Oxide ceramic materials like alumina (Al(2)O(3)) and zirconia (ZrO(2)) are frequently used for medical applications like implants and prostheses because of their excellent biocompatibility and high wear resistance. Unfortunately, oxide ceramics cannot be used for minimal invasive thin-walled implants like resurfacing hip prostheses because of their limited strength. The hypothesis of this study is that non-oxide ceramics like silicon nitride (Si(3)N(4)) and silicon carbide (SiC)-not previously used in the medical field-are not only high strength and mechanically reliable ceramic materials due to their high amount of covalent bonds, but also exhibit a suitable biocompatibility for use as medical implants and prostheses. Mechanical investigations and cell culture tests with mouse fibroblast cells (L929) and human mesenchymal stem cells (hMSC) were performed on the ceramics. An excellent cytocompatibility was demonstrated by live/dead stainings for both L929 cells and hMSC. HMSC were able to differentiate towards osteoblasts on all tested ceramics. The determined strength of silicon nitride and silicon carbide was shown as significantly higher than that of oxide ceramics. Our results indicate that the high strength non-oxide ceramics are material candidates in the future especially for highly loaded, thin-walled implants like ceramic resurfacing hip prostheses.
The aim of this study was to reveal the feasibility of adjusting aqueous nonoxide ceramic inks for producing complex-shaped functional ceramic parts by direct inkjet printing using the example of silicon nitride (Si 3 N 4 ) and molybdenum disilicide (MoSi 2 ). In a first step, aqueous Si 3 N 4 and MoSi 2 suspensions with high solid contents were prepared by the addition of organic and inorganic additives to meet the requirements regarding rheological properties of the printing system. For this purpose, viscosity, zeta potential, and surface tension were adjusted. Because of the physical conditions of the printing head, the particle size distribution of the suspensions was optimized. The experiments were verified by calculating the Ohnesorge number of suspensions. The results show that the values fit well into the required range. Printing of 3D-components and Si 3 N 4 /MoSi 2 multilayers was carried out. Optimal performance and control of the printing process resulted in fabrication of homogeneous green bodies without delaminations or other process-dependent defects.
Although ceramic prostheses have been successfully used in conventional total hip arthroplasty (THA) for many decades, ceramic materials have not yet been applied for hip resurfacing (HR) surgeries. The objective of this study is to investigate the mechanical reliability of silicon nitride as a new ceramic material in HR prostheses. A finite element analysis (FEA) was performed to study the effects of two different designs of prostheses on the stress distribution in the femur-neck area. A metallic (cobalt-chromium-alloy) Birmingham hip resurfacing (BHR) prosthesis and our newly designed ceramic (silicon nitride) HR prosthesis were hereby compared. The stresses induced by physiologically loading the femur bone with an implant were calculated and compared with the corresponding stresses for the healthy, intact femur bone. Here, we found stress distributions in the femur bone with the implanted silicon nitride HR prosthesis which were similar to those of healthy, intact femur bone. The lifetime predictions showed that silicon nitride is indeed mechanically reliable and, thus, is ideal for HR prostheses. Moreover, we conclude that the FEA and corresponded post-processing can help us to evaluate a new ceramic material and a specific new implant design with respect to the mechanical reliability before clinical application.
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