Phosphate-containing Solution Research Articles

Feasibility of electrodeionization for phosphate removal.

In this study, electrodeionization (EDI) in bath mode was tested regarding its capability to remove phosphate (PO4 3- ) ions from aqueous solutions. Various parameters affecting the phosphate removal rate via EDI were determined. The results showed that the phosphate removal rate depends on the applied voltage and that the optimum potential was 15 V, corresponding to a phosphate removal rate of 97%. Changing the stream rate of the phosphate-containing solution also affected the phosphate removal rate. Changing the pH of the phosphate-containing solution from 2 to 6 enhanced the phosphate removal rate from 80% to 97%. The presence of Cl- , NO3 - , and SO4 2- ions did not affect the phosphate removal rate. The highest mass transfer coefficient (k) of phosphate was calculated to be 7.85 × 10-4 m/s, and the flux was calculated to be 3.72 × 10-4 mol/m2 s1 at a flow velocity of 3L/h. Thus, the study results showed the feasibility of EDI as an alternative membrane process for removing phosphate from aqueous solutions. PRACTITIONER POINTS: Electrodeionization was employed for the removal of phosphate. The removal of phosphate exhibited dependence on applied potential. EDI demonstrated a remarkable 97% efficiency in phosphate removal. The pH of the solution was found to influence the removal rate.

Simplified regional citrate anticoagulation protocol for CVVH, CVVHDF and SLED focused on the prevention of KRT-related hypophosphatemia while optimizing acid-base balance.

Hypophosphatemia is a common electrolyte disorder in critically ill patients undergoing prolonged kidney replacement therapy (KRT). We evaluated the efficacy and safety of a simplified regional citrate anticoagulation (RCA) protocol for continuous venovenous hemofiltration (CVVH), continuous venovenous hemodiafiltration (CVVHDF) and sustained low-efficiency dialysis filtration (SLED-f). We aimed at preventing KRT-related hypophosphatemia while optimizing acid-base equilibrium. KRT was performed by the Prismax system (Baxter) and polyacrylonitrile AN69 filters (ST 150, 1.5 m2, Baxter), combining a 18mmol/L pre-dilution citrate solution (Regiocit 18/0, Baxter) with a phosphate-containing solution (HPO42- 1.0mmol/L, HCO3- 22.0mmol/L; Biphozyl, Baxter). When needed, phosphate loss was replaced with sodium glycerophosphate pentahydrate (Glycophos™ 20mmol/20mL, Fresenius Kabi Norge AS, Halden, Norway). Serum citrate measurements were scheduled during each treatment. We analyzed data from three consecutive daily 8-h SLED-f sessions, as well as single 72-h CVVH or 72-h CVVHDF sessions. We used analysis of variance (ANOVA) for repeated measures to evaluate differences in variables means (i.e. serum phosphate, citrate). Because some patients received phosphate supplementation, we performed analysis of covariance (ANCOVA) for repeated measures modelling phosphate supplementation as a covariate. Forty-seven patients with acute kidney injury (AKI) or end stage kidney disease (ESKD) requiring KRT were included [11 CVVH, 11 CVVHDF and 25 SLED-f sessions; mean Acute Physiology and Chronic Health Evaluation II (APACHE II) score 25±7.0]. Interruptions for irreversible filter clotting were negligible. The overall incidence of hypophosphatemia (s-P levels <2.5mg/dL) was 6.6%, and s-P levels were kept in the normality range irrespective of baseline values and the KRT modality. The acid-base balance was preserved, with no episode of citrate accumulation. Our data obtained with a new simplified RCA protocol suggest that it is effective and safe for CVVH, CVVHDF and SLED, allowing to prevent KRT-related hypophosphatemia and maintain the acid-base balance without citrate accumulation. NCT03976440 (registered 6 June 2019).

Evaluation by Means of Electrochemical Impedance Spectroscopy of the Transport of Phosphate Ions through a Heterogeneous Anion-Exchange Membrane at Different pH and Electrolyte Concentration

Electrodialysis is an innovative technique to reclaim phosphates from municipal wastewater. However, chemical reactions accompany the transport of these ions through ion-exchange membranes. The present study investigates the dependence of these phenomena on the initial pH and concentration of the phosphate-containing solution using a heterogeneous anion-exchange membrane. Linear sweep voltammetry, electrochemical impedance spectroscopy, and chronopotentiometry experiments were conducted for different phosphate-containing systems. For the most diluted solution, two limiting current densities (ilim) have been observed for pH 5 and 7.2, while only one ilim for pH 10, and correlated with the appearance of Gerischer arcs in EIS spectra. For pH 7.2, sub-arcs of Gerischer impedance were separated by a loop, indicating the involvement of the membrane functional groups. Increasing the phosphate concentration changed the system’s characteristics, reporting a single ilim. In the EIS spectra, the absence of Gerischer elements determined the attenuation of chemical reactions, followed by the development of a diffusion boundary layer, as indicated by the finite-length Warburg arcs. Chronopotentiometry clarified the mass transport mechanism responsible for distorting the diffusion boundary layer thickness at lower concentrations. The obtained results are expected to contribute to the phosphates recovery using electrodialysis in the most varied conditions of pH and concentration available in the environment.

Effect of the Parameters of Pulsed Electric Fields on the Average Current Density in the Electrodialysis Desalination of a Phosphate-Containing Solution

Effect of the Parameters of Pulsed Electric Fields on the Average Current Density in the Electrodialysis Desalination of a Phosphate-Containing Solution

Snail Based Carbonated-Hydroxyapatite Material as Adsorbents for Water Iron (II)

Carbonated hydroxyapatite (CHAp) adsorbent material was prepared from Achatina achatina snail shells and phosphate-containing solution using a wet chemical deposition method. The CHAp adsorbent material was investigated to adsorb aqua Fe(II) complex; [Fe(H2O)6]2+ from simulated iron contaminated water for potential iron remediation application. The CHAp was characterized before and after adsorption using infrared (IR) and Raman spectroscopy. The IR and the Raman data revealed that the carbonate functional groups of the CHAp adsorbent material through asymmetric orientation in water bonded strongly to the aqua Fe(II) complex adsorbate. The adsorption behaviour of the adsorbate onto the CHAp adsorbent correlated well to pseudo-second-order kinetics model, non-linear Langmuir and Freundlich model at room temperature of a concentration (20–100 mg L−1) and contact time of 180 min. The Langmuir model estimated the maximum adsorption capacity to be 45.87 mg g−1 whereas Freundlich model indicated an S-type isotherm curvature which supported the spectroscopy revelation.

Evaluation of microstructural effects on corrosion behavior of AZ31B magnesium alloy with a MAO coating and electroless Ni-P plating

A bi-layer coating is deposited on the surface of the AZ31B Mg alloy for corrosion protection of the Mg alloy. The bi-layer coating is composed of a micro-arc oxidation coating (MAO), and an electroless plated Ni-P coating. The micro-arc oxidation (MAO) treatment in the electrolyte with or without the addition of phosphate ions is carried out under unipolar power mode. The microstructure and composition of the MAO coatings are analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The roughness of the MAO coatings is obtained by using 3D white light interferometry. The corrosion resistances are evaluated by potentiodynamic polarization test as well as electrochemical impedance spectroscopy (EIS) in a 3.5 wt.% NaCl solution and salt spray test. The adhesion test results of the MAO/Ni-P composite coatings by drawing test machine. The results showed that the micro-pores size of the MAO coating treated in the phosphate-free bath is uniform and smaller than the phosphate-containing solution, which could decrease the roughness and enhance the corrosion resistance. The corrosion resistance of MAO coating with the phosphate-free solution for 2.8 times was better than that of phosphate-containing solution. Moreover, phosphate-free MAO/Ni-P composite coating showed the corrosion rate is more than 4 times lower than the phosphate-containing MAO/Ni-P composite coating. Furthermore, the MAO/Ni-P composite coatings prepared by the MAO coating treated in the phosphate-free bath could suppress the erosion of aggressive media during exposure after 120 h salt spray test (corrosion area is approximately 5%) and present excellent adhesion.

Influence of preferred orientation on the bioactivity of hydroxyapatite: a potential tooth repair and implant surface coating material

Abstract Bioactive hydroxyapatite (HAp) material was synthesized using a simple wet chemical precipitation and heat-treatment method from snail (Achatina achatina) shells and a phosphate-containing solution. According to X-ray diffraction patterns obtained, the heat-treatment caused a crystallographic preferred orientation along the HAp c-axis and thus, affected the material mineralization and bioactivity modeled in vitro using simulated body fluid (SBF) for 7 and 21 days. After 21 days of immersion, calcium and phosphate mineral concentrations in SBF decreased by 66% and 83%, respectively. This corresponded to a transformation from a poor calcium amorphous apatite phase (calcium phosphate) to a resorbing crystalline calcium apatite indicated by scanning electron microscopy micrographs. The material crystallite size (~15 nm), lattice parameters, physicochemical properties, and morphological characteristics were all typical of the human enamel apatite and, therefore, could be considered ideal for use in tooth repairs and implant surface coatings.

P1096SAFETY AND EFFICACY OF A NEW SIMPLIFIED REGIONAL CITRATE ANTICOAGULATION PROTOCOL FOR SUSTAINED LOW EFFICIENCY DIALYSIS FOCUSED ON PREVENTION OF RRT-INDUCED HYPOPHOSPHATEMIA IN CRITICALLY ILL RENAL PATIENTS

Abstract Background and Aims Sustained-Low Efficiency Dialysis (SLED) is a hybrid Renal Replacement Therapy (RRT) increasingly used in critically ill patients with Acute Kidney Injury (AKI). Usually lasting 8-12 hours, this modality combines several advantages of both intermittent and continuous RRT (CRRT). Regional citrate anticoagulation (RCA) represents the most adequate anticoagulation strategy to avoid the extracorporeal circuit clotting. Hypophosphatemia (serum phosphorus, s-P, levels ≤ 2.5 mg/dl) is a common electrolyte disorder in critically ills, with an increased incidence in course of prolonged RRTs, especially when standard dialysis/replacement solutions and highly intensive modalities are employed. Given the potentially negative impact of hypophosphatemia on patients’ outcomes, strategies aimed at preventing its onset should be appropriately implemented. This pilot study is aimed at evaluation of safety and efficacy of a simplified RCA protocol for SLED, based on the combination of a low-concentrated citrate solution with a phosphate-containing solution. Methods a prospective observational study was conducted on critically ill patients with AKI requiring RRT or End Stage Renal Disease (ESRD) previously on RRT admitted to our renal Intensive Care Unit (ICU). SLED was performed by the Prismax system (Baxter) and polyacrylonitrile AN69 haemofilters (ST 150, 1.5 m2, Baxter). 8-hours SLED sessions were prescribed, in the SLED-f variant, by using a 18 mmol/l pre-dilution trisodium citrate solution (Regiocit 18/0, Baxter) combined with a phosphate-containing solution acting as dialysate (Ca2+ 0, HPO42- 1, Mg2+ 0.75, HCO3- 22 mmol/l; Biphozyl, Baxter) and a standard RRT solution acting as post-dilution replacement fluid (Prismasol 4, Baxter). Calcium chloride (CaCl 10%) was infused in a separate central venous line to maintain the systemic Ca2+ (s-Ca2+) within a normal range. Each patient underwent three consecutive daily SLED sessions. The activated coagulation time (ACT), acid–base parameters, s-Ca2+ and potassium were measured at SLED start and every 2 h. Phosphorus and magnesium losses with RRT were replaced, when needed, with sodium glycerophosphate pentahydrate (GlycophosTM 20 mmol/20 ml, Fresenius Kabi Norge AS, Halden, Norvegia) and magnesium sulphate. Results a total of 60 SLED-f sessions were performed in 20 ICU patients. At ICU admission, the average APACHE II score was 21.8 and half of patients were mechanically ventilated. Many of them showed hemodynamic instability and AKI was oliguric in 90% of cases. No premature interruptions for irreversible filter clotting occurred and the prescribed dialysis dose was delivered in 95% of cases. No statistically significant differences were observed between systemic ACT at SLED start and during RRT sessions, and no major hemorrhagic events were observed. Regarding RCA, no clinically relevant episode of hypo or hypercalcemia was observed, and calcium infusion rate remained constant in course of treatments. Acid-base status was effectively maintained during the entire period of treatment and no episodes of clinically relevant metabolic acidosis or alkalosis were registered. The analysis of the main laboratory variables at SLED start, in course and after 24 h of treatment did not show statistically significant differences. Regardless of starting values, s-P and s-Mg were progressively corrected and maintained within the normality range, limiting the need for exogenous supplementations. Conclusions These preliminary data suggest that our simplified RCA protocol for SLED, combining a low-citrate solution with a phosphate-containing solution, is safe and efficacious allowing to optimizing acid-base balance and to preventing RRT-related hypophosphatemia.

Phosphorus recovery from low phosphate-containing solution by electrodialysis

The use of electrodialysis to treat a low phosphorus-containing solution (0.011 g L−1 HxPO43-x) was evaluated aiming at the recovery of phosphorus from municipal wastewater. The study was held in galvanostatic mode using a five-compartment electrodialysis cell with two pairs of cation- and anion-exchange heterogeneous membrane. A two-stage electrodialysis setup was proposed to recover phosphorus from a low phosphate-containing municipal wastewater. At underlimiting current density conditions, a solution with a phosphate concentration higher than 0.100 g L−1 was obtained by consecutively changing the solution in the diluted reservoir after reaching a demineralization rate of 50.0%. A concentration factor of 9.7 was obtained and no significant changes that could compromise the efficiency of the process were observed. The phosphate ions of the concentrated solution could be then separated from coexisting ions, such as sulfate, by the employment of overlimiting current density conditions, with its feasibility dependent on the use of alkali resistance anion-exchange membranes.

Preventing Continuous Renal Replacement Therapy-Induced Hypophosphatemia: An Extended Clinical Experience with a Phosphate-Containing Solution in the Setting of Regional Citrate Anticoagulation

Aims: To evaluate the efficacy and safety of a commercially available phosphate-containing solution for continuous renal replacement therapy (CRRT) in preventing CRRT-related hypophosphatemia. Methods: In heart surgery patients undergoing continuous veno-venous haemodiafiltration (CVVHDF) with regional citrate anticoagulation (RCA), we combined an 18 mmol/l citrate solution with a phosphate-containing (1.2 mmol/l) dialysate/replacement fluid evaluating the incidence of hypophosphatemia and the need for parenteral phosphorus supplementation. Results: In 75 patients on RCA-CVVHDF, the mean filter life was 53.9 ± 33.6 h. Regardless of baseline levels, phosphoremia was progressively corrected and maintained in a narrow normality range throughout RCA-CRRT days (after 72 h: 1.14 ± 0.25 mmol/l). Considering the whole CRRT period, 45 out of 975 (4.6%) serum phosphorus determinations met the criteria for mild (<0.81 mmol/l) or moderate (<0.61 mmol/l) hypophosphatemia; severe hypophosphatemia (<0.32 mmol/l) never occurred. After 72 h 88% of the patients were normophosphatemic, 9% hyperphosphatemic and 3% hypophosphatemic. Conclusions: RCA-CVVHDF with a phosphate-containing solution enabled the maintenance of phosphorus levels within normophosphatemic range in most of the patients, minimizing the occurrence of CRRT-related hypophosphatemia.

Carbonate-containing hydroxyapatite synthesized by the hydrothermal treatment of different calcium carbonates in a phosphate-containing solution

Carbonate-containing hydroxyapatite (CHA) particles were synthesized by the hydrothermal treatment of calcium carbonates in a phosphate-containing solution. Three types of calcium carbonates were synthesized: aragonite particles with rough surfaces, calcite particles with rough surfaces by heat treatment of aragonite particles with rough surfaces, and aragonite particles with smooth surfaces. The effects of the calcium carbonate crystal phase and morphology on the synthesized CHA were investigated and morphological changes in the formed CHA particles were observed. The reaction rates varied depending on the calcium carbonate crystal phase and morphology and this difference in reaction rates mainly affected the morphology of the synthesized CHA. On the other hand, the carbonate content and lattice constants of formed CHA were almost independent of the calcium carbonate crystal phase and morphology. This is because the equilibrium mainly governed the composition of the synthesized CHA. The characteristics of the starting material were highly important factors in controlling the morphology of the synthesized CHA.

Continuous venovenous hemodiafiltration with a low citrate dose regional anticoagulation protocol and a phosphate-containing solution: effects on acid–base status and phosphate supplementation needs

BackgroundRecent guidelines suggest the adoption of regional citrate anticoagulation (RCA) as first choice CRRT anticoagulation modality in patients without contraindications for citrate. Regardless of the anticoagulation protocol, hypophosphatemia represents a potential drawback of CRRT which could be prevented by the adoption of phosphate-containing CRRT solutions. The aim was to evaluate the effects on acid–base status and phosphate supplementation needs of a new RCA protocol for Continuous Venovenous Hemodiafiltration (CVVHDF) combining the use of citrate with a phosphate-containing CRRT solution.MethodsTo refine our routine RCA-CVVH protocol (12 mmol/l citrate, HCO3- 32 mmol/l replacement fluid) (protocol A) and to prevent CRRT-related hypophosphatemia, we introduced a new RCA-CVVHDF protocol (protocol B) combining an 18 mmol/l citrate solution with a phosphate-containing dialysate/replacement fluid (HCO3- 30 mmol/l, Phosphate 1.2). A low citrate dose (2.5–3 mmol/l) and a higher than usual target circuit-Ca2+ (≤0.5 mmol/l) have been adopted.ResultsTwo historical groups of heart surgery patients (n = 40) underwent RCA-CRRT with protocol A (n = 20, 102 circuits, total running time 5283 hours) or protocol B (n = 20, 138 circuits, total running time 7308 hours). Despite higher circuit-Ca2+ in protocol B (0.37 vs 0.42 mmol/l, p < 0.001), circuit life was comparable (51.8 ± 36.5 vs 53 ± 32.6 hours). Protocol A required additional bicarbonate supplementation (6 ± 6.4 mmol/h) in 90% of patients while protocol B ensured appropriate acid–base balance without additional interventions: pH 7.43 (7.40–7.46), Bicarbonate 25.3 (23.8–26.6) mmol/l, BE 0.9 (-0.8 to +2.4); median (IQR). No episodes of clinically relevant metabolic alkalosis, requiring modifications of RCA-CRRT settings, were observed. Phosphate supplementation was needed in all group A patients (3.4 ± 2.4 g/day) and in only 30% of group B patients (0.5 ± 1.5 g/day). Hypophosphatemia developed in 75% and 30% of group A and group B patients, respectively. Serum phosphate was significantly higher in protocol B patients (P < 0.001) and, differently to protocol A, appeared to be steadily maintained in near normal range (0.97–1.45 mmol/l, IQR).ConclusionsThe proposed RCA-CVVHDF protocol ensured appropriate acid–base balance without additional interventions, providing prolonged filter life despite adoption of a higher target circuit-Ca2+. The introduction of a phosphate-containing solution, in the setting of RCA, significantly reduced CRRT-related phosphate depletion.

Preparation of hydroxyapatite coating on CoCrMo implant using an effective electrochemically-assisted deposition pretreatment

Abstract A hydroxyapatite (HA) coating is efficiently generated on CoCrMo implant alloys by employing an electrochemically-assisted deposition (ECAD) pretreatment followed by chemical immersion in a supersaturated calcification solution. CoCrMo was electrochemically treated in a calcium- and phosphate-containing solution for short time. A thin layer about 200 nm thicknesses, consisting mainly of amorphous calcium phosphate, was formed on the surface of the CoCrMo after the ECAD pretreatment. After the chemical immersion for 2 h, a layer of octacalcium phosphate was formed on the surfaces. A layer of HA was formed after 72 h immersion. The effectiveness of these treatments was demonstrated by comparison with the alkaline treated CoCrMo. Results showed that the ECAD pretreatment highly enhanced the capability of formation of HA on the CoCrMo surface, while only a small amount of CaP islands were formed on CoCrMo through traditional chemical treatment. A tensile test showed that the coating tightly bonded to the substrate. This work has explored an effective ECAD pretreatment to activate CoCrMo implant surface for generating HA coating.

Biomimetic remineralization of human dentin using promising innovative calcium-silicate hybrid “smart” materials

Introduction The hypothesis was that experimental ion-leaching bioactive composites enhance remineralization of apatite-depleted dentin. Materials and methods Calcium-aluminosilicate (wTC-Ba) or fluoride-containing calcium-aluminosilicate (FTC-Ba) Portland-derived mineral powders were mixed with HTP-M methacrylate HEMA/TEGDMA/PAA-based resin to prepare experimental composites. Controls were Vitrebond and Gradia Direct LoFlo. Calcium- and fluoride-release, pH of soaking water, solubility and water uptake were evaluated in deionized water using material disks (8 mm diameter and 1.6 mm thick). The apatite-formation ability (bioactivity) and the ability to remineralize previously demineralized dentin were assessed by ESEM-EDX and FTIR after soaking in a phosphate-containing solution. Human dentin slices (0.8 mm thickness) were demineralized in EDTA 17% for 2 h, placed in close contact with the material disks and immersed in a phosphate-containing solution (Dulbecco's Phosphate Buffered Saline, DPBS) to assess the ability of the materials to remineralize apatite-depleted dentin. Results Only the experimental materials released calcium and basified the soaking water (released hydroxyl ions). A correlation between calcium release and solubility was observed. FTC-Ba composite released more fluoride than Vitrebond and formed calcium fluoride (fluorite) precipitates. Polyacrylate calcium complexes (between COO − groups of polyacrylate and released calcium ions) formed at high pH. The formation of apatite was noticed only on the experimental materials, due to the combination of calcium ions provided by the materials and phosphate from the DPBS. Apatite deposits (spherulites showing Ca and P EDX peaks and IR bands due to phosphate stretching and bending) were detected early on the experimental material disks after only 24 h of soaking in DPBS. Only the experimental composites proved to have the ability to remineralize apatite-depleted dentin surfaces. After 7 days in DPBS, only the demineralized dentin treated with the experimental materials showed the appearance of carbonated apatite (IR bands at about 1400, 1020, 600 cm −1). EDX compositional depth profile through the fractured demineralized dentin slices showed the reappearance of Ca and P peaks (remineralization of dentin surface) to 30–50 μm depth. Conclusions The ion-leachable experimental composites remineralized the human apatite-depleted dentin. Ion release promotes the formation of a bone-like carbonated-apatite on demineralized dentin within 7 days of immersion in DPBS. The use of bioactive “smart” composites containing reactive calcium-silicate Portland-derived mineral powder as tailored filler may be an innovative method for the biomimetic remineralization of apatite-depleted dentin surfaces and to prevent the demineralization of hypomineralized/carious dentin, with potentially great advantage in clinical applications.

Fluoride-containing nanoporous calcium-silicate MTA cements for endodontics and oral surgery: early fluorapatite formation in a phosphate-containing solution

To test the chemical-physical properties and apatite-forming ability of experimental fluoride-doped calcium silicate cements designed to create novel bioactive materials for use in endodontics and oral surgery. A thermally treated calcium silicate cement (wTC) containing CaCl(2) 5%wt was modified by adding NaF 1%wt (FTC) or 10%wt (F10TC). Cements were analysed by environmental scanning electron microscopy with energy-dispersive X-ray analysis, IR and micro-Raman spectroscopy in wet conditions immediately after preparation or after ageing in a phosphate-containing solution (Dulbecco's phosphate-buffered saline). Calcium and fluoride release and pH of the storage solution were measured. The results obtained were analysed statistically (Tukey's HSD test and two-way anova). The formation of calcium phosphate precipitates (spherulites) was observed on the surface of 24 h-aged cements and the formation of a thick bone-like B-type carbonated apatite layer (biocoating) on 28 day-aged cements. The rate of apatite formation was FTC>F10TC>wTC. Fluorapatite was detected on FTC and F10TC after 1 day of ageing, with a higher fluoride content on F10TC. All the cements released calcium ions. At 5 and 24 h, the wTC had the significantly highest calcium release (P<0.001) that decreased significantly over the storage time. At 3-28 days, FTC and F10TC had significantly higher calcium release than wTC (P<0.05). The F10TC had the significantly highest fluoride release at all times (P<0.01) that decreased significantly over storage time. No significant differences were observed between FTC and wTC. All the cements had a strong alkalinizing activity (OH(-) release) that remained after 28 days of storage. The addition of sodium fluoride accelerated apatite formation on calcium silicate cements. Fluoride-doped calcium silicate cements had higher bioactivity and earlier formation of fluorapatite. Sodium fluoride may be introduced in the formulation of mineral trioxide aggregate cements to enhance their biological behaviour. F-doped calcium silicate cements are promising bone cements for clinical endodontic use.

Self-reparability of glass-ionomer cements: an in vitro investigation

Despite the advantages of glass-ionomer cement (GIC) restorative materials, they exhibit low mechanical properties and are susceptible to dissolution. The purpose of this study was to investigate the existence of self-reparability of a GIC material. Thirty Fuji IX discs were fabricated and subjected to desiccation. The discs were randomly separated into three groups: one group was kept in air, a second group was soaked in water, and a third group was placed in casein phosphoprotein-amorphous calcium phosphate-containing solution (Dentacal; NSI, Hornsby, Australia). After 21 d of incubation, all specimens were subjected to biaxial flexure testing. One-way ANOVA revealed a statistical difference in the biaxial flexure strength between the groups. Weibull statistics revealed that the Dentacal group demonstrated a lower probability of failure than the other groups. The air group exhibited the highest probability of failure. The difference between the specimens was expected as a result of enhanced cross-linking between the polyalkenoate chains and the GIC particles, and the diffusion of ionic components to the set GIC. Therefore, perhaps a form of reparative mechanism exists for precrazed GIC when it is exposed to a remineralizing solution. In addition to the benefit on natural tooth structures, this study indicates that remineralizing solutions are also beneficial for maintaining the mechanical integrity of GIC restorations.

Phosphate-containing dialysis solution prevents hypophosphatemia during continuous renal replacement therapy

BackgroundHypophosphatemia occurs in up to 80% of the patients during continuous renal replacement therapy (CRRT). Phosphate supplementation is time-consuming and the phosphate level might be dangerously low before normophosphatemia is re-established. This study evaluated the possibility to prevent hypophosphatemia during CRRT treatment by using a new commercially available phosphate-containing dialysis fluid.MethodsForty-two heterogeneous intensive care unit patients, admitted between January 2007 and July 2008, undergoing hemodiafiltration, were treated with a new Gambro dialysis solution with 1.2 mM phosphate (Phoxilium) or with standard medical treatment (Hemosol B0). The patients were divided into three groups: group 1 (n=14) receiving standard medical treatment and intravenous phosphate supplementation as required, group 2 (n=14) receiving the phosphate solution as dialysate solution and Hemosol B0 as replacement solution and group 3 (n=14) receiving the phosphate-containing solution as both dialysate and replacement solutions.ResultsStandard medical treatment resulted in hypophosphatemia in 11 of 14 of the patients (group 1) compared with five of 14 in the patients receiving phosphate solution as the dialysate solution and Hemosol B0 as the replacement solution (group 2). Patients treated with the phosphate-containing dialysis solution (group 3) experienced stable serum phosphate levels throughout the study. Potassium, ionized calcium, magnesium, pH, pCO2 and bicarbonate remained unchanged throughout the study.ConclusionThe new phosphate-containing replacement and dialysis solution reduces the variability of serum phosphate levels during CRRT and eliminates the incidence of hypophosphatemia.

Apatite formation on bioactive calcium-silicate cements for dentistry affects surface topography and human marrow stromal cells proliferation

The effect of ageing in phosphate-containing solution of bioactive calcium-silicate cements on the chemistry, morphology and topography of the surface, as well as on in vitro human marrow stromal cells viability and proliferation was investigated. A calcium-silicate cement (wTC) mainly based on dicalcium-silicate and tricalcium-silicate was prepared. Alpha-TCP was added to wTC to obtain wTC-TCP. Bismuth oxide was inserted in wTC to prepare a radiopaque cement (wTC-Bi). A commercial calcium-silicate cement (ProRoot MTA) was tested as control. Cement disks were aged in DPBS for 5 h (‘fresh samples’), 14 and 28 days, and analyzed by ESEM/EDX, SEM/EDX, ATR-FTIR, micro-Raman techniques and scanning white-light interferometry. Proliferation, LDH release, ALP activity and collagen production of human marrow stromal cells (MSC) seeded for 1–28 days on the cements were evaluated. Fresh samples exposed a surface mainly composed of calcium-silicate hydrates CSH (from the hydration of belite and alite), calcium hydroxide, calcium carbonate, and ettringite. Apatite nano-spherulites rapidly precipitated on cement surfaces within 5 h. On wTC-TCP the Ca-P deposits appeared thicker than on the other cements. Aged cements showed an irregular porous calcium-phosphate (Ca-P) coating, formed by aggregated apatite spherulites with interspersed calcite crystals. All the experimental cements exerted no acute toxicity in the cell assay system and allowed cell growth. Using biochemical results, the scores were: fresh cements > aged cements for cell proliferation and ALP activity (except for wTC-Bi), whereas fresh cements < aged cements for collagen synthesis. Summarizing (1) non-aged cements showed higher cell proliferation than aged cements, probably favoured by the presence of Si–OH gel and the early formation of apatite nano-spherulites; (2) the alpha-TCP doped cement aged for 28 days displayed the highest bioactivity and cell proliferation; (3) the deleterious effect of bismuth on cell proliferation was reduced by the progressive increase of the biocoating thickness on aged cement. In conclusion, the experimental cements have adequate biological properties to be used as root-end/root repair filling materials or pulp capping materials. The alfa-TCP doped cement represents a new potential bioactive material for expanded applications in dentistry.

Apatite‐forming ability (bioactivity) of ProRoot MTA

Apatite-forming ability, considered as an index of bioactivity (bond-to-bone ability), was tested on ProRoot MTA cement after immersion in phosphate-containing solution (DPBS). Disk samples were prepared and immersed in DPBS for 10 min, 5 h, 1 and 7 days. The cement surface was studied by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, by micro-Raman spectroscopy and by environmental scanning electron microscope with energy dispersive X-ray (ESEM-EDX) analyses. The pH of the storage solution was also investigated. Spectroscopic analyses revealed calcium phosphate bands after 5-h immersion in DPBS. After 1 day, an even coating composed of apatite spherulites (0.1-0.8 micron diameter) was observed by ESEM/EDX. After 7 days, its thickness had increased. Apatite nucleation had already occurred after 5-h immersion. At this time, the presence of portlandite (i.e. Ca(OH)(2) , calcium hydroxide) on the cement surface was also observed; at longer times, this component was released into the medium, which underwent a remarkable pH increase. The study confirms the ability of ProRoot MTA to form a superficial layer of apatite within hours. The excellent bioactivity of ProRoot MTA might provide a significant clinical advantage over the traditional cements used for root-end or root-perforation repair.

Bone-like nanocomposites based on self-assembled protein-based matrices with Ca2+ capturing capability

In the present work, bone-like nanocomposites have been successfully synthesized based on the mineralization of self-assembled protein-based microgels. Such mircogels were achieved by the in vitro reconstitution of collagen monomeric solutions in the presence of alginate in a microemulsion system. Microstructural observations revealed that the collagen-alginate composite beads possessed a nanofibrous three dimensional (3D) interconnected porous microstructure. The obtained microgels were pre-incubated in calcium-containing solution to capture Ca(2+) ions, and subsequently immersed in phosphate-containing solution to initiate the formation of hydroxyapatite (HA) by an alternative incubating procedure. It was observed that a substantial amount of bone-like apatite nanocrystals were orderly and homogeneously deposited throughout the porous fibrillar networks. Herein, the collagen-alginate composite microgels served as a mineralization template for the synthesis of HA-polymer nanocomposites, which could be ideal vehicles potentially for cell carriers, bone repair and proteins and drugs delivery in tissue regeneration.