PREPARATION OF HYDROXYAPATITE/CLAY MINERAL NANOCOMPOSITE

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1 PREPARATION OF HYDROXYAPATITE/CLAY MINERAL NANOCOMPOSITE Lenka PAZOURKOVÁ *1, Karla ČECH BARABASZOVÁ 1,2, Marianna HUNDÁKOVÁ 1,2 1 Nanotechnology Centre, VŠB Technical University of Ostrava, Ostrava, Czech Republic, EU, * lenka.pazourkova.st@vsb.cz 2 IT4 Innovations Centre, VŠB Technical University of Ostrava, Ostrava, Czech Republic, 2 karla.barabaszova@vsb.cz Abstract Surface of clay minerals montmorillonite (Mt) and vermiculite (Ver) was used as matrix for in situ preparation of hydroxyapatite (HAp). The hydroxyapatite was prepared by two processes: wet precipitation using mixing and ultrasound treatment. Prepared HAp/Mt and HAp/Ver nanocomposites were studied using XRF elemental analysis, X-ray diffraction phase analysis and scanning electron microscopy. The HAp particles of different size and morphology were formed dependency on the clay mineral Mt and Ver matrix. Keywords: Hydroxyapatite, Clay mineral matrix, Nanocomposite, Sonication 1. INTRODUCTION Hydroxyapatite (HAp), the chemical formula Ca10(PO4)6(OH)2, is naturally mineral in human body. The synthetic HAp is suitable material for medical application because of the similarity with HAp occurring in bone and teeth [1]. HAp nanoparticles significantly improve biocompatibility and bioactivity of biomaterials [2]. There are several processes for preparation of HAp nanoparticles. Wet precipitation is the most widespread method because prepared nanoparticles have regular morphology [2] and are very often used for preparation of HAp composites [3]. Sonication is another method that allows the preparation of uniform size of spherical shape wherein particles are smallest than those prepared by precipitation [4]. Utilization of clays is very demand, mainly in nanocomposites. Natural clay particles have hydrophilic property [5], high adsorption capacity, specific surface area, swelling capacity, solubility and nontoxicity for human [6]. Metal nanoparticles prepared on the clay mineral surface are strongly bonded to the silicate layer and do not aggregate [7,8]. The literature data concerning the HAp particles prepared on clay mineral matrix are spare [3,9]. Ambre et al. [3] created in situ mineralized hydroxyapatite on organically modified clay mineral matrix as nanocomposite bone biomaterials for their potential medical applications. The precursor of clay mineral and sodium phosphate was modified by addition of calcium chloride. The structure of in situ mineralized hydroxyapatite was different in comparison to the structure of ex situ hydroxyapatite. Autors [3] also studied interactions between clay mineral and apatite ions. The hydroxyapatite was prepared by wet precipitation by mixing with chitosan and montmorillonite solutions to the nanocomposite of polymer/clay mineral/hydroxyapatite for drug delivery applications [9]. This study aimed with the characterization of hydroxyapatite particles prepared on the natural clay minerals, montmorillonite (Mt) and vermiculite (Ver), by wet precipitation by using mixing and ultrasound. The influence of those methods on the prepared samples was characterized using XRF elemental analysis, X-ray diffraction phase analysis and scanning electron microscopy.

2 2. MATERIALS AND METHODS 2.1 Materials Montmorillonite (Mt) from Ivančice deposit (Czech Republic) and Vermiculite (Ver) from Santa Luzia (Brasil) were obtained from Grena, a.s., Czech Republic. Both of the samples were milled in vibratory mill and sieved to obtain the fraction smaller than 40 µm for experiment. Sodium phosphate dibasic dodecahydrate (Na2HPO4 12 H2O) and calcium chloride dihydrate (CaCl2 2 H2O) purchased from Vitrum VWR, Co. (Czech Republic) were used as HAp precursors. 2.2 Sample preparation Mixing procedure 100 ml of CaCl2 solution (12 mmol dm -3 in deionized water) was slowly added to the continuously mixed solution of Na2HPO4 (7.2 mmol dm -3 in deionized water) which contained 0.1 g of Mt or Ver. ph of resulting solution was adjusted to 7.45 by 1 mol dm -3 HCl. The precipitate was allowed to sedimentation for 24 h. After this period the supernatant was decanted and the precipitate was dried at 70 C. The samples were marked as HAp-Mt-1 and HAp-Ver-1. The pure Hap-1 was prepared by the same procedure [9] Sonication procedure The solution of Na2HPO4 (500 ml, 7.2 mmol dm -3 in deionized water) and 0.1 g of Mt or Ver was sonicated (Ultrasound processor UP 100H, 20 % amplitude) while adding 100 ml of CaCl2 solution (12 mmol dm -3 in deionized water). ph of resulting solution was adjusted using 1 mol dm -3 HCl to The precipitate was allowed to sedimentation for 24 h and the supernatant was decanted and the precipitate was dried at 70 C. The samples were marked as HAp-Mt-2 and HAp-Ver-2. The pure HAp-2 was prepared by same procedure. 2.3 Methods The X-ray powder diffraction (XRD) patterns were measured on X-ray diffractometer Rigaku Ultima IV (reflection mode, Brag-Brentano arrangement, CuKα1 radiation) in ambient atmosphere under constant conditions (40 kv, 40 ma). The images of samples were performed by Scanning electron microscopy (SEM) on PHILIPS XL-30 equipped with energy dispersive spectrometer EDS. The samples were coating by gold/palladium. The quantity of selected elements Ca and P was measured in cells using energy dispersive X-ray fluorescence spectroscopy (XRF) (SPECTRO XEPOS). 3. RESULTS AND DISCUSSION 3.1 Characterization of HAp prepared using mixing and sonication SEM micrographs in Fig. 1 show morphology of HAp-1 (Fig. 1a) and HAp-2 (Fig. 1b). Both samples include particles of different size. The XRD patterns and numbered reflections of HAp-1 and HAp-2 are in Fig.2. The d-values of numbered reflections are in good agreement with those of HAp on the PDF card no (Table 1), while their intensity distribution are slightly different. Reflection with the value d = nm on the pattern of the HAp-1 (Fig. 2a) was ascribed to the crystalline H3PO3 phase (PDF card no ) formed during mixing. This reflection is not present in XRD pattern of HAp-2. Reflections with d = 0.32 nm in HAp-1 and HAp-2 belongs to formed NaCl phase identified according to the PDF card no

3 Fig. 1 SEM micrographs of the HAp samples: a) HAp-1 and b) HAp-2. Fig. 2 XRD patterns of HAp samples prepared by mixing and sonication: a) HAp-1 and b) HAp-2 Table 1 The numbered reflections, d-values and intensities of HAp (PDF card no ) and measured values on the XRD patterns of the samples HAp-1 and HAp-2 HAp (ICSD PDF card) HAp-1 HAp-2 Reflection position d (nm) Intensity (relative,%) d (nm) Intensity (relative,%) d (nm) Intensity (relative,%)

4 3.2 Characterization of HAp-Mt and HAp-Ver prepared using mixing and sonication The chemical elemental analysis of samples that were prepared by the two methods confirmed the comparable content of Ca and P (Table 2). Table 2 XRF analysis of Ca and P in HAp-clay mineral samples prepared usong two methods Oxides Mt (%) Ver (%) HAp-Mt-1 HAp-Mt-2 HAp-Ver-1 HAp-Ver-2 (%) (%) (%) (%) CaO P2O Fig. 3 and 4 show XRD patterns of prepared HAp-Mt and HAp-Ver nanocomposites in comparison with pure HAp. The main intensive reflections (No. 6) of HAp on the XRD patterns are in HAp-Mt (Fig. 3c,e) and HAp- Ver (Fig. 4c,e) composites more broadened and less intensive in comparison with those of pure HAp (Fig. 3b,d and Fig. 4b,d) which may be due to decrease of crystallinity. It could be caused by many factors like different chemical environment for HAp nucleation in presence of Mt or Ver [3]. Basal reflection d(001) = nm of Mt (Fig. 3a) was shifted to lower value d = nm in HAp-Mt-1 (Fig. 3c) and d = nm in HAp-Mt-2 (Fig. 3e). The XRD pattern of Ver (Fig. 4a) shows basal reflections characteristic for mixed layered structure composed of one-two hydrated interlayer material with values d(001) = 2.34 nm, d(002) = 1.43 nm and 1.25 nm [10]. The HAp-Ver composites show in XRD patterns the absence of Ver reflection with d = 2.34 nm and shifting of the reflection with d = nm to d = nm in HAp-Ver-1 (Fig. 4c) and to d = nm in HAp-Ver-2 (Fig. 4e). These differences indicate the changes in structure of Mt and Ver modified with HAp in the acidic conditions. Fig. 3 XRD patterns of a) Mt, b) HAp-1, c) HAp-Mt-1, d) HAp-2, e) HAp-Mt-2

5 Fig. 4 XRD patterns of a) Ver, b) HAp-1, c) HAp-Ver-1 d) HAp-2, e) HAp-Ver-2 Morphology of particles of Mt and Ver and nanocomposite of HAp/clay minerals are in the SEM micrographs in Fig. 5 and Fig. 6. The flaky particles of Mt (Fig. 5a) are covered in composites HAp-Mt-1 and HAp-Mt-2 by platelet shape of HAp particles of different size (Fig. 5b and Fig. 5c). HAp particles are visibly attached on the MT surface. The HAp of the sample HAp-MT-1 (Fig. 5b) is platelet shape. As we can see, densely covered Mt particle surface with HAp was prepared using sonication (the sample HAp-Mt-2 in Fig. 5c) than using mixing (the sample HAp-Mt-1 in Fig. 5b). Fig. 5 SEM images of a) Mt, b) HAp-Mt-1 and c) HAp-Mt-2 Pure vermiculite exhibits typical flaky plate morphology of particles (Fig. 6a). The particles of HAp prepared using mixing procedure are slightly coarser (the sample HAp-Ver-1 in Fig. 6b) than using sonication (the sample HAp-Ver-2 in Fig. 6c). The HAp particles of different size and morphology were formed dependency on the Mt and Ver matrix, as we can see from Fig. 5 and Fig. 6.

6 Fig. 6 SEM images of a) Ver, b) HAp-Ver-1 and c) HAp-Ver-2 4. CONCLUSIONS The HAp/clay mineral nanocomposites were prepared by two methods and final samples were characterized and compared. The formulation of hydroxyapatite on clay mineral surface was confirmed by XRD patterns as well as the changes in the structure of Mt and Ver modified with HAp. The crystal structure of pure hydroxyapatite prepared by mixing and sonication are similar and in agreement with the published data. From the results of elemental analysis was investigate the enhancement of Ca and P amount in samples of nanocomposite of HAp and clay mineral. The SEM micrographs show surface of clay mineral covered by the HAp particles of different size and morphology on the Mt and Ver matrix. ACKNOWLEDGMENTS This work was supported by projects: Ministry of Education, Youth and Sport of Czech Republic SP2013/15 and IT4 Innovations Centre of Excellence project reg.no.cz.1.05/1.1.00/ ). Autors thank M. Valášková for expert assistance. LITERATURE [1] CAHN, R. W., HAASEN, P., KRAMER, E. J. Material science and technology. A comprehensive treatment. Medical and Dental Materials. Weinheim, ISBN: [2] SADAT-SHOJAI, M., KHORASANI, M-T., DINPANAH-KHOSHDARGI, E., JAMSHIDI, A. Synthesis methods for nanosized hydroxyapatite with diverse structures. Acta Biomaterialia, 2013, vol. 9, p [3] AMBRE, A., KATTI, K. S., KATTI, D. R. In situ mineralized hydroxyapatite on amino acid modified nanoclays as novel bone biomaterials. Materials Science and Engineering C, 2011, vol. 31, p [4] ROUHANI, P., TAGHAVINIA, N., ROUHANI, S. Rapid growth of hydroxyapatite nanoparticles using ultrasonic irradiation. Ultrasonics Sonochemistry, 2010, vol. 17, no. 5, p [5] SIMHA MARTYNKOVÁ, G., VALÁŠKOVÁ, M. In: Nalwa, H. S. (editor). Encyclopedia of Nanoscience and Nanotechnology. American Scientific Publishers, 2011, vol. 25, p , ISBN: [6] CARRETERO, M. I., POZO, M. Clay and non-clay minerals in the pharmaceutical industry Part I. Excipients and medical applications. Applied Clay Science, 2009, vol. 46, p [7] PATAKFALVI, R., OSZKÓ, A., DÉKÁNY, I. Synthesis and characterization of silver nanoparticle/kaolinite composites. Colloids and Surfaces A: Physicochem. Eng. Aspects, 2003, vol. 220, p [8] BAGCHI, B., KAR, S., DEY, S. K., BHANDARY, S., ROY, D., MUKHOPADHYAY, T. K., DAS, S., NANDY, P. In situ synthesis and antibacterial activity of copper nanoparticle loaded natural montmorillonite clay based on contact inhibition and ion release. Colloids and Surfaces B: Biointerfaces, 2013, vol. 108, p [9] ROUL, J., MOHAPATRA, R., SAHOO, S. K., TRIBHUVAN, N. Design and Characterization of Novel Biodegradable Polymer-Clay-Hydroxyapatite Nanocomposites for drug delivery applications. Asian Journal of Biomedical and Pharmaceutical Sciences, 2012, vol. 2, no.11, p [10] MARCOS, C., ARANGO, Y.C., RODRIGUEZ, I. X-ray diffraction studies of the thermal behaviour of commercial vermiculites. Appl. Clay Sci., 2009, vol. 42, p