Influence of silicon, strontium and aluminum oxides on silicon nitride ceramics for bone replacements

ABSTRACT Although silicon nitride ceramics have been shown very propitious to be used for bone replacements, some characteristics can be controlled to improve their osseointegrations process. One of them is the intergranular phase whose composition can be specified to stimulate mineralization and osteoblastic production. In this paper, the intergranular glassy phase was projected in order to contain silicon, strontium and aluminum oxides. Silicon nitride samples containing different contents of SiO2, SrO and Al2O3 were sintered at 1815oC for 1 hour and characterized by scanning electron microscopy and X-ray diffraction. Hardness and fracture toughness were determined by Vickers hardness test and compressive strength was evaluated using an universal material testing machine. The biological behavior was studied in regard to cytotoxicity and cell proliferation by means of in vitro experiments. The samples reached high densities (higher than 95 %TD), total α→β-Si3N4 transformation, fracture toughness higher than 6.5 MPa.m1/2, compressive strength up to 2500 MPa and Vickers hardness less than 9.8 GPa. All samples were non-cytotoxic and able to promote cell proliferation with great potential to be used as components for bone replacements. However, that sample with high content of strontium had the best results of cell proliferation, proving the importance of a careful choice of intergranular phase composition in silicon nitride ceramics.

摘要：尽管氮化硅陶瓷已被证实极具应用于骨置换假体的潜力，但可通过调控其部分特性以优化骨整合（osseointegration）过程。其中关键之一为晶界相（intergranular phase），其组成可被定制以刺激矿化进程与成骨细胞生成。本文设计了包含硅、锶及铝氧化物的晶界玻璃相。将不同含量二氧化硅（SiO₂）、氧化锶（SrO）与三氧化二铝（Al₂O₃）的氮化硅试样在1815℃下烧结1小时，随后采用扫描电子显微镜（scanning electron microscopy）与X射线衍射（X-ray diffraction）对试样进行表征。通过维氏硬度试验测定了试样的硬度与断裂韧性，利用万能材料试验机评估其抗压强度；并通过体外实验研究了试样的细胞毒性与细胞增殖相关的生物学行为。结果表明，所有试样均实现高致密度（高于95%理论密度）与完全的α相→β相氮化硅（Si₃N₄）相变，断裂韧性高于6.5 MPa·m^(1/2)，抗压强度可达2500 MPa，维氏硬度低于9.8 GPa。所有试样均无细胞毒性，且可促进细胞增殖，具备用作骨置换假体组件的巨大潜力。其中，高锶含量试样的细胞增殖效果最优，证明了在氮化硅陶瓷中谨慎选择晶界相组成的重要性。