In one direction our research group study the fundamental principles of RF-magnetron sputter deposition of calcium phosphate coating as an approach to enhance biocompatibility of metallic and polymer materials applied in regenerative medicine.
Due to the current trend of the population ageing the development of biomaterials for tissues regeneration plays a major role in the field of medical material science. Nowadays, the doctor should have a number of implant systems at his disposal allowing to choose the device for individual patient’s needs to solve any even the most difficult clinical problems. To achieve the favorable implant interaction with the living body the specified interface properties of devices should be created.
As it is considered the interaction between the implant and organism occurs by the aggression path. Human body interprets implant as a foreign substance and tries to get rid of it. The interaction between the cells and tissues with the biomaterials is strongly defined by the tissue-implant interface. The surface properties determine both the biological response to the implants and the material response to the physiological environment. Hence, surface engineering of biomaterials is aimed at modifying the material properties through changes in surface properties meanwhile maintaining the bulk properties of the implant. The application of a biocompatible coating to the implant is a well-documented strategy. Biocompatible coatings must be free from toxic substances, do not cause negative immune reactions, don’t degrade (or degrade in a predictable manner) in contact with living tissues, and show a high adhesion to the implant. Calcium-phosphates are proved to be a natural metabolite of bone. In the field of medical material science, there are numerous studies devoted to increasing of the biocompatibility and osteoinduction of metal implants using calcium phosphate coatings (CaP). Hydroxyapatite (HA, Ca10(PO4)6(OH)2) – is a typical example belonging to the family of CaP materials. As this material defines the bone matrix, it possesses a high biocompatibility.
Radio frequency (RF) magnetron sputtering method is used to obtain the functionally-graded HA thin films. Magnetron sputter deposition is a very attractive method due to the high adherence of the coating to the substrate material, the thickness uniformity of the deposited layer, and the ability to control the coating structure (amorphous or crystalline) and the Ca/P ratio by varying process conditions. Method allows to deposit coatings with predetermined features and to improve the performance of medical implants including devices with complex geometries. In order to develop coatings with additional functional properties there are some studies carried out in the direction of using the modified HA. In particular, we deal with HA material substituted with silver to obtain antibacterial effect and silicate ions to increase coating bioactivity.
Currently, there is no reliable information on the growth mechanisms of CaP based coatings during RF-magnetron sputter deposition. Generally, researchers focus only on the controlling of process parameters to optimize the coating properties in connection with biological studies without investigation of the fundamental aspects of the film growth. This fundamental understanding is the key approach for further technological improvements. This makes it necessary a detailed description of the different processes occurring at the substrate level and an in-depth characterization of the thin film properties. Only the combination of both thin film and plasma characterisation allows to elucidate the growth mechanisms.
Hence, the main objective is the investigation of the fundamental aspects of the deposition of HA coatings by means of RF-magnetron sputtering and the development of strategies to obtain coatings with tailored properties
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.
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].