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PubMed2003

Europium-doped bioapatite: a new photostable biological probe, internalizable by human cells.

The authors prepared at low temperatures (37 degrees C) a novel inorganic bioprobe. It consisted of mineral nanoparticles of apatitic tricalcium phosphate doped with europium, of size, structure and composition close to those of the mineral part of calcified tissues. In contrast to organic probes which degrade rapidly (photobleaching), the red luminescence of the new probe is photostable. Moreover, this luminescence can be obtained under visible irradiation, which makes it suitable for prolonged examination of live cells. Human pancreatic epithelial cells in culture were incubated with these particles and their internalization was observed by laser scanning confocal microscopy. Transmission electron microscopy and electron microdiffraction analysis confirmed that the particles were internalized retaining their original apatitic structure. This probe may thus be of value for biovectorization.

Apatites↗

PubMed2003

Preparation of poly(lactic acid) composites containing calcium carbonate (vaterite).

A new type of ceramic-polymer biomaterial having excellent apatite-forming ability in simulated body fluid was prepared by hot-pressing a mixture of poly(-L-lactic acid) (PLA) and calcium carbonate (vaterite). After PLA dissolved in methylene chloride was mixed with calcium carbonate consisting of vaterite, the mixture was dried completely and subsequently hot-pressed uniaxially under a pressure of 40 MPa at 180 degrees C. When 30 wt% vaterite was introduced, the modulus of elasticity was effectively improved by 3.5-6 GPa, which was about twice higher than the modulus of PLA. The composite showed no brittle fracture behavior and a comparably high bending strength of approximately 50 MPa. The composite containing 30 wt% vaterite formed a 5-15-microm-thick bonelike apatite layer on its surface after soaking in SBF at 37 degrees C even for 1-3d.

Apatites↗

PubMed1999

Quantitative comparison of osteoconduction of porous, dense A-W glass-ceramic and hydroxyapatite granules (effects of granule and pore sizes).

The osteoconductive potentials of dense, small porous and large porous apatite- and wollastonite-containing glass-ceramic (A-W GC) granules of various sizes implanted in rat tibiae were evaluated quantitatively, by determining their affinity indices. The average affinity indices of all types of A-W GC were high. The dense A-W GC granules had the highest values (97.0+/-5.5%), followed by the large porous (87.1+/-8.4%) and then the small porous granules (79.0+/-8.4%). There were no significant differences among the osteoconductive potentials of the different sizes of each form of A-W GC granule. The osteoconductive potentials of four types of commercially available porous hydroxyapatite (HA) granules were compared with those of the small porous A-W GC granules, using the affinity index and the proportion of newly formed bone relative to that of the granules in the bone defect. The values of the former parameter for three types of HA and those of the latter for four were significantly inferior to those of A-W GC. The difference between the osteoconductive potentials of A-W GC and HA was considered to be related to the rate of surface apatite layer formation.

Animals↗

PubMed1999

Evaluation of post-treatment solutions for clinical use with the calcium phosphate precipitation method.

OBJECTIVE: We have proposed a calcium phosphate precipitation (CPP) method that occludes dentine tubules with apatitic minerals for the treatment of dentine hypersensitivity. The current CPP method uses 1 mol/l NaOH as the post-treatment solution. However, its high pH is not desirable for clinical use. The aim of this study was to evaluate several solutions, especially buffer solutions, as post-treatment solutions for the CPP method. METHODS: The CPP solution was mixed with several post-treatment solutions at various mixing ratios in test tubes. The precipitates were collected, and freeze-dried in a vacuum. Their weights were measured to evaluate the feasibility of buffer solution for the post-treatment solutions. Among the solutions, we selected one buffer solution and have done further evaluation using human dentine disks. The degree of occlusion of dentine tubules was evaluated by scanning electron microscopic observation and measurement of dentine permeability. Also, the composition of the precipitate was analyzed using energy-dispersive X-ray microanalysis and powder X-ray diffraction. RESULTS: Among the solutions, 1 mol/l NaHCO3 gave sufficient amounts of precipitate at a relatively mild pH, and thus was considered to be a good candidate for a post-treatment solution. Scanning electron microscopic observation showed that dentine tubules were occluded with the precipitate to a depth of approximately 10 microns from the surface when the CPP treatment was done twice, and dentine permeability was reduced to 98.8%. The precipitate was dicalcium phosphate dihydrate (DCPD; CaHPO4-2H2O) when the post-treatment solution was free of NaF. In contrast, the precipitate was an apatitic mineral with CaF2 as a by-product when the post-treatment solution contained NaF. CONCLUSIONS: We concluded that 1 mol/l NaHCO3 containing 0.3 mol/l NaF would be suitable as the post-treatment solution for the CPP method as it has a relatively mild pH and occludes dentinal tubules well.

Adult↗

PubMed1997

Mineral induction by immobilized phosphoproteins.

Dentin phosphoproteins are thought to have a primary role in the deposition of mineral on the collagen of dentin. In this study we determined the type of binding between collagen and phosphoproteins necessary for mineral formation onto collagen fibrils and whether the phosphate esters are required. Bovine dentin phosphophoryn or phosvitin from egg yolk were immobilized on reconstituted skin type I collagen fibrils by adsorption or by covalent cross-linking. In some samples the ester phosphate was removed from the covalently cross-linked phosphoproteins by treatment with acid phosphatase. All samples were incubated at 37 degrees C in metastable solutions that do not spontaneously precipitate. Reconstituted collagen fibrils alone did not induce mineral formation. The phosphoproteins adsorbed to the collagen fibrils desorbed when the mineralization medium was added, and mineral was not induced. The mineral induced by the cross-linked phosphoproteins was apatite, and the crystals were confined to the surface of the collagen fibrils. With decreasing medium saturation the time required for mineral induction increased. The interfacial tensions calculated for apatite formation by either phosphoprotein cross-linked to collagen were about the same as that for phosphatidic acid liposomes and hydroxyapatite. This similarity in values indicates that the nucleation potential of these highly phosphorylated surfaces is about the same. It is concluded that phosphoproteins must be irreversibly bound to collagen fibrils for the mineralization of the collagen network in solutions that do not spontaneously precipitate. The phosphate esters of phosphoproteins are required for mineral induction, and the carboxylate groups are not sufficient.

Acid Phosphatase↗

PubMed1996

Calculation of intercrystalline solution composition during in vitro subsurface lesion formation in dental minerals.

Applications of a novel technique to calculate intercrystalline solution composition during enamel demineralization are presented. Bovine tooth enamel blocks and carbonated apatite (CAP) compressed disks were demineralized in an in vitro subsurface lesion system. The demineralization medium was a 0.1 M acetate buffer at pH 4.5, containing calcium, phosphate, and fluoride (0.5 ppm). Mineral samples were demineralized for various times, and fluoride profiles and mineral density profiles of these samples were determined by electron microprobe and X-ray microradiography, respectively. A model independent data analysis (MIDA) technique uses these data along with the differential equations for mass transfer and permits calculation of the local intercrystalline solution composition profiles inside the porous mineral matrix as functions of time and position. The invariance in diffusivity with time as calculated in the analysis was taken as an indicator of the physical reasonableness of the method. Current outcomes suggest that it is the sharp gradient of fluoride concentration in the intercrystalline solution which causes the formation of subsurface lesions. Since the driving force for mineral dissolution is a function of solution composition, a gradient of this driving force is consequently formed. Using a compressed disk of carbonated apatite powder as a model for block enamel excluded the possibility of the existence of a gradient of mineral composition which could also cause a gradient of the driving force for mineral dissolution. An FAP surface complex hypothesis is consistent with the current view that fluoride in the intercrystalline solution has a stronger inhibition effect on the dissolution of mineral than does fluoride in the mineral phase. With the help of the MIDA technique, calculated results indicate that the mechanism of the formation of subsurface lesions is dynamically controlled by the intercrystalline solution composition.

Animals↗

PubMed2004

Carbonate formation on bioactive glasses.

The system termed 58S is a sol-gel-synthesized bioactive glass composed of SiO2, CaO, and P2O5, used in medicine as bone prosthetic because, when immersed in a physiological fluid, a layer of hydroxycarbonate apatite is formed on its surface. The mechanism of bioactive glass 58S carbonation was studied in the vacuum by means of in-situ FTIR spectroscopy with the use of CO2, H2O, and CD3CN as probe molecules. The study in the vacuum was necessary to identify both the molecules specifically involved in the carbonation process and the type of carbonates formed. Bioactive glass 58S was compared to a Ca-doped silica and to CaO. On CaO, ionic carbonates could form by contact with CO2 alone, whereas on 58S and on Ca-doped silica carbonation occurred only if both CO2 and an excess of H2O were present on the sample. The function of H2O was not only to block surface cationic sites, so that CO2 could not manifest its Lewis base behavior, but also to form a liquid-like (mono)layer that allowed the formation of carbonate ions. The presence of H2O is also supposed to promote Ca2+ migration from the bulk to the surface. Carbonates formed at the surface of CaO and of Ca-bearing silicas (thus including bioactive glasses) are of the same type, but are produced through two different mechanisms. The finding that a water excess is necessary to start heavy carbonation on bioactive glasses seemed to imply that the mechanism leading to in-situ carbonation simulates, in a simplified and easy-to-reproduce system, what happens both in solution, when carbonates are incorporated in the apatite layer, and during sample shelf-aging.

Apatites↗

PubMedDate not supplied

Peripheral neuropathy and light-preliminary report indicating prevalence of nanobacteria in HIV.

Peripheral neuropathy is a common condition in HIV-positive patients and is often experienced in diabetes mellitus. The primary mechanism of the disease, which can considerably aggravate the patient's state, is unknown. The perineurium of patients with peripheral neuropathy is frequently enveloped by apatite. Nanobacteria (NB) are protectd by a mineral shell consisting of apatite. Light has been shown to elevate the vitality level of cells, and was predicted to inhibit deposition of stressed NB in the cardiovascular system. Results indicate that light can durably restore the condition of patients with severe peripheral neuropathy.

Apatites↗

PubMed1999

Chemical reduction of phosphate on the primitive earth.

If phosphorus played a role in the origin of life, some means of concentrating micromolar levels of phosphate (derived from the calcium phosphate mineral apatite), must first have been available. Here we show that simulated (mini)lightning discharges in model prebiotic atmospheres, including only minimally reducing ones, reduce orthophosphates, including apatite, to produce substantial yields of phosphite. Electrical discharges associated with volcanic eruptions could have provided a particularly suitable environment for this process. Production of relatively soluble and reactive phosphite salts could have supplied a pathway by which the first phosphorus atoms were incorporated into (pre)biological systems.

Apatites↗

PubMed1996

Evidence for life on Earth before 3,800 million years ago.

It is unknown when life first appeared on Earth. The earliest known microfossils (approximately 3,500 Myr before present) are structurally complex, and if it is assumed that the associated organisms required a long time to develop this degree of complexity, then the existence of life much earlier than this can be argued. But the known examples of crustal rocks older than 3,500 Myr have experienced intense metamorphism, which would have obliterated any fragile microfossils contained therein. It is therefore necessary to search for geochemical evidence of past biotic activity that has been preserved within minerals that are resistant to metamorphism. Here we report ion-microprobe measurements of the carbon-isotope composition of carbonaceous inclusions within grains of apatite (basic calcium phosphate) from the oldest known sediment sequences--a approximately 3,800-Myr-old banded iron formation from the Isua supracrustal belt, West Greenland, and a similar formation from the nearby Akilia island that is possibly older than 3,850 Myr. The carbon in the carbonaceous inclusions is isotopically light, indicative of biological activity; no known abiotic process can explain the data. Unless some unknown abiotic process exists which is able both to create such isotopically light carbon and then selectively incorporate it into apatite grains, our results provide evidence for the emergence of life on Earth by at least 3,800 Myr before present.

Apatites↗

PubMed2006

Renal crystal deposits and histopathology in patients with cystine stones.

We have biopsied the papillae of patients who have cystine stones asking if this stone type is associated with specific tissue changes. We studied seven cystine stone formers (SF) treated with percutaneous nephrolithotomy using digital video imaging of renal papillae for mapping and obtained papillary biopsies. Biopsies were analyzed by routine light and electron microscopy, infrared spectroscopy, electron diffraction, and micro-CT. Many ducts of Bellini (BD) had an enlarged ostium, and all such were plugged with cystine crystals, and had injured or absent lining cells with a surrounding interstitium that was inflamed to fibrotic. Crystal plugs often projected into the urinary space. Many inner medullary collecting ducts (IMCD) were dilated with or without crystal plugging. Apatite crystals were identified in the lumens of loops of Henle and IMCD. Abundance of interstitial Randall's plaque was equivalent in amount to that of non-SF. In the cortex, glomerular obsolescence and interstitial fibrosis exceeded normal. Cystine crystallizes in BD with the probable result of cell injury, interstitial reaction, nephron obstruction, and with the potential of inducing cortical change and loss of IMCD tubular fluid pH regulation, resulting in apatite formation. The pattern of IMCD dilation, and loss of medullary structures is most compatible with such obstruction, either from BD lumen plugs or urinary tract obstruction from stones themselves.

Adolescent↗

PubMed2001

Quantitative analyses of the biomineralization of different hard tissues.

The primary crystallites of the different developing hard tissues have an apatite structure. However, they have crystal lattice distortions representing an intermediate state between amorphous and fully crystalline. We have applied energy-filtering transmission electron microscopy in the selected area electron diffraction mode to analyse different stages of crystal formation in dentine, bone, enamel and inorganic apatite mineral. We have obtained quantitative information on the degree of crystal lattice distortion using the paracrystal theory of Hosemann and Bagchi. We have found that the early formed crystallites of the hard tissues being analysed have a paracrystalline character comparable to biopolymers. However, with maturation, the lattice fluctuations of the crystallites of the hard tissues bone, enamel and dentine decrease to form a typical (para)crystalline character. Also the decrease of the organic proportion in the matrix corresponds to the decrease of the lattice fluctuation of the crystallites in the different hard tissues during maturation.

Animals↗

PubMedDate not supplied

Augmentation of intraarticular calcaneal fractures with injectable calcium phosphate cement: densitometry, histology, and functional outcome of 18 patients.

Eighteen patients with intraarticular calcaneal fractures treated with open reduction and internal fixation and augmentation with an injectable carbonated apatite cement. Functional follow-up studies using the Zwipp Foot Score and densitometry were performed at 6-month intervals postoperatively. Histological samples of biopsies obtained at the time of hardware removal (6 months postoperatively) were also analyzed. The use of bone cement led to intermediate-term functional outcomes that were no better than those reported with conventional surgical procedures using bone graft. Patients demonstrated postoperative difficulties similar to those seen in other studies of this fracture, including pain, subtalar motion restrictions, peroneal impingement, and difficulties on uneven terrain and with toe- and heel-walking. However, compared to patients treated surgically without injectable carbonated apatite cement, full weight bearing on the affected extremity was regained at an average 4 weeks postoperatively. In addition, autogenous bone graft was not required to fill the osseous defect using this technique, minimizing morbidity and discomfort. During the present observation period of 3 years, only a slight decrease in the density of the peripheral zones of the cement block was observed. Histological examination revealed fibrous bone formation resulting from remodelling processes. Complete resorption and remodeling of the bone cement were not complete at 3 years. One patient developed a postoperative wound infection. Another displayed cement loosening secondary to failure of bony ingrowth.

Adult↗

PubMed1997

Dissolution of artificial (natural) stones in a standard model: first results.

In studying the dissolution of stones in vitro, the advantage of artificial stones in comparison to natural stones is that one can get substance-specific standardized and reproducible results. Our investigations were performed with artificial stones composed of natural material (calcium apatite). These stones were of spherical form and consisted of layers built up around a core. They were comparable to natural stones in their physical properties. Litholysis was performed in a special apparatus with continuous exposure to Suby G solution under standard conditions. Natural stones of the same chemical composition served as a reference. Statistical measurements were performed. By hardening of the artificial stones, it was possible to reach a dissolution comparable to natural stones composed of calcium apatite depending on the Suby G concentration (artificial 2.5 resp. 4.75 mg/h; natural 2.18 resp. 4.2 mg/h). For the first time, an artificial stone model has been created with reproducible behaviour in response to chemolitholysis and with properties of dissolution comparable to those of natural stones of identical chemical composition.

Apatites↗

PubMed1989

Physical chemical evidence of structural weakness in coronary arterial calcification.

Physical-chemical properties of calcified human coronary arteries were obtained through 857 electron probe microanalyses of samples of endarterectomy tissue from 12 patients and by X-ray and electron diffraction from separate samples. The calcific phase exhibited a weight percentage calcium to phosphorus ratio of 2.5 (SEM 0.15), a density of 2.95 (0.02) g.cm-3, and a crystalline unit cell volume of 530 (0.5) A3, or 53 (0.05) nm3. The phase has been characterised as a phosphorus deficient dahllite variant of apatite in which the crystal structure has been weakened by the incorporation of water molecules and tetrahedral hydroxyl groups in isomorphic substitution conforming with the McConnell-type defect. Isomorphic substitution within the apatitic cell appears sufficient to suggest that the crystal structure of the mineral deposit is weakened to the extent that means might be sought to attack the early formation of the pathological deposition.

Apatites↗

PubMedDate not supplied

Experimental study of bioactive polyurethane sponge as an artificial trachea.

An artificial trachea that has tissue reconstructive activity and elasticity that matches a biologic trachea was fabricated using a polyurethane sponge (PS). The inner surfaces of the PS were modified by immobilizing collagen, fibronectin, RGD peptide, a coating of collagen, and apatite. Two PS pore sizes were prepared, 150 to 350 microns (small pore) and 350 to 710 microns (large pore). When they were implanted in the subcutaneous tissue of rats, study of the implantation showed severe inflammatory cell infiltration with the treated PS, especially with collagen and collagen coating. Infiltration and maturity of fibroblasts inside the PS were noted with fibronectin. Infiltration of inflammatory cells and fibroblasts was noted with small pore PS compared with large pore PS. Partial tracheal defects were patched with PS. Better epithelization of PS patches was observed with fibronectin and apatite compared with the others. The artificial trachea made of PS was transplanted into the tracheas of dogs. No separation of the anastomosis and tissue reconstruction of the artificial trachea wall were observed; however, sputum absorption and tracheal granulation were seen.

Amino Acid Sequence↗

PubMed1994

In vitro efficiency of endodontic irrigation solutions on protein desorption.

The use of irrigating solutions is widely accepted as a necessary adjunct to biomechanical preparation to obtain adequate cleansing of the root canal system. In this study, the efficiency of three solutions was tested in an in vitro experimental system for the removal of protein from apatite surfaces: Salvizol (a bis-dequalinium acetate solution) and sodium hypochlorite at 0.5, 1, 3 and 6% at pH 7.4 and 11.5. Buffered Tris-HCl solutions at pH 7.4 and 11.5 were used as controls. All chemicals showed rapid kinetics effects since no variation of the process could be detected after 5 min. Salvizol was the least efficient solution since it induced only a 2% protein desorption. Sodium hypochlorite efficiency increased with concentration to reach a 70% protein desorption from the apatite surface. In general, alkaline solutions were more efficient than buffered ones, and the ionic strength did not appear to have a major effect on the protein desorption process.

Absorption↗

PubMed1989

Lattice fringe studies of (100) defects in enamel crystallites.

Lattice imperfections in the structure of shark (Nataprion brevirostrais) enamel crystallites have been studied by means of lattice-imaging in a high-resolution transmission electron microscope. Line defects exhibiting various lengths (100-2500 A) and widths (10-30 A) and demonstrating phase behaviour different from that of the host crystal were observed along the fringes representing (100) lattice planes. When defect sites were subjected to an electron beam, an annealing process was observed in which the difference in phase contrast eventually disappeared and the defect itself became an intricate part of the (100)-type lattice planes. A through-focal series of the defects show a reversal in phase contrast. By examining the contrast behaviour under certain focal conditions and by adopting the Fresnel diffraction mode, the refractive index of the defect regions was determined to be lower than that of the apatite crystal. Present findings suggest that the interlayering structure along the (100) planes is responsible for the line defects observed in enamel apatites.

Animals↗