Bioceramics for Bone and Joint Repair

Resume : Implants used in dentistry and surgery for bone repair have complex and varied shapes. Often, these implants should have the original form for a particular patient. For production of such implants we suggest to use powder technology of isostatic pressing in thermoplastic molds at elevated temperature. Moulds made of thermoplastic materials are well keep their shape under normal conditions. When heated, they melt into the plastic state and ensure the quality of the isostatic process. As a result, the shape of compacts may be as close as possible to the shape of the finished articles. Thermoplastic molds are manufactured using 3D-printing. Forms of molds can be designed according the patient's imaging data. This manufacturing method has the advantage that the isostatic pressing and 3D-printing of plastic materials are well-known technologies. Application of 3D-printing allowed to accelerate the production of thermoplastic molds and reduce their costs. The technology has been tested in the manufacture of surgical implants (plates and screws) and parts of surgical instruments (drills and screwdriver) made from partially stabilized zirconia ceramics. Also, it is possible to use this method for manufacturing compacts from metal powders. Compacts of cermet with a composition of 80% Ti + 20% hydroxyapatite were prepared. Some of advantages and problems inherent to the method are revealed and discussed.

Resume : The easiest method to obtain a coating on a porous titanium implant with interconnected pores of diameter bellow 400 µm is electrodeposition were titanium acts as a cathode. In the present work, how addition of the COOH functionalized carbon nanotubes,CNTs, to the electrolytic solution influences on the morphology and chemical composition of the created composite (Ca-P-CNTs) coatings is investigated. Furthermore, influence of a heat-treatment on the coatings crystallinity is shown. Cells interaction with new coatings is also evaluated. The Ca-P-CNTs coatings were successfully fabricated on the porous titanium scaffolds made by Selective Laser Melting (SLM). The calcium and phosphorous ions molarity in the electrolytic solution had a critical influence on the calcium-phosphate ceramic presented in the coating. Microscopic observations showed that higher calcium and phosphorous molarity facilitates brushite formation, while lower molarity results in hydroxyapatite. CNTs dispersed in the electrolyte had improved ionic transport in the solution hence coatings thickness. The X-ray diffraction results indicated that heat-treatment in temperatures below 700 ˚C did not cause CNTs degradation while it improved hydroxyapatite crystallinity. Summarizing, a very promising method for fabrication of the novel composite calcium-phosphate ceramic coating reinforced with CNTs was developed to improve bioactivity of porous titanium implants.

Resume : In the frame of the European Project Longlife (7th Framework Program), innovative zirconia-based nanocomposites materials have been designed and developed with the aim of fulfill the clinical requirements for strong, tough and stable ceramics used for dental applications. Ceria-stabilized zirconia (Ce-TZP) was selected as composite matrix in order to improve phase stability, while both equiaxial α-Al2O3 and elongated SrAl12O19 particles were selected as second phases in order to improve strength, hardness and toughness simultaneously. Furthermore, in order to obtain high transformability, the ceria content in the composite materials was carefully tailored: four different ceria contents (in the range 10.0-11.5 mol%) were investigated. As assessed by SEM and TEM analyses, a perfect tailoring of all the compositional and microstructural features in the developed materials was successfully obtained by applying a new nano-powder engineering approach. Precisely, the composite powders were produced by a simple but reliable surface coating process, in which zirconia powders were coated by inorganic precursors (nitrates aqueous solutions) of the second phases, which crystallize on the zirconia particles surface under proper thermal treatment. Composite materials were obtained by sintering slip cast bodies at 1450°C for 1 h. Mechanical properties were evaluated in terms of Vickers Hardness, flexural strength and fracture toughness revealing a strong influence of the ceria amount on the mechanical behavior: materials having 10.5 mol% of ceria showed the best results with σf of about 900 MPa and KIC above 10 MPa√m. Accelerated hydrothermal tests revealed stable materials in the time scale of biomedical applications when the ceria amount was above 10 mol%.