- Email: [email protected]
Diopside-magnetite; A novel nanocomposite for hyperthermia applications
Author’s Accepted Manuscript Diopside-Magnetite; A novel nanocomposite for hyperthermia applications Majid Abdellahi, Ebrahim Karamian, Aliakbar Najafinezhad, Amirsalar Khandan www.elsevier.com/locate/jmbbm
PII: DOI: Reference:
S1751-6161(17)30441-1 https://doi.org/10.1016/j.jmbbm.2017.10.015 JMBBM2535
To appear in: Journal of the Mechanical Behavior of Biomedical Materials Received date: 22 August 2017 Revised date: 5 October 2017 Accepted date: 8 October 2017 Cite this article as: Majid Abdellahi, Ebrahim Karamian, Aliakbar Najafinezhad and Amirsalar Khandan, Diopside-Magnetite; A novel nanocomposite for hyperthermia applications, Journal of the Mechanical Behavior of Biomedical Materials, https://doi.org/10.1016/j.jmbbm.2017.10.015 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 galley proof before it is published in its final citable 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.
Diopside-Magnetite; A novel nanocomposite for hyperthermia applications Majid Abdellahi*, Ebrahim Karamian, Aliakbar Najafinezhad, Amirsalar Khandan Department of Materials engineering, Najafabad University, Isfahan, Iran *Corresponding Author; Email: [email protected] ; Tel: +989132894596
Abstract In the present work, the releasing heat, scaffold apatite formation, and magnetic behavior of a novel diopside-magnetite nanocomposite with various contents of magnetite (Fe3O4) were evaluated. The N´eel and Brown relaxations did not have a significant effect on the specific absorption rate (SAR) of the composite samples. Indeed, magnetic saturation, Ms, indicated a crucial effect on the heat release of the samples. The sample with 30wt.% magnetite had the highest value of SAR, while the sample with 20wt.% magnetite, in the form of scaffold, allowed the high amount of apatite formation on its surface. Keywords: Hyperthermia; Bioceramics; Ceramic composite
1- Introduction When magnetic nanoparticles (MNPs) are placed in an alternating magnetic (AC) field, they release heat. This released heat as a therapeutic tool that is called “hyperthermia”, can destroy the cancer tumor cells by raising temperature within the range of 41–46 °C [1]. Fe3O4 (magnetite) nanoparticles, have shown a good potential for using in different biomedical applications including, magnetic resonance imaging, magnetic carriers for drug delivery, and hyperthermia [2]. In recent years, the incorporation of Fe3O4 nanoparticles into biophosphate materials with a good biocompatibility behavior was reported [3]. Bio-silicate materials, especially those containing Mg have also indicated an improvement of cell adhesion, proliferation, spreading, and differentiation, making them applicable for tissue
1
engineering applications [4]. Mg-containing bioceramics have shown a comparative advantage in bone tissue regeneration, among which diopside (CaMgSi2O6) has provided slower degradation rate and the ability of in vitro apatite formation and in vivo bone regeneration [5]. Magnetic scaffolds have recently attracted significant attention in tissue engineering, due to the prospect of improving bone tissue formation by conveying soluble factors such as growth factors, hormones and polypeptides directly to the site of implantation, and also because of the possibility of improving implant fixation and stability [6]. In the present study a diopside-magnetite nanocomposite was fabricated and the effect of various amounts of magnetite on the specific absorption rate and apatite formation of the nanocomposite samples, in powder and scaffold forms, was evaluated. 2- Materials and Methods Fe3O4 powder was purchased from Merck Co., while diopside powders in pure state (Fig. 1a), was synthesized according to the route mentioned in our previous work [7]. diopside-magnetite nanocomposite at different percentages of magnetite was obtained via mechanical milling for 10h and a subsequent sintering at 600°C for 3h (for crystallization). The obtained samples were then milled for 5h to obtain nanopowders. To prepare diopside-magnetite scaffolds by the space holder method [8], NaCl as the spacer with particle size of 300-420µm, was added to the composite nanopowder. The powder was then pressed under 100MPa in a cylindrical form. A sintering process was then performed at a rate of 5°/min to 1200°C for 4 h. The sintered samples were then immersed in deionized water for 24h in order to remove the remained NaCl. In the final stage, the scaffolds were immersed in simulated body fluid (SBF), to evaluate their apatite formation. The Archimedes technique [9] was used to estimate the porosity of the prepared scaffolds. Formation of the crystalline phase was studied via X-ray diffraction (XRD) spectra
2
using Cu-Kα radiation in the 2θ limitation of 20-60°. The magnetic properties including saturation magnetization and also coercivity of the obtained samples were determined by using a vibrating sample magnetometer (VSM, Kavir Co.,) at room temperature. Morphology of the samples in powder state was analyzed via field emission scanning electron microscopy (FESEM). The size of hydrodynamic nanoparticles was determined using dynamic light scattering (DLS) technique (model Nano ZS90). An AC magnetic field with a frequency of 200 kHz and amplitude of 10 Ôe was used for studying the heat releasing of nanoparticles. The amount of the analyzed powder was 25 mg for all samples. It was reported in calorimetric method that the specific absorption rate (SAR) value, is proportional to the initial heat, which is emitted from magnetic nanoparticles using AC magnetic field [10]: SAR dT / dt t 10
(1)
dT/dt is the initial heating rate of the nanoparticles under AC magnetic field. In fact, at the initial times, the temperature change rate is the same as with the adiabatic mode. The heating mechanism in superparamagnetic nanoparticles was reported is due to the relaxation processes. i.e. N´eel and Brown effects. The relaxation time of the Brown motion is [10]:
B 4 r 3 kT
(2)
and the N´eel relaxation time is: N 0 exp KV kT
(3)
where is the basic liquid viscosity, r the hydrodynamic radius of the particle, k the Boltzmann’s constant, K is the anisotropy constant, 0 the time constant, and V the particle volume.
3
According to the linear response theory [11], which is corrected for superparamagnetic nanoparticles, the relation between SAR and relaxation losses is:
SAR M s 2 2 1 2
2
(4)
where is the frequency and ( 1 1 B 1 N ) is the effective relaxation time. The relaxation process of the single domain nanoparticles occurs in the ethanol ferrofluid, under AC magnetic field. The relaxation process of the single domain nanoparticles occurs in the ethanol ferrofluid, under AC magnetic field. 3- Results and discussions XRD patterns of the diopside-xMagnetite nanocomposites (x=10wt.%,20 wt.%,30) are shown in Fig.1a. As can be seen, some major peaks of Fe3O4 overlap with some peaks of diopside and cannot be differentiated clearly from one another. Table 1, confirms that by increasing the magnetite content to 10, 20, and 30wt.%, diopside peaks move toward the higher angles. This ensures the substitution of Ca2+ ions (0.099 nm) by Fe3+ ions (0.068nm). The crystallite size of Fe3O4 in all samples is below the critical size of single domain particles which was reported to be 54nm [12] (Table 1). Fig. 1b shows the room temperature magnetization as a function of applied magnetic field for pure magnetite and composited samples. No hysteresis loop is observed, indicating that the resultant nanoparticles are superparamagnetic. The reduced Ms can be explained by considering the diamagnetic contribution of the diopside surrounding the magnetite cores, which will weaken the magnetic moment, whereas the low coercivity (Hc) may be resulted from the size of magnetite particles embedded into diopside. Significant changes in magnetic saturation and
4
coercivity are attributed to the dope of Fe3+ ions into diopside, and also the presence of nonmagnetic diopside phases. Fig. 1c shows the released heat of the suspended samples in ethanol (ferrofluid) under adiabatic conditions (in this work it was assumed that below 10s the adiabatic conditions are dominant). The higher average gradient during 10s ensures the higher specific absorption rate (SAR) values, according to Eq. 1 [10]. SAR is generally used to define the transformation of magnetic energy into heat and its high value allows reduction of ferrofluid dose in vivo. The SAR of superparamagnetic single domain nanoparticles in an external AC magnetic field can be attributed to the relaxation loss process. The relaxation process of a ferrofluid occurs with two distinct routes. The first route is based on the rotation of the single-domain particles (Brown relaxation), and the second corresponds to the rotation of the magnetic moments (N´eel relaxation). To assess the behavior of nanoparticles in the ferrofluid, FESEM images are provided, as shown in Fig. 2. As can be seen, by increasing Fe3O4 content (EDS analysis), agglomeration finds an increasing trend. As the MAP analysis confirms, as a result of the increase of single domain Fe3O4 nanoparticles, these nanoparticles are affected by permanent magnetic moment and therefore agglomerated (see MAP analyses). These agglomerated single domain Fe3O4 nanoparticles experience dipole-dipole interactions and the locally released magnetic energy (as an internal energy) is transformed into heat, which in turn can provide a leading stage for nanopowders/small agglomerates to stick to each other and form large agglomerates (as confirmed by large agglomerated clusters in Fig. 2c). With the above-mentioned description, it is now possible to understand the various rates of the heat release of the samples. As can be seen in Fig. 1b, the coercivity/anisotropy of all the samples is almost the same. This means that the
5
increase of Fe3O4 content does not make the N´eel relaxation a dominant factor in determining the SAR (Eq. 2). On the other hand, Fig. 2a-c shows that the diameter of almost all agglomerated clusters is more than 1µm, which is very high to have an effective Brown relaxation. This is confirmed by Eq. 3, in which whatever the dynamic size increases, the Brown relaxation time (
B ) also increases. This process reduces the Brown effect and hence the efficiency of nanoparticles heating. Brown relaxation time has therefore large values in all of the composite samples as a result of the agglomeration process. In other words, the hydrodynamic volume of all samples (with various content of magnetite) is large and therefore the Brown effect has almost the same values in all samples and does not have a determining effect in the SAR values. In general, in constant frequency, the SAR values of the composite samples is only dependent on the Ms but not (Eq. 4). The higher the Ms is, the higher the SAR will be. This is confirmed by Figs. 1b and 1c. (It should be noted that in superparamagnetic materials, the variation of Ms in AC magnetic field is in accordance with that of DC magnetic field). The cross-sectional morphology of the prepared diopside-magnetite scaffolds in various content of magnetite is seen in Fig. 3. A uniform distribution of holes with an average diameter of 500µm has been obtained at low amount of Fe3O4 (Fig. 3a). Increasing Fe3O4 content led to increase of true and interconnected porosities (Table 1) and also degradation of the surfaces (Fig. 3c). Although the increase of interconnected porosity can provide a highly permeable system for cell seeding, tissue ingrowth, and vascularization [8], the compressive strength of the samples decreases as a result of the increase of Fe3O4 content (Table 1). This means that the amount of apatite formation of the diopside-20wt.%Fe3O4 samples is more than in other samples. When the amount of Fe3O4 reaches 30wt.% (Fig. 4c), silicon and Fe peaks find an increasing trend which ensures a decrease in the tendency to apatite formation. This is most likely because of the
6
destruction of the surface as previously mentioned for the samples containing 30wt.% Fe3O4. These discussions lend support to the notion that the capability of apatite formation increases as a result of the increasing nanomagnetic particles up to 20%wt. This previously confirmed in the case of HA-Fe3O4 nanocomposite reported by Farzin et al. [3]. In general, the present study showed that the compositing process of the superparamagnetic Fe3O4 with biocompatible diopside can be argued from various dimensions: First, increasing the magnetic content in the composite nanopowders leads to the increasing SAR, as a result of the higher value of saturation magnetization (Ms). The higher values of SAR will reduce the dose of the drug and thus increases its safety factor in hyperthermia applications. Second, Although the increase of the magnetic content provides an interesting application for magnetic nanoparticles, in the magnetic scaffold samples the prominent factors are the compressive strength as well as the apatite formation but not the high value of SAR. Magnetic scaffolds can be used in hyperthermia applications when they have a high compressive strength as well as a high potential of apatite formation. This means that an appreciate ratio of biocompatible material (here diopside) and magnetic component (here Fe3O4) should be selected in order to achieve a good apatite formation. However, the use of more than optimal amount, converts the biocompatible material (here diopside) into a destructive agent because of the excessive loss of saturation magnetization (Ms) and hence SAR values. This reduces the efficiency of the magnetic scaffolds in the hyperthermia applications. Third, the appreciate amount of compressive strength and apatite formation also should be considered. If a high amount of biocompatible material is used, the compressive strength finds an increasing trend, however the potential of apatite formation experiences a downward trend (Table 1). In the magnetic scaffolds for hyperthermia applications, all three high values of SAR,
7
high compressive strength and high amount of apatite formation should be achieved. Diopside20%wt.% seems that is an optimized sample for using a magnetic scaffold in hyperthermia applications. Conclusions Diopside-magnetite nanocomposite powders (in different percentage of magnetite) had an agglomeration trend and their coercivity was near the zero. This agglomeration was because of the permanent magnetic moment of the single domain nanoparticles, which led to dipole-dipole interaction and producing magnetic energy. This magnetic energy was transformed to the heat by which the tendency to agglomeration increased. N´eel and Brown effects had not a potential to describe the difference between the SAR values of the nanopowder samples. The destruction of the surface occurred in the scaffolds with 30wt.% magnetite, which seems had a significant role in decreasing apatite formation.
References [1] Sharifi, I., H. Shokrollahi, and S. Amiri (2012) Ferrite-based magnetic nanofluids used in hyperthermia applications. J. Magn. Magn. Mater. 324:903–915 [2] Gupta, A.K., and M.Gupta (2005) Synthesis and surface engineering of iron oxide nanoparticles for biomedical applications. Biomaterials. 26: 3995–4021 [3] Farzin, A., M. Fathi and R.Emadi (2017) Multifunctional magnetic nanostructured hardystonite scaffold for hyperthermia, drug delivery and tissue engineering applications. 70: 21–31 [4] Chen, X., J.Ou, Y.Wei, Z.Huang, Y.Kang and G.Yin (2010) Effect of MgO contents on the mechanical properties and biological performances of bioceramics in the MgO–CaO–SiO2 system. J Mater Sci: Mater Med. 21:463–1471 [5] Wu, C., Y.Ramaswamy and H.Zreiqat (2010), Porous diopside (CaMgSi2O6) scaffold: a promising bioactive material for bone tissue engineering. Acta Biomaterialia. 6:2237–2245 [6] Bianchi M., S.Cauci, M.Marcacci and A.Russo (2004) OMICS Group eBooks 731 Gull Ave, 2nd ed., pp. 23-38, CA 94404, USA [7] Kazemi, A., M.Abdellahi, A.K.Sharafabadi and A.Khandan (2017) Study of in vitro bioactivity and mechanical properties of diopside nano-bioceramic synthesized by a facile method using eggshell as raw material. Mater. Sci. Eng. C. 71: 604–610
8
[8] Najafinezhad, A., M.Abdellahi, S. Nasiri-Harchegani, A.Soheily, M.Khezri and H.Ghayour (2017) On the synthesis of nanostructured akermanite scaffolds via space holder method: The effect of the spacer size on the porosity and mechanical properties. Journal of the Mechanical Behavior of Biomedical Materials. 69: 242–248 [9] Engin, N.O., and A.C. Tas (1999) Manufacture of macroporous calcium hydroxyapatite bioceramics. J Eur Ceram Soc. 19:2569–2672 [10] Natividad, E., M. Castro, and M. Mediano (2009) Accurate measurement of the specific absorption rate using a suitable adiabatic magnetothermal setup. Appl. Phys. Lett. 92:093116
[11] J. Carrey, B. Mehdaoui, and M. Respaud, Simple models for dynamic hysteresis loop calculations of magnetic single-domain nanoparticles: Application to magnetic hyperthermia optimization, Journal of Applied Physics 109(2011)083921. [12] Aharoni, A., and J.P. Jakubovics (1988) Cylindrical domains in small ferromagnetic spheres with cubic anisotropy. IEEE Trans Magn. 24:1892-1899.
9
Table 1: The characterization data of the composite samples Crystallite size of magnetite nanopowder (nm) 33 35 39
samples Di-10wt.%Fe3O4 Di-20wt.% Fe3O4 Di-30wt.% Fe3O4
2θ changes in diopside nanopowder peak
Interconnected porosity of the scaffold (%)
Total porosity of the scaffold (%)
Compressive strength of the scaffold (MPa)
35.72 35.77 35.80
84 85 86
87 89 91
2.6 2.4 1.9
80
(a)
(b) 60
diopside-30%Fe O 3
Pure Fe O 3
4
Ms (emu/gr)
40
diopside-20%Fe O 3
4
4
Di - 10%Fe Di - 20%Fe Di - 30%Fe
20 0 -20 -40
Fe Di
Intensity (a.u.)
Di Fe Di Di Di
-60
Di Di Di Fe Di
Di
-80 -1.5
diopside-10%Fe O Fe 3 4
-1
Di
Di Fe
0 Hc (Oe)
0.5
1
(c)
1.5 x 10
6
Di
4
diopside-30%Fe O 3
4
diopside-20%Fe O
5
3
Fe O - 00-001-1111 3
-0.5
Di
4
diopside-10%Fe O
4
3
4
T
4
3 2
Diopside - 01-0750945
10
1
20
30
40
2 (degree)
50
60
0
0
2
4
6
Time (s)
8
10
12
Fig. 1: a) XRD analysis (a), VSM analysis (b) and hyperthermia evaluation (c) of the samples.
Fig. 2: FESEM images, Map and EDS analyses of the diopside-X magnetite samples. a) X=10wt.%; b) X=20wt.%; c) X=30wt.%
11
Fig. 3: The morphology of the diopside-X magnetite scaffolds before soaking in SBF solution; a) X=10wt.%; b) X=20wt.%; c) X=30wt.%
12
Fig. 4: The morphology of the diopside-Xmagnetite scaffolds after soaking in SBF solution; a) X=10wt.%; b) X=20wt.%; c)X=30wt.%
-
Diopside-magnetite powders had an agglomeration trend and their coercivity was near the zero.
-
This agglomeration was because of the permanent magnetic moment of the single domain nanoparticles.
-
The magnetic energy was transformed to the heat by which the tendency to agglomeration increased.
-
N´eel and Brown effects could not to describe the difference between the SAR of samples.
13
PII: DOI: Reference:
S1751-6161(17)30441-1 https://doi.org/10.1016/j.jmbbm.2017.10.015 JMBBM2535
To appear in: Journal of the Mechanical Behavior of Biomedical Materials Received date: 22 August 2017 Revised date: 5 October 2017 Accepted date: 8 October 2017 Cite this article as: Majid Abdellahi, Ebrahim Karamian, Aliakbar Najafinezhad and Amirsalar Khandan, Diopside-Magnetite; A novel nanocomposite for hyperthermia applications, Journal of the Mechanical Behavior of Biomedical Materials, https://doi.org/10.1016/j.jmbbm.2017.10.015 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 galley proof before it is published in its final citable 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.
Diopside-Magnetite; A novel nanocomposite for hyperthermia applications Majid Abdellahi*, Ebrahim Karamian, Aliakbar Najafinezhad, Amirsalar Khandan Department of Materials engineering, Najafabad University, Isfahan, Iran *Corresponding Author; Email: [email protected] ; Tel: +989132894596
Abstract In the present work, the releasing heat, scaffold apatite formation, and magnetic behavior of a novel diopside-magnetite nanocomposite with various contents of magnetite (Fe3O4) were evaluated. The N´eel and Brown relaxations did not have a significant effect on the specific absorption rate (SAR) of the composite samples. Indeed, magnetic saturation, Ms, indicated a crucial effect on the heat release of the samples. The sample with 30wt.% magnetite had the highest value of SAR, while the sample with 20wt.% magnetite, in the form of scaffold, allowed the high amount of apatite formation on its surface. Keywords: Hyperthermia; Bioceramics; Ceramic composite
1- Introduction When magnetic nanoparticles (MNPs) are placed in an alternating magnetic (AC) field, they release heat. This released heat as a therapeutic tool that is called “hyperthermia”, can destroy the cancer tumor cells by raising temperature within the range of 41–46 °C [1]. Fe3O4 (magnetite) nanoparticles, have shown a good potential for using in different biomedical applications including, magnetic resonance imaging, magnetic carriers for drug delivery, and hyperthermia [2]. In recent years, the incorporation of Fe3O4 nanoparticles into biophosphate materials with a good biocompatibility behavior was reported [3]. Bio-silicate materials, especially those containing Mg have also indicated an improvement of cell adhesion, proliferation, spreading, and differentiation, making them applicable for tissue
1
engineering applications [4]. Mg-containing bioceramics have shown a comparative advantage in bone tissue regeneration, among which diopside (CaMgSi2O6) has provided slower degradation rate and the ability of in vitro apatite formation and in vivo bone regeneration [5]. Magnetic scaffolds have recently attracted significant attention in tissue engineering, due to the prospect of improving bone tissue formation by conveying soluble factors such as growth factors, hormones and polypeptides directly to the site of implantation, and also because of the possibility of improving implant fixation and stability [6]. In the present study a diopside-magnetite nanocomposite was fabricated and the effect of various amounts of magnetite on the specific absorption rate and apatite formation of the nanocomposite samples, in powder and scaffold forms, was evaluated. 2- Materials and Methods Fe3O4 powder was purchased from Merck Co., while diopside powders in pure state (Fig. 1a), was synthesized according to the route mentioned in our previous work [7]. diopside-magnetite nanocomposite at different percentages of magnetite was obtained via mechanical milling for 10h and a subsequent sintering at 600°C for 3h (for crystallization). The obtained samples were then milled for 5h to obtain nanopowders. To prepare diopside-magnetite scaffolds by the space holder method [8], NaCl as the spacer with particle size of 300-420µm, was added to the composite nanopowder. The powder was then pressed under 100MPa in a cylindrical form. A sintering process was then performed at a rate of 5°/min to 1200°C for 4 h. The sintered samples were then immersed in deionized water for 24h in order to remove the remained NaCl. In the final stage, the scaffolds were immersed in simulated body fluid (SBF), to evaluate their apatite formation. The Archimedes technique [9] was used to estimate the porosity of the prepared scaffolds. Formation of the crystalline phase was studied via X-ray diffraction (XRD) spectra
2
using Cu-Kα radiation in the 2θ limitation of 20-60°. The magnetic properties including saturation magnetization and also coercivity of the obtained samples were determined by using a vibrating sample magnetometer (VSM, Kavir Co.,) at room temperature. Morphology of the samples in powder state was analyzed via field emission scanning electron microscopy (FESEM). The size of hydrodynamic nanoparticles was determined using dynamic light scattering (DLS) technique (model Nano ZS90). An AC magnetic field with a frequency of 200 kHz and amplitude of 10 Ôe was used for studying the heat releasing of nanoparticles. The amount of the analyzed powder was 25 mg for all samples. It was reported in calorimetric method that the specific absorption rate (SAR) value, is proportional to the initial heat, which is emitted from magnetic nanoparticles using AC magnetic field [10]: SAR dT / dt t 10
(1)
dT/dt is the initial heating rate of the nanoparticles under AC magnetic field. In fact, at the initial times, the temperature change rate is the same as with the adiabatic mode. The heating mechanism in superparamagnetic nanoparticles was reported is due to the relaxation processes. i.e. N´eel and Brown effects. The relaxation time of the Brown motion is [10]:
B 4 r 3 kT
(2)
and the N´eel relaxation time is: N 0 exp KV kT
(3)
where is the basic liquid viscosity, r the hydrodynamic radius of the particle, k the Boltzmann’s constant, K is the anisotropy constant, 0 the time constant, and V the particle volume.
3
According to the linear response theory [11], which is corrected for superparamagnetic nanoparticles, the relation between SAR and relaxation losses is:
SAR M s 2 2 1 2
2
(4)
where is the frequency and ( 1 1 B 1 N ) is the effective relaxation time. The relaxation process of the single domain nanoparticles occurs in the ethanol ferrofluid, under AC magnetic field. The relaxation process of the single domain nanoparticles occurs in the ethanol ferrofluid, under AC magnetic field. 3- Results and discussions XRD patterns of the diopside-xMagnetite nanocomposites (x=10wt.%,20 wt.%,30) are shown in Fig.1a. As can be seen, some major peaks of Fe3O4 overlap with some peaks of diopside and cannot be differentiated clearly from one another. Table 1, confirms that by increasing the magnetite content to 10, 20, and 30wt.%, diopside peaks move toward the higher angles. This ensures the substitution of Ca2+ ions (0.099 nm) by Fe3+ ions (0.068nm). The crystallite size of Fe3O4 in all samples is below the critical size of single domain particles which was reported to be 54nm [12] (Table 1). Fig. 1b shows the room temperature magnetization as a function of applied magnetic field for pure magnetite and composited samples. No hysteresis loop is observed, indicating that the resultant nanoparticles are superparamagnetic. The reduced Ms can be explained by considering the diamagnetic contribution of the diopside surrounding the magnetite cores, which will weaken the magnetic moment, whereas the low coercivity (Hc) may be resulted from the size of magnetite particles embedded into diopside. Significant changes in magnetic saturation and
4
coercivity are attributed to the dope of Fe3+ ions into diopside, and also the presence of nonmagnetic diopside phases. Fig. 1c shows the released heat of the suspended samples in ethanol (ferrofluid) under adiabatic conditions (in this work it was assumed that below 10s the adiabatic conditions are dominant). The higher average gradient during 10s ensures the higher specific absorption rate (SAR) values, according to Eq. 1 [10]. SAR is generally used to define the transformation of magnetic energy into heat and its high value allows reduction of ferrofluid dose in vivo. The SAR of superparamagnetic single domain nanoparticles in an external AC magnetic field can be attributed to the relaxation loss process. The relaxation process of a ferrofluid occurs with two distinct routes. The first route is based on the rotation of the single-domain particles (Brown relaxation), and the second corresponds to the rotation of the magnetic moments (N´eel relaxation). To assess the behavior of nanoparticles in the ferrofluid, FESEM images are provided, as shown in Fig. 2. As can be seen, by increasing Fe3O4 content (EDS analysis), agglomeration finds an increasing trend. As the MAP analysis confirms, as a result of the increase of single domain Fe3O4 nanoparticles, these nanoparticles are affected by permanent magnetic moment and therefore agglomerated (see MAP analyses). These agglomerated single domain Fe3O4 nanoparticles experience dipole-dipole interactions and the locally released magnetic energy (as an internal energy) is transformed into heat, which in turn can provide a leading stage for nanopowders/small agglomerates to stick to each other and form large agglomerates (as confirmed by large agglomerated clusters in Fig. 2c). With the above-mentioned description, it is now possible to understand the various rates of the heat release of the samples. As can be seen in Fig. 1b, the coercivity/anisotropy of all the samples is almost the same. This means that the
5
increase of Fe3O4 content does not make the N´eel relaxation a dominant factor in determining the SAR (Eq. 2). On the other hand, Fig. 2a-c shows that the diameter of almost all agglomerated clusters is more than 1µm, which is very high to have an effective Brown relaxation. This is confirmed by Eq. 3, in which whatever the dynamic size increases, the Brown relaxation time (
B ) also increases. This process reduces the Brown effect and hence the efficiency of nanoparticles heating. Brown relaxation time has therefore large values in all of the composite samples as a result of the agglomeration process. In other words, the hydrodynamic volume of all samples (with various content of magnetite) is large and therefore the Brown effect has almost the same values in all samples and does not have a determining effect in the SAR values. In general, in constant frequency, the SAR values of the composite samples is only dependent on the Ms but not (Eq. 4). The higher the Ms is, the higher the SAR will be. This is confirmed by Figs. 1b and 1c. (It should be noted that in superparamagnetic materials, the variation of Ms in AC magnetic field is in accordance with that of DC magnetic field). The cross-sectional morphology of the prepared diopside-magnetite scaffolds in various content of magnetite is seen in Fig. 3. A uniform distribution of holes with an average diameter of 500µm has been obtained at low amount of Fe3O4 (Fig. 3a). Increasing Fe3O4 content led to increase of true and interconnected porosities (Table 1) and also degradation of the surfaces (Fig. 3c). Although the increase of interconnected porosity can provide a highly permeable system for cell seeding, tissue ingrowth, and vascularization [8], the compressive strength of the samples decreases as a result of the increase of Fe3O4 content (Table 1). This means that the amount of apatite formation of the diopside-20wt.%Fe3O4 samples is more than in other samples. When the amount of Fe3O4 reaches 30wt.% (Fig. 4c), silicon and Fe peaks find an increasing trend which ensures a decrease in the tendency to apatite formation. This is most likely because of the
6
destruction of the surface as previously mentioned for the samples containing 30wt.% Fe3O4. These discussions lend support to the notion that the capability of apatite formation increases as a result of the increasing nanomagnetic particles up to 20%wt. This previously confirmed in the case of HA-Fe3O4 nanocomposite reported by Farzin et al. [3]. In general, the present study showed that the compositing process of the superparamagnetic Fe3O4 with biocompatible diopside can be argued from various dimensions: First, increasing the magnetic content in the composite nanopowders leads to the increasing SAR, as a result of the higher value of saturation magnetization (Ms). The higher values of SAR will reduce the dose of the drug and thus increases its safety factor in hyperthermia applications. Second, Although the increase of the magnetic content provides an interesting application for magnetic nanoparticles, in the magnetic scaffold samples the prominent factors are the compressive strength as well as the apatite formation but not the high value of SAR. Magnetic scaffolds can be used in hyperthermia applications when they have a high compressive strength as well as a high potential of apatite formation. This means that an appreciate ratio of biocompatible material (here diopside) and magnetic component (here Fe3O4) should be selected in order to achieve a good apatite formation. However, the use of more than optimal amount, converts the biocompatible material (here diopside) into a destructive agent because of the excessive loss of saturation magnetization (Ms) and hence SAR values. This reduces the efficiency of the magnetic scaffolds in the hyperthermia applications. Third, the appreciate amount of compressive strength and apatite formation also should be considered. If a high amount of biocompatible material is used, the compressive strength finds an increasing trend, however the potential of apatite formation experiences a downward trend (Table 1). In the magnetic scaffolds for hyperthermia applications, all three high values of SAR,
7
high compressive strength and high amount of apatite formation should be achieved. Diopside20%wt.% seems that is an optimized sample for using a magnetic scaffold in hyperthermia applications. Conclusions Diopside-magnetite nanocomposite powders (in different percentage of magnetite) had an agglomeration trend and their coercivity was near the zero. This agglomeration was because of the permanent magnetic moment of the single domain nanoparticles, which led to dipole-dipole interaction and producing magnetic energy. This magnetic energy was transformed to the heat by which the tendency to agglomeration increased. N´eel and Brown effects had not a potential to describe the difference between the SAR values of the nanopowder samples. The destruction of the surface occurred in the scaffolds with 30wt.% magnetite, which seems had a significant role in decreasing apatite formation.
References [1] Sharifi, I., H. Shokrollahi, and S. Amiri (2012) Ferrite-based magnetic nanofluids used in hyperthermia applications. J. Magn. Magn. Mater. 324:903–915 [2] Gupta, A.K., and M.Gupta (2005) Synthesis and surface engineering of iron oxide nanoparticles for biomedical applications. Biomaterials. 26: 3995–4021 [3] Farzin, A., M. Fathi and R.Emadi (2017) Multifunctional magnetic nanostructured hardystonite scaffold for hyperthermia, drug delivery and tissue engineering applications. 70: 21–31 [4] Chen, X., J.Ou, Y.Wei, Z.Huang, Y.Kang and G.Yin (2010) Effect of MgO contents on the mechanical properties and biological performances of bioceramics in the MgO–CaO–SiO2 system. J Mater Sci: Mater Med. 21:463–1471 [5] Wu, C., Y.Ramaswamy and H.Zreiqat (2010), Porous diopside (CaMgSi2O6) scaffold: a promising bioactive material for bone tissue engineering. Acta Biomaterialia. 6:2237–2245 [6] Bianchi M., S.Cauci, M.Marcacci and A.Russo (2004) OMICS Group eBooks 731 Gull Ave, 2nd ed., pp. 23-38, CA 94404, USA [7] Kazemi, A., M.Abdellahi, A.K.Sharafabadi and A.Khandan (2017) Study of in vitro bioactivity and mechanical properties of diopside nano-bioceramic synthesized by a facile method using eggshell as raw material. Mater. Sci. Eng. C. 71: 604–610
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[8] Najafinezhad, A., M.Abdellahi, S. Nasiri-Harchegani, A.Soheily, M.Khezri and H.Ghayour (2017) On the synthesis of nanostructured akermanite scaffolds via space holder method: The effect of the spacer size on the porosity and mechanical properties. Journal of the Mechanical Behavior of Biomedical Materials. 69: 242–248 [9] Engin, N.O., and A.C. Tas (1999) Manufacture of macroporous calcium hydroxyapatite bioceramics. J Eur Ceram Soc. 19:2569–2672 [10] Natividad, E., M. Castro, and M. Mediano (2009) Accurate measurement of the specific absorption rate using a suitable adiabatic magnetothermal setup. Appl. Phys. Lett. 92:093116
[11] J. Carrey, B. Mehdaoui, and M. Respaud, Simple models for dynamic hysteresis loop calculations of magnetic single-domain nanoparticles: Application to magnetic hyperthermia optimization, Journal of Applied Physics 109(2011)083921. [12] Aharoni, A., and J.P. Jakubovics (1988) Cylindrical domains in small ferromagnetic spheres with cubic anisotropy. IEEE Trans Magn. 24:1892-1899.
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Table 1: The characterization data of the composite samples Crystallite size of magnetite nanopowder (nm) 33 35 39
samples Di-10wt.%Fe3O4 Di-20wt.% Fe3O4 Di-30wt.% Fe3O4
2θ changes in diopside nanopowder peak
Interconnected porosity of the scaffold (%)
Total porosity of the scaffold (%)
Compressive strength of the scaffold (MPa)
35.72 35.77 35.80
84 85 86
87 89 91
2.6 2.4 1.9
80
(a)
(b) 60
diopside-30%Fe O 3
Pure Fe O 3
4
Ms (emu/gr)
40
diopside-20%Fe O 3
4
4
Di - 10%Fe Di - 20%Fe Di - 30%Fe
20 0 -20 -40
Fe Di
Intensity (a.u.)
Di Fe Di Di Di
-60
Di Di Di Fe Di
Di
-80 -1.5
diopside-10%Fe O Fe 3 4
-1
Di
Di Fe
0 Hc (Oe)
0.5
1
(c)
1.5 x 10
6
Di
4
diopside-30%Fe O 3
4
diopside-20%Fe O
5
3
Fe O - 00-001-1111 3
-0.5
Di
4
diopside-10%Fe O
4
3
4
T
4
3 2
Diopside - 01-0750945
10
1
20
30
40
2 (degree)
50
60
0
0
2
4
6
Time (s)
8
10
12
Fig. 1: a) XRD analysis (a), VSM analysis (b) and hyperthermia evaluation (c) of the samples.
Fig. 2: FESEM images, Map and EDS analyses of the diopside-X magnetite samples. a) X=10wt.%; b) X=20wt.%; c) X=30wt.%
11
Fig. 3: The morphology of the diopside-X magnetite scaffolds before soaking in SBF solution; a) X=10wt.%; b) X=20wt.%; c) X=30wt.%
12
Fig. 4: The morphology of the diopside-Xmagnetite scaffolds after soaking in SBF solution; a) X=10wt.%; b) X=20wt.%; c)X=30wt.%
-
Diopside-magnetite powders had an agglomeration trend and their coercivity was near the zero.
-
This agglomeration was because of the permanent magnetic moment of the single domain nanoparticles.
-
The magnetic energy was transformed to the heat by which the tendency to agglomeration increased.
-
N´eel and Brown effects could not to describe the difference between the SAR of samples.
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