Fabrication of monticellite-akermanite nanocomposite powder for tissue engineering applications

Accepted Manuscript Fabrication of monticellite-akermanite nanocomposite powder for tissue engineering applications Fatemeh Shamoradi, Rahmatollah Emadi, Hamed Ghomi PII:

S0925-8388(16)32974-7

DOI:

10.1016/j.jallcom.2016.09.219

Reference:

JALCOM 39053

To appear in:

Journal of Alloys and Compounds

Received Date: 15 June 2016 Revised Date:

6 September 2016

Accepted Date: 20 September 2016

Please cite this article as: F. Shamoradi, R. Emadi, H. Ghomi, Fabrication of monticellite-akermanite nanocomposite powder for tissue engineering applications, Journal of Alloys and Compounds (2016), doi: 10.1016/j.jallcom.2016.09.219. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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FABRICATION OF MONTICELLITE-AKERMANITE NANOCOMPOSITE POWDER FOR TISSUE ENGINEERING APPLICATIONS Fatemeh Shamoradi a,*, Rahmatollah Emadi a , Hamed Ghomi b Department of Materials Engineering, Isfahan University of Technology, Isfahan

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a

84156-83111, Iran b

Young Researchers and Elite Club, Najafabad Branch, Islamic Azad University,

* Corresponding

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Najafabad, Iran author

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E-mail address: [email protected] Tel: ++98 313 3912750 Fax: ++98 313 3912752

Abstract:

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Mechanical activation (MA) is an efficient method to synthesize nano-structured materials. This is the first report of successful synthesis of monticellite- akermanite nanocomposite from talc, calcium carbonate and magnesium carbonate powders. The

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raw materials were milled for 10 minutes, 2, 5, 10, and 20 hours and then annealed in order to obtain monticellite- akermanite nanocomposite powder. The obtained powder

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was characterized by X-ray diffraction (XRD) and scanning electron microscopy

(SEM). The results indicated preparation of monticellite- akermanite nanocomposite powder with crystallite sizes about 30.76 ± 0.47 nm after 20 h mechanical alloying and sintering at 1200°C for 1 h. Absence of enstatite, a phase that causes a reduction in mechanical and bioactivity properties, is an important feature of the prepared powder. The compacted samples of fabricated nanocomposite powder, sintered at 1300 °C for 3

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h, exhibit significant improvements in compressive strength (60 ± 1.8 MPa) than single phase monticellite (43 ± 1.1 MPa) and hydroxyapatite (34 ± 1.4 MPa) which make it an appropriate candidate for bone tissue engineering applications.

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Keywords: mechanical activation, nanocomposite, monticellite, akermanite. 1. INTRODUCTION:

Repair and regeneration of bone injuries is still a main challenge in biomedical science,

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where finding the ideal bone substitute material is important [1]. In spite of substantial progress over the years, the most effective bone graft which is called autograft, where

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bone from the patient is transplanted from one place to another, is limited by the amount of bone available. The other common clinical substitute is allograft, where cadaveric bone is implanted; which includes the risk of viral infection transmission [2]. This has caused significant research in the field of bone tissue engineering, intending at repairing damaged bone and restoring its functions with the help of biocompatible materials [3].

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Previous studies have shown that some glasses and glass-ceramics containing Si, Ca, and Mg were highly bioactive and could be used for biomedical applications. In addition, release of Mg, Si and Ca ions from these materials in many cases showed to

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have good effect on cell propagation, differentiation and Adherence [4,5]. Some Ca, Si and Mg containing bioactive ceramics have better mechanical properties such as

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fracture toughness, bending strength and Young’s modulus compared to hydroxyapatite (HA) ceramics, which have been widely studied and clinically used as bone replacement materials [6,7].

Monticellite (CaMgSiO4), as a Ca, Si and Mg-containing bioceramic material, has been reported to have apatite-formation ability in the simulated body fluid (SBF) solution that contains ions in concentrations similar to those in the human blood plasma. The

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soluble ionic products from monticellite could significantly promote cell growth and propagation. Additionally, osteoblast cells are adhered and spread well on its surface. Previous studies have shown an enhancement in the fracture toughness and a substantial

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decrease in the Young’s modulus for the monticellite ceramic compared with sintered

HA. These results propose that monticellite ceramic as a bone graft material may meet the requirement of bone regeneration [8, 9].

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Akermanite (Ca2MgSi2O7), as another silicate bioceramic, has received more attention

due to its more controllable mechanical properties and possible application in

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biomedical field. The bioactivity of akermanite has been reported in some studies [10, 11]. Wu and Chang [11, 12] reported the formation of apatite on akermanite ceramic surface by soaking in simulated body fluid. Their results represented that the bending strength of akermanite ceramic was 176 MPa, which suggested better mechanical properties compared with HA ceramic. Huang et al. [13] recommended that akermanite

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is more bioactive and thus, better motivates the propagation and differentiation of bone marrow-derived stem cells in comparison with β-tricalcium phosphate ceramic. In addition, it increases bone regeneration because of its more degradation rate and

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biocompatibility.

Nano-structured ceramics in comparison to micro-structured ceramics have been

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interesting for many researchers due to their better and improved properties such as high contact area, high diffusion rates, high mechanical properties, better ion release from its surface and superior bioactivity. In addition, studies have presented the enhanced adhesion and proliferation of osteoblasts cells compared to usual ceramic. Mechanical activation has been recognized as an efficient way for fabrication of nanocrystalline

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structures and has the advantage of the enhancement of thermodynamic and kinetic reactions between raw powders. [14, 15, 16]. In many applications, there is a need for a composite material with a combination of

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properties. Composite materials are made of two or more basic materials with a preferred properties of each one, while reduce the limitation of each component.

Considering the properties of akermanite and monticellite, the blend of these

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bioceramics has been efficient for achieving nanocomposite materials with high mechanical and bioactivity properties.

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In this study, monticellite- akermanite nanocomposite powder was prepared by mechanical activation technique to utilize their superior mechanical and biological properties in tissue engineering applications.

2. MATERIAL AND METHODS

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2.1. Preparation of monticellite- akermanite nanocomposite powder Monticellite- akermanite nanocomposite powder was prepared by mechanical activation process using talc (Mg3Si4H2O12) (98 % purity, Merck), magnesium carbonate (MgCO3)

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(98 % purity, Aldrich) and calcium carbonate (CaCO3) (98 % purity, Merck) powders. In order to produce the powder, talc, MgCO3 and CaCO3 powders were mechanically

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activated in a high energy planetary ball mill with steel vial and balls with 2 cm diameter. The ball-to-powder weight ratio was 10:1 and the absolute rotational speed of disc was set at 445 rpm. The time of ball milling was chosen 10 minutes, 2, 5, 10, and 20 hours. The milled samples were sintered at 1200°C for 1 hour.

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2.2. Nanocomposite powder Characterization The sintered powders were analyzed by X-ray diffraction (XRD) analysis using a Philips X’PERT MPD diffractometer with Cu Kα radiation (λ = 0.154 nm at 20 kV and

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30 mA), and crystallite size and phase transformation during process were estimated by XRD patterns. The XRD patterns were recorded in the 2θ range of 20°- 80° (step size

0.05° and time per step 1s). The crystallite sizes were calculated by Williamson- Hall

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method as follows [17]. ߚ cos ߠ = 0.9ߣ/‫ ܦ‬+ 2ߝ ‫ߠ݊݅ݏ‬

is the diffraction peak width at half maximum intensity, θ the Bragg

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Where β

(1)

diffraction angle, D the crystallite size, λ the wavelength of the radiation, ε internal strain, and 0.9 the Scherrer constant.

The morphology of sintered powders was observed by scanning electron microscopy (SEM) in a Philips XL30 at an acceleration voltage of 30 kV. SEM images were used

using image analysis.

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for measuring the particle sizes of monticellite- akermanite nanocomposite powder

2.3. Mechanical properties evaluation

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For evaluation of the mechanical properties, hydroxyapatite, single phase monticellite and monticellite- akermanite nanocomposite powder were compacted into samples of 10

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mm diameter and 20 mm height by pressing with a universal experimental instrument (HOUNSFIELD: H50KS) in a steel die up to 10 kN. The compacted samples were then sintered at 1300 °C for 3 hour. Finally the compressive strength test were performed on the sintered specimens at a crosshead speed of 0.5 mm/min. The compressive strength was measured by dividing the maximum load to the original area. The results were reported based on an average of three samples for each composition.

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3. RESULT AND DISCUSSION 3.1. X-ray diffraction analysis Figure 1 represents XRD pattern of the raw materials. As it can be seen, patterns have

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good match with the standards for talc (JCPDS data file 00-029-1493), MgCO3 (JCPDS

data file 00-002-0871) and CaCO3 (JCPDS data file 01-072-1652) assembled by the Joint Committee on Powder Diffraction and Standards (JCPDS).

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Mechanical activation is a competent method to increase the contact area and the

interface of the reactants, which enhances the chemical homogeneity of the product and

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reduces the difficulty of heat treatment [18, 19]. The sintering temperature for synthesis of monticellite and akermanite powder in previous studies has been reported 1480°C and 1370°C, respectively [8, 11].

In the present study, pure monticellite- akermanite nanocomposite powder was synthesized by mechanical activation of a combination of talc, magnesium carbonate,

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and calcium carbonate powders and sintered at 1200 °C for 1 hour which shows a reduction in sintering temperature in comparison to results of other researches [8, 11]. Figure 2 shows the XRD patterns of the powders after different mechanical activation

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time with thermal treatment at 1200°C for 1 hour. Figure 2a shows the XRD pattern of sintered powder with 2 hours mechanical activation. As seen in figure 2a the typical

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peaks correspond to CaO (JCPDS data file 00-003-1123), SiO2 (JCPDS data file 00043-0784), monticellite (JCPDS data file 00-003-1107), akermanite (JCPDS data file 00-035-0592) and enstatite (JCPDS data file 01-071-0786). Therefore, the decomposition of talc to SiO2 and enstatite and the MgCO3 and CaCO3 to MgO and CaO occured, respectively. In addition, characteristic peaks of MgO didn't exist due to reaction with SiO2 and formation of enstatite.

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Increasing mechanical activation time due to reduction in particle size caused a reduction in peaks intensity and an enhancement in peaks width. Figure 2b represents the XRD pattern of sintered powder with 5 hours mechanical activation. In this figure,

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in compared to figure 2a, some typical peaks of CaO, SiO2 and enstatite disappeared and the intensity of their peaks were reduced which was due to the combination of enstatite with CaO and SiO2 in formation of monticellite and akermanite bioceramics.

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Figure 2c shows the XRD pattern of sintered powder after 10 hours of mechanical activation. This pattern is similar to previous, but the intensity of SiO2, CaO and

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enstatite peaks were reduced more after further progress of the reaction. Figure 2d reveals the XRD pattern of sintered powder after 20 hours of mechanical activation. Only the monticellite and akermanite typical peaks could be detected on the XRD pattern. Thus, after 20 hours of mechanical activation the formation of monticellite-

was achieved.

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akermanite nanocomposite powder was completed and a homogeneous combination

The crystallites size of monticellite- akermanite nanopowders were determined by Williamson- Hall equation according to broadening of peaks in diffraction patterns [17].

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The crystallite sizes of the sintered powders after 2, 5, 10, and 20 hours mechanical activation were evaluated about 53.30 ± 0.23, 47.79 ± 0.40, 36.47 ± 0.35, and 30.76 ±

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0.47 nm, respectively.

3.2. Mechanical properties evaluation Figure 3 shows the typical compressive stress- strain curves of the compacted samples of

hydroxyapatite,

single

phase

monticellite

and

monticellite-

akermanite

nanocomposite powder. As can be seen from figure 3, the compressive stress of the compacted samples of the prepared powder (60 ± 1.8 MPa) shows a 1.4-fold increase in

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comparison to single phase monticellite (43 ± 1.1 MPa) and a 1.8-fold increase in comparison to hydroxyapatite (34 ± 1.4 MPa). It is obvious that the compacted samples of fabricated nanocomposite powder, sintered at 1300 °C for 3 h, exhibit significant

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improvements in mechanical properties than single phase monticellite and hydroxyapatite which makes it a suitable candidate for using in bone tissue engineering applications.

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3.3. Monticellite- akermanite formation mechanism

As for figure 2, the formation of monticellite- akermanite during process is suggested to

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take place by several chronological reactions. Talc, MgCO3 and CaCO3 particles decomposed during ball milling according to following equations, respectively: Mg 3 Si4 O10 (OH ) 2 → 3MgSiO3 + SiO2 + H 2O ∆G1200 °C = -33.59 KJ mol-1 K-1

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MgCO3 → MgO + CO2

(2)

(3)

∆G1200 °C = -132.81 KJ mol-1 K-1 CaCO3 → CaO + CO2

(4)

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∆G1200 °C = -43.712 KJ mol-1 K-1

Tavangarian and Emadi [14] also showed that during the activation process MgCO3 and

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talc can be converted into these products. In addition, this is in agreement with Mirhadi et al. [20] results about decomposition of calcium carbonate. Deliverance of CO2 due to the decomposition of magnesium carbonate and calcium carbonate led to improved contact area and higher reactivity of materials [19]. Enstatite is a phase which is produced and is a member of MgO–SiO2 system. The presence of enstatite decreases mechanical and bioactivity properties of this

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nanocomposite powder because of its four different unstable polymorphs [21]. Enstatite also could be formed according to the following equation:

MgO + SiO2 → MgSiO3

(5)

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∆G1200°C = -14.49 KJ mol-1 K-1

In present study with increasing the milling time, enstatite phase was removed because

of the reaction with CaO and fabrication of monticellite and also the reaction with CaO

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and SiO2 and fabrication of akermanite according to equations 6 and 7, respectively:

∆G1200 °C = -95.93 KJ mol-1 K-1

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MgSiO3 + CaO → CaMgSiO4

MgSiO3 + 2CaO + SiO2 → Ca2 MgSi2 O7 ∆G1200 °C = -950.577 KJ mol-1 K-1

(6)

(7)

In this study all possible reactions between the raw materials were reported and the

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Gibbs free energy at 1200 °C was calculated. According to the Gibbs free energy as thermodynamic force all the above reactions have a high tendency to occur. However, thermodynamic force is a necessary condition for the spontaneous reaction and kinetic

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parameters are sufficient condition. As can be seen from the XRD patterns of the powders after different mechanical activation times (Figure 2), the reaction did not

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occur or partially occurred in the lower mechanical activation times: nonetheless increasing the mechanical activation times by increasing the reacting particles contacts lead to activation of raw materials to a level which could cause the reaction to occur completely. Mechanical activation activates the raw materials and facilitates the occurrence of the desired reaction as a beneficial method by fragmentation of particles, preparation of homogeneous mixture, and increasing the energy level of the system.

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3.4. Microstructure evaluation Figure 4 represents the SEM micrographs of monticellite- akermanite nanocomposite powders after different mechanical activation times and subsequent sintering at 1200 °C

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for 1 hours. As can be seen, the nanocomposite powder after 10 hours of mechanical activation (Figure 4a and 4b) consists of very tiny and agglomerated particles with sphere shapes. With increasing the ball milling time up to 20 hours, the size of

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agglomerated particles was reduced (Figure 4c and 4d). Several micrographs were used

for particle size determination and the average value was reported. The agglomerated

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particles size of nanocomposite powders fabricated by 10 and 20 hours mechanical activation and subsequent sintering at 1200°C for 1 hour were determined about 0.5 - 1 µm and 0.1 – 0.5 µm, respectively.

The manufactured nanocomposite powder, could be suitable for scaffold fabrication in tissue engineering applications because of its high mechanical and bioactivity

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properties.

Further studies will be focused on cell culture and in vitro and in vivo tests on scaffolds

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fabricated by the prepared powder.

4. CONCLUSION

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This paper is the first report of successful synthesis of the monticellite- akermanite nanocomposite powder by mechanical activation as a novel, efficient, simple, and economical method and subsequent annealing. The crystallite size of the prepared nanocomposite powder was 30.76 ± 0.47 nm after 20 hours mechanical activation and subsequent annealing at 1200°C for 1 hour. The agglomerated particles size was in the range of 0.1 – 0.5 µm. Lack of enstatite phase that causes a reduction in mechanical and

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bioactivity properties is a significant characteristic of the prepared powder. In present paper novel mechanism and new reactions for formation of monticellite and akermanite were presented. The prepared nanocomposite powder shows an improved compressive

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strength in comparison to single phase monticellite (43 ± 1.1 MPa) and hydroxyapatite (34 ± 1.4 MPa) and could be a good candidate for application in bone tissue

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engineering.

Acknowledgment:

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The authors are grateful to Isfahan University of Technology for supporting this research.

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Figure Captions: Figure 1. X-ray diffraction pattern of raw materials after 10 minutes of mechanical activation.

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Figure 2. X-ray diffraction patterns of the prepared powders after mechanical activation for: a) 2, b) 5, c) 10, and d) 20 hours and subsequent sintering at 1200°C for 1 hour.

Figure 3: The typical compressive stress- strain curves of the compacted samples of

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hydroxyapatite, single phase monticellite and monticellite- akermanite nanocomposite powders sintered at 1300 °C for 3 hour.

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Figure 4. SEM micrographs of the prepared powders after (a, b) 10 and (c, d) 20 hours of mechanical activation and subsequent annealing at 1200°C for 1 hour with various

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magnifications.

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Highlights: This is the first report of synthesis of monticellite- akermanite nanocomposite.

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Crystallite sizes have come to about 30.76±0.47 nm after 20 h mechanical

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alloying.

Novel mechanism for formation of monticellite and akermanite were presented.

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