Recombinant IGF-1 Induces Sex-Specific Changes in Bone Composition and Remodeling in Adult Mice with Pappa2 Deficiency

Deficiency of pregnancy-associated plasma protein-A2 (PAPP-A2), an IGF-1 availability regulator, causes postnatal growth failure and dysregulation of bone size and density. The present study aimed to determine the effects of recombinant murine IGF-1 (rmIGF-1) on bone composition and remodeling in constitutive Pappa2 knock-out (ko/ko) mice. To address this challenge, X-ray diffraction (XRD), attenuated total reflection-fourier transform infra-red (ATR-FTIR) spectroscopy and gene expression analysis of members of the IGF-1 system and bone resorption/formation were performed. Pappa2^ko/ko mice (both sexes) had reduced body and bone length. Male Pappa2^ko/ko mice had specific alterations in bone composition (mineral-to-matrix ratio, carbonate substitution and mineral crystallinity), but not in bone remodeling. In contrast, decreases in collagen maturity and increases in Igfbp3, osteopontin (resorption) and osteocalcin (formation) characterized the bone of Pappa2^ko/ko females. A single rmIGF-1 administration (0.3 mg/kg) induced short-term changes in bone composition in Pappa2^ko/ko mice (both sexes). rmIGF-1 treatment in Pappa2^ko/ko females also increased collagen maturity, and Igfbp3, Igfbp5, Col1a1 and osteopontin expression. In summary, acute IGF-1 treatment modifies bone composition and local IGF-1 response to bone remodeling in mice with Pappa2 deficiency. These effects depend on sex and provide important insights into potential IGF-1 therapy for growth failure and bone loss and repair.     

Resistance of pure and mixed rare earth silicates against calcium-magnesium-aluminosilicate (CMAS): A comparative study

Rare earth silicate environmental barrier coatings (EBCs) are state of the art for protecting SiC ceramic matrix composites (CMCs) against corrosive media. The interaction of four pure rare earth silicate EBC materials Yb₂SiO₅, Yb₂Si₂O₇, Y₂SiO₅, Y₂Si₂O₇ and three ytterbium silicate mixtures with molten calcium-magnesium-aluminosilicate (CMAS) were studied at high temperature (1400°C). The samples were characterized by SEM and XRD in order to evaluate the recession of the different materials after a reaction time of 8 hours. Additionally, the coefficient of thermal expansion (CTE) was determined to evaluate the suitability of Yb silicate mixtures as EBC materials for SiC CMCs. Results show that monosilicates exhibit a lower recession in contact with CMAS than their disilicate counterparts. The recession of the ytterbium silicates is far lower than the recession of the yttrium silicates under CMAS attack. Investigation of the ytterbium silicate mixtures exposes their superior resistance to CMAS, which is even higher than the resistance of the pure monosilicate. Also their decreased CTE suggests they will display better performance than the pure monosilicate.     

Apatite Formation on Calcium Phosphate Invert Glasses in Simulated Body Fluid

Calcium phosphate invert glasses, which contain P₂O₇²⁻ and PO₄³⁻ ions, have been prepared via the addition of a small amount of TiO₂. The formation of bonelike calcium phosphate apatite on the surface of the phosphate invert glasses was examined in simulated body fluid (SBF) at a temperature of 37°C. Soaking for 20 d resulted in the deposition of leaflike apatite particles on 6CaO·3P₂O₅·TiO₂ invert glass (based on molar ratio). The glass had much-greater chemical durability against SBF, in comparison with a metaphosphate glass; P ions were not dissolved excessively from the 6CaO·3P₂O₅·TiO₂ glass, so the apatite formation was not suppressed.     

仿生合成制备磷灰石涂层的工艺研究进展

采用仿生合成工艺制备磷灰石类涂层是近年来制备生物陶瓷涂层发展的新动向。在此工艺过程中,预处理工艺对基体表面的活化效果直接决定基体表面诱导钙、磷离子异相形核和沉积的能力,而模拟体液的成分、浓度、pH值和流动状态等因素会影响所形成的钙磷涂层的相组成、结晶度和生长速度等。因此,预处理和模拟体液对钙磷涂层的形成极为关键。文中着重介绍了对这2个主要影响因素研究的最新进展。     

微纳米生物活性玻璃诱导牙本质再矿化研究

封闭牙本质小管能有效减轻牙齿过敏症。本研究以不同粒径的微纳米生物活性玻璃球(MNBGs)为分散质、海藻酸钠-磷酸盐缓冲溶液为分散液, 制备了用于牙本质脱敏治疗的MNBGs糊剂(MNBGP)。在牙本质切片表面进行体外矿化并系统评价了糊剂与牙本质的结合性能, 以及糊剂体外诱导牙本质再矿化、封闭牙本质小管的能力。研究结果表明, 不同粒径MNBGs制备的糊剂均能与牙本质界面紧密结合, 粒径较小的MNBGs在脱矿牙本质切片表面分布更加均匀。MNBGP在人工唾液(AS)中能较好地诱导牙本质再矿化形成磷灰石(HA)以堵塞封闭牙本质小管, 脱矿牙本质切片表面形成的HA 层随矿化时间延长而增厚, 矿化28 d HA层的厚度可达到5~10 μm。MNBGs的尺寸影响其诱导牙本质再矿化的效果, 当颗粒大小与牙本质小管直径匹配时, MNBGs可以更好地封闭牙本质小管。因此, MNBGP具有良好的治疗牙本质过敏的应用前景。     

Chemical etching of micro-plasma oxidized titania film on titanium alloy and apatite deposited on the surface of modified titania film in vitro

TiO₂ film was deposited on titanium alloy by micro-plasma oxidization (MPO) in an electrolyte containing (NaPO₃)₆ and NaOH. A chemical etching (NaOH aqueous solution) was used to modify the surface of the MPO film to form specific surface structure favorable for apatite deposition. The surface of the MPO film was mainly composed of anatase, while that of the chemically etched MPO (CE-MPO) film shows anatase phase containing Na, Ti and O. Moreover, ribbon-like products with an interlaced morphology were found on the surface of the CE-MPO film. During the chemical etching process, phosphorus of the surface of the MPO film dissolved into the NaOH aqueous solution. Negatively charged HTiO₃⁻ ions are formed on the MPO film surface due to the attack of OH⁻ ions on TiO₂ phase of the MPO film. The negatively charged HTiO₃⁻ ions could incorporate sodium ions from the NaOH aqueous solution to form sodium titanate. When incubated in a simulated body fluid (SBF) for 7 and 14 days, the MPO film does not exhibit apatite-forming ability; however, apatite was deposited on the CE-MPO film probably due to the formation of hydroxyl functionalized surface via an ionic exchange between Na⁺ ions of the CE-MPO film and H₃O⁺ ions of the SBF.     

Biomimetic Precipitation of Uniaxially Grown Calcium Phosphate Crystals from Full-Length Human Amelogenin Sols

Human dental enamel forms over a period of 2 - 4 years by substituting the enamel matrix, a protein gel mostly composed of a single protein, amelogenin with fibrous apatite nanocrystals. Self-assembly of a dense amelogenin matrix is presumed to direct the growth of apatite fibers and their organization into bundles that eventually comprise the mature enamel, the hardest tissue in the mammalian body. This work aims to establish the physicochemical and biochemical conditions for the synthesis of fibrous apatite crystals under the control of a recombinant full-length human amelogenin matrix in combination with a programmable titration system. The growth of apatite substrates was initiated from supersaturated calcium phosphate solutions in the presence of dispersed amelogenin assemblies. It was shown earlier and confirmed in this study that binding of amelogenin onto apatite surfaces presents the first step that leads to substrate-specific crystal growth. In this work, we report enhanced nucleation and growth under conditions at which amelogenin and apatite carry opposite charges and adsorption of the protein onto the apatite seeds is even more favored. Experiments at pH below the isoelectric point of amelogenin showed increased protein binding to apatite and at low Ca/P molar ratios resulted in a change in crystal morphology from plate-like to fibrous and rod-shaped. Concentrations of calcium and phosphate ions in the supernatant did not show drastic decreases throughout the titration period, indicating controlled precipitation from the protein suspension metastable with respect to calcium phosphate. It is argued that ameloblasts in the developing enamel may vary the density of the protein matrix at the nano scale by varying local pH, and thus control the interaction between the mineral and protein phases. The biomimetic experimental setting applied in this study has thus proven as convenient for gaining insight into the fundamental nature of the process of amelogenesis.     

磷灰石包覆金红石型TiO2纳米粉体的制备及表征

将金红石型TiO₂纳米粉体浸泡在模拟体液中, 于37℃经过不同时间, 制备出磷灰石包覆金红石型TiO₂纳米粉体. 用XRD、SEM、TEM、EDX、FTIR、ICPAES和BET方法对复合粉体进行了表征, XRD结果表明,磷灰石的含量可随着金红石型TiO2在模拟体液中浸泡时间的延长而增加. FTIR结果中显示了磷灰石的O-H和PO₄^3-吸收峰, 说明复合粉体中有磷灰石存在. ICP-AES结果表明溶液中Ca和P浓度随浸泡时间延长而下降, 表明时间延长后更多的Ca和P被消耗. TEM和EDX结果证明了金红石型TiO₂表面有磷灰石存在, HRTEM结果显示磷灰石（211）面的晶格间距为0.27nm, 晶粒尺寸约为40nm.     

纳米类骨磷灰石晶体合成

采用硝酸钙和磷酸钠水溶液以不同滴定顺序,于70℃下合成了纳米羟基磷灰石(n-HA)沉积物.结果表明,不同的滴定顺序得到的产物都是n-HA晶体,合成的n-HA具有与骨磷灰石晶体十分类似的组成成分、尺寸、结晶度和形貌,因此,合成的n-HA可称为类骨磷灰石晶体.考察了不同滴定顺序对n-HA形貌、结晶度和尺寸的影响;发现相同温度下,磷酸钠滴定硝酸钙得到的磷灰石呈现相对规整的针状晶体,结晶度高,杂质离子少.     

钛金属低温生物活化

利用含微量TaCl5的双氧水溶液在低于100℃温度下与钛金属之间的化学反应,在钛金属表面直接生成具有良好生物活性的锐钛矿与金红石混合结构晶态二氧化钛薄膜.研究了双氧水浓度和处理温度的影响.结果表明,80℃下,双氧水浓度大于6wt.%时即可在钛金属表面获得具有良好生物活性的晶态二氧化钛薄膜,进一步增加双氧水浓度直到30wt.%对结果没有明显的影响.处理温度强烈影响钛金属表面的产物及其在模拟体液中诱导沉积羟基磷灰石的能力.