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.     

Morphology and microstructure of electrochemically deposited calcium phosphates in a modified simulated body fluid

Calcium phosphates were deposited on a pure titanium plate for various loading times under 1.3 and 12.9 mA/cm2 in a modified simulated body fluid at 52-92 degrees C. The plate-like crystals formed under 1.3 mA/cm2 were identified to be octacalcium phosphate (OCP) and/or carbonate-containing apatite. OCP converted to carbonate-containing apatite with the elapsing time of the loading current. The needle-like precipitates formed under 12.9 mA/cm2 were identified to be carbonate-containing apatite crystals elongated parallel to the c-axis direction. The degrees of crystallinity of the deposits formed under 1.3 mA/cm2 showed the highest value around 72 degrees C, whereas those under 12.9 mA/cm2 increased with the electrolyte temperature. The carbonate content of the deposits decreased with the electrolyte temperature and the flow current. The degree of crystallinity of the electrochemically deposited calcium phosphates decreased with the carbonate content.     

Quasi-biological apatite film induced by titanium in a simulated body fluid

Cytosolic Ca2+ ([Ca2+]i) plays an important role in endothelial cell signaling. Although it has been suggested that the influx of Ca2+ can be triggered by depletion of intracellular Ca2+ stores, the mechanism (or mechanisms) underlying this phenomenon needs further elaboration. In the present study, involvement of myosin light-chain kinase (MLCK) in the regulation of Ca2+ signaling was investigated in agonist- and fluid flow-stimulated endothelial cells loaded with Ca2+-sensitive dyes. Bradykinin (BK) and thapsigargin caused an increase in [Ca2+]i followed by a sustained rise due to Ca2+ influx from extracellular space and shifted total myosin light-chain (MLC) from the unphosphorylated to the diphosphorylated form. ML-9 (100 microM), an inhibitor of MLCK, abolished Ca2+ influx and prevented MLC diphosphorylation in BK- and thapsigargin-treated cells, but did not affect Ca2+ mobilization from internal stores. Fluid flow stimulation (shear stress=5 dynes/cm2) increased [Ca2+]i and enhanced MLC phosphorylation. ML-9 also inhibited Ca2+ response and MLC phosphorylation in fluid flow-stimulated cells. The Ca2+ influx in response to BK was linearly correlated with the diphosphorylation of MLC in ML-9 treated cells. Effects of ML-5 and ML-7, analogs of ML-9, to inhibit Ca2+ influx paralleled their potencies to inhibit MLCK activity. These findings demonstrate that MLCK plays an essential role in regulating the plasmalemmal Ca2+ influx in agonist- and fluid flow-stimulated endothelial cells. This study is the first to report the close relationship between Ca2+ influx and MLC diphosphorylation.     

Surface structural change of bioactive inorganic filler-resin composite cement in simulated body fluid: effect of resin

Recently much attention has been paid to bioactive filler-resin composite cements because they can solidify in a few minutes to give high mechanical strengths and they can bond to living bone. In this study the dependence on resin of apatite-forming ability in simulated body fluid (SBF) was investigated for the composite cements of bioactive CaO-SiO2-P2O5-CaF2 glass with polymethyl methacrylate (PMMA) or bisphenol-a-glycidyl methacrylate/triethyleneglycol (Bis-GMA/TEGDMA) resin. The PMMA-containing composite cement did not show the apatite-forming ability in SBF because the reaction of the glass grains with SBF was inhibited due to the complete covering of the grains with PMMA. To the contrary, the Bis-GMA/TEGDMA-containing cement exhibited high apatite-forming ability in SBF; these monomers significantly dissolved from the composite surface into SBF, causing a direct exposure of the glass grains to SBF to convert into silica gel. It is assumed that thus formed silica gels, and the silicate ions that were dissolved and adsorbed onto the composite surface, induced the apatite nucleation between the spaces of the glass grains and on the composite surface, respectively. A continuous bone-like apatite layer was formed on the top surface of the glass-Bis-GMA/TEGDMA composite cement in a short period.     

磷酸钙骨水泥生物材料用磷酸四钙的制备

采用CaCO3和CaHPO4的混合粉分别在空气和真空2种气氛条件下制备磷酸四钙。结果表明:在空气中较难制得磷酸四钙,这主要是由于潮湿的空气中含有较多水分和制备工艺中采取随炉缓慢冷却,对反应产生了不利影响;在真空条件下,采用n(Ca)∶n(P)=2∶1,1.8∶1和1.5∶1的3种混合粉均容易制得磷酸四钙,但同时都含有其它杂质相,对其纯度有影响,其中以n(Ca)∶n(P)=2∶1的混合粉制备的磷酸四钙纯度最高,其产物中仅含少量CaO杂质相,这种磷酸四钙可用于磷酸钙骨水泥。     

Resorbable calcium phosphate bone substitute

Bacteroides fragilis strains isolated from different sources, i.e. 1 strain (AA1) from an aquatic environment, 1 strain from normal flora (118310) and the type strain (ATCC 25285) originally isolated from clinical material, were analysed for both cell envelope proteins composition and surviving under oxidative stress starvation. All strains examined showed a similar survival response when cultured in drinking water with a ten-fold decrease in viable counts per day during the 7 days of analysis. The outer membrane protein (OMP) profiles of all strains were quite similar during the stress period as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). However, the periplasmic proteins of the strain 118310 showed two protein bands at 48 and 58 kDa, respectively, that were absent in the strains AA1 and ATCC 25285 during the incubation period in potable water. Whole cells and periplasmic 35S-labelled proteins from bacteria cultured in drinking water showed a significant increase in proteins at 16, 18, 24, 26, 35, 48, and 58 kDa and 18, 22, 24, 48, 58, and 70 kDa, respectively, in all strains when compared to cells grown in BHI-PRAS media as detected by autoradiography following SDS-PAGE. These data suggest that B. fragilis may have a synthesis mechanism that allows them to adapt to adverse environments.     

Influence of extracellular fluid volume expansion on magnesium, calcium and phosphate handling along the rat nephron

Renal tubular handling of P, Ca, Mg and Na was studied in the rat both before and during mild hypertonic NaCl loading (ECVE), using micropuncture and clearance techniques and electron microprobe analysis. Micropuncture was performed at the late proximal and early distal tubule sites. ECVE significantly increased the urinary output of all four elements. In the case of Mg, the increase was relatively small and depended on slight but statistically unsignificant inhibition of reabsorption all along the entire length of the nephron. For Ca, it depended on the inhibition of proximal reabsorption, partially compensated by increased reabsorption along the loop. For P, it depended on proximal inhibition, no important net phosphate movement occurring in the loop during both periods. Ca reabsorption was highly correlated to that of sodium along the proximal tubule and Henel's loop, Ca and Mg reabsorption were closely related to the load delivered at the beginning of the structure. These observations are compatible with the view that tubular reabsorption of Ca and Mg is concentration rather than Tm limited, and that reabsorption of Ca, unlike that of Mg, is linked to the movements of sodium. Following ECVE, the difference between early distal and urinary deliveries increased significantly for Ca and P, but not for Mg. For phosphate, this difference accounted for by 45% of the delivery at the early distal tubule site, at variance with microinjection data obtained in the rat under similar salt loading conditions, which indicated that 17% only of the phosphate distal delivery were reabsorbed along the terminal segments. This discrepancy is discussed in terms of nephron functional heterogeneity.     

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.     

Evaluation of cytotoxicity of calcium phosphate cement consisting of alpha-tricalcium phosphate and dicalcium phosphate dihydrate

Elimination of the data processing bottleneck in high-throughput sequencing will require both improved accuracy of data processing software and reliable measures of that accuracy. We have developed and implemented in our base-calling program phred the ability to estimate a probability of error for each base-call, as a function of certain parameters computed from the trace data. These error probabilities are shown here to be valid (correspond to actual error rates) and to have high power to discriminate correct base-calls from incorrect ones, for read data collected under several different chemistries and electrophoretic conditions. They play a critical role in our assembly program phrap and our finishing program consed.     

Effects of hypoxia on membrane potential and intracellular calcium in rat neonatal carotid body type I cells

1. We have studied the effects of hypoxia on membrane potential and [Ca2+]i in enzymically isolated type I cells of the neonatal rat carotid body (the principal respiratory O2 chemosensor). Isolated cells were maintained in short term culture (3-36 h) before use. [Ca2+]i was measured using the Ca(2+)-sensitive fluoroprobe indo-1. Indo-1 was loaded into cells using the esterified form indo-1 AM. Membrane potential was measured (and clamped) in single isolated type I cells using the perforated-patch (amphotericin B) whole-cell recording technique. 2. Graded reductions in PO2 from 160 Torr to 38, 19, 8, 5 and 0 Torr induced a graded rise of [Ca2+]i in both single and clumps of type I cells. 3. The rise of [Ca2+]i in response to anoxia was 98% inhibited by removal of external Ca2+ (+1 mM EGTA), indicating the probable involvement of Ca2+ influx from the external medium in mediating the anoxic [Ca2+]i response. 4. The L-type Ca2+ channel antagonist nicardipine (10 microM) inhibited the anoxic [Ca2+]i response by 67%, and the non-selective Ca2+ channel antagonist Ni2+ (2 mM) inhibited the response by 77%. 5. Under voltage recording conditions, anoxia induced a reversible membrane depolarization (or receptor potential) accompanied, in many cases, by trains of action potentials. These electrical events were coincident with a rapid rise of [Ca2+]i. When cells were voltage clamped close to their resting potential (-40 to -60 mV), the [Ca2+]i response to anoxia was greatly reduced and its onset was much slower.(ABSTRACT TRUNCATED AT 250 WORDS)     

Serum calcium, phosphate and alkaline phosphate levels in epileptic children treated with phenobarbitone

A longitudinal study to estimate the serum calcium, phosphate and alkaline phosphatase levels of 89 ambulatory epileptic children, aged between 3 years and 12 years, and having generalised tonic-clonic seizures, was carried out. None was on any form of medication for the treatment of seizures prior to presentation. Each patient received only phenobarbitone during the period of study. Serum levels of the biochemical parameters were determined at presentation, 6 months and 12 months, while serum phenobarbitone levels were estimated at 6 months and 12 months. Mean serum calcium, phosphate and alkaline phosphatase of the patients remained within the normal range. Using the paired 't' test, the differences in the levels of the parameters at the three measurements were not statistically significant (P > 0.05). Serum phenobarbitone levels remained within the therapeutic range during the period of study. Our results show that over a 12-month period, serum levels of calcium, phosphate, and alkaline phosphatase, remain normal in ambulant epileptic children treated with phenobarbitone.     

Effect of calcium carbonate on clinical compliance of apatitic calcium phosphate bone cement

Incidentally discovered adrenal masses are common since the advent and application of sensitive noninvasive imaging methods. The significance of these so-called "incidentalomas" and the question of further evaluation or treatment remains elusive. This report describes a retrospective study of 86 patients with incidentaloma. Adrenalectomy was performed on 26 patients during initial admission. Histologically, two cortisol-producing adenomas, an adenoma with subclinical cortisol production, and two pheochromocytomas (all of the preceding detected during the preoperative hormonal evaluation), three cystic lesions, one myelolipoma, and one hematoma were found. One primary and two metastatic adrenal carcinomas were also found in this series. Sixty patients with a nonfunctioning incidentaloma smaller than 6 cm were observed in an average of 43 months with serial CT scans performed at 3, 9, and 18 months after the initial diagnosis. Enlargement of the mass was detected in two patients; both proved to be nonfunctioning adenomas. Based on these observations, it is concluded that the initial laboratory evaluation is mandatory in cases of incidentalomas, including parameters of adrenocortical and medullar function. Hormonally active incidentalomas and those suspected for malignancy should be treated surgically. Masses greater than 6 cm should also be removed. Smaller incidentalomas without endocrine activity or signs of malignancy should be followed by CT scan at 3, 9, and 18 months after the initial diagnosis.     

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.     

放电等离子烧结温度对Ti-13Nb-13Zr合金在人工模拟体液中耐腐蚀性能的影响

利用放电等离子烧结技术(spark plasma sintering,SPS)制备Ti-13Nb-13Zr(TNZ)生物医用合金,采用开路电位、动电位极化曲线、电化学阻抗谱和X射线光电子能谱等研究烧结温度对合金在Hank’s人工模拟体液中电化学腐蚀性能的影响,并与纯Ti(TA1)和Ti-6Al-4V(TC4)合金进行对比。结果表明:与TA1和TC4合金相比,SPS制备的TNZ合金具有较高的自然腐蚀电位Ecorr、较低的极化电流密度icorr以及较高的线性极化电阻Rp,并随烧结温度升高,耐腐蚀性能逐渐增强。该合金在模拟人工体液中耐腐蚀性能优异的主要原因是合金表面形成稳定、均匀且保护性更强的复合氧化物钝化膜,钝化膜由Ti O2,Nb2O5和Zr O2组成;随烧结温度升高,合金获得较高的致密度和近β型单相组织,耐腐蚀性能提高。     

Effect of calcium carbonate on the compliance of an apatitic calcium phosphate bone cement

Clinical requirements for calcium phosphate bone cements were formulated in terms of the initial setting time, the final setting time, the cohesion time and the ultimate compressive strength. Three cement formulations were tested. The previously developed Biocement H was made of a powder containing alpha-tertiary calcium phosphate and precipitated hydroxyapatite. Biocement B2 powder was made by adding some CaCO3 to Biocement H, whereas Biocement B1 was made by adding some CaCO3 but with simultaneous adjustment of the amount of precipitated hydroxyapatite.The liquid/ powder ratio of the cement paste and the accelerator concentrations (percentage Na2HPO4) in cement liquid were varied. For Biocement H there was no combination of L/P ratio and percentage Na2HPO4 for which all clinical requirements were satisfied. However, there was an area of full compliance for Biocements B1 and B2, of which that for B1 was the largest. Therefore, Biocement B1 may be applied in clinical situations as those in orthopaedics, plastic and reconstructive surgery and oral and maxillofacial surgery, even when early contact with blood is inevitable.     

Effect of hydrocortisone on total body calcium in rats

Administration of 5 mg. of hydrocortisone acetate to rats every other day for 2 weeks resulted in growth retardation and weight loss as indicated by body weights of experimental animals, which averaged 33 per cent lower than those of the controls, and a significant decrease in the length of the tibiae and femurs (p less than 0.01 for treated vs controls). However, despite the smaller size of the treated animals, the values for total body calcium (TBCa) and the calcium in the tibia and femur did not differ significantly from control values. Thus, there was more calcium per unit length of bone, resulting in an increase in the skeletal density of treated rats. This finding was confirmed by x-ray examination of these bones. The net intestinal absorption of calcium (rate of initial entry) calculated from plasma levels following an oral and intravenous dose of 47Ca and 85Sr, respectively, was not significantly different in hydrocortisone-treated rats compared to controls. This would indicate that the rate of intestinal absorption of calcium is unimpaired despite the administration of massive doses and corticosteroids. When the animals were placed on a calcium-deficient diet, both TBCa and tibia and femur calcium levels were decreased. Subsequent administration and hydrocortisone did not alter the calcium values. The results of this study are compatible with the hypothesis that hydrocortisone promotes weight loss, retards growth, but inhibits the rate of bone resorption.     

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.     

Variation of salivary calcium, phosphate and buffering capacity in adolescents

Calcium, phosphate and buffering capacity were measured in children's (n=43) unstimulated saliva between September 1990 and June 1991 inclusive. Saliva samples were collected in the afternoon, once a month, on 10 consecutive occasions. Buffering capacity was assessed immediately after sample collection using the Dentobuff strip method. The remainder of the saliva sample was then stored at -18 degrees C and, after thawing, total calcium and inorganic phosphate were measured. The intra-individual variation of buffering capacity over time was statistically significant (Friedman two-way ANOVA, p < 0.001). The intra-individual variability of salivary calcium was also statistically significant (repeated-measures ANOVA, p < 0.001). However, no evidence of a statistically significant variation in phosphate was observed. It is concluded that a combination of flow-rate fluctuation over time and the methods used to assess salivary constituents might have contributed to this variability.