Preparation of octacalcium phosphate from calcium carbonate powder

We have studied a process for the preparation of apatite precursors through calcium carbonate conversion into dicalcium phosphate dihydrate, which is then hydrolyzed to octacalcium phosphate. The process enables the preparation of both phase-pure octacalcium phosphate and calcium phosphate mixtures with variable dicalcium phosphate dihydrate : octacalcium phosphate and hydroxyapatite : octacalcium phosphate ratios.     

Formation of carbonate apatite on calcium phosphate coatings containing silver ions

The prerequisite for bioactive materials to bond to living bone is the formation of biologically equivalent carbonate apatite on their surfaces in the body. Calcium phosphate ceramic surfaces can be transformed to a biological apatite through a series of surface reactions including dissolution–precipitation and ion exchange. In the present work, apatite coatings with different crystallinity, compositions and crystal sizes, including a well-crystallized hydroxyapatite coating, were synthesized electrochemically and doped with silver ions in silver nitrate solution at room temperature. The formation of a new carbonate apatite on the surface of these coatings was investigated in an acellular simulated body fluid with ion concentrations comparable with those of human blood plasma, using scanning electron microscopy and Fourier transform-infrared spectroscopy. The results show that small quantities of silver ions incorporated into apatite coatings may have a strong stimulatory effect on the formation of carbonate apatite without adversely affecting the chemical stability of these coatings.     

多孔磷酸钙骨水泥组织工程支架的高分子灌注增强

利用棒状谷氨酸钠晶体作为造孔粒子,采用可溶盐造孔法,制备了三维连通的大孔径多孔磷酸钙骨水泥支架,分别将明胶(Gelatin) 、聚乳酸2羟基乙酸共聚物(PLGA) 、聚乳酸(PLA) 、聚己内酯(PCL) 、聚羟基丁酸戊酸酯(PHBV)灌注到多孔磷酸钙骨水泥(CPC)支架的孔隙中以改善支架材料的力学性能。结果表明,5 种高分子材料与水的接触角大小顺序为PHBV > PCL > PLA > PL GA > Gelatin , 复合支架材料的强度随高分子材料与水接触角的减小而增大;除PHBV外,其余4种均有明显的增强效果,其中Gelatin/CPC复合支架增强效果最好,强度达到2. 25 MPa±0. 02 MPa ,是CPC支架强度的25倍。经过增强的大孔径多孔磷酸钙骨水泥复合支架可用作骨组织工程支架材料。      

The crystallization of calcium carbonate on sodium cholate

Recent studies in the bibliography showed that calcium carbonate was the major constituent (77.8%) in gall stones, and the polymorph calcite was at 62.5% of the cases examined. The kinetics of crystallization of calcite on sodium cholate has been studied using the constant composition technique. Analysis of the initial rates as a function of the solution supersaturation, according to the classical nucleation theory, yielded a value of 33 mJ m^-2 for the surface energy of the growing phase and a five-ion cluster, forming the critical nucleus. The apparent order for the calcite crystallization was found to be 4.5±0.7 indicative of a surface nucleation mechanism. The formation of calcite may be initiated through the interaction of Ca²⁺ ions with the negative end of the C=0 bond of the sodium cholate molecule.     

相变恒温材料六水氯化钙的研究

有关相变恒温材料，目前应用较多的是固液相变材料，而固液相变温度是混合相变材料应用的基础。本文着重研究了以氢氧化钡为成核剂和不同用量的无机相变材料六水氯化钙。利用步冷曲线法测定了添加质量分数分别为1．0％、2．0％和3．O％的氢氧化钡时六水氯化钙的相变温度。测定结果表明3．0％氢氧化钡添加量时，相变效果较好，相变温度为28．10℃。     

Technological applications of functionalized polymers

In most of the major applications of polymeric materials their mechanical properties are often of paramount importance. Even in such applications as electrical insulators their stiffness, cut and abrasion resistance will be of importance as well as their low conductivity. Now, polymers containing specific functional groups are being utilized in analytical and many synthetic organic chemical procedures [1–4], in biologically and pharmacologically active systems, in food additives, and in the field of agricultural chemicals [5]. Following their successful applications in the laboratory and industrial processes, the introduction of active functional groups, other than those previously discussed, into polymers will be discussed in the present article. It is meant only to illustrate selected aspects of more general areas of polymers in the technological uses based on their specific active functional groups, in additon to the advantageous properties of the polymeric material.     

碳酸钙晶须合成及其应用

本文介绍了碳酸钙晶须的制备方法，性能特征及其应用。     

The growth of calcium phosphate on ceramic surfaces

Calcium phosphate ceramics are very important materials for prosthetic applications because of their excellent biocompatibility. The chemical composition of the ceramics is determining, both with respect to their capability of inducing calcium phosphate formation and regarding the crystalline phase formed. From a series of porous ceramics based on hydroxyapatite (HAP) containing metal oxides, it was found that only those containing ZrO₂ stabilized with 8% Y₂O₃ were able to induce calcium phosphate formation upon introduction into calcium phosphate supersaturated solutions. The overgrowing phase was increasingly crystalline, did not show any other characteristic X-ray peaks and infrared bands than those pertinent to a-tricalcium phosphate and had a molar CaP ratio of 32. Kinetics analysis with respect to Ca(PO₄)₂ yielded an apparent order of reaction of 5.0±0.5, suggesting polynuclear nuclei above nuclei growth. The surface energy calculated from the kinetics data for the crystalline overgrowth was found to be 88 mJ m^–2.     

The co-effect of collagen and magnesium ions on calcium carbonate biomineralization

The process of calcium carbonate biomineralization in the solution containing collagen and magnesium ions was studied in this paper. The results were characterized by using powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effect rules were obtained by the cooperation of collagen and magnesium ions in different concentration. The experiment results showed that in the presence of both collagen and magnesium ions, aragonite and vaterite were precipitated at low Mg/Ca ion concentration ratio, while only aragonite with regular spherical morphology was precipitated at high Mg/Ca ion concentration ratio. It indicated that collagen has a promotional effect on magnesium ions in controlling the polymorph of calcium carbonate crystal. A much wider range of calcium carbonate morphologies was observed in the presence of both collagen and magnesium ions. The experiments suggested that collagen acts in combination with magnesium ions to inhibit calcite crystal growth, while favoring the formation of aragonite crystals.     

The growth of self-aligned calcium carbonate precipitates on inorganic substrates

Calcium carbonate has been found to precipitate into tablets which were self-aligned with respect to each other on limestone aggregates in Portland cement-based materials. A surface layer of water and reaction in 100% relative humidity air environments were critical for alignment of precipitates. The organization of the calcium carbonate precipitates resembled the cross-section of nacre, but without an organic phase. Possible implications for organized material synthesis, as well as biomineralization, are discussed. © 1998 Kluwer Academic Publishers     

一种基于微生物沉积的水泥砂浆表面改性技术

某些微生物能诱导沉积出具有胶凝和矿化作用的碳酸钙,可以用来修复和密实水泥基材料。但是目前微生物沉积技术工艺复杂,成本高,不利于推广和工程应用。尝试采用水泥砂浆粉作为覆膜载体,利用巴斯德芽孢杆菌对水泥砂浆进行表面处理。研究结果表明,采用该方法能使巴斯德芽孢杆菌在水泥试块表面诱导沉积出碳酸钙,有效减少水泥砂浆的吸水性能。当微生物采用含有尿素的培养基培养时,表面改性后的水泥砂浆吸水系数降低了58%。采用压汞测试仪(MIP)分析了处理前后水泥试块表层的孔隙率以及孔结构特征。发现采用巴斯德芽孢杆菌处理后,样品孔隙率显著降低,大孔的含量显著减少,当微生物采用含有尿素的培养基培养时,总孔隙率降低了40%。X射线衍射仪(XRD)和场发射扫描电镜(SEM)分析表明,经微生物技术处理后水泥试块内部的孔洞和裂缝被球霰石和方解石填充。     

Enhanced sintering ability of biphasic calcium phosphate by polymers used for bone scaffold fabrication

Biphasic calcium phosphate (BCP), which is composed of hydroxyapatite [HAP, Ca₁₀(PO₄)₆(OH)₂] and β-tricalcium phosphate [β-TCP, β-Ca₃(PO₄)₂], is usually difficult to densify into a solid state with selective laser sintering (SLS) due to the short sintering time. In this study, the sintering ability of BCP ceramics was significantly improved by adding a small amount of polymers, by which a liquid phase was introduced during the sintering process. The effects of the polymer content, laser power and HAP/β-TCP ratios on the microstructure, chemical composition and mechanical properties of the BCP scaffolds were investigated. The results showed that the BCP scaffolds became increasingly more compact with the increase of the poly(l-lactic acid) (PLLA) content (0–1 wt.%) and laser power (6–10 W). The fracture toughness and micro-hardness of the sintered scaffolds were also improved. Moreover, PLLA could be gradually decomposed in the late sintering stages and eliminated from the final BCP scaffolds if the PLLA content was below a certain value (approximately 1 wt.% in this case). The added PLLA could not be completely eliminated when its content was further increased to 1.5 wt.% or higher because an unexpected carbon phase was detected in the sintered scaffolds. Furthermore, many pores were observed due to the removal of PLLA. Micro-cracks and micro-pores occurred when the laser power was too high (12 W). These defects resulted in a deterioration of the mechanical properties. The hardness and fracture toughness reached maximum values of 490.3 ± 10 HV and 1.72 ± 0.10 MPa m^1/2, respectively, with a PLLA content of approximately 1 wt.% and laser power of approximately 10 W. Poly(l-lactic-co-glycolic acid) (PLGA) showed similar effects on the sintering process of BCP ceramics. Rectangular, porous BCP scaffolds were fabricated based on the optimum values of the polymer content and laser power. This work may provide an experimental basis for improving the mechanical properties of BCP bone scaffolds fabricated with SLS.     

A new antacid drug from activated carbon modified with calcium carbonate

Activated carbons were previously modified with different sodium carbonate solutions and then, they were soaked in a calcium nitrate solution. This procedure allowed to precipitate calcium carbonate on the microporous carbons. Then, these solids were washed with abundant distillated water. These modified carbons were characterized by means of XRD, SEM, HRTEM and BET surface area measurements. XRD confirmed the presence of calcium carbonate species, while the surface area measurements indicated that microporous solids were partially blocked. SEM and HRTEM showed that precipitated calcium carbonate crystals were found on the surface of the activated carbon. These solids were tested as antacids in a synthetic gastric juice and they were able to neutralize it. A commercial compound formulated with calcium carbonate was used as a reference system.     

The effect of acetaminophen on the crystal growth of calcium carbonate

The effect of acetaminophen, a well known analgesic and fever-reducing medicine, on the calcium carbonate crystal growth was investigated under plethostatic conditions. The calcification rates measured was reduced by 9.1–63.2% in the presence of acetaminophen. Kinetic analysis according to a Langmuir-type adsorption isotherm lead to the calculation of an affinity constant K _aff = 8.33 × 10² dm³ mol⁻¹. The apparent order found from kinetic data was two suggesting a surface diffusion controlled spiral growth mechanism.     

Effect of uncoated calcium carbonate and stearic acid coated calcium carbonate on mechanical,thermal and structural properties of poly(butylene terephthalate) (PBT)/calcium carbonate composites

PBT/CaCO₃ composites were prepared in a single screw extruder with particle content varying from 0–30% by weight. The influence of surface treatment of the particles, with and without stearic acid (SA), on the mechanical, thermal and structural properties was studied. The experiments included tensile tests, impact tests, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy. The composite systems containing SA coated CaCO₃ were found to exhibit better mechanical properties as compared to composite systems containing uncoated CaCO₃, with the S3 system (20% of SA coated CaCO₃) exhibiting best combination of mechanical properties. Thermal study revealed that particle type and content had no influence on the melting temperature but the crystallization temperature, % crystallinity and thermal stability increased on increasing the CaCO₃ content in PBT matrix. Morphological observation indicated that in PBT composites containing SA coated CaCO₃, the coupling agent favours a better polymer filler interaction rendering inorganic polymer interface compatible, which is also evident from better mechanical and thermal properties.     

新常态下重质碳酸钙产业技术创新与结构调整

为了实现经济新常态下国内重质碳酸钙粉体产业技术创新与结构调整的升级发展,结合创新驱动"质的增长"要求和市场应用的个性化需求等产业现状,研究重质碳酸钙加工装备大型化、工业生产技术精细化和功能化等技术创新方向,及重质碳酸钙的产品结构完善与企业优势重组等产业结构调整模式,提出国内重质碳酸钙企业应学习借鉴国际上先进的产业技术创新路线与结构调整模式,打造出中国的产业品牌。     

脲解型微生物诱导碳酸钙沉积研究

研究了钙源种类对脲解型微生物诱导碳酸钙沉积的生物-化学过程的影响。利用电位分析法实时测试了沉积过程中钙离子、铵离子及pH值的变化,并利用显微计数对细菌浓度进行了监测。采用扫描电镜(SEM)、X射线衍射(XRD)和分析红外光谱(IR)对沉积产物进行了研究。结果表明,不同钙源环境下脲解型微生物诱导矿化沉积都存在化学沉淀、微生物诱导矿化沉积和沉淀完全3个阶段;有机钙源环境下细菌的产矿动力比在无机钙源中高,且两种钙源所获得的方解石晶体沉积物在形貌上差异显著。     

PP/elastomer/calcium carbonate composites: effect of elastomer and calcium carbonate contents on the deformation and impact behavior

The morphology and mechanical behavior of ternary polypropylene/ethylene-octene copolymer/calcium carbonate composites have been investigated as a function of elastomer and filler contents. A separate dispersion of phases was observed. Increasing concentration of EOC and CaCO₃ promotes a decrease of matrix ligament thickness between elastomer particles resulting in a huge increase of the toughness. The stiff filler used in this study provided the unusual additional benefit of substantially increasing in Young's and flexural modulus of the composites.