Enhanced sinterability and in vitro bioactivity of barium-doped akermanite ceramic

This paper reports on the influence of substituting barium (Ba²⁺) ions on the structural, mechanical and in vitro biological properties of akermanite prepared via high-energy wet planetary ball milling and sintering. The results obtained showed that the properties of the prepared bioceramics are highly dependent on Ba²⁺ content. It was found that Ba²⁺ resulted in improved densification (≥90%), and better apatite-forming ability of akermanite ceramic, without altering phase composition. Herein, the enhancement in diametral tensile strength (DTS), Vickers microhardness (H_V) and fracture toughness (K_IC) for Ba²⁺-doped akermanite bioceramics are reported for the first time. It was also found that after 21 days of immersion in simulated body fluid (SBF) solution, the doped ceramic surface was completely covered with apatite crystals, indicating Ba²⁺ encouraged apatite crystals deposition. Therefore, Ba²⁺-doped akermanite bioceramic could be an attractive alternative bioresorbable material for bone tissue engineering applications.     

晶化温度对不锈钢渣微晶玻璃析晶及性能影响

利用不锈钢渣制备微晶玻璃实现了废弃资源的二次利用.本文以不锈钢渣、尾矿及废玻璃为原料,采用熔融法制备主晶相为镁黄长石相的微晶玻璃.利用DSC、XRD、SEM等测试分析手段研究晶化温度对微晶玻璃晶相、微观组织和性能的影响.结果表明:在800 ～ 920℃范围内,随晶化温度升高,主晶相镁黄长石XRD衍射峰强度不断升高,在850℃出现透辉石相;微晶玻璃晶粒由球形颗粒变为针叶状,最后成网络结构;在晶化温度850℃时性能达到较优,显微硬度最大值为6.55 GPa,密度最大值为3.02 g/cm3,吸水率最小值为0.09％.     

溶胶-凝胶法与两步沉淀法制备的镁黄长石粉体的体外生物活性比较

通过溶胶-凝胶法和两步沉淀法分别合成镁黄长石(Ca2MgSi2O7)粉体,并通过模拟体液浸泡对这两种方法合成的镁黄长石的体外生物活性进行比较。用X射线衍射、扫描电镜、原子发射光谱(ICP-AES)以及pH计分别对浸泡后形成的羟基磷灰石的物相、形貌以及浸泡后模拟体液的离子浓度变化、pH值进行表征。结果表明：两步沉淀法合成的镁黄长石在浸泡5d后就能明显检测到羟基磷灰石生成,而溶胶-凝胶法合成的镁黄长石在浸泡7d后才能检测到羟基磷灰石生成;两步沉淀法合成的镁黄长石诱导的羟基磷灰石呈结晶较好的虫状结构,而溶胶-凝胶法合成的镁黄长石诱导的羟基磷灰石呈结晶不完整的圆形颗粒结构;而且,两步沉淀法合成的镁黄长石具有更快的Ca离子释放能力。因此,两步沉淀法合成的镁黄长石相对于溶胶-凝胶法合成的镁黄长石具有更好的诱导羟基磷灰石形成能力和生物活性。     

SPS烧结制备生物活性镁黄长石陶瓷

钙硅基生物陶瓷具有良好的生物活性和细胞相容性, 在生物医疗领域具有广阔的发展前景。但是其粉体烧结性能差的缺点导致很难获得致密的陶瓷材料, 阻碍了其应用的进程。本研究采用化学共沉淀法制备了纯度高且烧结活性好的镁黄长石粉体, 然后采用放电等离子烧结技术(SPS)制备了镁黄长石陶瓷材料。通过X射线衍射(XRD)和扫描电子显微镜(SEM)表征了样品的组成结构和显微形貌, 并通过阿基米德法和模拟体液浸泡法分析了镁黄长石陶瓷样品的致密度和生物活性。研究结果表明, 采用SPS技术在1170℃、70 MPa保温5 min条件下可获得致密度超过99%的镁黄长石陶瓷材料。在模拟体液中浸泡3 d, 陶瓷样品表面出现磷酸盐的沉积, 浸泡7 d后生成了类骨羟基磷灰石, 说明SPS技术制备的致密镁黄长石生物陶瓷具有良好的诱导沉积类骨磷灰石能力。     

准东煤灰中的钙镁黄长石生成机理研究

借助管式炉实验台在不同温度下研究了燃烧天池南矿、五彩湾、宜化三种典型准东煤过程中煤灰矿物质的形成机理,并利用XRD手段分析矿物质组成,结果表明：1100℃时有大量钙镁黄长石生成,是1100℃下煤灰中的重要矿物质;钙镁黄长石生成路径的第一步是形成硅灰石,然后再与氧化镁反应形成钙镁黄长石。基于实验结果,采用密度泛函理论在B3LYP/6-311G++（d,p）水平上对钙镁黄长石的生成路径进行研究,并进行动力学分析。结果表明,硅灰石的形成过程中路径2更容易进行,且该反应的决速性步骤是CaO与SiO₂相连成键后,SiO₂上的O原子转移步骤;之后,CaSiO₃进行无势垒络合,形成2CaSiO₃后再与MgO发生反应,最终形成Ca₂MgSi₂O₇,该反应中的最大势垒出现在2CaSiO₃与MgO相连成键后各原子的转动过程中。     

Recent advances on akermanite calcium-silicate ceramic for biomedical applications

Owing to great biocompatibility and high capacity of apatite formation, bioceramics, especially calcium silicate-based compounds, were extensively employed in orthopedic and dental uses concerning biomedical applications. Lately, akermanite (AK; Ca₂MgSi₂O₇), as a bioceramic containing Ca-, Mg- and Si, has gained an increased level of attention because of its more tunable mechanical characteristics and degradation rate. All studies indicate that this magnesium incorporating Ca-silicate ceramic has a great capacity to use as a bone graft material to fulfill the necessity of bone reconstruction. Despite the rising interest in using these materials in biomedical fields, there has not yet been an extensive overview of this bioceramic property and its potential benefits. Thus, it has been speculated that this concept and the emergence of akermanite bioactive ceramics might lead to significant upcoming advancements in the field of bone tissue engineering (BTE). Definitely, the approach still requires additional advances to considerably better respond to the vital concerns regarding the clinical application. The review tackles the present research trends on akermanite ceramics for biomedical purposes such as bone scaffold, coating materials, bone cement, and treatment of osteoporotic bone defects, commencing with recent status and shifting to upcoming developments.     

Sensing of toxic metals through pH changes using a hybrid sorbent material: Concept and experimental validation

This article reports a new hybrid sorbent material that is capable of detecting trace concentration of toxic metals, such as zinc, lead, copper, nickel, etc., through pH changes only. The material is essentially a composite granular material synthesized through rapid fusion of a mixture of amorphous hydrated ferric oxide (HFO) and akermanite or calcium magnesium silicate (Ca₂MgSi₂O₇). When a water sample is rapidly passed through a mini‐column containing this hybrid material, effluent pH at the exit always remains alkaline (≈9.0) because of slow hydrolysis of akermanite and steady release of hydroxyl (OH^?) ions. This exit solution turns pink through the addition of a phenolphthalein indicator. Commonly encountered electrolytes containing sodium, calcium, chloride, and sulfate have no impact on the exit pH from the mini‐column. However, when trace concentration of a heavy metal (say lead) is present in the sample water, a considerable drop in pH (>2 units) is observed for the exiting solution. At this point, the solution turns colorless through the addition of a phenolphthalein indicator. Moreover, the change in the slope of pH, i.e., ?dpH/dBV, provides a sharp, noticeable peak for each toxic metal where BV is the bed volumes of solution fed. The technique allowed detection of zinc and lead through pH swings in synthesized samples, spiked Bethlehem City water, and also in Lehigh River water in the presence of phosphate and natural organic matter (NOM). Using a simple preconcentration technique, lower than 10 μg/l of lead was detected with a significant peak. From a mechanistic viewpoint, high sorption affinity of HFO surface sites toward toxic metal cations, ability of akermanite to maintain near‐constant alkaline pH for a prolonged period through slow hydrolysis and labile metal‐hydroxy complex formation causing dissipation of OH^? ions from the aqueous phase provide a synergy that allows detection of toxic metals at concentrations well below 100 μg/l through pH changes. Nearly all previous investigations pertaining to toxic metals sensing use metal‐selective enzymes or organic chromophores. This simple‐to‐operate technique using an inexpensive hybrid material may find widespread applications in the developing world for rapid detection of toxic metals through pH changes. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

真空和大气等离子喷涂镁黄长石生物活性涂层的对比研究

大气喷涂法制备的镁黄长石涂层是一种具有优良生物活性的新型骨科移植体涂层材料, 但其结晶度较低, 影响涂层的化学稳定性。本研究采用真空等离子喷涂法在钛合金表面制备了高结晶度的镁黄长石涂层。与大气喷涂镁黄长石涂层相比, 真空喷涂镁黄长石涂层具有更高的磷灰石矿化能力, 在SBF中浸泡6 d后表面即沉积了一层类骨磷灰石层, 浸泡14 d后表面沉积的磷灰石层的厚度约为大气涂层的4倍。真空喷涂镁黄长石涂层的离子释放明显低于大气涂层, 显示出更高的化学稳定性。骨髓间充质干细胞在真空和大气喷涂镁黄长石涂层表面粘附和铺展良好, 在两种涂层表面的增殖速度均明显高于HA涂层。本研究表明真空等离子喷涂的镁黄长石陶瓷涂层因其显著提高的生物活性及化学稳定性, 可能更适合用作人工关节涂层材料。     

Upconversion luminescence Ca--Mg--Si bioactive glasses synthesized using the containerless processing technique

In this study, a series of Er³⁺/Yb³⁺ co-doped Ca--Mg--Si glasses were prepared via the containerless processing. Phase composition and luminescent properties of the prepared materials were investigated through XRD and spectrometry, and bioactivity, biocompatibility and cytotoxicity were evaluated. The XRD patterns indicated that akermanite (AKT) ceramic powders were completely transformed into the glassy phase (AKT-G, EYA) through the containerless processing, which exhibit upconversion luminescence, and the luminescence intensity increased with the increase of the doping amount of Er³⁺ and Yb³⁺. High amount of Yb³⁺ doping and existence of Ca²⁺ in glasses resulted in more intensive red-light emission. The SEM observation, combined with EDS analysis, and cell culture experiments showed that the as-prepared glasses were nontoxic, biocompatible and bioactive. All these results demonstrated that the contai-nerless processing is a facile method for preparing homogeneous luminescent bioactive glasses. Furthermore, this luminescent Ca--Mg--Si glasses may be used as bone implant materials to study the in vivo distribution of degradation products of bone implants, which may be of great significance for the development and clinical application of new bone grafting materials.