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PubMed1999

Composition and structure of the apatite formed on PET substrates in SBF modified with various ionic activity products.

An apatite layer was formed on polyethyleneterephthalate (PET) substrates by the following biomimetic process. PET substrates were placed on granular particles of a CaO-SiO2-based glass in simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma to form apatite nuclei on their surfaces (first treatment). They then were soaked in modified SBFs, the ion concentrations of which were changed to give a variation in ionic activity product of apatite (IP), in order to make the apatite nuclei grow (second treatment). The Ca/P atomic ratio and the lattice constant c of the formed apatite decreased from 1.54 to 1.40 and from 6.880 to 6.838 A, respectively, with increasing ion concentrations from 0.75 to 2.00 times those of SBF, that is, with increasing IP from 10(-96.6) to 10(-91.9). This was attributed to an increase in the concentration of HPO4(2-) ion substituting for the PO4(3-) ion sites, which gave an increase in the Ca2+ in the apatite. Even the apatite formed in 1.00 SBF showed a Ca/P ratio of 1.51 and lattice constants a of 9.432 A and c of 6.870 A. The Ca/P ratio and lattice constant c were smaller and the lattice constant a was larger than those of the bone apatite; its Ca/P ratio and its lattice constants a and c, were 1.65, 9.419 A, and 6.88 A, respectively. This was attributed to the lower content (2.64 wt%) of the CO3(2-) ion substituting for the PO4(3-) ion sites of the apatite compared to that of the bone apatite (5.80 wt%). The lower content of the CO3(2-) ion in the apatite might be caused by the lower concentration of HCO3- ion in 1.00 SBF compared to that in human blood plasma.

Apatites↗

PubMed2003

Deposition of bone-like apatite on silk fiber in a solution that mimics extracellular fluid.

The fabrication of apatite-organic polymer hybrids is one of several attractive methods for the development of biomaterials as a substitute for bone. Such materials have both bone-bonding ability and mechanical properties analogous to natural bone. The biomimetic process has focused attention on fabricating such hybrids, where bone-like apatite is deposited on an organic polymer surface in solutions that mimic physiological conditions. In this process, a bone-like apatite layer can be coated onto organic substrates either by using a simulated body fluid (SBF) with ion concentrations nearly equal to those of human extracellular fluid, or by using fluids that are supersaturated with respect to apatite at ambient conditions. In this study, we investigated the ability of natural silk and its related materials to facilitate apatite deposition under biomimetic conditions. Cloths made of raw silk or normal silk fibers were soaked in 1.5SBF, which has 1.5 times the ion concentration of SBF. Sericin film, which is made from an extract of degummed raw silk, was soaked in 1.5SBF. The cloth and the film soaked in 1.5SBF then were characterized by scanning electron microscopic (SEM) observation, energy dispersive X-ray microanalysis (EDX), and thin-film X-ray diffraction (TF-XRD). Apatite deposition was observed on the surface of cloth made from raw silk fiber after it was soaked in 1.5SBF, but it was not observed on cloth made from normal silk fibers. The apatite deposition on the raw silk fiber cloth was accelerated when the fibers were subjected to treatment with CaCl(2) solution at a concentration of at least 1 kmol/m(3) before immersion in 1.5SBF. Apatite deposition also was observed on the sericin film after the film was soaked in 1.5SBF for 7 days. These results indicate that apatite deposition on raw silk cloth is attributable to the catalytic effect of sericin because the surface of raw silk consists of sericin whereas that of normal silk contains fibroin. The deposition of the apatite and its crystal growth are accelerated by the presence of calcium ions on the sericin after treatment with CaCl(2) solution. Thus, sericin on natural silk fiber has the potential to facilitate apatite deposition and can be useful as a polymer material in the fabrication of hybrid materials analogous to bone through biomimetic processes.

Apatites↗

PubMed2005

The effect of biomimetic apatite structure on osteoblast viability, proliferation, and gene expression.

The conventional biomimetic apatite coating process can be accelerated by immersing substrates into concentrated simulated body fluid (5 x SBF) at 37 degrees C to form an initial coating of apatite precursor spheres, and transform the precursors into plate-like apatite structures. Depending on processing parameters, different apatite structures can be created over the same substrate. The purpose of this study is to investigate the effects of the different apatite microenvironment on cell spreading, viability, proliferation, and gene expression. MC3T3-E1 preosteoblasts were cultured on five surfaces: conventional apatite (CA), precursor apatite spheres (PreA), large plate-like apatites (LgA), small plate-like apatites (SmA), and tissue culture grade polystyrene (TCPS). PreA induced significantly higher cell death during the first two weeks. TCPS supported more uniform spreading (1 day) and higher proliferation (2 weeks) than CA, LgA, and SmA. Apatites restricted spreading and promoted the extension of cellular projections along the textured surfaces under confocal microscopy observation. By 3 weeks, LgA induced highest expression of mature osteogenic markers osteocalcin (OCN) and bone sialoprotein (BSP) in both regular and osteogenic culture media based on quantitative real-time RT-PCR. The results of this study suggest differential cell responses to subtle changes in apatite microenvironment.

3T3 Cells↗

PubMed1989

High resolution electron microscopy of nonstoichiometric apatite crystals.

The application of high resolution electron microscopy, computer image processing, and image simulation techniques to the investigation of synthetic nonstoichiometric apatites has provided new details of apatite crystal growth mechanisms. Under certain precipitation conditions, calcium-deficient apatites with distinct octacalcium phosphate (OCP)-apatite intergrowths have been observed. Apatite crystals with unit-cell thick overgrowths of OCP on their surfaces confirmed the stepwise hydrolysis crystal growth mechanism initially proposed by Brown (Nature 196:1048-1050). However, many crystals also contained a central two-dimensional OCP inclusion one to two unit cells thick, embedded in an apatite matrix. Similar planar defects have been observed in dental enamel, dentin, and bone crystals. We have developed a modified version of Brown's stepwise OCP hydrolysis apatite crystal growth mechanism to explain the formation of crystals with OCP central planar defects. The mechanism involves the nucleation of an OCP seed that grows until it reaches a critical size, rh, before OCP hydrolysis occurs. Apatite subsequently grows epitaxially on the OCP seed, thereby embedding it in the center of an apatite crystal. Apatite growth is facilitated by partial screw dislocations emanating from the planar defect.

Animals↗

PubMed2001

Apatite coating on hydrophilic polymer-grafted poly(ethylene) films using an alternate soaking process.

Previously, we developed a novel alternate soaking process and clarified that bone-like apatite was formed on/in organic polymer hydrogel matrices using this process. The present study focused on the apatite coating on hydrophilic polymer grafted poly(ethylene) (PE) films with various grafting densities and commonly used hydrophilic polymers, poly(acryl amide) (PAAm) and poly(acrylic acid) (PAAc) were employed. From X-ray diffraction analysis, hydroxyapatite was coated on PAAm- or PAAc- grafted PE films. The amount of apatite coated on PAAm-grafted PE (PAAm-g-PE) films increased with an increase in the reaction cycles and the grafting density of PAAm. Similar to PAAm-g-PE, the amount of apatite coated on PAAc-grafted PE (PAAc-g-PE) films increased linearly with an increase in the grafting density of the PAAc up to around 30 microg/cm2. While, no significant increase in the apatite coating on the PAAc-g-PE films was observed even after 50 reaction cycles when the grafting densities of PAAc were over 30 microg/cm2. Apatite coating was not observed on original PE films. Scanning electron microscopic images reveal that the aggregation of apatite crystals on all PAAm-g-PE films and PAAc-g-PE films with grafting density from 10 to 30 microg/cm2. On the other hand, a dense apatite layer with some cracks was coated when the grafting density of the PAAc chains was over 30 microg/cm2. These results indicated that it was possible to coat apatite on hydrophilic polymer grafted PE films by an alternate soaking process and that the apatite crystal morphology could be controlled as a function of polymer type and density.

Apatites↗

PubMed2001

Petal-like apatite formed on the surface of tricalcium phosphate ceramic after soaking in distilled water.

In the present study six types of tricalcium phosphate ceramic were prepared and soaked in distilled water for different periods to investigate whether a surface apatite layer was formed on TCP ceramics or not. X-ray diffractometry (XRD) and Fourier-transformed infrared (FTIR) spectrometer were used to examine the changes in crystalline phases and functional groups of TCP ceramics for different soaking periods. Calcium and phosphate ions released from TCP ceramics during soaking were recorded by atomic absorption analysis and ion-coupled plasma. Results revealed that alphaTCP, alphaTCP/betaTCP mixture (alphabetaTCP) and betaTCP ceramic were gradually dissolved. There was no apatite layer formed on their surface after being immersed in distilled water for different durations of time. Mg-TCP ceramic, tricalcium phosphate doped with Mg ions, exhibited a lower dissolution rate than the other types of TCP ceramics. Apatite crystals were also not formed on the surface of Mg-TCP ceramic when immersed in distilled water. Tribasic calcium phosphate, prepared from wet precipitation method, was converted to betaTCP/HAP (HbetaTCP) or alphaTCP/betaTCP/HAP (HalphabetaTCP) crystalline composition at different sintering temperatures (1,150 degrees C and 1,300 degrees C). The surface apatite layer did not appear on HbetaTCP ceramic after soaking. We observed that petal-like apatite was formed on the HalphabetaTCP ceramic surface after being immersed for 2 weeks. alphaTCP phase of HalphabetaTCP ceramic was not directly converted to apatite during soaking. The surface apatite layer formed on the HalphabetaTCP ceramic surface was due to the precipitation of the calcium and phosphate ions released from alphaTCP dissolution. HAP, which existed in the structure of HalphabetaTCP ceramic, plays a role as apatite-precipitating seed to uptake calcium and phosphate ions. TCP ceramics which lacked alphaTCP and HAP content neither converted to apatite nor formed surface apatite on their surfaces during immersion.

Apatites↗

PubMed2002

Apatite-forming ability of CaO-containing titania.

It was recently shown that titanium metal and its alloys spontaneously form a bonelike apatite layer on their surfaces in the living body and bond to the bone through the apatite layer, when the sodium ions are incorporated into titanium oxide layer of their surfaces by chemical and heat treatments. It is expected that their apatite-forming ability, and hence their bone-bonding ability, could be enhanced, if the calcium ions are incorporated into their surface titanium oxide layers instead of the sodium ions, because the calcium ions released from their surface layers can increase the ionic activity product of the apatite of the surrounding fluid more effectively than the sodium ions. In the present study, in order to investigate the effect of incorporation of the calcium ions into the titanium oxide layer on its apatite-forming ability, apatite-forming abilities of titania gels which have different CaO contents and subjected to different heat treatments were examined in a simulated body fluid with ion concentrations nearly equal to those of the human blood plasma. It was found that CaO-containing gels do not form the apatite on their surfaces as far as they take an amorphous phase in spite of the fact that they release larger amounts of the calcium ions with increasing CaO contents of the gels. They form the apatite when they take an anatase-like structure even though they do not contain CaO. These results indicate that a specific structure of the titanium oxide is more important for the apatite nucleation than the magnitude of the ionic activity products of the apatite in the surrounding fluid.

Apatites↗

PubMed1990

Effect of solution composition on morphological and structural features of carbonated calcium apatites.

The composition of enamel mineral corresponds to that of a calcium carbonato-apatite. For insight to be gained into the precipitation of carbonato-apatites having specific properties (crystal size, morphology, and carbonate incorporation into the crystal lattice), apatites were prepared at 80 degrees C in aqueous systems having various CO3 concentrations and pH values of around 7.5 or 10.5 (+/- 0.5). The various preparations had a wide range (0.005 to 0.19) of CO3/Ca molar ratios that bracket the ratios found in porcine enamel mineral at various developmental stages. Fourier transform infrared spectroscopy (FTIR) and x-ray diffraction analyses showed that the calcium apatites precipitating at neutral pH incorporated the carbonate into both the hydroxyl and phosphate ion sites in their lattices (A,B-types), whereas the preparations made at the alkaline pH (high OH-(-)CO3(2-)-competition) or in the presence of fluoride (F-(-)CO3(2-) competition) yielded only the B-type carbonato-apatite. It was also ascertained that the size and morphology of the carbonato-apatites, assessed by specific surface area determination and high-resolution electron microscopy, were highly dependent on the driving force for precipitation and the presence of regulators (CO3(2-) and F-) in solution. In neutral media, early precipitates were thin-ribbon in appearance, but grew into crystals having flattened-hexagonal cross-sections. In the presence of fluoride or in alkaline media, acicular apatite crystals, precipitated initially, grew into large rod-like carbonato-apatites having a symmetric-hexagonal cross-section. In both neutral and alkaline solutions, carbonate inhibited the growth of apatite crystals along their c axis, leading to the formation of bulkier crystals. The formation of carbonato-apatites at the neutral pH and their properties are consistent with observations made on enamel minerals formed in the early developmental stages.

Apatites↗

PubMed1996

Magnesium and carbonate in enamel and synthetic apatites.

This study aimed to: determine the Mg and CO3 distribution in the outer (surface), middle, and inner (closest to the enamel-dentin junction, EDJ) layers of human enamel; and determine the factors affecting the incorporation of Mg into synthetic apatites and the consequence of such incorporation on the properties of the apatites. Results demonstrated that the concentrations of Mg, CO3, and organic components increased from the surface to the inner layers close to the EDJ and a difference in crystallinity from the outer to the inner layers. Initial results indicated that the extent of dissolution of the inner layer enamel is greater than that in the outer or surface enamel. Results on synthetic apatites showed the following: (1) Limited Mg incorporation into apatite was dependent on solution [Mg/Ca] molar ratio, temperature, pH, and the presence of CO3 or fluoride (F); (2) incorporation of Mg causes reduction in crystallinity and an increase in the extent of dissolution of the apatite; (3) the negative effect of Mg on the properties of apatites is synergistic to that of CO3 and antagonistic to that of F; and (4) exposure to acid of Mg-containing apatites causes the dissolution of Mg-rich apatite and precipitation of Mg-poor apatite. The observed decrease in the [Mg/Ca] of enamel and synthetic apatites after acid exposure may explain the observed 'preferential loss' of Mg and CO3 in the initial stages of caries.

Apatites↗

PubMed1991

Thermal decomposition of Lingula shell apatite.

Lingula shell is composed of apatite with a preferred orientation. The shell apatites of Lingula unguis(Lu) and Lingula shantoungensis(Ls) were characterized and compared with apatite of human tooth enamel. Insight into the Lingula apatite was studied by following the change of lattice parameter, transformation to beta-tricalcium phosphate (beta-TCP), and the loss and change of CO3, OH, and H2O after heating up to 1,000 degrees C in air and N2 for 24 hours. The OH stretching band was not observed in unheated apatites and in apatites heated in dried N2. Lu and Ls apatite produced 26 and 17 wt% of beta-TCP at 700 degrees C, respectively. Fifty to 60% of H2O was lost at 200 degrees C, being accompanied by a drastic contraction of the a- and c-axis and a drastic decrease in the crystallinity. These results indicate that (1) Lu and Ls shell apatite is CO3 containing F + Cl-apatite, and (2) the structural H2O of the Lingula apatite is loosely bounded such that they are lost at lower temperature than tooth enamel.

Animals↗

PubMedDate not supplied

Morphometric studies on synovium in advanced osteoarthritis: is there an association between apatite-like material and collagen deposits?

OBJECTIVE: To look for the frequency and the influence of apatite-like deposits in the synovial membrane of advanced osteoarthritic joints. METHODS: Synovium of 16 joints undergoing total arthroplasty for advanced primary osteoarthritis was embedded in paraffin. Adjacent sections were stained with alizarin red S, Mowat's pentachrome, Hematoxylin-eosin and Gomori to show apatite-like deposits, collagen, cartilage fragments, vessels, cells and iron respectively. Histomorphometry was carried out for the apatite-like and collagen deposits by the point counting method; the density of vessels and cells was also quantified. RESULTS: 14 out of the 16 specimens contained apatite-like material, mostly on the synovial surface or just beneath. There was no correlation between the apatite-like deposits and any other measured histological parameter (fibrosis, villus length, synovial lining cell width, density of synovial vessels or cells). Interestingly, the p value for a correlation between the amounts of apatite and collagen deposits was close to significance (r = 0.53; p = 0.055) when the relative volume of the apatite-like material was less than 1.2% (n = 13). CONCLUSIONS: Apatite-like deposits are frequently observed in the synovium of late stage osteoarthritis. Although not statistically significant, these results suggest a possible association between apatite-like and collagen deposits when the amount of apatite deposits is low. Further quantitative studies are recommended to investigate this observation.

Aged↗

PubMed2000

Preparation and characterization of apatite deposited on silk fabric using an alternate soaking process.

Apatite-deposited silk fabric composite materials were developed using a new alternate soaking process. The characteristics of deposited apatite were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectrophotometry (FTIR), and X-ray photoelectron spectroscopy (XPS). Apatite weight increased with alternating soaking in a calcium solution [200 mM aqueous calcium chloride solution buffered with tris(hydroxymethyl) aminomethane and HCl (pH 7.4)] and a phosphate solution (120 mM aqueous disodium hydrogenphosphate) changed every hour. SEM showed that apatite deposited after 21 or more repeated soakings was over 20 microm thick. XRD showed that with alternate soakings, the apatite crystals deposited on silk fabric elongated along the c axis. FTIR and XPS indicated the existence of carbonate, HPO(4)(2-), and Na(+) ions in addition to constituent ions of hydroxyapatite. A loss of HPO(4)(2-) and Na(+) ions in the deposit upon further soaking might be associated with an increasing apatite crystallinity. Apatite deposited on silk by the alternate soaking process was a deficient apatite containing carbonate, HPO(4)(2-), and Na(+) ions as in a natural bone tissue. Thus, this apatite-silk composite material might be potentially bioactive.

Animals↗

PubMed2002

Micropattern formation of apatite by combination of a biomimetic process and transcription of resist pattern.

Two kinds of methods combining a biomimetic process and transcription of resist pattern were conducted to form an apatite micropattern. For method 1, apatite nuclei were formed on a resist pattern printed substrate by setting it in contact with CaO-SiO(2)-based glass in a simulated body fluid (SBF) with inorganic ion concentrations nearly equal to those of human blood plasma. Next, apatite was grown from the nuclei by soaking the substrate in an aqueous solution with ion concentrations 1.5 times those of SBF (1.5 SBF). Then, the resist material was dissolved off by organic solvent with the apatite just formed on it. Apatite micropattern transcribing the resist pattern was obtained. For method 2, apatite nuclei were formed on a resist pattern printed substrate by setting it in contact with CaO-SiO(2)-based glass in SBF. Next, the resist material was dissolved off with the apatite nuclei just formed on it. Then, the substrate was soaked in 1.5 SBF to grow the remaining nuclei and an apatite micropattern transcribing the resist pattern was obtained. For both methods, minute apatite patterns with various shapes as straight lines, bending lines, and blocks were clearly formed. The minimum line width of the obtained pattern was 2 microm. These methods are promising for producing multifunctional materials with bioaffinity.

Apatites↗

PubMed2005

In vitro response of MC3T3-E1 pre-osteoblasts within three-dimensional apatite-coated PLGA scaffolds.

Biomimetic apatites have been reported to promote osteogenic activities in numerous in vivo and in vitro models, but the precise mechanism by which the apatite microenvironment promotes such activities is not well understood. Such mechanistic studies require reproducible model systems that are relevant to tissue engineering practices. Although two-dimensional (2D) apatite-coated polystyrene culture dishes provide practicality and reproducibility, they do not simulate the effects of the three-dimensional (3D) microenvironment and degrading polymeric substrates. A simple 3D model system to address these relevant effects, and its utilization in the investigation of apatite-promoted osteoblastic differentiation in vitro is reported in this paper. Apatite coating was achieved by sequentially immersing poly(lactide-co-glycolide) (PLGA) scaffolds into different simulated body fluids (SBF). SEM, EDX, FTIR, TEM electron diffraction confirmed the apatite coating to comprise of calcium-deficient carbonated hydroxyapatite crystals. While both apatite-coated and non-coated PLGA scaffolds supported MC3T3-E1 attachment, spreading, and proliferation, significant differences in osteoblastic differentiation were observed. Relative to non-coated controls, quantitative real-time PCR revealed significant apatite-associated suppression of alkaline phosphatase (ALP), early upregulation of osteopontin (OPN) at 3 days, and upregulation of osteocalcin (OCN) and bone sialoprotein (BSP) at 4 weeks. In summary, apatite-promoted osteoblastic differentiation can be observed in a 3D model system that is relevant to tissue engineering.

Animals↗

PubMed1992

Effects of F- on apatite-octacalcium phosphate intergrowth and crystal morphology in a model system of tooth enamel formation.

In order to study the effect of F- on tooth enamel-like apatite formation, crystal growth experiments were carried out in the presence of 0.1 approximately 2 ppm F- at 37 degrees C and at pH 6.5 in a model system of enamel formation where octacalcium phosphate (OCP) was stable. Morphology changed from long and thin ribbons to small needle-like plates, and the product changed from OCP to apatite with an increase in F- concentration. In the presence of 0.1-1 ppm F-, apatite-OCP intergrowth took place, and crystals composed of apatite and OCP lamellas were formed. These crystals showed long and thin plate-like morphology and embeded an OCP lamella in the center of the crystal. The OCP lamella and its (100) planes were parallel to the (100) planes of apatite. The thickness of OCP decreased and that of apatite increased with an increase in F- concentration. Some apatite crystals obtained at 1 ppm F- embedded a central plane instead of the distinct OCP lamella. The result indicates that initially formed, thin, plate-like OCP acted as a template for the subsequent epitaxial overgrowth of apatite and, moreover, F- played an important role in regulating the apatite-OCP intergrowth.

Apatites↗

PubMed1989

Crystal dissolution of biological and ceramic apatites.

High resolution transmission electron microscopy (Hr TEM) studies on biological and synthetic calcium phosphate have provided information on the dissolution process at the crystal level. The purpose of this study was to investigate the dissolution of ceramic hydroxyapatite (HA) after implantation using Hr TEM. Recovered HA ceramic implanted in bony and nonbony sites in animals and in periodontal pockets in humans were used for the study. For comparison, sections of human fluorotic enamel with caries and sections of shark enameloid previously exposed to 0.1 HCl were similarly investigated. Hr TEM studies demonstrated that in both the biological and ceramic apatites, the lattice and atomic defects were the starting points in the dissolution process. However, significant differences in the process of dissolution were observed: (1) biological apatite crystals showed preferential core dissolution whereas ceramic apatite crystals showed nonspecific dissolution at the cores and at the surfaces; (2) the dissolution of biological apatites appeared to consistently extend along the crystal's c-axis whereas dissolution of the ceramic HA did not appear to be correlated with the crystal's c-axis. The observed differences in crystal dissolution between biological and ceramic apatites may be attributed to the following: (1) the unique crystal/protein interaction present with biological apatites but absent in ceramic HA; (2) differences in defect distribution between biological and ceramic apatites which are due to the differences in the original of these defects; and (3) the longer morphological c-axis of biological apatites compared with that of ceramic apatites.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1996

Ultrastructural study of an apatite layer formed by a biomimetic process and its bonding to bone.

A dense and uniform apatite layer about 20 microns thick was formed on a poly(ether sulphone) (PESF) substrate treated with glow discharge in O2 gas by a biomimetic process. The apatite-polymer composite obtained was implanted into a rabbit tibia and the structure of the PESF-apatite-bone interface was observed under a scanning and a transmission electron microscope 8 weeks after implantation. The apatite layer formed by the biomimetic process was confirmed to consist of small crystals of apatite with a structure similar to that of apatite in bone. The apatite layer remained on the substrate in the body, and bonded to the apatite in bone directly. This type of apatite-organic polymer composite expected to be useful as bone-repairing material.

Animals↗

PubMed2006

Phosphorus removal from wastewater by mineral apatite.

Natural apatite has emerged as potentially effective for phosphorus (P) removal from wastewater. The retention capacity of apatite is attributed to a lower activation energy barrier required to form hydroxyapatite (HAP) by crystallization. The aim of our study was to test the P removal potential of four apatites found in North America. Minerals were collected from two geologically different formations: sedimentary apatites from Florida and igneous apatites from Quebec. A granular size ranging from 2.5 to 10mm to prevent clogging in wastewater applications was used. Isotherms (24 and 96 h) were drawn after batch tests using the Langmuir model which indicated that sedimentary apatites presented a higher P-affinity (K(L)=0.009 L/g) than igneous apatites (K(L) approximately 0.004 L/g). The higher density of igneous material probably explained this difference. P-retention capacities were determined to be around 0.3mg P/g apatite (24 h). A 30 mg P/L synthetic effluent was fed during 39 days to four lab-scale columns. A mixture of sedimentary material (apatite and limestone 50-50%, w/w) showed a complete P-retention during 15 days which then declined to 65% until the end of the 39 days lab scale test period. A limitation in calcium may have limited nucleation processes. The same mixture used in a field scale test showed 60% P-retention from a secondary effluent (30 mg COD/L, 10 mg Pt/L) during 65 days without clogging.

Apatites↗