Composite bio-compatible material on the basis of titanium alloys and vitreous carbon coating intended for endoprosthesis

The Bulgarian research unit conducts R&D in metal science, specialised coatings, heat treatment, casting, crystallisation, structure and properties of metals, alloys and composites and nano-materials, plasticity modelling, destruction of materials, etc. They have excellent experience in international collaboration and project implementation. Titanium alloys are the basis for the production of endo-prostheses as titanium is a bio-compatible material for the human body. After a stay in the human body it is possible that part of the Al and V present in the titanium alloy can be partially ionized and corrosion and loosening of the bond between the titanium implant and the human bone may occur. Deposition of layer of vitreous (nascent) carbon, which is also proven to be bio compatible, on the titanium matrix neutralises the biochemical corrosion. The fabrication of the hip joint or other endo-prosthesis can be made by traditional metal working of titanium. On the other hand, additive manufacturing may be used to prepare implant for each individual case. The 3-D printer with titanium powder will follow the shape and the dimensions of the damaged organ to produce an individual implant. The different use of the implant needs different surface smoothness, e.g. the stem of the hip joint prosthesis is preferred to be more rough for better intergrowth with the bone whilst the femoral head must be polished to decrease the friction with the acetabular shell and polyethylene insert. The surface roughness is achieved by plasma spraying of titanium particles and the smoothness – by mechanical polishing. The glassy carbon coating is prepared by applying a solution of heat treated long chain organic substance on the surface of the titanium sample. Then the item is dried and heat treated. In order to improve the adhesion of the vitreous carbon layer the heat treatment was performed at 1350 – 1400 degrees Celsius in inert environment. Titanium carbide was created during this heat treatment which is an intermediary layer between the titanium substrate and the vitreous carbon coating. In order to have better layer this procedure is repeated several times. After the heat treatment only carbon in vitreous (glassy) state remains on the surface. It has amorphous structure and its hardness is that of normal silicate glass (7 by Mohs scale). Since the coating is only carbon it is at least or even more bio-compatible than the titanium and titanium alloys. The institute is looking for industrial and research partners for technical cooperation agreements and research cooperation agreements in order to further develop the technology and adapt it to the specific needs.