Comparison between different dialysate calcium concentrations in nocturnal hemodialysis

Benefits of dialysate with greater calcium (Ca) concentration are reported in nocturnal hemodialysis (NHD) to prevent Ca depletion and subsequent hyperparathyroidism. Studies with patients dialyzing against 1.25 mmol/L Ca baths demonstrate increases in alkaline phosphatase (ALP) and parathyroid hormone (PTH) and increasing dialysate Ca subsequently corrects this problem. However, whether 1.5 or 1.75 mmol/L dialysate Ca is most appropriate for NHD is yet to be determined, and differences in the effect on mineral metabolism of daily vs. alternate daily NHD have also not been well defined. We retrospectively analyzed mineral metabolism in 48 patients, from 2 institutions (30 at Monash and 18 at Geelong), undergoing home NHD (8 hr/night, 3.5-6 nights/week) for a minimum of 6 months. Thirty-seven patients were dialyzed against 1.5 mmol/L Ca bath and 11 patients against 1.75 mmol/L. We divided patients into 4 groups, based on dialysate Ca and also on the hours per week of dialysis, <40 (1.5 mmol/L, n=29 and 1.75 mmol/L, n=8) or > or =40 (n=4 and 7). We compared predialysis and postdialysis serum markers, time-averaged over a 6-month period, and the administration of calcitriol and Ca-based phosphate binders between 1.5 and 1.75 mmol/L Ca dialysate groups. Baseline characteristics between all groups were similar, with a slightly longer, but nonsignificant, duration of NHD in both 1.75 mmol/L dialysate groups compared with 1.5 mmol/L. The mean predialysis Ca, phosphate, and Ca x P were similar between the 1.5 and 1.75 mmol/L groups, regardless of NHD hr/week. Postdialysis Ca was significantly greater, with 1.75 vs. 1.5 mmol/L in those dialyzing <40 hr/week (2.64+/-0.19 vs. 2.50+/-0.12 mmol/L, p=0.046), but postdialysis Ca x P were similar (2.25+/-0.44 vs. 2.16+/-0.29 mmol(2)/L(2), p=0.60). Parathyroid hormone was also lower with 1.75 vs. 1.5 mmol/L baths in the <40 hr/week groups (31.99+/-26.99 vs. 14.47+/-16.36 pmol/L, p=0.03), although this difference was not seen in those undertaking NHD > or =40 hr/week. Hemoglobin, ALP, and albumin were all similar between groups. There was also no difference in vitamin D requirement when using 1.75 mmol/L compared with the 1.5 mmol/L dialysate. Multivariate analysis to determine independent predictors of postdialysis serum Ca showed a statistically significant positive association with predialysis Ca, dialysate Ca, and total NHD hr/week. An elevated dialysate Ca concentration is required in NHD to prevent osteopenia but differences in serum markers of mineral metabolism between 1.5 and 1.75 mmol/L Ca dialysate in NHD in our study were few. This was similar for patients undertaking NHD <40 or > or =40 hr/week, although differences in the frequency of NHD may also be as important as dialysate Ca with regard to serum Ca levels. With concerns that prolonged higher Ca levels contribute to increased cardiovascular mortality, the optimal Ca dialysate bath is still unknown and further studies addressing bone metabolism with larger NHD numbers are required.     

The effects of nocturnal compared with conventional hemodialysis on mineral metabolism: A randomized‐controlled trial

Hyperphosphatemia is common among patients receiving dialysis and is associated with increased mortality. Nocturnal hemodialysis (NHD) is a long, slow dialytic modality that may improve hyperphosphatemia and disorders of mineral metabolism. We performed a randomized‐controlled trial of NHD compared with conventional hemodialysis (CvHD); in this paper, we report detailed results of mineral metabolism outcomes. Prevalent patients were randomized to receive NHD 5 to 6 nights per week for 6to 10 hours per night or to continue CvHD thrice weekly for 6 months. Oral phosphate binders and vitamin D analogs were adjusted to maintain phosphate, calcium and parathyroid hormone (PTH) levels within recommended targets. Compared with CvHD patients, patients in the NHD group had a significant decrease in serum phosphate over the course of the study (0.49 mmol/L, 95% confidence interval 0.24–0.74; P=0.002) despite a significant reduction in the use of phosphate binders. Sixty‐one percent of patients in the NHD group compared with 20% in the CvHD group had a decline in intact PTH (P=0.003). Nocturnal hemodialysis lowers serum phosphate, calcium‐phosphate product and requirement for phosphate binders. The effects of NHD on PTH are variable. The impact of these changes on long‐term cardiovascular and bone‐related outcomes requires further investigation.     

Kinetics of calcium molybdate crystallization

Kinetics of crystallization of calcium molybdate from unstirred molten solutions of lithium chloride of low to medium supersaturation in platinum crucibles by the process of continuous cooling at 5° C hr⁻¹ from temperaturesT ₀=700 and 750°C are investigated. The crystal size measured by optical microscopy for different crystallization periods reveals that both crystal length and width generally increase with cooling period. The degree of crystallizationα _t,also increases with cooling period, attaining a maximum of 0·90. The diffusion rate constants,K _Dlat 700 and 750°C are 0·0776 and 0·1138 respectively. The effect of variation of the crystallization temperature on the crystal size and their number is also studied.     

Synthesis of calcium phosphate hydrogel from waste incineration fly ash and bone powder

Waste incineration fly ash and bone powder could be successfully recycled into calcium phosphate hydrogel, a type of fast proton conductor. Various properties of the intermediate and calcium phosphate hydrogel from them were characterized and compared with that from calcium carbonate reagent. It was found that the intermediate from the incineration fly ash and calcium phosphate glass was more brittle than that from bone powder and calcium carbonate reagent. The electric conductivity of crystallized hydrogel obtained from all raw materials increases exponentially with temperature. However, the crystallized hydrogel from incineration fly ash has lower electric conductivity and lower crystallinity than that from bone powder and the reagent. Moreover, the difference in electric conductivity between these crystallized hydrogels decreases with temperature. Compared with using the reagent as a raw material, bone powder provides a 25% reduction in the usage of H(3)PO(4) to acquire the crystallized hydrogel which has the highest conductivity. These experimental results suggest that the incineration fly ash and bone powder are useful calcium sources for the synthesis of calcium phosphate hydrogel.     

Self-assembly of mineralized collagen composites

This paper presents a review of the current understanding of the structure, self-assembly mechanisms, and properties of mineralized collagen fibril composites in connective tissues, such as in lamellar bones, woven bones, zebrafish skeletal bone, and ivory. Recent work involving biomimetic synthesis of new materials with the structure of mineralized collagen is described. The focus in the paper is mainly on materials containing type I collagen, with mineralization by Ca–P crystals although some other systems are also described. Investigation and simulation of naturally occurring fibril structures can offer some new ideas in the design and fabrication of new functional materials, for applications such as bone grafts or for use as scaffolds in tissue engineering and biomimetic engineering materials. The development of bone grafts based on the mineralization of self-assembled collagen fibrils in vivo and in vitro is an active area of research. This kind of bone graft composite has already shown great promise and success in clinical applications, on account of its compositional and structural similarity to autologous bone. It is suggested that future work in this should focus on both basic theoretical aspects as well as the development of applications. In particular issues including control of morphology, incorporation of foreign ions, interaction with biomolecules, and the assembly of organic and inorganic phases are all still not well understood. In the area of applications, the design of composite materials with a hierarchical structure closer to that of natural hard tissues, and the synthesis of bone grafts and tooth regenerative materials, as well as biomimetic functional materials, are areas currently being examined by many research groups.     

On the development of an apatitic calcium phosphate bone cement

Development of an apatitic calcium phosphate bone cement is reported. 100 μ Particles of tetracalcium phosphate (TTCP) and dicalcium phosphate dihydrate (DCPD) were mixed in equimolar ratio to form the cement powder. The wetting medium used was distilled water with Na₂HPO₄ as accelerator to manipulate the setting time. The cement powder, on wetting with the medium, formed a workable putty. The setting times of the putty were measured using a Vicat type apparatus and the compressive strength was determined with a Universal Testing Machine. The nature of the precipitated cement was analyzed through X-ray diffraction (XRD), fourier transform infrared spectrometry (FTIR) and energy dispersive electron microprobe (EDAX). The results showed the phase to be apatitic with a calcium-to-phosphorous ratio close to that of hydroxyapatite. The microstructure analysis using scanning electron microscopy (SEM) showed hydroxyapatite nano-crystallite growth over particulate matrix surface. The structure has an apparent porosity of ∼ 52%. There were no appreciable dimensional or thermal changes during setting. The cement passed the in vitro toxicological screening (cytotoxicity and haemolysis) tests. Optimization of the cement was done by manipulating the accelerator concentration so that the setting time, hardening time and the compressive strength had clinically relevant values.     

Residential gas-fired absorption heat pump based on R22-DEGDME pair. Part 2 design, computer simulation and testing of a prototype

A prototype absorption heat pump system whose rated capacities are 4000 kcal h⁻¹ for cooling and 8000 kcal h⁻¹ for heating was designed, constructed and tested. A mathematical model of this system was developed which demonstrates the superiority of DEGDME over TEGDME as solvent. The coefficients of performance of the constructed prototype are 0.55 for cooling and 1.25 for heating.     

银型磷酸钙无机抗菌功能材料的研究

待抗菌成分Ａｇ＾＋离子及其化合物结合于磷酸钙而制得无机抗菌功能材料。采用三种典型的细菌研究了材料的抗菌性能,同时研究了烧结温度对杀菌效果的影响,以及抗菌功能材料的抗菌持久性、使用安全性。实验结果表明,银型磷酸钙抗菌功能材料具有良好的广谱抗菌性、抗菌持久性和使用安全性。     

Calcium phosphate-gold nanoparticles nanocomposite for protein adsorption and mediator-free H2O2 biosensor construction

This work reports a new method for the preparation and application of a kind of biocompatible calcium phosphate-gold nanoparticles (Ca₃(PO₄)₂-AuNPs) nanocomposite. UV-vis spectroscopy and transmittance electron microscopy (TEM) have been used to monitor the formation process of the nanocomposite and to examine the interaction between calcium phosphate and gold nanoparticles (AuNPs). The nanocomposite has multiple sites and improved conductivity which make it suitable for the binding of proteins to construct electrochemical sensors. Myoglobin (Mb) adsorbed on the nanocomposite retained its native structure which was proved by Fourier transform infrared spectroscopy (FTIR). Direct electron transfer between the adsorbed Mb and the electrode was observed. Further results demonstrated that the adsorbed Mb has good electrocatalytic activity towards the reduction of H₂O₂ in the absence of any mediator.     

Nano-sized calcium phosphate (CaP) carriers for non-viral gene deilvery

Gene therapy has garnered much interest due to the potential for curing multiple inherited and/or increases in the acquired diseases. As a result, there has been intense activity from multiple research groups for developing effective delivery methods and carriers, which is a critical step in advancing gene delivery technologies. In order for the carriers to effectively deliver the genetic payloads, multiple extracellular and intracellular barriers need to be overcome. Although overcoming these challenges to improve the effectiveness is critical, the development of safe gene delivery agents is even more vital to assure its use in clinical applications. The development of safe and effective strategies has therefore been a major challenge impeding gene therapy progress. In this regard, calcium phosphate (CaP) based nano-particles has been considered as one of the candidate non-viral gene delivery vehicles, but has been plagued by inconsistent and low transfection efficiencies limiting its progress. There has been major research effort to improve the consistency and effectiveness of CaP based vectors. Currently, it is therefore thought that by controlling the various synthesis factors such as Ca/P ratio, mode of mixing, and type of calcium phosphate phase, such variability and inefficiency could be modulated. This review attempts to provide a comprehensive analysis of the current research activity in the development of CaP based ceramic and polymer-ceramic hybrid systems for non-viral gene delivery. Preliminary transfection results of hydroxyapatite (HA or NanoCaPs), amorphous calcium phosphate (ACP) and brushite phases are also compared to assess the effect of various CaP phases, and correspondingly, changes in the dissolution characteristic of the pDNA-CaP complex on the gene transfection efficiency.     

Comparison between fixed and fluidized bed continuous pea freezers

Analytical equations for predicting production rates of continuous fixed bed pea freezers are derived on the basis of a simplified model for freezing individual particles. Comparisons with models of continuous fluidized bed freezers of the same dimensions show production rates 20–30% higher for fluidized beds. The bed height proves to be an important operating variable for obtaining the maximum production rate in these types of freezers. From the standpoint of power consumption in blowers the fixed bed requires 1.7–2.1 times more power for attaining equal production rates.     

Comparison between fixed and fluidized bed continuous pea freezersComparaison des congélateurs continus pour petits pois à lit fixe et à lit fluidisé

Analytical equations for predicting production rates of continuous fixed bed pea freezers are derived on the basis of a simplified model for freezing individual particles. Comparisons with models of continuous fluidized bed freezers of the same dimensions show production rates 20–30% higher for fluidized beds. The bed height proves to be an important operating variable for obtaining the maximum production rate in these types of freezers. From the standpoint of power consumption in blowers the fixed bed requires 1.7–2.1 times more power for attaining equal production rates.     

Quality deterioration of refrigerated foods and its time-temperature mathematical relationships

Although the quality of refrigerated foodstuffs is generally an arbitrary notion, one can try to develop a model or a hypothesis to quantify it. In practice quality always exists in the commercial field as one of the factors that determine price. To this end a general formula has been established as a double function of time and temperatures (QTTT); some numerical constants are presented here which make it possible to interpret the time-temperature tolerances. We have established mathematically the possibility of passing from the chemicals tests or the evolution and variation of the quality indices to a quality criterion, particularly in the case of meat, within the limits of a scale of 0–100, whatever refrigeration treatments may be applied.     

Corrosion resistance of biomimetic calcium phosphate coatings on magnesium due to varying pretreatment time

Calcium phosphate coatings were prepared on magnesium substrates via a biomimetic coating process. The effects of a magnesium hydroxide pretreatment on the formation and the ultimate corrosion protection of the coatings were studied. The pretreatment layer was found to affect the amount of defects present in the coatings. Corrosion resistance of the coatings was studied in vitro using two simulated body fluids, 0.8% NaCl and Hanks solution. In NaCl, the resistance to corrosion of all samples decreases with time as corrosion proceeded through cracks and other defects in the coatings. Samples with no pretreatment displayed the highest corrosion resistance as these samples had the fewest defects in the coating. However, in Hanks solution, corrosion resistance increased with time due to additional nucleation of calcium phosphate from the fluid on to the substrate. In this solution, additional pretreatment time was beneficial to the overall corrosion resistance.     

Single-step rapid microwave-assisted synthesis of polyacrylamide-calcium phosphate nanocomposites in aqueous solution

Organic-inorganic polyacrylamide-calcium phosphate (PAM-CP) nanocomposites with calcium phosphate (CP) nanoparticles homogeneously dispersed in the polymer matrix have been successfully synthesized using calcium salt, phosphate and acrylamide monomer in aqueous solution by a single-step microwave-assisted method. When the experiment is conducted in a basic medium, the CP phase obtained consists of hexagonal hydroxyapatite (HAP) nanorods, and HAP nanorods are homogeneously dispersed in the polyacrylamide (PAM) matrix. While the preparation is in a weak acidic medium, the amorphous calcium phosphate (ACP) nanoparticles are formed and dispersed in the PAM matrix. The reported method has advantages of being simple, rapid, low-cost, and environmentally friendly. The products are characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TG).     

Role of macropore size in the mechanical properties and in vitro degradation of porous calcium phosphate cements

The goal of the present study was to investigate the effect of macropore size on the compressive strength and in vitro degradation of porous calcium phosphate cements (CPCs). For this purpose, a series of porous CPCs with three different macropore sizes (200-300 μm, 300-450 μm and 450-600 μm) and comparable porosity were prepared by salting-out method, and the study of in vitro degradation behavior was carried out under a constant fluid flow environment. The results showed that the increase in macropore size of CPCs with invariant porosity resulted in a decrease in the compressive strength but an increase in the degradation rate of CPCs significantly, suggesting the possibility that the degradation rate and compressive strength of biomaterials can be regulated by varying the macropore size while maintaining the porosity unchanged.