Synthesis and characterization of molecular sieve with AlPO4-5 framework. Preliminary biomedical essays

October

*H &.__

1996

__ i!iB ELSEVIER

Materials Letters 28

(I 996) 507-5 1 I

Synthesis and characterization of molecular sieve with AlPOdframework. Preliminary biomedical essays A. Jacas Rodriguez a, M. Hernindez-Vklez a3*, R. Roque-Malherbe E. Gonziilez Arag6n a, J. Oiiate-Martinez ’

by

I.S.P. “E.J. Varona”, Grupo de Zeolitas y Propiedades Diele’ctricas en So’lidos, C. Libertad, Marianuo, La Habana, Cuba ’ Institute de Tecnologia Q&mica, UPV-CSIC, Ace. de 10s Naranjos s/n. 46022 Valencia, Spain ’ Laboratorium fur Kristallographie, Swiss Federal Institute of Technology ETH-Zentrum, CH-8092 Zurich, S\vitzerland

a Fucultadde F&a,

Received

15 April 1996; accepted 29 April 1996

Abstract A molecular sieve including Ca in AlPO,-5 framework was synthesized. The highly crystalline synthetic products were characterized by X-ray fluorescence analysis, X-ray diffraction and NH, adsorption. Sterilized CaAPO-5 was implanted in powder form in alive animals and a preliminary evaluation of their bioactive properties was made by elementary preclinical

tests. Kexwordst Aluminophosphate;

Molecular

sieve; Hydrothermal

synthesis;

1. Introduction The hydrothermal synthesis of new types of molecular sieves, i.e. crystalline microporous phosphate based oxides, was initiated by Wilson et al. in 1982 [l], who obtained materials with aluminophosphate composition. An important progress in the science and technology of this kind of materials was the synthesis of silicoaluminophosphates in 1984 [2]. The number of structures and different types of crystalline microporous oxides have increased in the last years [3-61. Up to date eighteen elements from the periodic chart can be combined with P(V) in

* Corresponding author. Present address: Applied Physics Department, Science Faculty, M6d. C-XII, Madrid Autdnoma University, Cantoblanco, 28049 Madrid, Spain. 00167-577X/96/$12.00 Copyright PII SO167-577X(96100105-X

Bioactive

material;

Osseous implantation

different frameworks [7]. The diversity of these materials has increased their application field, being of great interest, the development of those that exhibit bioactive properties. In that sense, the most used materials that could be mentioned are the hydroxiapatities and their combinations with wallastonite, pwitlockite and other calcium phosphates and sulfates [8,9]. On the other hand, different zeolites or zeolite-like materials with excellent antibacterial properties have been obtained [lo]. The inclusion of certain metals seems to be the most interesting fact. The aim of the present Letter is to report the synthesis and characterization of Ca substituted AlPO,-5 molecular sieves, which, as far as we know, constitute a new member of these aluminophosphate family. The obtained material has been used as bony filling to evaluate its bioactive properties. The pre-

0 1996 Elsevier Science B.V. All rights reserved.

508

A. Jacas Rodriguez

liminary results of these experiments this work.

et al./Materials

Letters 28 (1996) 507-51

I

are reported in

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2. Experimental The gels for the hydrothermal synthesis process were prepared using Alumina (Merck), orthophosphoric acid (85%, BDH) and CaSO, .2H,O (BDH) as starting materials. The template in all cases was triethylamine (TEA) (BDH). Gels were crystallized using stainless steel autoclaves at 200°C. As a reference AlPO,-5 was synthesized similarly but in the absence of the metal salt. The synthesis procedure can be described as follows: (a) Alumina is slurred in a half-quantity of water which will be used for the synthesis. (b) The calcium sulfate is added to the above described slurry. (c) Phosphoric acid is diluted in the other half of water. (d) The phosphoric acid solution is added to the alumina plus salt slurry. (e) The precursor is stirred during 20 min. (f) Triethylamine is added to the precursor mixture under rapid agitation. (g) The mixture is charged into autoclaves and statistically heated at 200°C by 24 h. The elementary composition of the as-synthesized products was measured with a Canberra X-ray fluorescence spectrometer set with an Si-Li (200 eV resolution) detector and lo9Cd source using two hours as measuring time. The qualitative phase analysis and cell parameters determination were performed by X-ray powder diffraction in a TUR M-62 Carl Zeiss powder diffractometer using Cu Ko radiation and CaF2 as internal standard. Fig. 1 and Fig. 2 show the X-ray powder diffraction patterns of AlPO,-5 and CaAPO-5 cl%), respectively. Adsorption isotherms of NH, at 300 K were measured by the volumetric method [ 111. For this study, the as-synthesized products were activated for 40 h in vacuum (lo-’ Pa) at 680 K. The maximum magnitude of adsorption (a,), the characteristic adsorption energy (E) and the optimum empirical parameter IZ taking into account a combination of the

I

4~

I

I

40

36

32

28

24

20

16

12

e

Fig. 1, X-ray powder pattern of AlPO-5.

Dubinin [ 121 and osmotic [ 131 isotherm equations, were calculated. The Dubinin equation for adsorption isotherm is: In a = In a, - ( RT/E)

” [ ln( PO/P)]

‘,

where a is the magnitude of adsorption, a, is the maximum magnitude of adsorption, T is the experimental temperature of the adsorption, PO is the vapor pressure at the temperature T, P is the equilibrium pressure and y1 is an empirical parameter. The preliminary biomedical essays were carried out in the Carlos J. Finlay Hospital (Havana, Cuba). For this purpose, twenty-four healthy dogs were submitted to clinical analysis before the implantations of the synthetic materials. For pre-clinical studies, the dogs femur zone was selected because of its high vascularity. For the implantations, a trephine drill defect (4 = 6 mm) was produced in the medial aspects of the dogs femurs shown in Fig. 3. The obtained synthetic material in powder form was filtered, washed, dried and calcined at 450°C for the

Ca APO-5

Fig. 2. X-ray powder pattern of CaAPO-5

(1 SC).

A. Jocas Rodriguez et al./Materials

Letters 28 (1996) 507-511

Table 2 Parameters at 300°K

509

of the Dubinin adsorption

isotherm equation

for NH,

Sample

a, (mmol/g)

w (cm’/g)

E&J/m00

IZ

AlPOdCaAPO-5

6.10+0.05 7.20f0.05

0.146+0.005 0.173+0.005

15.0+0.5 16.4+0.5

4 4

’

= l%Ca.

Fig. 3. Radiography of the zone in which CaAPO was implanted obtained 30 days after the implantation. Note that there are almost no differences between the density of the bone and the density of the implanted material.

elimination of the organic template agent and sterilization before it was implanted by pressure into the defect previously washed with physiological serum solution.

3. Results and discussion Chemical analysis provided the framework composition of as-synthesized samples that are shown in Table 1, indicating the incorporation of about 1 and 2% of Ca to the aluminophosphate framework. If the normalized oxide composition is represented as Ca,Al,PZO,. then x= 0.0094 and 0.0179 for the obtained samples, The synthesized products exhibit high crystallinity and no crystalline impurities were detected. Only a small amount of an amorphous phase is present which was shown using the values reported for the maximum adsorption of NH, and the total volume of the adsorption space (w = a,V,, where V, = 20.8

Table 1 Normalized

Table 3 Parameters oxide composition

Sample &APO-5 CaAPO-5

cm3/mol is the molar volume of NH, at 300 K) shown in Table 2, taking into account that the volume of the adsorption space for AlPOd- was previously reported [15] to be 0.14 t- 0.01 cm3/g and that the proportionality of the magnitude of adsorption was tightly related to the zeolite content in the sample. All these facts indicate that the efficiency of the synthesis process was very close to 100%. Table 3 shows the cell parameters and cell volume for both CaAPO-5 samples (with 1% and 2% Ca incorporated in the framework) and for the AlPO,-5 reference sample. It is noticeable an increase in the last parameter due to the Ca inclusions in th$ AFl framework and its higher ionic radius: 0.99 A compared to the ionic radius of P(V): 0.34 A as well as, the ionic radius of Al(II1): 0.5 A. As is well established [7], isomorphic substitution generates framework negative charge, which can be effectively balanced by the organic template, which become positively charged by protonation in the case of amines, like it is happening in our case. The results mentioned above along with other termogravimetric studies [8] clearly indicate the fact that Ca(I1) isomorphically substitutes Al(II1) in the AlPO,-5 framework. For the preclinical studies CaAPO-5 and the reference AlPO,-5 were used. The most important observation at the first level of the pre-clinical test was that the artificial defects done in the dogs femurs were in all cases successfully reconstructed as can be

(1%) (2%)

expressed

as Ca, Al,P,O,

x

Y

z

0.0094 0.0179

0.4906 0.482 1

0.5000 0.5000

of the hexagonal

Sample AlPOdCaAPO-5 CaAPO-5

(1%) (2%)

lattice of CaAPO-5

and AIPO,-5

a (A,

c (“Q

V(K)

13.61 kO.02 13.67f0.02 14.15+0.02

8.54 + 0.02 8.49 + 0.02 8.41 kO.02

1369.9 1373.9 1458.2

A. Jacas Rodriguez et al./Materials

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Letters 28 (1996) 507-511

4. Conclusions

04 0

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5

10

15

20

25

r 30

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35

Time (days) Fig. 4. Evolution of calcium and phosphorous levels in blood at 7, 14, 21, 33 days after the implantation, ( n ) and (0) correspond to operated animals; (0) and (0) correspond to reference animals that did not undergo an operation.

observed in Fig. 3a. The radiography showed a tendency to bony union of the implanted material to the underlying bone. The density and union with the underlying material were better for CaAPO-5 than for AlPO,-5. Blood analyses to control Ca and P levels evolution (Fig. 4) after the implantation were carried out at 7, 14, 21 and 30 days after the implantation. Ca and P levels in blood were satisfactory after 27 days after the implantation. The evaluations from the histological and toxicological point of view do not reflect macrocells or any signal of adverse reaction [14]. All implants were well accepted by the host bone judging from criteria of minimal inflammation, degree of fixation and no rejection. Furthermore, no sign of toxicity was found in the animals. These preliminary tests confirm the potentiality of the synthesized materials like biocompatible materials [14]. We consider that this satisfactory biomedical behaviour is related to the chemical composition of the samples and probably their microporous structure which permit some osteal tissue ingrowth and the flux of nutrients. One drawback in the implantation of the powders is that they form up colloidal suspension with the blood of the provocated wound. We hope that this fact could be solved making up ceramics granulated composites using &APO-5 as starting material, which are actually in progress.

&APO-5 was synthesized adding calcium sulfate to the precursor gel used for AlPO,-5 synthesis. The as-synthesized samples exhibit a degree of substitution, in normalized oxide composition, x = 0.0094 and x = 0.0179. The lattice parameters corresponding to CaAPO-5 are larger than those corresponding to AlPO,-5, indicating the incorporation of Ca(I1) in the aluminophosphate framework. The different biomedical research carried out after 7, 14 21 and 30 days of the implantation of AlPO,-5, and CaAPO-5 (2%) showed that the obtained materials are biocompatibles, although CaAPO-5 is more perspective than AlPO,-5 [ 141. These results indicate the high possibilities, up to date unknown, of application of metalaluminophosphates molecular sieves in the biocompatible materials field mainly because of the ability of these powders in the transport of nutrients through the molecular sieve primary and secondary porosity which promote tissue and vascular grow without toxicity and rejection.

Acknowledgements The authors wish to thanks Dr. J.M. MartmezDuart from Applied Physics Department of Universidad Autonoma (Madrid, Spain) for the useful suggestions and the partial support in the preparation of this work; at the same time we also are grateful to Dr. J. Marrero-Dedin for the X-ray fluorescence measurements and M. Carreras-Gracial for his technical assistance.

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A. Jacns Rodriguez

ef al./ Materials

[5] C. Montes, M.E. Davis, B. Murray and M. Narayana, J. Phys. Chem. 94 (1990) 6431. [6] MS. Rigutto and H.3. van Bekkum, Mol. Catal. 81 (1993) Il.

[7] J.A. Martens

and P.A. Jacobs,

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(1994) 653. [8] T. Kokubo, S. Ito, Z.T. Huang, S. Sakka, T. Kiksugi, T.J. Yamamuro. J. Biomed. Mater. Res. 24 (1990) 331. [9] J.M. Thoman, J.C. Voegel and P. Gramain, Calcif. Tissue Int. 46 (1990) 121. [IO] H. Zenji, 0. Hideo, K. Shigetaka, N. Saburo, I. Shunya and

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T. Kenichi, in: Particle-packed fiber having antibacterial property. Kanebo Ltd. Kanto Chemical Co. Inc. Kanebo Ltd. Jp Patent. 62-7748. [l 11 S. Ross and J.P. Olivier, in: On physical adsorption (Interscience, New York, 1964) p.31. 1121 M.M. Dubinin, Progr. Surface Membrane Sci. 9 (1975) I [ 131 B.P. Bering and V.V. Serpinskii, Izv. Akad. Nauk. SSSR Ser. Xim. (1974) 2427. [14] R. Ortega and R. Ceballos, in preparation. [15] V.R. Choudhary. D.B. Akolekar, A.P. Singh and S.D. Sansare. J. Catal. I I1 (1988) 23.