Advances in medical technology come with a large amount of materials that are currently under consideration for possible implantation into the human body. With the object to be compatible with the body these potential materials need do not cause any further harm. Biodegradable materials are dispelling the current stereotype in biomaterial science to research and produce only corrosion resistant materials. Especially, materials which consist of nutrients existing in the human body are high-potential expectants for this approach. The main point is that biodegradable implants and coatings can support tissue regeneration and healing in the process of material degradation and can gradually dissolve with replacement by natural tissue.
Biodegradable metals take priority over current biodegradable materials for example bioactive glasses, polymers or ceramics as applied to loads in body that require a higher tensile strength and a Young’s modulus that is closer to bone.
The magnesium has drawn great consideration in capacity of biodegradable material for bone joint replacement due to its similar mechanical properties with human bone, biodegradation and biocompatibility. By the way, the high degradation rate of magnesium delimitates its application as bioimplant materials. In the past decade, various approaches have been investigated to improve the degradation behaviour of magnesium. Development of biocompatible coatings and alloying are the most common methods that have been investigated. It has to be said, biocompatible calcium phosphate (CaP) has limelighted great attention in recent years as a coating material on magnesium and its alloys.
The development of biocompatible CaP coating on the surface of magnesium alloys is one of the way to control their degradation rate. Thick CaP coatings that were prepared by wet-chemical methods are well known. Nevertheless, wet-chemical methods of CaP coating deposition on the surface of magnesium alloys often is afflicted with weak adhesive strength. Currently, researchers are prone to establish a thin protective surface layers on the surface of alloys, which allows to keep the initial substrate topography and enhance the corrosion resistance. However, even by now, there is insufficient information on the corrosion resistance of these coatings. The RF magnetron sputtering is a preeminent method for deposition of pure HA. On top of everything else, a HA coating received by RF magnetron sputtering is well-adhered to the substrate.
At present in medicine, the question is about creation of artificial tissue reproducing the functions and structure of living tissue for a limited period. Therefore, the development of bulk (3-D) scaffolds based on biodegradable polymers is an important area of bioengineering.
Biodegradable polymers are specific materials that are capable of degradation caused by microbiological and chemical processes. The development of biomaterials from biodegradable polymers will allow us to form the bone implants for the treatment of a broad spectrum of fractures that not only will support and serve as a damaged bone, but also to stimulate its growth and recovery. Biodegradable implants have all the advantages of conventional implants (from metal). Additional advantage is gradually breakdown in a patient organism to result in non-toxic products. After that, the decomposition products are extracted from the body during metabolism. It is therefore possible to remove the implants from a patient's body without repeated surgery. All these factors determined the great interest in search of technology, focused on a construction of materials and implants based on biodegradable polymeric materials.
The purpose of this research is the formation of a new hybrid composite material based on biodegradable polymers for regenerative medicine. New material should have gradient porosity to make imitation of bone structure. It should have mechanical properties similar with properties of damaged part of bone and repeat chemical composition of hard tissue, which contains 90% of calcium phosphate. In addition, implant surface should provide a good cell adherence to stimulate ingrowth of tissue into the matrix material.
Work is carried out with the collaboration of Technology Centre of Institute of Physics and Technology National Research Tomsk Polytechnic University, Fraunhofer Institute for Interfacial Engineering and Biotechnology, the University of Duisburg-Essen and Karlsruhe Institute of Technology KIT in Germany.
At present, synthesis and formation of 3-D bulk scaffolds are performed based on Technology Centre by using method of electrospinning. Materials are produced from next biodegradable polymers: polycaprolactone, poly-3- hydroxybutyrate and copolymer poly (3-hydroxybutyrate-co- 3-hydroxyvalerate). The method of electrospinning allows to synthesize 3-D bulk materials with fibrous structure and to control pore size and mechanical properties.
In Fraunhofer Institute for Interfacial Engineering and Biotechnology the polymeric films and 3-D scaffolds were modified by using radio-frequency (RF) reactive plasma. Studies have shown that surface of untreated polymer was hydrophobic, poor wettability, had low surface energy, that leads to bad cell adherence on the material surface. After plasma treatment the polymer's wettability improved significantly and surface energy increased. The advantage of plasma treatment is that it enables to form functional groups on the surface, which then allows an attachment of macromolecular compounds to the polymer. The results of performed researches
are presented in follow articles [Materials Letters 163 (2016) 277–280, Materials Science and Engineering: C, 62 (2016) 450–457].
Formation of personalized implants with an individual form for each patient is a new step in the development of biomedicine. The ability to model implants of any shape and size, the functionality of the components and properties, price ratio in the production of single or small series of products, all of these advantages belong additive technology (AT), or more commonly known as the technology of 3-D printing.
In our work, we use a method of electron-beam melting which is one of the most advanced among the three-dimensional printing technology. It includes the distribution of the working material layer-by-layer and its melting under the influence of the electron beam. Metal implants prepared in this way can also successfully “to repeat” complex microstructure of bone, which improves the integration process of the implant and its long-term stability in the body.
In this case titanium alloy, Ti6Al4V powder is working material for electron beam melting because it is widely used in biomedicine for hard tissue replacement of dysfunctional due to high strength, light weight, good biocompatibility and corrosion resistance. However, we aim to create an even more improved biocompatibility of the surface by deposition of bioactive calcium phosphate coatings and antimicrobial silver nanoparticles. These modification methods already have proved themselves in the field of plasma technology and colloid chemistry.
To date, we carry out experimental and theoretical studies of the properties of the modified surfaces, including research of the wettability mechanisms biocomposites, the influence of the porosity and chemical composition of the surface on hysteresis, surface energy, the impact of the structure, chemical, phase composition and roughness parameters on the physical and mechanical properties (micro-hardness, Young's modulus) of the biocomposites.