CPP/α-TCP骨水泥复合材料研究

自固化磷酸钙骨水泥(CPC)作为一种新型人工骨替代材料，以其良好的生物相容性、骨传导性和可任意塑形，可广泛用于临床骨缺损修复．但其强度低、脆性大，不能用于负重部位，使其应用受到限制．本文利用纤维增强机理，用CPP／α-TCP骨水泥为基体材料，具有良好生物相容性的聚磷酸钙纤维(CPP)为增强材料制备出了CPP／α-TCP骨水泥复合材料．实验结果表明，CPP纤维在一定程度上可对骨水泥起到增强作用．SEM显示两者结合程度适中，在Ringer溶液中浸泡两个月后，纤维未发生明显降解作用，仍具有一定的增韧效果．     

MPC骨水泥纤维蛋白胶复合BMP人工骨支架材料对山羊松质骨缺损的修复

研制MPC/CPC骨水泥纤维蛋白胶复合BMP新型人工骨的制备及人工骨修复骨缺损的性能.通过对成年山羊双侧股骨髁部分别制备1处直径10mm、深15mm松质骨缺损,制备MPC/CPC/FG/BMP(A组)、MPC/CPC/FG(B组)、CPC/FG(C组)人工骨支架材料,分别植入各组实验观察材料,分别于6周、12周进行影像学、组织学、形态计量学观察骨缺损修复情况.说明新型MPC骨水泥纤维蛋白胶复合BMP新型生物活性人工骨支架材料在促进成骨、加快磷酸钙骨水泥降解速度上优于MPC/CPC/FG、CPC/FG的人工骨,同时新型MPC骨水泥复合纤维蛋白胶的成骨和促骨水泥降解作用优于单纯CPC复合FG的人工骨.     

水泥基复合材料中纤维和裂缝的几何关系及其模拟

基于裂缝和纤维随机分布于基体中这一理想假设,借助随机几何学和积分几何学的基本理论知识,分别从纤维和裂缝的角度探究了水泥基复合材料中乱向分布的裂缝和纤维之间的量化关系.建立了基体中纤维和裂缝的关系模型,包括多尺度纤维和单个圆盘状裂缝关系模型及单个纤维和多尺度圆盘状裂缝关系模型.结果表明,量化关系由其各自在水泥基复合材料中...     

纤维水泥石抗拉强度模型研究

为了将纤维水泥浆体系更好地应用于固井工程中,有必要对纤维改善水泥石强度机理进行研究并建立强度模型.利用岩石力学三轴实验机对纤维水泥石试块进行弹性模量测试,得到了纤维水泥石单轴应力-应变实验图.根据细观力学理论和能量守恒原理,在建立顺向分布纤维水泥抗拉强度模型的基础上得到了乱向分布纤维水泥的抗拉强度模型.模型分析结果表明,随着纤维掺量的增加,水泥石的抗拉强度有先增大后降低的趋势,这与实验室试验所得规律相同.     

纤维网片复合方式对纤维增强水泥基材料性能的影响

在分析渍浆纤维混凝土(SIFCON)和渍浆网片混凝土(SIMCON)各自优缺点的基础上，研究了不同性质乱向短纤维和定向纤维网片复合及不同性质网片组合方式对纤维增强混凝土性能的影响．实验结果表明：各种纤维体积分数下定向网片与乱向短纤维复合增强混凝土各项性能明显优于单用乱向短钢纤维增强混凝土；当纤维总体积分数为8％时，由2层细孔编织钢丝网和3层细孔玻纤网组合网片型式B(网片体积分数为0．7％)与乱向短纤维(体积分数为7．3％)复合增强混凝土，其抗弯强度、抗剪强度、弯曲韧性(I5)比短切钢纤维增强混凝土(SIFCON)分别提高了45％，25％和46％，从而揭示了高弹模与低弹模纤维复合、乱向纤维与定向纤维网复合，优化纤维分布和取向，使其在材料层次和结构层次协同作用的优势得以发挥，并以较低的成本和较方便的施工工艺制备了高性能纤维增强水泥基复合材料。     

自固化载硒纳米微球/磷酸钙复合骨修复材料的制备及性能

研究制备具有促修复、抗肿瘤的可注射缓释硒纳米微球复合磷酸钙骨水泥材料.采用乳化交联法制备Na_2SeO_3/CS缓释硒纳米微球,将微球与磷酸钙骨水泥(CPC)复合,制备Na_2SeO_3/CS/CPC骨修复系统,对该系统的固化时间、力学强度、缓释硒及降解性能、形貌、晶相构成进行测定和表征分析,并对其体外细胞活性进行研究.结果表明:相对于纯的CPC,当掺入Na_2SeO_3/CS纳米微球的量为4%时,复合CPC的注射性良好,固化时间5.75～11.5 min,固化强度提高,微观结构显示CPC均匀地包裹在壳聚糖微球表面并形成了针片状HA晶体,微球的添加对复合CPC材料的晶相组分无显著影响,缓释硒效应良好,有效缓释达22 d,降解性优于纯CPC,形成了蜂窝状完善的网状三维立体多孔结构,利于组织细胞和血管及神经的黏附长入.体外细胞实验表明,复合CPC对人乳腺癌细胞MCF-7及MG-63人骨肉瘤细胞增生的抑制作用显著,且对两株细胞增生的抑制性差异不显著.本研究为非承骨微创、缺陷修复及骨肿瘤的术后恢复、防止复发和转移的预防和治疗提供一种新思路,同时为拓展功能元素硒的合理应用奠定实验基础.     

纤维水泥稳定土的无侧限抗压强度试验研究

为进一步研究掺加聚丙烯纤维对水泥稳定土强度的影响,进行了纤维水泥稳定土的7d无侧限抗压强度试验.结果表明,水泥稳定土的无侧限抗压强度随着纤维掺量及纤维长度的改变而变化,纤维掺量对水泥稳定土7d无侧限抗压强度的影响大于纤维长度的影响,水泥稳定土中掺加纤维与否的破坏形态有明显区别,当水泥含量为10%、纤维掺量为1‰、纤维长度为12mm时,水泥稳定土的无侧限抗压强度增幅较大.工程应用中可优先考虑通过提高纤维掺量来有效提高水泥稳定土的无侧限抗压强度.     

多巴胺改性PCL纤维增强掺锶磷酸钙骨水泥的制备与表征

在掺锶磷酸钙骨水泥的基础上,利用多巴胺改性PCL纤维和未改性PCL纤维对其进行增强并表征。制备掺锶磷酸钙骨水泥样条,用多巴胺改性PCL纤维和未改性PCL纤维增强,制得骨水泥样条,对样条的凝固时间和力学性能等特征参数进行测定。结果显示,多巴胺改性纤维增强的骨水泥凝固时间更短,力学强度更高,在一定条件下改善了传统磷酸钙骨水泥的缺点。     

"劳氏曲线"的分析与修正建议

纤维在复合材料中的方向系数是描述纤维分布形态的重要参数,对纤维的增强、增韧与阻裂效应有着显著的影响.C.V.S.KameswaraRao在J.P.Romualdi的无限制纤维取向研究的基础上研究了边壁效应对二维乱向纤维方向系数的影响,并得出了有边壁存在时方向有效系数的分布曲线,即著名的"劳氏曲线";通过分析C.V.S.KameswaraRao的研究论文,指出了其中的失误;并对"劳氏曲线"作了修正建议.图5,参4.     

纤维水泥石抗拉强度模型研究

为了将纤维水泥浆体系更好地应用于固井工程中,有必要对纤维改善水泥石强度机理进行研究并建立强度模型。利用岩石力学三轴实验机对纤维水泥石试块进行弹性模量测试,得到了纤维水泥石单轴应力-应变实验图。根据细观力学理论和能量守恒原理,在建立顺向分布纤维水泥抗拉强度模型的基础上得到了乱向分布纤维水泥的抗拉强度模型。模型分析结果表明,随着纤维掺量的增加,水泥石的抗拉强度有先增大后降低的趋势,这与实验室试验所得规律相同。     

The structural basis of calcium transport by the calcium pump

The sarcoplasmic reticulum Ca2+-ATPase, a P-type ATPase, has a critical role in muscle function and metabolism. Here we present functional studies and three new crystal structures of the rabbit skeletal muscle Ca2+-ATPase, representing the phosphoenzyme intermediates associated with Ca2+ binding, Ca2+ translocation and dephosphorylation, that are based on complexes with a functional ATP analogue, beryllium fluoride and aluminium fluoride, respectively. The structures complete the cycle of nucleotide binding and cation transport of Ca2+-ATPase. Phosphorylation of the enzyme triggers the onset of a conformational change that leads to the opening of a luminal exit pathway defined by the transmembrane segments M1 through M6, which represent the canonical membrane domain of P-type pumps. Ca2+ release is promoted by translocation of the M4 helix, exposing Glu 309, Glu 771 and Asn 796 to the lumen. The mechanism explains how P-type ATPases are able to form the steep electrochemical gradients required for key functions in eukaryotic cells.     

Three types of neuronal calcium channel with different calcium agonist sensitivity

How many types of calcium channels exist in neurones? This question is fundamental to understanding how calcium entry contributes to diverse neuronal functions such as transmitter release, neurite extension, spike initiation and rhythmic firing. There is considerable evidence for the presence of more than one type of Ca conductance in neurones and other cells. However, little is known about single-channel properties of diverse neuronal Ca channels, or their responsiveness to dihydropyridines, compounds widely used as labels in Ca channel purification. Here we report evidence for the coexistence of three types of Ca channel in sensory neurones of the chick dorsal root ganglion. In addition to a large conductance channel that contributes long-lasting current at strong depolarizations (L), and a relatively tiny conductance that underlies a transient current activated at weak depolarizations (T), we find a third type of unitary activity (N) that is neither T nor L. N-type Ca channels require strongly negative potentials for complete removal of inactivation (unlike L) and strong depolarizations for activation (unlike T). The dihydropyridine Ca agonist Bay K 8644 strongly increases the opening probability of L-, but not T- or N-type channels.     

氢氧化钙和碳酸钙混合物的分析方法

在甲醇存在下,用EDTA四钠盐能准确而精密地络合滴定Ca(OH)2和CaCO3混合物.当甲醇与水的体积比在0.2～0.6之间时,CaCO3 对Ca(OH)2的滴定不干扰,且能准确滴定Ca(OH)2.本法可用来监测石灰乳碳化的全过程.     

Structural changes in the calcium pump accompanying the dissociation of calcium

In skeletal muscle, calcium ions are transported (pumped) against a concentration gradient from the cytoplasm into the sarcoplasmic reticulum, an intracellular organelle. This causes muscle cells to relax after cytosolic calcium increases during excitation. The Ca(2+) ATPase that carries out this pumping is a representative P-type ion-transporting ATPase. Here we describe the structure of this ion pump at 3.1 A resolution in a Ca(2+)-free (E2) state, and compare it with that determined previously for the Ca(2+)-bound (E1Ca(2+)) state. The structure of the enzyme stabilized by thapsigargin, a potent inhibitor, shows large conformation differences from that in E1Ca(2+). Three cytoplasmic domains gather to form a single headpiece, and six of the ten transmembrane helices exhibit large-scale rearrangements. These rearrangements ensure the release of calcium ions into the lumen of sarcoplasmic reticulum and, on the cytoplasmic side, create a pathway for entry of new calcium ions.     

稀土尾矿中钙的提取及硫酸钙晶须的制备

本研究采用稀硫酸溶解稀土尾矿,稀土尾矿中难溶的稀土矿物和钙的溶解产物硫酸钙存在于硫酸不溶物中,固液分离后用稀盐酸进一步溶解硫酸不溶物,使固态的硫酸钙溶解在稀盐酸中.尾矿中的稀土富集于盐酸不溶物中,盐酸不溶物中稀土氧化物质量分数为43.60％.采用乙醇结晶的方法制备硫酸钙晶须,确定结晶制备的最佳条件为:室温下,硫酸钙的初始浓度为0.009 mol/L左右,pH为1.0～1.5,溶液与乙醇的体积比为1:2,静置时间为2h.在此最佳条件下,稀土尾矿中钙的回收率大于85％,产品硫酸钙晶须纯度达98％以上,晶须平均直径为1 μm,平均长径比达80.     

天门冬氨酸钙和葡萄糖酸钙兔体内吸收度的研究

用原子吸收分光光度法测定兔血清钙浓度,结果表明,天门冬氨酸钙和葡萄糖酸钙的吸收度无显著性差异。     

Formation mechanism of calcium hexaluminate

To investigate the formation mechanism of calcium hexaluminate (CaAl₁₂O₁₉, CA₆), the analytically pure alumina and calcia used as raw materials were mixed in CaO/Al₂O₃ ratio of 12.57:137.43 by mass. The raw materials were ball-milled and shaped into green specimens, and fired at 1300–1600°C. Then, the phase composition and microstructure evolution of the fired specimen were studied, and a first principle calculation was performed. The results show that in the reaction system of CaO and Al₂O₃, a small amount of CA₆ forms at 1300°C, and greater amounts are formed at 1400°C and higher temperatures. The reaction is as follows: CaO·2Al₂O₃ (CA₂) + 4Al₂O₃ → CA₆. The diffusions of Ca2+ in CA₂ towards Al₂O₃ and Al3+ in Al₂O₃ towards CA₂ change the structures in different degrees of difficulty. Compared with the difficulty of structural change and the corresponding lattice energy change, it is deduced that the main formation mechanism is the diffusion of Ca2+ in CA₂ towards Al₂O₃.     

Depletion of intracellular calcium stores activates a calcium current in mast cells.

In many cell types, receptor-mediated Ca2+ release from internal stores is followed by Ca2+ influx across the plasma membrane. The sustained entry of Ca2+ is thought to result partly from the depletion of intracellular Ca2+ pools. Most investigations have characterized Ca2+ influx indirectly by measuring Ca(2+)-activated currents or using Fura-2 quenching by Mn2+, which in some cells enters the cells by the same influx pathway. But only a few studies have investigated this Ca2+ entry pathway more directly. We have combined patch-clamp and Fura-2 measurements to monitor membrane currents in mast cells under conditions where intracellular Ca2+ stores were emptied by either inositol 1,4,5-trisphosphate, ionomycin, or excess of the Ca2+ chelator EGTA. The depletion of Ca2+ pools by these independent mechanisms commonly induced activation of a sustained calcium inward current that was highly selective for Ca2+ ions over Ba2+, Sr2+ and Mn2+. This Ca2+ current, which we term ICRAC (calcium release-activated calcium), is not voltage-activated and shows a characteristic inward rectification. It may be the mechanism by which electrically nonexcitable cells maintain raised intracellular Ca2+ concentrations and replenish their empty Ca2+ stores after receptor stimulation.