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.     

Plectin in the human central nervous system: predominant expression at pia/glia and endothelia/glia interfaces

Major problems with the treatment of osteomyelitis are associated with poor antibiotic distribution at the site of infection due to limited blood circulation to the skeletal tissue. Improved treatment procedures have been used in drug delivery systems that include bioceramics and natural and synthetic polymers. This work reports the development of anionic collagen:hydroxyapatite composite paste for sustained antibiotic release. Antibiotic release by the composite was characterized by two steps. In the first, 15.0+/-4.9% was released in the first 5 h (n = 53) by a normal Fick diffusion mechanism. In the second step, only 16.8+/-2.2% was released after 7 days. In conclusion, hydroxyapatite:anionic collagen composite can be an efficient support for sustained antibiotic release in the treatment of osteomyelitis because most of the antibiotic release may be associated with composite bioresorption, thus permitting antibiotic release throughout the healing process. Hydroxyapatite:anionic collagen paste showed good biocompatibility associated with bone tissue growth with material still being observed after 60 days from the time of implants.     

Selective Precipitation of Phosphate from Semiconductor Wastewater

Selective precipitation of phosphate from fluoride-containing wastewater was studied using magnesium salts. Wastewater sampled from a semiconductor manufacture was found to contain 936 mg/L of fluoride (F?), 640 mg/L of sulfate (SO42?), 118 mg/L of phosphate (PO43?), and 26.72 mg/L ammonium (NH4+). Magnesium chloride (MgCl2) was more effective than magnesium oxide (MgO) in inducing precipitation reactions between magnesium and phosphate. Effects of both molar ratio ([Mg2+]:[PO43?]) and pH were examined and experimental results were compared with those from equilibrium modeling by PHREEQC. A total of 41.72% of phosphate was removed and recovered when at molar ratio of 3:2 and pH of 10. Precipitation of phosphate increased with increasing molar ratio and 66.19% of phosphate was recovered when molar ratio was 3:1. Precipitation of phosphate increased as pH changed from 8 to 10. However, it decreased as pH increased from 10 to 12, probably because of competition between phosphate and hydroxyl (OH?) ions. Solid precipitates were characterized by field emission scanning electron microscope with energy dispersive spectrometer and X-ray diffraction. In accordance with theoretical modeling, it was found that the precipitate in pH range of 8–10 was predominantly bobierrite [Mg3(PO4)2.8H2O] and some amorphous precipitates. However, brucite [Mg(OH)2] precipitate would start to form when pH became higher than 10. Results showed that MgCl2 can be a selective precipitation reagent for phosphate removal from semiconductor wastewater since it does not form precipitate with fluoride, sulfate, and ammonium.     

Mechanical properties of bone cements containing large doses of antibiotic powders

The addition of up to 10 g gentamicin sulfate antibiotic powder to 60 g units of Simplex-P acrylic bone cement caused gradual, proportional decreases in the bulk muchanical properties of compressive and diametral tensile strengths. Water leaching of the antibiotic from the cement did not significnatly decrease these strenghts. Scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS) showed the antibiotic to reside in the acrylic matrix as discrete particles not usually associated with internal porosity. The surface-sensitive flexural strength of a proprietary bone cement was lowered immediately by small quantities of antibiotic powder, and continued to decrease as doses of up to 10 g/unit were admixed. Water leaching caused channeling as the antibiotic was removed from the surface, but it did not create further changes in flexural strength.     

Isotope dilution analysis of bromate in drinking water matrixes by ion chromatography with inductively coupled plasma mass spectrometric detection

Bromate is a disinfection byproduct in drinking water which is formed during the ozonation of source water containing bromide. This paper describes the analysis of bromate via ion chromatography-inductively coupled plasma mass spectrometry. The separation of bromate from interferences such as bromide and brominated haloacetic acids is achieved using a PA-100 column in combination with a 5 mM HNO3 + 25 mM NH4NO3 mobile phase. Polyatomic ions are observed on masses 79 and 81 in a synthetic phosphate matrix and in ozonated drinking waters. These polyatomic ions have been tentatively identified as PO3+ and H2PO3+. These polyatomic ions do not interfere with the detection of bromate because phosphate elutes prior to bromate. A polyatomic ion is observed on mass 81 in a synthetic sulfate matrix and in ozonated drinking waters. This polyatomic ion has been tentatively identified as HSO3+ and does not interfere with the detection of bromate because sulfate elutes after bromate. Isotope dilution analysis produces a relative standard deviation (RSD) of approximately 5% for both enriched isotopic additions at sample concentrations of 10 ng/g. The RSD associated with the direct analysis of bromate is 3.2% at sample concentrations of 10 ng/g. The bromate concentrations determined in ozonated drinking waters via isotope dilution analysis are within 10% of the concentrations determined via direct analysis for sample concentrations above 2 ng/g. The detection limit for the direct analysis of bromate via IC-ICPMS is 0.3 ng/g.     

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.     

Synthesis of antibiotic-loaded interporous hydroxyapatite blocks by vacuum method and in vitro drug release testing

Interporous hydroxyapatite ceramic (Ca10(PO4)6(OH)2) has excellent bio-compatibility and interlinked pore structure, antibiotics could be loaded into pores in vacuum system. To confirm penetration of the agent to the HAb (2 cm3 cubic block), the aminoglycoside antibiotic (Isepamicin Sulfate; ISP) dissolved in eosin dye at various vacuum pressures. In ISP slow release study, the blocks were placed in 5 ml of PBS at a temperature of 37 degrees C. The PBS was replaced every 48 h and samples containing released ISP were stored until assay. All were found to release the drug maintaining a mean concentration of 0.41 microg ml(-1) even after 18 days of nine exchanges. This concentration of antibiotic exceeded the minimum inhibitory concentration against the common causative organisms of osteomyelitis. The results suggest that HAb impregnated with antibiotics using a simple vacuum system may serve as a valuable new method of administering local chemotherapy, primarily when used as a strut graft for bone defects.     

高活性阿利特硫铝酸盐水泥及其水化反应

利用青海省当地原材料制备阿利特硫铝酸盐水泥熟料.该熟料结合了硅酸盐熟料和硫铝酸盐熟料的优点,具有碱性与硫酸根离子的双重激发作用,能很好地激发矿渣、粉煤灰等活性矿物材料.在此基础上,提出了高活性阿利特硫铝酸盐水泥方案.通过微观结构分析,探讨其水化反应的机理与过程,并阐明了复合胶凝体系的优势互补作用的原理.实验证明,高活性阿利特硫铝酸盐水泥,能充分发挥熟料自身独特的矿物组成特性和活性矿物材料的火山灰效应,使硬化浆体中Ca(OH)2含量降低,并因此而获得较为适宜的晶/胶比,使其后期强度明显提高.     

Controlled release of lidocaine from injectable gels and efficacy in rat sciatic nerve block

PURPOSE: Methods of delaying the action of local anesthetics are important, since short duration of action limits their use in the treatment of postoperative and chronic pain. The present study evaluated the use of low-viscosity gels in prolonging the release of lidocaine. METHODS: Release of lidocaine from 2% lidocaine.HCl containing methylcellulose (MC), hydroxypropylmethylcellulose (HPMC), sodiumcarboxymethyl cellulose (CMC), and poloxamer 407 (PO) gels was studied in phosphate buffer, pH 7.4, at 37 degrees C. Commercial metylcellulose gel (MCcom) served as control. The in vivo efficacy of the respective gel formulations were evaluated in rats. The gel was injected into the vicinity of the sciatic nerve and nociception and motor function were tested. RESULTS: The cumulative amount of lidocaine released during 8 hr was slowest from the PO gel, followed by the CMC, HPMC and MC gels. The antinociceptive effect was not prevented by the motor block and lasted longest with the PO gel. Good linear and rank order correlation was obtained between in vitro and in vivo results. The microscopic examination of the tissue samples revealed only mild or no irritation of the skeletal muscle tissue by the PO, HPMC, and CMC gels. CONCLUSIONS: Based on these results poloxamer gel proved to be the most promising carrier for lidocaine.     

The in vitro and in vivo indomethacin release from self-setting bioactive glass bone cement

The in vivo and in vitro drug release profiles from a self-setting bioactive CaO-SiO2-P2O5 glass bone cement containing indomethacin as a model drug were investigated. The cement containing 2% and 5% indomethacin (IMC) powder hardened within 5 min after mixing with ammonium phosphate buffer. After setting, in vitro drug release from drug-loaded cement pellets in a simulated body fluid (SBF) at pH 7.25 and 37 degrees C continued for two weeks. The hardened cement gradually formed low-crystallinity hydroxyapatite during the drug release test in SBF. An IMC-loaded cement device (2% and 5% drug) was implanted in the subcutaneous tissue on the back of rats. The in vivo IMC release from the cement increased and attained maximum levels (Cmax of 2% and 5% drug-loaded cements was 0.27 and 3.37 micrograms/ml, respectively) at Tmax, 3 and 0.5 d, respectively, upon subcutaneous (s.c.) administration in rats. This suggested that the s.c. administration of the cement provided IMC release for a much longer period than s.c. administration of the solution, and the plasma IMC concentration was dependent on the drug concentration in the cement. The plasma IMC concentration and the area under the curve from 2% and 5% IMC-loaded cements in rats were dependent on the concentration of IMC in the cements. The in vivo IMC concentration in plasma obtained by the deconvolution method was much lower than that delivered in SBF in vitro. Scanning electron microscopy and photomicrographs of cross sections showed that the bioactive bone cement had excellent biocompatibility with the surrounding soft tissues.     

Uptake and release of fluoride by saliva-coated glass ionomer cement

The 'recharging' of aged glass ionomer cement restorations with fluoride by exposing them to a concentrated NaF solution has been suggested to improve their performance as devices with slow fluoride release. We have studied the interference of salivary coatings on glass ionomer cement with the uptake of fluoride in vitro. Freshly prepared glass ionomer discs were leached in distilled water for 14 weeks, then incubated in human saliva for 2 h, 24 h or 1 week before exposure to 0.53 M NaF (1% fluoride) for 5 min. Fluoride uptake by the cement was measured indirectly as the subsequent increase in fluoride release. A 2-hour incubation in saliva reduced the fluoride uptake by half, a 24-hour incubation by 74%. The major part (93-95%) of the fluoride that was taken up was released on the first day. A 1-week salivary coating reduced the uptake by 49%, but also caused some retardation of the fluoride release: 80% of the total release was on the first day. It was concluded that despite the considerable interference by salivary coating, the amount of fluoride that can be taken up by aged glass ionomer cement remains significant. However, the fast release will limit the usefulness of such recharging in vivo.     

Bone-derived growth factor release from poly(alpha-hydroxy acid) implants in vitro

Matrix proteins were extracted from bovine cortical bone and polymer implant discs (13 mm x 2 mm composed of 50:50 poly DL-lactide-co-glycolide; mol. wt. approximately 9000) prepared by compression moulding granules with lyophilized bone matrix extracts (BMX) 10.1 (w/w). BMX-containing polymers were cultured for 5 wk in either serum-free Dulbecco's modification of Eagle's medium (DMEM) or phosphate buffer, and growth factor activity released into the media assayed by its ability to stimulate the proliferation of murine fibroblast BALB/c/3T3 cells. Approximately 60-75% of the biological activity was released during the first week of culture; however, less than half of the growth factor units originally incorporated into the implants retained biological activity. Scanning electron microscopy revealed the development of significant internal porosity by week 2; the size of the channels, pores and surface openings suggested they were of the right order for bone ingrowth. These preliminary findings suggest that poly(alpha-hydroxy acid) polymers containing bone-derived growth factors could have potential for stimulating osseous regeneration in vivo.     

Bean Dwarf mosaic geminivirus movement proteins recognize DNA in a form- and size-specific manner

Various ratios of succinic acid to fenoldopam mesylate, ranging from 0:1 to 18:1 were incorporated in pellets and coated with 1.5-12% w/w Surelease. Even though the coating level did influence the rate and amount of fenoldopam release, the influence of the succinic acid to drug ratio was much more important and evident at all coating levels. Being a weakly basic drug, fenoldopam release ceased when testing in SIF for succinic acid to drug ratios of 0:1-4:1, with the end of release being more abrupt for the 0:1 than for the 4:1 ratio. Only for a succinic acid to drug ratio of > or =5 was fenoldopam release constant for 6-8 h and independent of the pH-value of dissolution media. For a thin coat of about 2.5% w/w Surelease, those pellets showed an ideal controlled release behaviour with release rates of about 5-10%/h and a total release of almost 80% in 8 h. The dissolution profiles of Surelease coated pellets with high succinic acid to drug ratios (> or =5) and different coating levels, were evaluated for best fits to commonly used kinetic models. Sustained release mechanisms are discussed according to best fit models. The quantification of the pH-adjuster succinic acid, released from pellets with an acid to drug ratio of < or =1 showed, that despite their failure as a controlled release system for fenoldopam, the investigated coats could control the release of succinic acid effectively at optimized coating levels. For increasing succinic acid to drug ratios (< or =4) succinic acid was released at an ever more constant rate and release rates, though still faster than the release rates of fenoldopam, decreased steadily for increasing ratios. At a 5:1 ratio finally release rates of succinic acid and fenoldopam were almost identical. Therefore those pellet cores were almost completely emptied during dissolution testing, with both fenoldopam and succinic acid leaving at a constant rate and a total release of about 80% each for a 2.5% Surelease coat, while lower succinic acid to drug ratios had failed to show any sustained release for such thin Surelease coats. A similar formulation with fumaric acid instead of succinic acid failed to show the desired release pattern, indicating that it is the presence of a sufficiently high amount of succinic acid rather than the presence of an acidic compound in general, that ensures fenoldopam solubility at higher pH-values.     

Cationic polymers for selectivity control in the capillary electrophoretic separation of inorganic anions

The capillary electrophoretic (CE) separation of the inorganic anions bromide, chloride, nitrate, nitrite, fluoride, sulfate and phosphate is described in 0.005 mol/L sodium chromate electrolyte in the presence of soluble polydisperse ionic polymers (polyelectrolytes). The cationic polyelectrolytes used were as follows: poly(1,1-dimethyl-3,5-dimethylenepiperidinium) chromate, hexadimethrine chromate, poly(1,1-dimethyl-3,5-dimethylenepyrrolidinium) chromate and ((diethylamino)ethyl)-dextran chromate in the concentration range 0.004-0.6% (w/v). These polyelectrolytes were shown to be capable of reversing the direction of the electroosmotic flow as well as inducing changes in analyte electrophoretic mobility, separation selectivity, and resolution. Changes in electrophoretic mobility by as much as 25% were observed for the sulfate anion, and the resolution of fluoride and phosphate was enhanced by a factor of 7.8. In the presence of 0.05-0.17% w/v poly(1,1-dimethyl-3,5-dimethylenepyrrolidinium) chromate at pH 8, separation currents were found to increase only slightly as compared to an electrolyte containing equivalent amounts of sodium chromate. Electroosmotic flow was also found to be fairly constant (+/- 16%) in the pH range 6.55-10.02 for 0.01% (w/v) poly(1,1-dimethyl-3,5-dimethylenepiperidinium) chromate at an ionic strength of 0.04, compared to a 400% change in the absence of the polyelectrolyte. The reproducibility of the electroosmotic mobility was between 0.36 and 6% RSD, and analyte electrophoretic mobility was between 0.01 and 1.6% RSD. Peak height reproducibility was 0.2-8.0% RSD. Separation efficiencies were between 258,000 and 780,000 theoretical plates, and detection limits were between 4.4 x 10(-7) and 9.1 x 10(-6) mol/L.     

Discovery of the ammonium substrate site on glutamine synthetase, a third cation binding site

Glutamine synthetase (GS) catalyzes the ATP-dependent condensation of ammonia and glutamate to yield glutamine, ADP, and inorganic phosphate in the presence of divalent cations. Bacterial GS is an enzyme of 12 identical subunits, arranged in two rings of 6, with the active site between each pair of subunits in a ring. In earlier work, we have reported the locations within the funnel-shaped active site of the substrates glutamate and ATP and of the two divalent cations, but the site for ammonia (or ammonium) has remained elusive. Here we report the discovery by X-ray crystallography of a binding site on GS for monovalent cations, Tl+ and Cs+, which is probably the binding site for the substrate ammonium ion. Fourier difference maps show the following. (1) Tl+ and Cs+ bind at essentially the same site, with ligands being Glu 212, Tyr 179, Asp 50', Ser 53' of the adjacent subunit, and the substrate glutamate. From its position adjacent to the substrate glutamate and the cofactor ADP, we propose that this monovalent cation site is the substrate ammonium ion binding site. This proposal is supported by enzyme kinetics. Our kinetic measurements show that Tl+, Cs+, and NH4+ are competitive inhibitors to NH2OH in the gamma-glutamyl transfer reaction. (2) GS is a trimetallic enzyme containing two divalent cation sites (n1, n2) and one monovalent cation site per subunit. These three closely spaced ions are all at the active site: the distance between n1 and n2 is 6 A, between n1 and Tl+ is 4 A, and between n2 and Tl+ is 7 A. Glu 212 and the substrate glutamate are bridging ligands for the n1 ion and Tl+. (3) The presence of a monovalent cation in this site may enhance the structural stability of GS, because of its effect of balancing the negative charges of the substrate glutamate and its ligands and because of strengthening the "side-to-side" intersubunit interaction through the cation-protein bonding. (4) The presence of the cofactor ADP increases the Tl+ binding to GS because ADP binding induces movement of Asp 50' toward this monovalent cation site, essentially forming the site. This observation supports a two-step mechanism with ordered substrate binding: ATP first binds to GS, then Glu binds and attacks ATP to form gamma-glutamyl phosphate and ADP, which complete the ammonium binding site. The third substrate, an ammonium ion, then binds to GS, and then loses a proton to form the more active species ammonia, which attacks the gamma-glutamyl phosphate to yield Gln. (5) Because the products (Glu or Gln) of the reactions catalyzed by GS are determined by the molecule (water or ammonium) attacking the intermediate gamma-glutamyl phosphate, this negatively charged ammonium binding pocket has been designed naturally for high affinity of ammonium to GS, permitting glutamine synthesis to proceed in aqueous solution.     

Anoxic Biological Phosphorus Uptake∕Release with High∕Low Intracellular Polymers

This study investigates the denitrification∕phosphate uptake and denitrification∕phosphate release characteristics among denitrifying phosphate accumulating organisms (DNPAO), denitrifier, and nondenitrifying phosphate accumulating organisms (non-DNPAO) in a biological nutrient removal process named TNCU-I, using a series of anoxic batch experiments with and without added acetate under high∕low intracellular polymer conditions. The results showed 47% phosphate uptake in the anoxic tank of the TNCU-I process. Additionally, due to the combined attribution of denitrifier and DNPAO, the experiments with both added acetate and phosphate produced higher denitrification rates than experiments with only acetate added. Furthermore, DNPAO contributed 42% of the denitrification reaction. The sludge exhibited simultaneous phosphate uptake and release under anoxic conditions when acetate was added. When no acetate was added, the specific phosphate uptake rate for the high intracellular polymer level was higher than that found at the low intracellular polymer level. Moreover, the phosphate uptake rate of non-DNPAO was observed to be 2.46 times greater than that of the DNPAO. The phosphate uptake per unit polyhydroxyalkanoates (PHA) consumption (γPO4/PHA) for the non-DNPAO was 1.08 times greater than that of DNPAO. Thus, this study demonstrates that the utilization efficiency of PHA by non-DNPAO is not significantly different with the utilization efficiency of PHA by DNPAO.     

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.     

汞(Ⅱ)在罗丹明B-乙醇-硫酸铵体系中的析相萃取分离

研究了罗丹明B-乙醇-硫酸铵体系析相萃取Hg²⁺的行为及与一些金属离子分离的条件。结果表明,乙醇的水溶液在硫酸铵的作用下分成醇/水两相,在分相过程中,HgCl₄^2-与罗丹明B(RhB)生成的[HgCl₄^2-][RhB⁺]₂能被乙醇相萃取。当溶液中罗丹明B、乙醇和硫酸铵的浓度分别为0.21 mg/mL、30%(V/V)和0.30 g/mL时,HgCl₄^2-的萃取率达到96.8%以上,Co²⁺、Cr(Ⅲ)、Ag⁺、Mg²⁺、Ni ²⁺、Al³⁺、Ti(Ⅳ)、Pb²⁺、Fe³⁺、Sn(Ⅳ)和Ru³⁺基本不被萃取,实现了Hg²⁺与上述金属离子的分离。     

The formulation of glass ionomers and their degree of fluoride

The glass-ionomer cements (GIC) were developed in the late sixties. The set cement is the result of an acid-base reaction between an ion-leachable glass (the base) and a poly (alkenoic acid). Through the years, the number of applications of these GIC has increased steadily. The evolution has to be referred to the fact that the composition of both acid and base can be changed considerably. This has resulted in the marketing of GIC with different physical and chemical formulations. Furthermore resin-modified GIC were introduced in the late eighties. One of the major GIC advantages remains the fluoride release. The fluoride in GIC is a component of the material itself and is not added afterwards. Beneficial for the GIC in this respect is that the released fluoride is not of structural importance in the set cement. Furthermore the fluoride release does not result on itself in a reduction of physical properties or an increase in porosity.     

Bioaccumulation of nickel by intercalation into polycrystalline hydrogen uranyl phosphate deposited via an enzymatic mechanism

A Citrobacter sp. accumulates uranyl ion (UO2(2+)) as crystalline HUO2PO4.4H2O (HUP), using enzymatically generated inorganic phosphate. Ni was not removed by this mechanism, but cells already loaded with HUP removed Ni2+ by intercalative ion-exchange, forming Ni(UO2PO4)2.7H2O, as concluded by x-ray diffraction (XRD) and proton induced x-ray emission (PIXE) analyses. The loaded biomass became saturated with Ni rapidly, with a molar ratio of Ni:U in the cellbound deposit of approx. 1:6; Ni penetration was probably surface-localized. Cochallenge of the cells with Ni2+ and UO2(2+), and glycerol 2-phosphate (phosphate donor for phosphate release and metal bioprecipitation) gave sustained removal of both metals in a flow through bioreactor, with more extensively accumulated Ni. We propose 'Microbially Enhanced Chemisorption of Heavy Metals' (MECHM) to describe this hybrid mechanism of metal bioaccumulation via intercalation into preformed, biogenic crystals, and note also that MECHM can promote the removal of the transuranic radionuclide neptunium, which is difficult to achieve by conventional methods.