.Microscopy in order to determine the particles shape.

77e show the micrographs of the 92S6e show the micrographs of the 92S6

respectively, before soaking in SBF. The morphological structure result in the formation of respectively, before soaking in SBF. The morphological structure result in the formation of

spherical mesoporous particles exhibiting a dense and smooth appearance (high coalescencespherical mesoporous particles exhibiting a dense and smooth appearance (high coalescence

degree), whatever the length of the surfactant tail. degree), whatever the length of the surfactant tail.

11

Fig. 7b, 7d, 7f show the surface morphology of glasses specimen incubated in SBF for 2

weeks. All mineral coating formed on glasses surface were continuous layers, with

differences in microscale morphologies. The surface morphology changed as the length of the

surfactant tail increased. 92S6-C7 glass (Fig. 7b) shows the formation of spherical particles

coating the whole surface. With increasing the length of surfactant tail to 16, apatite grains

(Fig. 7d) were spherical but the density of the micro spherical particles of 92S6-C16 glass was

approximately 3 times lower than those of 92S6-C7 glass (Fig. 7b). For 92S6-C19 glass, a

layer composed of needle-shaped crystallites covers the surface.

It is well known that the reactivity of solids begins on their surface. The silanol groups (Si-

OH) on the bioactive glasses surface play an important role in the hydroxyapatite formation

[18]. The increase of glass surface specific area favors ionic exchanges, it becomes easier to

attract calcium and phosphorous ions on the surfaces of glass, it induces formation of silanol

groups and increase the local ions concentrations and consequently improves the nucleation

and the growth of bone-like apatite nanocrystals and enhance bone forming bioactivity [34].

Moreover, previous studies showed that the increase of mesopore volume may contribute to

the increase of apatite nucleation [20] and porous structures may facilitate the transportation

of dissolved Ca2+ ions as well as the subsequent deposition of bone-like hydroxyapatite [35].

So, the clusters and the grains observed at these surfaces are attributed to the formation of

phosphate phases (HCA as confirmed by ICP-OES) for all glasses. Furthermore, our results

indicate that the thickness of the HCA layer and the spherical particles with needlelike

crystallites increase with decreasing the number of surfactant’s carbons.

Furthermore, SBF immersion tests reveal that 92S6-C19 glass required 21 days in SBF to

form a new apatite phase, indicating the low bioactive behavior of this sol-gel glass. After 30

days in SBF, the surface appears fully covered by crystallites of calcium phosphate

characteristic of the growth of apatite phase on a bioactive material surface. However, the use

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Tthat the reactivity of solids begins on their surface. Thethat the reactivity of solids begins on their surface. The silanol groups (Sisilanol groups (Si

OH) on the bioactive glasses surface play an important role in the hydroxyapatite formation OH) on the bioactive glasses surface play an important role in the hydroxyapatite formation

f glass surface specific area favors ionic exchanges, it becomes easier to f glass surface specific area favors ionic exchanges, it becomes easier to

attract calcium and phosphorous ions on the surfaces of glass, it induces formation of silanol attract calcium and phosphorous ions on the surfaces of glass, it induces formation of silanol

concentrations and consequently improves the concentrations and consequently improves the

like apatite nanocrystals and enhance bone forming bioactivity [like apatite nanocrystals and enhance bone forming bioactivity [

Moreover, previous studies showed that the increase of mesopore volume may contribute to Moreover, previous studies showed that the increase of mesopore volume may contribute to

the increase of apatite nucleation [20] and porous structures may the increase of apatite nucleation [20] and porous structures may

ions as well as the subsequent deposition of boneions as well as the subsequent deposition of bone

So, the clusters and the grains observed at these surfaces are attributed to the formation of So, the clusters and the grains observed at these surfaces are attributed to the formation of

phosphate phases (HCA as confirmed by phosphate phases (HCA as confirmed by

indicate that the thickness of the HCA layer and the spherical particlesindicate that the thickness of the HCA layer and the spherical particles

crystallites increase with decreasing the number of surfactant’s carbons. crystallites increase with decreasing the number of surfactant’s carbons.

Furthermore, SBF immersion tests reveal tFurthermore, SBF immersion tests reveal t

12

of the C7 or C16 surfactant induces a formation of apatite layer at the surface after only 15

days of soaking in SBF. Additionally, as it is shown in table 1, lower pore size lead to fast

ionic exchanges with surrounding medium, and contribute to a high bioactive feature 92S6-C7

glass. The above results indicate that the 92S6-C7 glass can induce the formation of a HCA

layer on its surface faster than 92S6-C16 and 92S6-C19. So, the decrease of pore size may

contribute to the increase of apatite nucleation.

In literature data, there were many studies that investigated the effect of synthesis parameters

on characteristics and bioactivity of bioactive glass. Mesoporous bioactive glasses with

different compositions (100S, 90S5C, 80S15C, 70S25C, 60S35C) have been synthesized and

extensively characterized by Yan et al. [26]. By comparing the texture properties and

bioactivity of different glasses, authors concluded that the formation mechanism (pore-

composition dependence) and bioactivity are different from glass to other. The influence of

synthesis method (sol-gel versus melting technique) on the structure, pore morphology and

bioactivity of 52S4 glass (52% SiO2, 30% CaO, 14% Na2O, 4% P2O mol %) was also studied

by Mezahi et al. [32]. The in vitro bioactivity of glasses was studied. Authors demonstrated

that prepared 52S4 bioactive glass by sol-gel technique has higher bioactivity than those made

by melting technique.

So, in our study, we chose to synthesize glasses with a same composition using the same

technique (sol-gel), in presence of surfactants with different carbon chain length. Our results

showed a direct correlation between the surfactant and textural properties and structural

characteristics. We demonstrated that the bioactivity may be significantly modified by a

change on surfactant.

4. Conclusions

The solids surface reaction is of particular importance in the field of biomaterials, since they

will be in contact with an aqueous medium and in presence of cells and proteins.

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Ton characteristics and bioactivity of bioactive glass. Mesoporous bioactive glasses with on characteristics and bioactivity of bioactive glass. Mesoporous bioactive glasses with

ferent compositions (100S, 90S5C, 80S15C, 70S25C, 60S35C) have been synthesized and ferent compositions (100S, 90S5C, 80S15C, 70S25C, 60S35C) have been synthesized and

[26]. By comparing the texture properties and [26]. By comparing the texture properties and

bioactivity of different glasses, authors concluded that the formation mechanism (porebioactivity of different glasses, authors concluded that the formation mechanism (pore

composition dependence) and bioactivity are different from glass to other. The influence of composition dependence) and bioactivity are different from glass to other. The influence of

melting technique) on the structure, pore morphology and melting technique) on the structure, pore morphology and

% CaO, % CaO, 1414% Na% Na

bioactivity of glasses was studied. Authors demonstrated bioactivity of glasses was studied. Authors demonstrated

that prepared 52S4 bioactive glass by solthat prepared 52S4 bioactive glass by sol gel technique has higher bioactivity than those made

So, in our study, we chose to synthesize glasses with a same composition using the same So, in our study, we chose to synthesize glasses with a same composition using the same

technique (soltechnique (sol--gel), gel), in presence of surfactants with different carbon in presence of surfactants with different carbon

showed a direct correlation between theshowed a direct correlation between the

characteristics. We demonstrated that the bioactivity may be significantly modified by characteristics. We demonstrated that the bioactivity may be significantly modified by

change on surfactantchange on surfactant

13

This study compares the surface properties and the bioactivity of sol-gel glasses prepared with

same composition but with different surfactants. Factors such as the length of carbons chain

of the surfactant used in the reaction mixture determine, as it has been shown here, the

particle morphology and the porous characteristics of the final mesoporous glasses and then

induce bioactivity features.

We have demonstrated here in convincing manner the importance of glasses surface

chemistry on the bioactivity: the self assembly of surfactants at the surface can modify the

surface properties and thus leads to their many applications.

Our results show that the properties of those glasses are extremely dependent on the

properties of the surfactants used as templates in their synthesis.

Acknowledgments

The authors would like to acknowledge Joseph Le Lannic, from the CMEBA, Université de

Rennes 1, for SEM, and Odile Merdrignac-Conanec, from Laboratoire Verres et Céramiques,

Université de Rennes 1, for BET studies.

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Fig. 1. SAXRD patterns of powders of 92S6-C7, 92S6-C16 and 92S6-C19 glasses surfaces

before soaking in SBF solution.

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T, F. Z. Mezahi, M. Mami, H. Oudadesse, A. Harabi and M. Le Floch. J. , F. Z. Mezahi, M. Mami, H. Oudadesse, A. Harabi and M. Le Floch. J.

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[33] Powder diffraction File, No. 09[33] Powder diffraction File, No. 09

] D. Zhao, J. Feng, Q. Huo, N. Melosh, G.H. Fredrickson, B.F. Chmelka, G.D. Stucky, ] D. Zhao, J. Feng, Q. Huo, N. Melosh, G.H. Fredrickson, B.F. Chmelka, G.D. Stucky,

Science 279 (1998) 548.Science 279 (1998) 548.

35] X. Y] X. Yan, C. Yu, X. Zhou, J. Tang, D. an, C. Yu, X. Zhou, J. Tang, D.

16

Fig. 2. WAXRD patterns of different glasses before soaking in SBF solution.

Fig. 3. N2 adsorption/desorption isotherms of (a) 92S6-C7, (b) 92S6-C16 and (c) 92S6-C19.

Fig. 4. FTIR spectra of prepared glasses: 92S6-C7 (a), 92S6-C16 (b) and 92S6-C19 (c).

Fig. 5. Evolution of Si (a), Ca (b) and P (c) concentrations in SBF, versus soaking time for

92S6-C7, 92S6-C16 and 92S6-C19 glasses.

Fig. 6. WAXRD patterns of glass surfaces before and after different soaking times in SBF

solution: 92S6-C7 (a), 92S6-C16 (b) and 92S6-C19 (c).

Fig. 7. SEM micrographs of bioactive glasses (a,b) 92S6-C7, (c,d) 92S6-C16 and (e,f) 92S6-

C19 surfaces before (x 50000) and after soaking for 2 weeks in SBF solution (x 20000).

Table 1 Textural properties of sol-gel glasses synthesized with different length of the carbon chain template. Samples SBET a (m2/g) Vp b (cm3/g) Dp

c (nm)

92S6-C7 248 0.28 2.6

92S6-C16 224 0.16 4.85

92S6-C19 88 0.13 8.24

a BET specific surface area.

b Pore volume.

c Pore diameter calculated by BJH method.

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urfaces before (x 50000) and after soaking for 2 weeks in SBF solution urfaces before (x 50000) and after soaking for 2 weeks in SBF solution ((x 20000)x 20000)

gel glasses synthesized with different length of the carbon chaingel glasses synthesized with different length of the carbon chain

(m(m22(m(m(m /g)/g)

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248248

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224224

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specific surface areaspecific surface area

Pore volume.Pore volume.

Pore diameter calculated by BJH method.Pore diameter calculated by BJH method.

17

Fig. 1.

Fig. 2.

1 2 3 4 5 6 7 8

2 θ (°)

2 θ (°)

92S6-C7

Inte

ns

ity

(u

.a)

92S6-C16

92S6-C19

10 20 30 40 50 60 70

92S6-C7

Inte

ns

ity (

u.a

)

2θ (°)

92S6-C16

92S6-C19

77

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18

0,0 0,2 0,4 0,6 0,8 1,0

0

100

200

Ad

so

rbe

d V

olu

me

(c

m3/g

)

P/P0

92S6-C7(a)

0,0 0,2 0,4 0,6 0,8 1,0

0

100

200

Adso

rbed

Vo

lum

e V

ad

s(c

m3.g

-1)

P/P0

92S6-C16(b)

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Adso

rbed

Vo

lum

e V

Adso

rbed

Vo

lum

e V

19

Fig. 3.

0,0 0,2 0,4 0,6 0,8 1,0

0

100

200

Volu

me A

dsorb

ed

Vads(c

m3/g

-1)

P/P0

92S6-C19(c)

2000 1800 1600 1400 1200 1000 800 600 400

12

38

P-O

Si-

O-S

i

16

48

14

91

14

21

106

0

97

3

80

7

67

3

60

6

OH

- (H2O

)

C-O

C-O

Si-

O-S

i

P-O

Si-

O-S

i

CO

2

P-O

Tra

nsm

itta

nc

e (

%)

Wavenumber (cm-1

)

a: 92S6-C7

46

5

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Fig. Fig. 3.

0,80,8

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38

12

38

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21

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Tra

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Tra

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nc

e (

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Fig. 4.

2000 1800 1600 1400 1200 1000 800 600 400

Si-

O-S

i

P-O

970

P-O

606

1418

1506

C-O

C-O

1635

1238

1075

798

670

467

OH

- (H2O

)

P-O

Si-

O-S

i

Si-

O-S

i

CO

2

Tra

nsm

itta

nc

e (

%)

Wavenumber (cm-1

)

b:92S6-C16

2000 1800 1600 1400 1200 1000 800 600 400

Si-

O-S

i

P-O

967

P-O

606

1427

1511

C-O

C-O

1645

1232

1075

793

670

467

OH

- (H2O

)

P-O

Si-

O-S

i

Si-

O-S

i

CO

2

Tra

nsm

itta

nce

(%

)

Wavenumber (cm-1

)

c:92S6-C19

ACCEPTED MANUSCRIP

T800800 600600

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

TSi-

O-S

iS

i-O

-Si

P-O

P-O

20002000

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T967

967

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T1232

1232

1075

1075

OH

OH

-- (H22OO

))

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

c:92S6-C

21

ACCEPTED MANUSCRIP

T

22

Fig. 5.

10 20 30 40 50

In

ten

sit

y(u

.a)

2 θ (°)

HA

30 days

21 days

15 days

7 days

0 days

(202)

(30

0)

(112

)

(21

1)

(210)

(10

2)(0

02)

a: 92S6-C7

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T30

0)

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T(1

12

)

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T(2

11)

(210)

(10

2)

23

10 20 30 40 50

HA

30 days

21 days

15 days

7 days

0 days

2 θ (°)

(202

)(300

)

( 11

2)

(21

1)

( 210

)

(10

2)(0

02

)

Inte

ns

ity (

u.a

)b: 92S6-C16

10 20 30 40 50

2 θ (°)

HA

30 days

21 days

15 days

7 days

0 days

(30

0)

(112

)

(21

1)

(21

0)

(102

)(002)

Inte

ns

ity

(u

.a)

c: 92S6-C19

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T40

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T15 days

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T1

12

112

112

))

(21

1)

(21

0)

102

)

Inte

ns

ity

(u

.a)

24

Fig. 6.

(a) (b)

(c) (d)

(e) (f)

Fig. 7.

ACCEPTED MANUSCRIP

T

ACCEPTED MANUSCRIP

T(b)(b)