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PubMed1992

Microhardness measurements of renal calculi: regional differences and effects of microstructure.

Microhardnesses of five types of renal calculi: calcium apatite (82.5%)/magnesium ammonium phosphate hydrogen (10%)/calcium oxalate monohydrate (7.5%); calcium apatite (95%)/calcium oxalate monohydrate (5%); magnesium ammonium phosphate hydrogen (90%)/calcium apatite (10%); calcium oxalate monohydrate (85%)/calcium apatite (15%); and cystine (100%) were measured. Using Knoop and Vickers indenters the effects of chemical composition and microstructure on the microhardness measurement were assessed. Calcium oxalate monohydrate, magnesium ammonium phosphate hydrogen, and cystine stones, without apparent structure pattern, showed neither regional nor directional differences in their microhardness. In contrast, calcium apatite stones, with distinctly concentric laminae structure, showed regional variations which were correlated with the chemical composition of stone constituents. Scanning electron microscopy of the indenter impressions were taken to help in interpreting the directional dependence in Knoop hardness measurements with respect to the microstructure of the calculi. Vickers measurements showed the crystalline stones were isotropic within a layer. Combined results of Knoop and Vickers measurements indicate that the anisotropic Knoop hardness readings seen in the laminated regions were structural but not material-based. Implications of the results for the fragmentation of renal calculi in extracorporeal shock wave lithotripsy are discussed.

Hardness Tests↗

PubMed2003

Modification of calcium-phosphate coatings on titanium by recombinant amelogenin.

Amelogenin proteins, the principal components of the developing dental enamel extracellular matrix, have been postulated to facilitate the elongated and oriented growth of the carbonated apatite crystals during enamel formation. We previously reported that amelogenin caused modulation of apatite crystals nucleated on a bioactive glass (Bioglass(R)) in vitro. Here, the effects of amelogenin on the growth morphology of calcium-phosphate crystals nucleated on a titanium surface were investigated in order to gain a better understanding of the role of amelogenins during enamel biomineralization and to explore their potential application in the design and development of novel biomaterials. The dose-dependent effects of a recombinant mouse amelogenin (rM179) were found to be different from those of bovine serum albumin, which significantly inhibited apatite crystal growth and caused the octacalcium phosphate (OCP) crystals to change from a plate-like shape to a curved shape, indicating a general inhibitory effect. The effects of rM179 on the crystal growth of OCP at 12.5-100 microg/mL and of apatite at 50 microg/mL were insignificant while the apatite crystals were remarkably elongated along their c-axes upon the use of 100 microg/mL of rM179. The unique modulation of the calcium-phosphate coatings on titanium by rM179 supports the view that amelogenins have a great potential for applications designed to develop novel biomimetic materials.

Amelogenin↗

PubMed2004

Comparison of bone graft matrices for human mesenchymal stem cell-directed osteogenesis.

Scaffolds to support cell-based tissue engineering are critical determinants of clinical efforts to regenerate and repair the body. Bone tissue engineering requires materials that are biocompatible, well vascularized, mechanically suited for bone function, integrated with the host skeleton, and support osteoinduction of the implanted cells that form new bone. The aim of this study was to compare the osteogenic potential of bone marrow-derived, culture expanded human mesenchymal stem cells (hMSCs) adherent to different scaffolds composed of various calcium phosphates. Cells were loaded onto 2 x 2 mm cubes of coral calcium carbonate-derived apatite, bovine bone-derived apatite, synthetic hydroxyapatite (HA)/tricalcium phosphate (TCP) (60:40%), or synthetic HA/TCP (20:80%) and placed into the dorsum of SCID mice for 5 weeks. Subsequent histomorphometric analysis of bone formation within the cubes revealed the absence of bone formation within the coral-derived apatite and the bovine bone-derived apatite. Bone formation within synthetic HA/TCP scaffolds was measured to be 8.8% (+/-2.7%) and 13.8% (+/-3.6%) of the total tissue present for the 60:40% and 20:80% materials, respectively. Minimal resorption was observed at this early time point. Scanning electron microscopy evaluation of loaded scaffolds indicates that cell loading was not a variable affecting the different bone formation outcomes in these four scaffolds. In this ectopic model, different apatite-containing scaffolds of similar morphology and porosity demonstrated marked differences in their ability to support osteoinduction by implanted hMSCs. The necessary induction of hMSCs along the osteoblastic lineage may be dependent, in part, on the local microenvironment established by the scaffold chemistry and interactions with the host.

Bone Regeneration↗

PubMed1999

Evolution of a rhythmic lamination in the organophosphatic shells of brachiopods

The secondary layer of organophosphatic-shelled brachiopods consists of stratiform laminae in glycosaminoglycans (GAGs), pervaded by canals with chitinous walls. The laminae are composed of various aggregates of protein-coated granules of apatite, 4-8 nm in size, 10 or so soluble proteins, beta-chitinous meshes and sheets, and a possibly proteinaceous actin-like network. The succession is disposed in rhythmic sets grading between predominantly apatitic and wholly membranous laminae. The most conspicuous set consists of apatitic rods (baculi) in trellised arrays associated with laminae of compacted mosaics and spherules of apatite. The baculi are composed of mosaics accreting around axial fibrous proteins; apatitic aggregates are also scattered throughout the GAGs and accrete on proteinaceous networks and chitinous meshes. Baculi, subtended between two compact laminae, first appeared in Early Cambrian times and are a synapomorphy of lingulides. Subsequently, the secretion of one or another of the compact laminae was suppressed in the two surviving clades, with sets of the lingulid Glottidia and the discinids, respectively, grading inwardly from, and to, compact laminae. Suppression of baculate secretion also occurred in the dorsal valve of living Discinisca while, in Lingula, baculi have been replaced by botryoidal aggregates of mosaics at least since Carboniferous times. Copyright 1999 Academic Press.

Journal Article↗

PubMed1983

An intermediate state in hydrolysis of amorphous calcium phosphate.

The hydrolysis of previously prepared amorphous calcium phosphate (ACP) was studied in a solution "saturated" with ACP; this eliminated the initial consumption of acid due to ACP dissolution. The procedure established that conversion of high-concentration ACP slurry to an apatite involves two processes: the first process consumes acid and indicates the formation of a more acidic calcium phosphate intermediary with the solubility of octacalcium phosphate (OCP); the second process consumes base and indicates the conversion of the intermediary to apatite and, possibly, direct conversion of ACP to apatite. The thermodynamic analysis of the solution composition data suggests that ACP converts into a nonstoichiometric apatite when the OCP-like intermediary is formed, and a stoichiometric apatite is formed when no OCP-like intermediary is involved.

Calcium Phosphates↗

PubMed1981

Lattice parameters and cation distribution of solid solutions of calcium and lead hydroxyapatite.

Solid solutions of calcium hydroxyapatite (CaOHA) and lead hydroxyapatite (PbOHA) of the formula Ca10-x Pbx (PO4)6 (OH)2 were prepared by coprecipitation followed by heating at 800 degrees C in a steam of CO2-free water vapor of 1 atm. The samples were apatitic in the range 0 less than x less than 6 and contained lead phosphates as a second phase at higher Pb/Ca ratios. Lattice parameters and cation distribution of the apatitic samples were determined by X-ray diffraction. The lattice parameters varied linearly with x in the range considered, whereas all Pb2+ were located in the six-fold position for cations. There was a miscibility gap in the apatite series of solid solutions in the range 1 less than x less than 4, whereas apatites in the range 6 less than x less than 10 were not stable under the conditions of preparation. It is concluded that apatites in the range 4 less than x less than 6 represent a minimum in the free energy of solid solutions between CaOHA and PbOHA.

Calcium↗

PubMed1988

The effect of hydroxyapatite crystallinity on hemolysis.

Crystalline hydroxyapatite is a component of bone, teeth, and numerous pathological calcifications. The apatite crystal structure can accommodate a wide variety of atomic substitutions which gives apatite crystals an unusually high degree of variability in biochemical and physical properties. Apatite crystallites interact with numerous cellular systems in vivo, and some of these interactions may lead to altered cellular function. One measure of crystal-membrane interactions is crystal-induced membranolysis of human red blood cells. Hemolytic potentials at constant crystal surface areas were measured at 1, 2, and 4 hours for 29 different preparations of apatite. Each apatite sample was characterized by its morphology, particle size, % CO3, zeta potential, and broadening of the (211), (112), (300), (202), and (002) diffraction maxima. Only the surface area/g and the X-ray powder diffraction line broadening showed a significant inverse correlation with hemolytic potential. These parameters were related to each other, and are indications of the degree of crystallinity.

Crystallization↗

PubMed1998

Ultrastructural and electron diffraction of the bone-ceramic interfacial zone in coral and biphasic CaP implants.

We investigated the influence of natural coral implants used as a bone substitute on the quality of bone ingrowth in rabbits 2, 3, and 6 weeks after implantation. Explants were characterized by transmission electron microscopy and electron diffraction. Bone ingrowth has been previously demonstrated by light microscopy, however, few have been performed in electron microscopy to compare mineralized tissue ingrowth in coral implants which occurs at the expense of calcium carbonate to that of calcium phosphate (CaP) implants. The interface between coral aragonite and mineralized tissue or bone was abrupt, with no invasion of the aragonite structure by newly formed crystals, as occurs in micropores when biphasic CaP (BCP) ceramics were used. The restoring process appears to be different from that induced by BCP implants. Precipitation of needle-like apatite crystals on the CaCO3 implant surface was not observed. Instead, apatitic smooth-shaped crystals formed in aggregates. The coral dissolution process does not release phosphate and so precipitation of apatite does not occur in the micropores of the coral implant, thereby limiting the formation of an apatite layer and hence bone bonding to the outer surface of the implant. In addition, on the outer surface of the implant, close to bone and a phosphorus source, the CaP crystals that do form are in aggregates presumably due to the carbonate and mismatch between the aragonite and the apatite. This seems to result in a delayed bone attachment or weaker bone bonding than CaP implants which encourage an epitaxial biological crystal deposition.

Animals↗

PubMed2007

Bioactivity of CaSiO3/poly-lactic acid (PLA) composites prepared by various surface loading methods of CaSiO3 powder.

Mixing bioactive ceramic powders with polymers is an effective method for generating bioactivity to the polymer-matrix composites but it is necessary to incorporate up to 40 vol% of bioactive ceramic powder. However, such a high mixing ratio offsets the advantages of the flexibility and formability of polymer matrix and it would be highly advantageous to lower the mixing ratio. Since surface loading of ceramic powders in the polymer is thought to be an effective way of reducing the mixing ratio of the ceramic powder while maintaining bioactive activity, CaSiO(3)/poly-lactic acid (PLA) composites were prepared by three methods; (1) casting, (2) spin coating and (3) hot pressing. In methods (1) and (2), a suspension was prepared by dissolving PLA in chloroform and dispersing CaSiO(3) powder in it. The suspension was cast and dried to form a film in the case of method (1) while it was spin-coated on a PLA substrate in method (2). In method (3), CaSiO(3) powder was surface loaded on to a PLA substrate by hot pressing. The bioactivity of these samples was investigated in vitro using simulated body fluid (SBF). Apatite formation was not observed in the samples prepared by method (1) but some apatite formation was achieved by mixing polyethylene glycol (PEG) with the PLA, producing a porous polymer matrix. In method (2), apatite was clearly observed after soaking for 7 days. Enhanced apatite formation was observed in method (3), the thickness of the resulting apatite layers becoming about 20 microm after soaking for 14 days. Since the amount of CaSiO(3) powder used in these samples was only <or=0.4 vol%, it is concluded that this preparation method is very effective in generating bioactivity in polymer-matrix composites by loading with only very small amounts of ceramic powder.

Biocompatible Materials↗

PubMed1991

Crystallographic behaviour of fluoridated hydroxyapatites containing Mg2+ and CO3(2-) ions.

Fluoridated hydroxyapatites containing small amounts of magnesium and carbonate ions were synthesized at 80 and 60 degrees C to examine their inhibiting properties regarding apatite crystal growth, in contrast to the promoting action of fluoride. The shortening of a-axis and c-axis dimensions of the apatite crystals, as revealed by X-ray diffraction analysis, suggested that both magnesium and carbonate ions were substituted into the apatite crystals. The a-axis dimensions also decreased with the degree of fluoridation. The infrared spectra due to CO3(2-) ions at 875 cm-1 were shifted with increasing fluoride content. The overall crystallinity was inhibited in comparison with that of Mg and CO3-free fluoridated hydroxyapatites, but recovered considerably with increased fluoride content. The apparent solubility of the apatites at pH 4.0 and 37 degrees C was higher than that of Mg and CO3-free fluoridated hydroxyapatites at lower fluoride contents, but gradually approached the latter at higher fluoride content. After 1 month's incubation, dicalcium phosphate dihydrate was formed from fluoride-free Mg-CO3 apatite synthesized at 60 degrees C.

Carbonates↗

PubMed2002

Aging effect on the phase evolution of water-based sol-gel hydroxyapatite.

In a number of recent reports on the synthesis of sol-gel hydroxyapatite, aging of the precursor solution has been found to be critical in developing an apatitic phase. Critical aging time is required to complete reaction between Ca and P molecular precursors to form a desired intermediate complex that permits a further transformation to apatite phase under appropriate thermal treatment. In this investigation, we employed a water-based sol-gel process recently developed to fabricate hydroxyapatite at relatively low temperatures. The aging effect on apatite formation was systematically studied in terms of aging time and temperature. Experimental results show that the aging time is considerably reduced as aging temperature rises. Long-term thermal aging was unfavorable for apatite formation. The optimal aging parameters for apatite formation were experimentally determined, which was further consolidated into a phase evolution map. Aging kinetic was investigated by monitoring the variation of solution pH, following the determination of an apparent activation energy, which has a value as high as 10.35 kcal/mol, for the chemical reaction occurring upon aging. Optimal solution chemistry was elucidated based on the corresponding phase evolution map.

Biocompatible Materials↗

PubMed2003

Novel bioactive materials with different mechanical properties.

Some ceramics, such as Bioglass, sintered hydroxyapatite, and glass-ceramic A-W, spontaneously bond to living bone. They are called bioactive materials and are already clinically used as important bone substitutes. However, compared with human cortical bone, they have lower fracture toughness and higher elastic moduli. Therefore, it is desirable to develop bioactive materials with improved mechanical properties. All the bioactive materials mentioned above form a bone-like apatite layer on their surfaces in the living body, and bond to bone through this apatite layer. The formation of bone-like apatite on artificial material is induced by functional groups, such as Si-OH, Ti-OH, Zr-OH, Nb-OH, Ta-OH, -COOH, and PO(4)H(2). These groups have specific structures revealing negatively charge, and induce apatite formation via formations of an amorphous calcium compound, e.g., calcium silicate, calcium titanate, and amorphous calcium phosphate. These fundamental findings provide methods for preparing new bioactive materials with different mechanical properties. Tough bioactive materials can be prepared by the chemical treatment of metals and ceramics that have high fracture toughness, e.g., by the NaOH and heat treatments of titanium metal, titanium alloys, and tantalum metal, and by H(3)PO(4) treatment of tetragonal zirconia. Soft bioactive materials can be synthesized by the sol-gel process, in which the bioactive silica or titania is polymerized with a flexible polymer, such as polydimethylsiloxane or polytetramethyloxide, at the molecular level to form an inorganic-organic nano-hybrid. The biomimetic process has been used to deposit nano-sized bone-like apatite on fine polymer fibers, which were textured into a three-dimensional knit framework. This strategy is expected to ultimately lead to bioactive composites that have a bone-like structure and, hence, bone-like mechanical properties.

Animals↗

PubMed1981

Hereditary deafness with hydrops and anomalous calcium phosphate deposits.

The temporal bones from a 58-year-old white woman who had had hereditary congenital deafness were examined with the techniques of microdissection and surface preparations followed by sectioning of the modiolus. There was bilateral, almost total sensorineural degeneration, which also involved the saccule. The degeneration of the distal processes of the cochlear neurons in the osseous spiral lamina was almost complete, whereas numerous ganglion cells and proximal processes remained in the modiolus and the internal auditory canal. Severe cochleo-saccular hydrops was present in the left ear with Reissner's membrane bulging into the horizontal canal. X-ray diffraction and electron probe analysis were used to study the abnormal crystalline deposits in both ears. On the left side the saccular otoconia were composed of calcite, but the utricular macula was covered by a crust of apatite spherulites. More apatite occurred around the maculae and in the scala media. The cupulae were composed of apatite and octacalcium phosphate. On the right side the utricular otoconia were of normal calcite, but there was a deposit of apatite on the macula sacculi. The upper part of the scala media was completely filled by a deposit of apatite and octacalcium phosphate.

Adolescent↗

PubMed1998

Chemical surface treatment of silicone for inducing its bioactivity.

It has been confirmed that the apatite nucleation is induced by silanol (Si-OH) groups formed on the surfaces of materials and/or silicate ions adsorbed on them. It was previously shown that apatite nuclei are formed on organic polymers when the polymers are placed on CaO, SiO2-based glass particles soaked in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma, and that they grow spontaneously to form a dense and uniform apatite layer together with high adhesive strength to the substrates when the polymers are soaked in another solution with ion concentrations 1.5 times the SBF. In the present study, silanol groups bonded covalently to the surface of the silicone substrate were formed and its apatite-forming ability was examined. When silicone substrates were treated with 5 or 10 M NaOH with pH 7.25 at 36.5 degrees C for more than 3 h, silanol groups were formed on the surfaces of the substrates. When thus NaOH-treated substrates were soaked in 1.5SBF at 36.5 degrees C, a bone-like apatite was formed on the substrates in a short period.

Journal Article↗

PubMed2000

Effect of sintering parameters on the density and microstructure of carbonate hydroxyapatite.

This work documents an investigation into the effect of water on the density and microstructure of carbonate hydroxyapatite in carbon dioxide sintering atmospheres. Carbonate apatites with carbonate contents of between 3.2 and 7.8 wt % were precipitated and the precipitates were formed into dry gels. Isothermal and isochronal sintering experiments were performed under dry carbon dioxide and wet carbon dioxide (containing 3 wt % water) atmospheres. The effect of carbonate content was studied by using two gels both with a green density of 37% and with carbonate contents of 5.8 and 7.8 wt %. Both isothermal and isochronal experiments demonstrated that bloating of the apatite occurred and this behavior was associated with the loss of carbonate from the apatite. It was found that only in wet carbon dioxide atmospheres fully dense translucent carbonate apatite could be formed. 93% dense carbonate apatite was formed after 4 h sintering at temperatures as low as 700 degrees C.

Journal Article↗

PubMed2003

Stone fragility: its therapeutic implications in shock wave lithotripsy of upper urinary tract stones.

OBJECTIVE: To analyse the impact of stone composition on stone fragility (fragmentation) and clearance of upper urinary tract stones after shock wave lithotripsy (SWL). MATERIAL AND METHODS: Between 1st July 1998 and 31st July 2001, 300 renal and ureteric units of 290 patients (10 being bilateral) underwent SWL for upper urinary tract calculi. The degree of fragmentation was divided into four types: (I) Excellent, (II) Good, (III) Fair and (IV) No fragmentation. Stone composition was done by X-ray diffraction crystallography. A statistical comparison was made between degree of fragmentation, number of shock waves delivered, voltage setting, number of sessions required and requirements of adjuvant procedures according to the stone composition. RESULTS: Stone analysis revealed that 90% of the patients had calcium oxalate stones. Of these 80% were calcium oxalate monohydrate (COM) and 20% calcium oxalate dehydrate (COD). Struvite, apatite and uric acid stones comprised of 6%, 3% and 1% respectively. Type-I fragmentation was achieved up to 63.96%, 50% and 100% in COD, struvite and uric stones respectively as compared to 44.9% and 44.44% for COM and apatite stones. Type-III fragmentation was seen up to 8.79% and 33.3% respectively in COM and apatite as compared to 5.55% or less in other types of the stones suggesting that COM and apatite stones produce larger fragments. The mean number of shock waves, voltage and number of treatments was significantly higher for COM and apatite stones (p value < 0.005) with a stone free rate of only 65-66% and 65-68% respectively at three months (p value < 0.001). Similarly the number of adjuvant procedures required in COM alone was more, i.e. 31 as compared to 17 procedures in rest of the other kinds of stones (p value < 0.05). CONCLUSION: Stone composition in Indian subcontinent is different from the western world. Fragility of a stone varies with the composition of the stone and affects the therapeutic results.

Adolescent↗

PubMed1999

Nanobacteria: an infectious cause for kidney stone formation.

BACKGROUND: Nanobacteria are cytotoxic, sterile-filterable, gram-negative, atypical bacteria detected in bovine and human blood. Nanobacteria produce carbonate apatite on their cell walls. Data on Randall's plaques suggest that apatite may initiate kidney stone formation. We assessed nanobacteria in 72 consecutively collected kidney stones from Finnish patients. METHODS: Nanobacteria and kidney stone units were compared using scanning electron microscopy (SEM). Demineralized kidney stones were screened for nanobacteria using a double-staining method and a specific culture method. Isolated nanobacteria were analyzed for mineral formation in vitro with Ca and 85Sr incorporation tests. RESULTS: SEM highlighted the resemblance in size and morphology of nanobacteria and the smallest apatite units in the kidney stones. Nanobacterial antigens could be detected after the demineralization of the stones in 1 N HCl. Nanobacteria were surprisingly resistant to this treatment, and cultures could be established from 93.1% of the stones. Only struvite stones had common bacteria, in addition to the nanobacteria. When the results of all of the assays were combined, 70 of the 72 stones (that is, 97.2%) were nanobacteria positive. Although apatite stones indicated highest nanobacteria antigen signals, the overall nanobacteria positivity did not depend on the stone type. The isolated nanobacteria produced apatite stones in vitro, measured by Ca and 85Sr incorporation. CONCLUSIONS: We propose that kidney stone formation is a nanobacterial disease analogous to Helicobacter pylori infection and peptic ulcer disease. Both diseases are initiated by bacterial infection and subsequently endogenous and dietary factors influence their progression.

Calcium↗

PubMed2001

Familial calcium crystal diseases: what have we learned?

The spectrum of heterotopic calcification or ossification is expanding because of the reports of several kindreds with calcium pyrophosphate deposition disease, apatite deposition disease, and others with less common syndromes associated with extracellular matrix calcification, such as fibrodysplasia ossificans progressiva and related syndromes. Genomic DNA studies in both humans and mice provide a shortcut to understanding the genetic basis of promotion and prevention of ECM calcification. Mutation in the COL2A1 gene has been identified in one family with spondyloepiphyseal dysplasia and calcium pyrophosphate and apatite crystalline deposits. In another kindred with precocious osteoarthritis without spondyloepiphyseal dysplasia, the phenotype was linked to markers of chromosome 8. In four other kindreds, the phenotypes were linked to an area of chromosome 5p. Two genes located in this region, which are expressed in articular cartilage, are being investigated as possible calcium pyrophosphate deposition disease genes. The results of linkage studies in three kindreds with articular/periarticular ADD with the COL2A1 gene were noninformative. Two different mouse mutations, the ank/ank and the ttw/ttw mice, are associated with intra-articular and ligament apatite deposits caused by a decrease in extracellular pyrophosphate concentrations, mimicking human arthritis caused by apatite deposition disease. Mutations in the matrix GLA protein, both in mice and in humans, are also associated with vascular and articular calcification. These mouse mutations provide cutting-edge information in the investigation of the mechanisms of apatite deposition in humans.

Calcinosis↗