Biological Calcium Phosphates Research Articles

Biological calcium phosphate nanorods for piezocatalytical extraction of U(VI) from water

Biological calcium phosphate nanorods for piezocatalytical extraction of U(VI) from water

Cantilever-enhanced photoacoustic spectroscopy applied in the research of natural and synthetic calcium phosphate

This study demonstrates the significant potential of cantilever-enhanced Fourier transform infrared photoacoustic spectroscopy (FTIR PAS) principles. The improved sensitivity and reproducibility of this method presents a potent tool in the study of biomaterials. The article discusses aspects of the application of cantilever-enhanced FTIR PAS in the research of natural and biological calcium phosphate and the statistical evaluation of the FTIR PAS sampling method. The improved constructions of the FTIR PAS accessory reduce limitations of the conventional capacitive microphone and provide a sensitive tool for samples or processes unreachable by more traditional transmittance methods, or ATR sampling technique. The most common and important applications have been discussed in-depth to show the wide range of problems solved by FTIR PAS.

Biofilm formation by staphylococci on fresh, fresh-frozen and processed human and bovine bone grafts

Biofilm formation is a multi-step process influenced by surface properties. We investigated early and mature biofilm of Staphylococcus aureus on 4 different biological calcium phosphate (CaP) bone grafts used for filling bone defects. We investigated standardised cylinders of fresh and fresh-frozen human bone grafts were harvested from femoral heads; processed humanand bovine bone grafts were obtained preformed. Biofilm formation was done in tryptic soy broth (TSB) using S. aureus (ATCC 29213) with static conditions. Biofilm density after 3h (early biofilm) and 24h (mature biofilm) was investigated by sonication and microcalorimetry. After 3h, bacterial density was highest on fresh-frozenandfresh bone grafts. After 24h, biofilm density was lowest on freshbone grafts (p<0.001) compared to the other 3 materials, which did not differ quantitatively (p>0.05). The lowest increase in bacterial density was detected on fresh bone grafts (p<0.001). Despite normal shaped colonies, we found additional small colonies on the surface of the fresh and fresh-frozen samples by sonication. This was also apparent in microcalorimetric heat-flow curves. The four investigated CaP bone grafts showed minor structural differences in architecture but marked differences concerning serum coverage and the content of bone marrow, fibrous tissue and bone cells. These variations resulted in a decreased biofilm density on freshand fresh-frozenbone grafts after 24h, despite an increased early biofilm formation and might also be responsible for the variations in colony morphology (small colonies). Detection of small colony variants by microcalorimetry might be a new approach to improve the understanding of biofilm formation.

High-resolution solid state NMR experiments for the characterization of calcium phosphate biomaterials and biominerals

Abstract

In vivo corrosion of four magnesium alloys and the associated bone response

Degrading metal alloys are a new class of implant materials suitable for bone surgery. The aim of this study was to investigate the degradation mechanism at the bone–implant interface of different degrading magnesium alloys in bone and to determine their effect on the surrounding bone. Sample rods of four different magnesium alloys and a degradable polymer as a control were implanted intramedullary into the femora of guinea pigs. After 6 and 18 weeks, uncalcified sections were generated for histomorphologic analysis. The bone–implant interface was characterized in uncalcified sections by scanning electron microscopy (SEM), element mapping and X-ray diffraction. Results showed that metallic implants made of magnesium alloys degrade in vivo depending on the composition of the alloying elements. While the corrosion layer of all magnesium alloys accumulated with biological calcium phosphates, the corrosion layer was in direct contact with the surrounding bone. The results further showed high mineral apposition rates and an increased bone mass around the magnesium rods, while no bone was induced in the surrounding soft tissue. From the results of this study, there is a strong rationale that in this research model, high magnesium ion concentration could lead to bone cell activation.

Calcium phosphates as substitution of bone tissues

Abstract Calcium phosphates with clinical applications are used in reconstructive surgery. When dealing with the repairing of a skeletal section, two extremely diverse routes could be initially considered: to replace the damaged part or to substitute it regenerating the bone. This second option is in fact the role played by calcium phosphates, which can be classified among the bioactive ceramics group. Bioceramics, and therefore, calcium phosphates, exhibit very good biocompatibility and bone integration qualities, and constitute the materials showing closest similarity to the mineral component of bone; this fact, together with their bioactivity, make them very good candidates for bone regeneration. This review is focused on calcium phosphate ceramics; therefore, it is important to analyse firstly the biological calcium phosphates as components of natural hard tissues, that is, bone and teeth, and then to look for synthetic methods able to produce calcium deficient carbonate apatites with nanometric size, i.e., showing similar features to the biological apatites. In the present work, we describe the synthesis procedures to obtain in the laboratory calcium deficient carbonate nanoapatite both in bulk and thin film forms, as well as the characterization methods applied to these materials, with particular incidence in the electron microscopy.

103. Kyphoplasty with a new biological calcium phosphate cement

103. Kyphoplasty with a new biological calcium phosphate cement

Distribution and incorporation of zinc in biological calcium phosphates

AbstractHuman dental calculi are biological calcium phosphates, which consist of an organic phase and an inorganic or mineral phase. In the latter phase, spectrochemical analyses have revealed the presence of several different magnesium and calcium phosphates. As the crystalline structure of the calculus passes through several stages during its allocation in the mouth, special attention is paid to some elements, such as zinc, that can modify the mineralization process. Several in vitro studies relating to the dental calculus mineralization process have been performed so far, but there is a lack of data obtained from biologically synthesized samples. The knowledge of the zinc distribution and incorporation in biological calcium phosphates is of great interest in providing more information about the biological process of calculus formation. In this paper we present surveys of the elemental distribution and incorporation of zinc in human dental calculus, by using a combination of different techniques: x‐ray microfluorescence using synchrotron radiation, scanning electron microscopy and x‐ray absorption spectroscopy. One‐dimensional x‐ray microfluorescence of zinc and magnesium measurement shows that there is a high accumulation of both elements in the sub‐gingival region of the calculus and a strong correlation of their spatial distribution. Experimental Ca/P molar ratios were determined by energy‐dispersive spectroscopy to identify different calcium phosphate phases, the sub‐gingival region being composed of a mixture of highly and poorly calcified phosphates and the supra‐gingival region composed mainly of carbonated hydroxyapatite. Finally, x‐ray absorption measurements were carried out at the zinc K edge on synthetic and biological samples. The Zn—O distance and coordination number of the synthetic samples and the supra‐gingival calculus show that zinc is adsorbed on these structures, whereas in the sub‐gingival samples it is allocated in a cation site. The results are indicative of the active participation of zinc in the calcification process of sub‐gingival calculus. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Constant composition dissolution of mixed phases: II. Selective dissolution of calcium phosphates

Characterization of the dissolution kinetics of individual synthetic and biological calcium phosphates is of considerable importance since these phases often coexist in biological minerals. The constant composition method has been used to study the dissolution kinetics of a series of synthetic calcium phosphates, brushite (DCPD), beta-tricalcium phosphate (TCP), octacalcium phosphate (OCP), hydroxyapatite (HAP), and carbonated apatite (CAP) in the presence and absence of citric acid, as a function of pH and thermodynamic driving force. While citric acid markedly accelerates the dissolution of TCP, HAP dissolution is significantly inhibited. Moreover, this additive has almost no influence on the dissolution of DCPD, OCP, and CAP. Dual constant composition dissolution studies of mixed calcium phosphates in the presence of citric acid have also been made. Another factor, pH, also plays an important role in the dissolution of these calcium phosphates. In suspensions of calcium phosphate mixtures, specific phases can be selectively dissolved by changing experimental parameters such as pH and the presence of rate modifiers. This result has important applications for the dissolution control of dental hard tissues such as dentin, enamel, and calculus.

Biological calcium phosphates and Posner’s cluster

A calcium phosphate amorphous to x-ray diffraction (ACP) exists in bone mineral in addition to the main bone apatite component, such as hydroxyapatite (HA). Experimental studies found that ACP has definite local atomic order and contains microcrystallites about 9.5 Å in extent rather than a random network structure. Experimental evidence indicates that Posner’s cluster (PC), Ca9(PO4)6, could be the basic component of ACP. In addition, it is present in various simulated body fluids and could be the growth unit of HA. In the transformation from ACP to HA, ACP need only dissociate into the clusters rather than undergo complete ionic solvation. Although PC could bridge the biologically important gap between ACP and HA, the form it is likely to take in body fluids is not known. In this study, we have performed ab initio density functional calculations to investigate the structure and stability of PC alone in vacuum and in the presence of H+, OH−, Na+, and Cl− ions mimicing the interaction with water and other constituents of body fluids. We find that the cluster with C1 symmetry is the most stable isomer in vacuum. The interaction of PC with sodium ions and especially with protons leads to a great increase in its stability and surprisingly, the cluster with six protons and six OH− recovers the C3 symmetry and similar atomic arrangement it has as a structural unit in HA crystal. This may be a key factor in the transformation from ACP to HA crystal.

Surface structure study of biological calcium phosphate apatite crystals from human tooth enamel.

A surface-structure study of human tooth enamel crystals has been carried out by high-resolution electron microscopy (HREM). The surfaces of several crystals have been examined and the surfaces of a single crystal are described here. The observations made on this crystal are similar to the observations made on the other crystals, although the difference of morphology in the crystals observed indicates that the growth control by matrix proteins takes only place on the [011 macro 0] surfaces of the crystals. The crystal described here is oriented along the [112 macro 0] direction, and the following surfaces have been analyzed: (11 macro 00), (011 macro 1), (01 macro 11) and (0001). A subsurface reconstruction is observed just below the surface of the crystal not bonded to the matrix and lying above the supporting film. Observation of the matrix surrounding the crystal shows the existence of poorly crystalline phases with a structure close to that of hydroxyapatite (OHAP). Finally, a comparison of the images of the (011 macro 0) surface with computer-simulated images calculated for several models of the OHAP surface structure shows that the surface itself is stoichiometric and contains both calcium and phosphate groups. The knowledge of the binding sites of proteins on biomineral crystals such as the ones found in human tooth enamel is of prime importance for the understanding of their growth process. In this study, the first structure determination of the surface of human tooth enamel crystals is presented.

Structure and substitutions in fluorapatite.

Fluorapatite, Ca10(PO4)6F2. is a widely spread form of calcium phosphate present particularly in biological material. Human hard tissues contain crystals structurally related to apatite. Fluoride can be found in various natural sources and is also used for its beneficial action in caries prevention. Fluorapatite belongs to the spatial group P6(3/m) (C(6h)2) and consists of 3 ions: F-, Ca2+, PO4(3-). In the present paper, we have carried out a crystallographic study of the fluorapatite structure and of the changes induced by the substitutions. The fluorapatite structure and the presence of a large number of ionic bonds make fluorapatite a very suitable host for many substituents, some of them harmless for the human organism, some not. According to the substitution site, we can describe four types of substitution. The F- substitution, also called Type A substitution, is the main one, and the best known. Only the Ca2+ substitution implies changes in the crystal structure. However, some questions remain, in particular for the PO4(3-) substitution, which is the main substitution present in the biological calcium phosphates.

Zinc incorporation in human dental calculus.

We present here the first study of the local environment of zinc ions in biological calcium phosphates. It was suggested from in vitro studies that zinc inhibits the formation of hydroxyapatite and promotes the formation of more soluble phases, like tricalcium phosphate. Several mechanisms of zinc - calcium phosphate interaction were proposed, yielding either to the adsorption or to the incorporation of zinc ions into the phosphate structure. The results obtained here show that, under in vivo conditions, the zinc atoms are fully incorporated into the crystalline structure of the calcium phosphates.

Kinetics and Surface Energy Approaches to the Crystallization of Synthetic and Biological Calcium Phosphates

Constant composition methods have been used to investigate the mechanisms of crystal growth and dissolution of synthetic and biological calcium phosphates. Interfacial tensions between water and each of these surfaces were calculated from measured contact angles using surface tension component theory. The data, 4.5 x 10−3, 8.8 x 10−3 and 10.4 x 10−3 J m−2 for human dentin, human enamel and hydroxyapatite, respectively, compared well with the data calculated from dissolution kinetics experiments and provided information concerning the growth and dissolution mechanisms. The ability of a surface to nucleate other phases is closely related to the magnitude of the interfacial energies.

Kinetics and Surface Energy Approaches to the Crystallization of Synthetic and Biological Calcium Phosphates

Kinetics and Surface Energy Approaches to the Crystallization of Synthetic and Biological Calcium Phosphates

The NEXAFS of biological calcium phosphates

The absorption cross section of a number of calcium salts has been assessed at the calcium L edge by measuring the total electron yield (TEY) at the NSLS U13UA beamline. TEY was used because of distortions introduced by instrumentation when using a transmission signal. The effect of these distortions has been evaluated and is presented. The TEY signal was normalized to the incident beam using the signal from a new beam monitor which is detailed here. Comparative spectra are presented for some calcium salts associated with osteoarthritis.

Fourier transform Raman spectroscopy of synthetic and biological calcium phosphates.

Fourier-transform (FT) Raman spectroscopy was used to characterize the organic and mineral components of biological and synthetic calcium phosphate minerals. Raman spectroscopy provides information on biological minerals that is complimentary to more widely used infrared methodologies as some infrared-inactive vibrational modes are Raman-active. The application of FT-Raman technology has, for the first time, enabled the problems of high sample fluorescence and low signal-to-noise that are inherent in calcified tissues to be overcome. Raman spectra of calcium phosphates are dominated by a very strong band near 960 cm-1 that arises from the symmetric stretching mode (v1) of the phosphate group. Other Raman-active phosphate vibrational bands are seen at approximately 1075 (v3), 590 (v4), and 435 cm-1 (v2). Minerals containing acidic phosphate groups show additional vibrational modes. The different calcium phosphate mineral phases can be distinguished from one another by the relative positions and shapes of these bands in the Raman spectra. FT-Raman spectra of nascent, nonmineralized matrix vesicles (MV) show a distinct absence of the phosphate v1 band even though these structures are rich in calcium and phosphate. Similar results were seen with milk casein and synthetic Ca-phosphatidyl-serine-PO4 complexes. Hence, the phosphate and/or acidic phosphate ions in these noncrystalline biological calcium phosphates is in a molecular environment that differs from that in synthetic amorphous calcium phosphate. In MV, the first distinct mineral phase to form contained acidic phosphate bands similar to those seen in octacalcium phosphate. The mineral phase present in fully mineralized MV was much more apatitic, resembling that found in bones and teeth.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthetic calcium phosphates: Models for biological crystals?

Characterization of the mineral phases of calcified tissues or ectopic calcifications has demonstrated the complexity of biological calcium phosphate salts Chemists and numerous biologists involved in calcified tissue research have generally described bone and teeth crystallites as hydroxyapatite rather than biological apatites. All biological calcium phosphates have a non-stoichiometric formula, and numerous and variable substitutions. Moreover, in vivo transformations/maturations occur. There is no particular representative synthetic calcium phosphate crystal either for the normal mineral phases of calcified tissues or for the pathological phases. However, they constitute efficient models for the understanding of biological mineralization, and are good approaches to in vitro studies of biomaterials.

Preparation of amorphous calcium-magnesium phosphates at pH 7 and characterization by x-ray absorption and fourier transform infrared spectroscopy

Amorphous calcium-magnesium phosphates were prepared by precipitation from moderately supersaturated aqueous solutions at pH 7. Chemical analysis of the samples by ion chromatography showed that up to about 50% of the phosphate ions were protonated, the proportion increasing with the magnesium to calcium ion activity ratio in the solution. When left it contact with the supernatant, the amorphous precipitates matured to form the crystalline calcium phosphate brushite (CaHPO4·2H2O). The amorphous phases were characterized by X-ray absorption spectroscopy and by Fourier transform infrared spectroscopy and their properties compared with those of a basic amorphous tricalcium phosphate precipitated at pH 10. The X-ray absorption spectra near the K edge of calcium were very similar for all samples but there were differences in the infrared spectra between the basic and the more acidic salts. In the phosphate stretching region, the main band of the more acidic materials occured at higher wavenumber and was broader. Also there was a broad band of medium intensity at about 890 cm-1 whereas there was virtually no absorption band in this region in the spectrum of the amorphous tricalcium phosphate. The acidic amorphous calcium phosphates may be useful as model compounds in describing some complex biological calcium phosphates that form near neutral pH.

Formation and transformation of biological calcium phosphates: effects of calcium, magnesium and phosphate

Formation and transformation of biological calcium phosphates: effects of calcium, magnesium and phosphate