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PubMed1997

Healing of gaps around calcium phosphate-coated implants in trabecular bone of the goat.

Hydroxylapatite coatings are under clinical investigation in orthopaedics and dentistry. Bone formation on apatite coatings in the presence of gaps is important for clinical applications. The importance of the stability of the coating is not known at present. By varying the plasma-spray parameters, and by the addition of fluoride, the crystallinity and stability of calcium phosphates can be changed. It is suggested that bone formation is enhanced by dissolution of the apatite coating. We studied apatite coatings of varying stability with regard to their gap-healing characteristics, and we examined what the maximum gap would be that can be bridged if a coating is applied. Ti-6A1-4V implants coated with 62% crystalline hydroxylapatite, 30% crystalline hydroxylapatite or fluorapatite, or noncoated Ti-6A1-4V were implanted in 16 goats. The implants were surrounded by gaps of 1 or 2 mm, and the follow-up period was 6 weeks. Histological examination and histometry revealed that gaps of 1 mm can be bridged by bone if an apatite coating is applied. However, only a minimal amount of bone contact was seen on the apatite coatings with 2 mm gaps. Uncoated implants demonstrated no bone contact at all. Among the three different coatings there were no differences in gap healing. It can be concluded that in the goat, gaps of 2 or more mm between coated implants and host bone tissue inhibit bone deposition on the coating (p < 0.05), but the stability of the coating does not influence gap-healing characteristics.

Alloys↗

PubMed1998

Surface structural change of bioactive inorganic filler-resin composite cement in simulated body fluid: effect of resin.

Recently much attention has been paid to bioactive filler-resin composite cements because they can solidify in a few minutes to give high mechanical strengths and they can bond to living bone. In this study the dependence on resin of apatite-forming ability in simulated body fluid (SBF) was investigated for the composite cements of bioactive CaO-SiO2-P2O5-CaF2 glass with polymethyl methacrylate (PMMA) or bisphenol-a-glycidyl methacrylate/triethyleneglycol (Bis-GMA/TEGDMA) resin. The PMMA-containing composite cement did not show the apatite-forming ability in SBF because the reaction of the glass grains with SBF was inhibited due to the complete covering of the grains with PMMA. To the contrary, the Bis-GMA/TEGDMA-containing cement exhibited high apatite-forming ability in SBF; these monomers significantly dissolved from the composite surface into SBF, causing a direct exposure of the glass grains to SBF to convert into silica gel. It is assumed that thus formed silica gels, and the silicate ions that were dissolved and adsorbed onto the composite surface, induced the apatite nucleation between the spaces of the glass grains and on the composite surface, respectively. A continuous bone-like apatite layer was formed on the top surface of the glass-Bis-GMA/TEGDMA composite cement in a short period.

Apatites↗

PubMed1999

Porous poly(L-lactic acid)/apatite composites created by biomimetic process.

Highly porous poly(L-lactic acid)/apatite composites were prepared through in situ formation of carbonated apatite onto poly(L-lactic acid) foams in a simulated body fluid. The highly porous polymer foams (up to 95% porosity) were prepared from polymer solution by solid-liquid phase separation and subsequent sublimation of the solvent. The foams were then immersed in the simulated body fluid at 37 degrees C to allow the in situ apatite formation. After incubation in the simulated body fluid for a certain period of time, a large number of characteristic microparticles formed on the surfaces of pore walls throughout the polymer foams. The microparticles were characterized with scanning electron microscopy, energy dispersive spectroscopy, Fourier transform IR spectroscopy, and X-ray diffractometry. These porous spherical microparticles were assemblies of microflakes. They were found to be carbonated bonelike apatite. A series of composite foams with varying sizes and concentrations of the apatite particles was obtained by varying incubation time and conditions. These porous composites may be promising scaffolding materials for bone tissue engineering and regeneration because the excellent bone-bonding properties of the apatite may provide a good environment for osteoblast and osteoprogenitor cells' attachment and growth.

Apatites↗

PubMed2000

Improvement of bioactivity of H(2)O(2)/TaCl(5)-treated titanium after subsequent heat treatments.

Commercially pure titanium was treated with a H(2) O(2)/3mM TaCl(5) solution at 80 degrees C for various periods and a titania gel layer was formed on the surface. This gel remained amorphous when heating for 1 h below 200 degrees C and transformed to anatase after heating between 300 degrees and 600 degrees C. The anatase titania gel layers were found to be bioactive as to deposit carbonate ion-incorporated apatite within 1 day of immersion in the Kokubo solution, whereas the amorphous layers did not deposit apatite within 7 days. The apatite particles were found to nucleate preferentially inside the cracks prevailing in the thicker gel layers of 1-h chemically treated specimens. After immersing for 2 days, the titanium specimens were almost completely covered by apatite. Elimination of peroxide radicals from the titania gel and formation of anatase upon subsequent heating are considered to be responsible for the enhanced ability of apatite deposition.

Apatites↗

PubMed2003

Bioactive PMMA bone cement prepared by modification with methacryloxypropyltrimethoxysilane and calcium chloride.

Bone cement consisting of polymethylmethacrylate (PMMA) powder and methylmethacrylate (MMA) liquid is used extensively for fixation of implants such as artificial hip joints with living bone. This type of cement, however, does not show direct bonding to the living body, and hence the fixation is liable to loosen over a long implantation period. Bioactive materials have received much attention because of their capability for bone-bonding, i.e., bioactivity, when implanted in bony defects. Osteoconduction of the bioactive materials is caused by formation of a bone-like apatite layer through a surface reaction between the material and surrounding body fluid. The apatite formation can be induced by a silanol (Sibond;OH) group formed on the materials as well as a dissolution of calcium ion (Ca(2+)) from the material. Incorporation of alkoxysilane and calcium chloride (CaCl(2)) may provide PMMA bone cement with bioactivity, because alkoxysilane gives Sibond;OH after hydrolysis, whereas CaCl(2) releases Ca(2+). In this study, we investigated the potential on bioactivity of the modified PMMA bone cement with alkoxysilane and calcium chloride. PMMA powder was mixed with various amounts of CaCl(2), and MMA liquid with various amounts of 3-methacryloxypropyltrimethoxysilane (MPS). The mixed paste was immersed in a simulated body fluid (Kokubo solution) that has a similar concentration in inorganic constituents to human blood plasma. After soaking for various periods, apatite formation on the cement was examined. Apatite formation was observed by the addition of CaCl(2) with contents of 16 mass % and more. Incorporation of MPS accelerates the apatite formation. Setting time of the cement was significantly elongated after the addition of MPS, whereas compressive strength significantly decreased with increasing the contents of CaCl(2) and MPS. The hardened cement containing 20 mass % of CaCl(2) in the powder and 20 mass % of MPS in the liquid showed a tendency to be more osteoconductive to living bone after implantation in rabbit tibiae than the unmodified cement. These results indicate that bioactivity of the modified PMMA bone cement increases with increasing amounts of MPS and CaCl(2). Bioactive bone cement is successfully obtained when it contains appropriate concentrations of alkoxysilane and calcium chloride.

Animals↗

PubMed1991

Resolution-enhanced Fourier transform infrared spectroscopy study of the environment of phosphate ion in the early deposits of a solid phase of calcium phosphate in bone and enamel and their evolution with age: 2. Investigations in the nu3PO4 domain.

Resolution-enhanced Fourier Transform Infrared (FTIR) spectra of early mineral deposits in enamel and bone show bands at 1020, 1100, 1110, 1125, and 1145 cm-1 in the nu3PO4 domain which do not belong to well crystallized stoichiometric hydroxyapatite. Bands at 1020 and 1100 cm-1 have been shown to occur in nonstoichiometric apatites containing HPO4(2-) ions and the weak band at 1145 cm-1 has been assigned to HPO4(2-) ions. Though the bands at 1110 and 1125 cm-1 have not been found in any well crystallized apatite, they are present in newly precipitated apatite. These latter bands disappear progressively during maturation in biological as well as synthetic samples, and partial dissolution of synthetic apatites shows that they belong to species that exhibit an inhomogeneous distribution in the mineral, and that are the first to be solubilized. Comparison of the FTIR spectra of biological apatites with those of synthetic, nonapatitic-containing phosphate minerals shows that the presence of these bands does not arise from nonapatitic, well-defined phases; they are due to the local environment of phosphate ions which may possibly be loosely related or perhaps unrelated to the phosphate groups present in the well-crystallized nonapatitic calcium phosphates. Resolution-enhanced FTIR affords a very precise characterization of the mineral phases which may be very useful in characterizing pathological deposits of Ca-P mineral phases.

Animals↗

PubMed1999

Causes of phosphate stone formation and the importance of metaphylaxis by urinary acidification: a review.

The most important phosphates involved in urinary stone disease are carbonate apatite, brushite, and struvite. Overall, phosphate stones account for 12-20% of all stones, with a downward trend for struvite and an increase in carbonate apatite being observed in the last decade. The physicochemical basis for the formation of phosphate calculi is supersaturation. Once the solubility product has been exceeded, a metastable process of supersaturation begins, with slow crystalline growth. If a critical limit of supersaturation is exceeded, large-scale spontaneous precipitation of crystals occurs in a second stage. No urinary tract infection is involved in brushite stone formation. Although infection is not a prerequisite for the formation of carbonate apatite stones, infective conditions favor carbonate apatite formation. Struvite is the characteristic infection calculus, formed as a result of urinary tract infection with urease-producing bacteria. During the first episode of urinary stone disease a definitive diagnosis of the type of stone involved is very difficult without analysis of the latter by infrared spectroscopy or X-ray diffraction. In recurrent disease, appropriate treatment can be initiated on the basis of the previous stone analysis in the majority of cases. The best means of preventing recurrent disease involving any type of phosphate stone is definitive calculus removal by shock-wave lithotripsy, percutaneous stone removal, or open surgery (especially in children). Chemolysis via acidification of the urine with Suby G solution or hemicidrin supported by oral acidification, achieved by the metabolism of L-methionine, and antibiotic therapy (especially for infectious stones) are important adjuvant modalities of therapy. After therapy of phosphate stones, metaphylaxis involving controlled urinary acidification with L-methionine supports the treatment of infection and, at a pH value of less than 6.2 and urine dilution to 2.5 l/24 h, prevents the crystallization of struvite, brushite, and carbonate apatite.

Acids↗

PubMed1991

Bioactive glass ceramics: properties and applications.

Heat treatment of an MgO-CaO-SiO2-P2O5 glass gave a glass ceramic containing crystalline apatite (Ca10(PO4)6O,F2] and beta-wollastonite (CaO,SiO2) in an MgO-CaO-SiO2 glassy matrix. It showed bioactivity and a fairly high mechanical strength which decreased only slowly, even under load-bearing conditions in the body. It is used clinically as artificial vertebrae, iliac bones, etc. The bioactivity of this glass ceramic was attributed to apatite formation on its surface in the body. Dissolution of calcium and silicate ions from the glass ceramic was considered to play an important role in forming the surface apatite layer. It was shown that some new kinds of bioactive materials can be developed from CaO,SiO2-based glasses. Ceramics, metals and organic polymers coated with bone-like apatite were obtained when such materials were placed in the vicinity of a CaO,SiO2-based glass in a simulated body fluid. A bioactive bone cement which was hardened within 4 min and bonded to living bone, forming an apatite, was obtained by mixing a CaO,SiO2-based glass powder with a neutral ammonium phosphate solution. Its compressive strength reached 80 MPa comparable to that of poly(methyl methacrylate) within 3 d. A bioactive and ferromagnetic glass ceramic containing crystalline magnetite (Fe3O4) in a matrix of CaO,SiO2-based glassy and crystalline phases was obtained by a heat treatment of a Fe2O3-CaO.SiO2-B2O3-P2O5 glass. This glass ceramic was shown to be useful as thermoseeds for hyperthermia treatment of cancer.

Animals↗

PubMed2005

Ultrastructural study of calculus-enamel and calculus-root interfaces.

UNLABELLED: The attachment of dental calculus to the tooth (enamel or cementum) surface affects the ease or difficulty of its removal. Understanding the ultrastructural features of the calculus-tooth interface will help in the development of efficient strategies for efficient removal of dental calculus. OBJECTIVE: The aim of this study was to determine the ultrastructural characteristics of the calculus-tooth interface in relation to the occurrence of calculus fracture. DESIGN: Investigation of the ultrastructural characteristics of the calculus-tooth interface was made on eight human molars with mature supragingival and subgingival calculus using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and fourier transform infra-red (FT-IR) spectroscopy. RESULTS: Fractures were shown by SEM to consistently occur within the calculus itself, but not at the calculus-tooth interface. Higher magnification revealed that the enamel apatite crystals (in the case of supragingival calculus) or the cementum apatite crystals (in the case of subgingival calculus) appeared intimately connected with the calculus crystals at the calculus-enamel or calculus-cementum interface. TEM micrographs confirmed this intimate direct connection or fusion (epitaxial growth) of calculus crystals with enamel and cementum apatite crystals. FT-IR showed lower concentrations of organic phase attributed to microorganisms and higher concentrations of collagen at the calculus-cementum interface compared to that in the calculus away from the interface. CONCLUSION: Difficulty in complete calculus removal from tooth surfaces (especially from cementum or dentin) may be due in part to the intimate contact between the calculus and the tooth, due to the chemical bonding between the calculus crystals and the tooth apatite crystals and occasional fusion (i.e., epitaxial growth) of the calculus calcium phosphate crystals with the enamel, dentin or apatite crystals. This cohesive bonding results in fracture planes occurring within the calculus instead of at the calculus-tooth interface.

Apatites↗

PubMed2026

Associations of clinical and laboratory parameters with pediatric urolithiasis composition: A retrospective, single-center study.

OBJECTIVE: To investigate demographic, clinical, and laboratory factors associated with distinct stone compositions in children. METHODS: This retrospective study included 237 children aged <14 years who underwent stone composition analysis between July 2008 and November 2023. Demographic, clinical, and laboratory data were collected, and propensity score matching (PSM) was used to control for confounding factors. RESULTS: The urate component (uric acid anhydrous, ammonium acid urate, and sodium urate) was most prevalent in infants, males, and non-Han children, whereas the calcium oxalate component predominated in older children. Analysis of coexisting components revealed urate is the most common partner to calcium oxalate (67.6%), and vice versa (82.8%). Struvite most frequently coexisted with carbonate apatite (60%), while carbonate apatite most often coexisted with calcium oxalate (54%). After PSM, the urate component was independently associated with host metabolic dysregulation, including lower high-density lipoprotein (β = -0.175, 95% CI: -0.279 to -0.071, p = 0.001) and with coagulation dysfunction, as evidenced by a prolonged prothrombin time (β = 0.595, 95% CI: 0.125 to 1.064, p = 0.014). Additionally, preoperative urinary tract infection (UTI) and congenital urinary tract anomalies were independently associated with both carbonate apatite and struvite components, with directionally consistent but quantitatively unstable signals in the struvite cohort, whereas the calcium oxalate component exhibited an inverse association with UTI (OR = 0.156, 95% CI: 0.030 to 0.819, p = 0.028). Furthermore, the carbonate apatite component was also independently associated with an elevated systemic immune-inflammation index (β = 416.53, 95% CI: 60.05 to 773.01, p = 0.024) and systemic inflammation response index (β = 1.286, 95% CI: 0.086 to 2.487, p = 0.038). CONCLUSION: Urate component was prevalent in infants, males, and non-Han children, whereas calcium oxalate predominated in older children. After adjusting for confounders, urate composition was associated with metabolic abnormalities, the carbonate apatite component was linked to infection and anatomical malformations, and a similar directional pattern was observed in the struvite cohort.

Humans↗

PubMed2004

Preparation of bioactive titanium metal via anodic oxidation treatment.

Titania with specific structures of anatase and rutile was found to induce apatite formation in vitro. In this study, anodic oxidation in H(2)SO(4) solution, which could form anatase and rutile on titanium metal surface by conditioning the process, was employed to modify the structure and bioactivity of biomedical titanium. After the titanium metal was subjected to anodic oxidation treatment, thin film X-ray diffraction and scanning electron microscopy results showed the titanium metals surfaces were covered by porous titania of anatase and/or rutile. In simulated body fluid (SBF), the titanium anodically oxidized under the conditions with spark-discharge could induce apatite formation on its surface. The induction period of apatite formation was decreased with increasing amount of either anatase or rutile by conditioning the anodic oxidation. After the titanium metal, anodically oxidized under the conditions without spark-discharge, was subjected to heat treatment at 600 degrees C for 1 h, it could also induce apatite formation in SBF because the amount of anatase and/or rutile was increased by the heat treatment. Our results showed that induction of apatite-forming ability on titanium metal could be attained by anodic oxidation conjoined with heat treatment. So it was believed that anodic oxidation in H(2)SO(4) solution was an effective way to prepare bioactive titanium.

Apatites↗

PubMed2006

Calcium oxalate calculi found attached to the renal papilla: Preliminary evidence for early mechanisms in stone formation.

BACKGROUND: Calculi are commonly found attached to the renal papilla in calcium oxalate (CaOx) stone formers, but the mechanisms by which stones form in this manner are not well established. MATERIALS AND METHODS: Data are presented from three attached stones collected from different patients. Stone morphology and composition were determined using micro computed tomography (CT) and infrared microspectrometry. RESULTS: One of the stones was composed of CaOx with a peripheral region of apatite, such as might have come from a Randall's plaque. Another stone was covered with large CaOx crystals but contained at least two layers of apatite, with no apatite regions exposed at the surface. The third stone contained CaOx with inclusions of apatite and more apatite on its surface, along with a substantial volume of poorly mineralized material that could not be identified. CONCLUSIONS: The complexity of these stones and their differing morphologies do not by themselves allow inference of the mechanism of stone formation. Future work will require the careful documentation of attached stones on the papilla, as well as study of the papilla after the stone has been removed, before it can be determined whether such diverse CaOx stones originate from the same or different underlying etiologies.

Apatites↗

PubMed1982

Crystallographic and structural alterations in the mineral phase of human enamel with carious attacks.

The present study aims to obtain further information about the crystallographic and structural alterations in the mineral phase of enamel with the onset of caries. For this purpose, X-ray microbeam diffraction analysis was carried out on ground sections prepared from natural white spot lesions. Electron spin resonance (ESR) analysis was also performed on block samples cut from white spot lesions and from undamaged enamel of the same teeth. The results of crystallinity measurements showed that enamel apatite in demineralized lesions was lower in crystallinity than the apatite in the surface layer and surrounding sound enamel. This X-ray diffraction study also revealed the presence of two non-apatitic minerals in the demineralized lesions. One type of the mineral is whitlockite, giving spotty rings. The nature of the other mineral, giving a single ring-like reflection, remains to be elucidated. A comparison of ESR spectra taken from the caries-attacked and undamaged enamel provided evidence that the former samples have a lower degree of alignment of apatite microcrystals. The occurrence of non-apatitic mineral phases and the observed difference in microcrystalline alignment may be the results of a remineralization process.

Apatites↗

PubMed2006

Self-assembly and effect on crystal growth of the leucine-rich amelogenin peptide.

Amelogenins are a unique group of alternatively spliced proteins. While the full-length amelogenin is known to assemble into nanospheres and alter apatite crystal growth and alignment, the function of the leucine-rich amelogenin peptide (LRAP) in biomineralization is not understood. This study tested the hypothesis that LRAP self-assembles into a supramolecular structure and guides crystal growth similarly to the full-length protein. Synthetic LRAP and recombinant full-length amelogenin (rH175) were used at different concentrations and either immobilized onto fluoroapatite substrates (FAP) or immersed into saturated calcium-phosphate solutions. The structure of the assembled protein and the height of apatite crystals formed on the FAP template were determined using atomic force microscopy. Both LRAP and rH175 assembled into nanospheres. LRAP self-assembly, however, was only observed at concentrations of >0.5 mg ml-1 and limited to sizes between 5 and 30 nm. Apatite crystal growth was not significantly affected by LRAP, while rH175 accelerated crystal growth by up to 50-fold. The increased growth rate was only observed when rH175 precipitated at concentrations of >0.8 mg ml-1. It was concluded that the ability of amelogenins to self-assemble into nanospheres and to bind to apatite in vitro is not inevitably an indication for the ability to control apatite crystal growth.

Apatites↗

PubMed1976

Extraosseous calcification. Evidence for abnormal pyrophosphate metabolism in uremia.

The inorganic constituents and crystalline features of extraosseous calcium-phosphate deposits obtained from dialyzed uremic and hypercalcemic patients were studied. Visceral calcification (heart, lung, and kidney) in hypercalcemic patients exhibited either an amorphous or apatitic X-ray diffraction pattern. Uremic visceral calcification consistently gave an amorphous diffraction pattern. Although the calcium content of uremic and hypercalcemic visceral deposits was similar, other inorganic constituents were different. The mean pyrophosphate was 11 +/- 11.8 and magnesium 4.91 +/- 3.86 mg/g in the uremic group as compared to 0.92 +/- 0.24 and 1.36 +/- 1.26 mg/g in the hypercalcemic group (P less than 0.025). After incineration hypercalcemic visceral deposits having an amorphous diffraction pattern were found to generate pyrophosphate supporting the presence of brushite in these deposits. The small amount of pyrophosphate in apatitic deposits from both uremic and hypercalcemic patients actually decreased after incineration and the pyrophosphate content of uremic visceral deposits was unchanged by incineration. It is concluded that in hypercalcemic patients the initial visceral deposit is brushite which is subsequently transformed to apatite. Arterial and tumoral calcium-phosphate deposits in uremic patients were also apatite. Uremic visceral calcium-phosphate deposits are an unique mineral high in magnesium with approximately 30% of the phosphorus present as pyrophosphate. The high pyrophosphate content of these deposits could alter their crystalline structure and prevent the transformation to apatite. The infrared features, high magnesium content of the deposit, and resistance of pyrophosphate in the deposit to hydrolysis by pyrophosphatase suggests that the pyrophosphate may be deposited as the magnesium salt.

Apatites↗

PubMed1987

The influence of incorporated and adsorbed fluoride on the dissolution of powdered and pelletized hydroxyapatite in fluoridated and non-fluoridated acid buffers.

The effects of fluoride (F) incorporated into hydroxyapatite (HA), adsorbed onto the HA surface, and fluoride in solution were studied during HA dissolution. Dissolution rates at pH 5.0 and 25 degrees C were determined in fluoridated (0.1, 5.0 micrograms/mL) and non-fluoridated buffers for the following powdered and pelletized synthesized HAs: non-fluoridated HA, partially-fluoridated (100, 1000, 37,000 micrograms/g) HA, and surface-adsorbed fluoridated (100, 1000 micrograms/g) HA. The dissolution rate curves were used to derive two components we have called 'diffusion' and 'surface chemical reactivity'. With powders, the rate-determining factor was surface chemical reactivity during the first 60 min. Diffusion was reduced by increasing the F levels in the apatite or buffer. In non-fluoridated buffers, diffusion was reduced 29% for apatite with 100 micrograms/g incorporated F and 99% with 37,000 micrograms/g. Diffusion was reduced by 37% and 81% by 0.1 and 5.0 micrograms/mL F, respectively, in the buffer. With pelletized HA, the rate-determining factor during the first 10 min was surface chemical reactivity. Diffusion then became relatively more important, but the diffusion rate was independent of F content. During the dissolution of powdered apatites, F was taken up by the remaining apatite solid, as evidenced by the lower F concentration in solution than that calculated to be released during dissolution. There was also a decrease in the F concentration of the 0.1 microgram/mL buffer as reaction progressed. Pelletized apatites did not release enough F to influence dissolution significantly. Surface-adsorbed F was more effective than incorporated F in reducing HA dissolution.(ABSTRACT TRUNCATED AT 250 WORDS)

Acids↗

PubMed2004

Highly ordered interstitial water observed in bone by nuclear magnetic resonance.

UNLABELLED: NMR was used to study the nanostructure of bone tissue. Distance measurements show that the first water layer at the surface of the mineral in cortical bone is structured. This water may serve to couple the mineral to the organic matrix and may play a role in deformation. INTRODUCTION: The unique mechanical characteristics of bone tissue have not yet been satisfactorily connected to the exact molecular architecture of this complex composite material. Recently developed solid-state nuclear magnetic resonance (NMR) techniques are applied here to the mineral component to provide new structural distance constraints at the subnanometer scale. MATERIALS AND METHODS: NMR dipolar couplings between structural protons (OH(-) and H(2)O) and phosphorus (PO(4)) or carbon (CO(3)) were measured using the 2D Lee-Goldburg Cross-Polarization under Magic-Angle Spinning (2D LG-CPMAS) pulse sequence, which simultaneously suppresses the much stronger proton-proton dipolar interactions. The NMR dipolar couplings measured provide accurate distances between atoms, e.g., OH and PO(4) in apatites. Excised and powdered femoral cortical bone was used for these experiments. Synthetic carbonate ( approximately 2-4 wt%)-substituted hydroxyapatite was also studied for structural comparison. RESULTS: In synthetic apatite, the hydroxide ions are strongly hydrogen bonded to adjacent carbonate or phosphate ions, with hydrogen bond (O-H) distances of approximately 1.96 A observed. The bone tissue sample, in contrast, shows little evidence of ordered hydroxide. Instead, a very ordered (structural) layer of water molecules is identified, which hydrates the small bioapatite crystallites through very close arrangements. Water protons are approximately 2.3-2.55 A from surface phosphorus atoms. CONCLUSIONS: In synthetic carbonated apatite, strong hydrogen bonds were observed between the hydroxide ions and structural phosphate and carbonate units in the apatite crystal lattice. These hydrogen bonding interactions may contribute to the long-range stability of this mineral structure. The biological apatite in cortical bone tissue shows evidence of hydrogen bonding with an ordered surface water layer at the faces of the mineral particles. This structural water layer has been inferred, but direct spectroscopic evidence of this interstitial water is given here. An ordered structural water layer sandwiched between the mineral and the organic collagen fibers may affect the biomechanical properties of this complex composite material.

Animals↗

PubMed1997

[Calcification of cervical ligamentum flavum--analysis of calcium compounds and histopathological findings].

We operated 3 patients with cervical myelopathy due to calcification of ligamentum flavum (CLF). Specimens collected surgically were subjected to X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy (Raman) analysis and also histopathological examination. The calcium compounds deposited were calcium pyrophosphate dihydrate (CPPD) in Case 1, apatite in Case 2, and a double-layer structure with an outer CPPD layer and an inner carbonate apatite layer in Case 3. Histopathologically, CPPD deposition in Case 1 could be distinguished from apatite deposition in Case 2 and 3 by hematoxylin-eosin stain. Chondrocytes were observed in all 3 cases, suggesting the chondrocytes may have played a role in calcification in these three cases. To date, 62 cases of CLF (including the present cases) have been reported, and analysis of calcium compound has been performed for 29 of them. Of these 29, 15 were analyzed as calcium phosphate compounds, 9 as CPPD and 4 cases as mixed crystals like Case 3. However the analysis method and result about CPPD are no problem, the analysis result of calcium phosphate compounds depends on the using methods. Calcium phosphate or undetectable compounds was identified by XRD as hydroxyapatite (HAp), and by FTIR as calcium phosphate or undetectable compound. Analysis of calcium phosphate compounds should be condacted and identified by XRD, FTIR, and Raman. We propose two possible mechanisms for the formation of the double-layer structure in Case 3: one is formation of apatite first followed by deposition of CPPD outside, and the other is formation of CPPD first followed by conversion of CPPD in the central region to apatite. What the process of formation of the double-layer was in this cases remains unclear.

Aged↗