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适用于骨置换假体，但可通过调控其部分特性以优化骨整合(osseointegration)过程。其中核心调控靶点之一为晶界相(intergranular phase)，通过精准设计其组成可刺激矿化(mineralization)过程与成骨细胞生成(osteoblastic production)。本文设计了含硅、锶及铝氧化物的晶界玻璃相(intergranular glassy phase)，制备了掺杂不同含量二氧化硅(SiO₂)、氧化锶(SrO)及三氧化二铝(Al₂O₃)的氮化硅陶瓷试样，并于1815℃下烧结1小时。采用扫描电子显微镜(Scanning Electron Microscopy, SEM)与X射线衍射(X-ray Diffraction, XRD)对试样进行表征；通过维氏硬度试验(Vickers hardness test)测定其硬度与断裂韧性(fracture toughness)，借助万能材料试验机(universal material testing machine)评估抗压强度(compressive strength)；通过体外(in vitro)实验研究了试样的细胞毒性(cytotoxicity)与细胞增殖(cell proliferation)等生物学性能。结果表明，所得试样均具备高致密度（高于95%理论密度(Theoretical Density, TD)），实现了α相到β相氮化硅的完全转变，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应用潜力。但其中锶含量较高的试样展现出最优的细胞增殖效果，证实了精准调控氮化硅陶瓷晶界相组成的重要性。