Setting reaction and hardening of an apatitic calcium phosphate cement

The combination of self-setting and biocompatibility makes calcium phosphate cements potentially useful materials for a variety of dental applications. The objective of this study was to investigate the setting and hardening mechanisms of a cement-type reaction leading to the formation of calcium-deficient hydroxyapatite at low temperature. Reactants used were alpha-tricalcium phosphate containing 17 wt% beta-tricalcium phosphate, and 2 wt% of precipitated hydroxyapatite as solid phase and an aqueous solution 2.5 wt% of disodium hydrogen phosphate as liquid phase. The transformation of the mixture was stopped at selected times by a freeze-drying techniques, so that the cement properties at various stages could be studied by means of x-ray diffraction, infrared spectroscopy, and scanning electron microscopy. Also, the compressive strength of the cement was measured as a function of time. The results showed that: (1) the cement setting was the result of the alpha-tricalcium phosphate hydrolysis, giving as a product calcium-deficient hydroxyapatite, while beta-tricalcium phosphate did not participate in the reaction; (2) the extent of conversion of alpha-TCP was nearly 80% after 24 hr; (3) both the extent of conversion and the compressive strength increased initially linearly with time, subsequently reaching a saturation level, with a strong correlation observed between them, indicating that the microstructural changes taking place as the setting reaction proceeded were responsible for the mechanical behavior of the cement; and (4) the microstructure of the set cement consisted of clusters of big plates with radial or parallel orientations in a matrix of small plate-like crystals.     

Formation of hydroxyapatite in new calcium phosphate cements

Tetracalcium phosphate (TTCP) has been shown previously to be an essential component of self-setting calcium phosphate cements that form hydroxyapatite (HA) as the only end-product. We report herein on a new self-setting calcium phosphate cement that does not contain TTCP. These cements consist of dicalcium phosphate anhydrous (DCPA), dicalcium phosphate dihydrate (DCPD), alpha-tricalcium phosphate, or amorphous calcium phosphate and, as an additional source of calcium, calcium hydroxide or calcium carbonate. These cements require the use of a phosphate (0.2 moll(-1) or higher) solution or a high pH solution as the cement liquid. The cements harden in relatively short time (5-30 min) and form HA as the dominant end-product in 24 h. The diametral tensile strengths of the 24-h samples are in the range of 0.2 to 7.5 MPa. Results from X-ray diffraction studies suggest that the cement setting is caused by rapid HA formation induced by the high phosphate concentration of the cement liquid. Because DCPA and DCPD are highly soluble at pH values above 12.7, which is the pK3 of phosphoric acid, high phosphate concentration in the slurry solution was also attainable by using a highly alkaline solution as the cement liquid. The physicochemical properties of these cements are comparable to those of TTCP-containing cements, and the new cements may be expected to have in vivo characteristics similar to those of TTCP-containing cements as well.     

Quality of life and productivity in nurses reporting migraine

Calcium phosphate bone cements (CPBCs) are osteotransductive, i.e. after implantation in bone they are transformed into new bone tissue. Furthermore, due to the fact that they are mouldable, their osteointegration is immediate. Their chemistry has been established previously. Some CPBCs contain amorphous calcium phosphate (ACP) and set by a sol-gel transition. The others are crystalline and can give as the reaction product dicalcium phosphate dihydrate (DCPD), calcium-deficient hydroxyapatite (CDHA), carbonated apatite (CA) or hydroxyapatite (HA). Mixed-type gypsum-DCPD cements are also described. In vivo rates of osteotransduction vary as follows: gypsum-DCPD > DCPD > CDHA approximately CA > HA. The osteotransduction of CDHA-type cements may be increased by adding dicalcium phosphate anhydrous (DCP) and/or CaCO3 to the cement powder. CPBCs can be used for healing of bone defects, bone augmentation and bone reconstruction. Incorporation of drugs like antibiotics and bone morphogenetic protein is envisaged. Load-bearing applications are allowed for CHDA-type, CA-type and HA-type CPBCs as they have a higher compressive strength than human trabecular bone (10 MPa).     

In vivo setting behaviour of fast-setting calcium phosphate cement

The in vivo setting behaviour of fast-setting calcium phosphate cement (FSCPC) between femoral muscles of the rat was investigated to evaluate the possible value of FSCPC for medical and dental application. Conventional CPC (c-CPC) and FSCPC were implanted between femoral muscles, and various aspects of the setting behaviour such as setting time, mechanical strength and conversion ratio of cement into hydroxyapatite (HAP: Ca10(PO4)6(OH)2) were measured by the Vicat needle method, diametral tensile strength (DTS) measurement, and quantitative powder X-ray diffraction (XRD) analysis, respectively. The setting time of FSCPC in vivo was 5-7 min, in contrast to 48 min for c-CPC. As a result of its fast setting, set specimens of FSCPC showed higher mechanical strength from the initial stage than c-CPC. Higher DTS values were observed in FSCPC than c-CPC implanted after 24 h. Powder XRD analysis revealed faster conversion of FSCPC than c-CPC into HAP, which was responsible both for the faster setting and higher mechanical strength from the initial stage. We concluded, therefore, that FSCPC may be used for a wide range of clinical applications, i.e. fields where fast setting is required such as orthopaedic, plastic and reconstructive, and oral and maxillofacial surgery.     

A novel skeletal drug-delivery system using self-setting calcium phosphate cement. 4. Effects of the mixing solution volume on the drug-release rate of heterogeneous aspirin-loaded cement

The effect of the mixing solution volume was investigated on the in vitro drug-release rate of a novel drug-delivery device based on a self-setting bioactive calcium phosphate cement containing aspirin as a model drug. Equimolar mixtures of metastable calcium phosphate powders containing various proportions (3-40 w/w %) of seed hydroxyapatite crystals transformed into hydroxyapatite after being mixed with dilute phosphoric acid. The drug release from cement pellets in vitro into a 0.1 mol/L phosphate buffer at pH 7.40 and 37 degrees C by the rotating disk method continued for more than 1 week. The drug-release rate from the cement increased with increasing volumes of mixing solution. The relationship between the liquid/powder ratio and the porosity of the cement was a straight line, indicating that the cement porosity depended on the amount of the mixing solution, but was independent of the amount of seed crystals. Drug release from the cement followed the modified Fick's law, with the rate increasing with the amount of mixing solution, since the porosity depended on the amount. The tortuosity of the cements was estimated from the modified Fick's equation, and the relationships between the drug release rate and the tortuosity of the pore in the drug-loaded cement in the plots were nonlinear. The results suggested that the drug-release rates from the cement were controlled by the drug diffusion in the pores.     

精炼钢包用MgO-CaO浇注料的抗渣性研究

采用动态回转法研究了MgO-SiO2-H2O结合和聚磷酸盐结合的MgO-CaO浇注料的抗渣性。以MgO-CaO砂和CaCO3作CaO源，比较了CaO的引入方式对其抗渣性的影响。利用X射线衍射分析测定了各类浇注料在1600℃烧后的相组成，借助SEM和EDAX分析了MgO-CaO浇注料经渣蚀后的显微结构。研究表明。MgO-CaO浇注料中的CaO在高温烧成时参与了基质相的反应。CaCO3细粉的引入加大了CaO在基质中参与反应的程度。聚磷酸钠结合的MgO-CaO浇注料在高温烧成时生成高熔点的结合相硅磷钙钠（NC4PS），有助于提高抗渣能力。MgO-SiO2-H3O结合浇注料中的低熔点相钙镁橄榄石和镁蔷薇辉石（CMS、C3MS2）随CaCO3的引入而增多，对抗渣性不利。     

Mechanical strength of calcium phosphate cement in vivo and in vitro

Two different kinds of calcium phosphate cement were developed for implant fixation: cement A comprised of alpha-tricalcium phosphate (alpha-TCP) 95% and dicalcium phosphate dihydrate (DCPD) 5%, and cement B comprised of alpha-tricalcium phosphate 90% and dicalcium phosphate dihydrate 10%. The compression strength and pullout force of the new materials were tested both in vitro and in vivo. Microscopic observations were performed on the interface between bone and cement. Cement A showed a greater mechanical strength than cement B. The results suggest the clinical possibility of this calcium phosphate cement, which could be used as a material for enhancing implant fixation.     

Study on Optimal Conditions for Recovery of EDTA from Soil Washing Effluents

The recovery of ethylenediaminetetraacetic acid (EDTA) from washing effluents is essential to reduce the cost of EDTA-enhanced soil washing and the production of wastewater. This study evaluated a recovery method, in which Pb or Zn was first dissociated from Pb– or Zn–EDTA complex through the replacement reaction by adding FeCl3 and then removed as phosphate precipitates through adding Na2HPO4. Finally, Fe(III) was removed as Fe(OH)3 precipitates through adding Ca(OH)2. As a result, EDTA was recovered as Ca–EDTA for further use in soil washing process. The optimal conditions for EDTA recovery, including the molar ratios of FeCl3 and Na2HPO4 to EDTA as well as the pH after adding Na2HPO4 and adding Ca(OH)2, were well investigated. Under the optimal conditions, 96% of Pb or 83% of Zn was removed from the Pb– or Zn–EDTA, respectively. The four-cycle recovery and reuse of EDTA experiments indicated the recovered EDTA from soil washing effluents did not lose much chelating capacity for Pb removal. However, there is a loss of 15% of its chelating capacity in the first cycle reuse for Zn-contaminated soil washing due to substantial Zn residual in the recovered EDTA solution.     

含银无机抗菌剂的研制和抗菌性能初探

采用不同工艺制备了载银磷酸钙和载银碳酸钙粉末 ,通过大肠杆菌培养实验 (抑菌环法 )比较了银离子存在形式对抑菌性能的影响 ,证实了银离子释放是灭菌的关键。     

Human discrimination of the implicit orientation of simple symmetrical patterns

A hydraulic calcium phosphate cement made of beta-tricalcium phosphate [beta-Ca3(PO4)2], monocalcium phosphate monohydrate [Ca(H2PO4)2-H2O], and water was used as a delivery system for the antibiotic gentamicin sulfate (GS). GS, added as powder or as aqueous solution, was very beneficial to the physicochemical properties of the cement. The setting time increased from 2 to 4.5 min with 3% (w/w) GS and then slowly decreased to 3.75 min with 16% (w/w) GS. The tensile strength increased from 0.4 to 1.6 MPa with 16% (w/w) GS. These effects were attributed to the presence of sulfate ions in GS. The release of GS from the cement was measured in a pH 7.4 phosphate-buffered saline solution at 37 degrees C by USP paddle method. Factors such as cement porosity, GS content and presence of sulfate ions or polymeric additives were investigated. The amount of GS released was roughly proportional to the square root of time up to approximately 50% release. Afterwards, the release rate markedly slowed down to zero. In all but two cement formulations, the total dose of GS was released within 7 days, indicating that no irreversible binding occurred between the cement paste and the antibiotic. When small amounts of hydroxypropylcellulose or poly(acrylic acid) were added to the cement, the maximum fraction released was a few percent lower than the total GS dose, suggesting some binding between the polymer and GS. The GS release rate was strongly influenced by the presence of sulfate ions in the cement paste and by the cement porosity. The higher the sulfate ion content of the cement paste, the lowe the GS release rate. This influence was attributed to the finer cement micro-structure induced by the presence of sulfate ions. Furthermore, when the initial cement porosity was increased from 38 to 69%, the release rate almost tripled (0.16 to 0.45 h-1/2). Finally, the biological activity of GS in the cement was maintained, as measured by assaying the release medium.     

Repair of craniofacial defects with hydroxyapatite cement

PURPOSE: The objective of this study was to evaluate the course of healing of craniofacial bone defects when filled with hydroxyapatite cement and to determine whether adding various percentages by weight of demineralized bone powder to the cement will result in enhanced bone formation. MATERIALS AND METHODS: The model for the study was the canine calvarium. The implants were placed into cranial defects and harvested at 3 or 6 months for qualitative evaluation by light microscopy, microradiography, and quantitative histomorphometry. RESULTS: The implantation of hydroxyapatite cement resulted in characteristic replacement of the material with new bone ingrowth. The addition of demineralized bone powder to the hydroxyapatite cement appeared to improve the handling characteristics of the cement; however, improvement in the replacement of the material by bone was not observed. The implantation of only allogeneic demineralized bone showed limited new bone formation within the defect site. CONCLUSIONS: Hydroxyapatite cement formed an effective osseoconductive scaffold for bone replacement. The addition of demineralized bone powder to the cement to serve as a carrier of osseoinductive factors did not result in additional bone being formed.     

Characterization of calcium phosphates precipitated from simulated body fluid of different buffering capacities

The purpose of this experiment was to study the properties of calcium phosphate precipitated from simulated body fluids (SBFs) with different buffering capacities. The Ca/P molar ratios of the precipitates were determined and the microstructure of a sintered precipitate was studied. The results indicate that the pH of the SBF increases during calcium phosphate precipitations, which affects the Ca/P molar ratios and chemical compositions of these precipitates. A precipitate with a Ca/P molar ratio close to the stoichiometric molar ratio of hydroxyapatite was obtained when the pH of the SBF was continuously adjusted to 7.26 during precipitation. This precipitate has a fine-grained and laminated microstructure after sintering at 1000 degrees C in air. It seems that SBF can be used as a tool to study apatite-like precipitation in vitro when the pH of the solution is carefully controlled.     

Histological, chemical, and crystallographic analysis of four calcium phosphate cements in different rabbit osseous sites

Four calcium phosphate cement formulations were implanted in the rabbit distal femoral metaphysis and middiaphysis. Chemical, crystallographic, and histological analyses were made at 2, 4, and 8 weeks after implantation. When implanted into the metaphysis, part of the brushite cement was converted into carbonated apatite by 2 weeks. Some of the brushite cement was removed by mononuclear macrophages prior to its conversion into apatite. Osteoclastlike cell mediated remodeling was predominant at 8 weeks after brushite had converted to apatite. The same histological results were seen for brushite plus calcite aggregate cement, except with calcite aggregates still present at 8 weeks. However, when implanted in the diaphysis, brushite and brushite plus calcite aggregate did not convert to another calcium phosphate phase by 4 weeks. Carbonated apatite cement implanted in the metaphysis did not transform to another calcium phosphate phase. There was no evidence of adverse foreign body reaction. Osteoclastlike cell mediated remodeling was predominant at 8 weeks. The apatite plus calcite aggregate cement implanted in the metaphysis that was not remodeled remained as poorly crystalline apatite. Calcite aggregates were still present at 8 weeks. There was no evidence of foreign body reaction. Osteoclastlike cell remodeling was predominant at 8 weeks. Response to brushite cements prior to conversion to apatite was macrophage dominated, and response to apatite cements was osteoclast dominated. Mineralogy, chemical composition, and osseous implantation site of these calcium phosphates significantly affected their in vivo host response.     

预处理对铜钴铁合金中钴浸出率的影响

主要研究了铜钴铁合金掺CaCO3焙烧对合金中钴浸出率的影响。合金分别添加5%、10%、15%、20%的CaCO3在900℃、1 000℃1、100℃、1 200℃、1 300℃下煅烧保温10 h,底层金属富集区与上层渣分离后破碎筛分,溶于H2SO4中。结果表明合金粉在900℃、1 000℃、1 100℃下煅烧时,钴浸出率随CaCO3添加量增加而提高;合金粉添加10%CaCO3在1 300℃下煅烧后浸出,钴浸出率达到峰值,约为95%,其后钴浸出率随CaCO3添加量增加而下降。     

Role of calcium carbonate administration timing in relation to food intake on its efficiency in controlling hyperphosphatemia in patients on maintenance dialysis

A study has claimed that at an equal elemental calcium dose, CaCO3 was not less but equally as efficient in controlling predialysis hyperphosphatemia as calcium acetate, provided both calcium salts were ingested 5 min before meals instead of during meals because the higher acidity of the fasting gastric juice would allow for better dissociation of CaCO3. However, this study did not directly demonstrate that the efficiency of CaCO3 in controlling hyperphosphatemia was actually greater when it was administered before a meal than during a meal. To examine this point, we performed a 3 month randomized crossover trial in 12 reliable and stable patients maintained on chronic hemodialysis. Their plasma concentrations of calcium, protein, phosphate, bicarbonate, urea, and creatinine were measured before the first dialysis of each week and the amount of intact parathyroid hormone (PTH) at the beginning and at the end of each of the 3 months. Comparison of the plasma concentrations measured during the 2 modes of administration showed no significant differences in creatinine, urea, bicarbonate, or intact PTH. The mean (+/-SD) plasma concentration of PO4 was not significantly lower (1.88+/-0.50 vs. 1.74+/-0.41 mM) whereas the corrected level of plasma Ca was significantly lower (2.30+/-0.17 vs. 2.38+/-0.16 mM; p < 0.04) when CaCO3 was given before meals than during meals. In conclusion, the administration of CaCO3 before a meal does not increase its efficiency in controlling hyperphosphatemia because the level of plasma PO4 was actually slightly higher with this timing of administration whereas the comparison of the creatinine and urea levels suggested a stability of phosphate intake and the comparison of the PTH and bicarbonate levels suggested the stability of osteolysis and of the transcellular membrane shift of phosphate. Also, administration of CaCO3 before a meal is associated with significantly lower plasma corrected calcium, suggesting less absorption of calcium, which may be an advantage but only in hypercalcemic patients. There is no reason other than the prevention of its hypercalcemic effect to recommend the administration of CaCO3 just before meals rather than during meals.     

Nucleation of hydroxyapatite by bone sialoprotein

Bone sialoprotein (BSP) and osteopontin, the major phosphorylated proteins of mammalian bone, have been proposed to function in the initiation of mineralization. To test this hypothesis, the effects of BSP and osteopontin on hydroxyapatite crystal formation were determined by using a steady-state agarose gel system. At low calcium phosphate concentrations, no accumulation of calcium and phosphate occurred in control gels or gels containing osteopontin. Gels containing BSP at 1-5 micrograms/ml, however, exhibited a visible precipitation band and significantly elevated Ca + PO4 contents. By powder x-ray diffraction, the precipitate formed in the presence of BSP was shown to be hydroxyapatite. These findings suggest that bone sialoprotein may be involved in the nucleation of hydroxyapatite at the mineralization front of bone.     

Restoration of pedicle screw fixation with an in situ setting calcium phosphate cement

STUDY DESIGN: Pedicle screws were pulled out of human cadaveric vertebrae before and after augmentation with polymethylmethacrylate or in situ-setting calcium phosphate cement. The fixation strength of screws augmented with calcium phosphate cement was compared with that of screws augmented with polymethylmethacrylate. OBJECTIVES: To determine whether a new in situ-setting calcium phosphate cement might be suitable for augmenting the fixation of pedicle screws. The principle objective was to compare the pull-out resistance of screws augmented with calcium phosphate cement with the pull-out behavior of screws augmented with polymethylmethacrylate. Polymethylmethacrylate augmentation was chosen as the standard because of its current clinical use. Five types of screws were tested to determine whether screw design had an effect on the efficacy of augmentation. SUMMARY OF BACKGROUND DATA: Although many factors affect the pull-out resistance of pedicle screws, a key determinant of their performance is the strength of their attachment to the spine. In elderly, osteopenic patients, the screw-bone interface is especially at risk for stripping during insertion or pull-out after surgery. In these patients, polymethylmethacrylate has been used to augment pedicle screw fixation, although its use is not without risk. In situ-setting calcium phosphate cements may provide an alternative to polymethylmethacrylate in this application. Like polymethylmethacrylate, calcium phosphate cements can be injected into the prepared screw hole. They have the added advantage of being resorbed and replaced during healing and normal bone remodeling. METHODS: Thirty human lower lumbar vertebrae (L3-L5) were implanted bilaterally with one of five types of pedicle screws (n = 6 for each screw type). The screws were pulled out 3.0 mm at 0.25 mm/sec with a servohydraulic materials testing machine. The 3.0-mm pull-out distance, which was slightly longer than one thread pitch, was designed to strip the screw-bone interface but to leave the pedicle otherwise intact. After the initial testing, the screws in each vertebrae were removed, and the screw tracks were filled with 2.0 cc of polymethylmethacrylate (one side) or calcium phosphate cement (contralateral side). After augmentation, the screws were reinserted, and the cements were allowed to harden for 24 hours. Postaugmentation testing followed the protocols for preaugmentation testing, and the pull-out resistance of screws augmented with calcium phosphate cement was compared with the pull-out resistance of screws augmented with polymethylmethacrylate. RESULTS: Mechanically, calcium phosphate cement compared favorably with polymethylmethacrylate for augmenting pedicle screws. Both restored the strength of the screw-bone interface: across all screw types, the average increase in pull-out strength was 147% with polymethylmethacrylate augmentation and 102% with calcium phosphate cement. There were no significant differences because of screw type with either type of augmentation. CONCLUSIONS: The in situ-setting calcium phosphate cement investigated in this study compared favorably with polymethylmethacrylate in a single-cycle, pull-out test of augmented pedicle screws in senile trabecular bone. With further evaluation, this cement may offer an alternative to polymethylmethacrylate for the enhancement of pedicle screw fixation clinically.     

EDTA络合滴定法测定钢渣面脱氧剂中氧化钙和氟化钙

建立了EDAT络合滴定法测定钢渣面脱氧剂中氧化钙和氟化钙含量的分析方法。试样用碳酸钠-硼酸混合熔剂熔融, 稀盐酸浸取, 六次甲基四胺分离铝离子和铁离子后, 以三乙醇胺掩蔽剩余干扰离子, 在强碱介质中, 以钙黄绿素作指示剂, 用EDTA标准滴定溶液滴定了试样中总氧化钙的含量。采用稀乙酸浸取分离试样中碳酸钙、氧化钙, 过滤分离氟化钙, 用锆-二甲酚橙褪色光度法测定了浸取液中的氟, 换算为氟化钙的量;同时用混合酸分解沉淀, 采用EDTA络合滴定法测定了沉淀中氟化钙的量;将二者相加后除以试样总量得到试样中氟化钙的含量。用总氧化钙的含量减去由氟化钙换算成的氧化钙含量, 即为试样中氧化钙的含量。采用方法对钢渣面脱氧剂试样进行6次平行测定, 相对标准偏差(RSD)小于1.5 %。选取高纯铝粉、基准三氧化二铝和基准氧化钙以及萤石标准物质合成钢渣面脱氧剂试样A1、A2、A3, 同时在精炼渣标准物质中加入基准氧化钙和萤石标准物质合成试样A4, 按照方法进行氧化钙和氟化钙的测定, 结果与理论值一致。在钢渣面脱氧剂试样中加入基准氧化钙和萤石标准物质进行加标回收试验, 回收率在94%～102%之间。     

Feasibility study of a natural crosslinking reagent for biological tissue fixation

The hardening properties of calcium phosphate cements in the CaHPO4-alpha-Ca3(PO4)2 (DCP-alpha-TCP) system have been investigated with interest focused on the compressive strength and microstructure development. Previous studies have shown that the addition of CaCO3(CC) leads to a modification of the calcium-deficient apatite structure of the reaction product, which results in a material more similar to the apatite in bone mineral. The addition of 10% w/w of CC to the initial DCP-alpha-TCP powder mixture resulted, with time, in a retardation of the development of compressive strength. However, the optimum compressive strength reached values up to 40% higher than CC-free samples. This retarding effect also has been monitored as a function of the calcium to phosphorus (Ca/P) ratio of the DCP and alpha-TCP mixture, showing the importance of the final cement properties of the relative quantities of the reactants in the mixture.     

A micro-Raman spectroscopic study of hydrazine-treated human dental calculus

Hydrazine has been used to remove organic components and to isolate the mineral(s) from human calculus. Micro-Raman measurements were performed on the mineral phase. After the hydrazine-treatment, not only a large reduction in fluorescence but also an increase in Raman signal was observed. The treatment was essential in minimizing thermally-induced chemical changes which could otherwise occur to the original calculus mineral due to the intense laser light. The Raman spectral features of the mineral were nearly all identical among the Raman spectra obtained at many randomly-selected sites by the micro-Raman microbe with a lateral resolution of approximately 1 micron, and were consistent with those of impure hydroxyapatite containing CO3(2-) and HPO4(2-). The spectra contained typical hydroxyapatite bands including PO4(3-)bands of the v1, v2, v3 and v4 modes and one OH- stretch band. Other minor bands due to the CO3(2-) v1 and v3 modes and bands possibly due to the HPO4(2-) v1, v2 and v4 modes were observable by the technique despite the hydrazine-treatment that could in principle remove the HPO4 and CO3 ions from the mineral. In comparison with pure synthetic hydroxyapatite, the intensity of the OH- stretch band relative to that of the PO4(3-) v1 band was approximately 70% weaker, and the bandwidth of the phosphate v1 band was 200% broader, reflecting various crystal imperfections presumably present in the calculus mineral.