Novel Ca9RE(PO4)7 biomaterials: synthesis and multi-methodological structural characterization via X-ray techniques

Joint research project

Project leaders: Francesco Capitelli, Mohamed Elaatmani
Agreement: MAROCCO - CNRST - Centre National pour la Recherche Scientifique et Technique
Call: CNR/CNRST 2016-2017
Department: Chemical sciences and materials technology
Thematic area: Chemical sciences and materials technology
Status of the project: New

Research proposal

ß-TCP (ß-tricalcium phosphate, ß-Ca3(PO4)2) is one of the most important biomaterials, owing to its feature to well reproduce the bone density [1]. ß-TCP are missing in biological calcifications, given that only the Mg-substituted form called whitlockite (ß-tricalcium magnesium phosphate, ß-(Ca,Mg)3(PO4)2) is found in dental calculi and urinary stones, dentinal caries, salivary stones, arthritic cartilage, as well as in some soft-tissue deposits [2]. For this reason, synthetised ß-TCP is an excellent candidate for bone cements and as well for bone substitution bioceramics [2], and it is known to present an excellent thermal stability and can be easily doped by trivalent ions as it offers various possibilities for doping by several cations [3]. Therefore, rare earth element (RE) and transition metal (TM) ions-doped TCPs show high interest as optical materials. These phosphates, especially in powder form,have been investigated fordifferentapplications, such as thermoluminescent dosimeters (TLD) for X-rays [4]. TCP is particularly suitable for TLD as it has an equivalent composition to human bones and teeth. Doped with Dy3+ or Tm3+, or other RE3+, the material absorbs X-rays in the way human tissues would do and stores charges before emitting light when thermally activated. Recently a crystal made up by Moroccan team, ß-TCP:Eu3+ presented an interest as a frequency-doubling material for non-linear applications [3].
However, despite the high interest in ß-TCP for many optical applications, the mechanism of dopant distribution is not well understood yet. This knowledge is crucial as optical properties depend on dopant-dopant and/or dopant-defect interactions and a careful control of the dopant distribution in ß-TCP would be required for the here above-mentioned applications. The main purposes of the present project thus should be: 1) the synthesis of ß-TCP phases doped with all RE series (La...Lu); they will be prepared by solid state reaction from a mixture of reagent-grade RE2O3, CaCO3 and (NH4)2HPO4, at temperatures up to 1200º. 2) the structural investigation of the site occupancy of RE3+ in doped Ca9RE(PO4)7 TCP phases. Such phases are expected to be isostructuralof ß-TCP:Eu3+ [3] already synthesized from the moroccan workgroup, owing to the so called phenomenon of lanthanide contraction observed in RE phosphates [5], with a substitution scheme (3Ca2+)®(2Eu+1ÿ) [3], isotypic to whitlockite Ca3(PO4)2 structure, rhombohedral with space group R3c (a=10.4352 Å, c=37.4029 Å) [4]. Five cationic positions exist, namely M1 to M5. Each of them is fully occupied with one Ca atom, except for the very small and irregular M4-oxygen polyhedron that has Ca deficiency. The site occupancy of RE3+in Ca9RE(PO4)7 structures can be investigated by means of X-ray diffraction (XRD). Complementary structural data of thermal expansion are also provided to conclude about crystal growth potentiality of the material.
The steps of the project can be achieved first, owing to the long term skill of scientists of Universitè Cadi Ayyad, Marrakech (Morocco), in high temperature synthesis of orthophosphates and in general on phosphorous chemistry, giving rise to several materials with well-established optical and thermal properties, as for example ß-TCP:Eu phase [4]. Moreover, for the structural characterizations, Single-Crystal and Powder X-ray diffraction (SCXD, PXD) are the most employed techniques used to investigate phosphorous and RE structural environments. But the analysis of such particular phosphates, usually thin layers plates or prisms of few microns of thick, is a crucial point worthy to be investigated also with other techniques, such as Small/Wide-Angle X-ray scattering (SWAXS), which are powerful tools useful also to investigate, over the crystal structure, also the domain of phosphate particles, as a function of their optical and thermal conductivity properties.
The CNR-IC has a long-time experience in new methodologies for structure solution from diffraction data [6-7] and analysis of materials at various scales, using different techniques [8]. It is equipped with SCXD and PXD modern diffractometers, and a SWAXS laboratory (XMI@Lab) for nanomaterials assembled on surfaces [9], as well as which, owing to the usual TCP shapes, seem to be a promising analytical technique over the more consolidated SCXD and PXD, the latter in any case mandatory for new phases crystal structures. As well, IC researchers have worked for long time also on structure investigation of phosphate materials, from natural terms [10] up to bioceramics applications [11-12]. Italian project leader, Dr. Capitelli, has experience in phosphate characterization [5,10, see curriculum vitae] and as well he collaborated with Moroccan project leader for the characterization of various materials [5, 13-14].

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3. Benhamou, Bessière, Wallez, Viana, Elaatmani, Daoud, Zegzouti, J. Sol. State Chem. 182 (2009), 2319-2325
4. Fukuda et al. Phys. Stat. Sol. 144 (1994) 107-111
5. Tahiri, El Bali, Lachkar, Piniella, Capitelli. Z. Kristallogr. 221 (2006) 173-177
6. Altomare, Burla, et al., J. Appl. Cryst. 32 (1999) 339-340
7. Burla, Caliandro, Camalli, Carrozzini, Cascarano, De Caro, Giacovazzo, Polidori, Siliqi, Spagna. J. Appl. Cryst. 40 (2007) 609-613
8. Fratini, Poccia, Ricci, Campi, et al. Nature 466 (2010) 841-844
9. Altamura, Lassandro, Vittoria, De Caro, Siliqi, Ladisa, Giannini. J. Appl. Cryst. 45 (2012) 869-873
10. Capitelli, Elaatmani, Lalaoui, Piniella. Kristallogr. 222 (2007) 676-679
11. Giannini, Siliqi, Bunk, Ladisa, Altamura, Stea, Baruffaldi. Sci. Reports 2 (2012) 435
12. Campi, Fratini, Bukreeva, Ciasca, Burghammer, Brun, Tromba, Mastrogiacomo, Cedola. Acta Biomater. 23 (2015) 309-316
13. Elaatmani, Zegzouti, Capitelli, et al. Z. Kristallogr. 218 (2003) 26-31
14. Capitelli, Rossi, Elaatmani, Zegzouti. Cryst. Res. Techn. 45 (2010) 1204

Research goals

The aim of the research activity is the realization of novel calcium phosphate biomaterials as possible bone replacement candidate, due to the traditional know-how of Moroccan universities in phosphate chemistry, and well as patents of such materials. At the same time, italian partner (IC Bari and Rome) will provide structural characterizations via multiple techniques due to the recent scientific strumentations availble and, as well as software (EXPO, SIR, QUALX, SUNBIM) developed by IC Bari for different data analysis.
Exchange experiences between both Italian and Moroccan workgroup, and as well to exploit other collaborations. Presentation of scientific results in National and International Meetings of Crystallography and Material Science, and publication of the same results on scientific journals as original papers.

Last update: 07/10/2024