Biocompatible implants for bone restoration
Bone nanotechnology
Vladislav Novikov, STRF.ru (photo by the author)
Spare parts are not given to us at birth. The regeneration of soft tissues occurs quite quickly, but what about when it is necessary to restore the bone? It turns out that medicine began using implants – artificial bone substitutes – even before our era. On the territory of modern Honduras, in the area of the plateau De Los Muertos, a fragment of the lower jaw of an Inca (VI century BC) with three dental implants from the shell of sea mussels was found. In the province of Chantambre (France), the skull of a woman who lived in the I century A.D. was found with a metal implant in the hole of the canine of the upper jaw.
The human body perceives any foreign body as hostile. And nowadays up to 35 percent of implants used in traumatology are rejected. And this means severe pain in patients, repeated operations. Our bone tissue consists mainly of hydroxyapatite nanocrystals (65 percent) and collagen (25 percent). It also contains specialized cells and proteins – growth factors. How can the biocompatibility of implants be improved? To make them as similar as possible to human bone tissue. Scientists and doctors have been trying to solve this problem for decades, using a variety of approaches. The technology of a fundamentally new level was proposed by biotechnologists from the FSBI "NIIEM named after N. F. Gamalei" of the Ministry of Health and Social Development of Russia.
The Gamalei Institute is famous for its advanced developments. The world-famous virologist and immunologist Lev Silber, who discovered the tick-borne encephalitis virus, created his own viral-genetic theory of the origin of cancer here, which laid the foundations of modern oncoimmunology. A leading specialist in the field of immunohematology, corresponding member of the Russian Academy of Medical Sciences Alexander Friedenstein, working here, discovered stromal stem cells of the bone marrow. His research in the field of bone tissue restoration and transplantation helped to create domestic technologies of osteoplastic materials.
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The Gamalei Institute served as the lead organization in the work on the creation of a new generation of implants, which was carried out within the framework of the project initiated by the Ministry of Education and Science "Development of pilot technologies for the production of hydroxyapatite/collagen composite preparations/coatings of implantable materials" according to the Federal Target Program "Research and development in priority areas of development of the scientific and technological complex of Russia for 2007-2012". Under the terms of the contract, 140 million rubles were allocated to the scientists and 3 years were allocated for the work
New generation materialsThe fundamental novelty of the implantation technology developed at the Gamalei Institute consists in the introduction of proteins – growth factors and bone regeneration into the implantable composite material, as well as in the creation of metal implants, the surface of which contributes to the retention of a bio-coating as close as possible in composition to bone tissue, also containing growth factors.
Due to the factors of bone tissue growth, the implant not only serves as a support on which the bone grows, but in itself becomes an active principle that initiates the formation of bone tissue.
Drugs of this kind have not been produced in our country until today. Bone growth factors were obtained on the basis of a genetic engineering approach in the laboratory of biologically active nanostructures of the Gamalei Institute under the leadership of Vladimir Lunin. In the USA, drugs containing growth factors and bone regeneration have been approved for use since 2002. Until now, there has been a significant lag in this area in our country, since bone morphogenetic proteins are in the first positions in the list of the most important innovations for medicine today.
Along with Lunin's laboratory, co-executors participated in the work. The basis of the implants – nanostructured titanium – was manufactured at the Ufa State Aviation Technical University (UGATU). To date, pure titanium is the most promising and widely used material for implantation. Theoretically, it is possible to increase its strength due to alloys with nickel and other metals, but these alloys are already toxic to the body. Therefore, strength increases are achieved with the help of nanotechnology, which allows you to change the structure of titanium, grinding the metal grain to nanoscale, and create the effect of Damascus steel. Only nanostructured titanium is not forged, but dragged and rolled. As a result, a titanium product can be made very thin, but at the same time it retains its strength. This is important, for example, for dental implants: teeth are under heavy loads, and since the jaw is thin, you can't "drive" a large screw there. And in addition to strength, titanium is a fairly light metal, which is especially important when the implant remains in the body for life.
Further, precision titanium rods with verified geometry are made from nanostructured titanium in UGATU, from which dental implants are produced at the Moscow company CJSC Konmet. The surface of the implants is sandblasted to create a relief.
Employees of the company INTC "Iskra" from Ufa, in close cooperation with Ufa surgeons – specialists in the treatment of injuries and diseases of the spine – have developed an original model of titanium implants for traumatology and orthopedics – a device for correction and fixation of the spine. The device itself, which is a set of screws and spokes that can be connected into various designs depending on the injury or illness of a particular patient, is manufactured at the NPO Deost enterprise near Moscow, in Pushchino-on-the-Oka.
At Belgorod State University (BelSU), the surface of one of the screws – a screw for transpedicular fixation – is modified in a special way, giving it special properties. After that, a bio-coating is applied to the implant, which is exactly the key link of the technology.
During this procedure, special screws are passed through the so-called legs of the vertebral arch (Latin pedicula arcus vertebrae) into the vertebral body; rods are held between them, connecting them together. This design blocks any movement in this segment, stabilizes it – VM.
How to increase biocompatibility?"When we started these studies," says Vladimir Lunin, "it was clear from the literature that we were faced with three tasks at once to create a surface optimal for its acceptance by the human body.
Firstly, the implant surface is hydrophobic, that is, it is necessary to ensure its wettability. Secondly, it is negatively charged, which is also bad, because the tissue cells also have a negative charge. There is a double repulsion of the cells of the human body from such an implant surface – due to the non-wettability and the same charge. And the third is the creation of a certain relief, that is, the surface should not be smooth."
The Swiss firm Straumann, the leading manufacturer of dental implants in the world, demonstrates the hydrophilicity of the implant surface in its brochures. Prior to treatment with a special preparation, the screw "squeezes out" water during immersion, and after treatment, the hydrophilic screw pulls the water up, just as a sheet of paper dipped into it with one end absorbs water. Swiss developers managed to make an implant that demonstrates the "rise" of fluid by 10 mm. The presentation presented to the commission from the Ministry of Education and Science shows a screw for fixing the spine with a surface treated using the MDO technology developed by specialists from BelSU. So, our scientists managed to create an implant that provides a "lift" of the liquid by 30 mm. And this is a serious achievement, competing with the world manufacturers of implants.
Changing the surface properties of materials is actively used in modern technologies. For example, a similar effect of wetting the surface is introduced by Toyota in the manufacture of glass for cars. Thanks to the creation of a hydrophilic film, water spreads over the glass, and no drops form on its surface. But here the task is somewhat different – to create a large smooth surface, and the implant, unlike car windows, should be as rough as possible so that the cells of the body have something to "catch on". The "ball–in-the-hole" principle applies here. The cell has a size of about 20 microns, so the cells on the surface of titanium should have a slightly larger diameter so that the cell can "crawl" and "sit down" there.
The basis of the technology for manufacturing hydrophilic and rough surfaces of titanium implants is electrolytic surface treatment in solutions containing one of the main components of bone – hydroxyapatite. This method is adapted for the implants developed in the project by specialists of BelSU, it is called MDO – microarc oxidation. With this treatment, hydroxyapatite atoms penetrate into the titanium structure. A gradient is created: the implant surface consists almost entirely of hydroxyapatite, titanium atoms begin to predominate deeper. Due to the gradient structure, the surface turns out to be very strong: there is no "peeling" of the surface layer when screwed into the bone. This technological solution provides not only high hydrophilicity (wettability) of the material, but also solves the problem of charge – such a surface is not charged – and the problem of biocompatibility, because hydroxyapatite is a "native" material for bone tissue. The problem of attachment of the cells of the body "building" bone to the surface of implants and the problem of fusion of the newly formed bone with the implant is also solved. During electrolysis, oxygen bubbles form on the surface of the implant, contributing to the formation of a porous structure, which is an ideal relief for the interaction of the implant with cells and bone.
Bone protein is produced by bacteriaHuman bone tissue contains 20 bone morphogenetic proteins, thanks to which our skeleton is formed.
"But we cannot reproduce nature completely," explains Anna Karyagina, chief researcher at the laboratory. – It is impossible to make 20 recombinant proteins – exactly the same as those synthesized in the human body, mix them into a "cocktail", "plant" them in the right places in the bones and "seal" them in the right way." Scientists are modeling the main mechanism that allows the body to quickly start regeneration processes and "delivers" ready-made building material to the injury site based on a single recombinant protein similar to human. (The picture shows chromatographic columns used in the purification of protein preparations.)
"With a bone fracture, there is a redistribution of bone density around the fracture," explains Anna Karyagina. – Building material is transferred from neighboring bones to the fracture area, and after a while the fracture site may become stronger than neighboring bone sections. With a broken arm, for example, even the rate of nail growth slows down. We bring high-quality building material from the outside to the injury site, which can be immediately used by the body."
In our country, drugs based on recombinant interferons are produced in large quantities. Unlike genetically modified foods, which still cause a negative attitude of the public, these drugs have been more fortunate, and they have widely entered medical practice. For the production of bone growth factors, as well as for the production of interferons, biotechnologists use bacteria. Thanks to the built-in human gene, these microorganisms begin to synthesize a protein similar to that formed in our body. Once in the human body, such a protein is recognized as "its own" and, along with its own proteins, is included in the composition of bone. Growth factors contribute to the differentiation of mesenchymal stem cells discovered at the time by A. Y. Friedenstein. They promote growth, mobilization of calcium and phosphorus from other cells and accelerate the germination of blood vessels. Thus, the layer of composite coating applied to the implant is used as a bait for the cells of the body and as a building material for growing your own bone.
Biomedical studies of the developed preparations and implants with a calcium-phosphate coating were carried out on rats and other laboratory animals. In particular, a hole was made in the rat's tibia, into which a coated implant was placed. In the control experiment, an uncoated implant was used. In all experiments with calcium-phosphate coating, the implant ingrowth into the bone occurred much faster, the implants were held in the bone more strongly.
It is worth mentioning here about the conditions of keeping laboratory animals. The vivarium at the Gamalei Institute is one of the best in our country, it is even certified according to the European standard. Each animal here is kept in a separate cage, there is an automatic system of nutrition and maintenance of all optimal living conditions. So they live there almost better than the laboratory staff. Although the employees here are surrounded by no less care. There is a refrigerator in the cozy dining room, which is personally replenished by the head of the laboratory to the delight of the whole team.
The main task is to attract specialistsNow the laboratory employs 46 people.
Each of them is a narrow specialist in their field. And all together, they, according to the head, "can solve any tasks at any time."
It is in scientists that Russian science is experiencing a shortage today. "If in the 90s there was an excess of unclaimed researchers," says Vladimir Lunin, "and at the same time there were not enough reagents, equipment, or space, now the situation is changing to the opposite. Reagents and equipment are relatively cheap, but there are not enough people who could organize it all, build technological chains, make a single technological process for studying something."
Lunin's laboratory also has employees who are engaged only in the development and approval of documents. There are specialists in economic issues, accounting, contract execution. There is a specialist in technological issues of production. The team did a tremendous job at the stage of state certification of the developed drugs. The administration of the Institute was shocked when, in just six months, the laboratory managed to go all the way from the beginning of medical trials of drugs to their registration. Everything was literally calculated by the days: today to go there, tomorrow to sign it. The work on closing the project was worth no less effort.
Reporting on only one final stage of the project weighed about 11 kilograms, and all the reports and technological documentation together is almost a whole cabinet full of documents.
The Institute patents technological developments jointly with the Ministry of Education and Science. However, many developments cannot be patented. According to Vladimir Lunin, the "simplest" technological solutions remain at the know-how level.
Under the terms of the contract, the institute has created a production site where they receive a composite preparation for covering implants. The production of pilot batches and quality control of drugs are carried out here under GMP (Good Manufacturing Practice) production conditions. This is an international system of norms and rules created for the production of medicines and medical products. According to this system, not a sample batch is checked, but absolutely all parameters of production and products are controlled.
In November 2010, the developers received a registration certificate and a certificate of conformity for the composite preparation Gamalant-Forte paste for bone implantation and joint use with metal implants. Approximately, the drug will be available in February 2011.
A natural and important question arises: who will be the organizer of training doctors to work with these materials of a new generation?
"Our task is to attract large specialists who understand the need for such training," explains Vladimir Lunin. – This drug cannot be introduced into medical practice through advertising booklets. It should be applied clearly according to the instructions, and professional surgeons should do it. If the drug is applied carelessly, growths may form around the bone. If you put the drug in a muscle, then a bone can grow there too. Fortunately, when the work on the project was nearing completion, there were many professional surgeons who “understand" the drug. Now we cooperate with many departments of the CITO (N. N. Priorov Central Research Institute of Traumatology and Orthopedics - STRF.ru ), and the transition of CITO to work with these materials is already planned."
Lunin's laboratory continues to work on new bone-plastic materials. At the moment, scientists are creating minimally invasive forms – these are drugs that can be injected through a syringe or catheter directly into the fracture site. If the fracture does not require the installation of metal structures and external fixation is sufficient, but there has been a partial destruction of the bone, such drugs can be introduced there without injuring the body. These works are carried out on another project, which is funded by the Ministry of Industry and Trade. In accordance with the contract, the production of these drugs should be established on the basis of the Gamalei Institute in 2011.
Portal "Eternal youth" http://vechnayamolodost.ru21.12.2010