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New materials for Osseous Implants

#2555


Development of New Materials for Various Types of Osseous Implants

Tech Area / Field

  • MAT-COM/Composites/Materials
  • CHE-SYN/Basic and Synthetic Chemistry/Chemistry
  • MED-DRG/Drug Discovery/Medicine

Status
3 Approved without Funding

Registration date
28.06.2002

Leading Institute
Moscow State Technical University of Radioengineering, Electronics and Automation, Russia, Moscow

Supporting institutes

  • Institute of Microelectronics and Informatics of Russian Academy of Sciences, Russia, Yaroslavl reg., Yaroslavl\nTsKB of High Energy Lasers "Granat", Russia, Moscow\nMISIS (Steel and Alloys), Russia, Moscow

Collaborators

  • Lawrence Livermore National Laboratory, USA, CA, Livermore

Project summary

Main purpose of the project is the development of physical and chemical basis of technology and production of bond implants for applications in medicine. The implants are produced with use of new materials - synthetic apatite in form of thin powder solidifying at water or water solutions, or in form of coating on metallic or ceramic implants.

Creation of artificial implants of human bond tissue with the properties of bonds, providing shortening of rehabilitation period is of important problem of modern material science and practical medicine. The implants itself are used in modern traumatology, neuro and facial surgery, cosmetology and so on.

At present moment considerable number of materials used as implants are known: metals, polymers, ceramics and so on. Among them the materials based on calcium phosphate – hydrohyapatite- Са10(РО4)6(ОН)2 (НАр) and Са3(РО4)2(TKF) have the best combination of biological matching, physical, chemical and mechanical properties corresponding to human bonds.

The Hap materials in form of powders, granules, ceramic elements provide acceleration of the process of rehabilitation at human bonds, complete recreation of bond structure, antiseptic effect, strong adhesion to bond and soft tissues, biochemical binding of the ceramic with bond[1].

The HAp coatings on metallic, orthopedic and stomatological implants considerable enhance integration of implant with bond.

New generation of implants based on CaP compounds was proposed about 15 years ago, when it was shown that the process of bio resorption can be intensified, when using as an implant two component or more complex mixture, which at water solution transformed into HAP [2-4].

Main guidelines for the choice of components for obtaining phosphate cements were solubility diagram of CaP in threefold system СаО – Р2О5 – Н2О and isotherm of maximum saturation of solutions arising in phase system in dependence on pH value. For joint precipitation and further use of CaP materials in form of cements – it is necessary that the point of singularity of two phosphates should be located above the HAp isotherm. Only in that case HAp will precipitate. For the processes of bonds restoration the speed of HAp precipitation should be small enough, that is the solution composition should not strongly deviate from the composition corresponding to HAp isotherm. These conditions are met in best extent by the following combinations of pairs of twofold phosphates: Ca4P2O9(4:1) and CaHPO4 2H2O; (4:1) and CaHPO4(2:1); (4:1) and b-TKF.

For all that the following chemical reactions with HAp precipitation will take place, for example: (4:1) + СаНРО4.2Н2О = НАр +2О. For required pH of environment one can choose corresponding pair of phosphates with required singular point. For example for pH being about 7.5 it is necessary to use the pair of CaHPO4. 2H2O with (4:1).

Before application the phosphate cement is mixed with water and as obtained paste introduced in the zone of bond defect, where then transformation to HAp takes place. The advantage of presented method consist in its active chemical form, possessing recreative properties. It allows to the human body to fasten formation of biomatching bond tissue.

For all that the phosphate cement solves the following technical problems:

– filling voids and holes of different nature inside bond tissue;


– creation and stabilization in the wound zone of specific physical and chemical conditions for intensive rehabilitation;
– mutual enhancement of treatment effects of separate parts and complexes of components of mixture, and also biological active compounds produced by human body;
– prevention of damaging effect of external mechanical loads on the processes of bond tissue regeneration;
– giving to human body building material and matrix for bond tissue regeneration.

However this material has incomplete matching of its chemical composition with human bond tissue (inorganic part contains besides calcium and phosphorus oxides small amount of oxides of other elements such as: Mg, Na, K, C, and ions of F, Cl, and others). There exist some technological problems (for fast solidification of cement the size of powder particles should be about 1-10 mm, that requires the use of special technological equipment). Presented project is dedicated to solution of these problems. In chemistry of appatites the most interesting (for practice) aspect is related to mutual transmutations: ”TKF – HAp – Dallit ” during formation and aging of bond (crystal chemistry, kinetics, catalytic activity of impurity ions, playing important role in the most of physiological processes). Complication of atomic composition of the compound during the process of carbonate ions and some cations introduction leads to the necessity of studies of CaO-P2O5-H2O-CO2 diagram, more precisely systems of CaCl2-(NH4)HPO4-NaHCO3-MgCl2-KF-NH3-H2O in the region of HAp precipitation. For all that there appears additional opportunity to control non stoichiometry and properties of hydrohilappatites of composition Са10-х-уMgxNay(РО4):6(ОН)2-z-wFz(CO3)w (СНАр).

These semiamorphous phases are related to the class of bioappatites, with Ca deficit. The studies of this materials by methods of X-ray diffraction and infrared spectroscopy will contribute to the understanding of the processes going inside phosphate cements during its solidification, and help investigations of kinetics and mechanisms of low temperature (25-37°C) synthesis of CHAp from CaO2-PO2, CaO-P2O5-H2O-CO2 with some cations adding in dependence on the extent of components dispersion, composition of solidificated solution and effects on the process of laser irradiation.

Synthetic implants in form of phosphate cements, obtained from ultra pure components, contain 100-1,000 times smaller amount of heavy metals, than similar samples of animal bonds. That completely excludes all possible immune and inflammatory processes, allows regulation of chemical and biological properties of the preparation, it also make possible to solve many specific medical problems, such as adsorption of antibiotics and other substances on the surface of the material.

Preliminary physical and chemical studies of collagen containing carbonate hydrohyappatites, obtained by the method of residual concentrations by I.V. Tananaev showed that these composition materials can be used as independent implants, and as supplements to known phosphate cements.

Titan implants are widely used in stomatology, facial surgery and orthopaedy in form of special fixing plates, screws and so on. For providing better conditions for implant grow together in bond tissue the appatite coating should posses well developed porous structure with voids size decreasing from the surface to the depth. Major advantage of CHAp coatings in comparison with other bioceramics is of its good combining with living tissues. Further developments in that field assumes work the improving of the adhesion. For that purpose the surface of metallic implant is covered by 3 intermediate layers: porous titanium with dispersion of 3-10 mm, porous titanium with dispersion of 50-100 mm, porous composition (60% Ti + 40% HAp). Such developed structure of the surface allows very strong adhesion of plasma sprayed CHAp particles on the surface of implant.

Thus, as a result of the project physical and chemical basis of the technology and production of bond implants with use of new materials of synthetic apatites (close by chemical composition to the bond tissue) in form of thin powders, solidifying at water solution or polymorphic mixtures of biopatites, in form of composition collagen containing materials on the base of biopatite, in form of plasma sprayed coatings on titanium or ceramic implants.

The experience obtained by the project participants on synthesis and studies of inorganic materials gives hope on successful solution of described problems.

References.

1. B.V.Rejda, J.G.Peelen, K.De Groot \ Philips Tech.Rev. 1977, 37, 234.


2. W.E.Brown, L.C.Chow\Cements Res.Progress 1986, ed. P.W.Brown, pp. 352-379.
3. K.Ishikawa, S.Takagi, L.C.Chow\ j.Mater.Sci. Mater.Med. 6, 528-533 (1995).
4. Patent USA 5, 997, 624. Chow, et al. December 7, 1999.


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