Hydroxyapatite Pellets Research Articles

Thermal diffusion of molybdenum in apatite

One of the solutions to store high level nuclear wastes (actinides and fission products) is deep geological repository. Since some of these radionuclides have extremely long half-lives, they require an appropriate durable immobilisation system. Several materials, including apatites, are studied as potential inertial matrices. One of the most fed long life fission isotopes, 99Tc (half-life t 1/2=2 × 10 5 yr) is produced by the 99Mo → 99Tc filiation. Therefore, we focused on the migration study of molybdenum in hydroxyapatite Ca 10(PO 4) 6(OH) 2. Molybdenum was introduced by ion implantation, 40 nm deep, in pellets of hydroxyapatite. Then the samples were heated under air. The evolution of the molybdenum profiles after each annealing step was followed by Rutherford backscattering spectroscopy (RBS), showing a volatilization of molybdenum. Moreover, XPS analysis made on molybdenum led us to think that the volatile species formed is MoO 3.

Sintering of Hydroxyapatite Ceramics, with the Aid of Optical Transmittance — Temperature Spectra

The optical transmittance — temperature spectra of well-translucent thin pellets of hydroxyapatite prepared by the high isostatic pressure consolidation of xerogel particles were measured by a newly-developed thermal analysis technique. From these spectra, it was possible to identify temperature intervals with increased or decreased levels of light transmittance, clearly associated with microstructural changes. The thermal processing of treated pellets was stopped at temperatures deliberately chosen with respect to the specific transmittance states. Samples with increased transparency were prepared when the heating of pellets was stopped at the temperatures of the locally highest light transmittance measured.

Effect of compaction pressure and atmosphere on sintering of nanometric iron powders : J. Bigot et al (CRNS, Vitry sur Seine, France)

This study describes the effect of sintering temperature on the microstructural, calcium/phosphorus (Ca/P) ion ratios and mechanical properties of non-separated biowastes processed hydroxyapatite (HAp) prepared through a low cold compaction protocol. The HAp was produced by a sintering temperature of 900 °C. Furthermore, HAp sintered at 900 °C was subjected to sintering temperatures of 1000 and 1100 °C.The structural and morphological evolution of the fabricated biomaterials were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with electron dispersive X-ray analysis (EDX) respectively. Uniaxial compaction using a pressure of 500 pa was used to produce rectangular shaped pellets to investigate the influence of sintering temperature on the mechanical properties of the produced pellets. From XRD analysis, it was found that hydroxyapatite derived from the biowastes showed good thermal stability and did not exhibit phase instability with traces of other calcium phosphates. The SEM micrographs showed microporous structure of the biomaterials and an increase in temperature reduced the porosity and enhanced the mechanical properties. It was also noticed that the trend of transformation of the average shape of pores was from strongly flattened to round at higher sintering temperatures. Electron dispersive X-ray analysis (EDX) revealed that the atomic Ca/P ratios of the as-sintered HAp specimens ranged from 1.58 to 1.79 for sintering temperatures of 900–1100 °C. The synthesized hydroxyapatite powder showed inclusion of the fluorapatite phase at sintering temperature of 1000 °C with a reduction in the crystallite size. For both scenarios (sintering temperature and compaction pressure), a consistent trend in mechanical properties (microhardness, fracture toughness and Young's modulus) is noticed at every point of measurement except for compressive strength. The reduction in compressive strength when compaction pressure was applied could be as a result of the stress induced in the HAp powders during compaction which may have made it more susceptible to cracks. The hardness value obtained for the synthesized hydroxyapatite pellets is in the range of that of actual human femoral cortical bone.

Bone Induction of Hydroxyapatite Combined with Bone Morphogenetic Protein and Covered with Periosteum

Using a rabbit model, we evaluated the role of the periosteum in bone induction using hydroxyapatite ceramic pellets, some of which had been coated with bone morphogenetic protein. Eighteen rabbits were divided into two groups, a control group that received pellets soaked in phosphate-buffered saline alone and another group for which the pellets had been supplemented with bone morphogenetic protein. After making a skin incision on the head of each rabbit, two caudally pedicled periosteal flaps measuring 1 cm in width and 2.5 cm in length were elevated. These flaps were wrapped around hydroxyapatite pellets manufactured from limestone and fixed with sutures. After implantation, both groups of rabbits were returned to their cages, maintained for 3, 6, or 9 weeks [every group consisted of 3 rabbits (6 pellets)], and then sacrificed. In this study, the extent of bone induction, which was measured with a dual x-ray densitometer, that resulted from covering the hydroxyapatite pellet with periosteum alone (control group) was minimal. On the contrary, since osteogenesis from the periosteum toward the pores of the pellet was observed in the bone morphogenetic protein group much more than in the control group, the usefulness of our technique was confirmed. However, active osteogenesis was observed with subperiosteal implantation of the hydroxyapatite-bone morphogenetic protein complex in the bone morphogenetic protein group, but the osteogenesis observed was not distributed over the entire pellet.

タンニン・フッ化物合剤(HY剤)を配合したグラスアイオノマーセメントの合成ハイドロキシアパタイトペレットに及ぼす影響

タンニン・フッ化物合剤(HY剤)を配合したグラスアイオノマーセメントの合成ハイドロキシアパタイトペレットに及ぼす影響

Characterization of cytoplasmic T3 binding sites by adsorption to hydroxyapatite: effects of drug inhibitors of T3 and relationship to glutathione-S-transferases.

To facilitate studies of thyroid hormone (T3) binding to cytoplasmic proteins, we prepared monkey (M. fascicularis) liver cytosol (100,000g supernatant) and examined T3 binding using hydroxyapatite (HAP) separation. HAP adsorbs cytoplasmic and nuclear binding sites but not serum T4 binding proteins. Cytosol was incubated with [125I]T3 for 30 min at 4 degrees C and separated by adding an equal volume of HAP (15 g/100 mL). After a further incubation of 10 min, the HAP pellet was washed three times in buffer containing Triton X-100, 0.5%. With this method, a single class of T3 binding site was observed with Kd 15.8 +/- 1.2 nM, concentration 0.62 +/- 0.17 pmol/mg protein (n = 3, mean +/- SD). We used this assay to assess potential drug inhibitors of cytoplasmic binding and to evaluate the proposal that glutathione-S-transferases (GST) and cytoplasmic T3 binding proteins are identical. Displacement of [125I]T3 by unlabeled iodothyronines relative to T3 (100) was T4 58, Triac 7, rT3 7, Tetrac less than or equal to 1. This hierarchy indicates that this binding site is distinct from nuclear or serum binding sites. T3 binding was displaceable by nonsteroidal anti-inflammatory drugs (NSAID) and nonbile acid cholephils (NBAC). Half-inhibitory concentrations (microM, mean +/- SD, n greater than or equal to 3) were diclofenac 4.9 +/- 1.3, mefenamic acid 13.6 +/- 0.6, bromosulphthalein 45 +/- 3, iopanoic acid approximately 200. Amiodarone and furosemide were inactive up to 100 microM. No displacement was observed with cortisol or the bile acid taurocholate, up to 100 microM. Dithiothreitol, 5 mM, did not change binding affinity or capacity.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of Laser Irradiation on the Dissolution Kinetics of Hydroxyapatite Preparations

This research investigated the effects of a laser irradiation treatment on the dissolution characteristics of hydroxyapatite (HAP), and the results provide an insight into the relationship between the effects of laser treatment and the two-site dissolution kinetics of HAP samples. The HAP samples prepared by aqueous precipitation and digestion at ~100°C were irradiated with a CO2 laser (20–50 W) with a beam diameter of 14mm for a total of 10–400s. Dissolution rates of the laser-treated HAP samples were subsequently determined in acetate buffer (pH = 4.5, μ = 0.50) at various levels of partial saturation (0–24% with respect to the HAP thermodynamic solubility of pKsp = 116). The following were the important findings. The X-ray diffraction and the IR spectroscopy results suggested that the HAP crystalline structure was not changed by laser treatment. Laser treatment of HAP powder at 50W for 400 s, however, caused an ~3.5-fold reduction in the specific surface area of HAP and reduced the initial dissolution rate of HAP in acetate buffer by a factor of ~22.9. Also, this laser treatment appeared to reduce the dissolution rate of HAP in 16 and 24% partially saturated acetate buffer from substantial levels to essentially zero. These results may be summarized as follows. Laser treatment of HAP results in a reduction in the dissolution rate and also a reduction in the specific surface area of this material. However, the dissolution rate reduction is significantly greater than the reduction in the specific surface area. Also, the percent reduction in the dissolution rate of laser-treated HAP in partially saturated buffers appears to be much greater than that for non-laser-treated HAP. In order to independently evaluate the effects of laser irradiation on the ion activity product (IAP) of HAP, a rotating disk dissolution study (based on Levich theory) of lased HAP pellets (50W for 400 s, 13 kJ/cm2) was performed. The ion activity product (KHAP) governing the dissolution of the lased HAP pellet was found to be 1 × 10−129.2 ± 0.7. This value for KHAP, together with the HAP powder results (above), strongly suggests that laser irradiation converts HAP possessing a two-site character to a HAP of a lower effective solubility (i.e., site #2 only).

Physicochemical characterization of deposits associated with HA ceramics implanted in nonosseous sites.

Pellets of well-characterized microporous hydroxyapatite (HA) ceramic were implanted in hamsters in two nonosseous sites: (1) in the fatty tissue of the gingival crease, far from bony tissue and (2) in intraperitoneal sites. The implants in site 1 were placed directly in contact with tissues, cells, and extracellular fluids while the implants in site 2 were placed in special chambers made of plexiglass cylinders covered in both ends with millipore filters, preventing contact with tissues and cells, but not with extracellular fluids. The hamsters were sacrificed and the implants recovered after 8, 16, 30, 150, and 365 days. The pellets were characterized using x-ray diffraction, infrared absorption, thermogravimetry, scanning and transmission electron microscopy, and calcium and phosphate analyses before and after implantation. Physicochemical analyses of HA ceramic implants before and after implantation demonstrated the formation of new material which was significantly different from the HA ceramic in terms of the following: (a) morphology (size of shape) of crystals; (b) intimate association of the inorganic phase of the new material with an organic phase similar to inorganic/organic association in bone; (c) the inorganic phase of the new material is a CO3-apatite, similar to that of bone, while the HA in ceramic is CO3-free; (d) electron diffraction of apatite of new material is similar to that of bone apatite. This study also demonstrated that the new material associated with the HA ceramics implanted in two different nonosseous sites were identical in spite of the differences in their microenvironment (cellular and acellular).

The influence of ion activity product on remineralization behavior of carbonate-apatite pellets, hydroxyapatite pellets and hydroxyapatite powder

The effect of the ion activity product, K FAP(a 10 Ca 2+ a 6 PO 4 3− a 2 F − ) of the remineralizing solution on the remineralization behavior of carbonate-apatite pellets, hydroxyapatite pellets and hydroxyapatite powder have been studied. The pellets were demineralized in partially saturated 0.1 M acetate buffer, pH = 4.5, then rernineralized in 0.1 M acetate buffer containing 10 ppm F and various equimolar levels of 45Ca and phosphate. The hydrodynamics was controlled by using the rotating disk apparatus. The acid-abrasion and acid-etch methods were used to determine F, 45Ca and P levels at different depths. For powder remineralization studies, hydroxyapatite seed crystals were added to similar acetate buffer solutions containing Ca, P and F. The seed crystals were sonicated and maintained in uniform suspension in a thermostated beaker using a magnetic stirring bar. For carbonate-apatite pellets, there was mainly) remineralization when the ion activity product of the remineralizing solution was 1 × 10 −108. When the K FAP = 10 −112 and 10 −116, there was simultaneous demineralization/remineralizatton. The F concentration profiles in the lesion were steepest at 1 × 10 −108 and broadened with decreasing K FAP, The molar F/ 45Ca ratios obtained with carbonate-apatite pellets were essentially in quantitative agreement with those previously obtained with bovine dental enamel but differed somewhat from those obtained with hydroxyapatite pellets. In the hydroxyapatite powder studies the rates of crystal growth were relatively rapid at an ion activity product of 10 −108, but decreased significantly at K KAP = 10 −112 and were very slow at K FAP = 10 −116 These powder remineralization results are consistent with remineralization behavior in the surface region of hydroxyapatite and the carbonate-apatite pellets.

Correlation of microenvironmental drug concentration with inhibition of growth of microorganisms on surfaces.

Methodologies have been developed to study the concept of microenvironmental drug concentration (C*) near or around microorganisms. C* may be calculated from data on drug release from a depot site by using appropriate diffusion relationships. By following C* and correlating this with the minimum inhibitory concentration (CMIC), one could attempt to predict the effectiveness of an antiplaque agent. When C* is less than CMIC, growth would be expected to occur; when C* is higher than or equal to CMIC, growth would not be expected. Chlorhexidine diacetate was chosen for this study, which used a system involving microorganisms present on the surface of drug-treated hydroxyapatite pellets. CMIC, defined as the lowest concentration to inhibit bacterial growth, was determined independently and under conditions similar to those used in the C* experiments. Surface growth of adhering microorganisms (Streptococcus mutans SL1) was followed by scanning electron microscopy. The parameters used in the calculation of C* were determined independently. Diffusion coefficients of the drugs and the diffusion layer thickness were determined under conditions similar to those employed in the release rate studies. Surface growth was generally found to be inhibited whenever C* was significantly greater than CMIC, and growth occurred whenever C* was significantly smaller than CMIC. These findings demonstrate how C* may determine the action of a topically administered antimicrobial agent and how the various physical and chemical factors play roles in influencing this quantity.

Solution Activity Product (KFAP) and Simultaneous Demineralization–Remineralization in Bovine Tooth Enamel and Hydroxyapatite Pellets

The effects of changing the ion activity product of the remineralization solution at pH 4.5 (pKFAP 108–118) on the remineralization behavior of demineralized bovine tooth enamel and hydroxyapatite pellets have been studied. Solutions containing calcium-45, phosphate, and fluoride in acetate buffers were used. The 45Ca/F molar ratios indicated the formation of fluoridated hydroxyapatite in the enamel or the pellet when the pKFAP values for remineralizing solutions were <112. When the pKFAP values were >112, the 45Ca/F ratios were found to be «5. Also, when the pKFAP values were large (>112), the remineralization patterns based on the fluoride distribution in the tooth (or pellet) were found to be different than when the pKFAP values were small (<112). The hypothesis that a pKFAP value of 112 is the demarcation between remineralization only and simultaneous dissolution-remineralization has been proposed based on these results.

Dissolution rate of apatite powders in acidic fluoride solutions and the relationship to hydroxyapatite disk and bovine enamel behavior

The dissolution kinetics of synthetic hydroxyapatite (HAP) and carbonate-containing HAP powders have been studied in fluoride-containing acetate buffer solutions partially saturated with respect to HAP ( K FAP = 10 −115 to 10 −123). The experimental results indicate that in the case of HAP powders the dissolution rates become very slow when the K FAP values of the dissolution medium are larger than 10 −119. For the carbonate-containing apatites, however, there is a significant dissolution in the region 10 −115 ≥ K FAP ≥ 10 −119 which is in the region of physiological and therapeutic significance. The present results with the HAP powder together with HAP pellet data show that the dissolution of HAP pellets in the region 10 −114 > K FAP > 10 −119 results from an extended transient period rising from sustained deposition of F − on the surface and at intermediate depths in the ‘lesion’. Similar effects have also been observed with bovine teeth dissolution in acidic F − solutions.

The intact surface layer in natural enamel caries and acid‐dissolved hydroxyapatite pellets

The crystallographic features of various histological sites found in enamel carious lesions were studied by means of X-ray microbeam diffraction. The most interesting finding was the crystallinity of apatite crystals in the intact surface layer covering the demineralized lesions was higher than that of the crystals in the subsurface lesions or unaffected areas. Acid-dissolution experiments using synthetic hydroxyapatite pellets showed that a well mineralized layer was produced on the pellet surface under the condition that no Ca and PO4 ions were added to the initial acidic solution. Furthermore, X-ray diffraction analysis revealed that half-line breadth values of 004, 222, and 310 reflections of apatite pellets decreased, and their integrated peak intensities increased with dissolution time. These findings are in agreement with the results obtained in the study of enamel carious lesions, leading to the conclusion that the intact surface layer is formed by deposition of the mineral ions from dissolving subsurface lesions, and that this process is accompanied by the improvement in crystallinity of apatite crystals, possibly due to growth of the crystals.

Solid-solution interfacial phenomena at the synthetic hydroxyapatite pellet surface

[in Japanese]

A new two-site model for hydroxyapatite dissolution in acidic media

A physical model featuring two distinct types of dissolution sites for hydroxyapatite (HAP) crystals is presented. One of these sites (site No. 1) is associated with dissolution along c axis dislocations of HAP crystals and is the important site when dissolution occurs into partially saturated solutions. Site No. 2 is active only when dissolution occurs into nearly completely unsaturated solutions, and, because of its greater apparent rate constant, is the more important dissolution site under these conditions. In the physical model block dental enamel or a compressed HAP pellet is represented as a porous matrix of these HAP crystals with interstitial spaces which are permeated by the dissolution medium. The behavior of the model for various situations can be calculated by combining Fick's second law equation for diffusion with the kinetic equations for the behavior of the dissolution sites and solving the resulting boundary value problem. This model is capable of accounting for dissolution kinetics over a range of variation of experimental variables (degree of undersaturation, Ca P ratio, and effective diffusion layer thickness). The model also correctly predicts the conditions necessary for zonal as opposed to surface dissolution: high partial saturation, a viscous dissolution medium, or the presence of a site No. 2 dissolution inhibitor. Electron microscopic studies of dissolution morphology at the single crystal level are also in full agreement with the model. Finally, an examination of the available data on enamel remineralization suggests that the holes formed as a result of site No. 1 dissolution are likely the primary sites for remineralization.

A possible second site for hydroxyapatite dissolution in acidic media

Dissolution of human dental enamel and of synthetic hydroxyapatite pellets in completely unsaturated acetate buffer solutions was previously shown to follow a model in which a single dissolution site was employed. The present investigation reports similar studies carried out under the clinically more relevant conditions of dissolution into solutions partially saturated with respect to hydroxyapatite, and it is shown that under these conditions the dissolution kinetics may be described by a site which has properties different from the site responsible for dissolution into completely unsaturated solutions. The properties of this second site were consistent with experiments in which bulk solution conditions (degree of partial saturation, Ca P ratio) and effective diffusion layer thickness were varied. Thus, dissolution kinetics studies indicate that hydroxyapatite crystals have at least two different types of sites that are important in dissolution.

Solid-solution interfacial phenomena at the synthetic hydroxyapatite pellet surface

Solid-solution interfacial phenomena at the synthetic hydroxyapatite pellet surface

X-Ray Diffraction Study on Remineralization Using Synthetic Hydroxyapatite Pellets

Crystallographic changes of the surface layer of synthetic hydroxyapatite pellets dissolved in acetate buffer (pH 4.0) were investigated by X-ray diffraction. In both agitated and nonagitated systems,

Kinetics and mechanism of hydroxyapatite crystal dissolution in weak acid buffers using the rotating disk method.

The model given in this report and the rotating disk method provide a useful combination in the study of dental enamel and hydroxyapatite dissolution kinetics. The present approach is a significant improvement over earlier studies, and both the ionic activity product that governs the dissolution reaction and the apparent surface dissolution reaction rate constant may be simultaneously obtained. Thus, these investigations have established the baseline for the dissolution rate studies under sink conditions. Concurrent studies, under conditions where the acidic buffer mediums are partially saturated with respect to hydroxyapatite have shown another dissolution site for hydroxyapatite that operates at a higher ionic activity product but has a much smaller apparent surface reaction rate constant. This has raised the question of whether the presence of this second site may interfere with the proper theoretical analysis of the experimental results obtained under sink conditions. A preliminary analysis of the two-site model has shown that the dissolution kinetics of hydroxyapatite under sink conditions is almost completely governed by the sink condition site (KHAP = 10(-124.5), k' = 174) established in this report. The difference between the predicted dissolution rate for the one-site model and the two-site model are generally of the order of 4 to 5% where the experiments are conducted under sink conditions and over the range of variables covered in the present study.

Batch procedure for thermal elution of DNA from hydroxyapatite

Thermal elution of reassociated DNA on hydroxyapatite columns is time-consuming because it is difficult to run more than two samples simultaneously. A batchwise hydroxyapatite thermal elution method that allows simultaneous handling of up to ten samples is described. In this method, DNA samples are mixed with hydroxyapatite contained in test tubes. In each elution step the test tubes are rapidly centrifuged in a heated centrifuge and wash solution is decanted. Fresh, prewarmed wash solution is added and mixed with the hydroxyapatite pellet. This centrifuge method was used successfully for: (a) fractionating single- and double-stranded DNA in reactions exhibiting low and high levels of reassociation; (b) thermal elution reactions using DNA from the same or different bacteria; ( c) time-course reassociation studies; ( d) reactions carried out at different incubation temperatures. Sensitivity and reproducibility of the centrifuge hydroxyapatite assay were identical to those observed in the column assay.