New Materials for Intra-Osseous Implants and Methods of Their Biocompatibility Estimation
Tech Area / Field
- MAT-ALL/High Performance Metals and Alloys/Materials
- CHE-SYN/Basic and Synthetic Chemistry/Chemistry
- MAT-SYN/Materials Synthesis and Processing/Materials
3 Approved without Funding
NIIEFA Efremov, Russia, St Petersburg
- Institute of Microelectronics and Informatics of Russian Academy of Sciences, Russia, Yaroslavl reg., Yaroslavl\nMoscow State Technical University of Radioengineering, Electronics and Automation, Russia, Moscow
- Forschungszentrum Karlsruhe Technik und Umwelt / Institut für Hochleistungsimpuls und Mikrowellentechnik, Germany, Karlsruhe
Краткое описание проектаThe aim of the project is improvement of biocompatibility and mechanical properties of intra-osseous titanium implants by modification of chemical composition and surface; development of the tests for a rapid analysis of a bio-neutrality and biocompatibility of implanted material.
Project includes the whole spectrum of physical-chemical, technological and medical-biological researches:
- Physical-chemical investigations are needed for development of new materials for implants on a titanium base with improved strength, corrosion resistance and bio-neutrality; the project includes development of titanium alloys with a series of other elements and investigation of their properties: size of homogeneity areas in dependence from temperature; dependence of strength from chemical composition etc.
- Technological investigations are needed for development of new coatings and new methods of coatings formation; hydroxyl apatite (НАp), carbonate-hydroxyl-apatite, three-calcium-phosphate (TCP) and other types of bio-ceramics are deposed on titanium implants by method of plasma deposition by two stages (1 - formation of a intermediate layer of metal - bioceramics by a method of plasma-stimulated growth in vacuum, 2 - escalation of a bioceramics layer by a method plasma deposition in air).
- The medico-biological investigations are needed for estimation of biocompatibility of a material; the project includes investigation of the following tests: chemoluminiscent with luminol (fast and wide screening of tested components), secretion by the neutrofils of elastaza (fermentative method), apoptose of neutrofils (by flowing cito-fluoric-meter with mark of PI - propidium iodide).
Bone implants in surgery and stomatology are produced from titanium, because titanium has needed combination of mechanical characteristics, corrosion resistance and bio-inert properties. The products from titanium and its alloys, such as BT1-00 and BT1-0, (foreign analogs Grade 1, Grade 2), BT5 (foreign analog Grade 4, Ti5Al) and BT6 (foreign analog Grade 5, Ti-6Al-4V) are most distributed in modern stomatological practice. From the bio-tolerance point of view, the alloy BT1-00 is the most expedient material for manufacturing dental-plate implants; it is pure titanium (technical level), which chemical composition according to OST 1.90013-80 is following: Ti – base, Al Ј 0.7%, C Ј 0.07%, Fe Ј 0.3%, Si Ј 0,1%, O Ј 0.2%, N Ј 0.04%, H Ј 0.01%, total percent of other impurities less than 0,3 %. The Russian alloy BT1-0 (pure titanium) has less impurities, than foreign analog Grade2, which chemical composition is the following (ASTM standard): Ti - base, Al Ј 1%, C Ј 0.1%, Si Ј 0.2%, Fe Ј 0.2%, O Ј 0.25%, N Ј 0.05%, H Ј 0.015%, total percent of other impurities less than 0,5%.
This alloy has improved corrosion resistance, bio-neutrality, technological plasticity; it has high level of strength (s=575 МPа).
Application of this titanium alloys for implants is most rationally because the products from this alloy can be exposed to g-sterilization without appearance of the residual radio-activity phenomenon.
The distinction in a level of strength between technical titanium and alloys BT5 and BT6, reaching in some cases 400 МPа can be compensated by applying constructive changes or special ways of surface processing of an implant.
One of the operation purposes is improving of mechanical properties of the titanium alloys with maintenance of corrosion resistance and bioinertness.
The project deals with the physical-chemical and structural approach during development of new types of alloys. It is known that the alloy BT1-0 crystallizes in a-phase. The occurrence of a2-phase in titanium structure (for example, during alloying by aluminum) leads to considerable deterioration of electrochemical properties of titanium. Alloying of titanium by vanadium, which is b-isomorphic stabilizer, leads to some diminution of alloy corrosion resistance in the case of appearance of b-phase.
Oxygen and nitrogen are stabilizers of a-phase; they increase mechanical properties of titanium. However, the content of these components in an alloy should be restricted by particular limits, because big their concentration deteriorates the plastic properties of alloys considerably. It is possible to explain this deterioration of plastic properties by formation of ranked phases of TiOx type, which sharply changes the deformation mechanism of the material; therefore content of oxygen in alloy must not exceed 0.6% (mass) and content of nitrogen must not exceed 0.1% (mass). The complex alloying by a- and b-stabilizers is used for wide management of structure and phase composition. Quantity of b-stabilizers must provide formation of 5-10% residual b-phase. In our case it is possible to use iron as the b-stabilizer in amount of 0.6-1% of masses; that will allow obtaining high adaptability to manufacture of an alloy and will not decrease bio-inertial properties in comparison with widely applicable in medicine alloy BT1-0. Thus, the basic idea of an alloy is a composition of Ti-O-N-Fe, which should provide obtaining alloy with a+b-structure (with a particular ratio between these phases), having a level of strength 800 - 1000 MPa, i.e. about equal to a level of strength of an alloy BT6 or in 2-2,5 times exceeding strength of an alloy BT1-0, without losing its degree of a bioneutrality.
The following stage of implant development (after increasing of mechanical properties and bioneutrality) is improvement of biocompatibility and decreasing of period of joining of bone and implant. For solving this problem, covering from HAp and TCP (inorganic basis of the bone tissue) is deposed on implant surface; covering has developed porous structure and the size of pores on the surface is bigger than size of pores inside body of covering. The main advantage of HAp (in comparison with other bio-ceramics) is not only its perfect compatibility with alive tissue, but also ability to dissolve inside bone tissue (at the same time actively boosting the process of bone tissue formation).
Wide-known problem of HAp deposition is adhesion with titanium alloys. For increasing stability of covering (adhesion-cohesion strength) and improvement of growing of bone tissue in pores of covering, the project deals with following specific technological operations:
- preliminary electron beams treatment of surface of titanium implant;
- using multi-layer technology with surface modification by concentrated energy flows; creation of multi-layered structure (dense ultra-dispersed titanium, porous big-dispersed titanium, mixture of titanium with HAp);
- ultrasonic vibration of base during deposition process.
The main disadvantage of all artificial implant materials is probability of reaction between implant material and organism (implant is alien material for organism). That is why development of improved tests for estimation of harmlessness and biocompatibility of new materials for organism is actual task. Neutrofils (fagocitate of blood cells) play paramount role in inflammatory response, which is attribute of the answer organism on the stranger agents. The project deals with investigation of neutrofils reaction to various implant chemical composition. Test on neutrofils damage can show level of biocompatibility, because implant materials toxicity leads to destroying neutrofils up to fissile oxygen radicals and enzymes, in particular, elastase. Analysis of cellular destruction at interaction with a surface of an implant can be the important test as well.
So, as result of the project, the following physical-chemical bases will be created:
- basis for development of new titanium alloys for intra-bones implantology with various chemical composition (with HAp coating and without it) with the improved mechanical and bioinertial properties;
- basis for modification of surface of implants by electron beams methods (as a stage of developed method of implant production).
The harmlessness and biocompatibility of the developed materials will be tested with help of designed procedures of a rapid analysis.
Experience of institutions-executors in synthesis and investigation of inorganic materials properties gives reliance of the successful solution of the formulated problem.
For development of new materials with improved reproduce-able needed complex of structural-sensing properties and optimal microstructure, it is necessary to execute the following basic stage of the project:
1. Development of conditions of synthesis of equilibrium multiphase alloys from systems of “Ti-O-N” and “Ti-O-N-Fe”.
2. Investigation of areas of homogeneity and phase properties in systems Ti-O-N and Ti-O-N-Fe (more 99% mass. of Ti).
3. Establishment of interrelation between content of a- and b-phase in investigating alloys and mechanical properties.
4. Synthesis of HAp ceramics and choice of a target composition for a deposition.
5. Synthesis and physical-chemical investigation of collagen-contented carbonate-hydroxyl-apatites; investigation of influence of various factors on process of hardening of composites.
6. Modification of implant surface by electron beams for improvement of adhesion and bio-neutrality after deposition of HAp ceramics.
7. Development of the bio-inertness and biocompatibility estimation test for implants from designed alloys and alloys with НAp coatings.
8. Creation of database of main properties of developed implants in dependence of technological; conditions of synthesis.
9. Implementation of estimation of implants during clinic tests in medical organizations.
10. Manufacturing of experimental batches of various implants from developed materials.