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PubMed2003

Biopex acquires anti-washout properties by adding sodium alginate into its liquid phase.

Biopex sets upon mixing with its liquid phase due to chelate reaction between sodium succinate and calcium phosphate, then gradually transforms to apatite. As a result of apatite formation, set Biopex shows excellent tissue responses and good osteoconductivity. However, Biopex would be washed out when the paste is exposed to body fluid before its setting reaction. Washed out cement causes an inflammatory response. In this investigation, therefore, sodium alginate was added to the liquid phase of Biopex and its effects on washout properties and transformation to apatite were studied. We found that cement remaining ratio, an index of the anti-washout property, of the Biopex increased by increasing the amounts of added sodium alginate to reach 100% when the liquid phase of Biopex contained 0.6% or more sodium alginate. Biopex gradually transformed to apatite regardless of the amount of added sodium alginate at least when the concentration of the sodium alginate in the liquid phase was 1.0% or less. It is concluded therefore, that addition of sodium alginate is very useful for Biopex to acquire the anti-washout property.

Alginates↗

PubMed1997

[Mineralization mechanism and crystal chemistry in developing enamel].

The purpose of this study was to investigate the mineralization mechanism in developing enamel using the pH staining technique. Unerupted bovine teeth were used in the experiment. Activity of a proteolytic enzyme against enamel protein obtained from bovine enamel was evaluated. Crystals in developing enamel, which were classified into neutral zones 1 (N1) and 2 (N2) and acid zones 1 (A1) and 2 (A2), were investigated using infrared spectroscopy, thermal analysis, and power X-ray diffractometry. The proteolytic enzyme showed highest activity at approximately pH6, which was in accordance with the pH in the acidic zone (A1). Most of the organic components of the enamel decomposed at 580 degrees C except for the carbonate and hydrogen phosphate groups included in the apatite crystals. In the developing enamel, (Ca + Mg)/P molar ratio was lower than that of the stoichometric hydroxyapatite. The replacement of OH and PO4 sites in apatite crystals was higher than that in matured enamel. The a-axis dimension of the apatite crystals in the secretory stage enamel (N1) was found to be greater than that in A2 and matured enamel. These results suggested that enamel mineralization is followed by decarbonation in carbonate apatite.

Animals↗

PubMed1975

[Lead and arsenic resorption in the hard tissues (crystallochemical studies)].

Histologic-analytical observations on the resorption of lead and arsenic compounds are put into relationship with crystal-chemical analogies in the composition of hard tissue and the structure of calcium phosphate apatites with lead and arsenic substitution. Chemical analyses and x-ray diffraction of calcium and lead apatites with phosphate and arsenate represented as mixed precipitates in solution equilibrium show that - with the exception of calcium arsenate apatite - linear diadochocinetic substitution conditions are existing. The composition of calcium arsenate apatite is clearly shown to contain much less arsenic. This result is explained by the crystallographic laws of substitution in the crystal lattice (diadochocinetic laws). The clinical and physiological findings in lead and arsenic resorption are confirmed by the found distributional equilibria.

Apatites↗

PubMed1998

The interface of bone microstructure and an innovative coating: an X-ray diffraction study.

The in vivo compatibility and degradation aspects of an innovative coating to be sprayed onto titanium implants were investigated. The surface of fluorinated apatite (fHA), consisting of fluorhydroxyapatite plasma sprayed in a vacuum atmosphere, was treated with carbonate to improve its biological compatibility. fHA coating was compared with titanium implants coated (a) with hydroxyapatite (HA) by the traditional plasma spraying, and (b) with titanium oxide (TiOx). Screw-shaped implants were inserted in the cortical bone of sheep tibiae. X-ray diffraction (XRD) analysis of bone tissue and coatings was carried out at 2, 4, 12 and 36 weeks after surgery. The crystallographic habit of the implant-facing bone, as well as the structural stability of the coating, were evaluated. For each time period and type of ceramic bone apatite lattice at the interface, no significantly different reference apatite lattice and no foreign peak were recorded. Two weeks after implantation, the bone at the interface was strongly unmineralized in all samples; after 4 weeks, poorly mineralized bone microareas decreased. At 12 weeks, the newly formed bone tissue at the interface with both the new coating and HA coating was shown to be fully mineralized; this crystallographic habit was retained at 36 weeks, when particle release from the tested material was lower compared to the controls. The XRD pattern of bone apatite surrounding the coating particles was unmodified. The innovative coating did not alter the mineralization process at the interface. It improved implant osteointegration, mainly due to a limited release of particles. Consequently, clinical performance of external fixation treatment could be improved by modifying the chemical composition of the implant surface.

Animals↗

PubMed1999

Osteoclastic responses to various calcium phosphates in cell cultures.

Disks made of hydroxyapatite, beta-tricalcium phosphate, carbonate apatite, tetracalcium phosphate, alpha-tricalcium phosphate, dicalcium phosphate dihydrate, and octacalcium phosphate were incubated in osteoclastic cell cultures for 2 days. The first five salts were sintered and the last two were compressed before incubation. Osteoclasts resorbed only the sintered carbonate apatite disks. However, osteoclasts were able to resorb octacalcium phosphate disks that were preincubated for 1 day in medium without cells, indicating that surface conditioning was important for osteoclastic resorption of this calcium phosphate. Although resorption did not occur, medium calcium and phosphorus changed to an appreciable extent after a 2-day incubation of beta-tricalcium phosphate, tetracalcium phosphate, alpha-tricalcium phosphate, and dicalcium phosphate dihydrate. These changes in the medium calcium and phosphate concentrations could explain why osteoclasts appeared to have lost their activity on these calcium phosphate disks and were not capable of resorbing them. With hydroxyapatite disks no changes were observed in the medium calcium and phosphorus before and after incubation. Moreover, the osteoclasts appeared to be essentially the same as with the sintered carbonate apatite disks and with bone slices used as a control. Nevertheless, no pits or lacunae were observed on the hydroxyapatite disks, indicating that sintered carbonate apatite should be superior to sintered hydroxyapatite as a bioresorbable bone substitute.

Animals↗

PubMed2000

Conversion of octacalcium phosphate in calcium phosphate cements.

This study investigated the in vitro conversion reaction in calcium phosphate cements (CPCs) containing octacalcium phosphate (OCP) as one of the reagents. OCP is known to be a precursor for apatite formation in vivo. The reaction products were characterized using infrared spectroscopy and X-ray diffraction. Although the conversion of OCP into hydroxyapatite is thermodynamically favorable, OCP only yields apatite formation in CPC provided it is combined with a highly soluble Ca(2+) and OH(-) releasing reaction partner. In this respect, tetracalcium phosphate is a promising compound. Adding small amounts of monocalcium phosphate monohydrate can stimulate the setting through intermediate brushite formation. The preparation method of OCP might drastically affect the performance of the cement. The reaction path of the setting of these CPC probably does not conform to the singular point principle described in the literature, and an in situ hydrolysis of OCP to apatite is conceivable. Simulation of apatite formation using OCP as the precursor and/or seed in CPC might be beneficial for some biomedical applications.

Bone Cements↗

PubMed2002

Hydroxylapatite with substituted magnesium, zinc, cadmium, and yttrium. I. Structure and microstructure.

Hydroxylapatite (HA) was made containing magnesium, zinc, cadmium, and yttrium. Salts of these cations were added to precipitating HA; the precipitates were dried and sintered at 1100 degrees C for 1 h. Lattice parameters from X-ray diffraction spectra showed that these elements were incorporated into the apatite structure at a level of 2% added fraction of calcium in HA and up to 7% for yttrium. The densities of different substituted apatites were close to theoretical for pressed and sintered samples, which is evidence for low bulk porosity. The grain sizes of substituted apatites were smaller than those of pure HA except for cadmium-containing apatite. Surfaces of etched samples showed no second phases, whereas surfaces of unetched samples showed second phases and higher porosity than etched surfaces.

Biocompatible Materials↗

PubMed1991

Calcium phosphate formation at the surface of bioactive glass in vitro.

The calcium phosphate formation at the surface of bioactive glass was studied in vitro. Glass rods and grains were immersed in different aqueous solutions and studied by means of scanning electron microscopy and energy dispersive x-ray analysis. Surface morphological changes and weight loss of corroded grains were monitored. In-depth compositional profiles were determined for rods immersed in the different solutions. The solutions used were tris-buffer (tris-hydroxymethylaminomethane + HCl), tris-buffer prepared using citric acid (tris-hydroxymethylaminomethane + C6H8O7.H2O), and a simulated body fluid, SBF, containing inorganic ions close in concentration to those in human blood plasma. It was found that the calcium phosphate formation at the surface of bioactive glass in vitro proceeds in two stages. When immersing the glass in tris or in SBF a Ca,P-rich surface layer forms. This accumulation takes place within the silica structure. Later, apatite crystals forming spherulites appear on the surface. The Ca/P-ratio of initially formed calcium phosphate was found to be about unity. It is proposed that this is due to bonding of phosphate to a silica gel. The surface is stabilized, i.e., leaching is retarded, by the rapid Ca,P-accumulation within the silica structure before apatite crystals are observed on the surface. It is proposed that the initially formed calcium phosphate is initiated within the silica gel. The crystallizing surface provides nucleation sites for extensive apatite formation on the glass surface. In the presence of citrate no Ca,P-accumulation occur at the glass surface, but soluble Ca-citrate complexes form. By comparing the weight loss during corrosion in tris with that in the calcium and phosphate containing SBF, it is possible to establish whether the glass can induce apatite formation at its surface or not.

Biocompatible Materials↗

PubMed2003

Effects of materials parameters on mineralization and degradation of sol-gel bioactive glasses with 3D-ordered macroporous structures.

Bioactive glasses (BGs) with three-dimensionally ordered macroporous (3DOM) structures were prepared by combining a sol-gel synthesis with colloidal crystal templating. 3DOM sol-gel BGs with two compositions (20 mol % CaO-80% SiO2 and 20 mol % CaO-4% P2O5-76% SiO2) and three macropore sizes (average: 345, 440, and 790 nm) were prepared. Glasses were separated into two particle sizes (212 microm< small < 355 microm and 600 microm < large < 1000 microm). The glasses were soaked in simulated body fluid at 37 degrees C for 2 or 4 days and the effects of composition, particle size, and macropore size on the formation of apatite and glass degradation were characterized. Within the parameter range of the experiments, several comparisons could be made. First, the formation of apatite and degradation of the glass were slightly enhanced for the phosphate containing composition. Second, large particles formed less apatite and degraded less completely compared with small particles. Lastly, an increase in macropore size slowed down the glass degradation and apatite formation processes, an effect related to the decreased internal surface area of the larger pore materials.

Gels↗

PubMed2004

Novel bioactive and biodegradable glass ceramics with high mechanical strength in the CaO--SiO2--B2O3 system.

Novel bioactive and biodegradable glass ceramics with high mechanical strength in the (50-x/2)CaO. SiO(2)--xB(2)O(3) (4.2 < or = x < or = 17.2) system were investigated. The systems consisted of three phases: monoclinic wollastonite, calcium metaborate, and amorphous borosilicate matrix. The glass ceramics containing 4.2 mol% and 8.4 mol% B(2)O(3) showed high bulk density and a dense microstructure. Mechanical strengths of the glass ceramics were higher than those of other bioactive ceramics: high compressive strength (2813 MPa), bending strength of 212 MPa, and fracture toughness of 3.12 MPa. m(1/2). The glass-ceramic formed apatite layer on their surface in the simulated body fluid and showed significant biodegradation. The degree of apatite formation in the glass ceramics depended on the calcium metaborate content and borosilicate glassy matrix. Additional calcium metaborate and borosilicate glassy matrix increased the apatite formation rate on the surface. It might be likely that calcium metaborate causes supersaturation of Ca ions, for its high solubility in SBF and the water-reactive borosilicate glassy matrix formed Sibond;OH groups on the surface to provide nucleation sites for apatite formation. Also, through in vitro test for the biocompatibility of the CaO--SiO(2)--B(2)O(3) glass ceramics, no cytotoxicity of the glass ceramics were found. The results on bioactivity and noncytotoxicity indicated that glass ceramics in the (50-x/2)CaO. SiO(2)--xB(2)O(3) (4.2 < or = x < or = 17.2) system could be useful as a biodegradable bone replacement material.

Biocompatible Materials↗

PubMed2003

Bioinspired organic-inorganic composite materials prepared by an alternate soaking process as a tissue reconstitution matrix.

Poly(acrylic acid) (PAAc) grafted poly(ethylene) (PE) (PAAc-g-PE) film-apatite or calcium carbonate (CaCO3) composite materials were prepared by an alternate soaking process, which simply forms apatite or CaCO3 on the polymer materials by alternate soaking in Ca(2+)- and PO(3-)4- or CO(3)2- -containing solutions. X-ray diffraction analysis of the composite films indicated the presence of hydroxyapatite or CaCO3 on the film. Scanning electron microscopic observation revealed that the whole surface of the film was covered by the apatite or CaCO3. Cell compatibility tests of the apatite- or CaCO3-coated film suggested that the greater number of cells adhered on the films and that the cell proliferation properties were extremely greater on the films.

Animals↗

PubMed2005

Mechanical performance and osteoblast-like cell responses of fluorine-substituted hydroxyapatite and zirconia dense composite.

A fluorine-substituted hydroxyapatite (FHA) and zirconia (ZrO(2)) dense composite (50:50 by volume) was fabricated, and its feasibility for hard tissue applications was investigated in terms of its mechanical properties and osteoblast-like cell (MG63) responses in vitro. The incorporation of fluorine into the hydroxyapatite (HA) structure was highly effective in producing a completely dense apatite-ZrO(2) composite through a pressureless sintering route, by preventing the thermal degradation of the apatite and ZrO(2). The resultant FHA-ZrO(2) dense composite had excellent mechanical properties, such as flexural strength (310 MPa), fracture toughness (3.4 MPam(1/2)), hardness (10 GPa), and elastic modulus (160 GPa). The flexural strength and fracture toughness of the composite showed a noticeable improvement by a factor of approximately 4 with respect to the pure apatites (HA and FHA). The MG63 cellular responses to the composite were assessed in terms of the cell proliferation (cell number and [(3)H]-thymidine incorporation) and differentiation (alkaline phosphatase activity, osteocalcin, and collagen production). The cells on the FHA-ZrO(2) composite spread and grew well, and proliferated actively during the culture period. The expression of alkaline phosphatase, osteocalcin, and collagen by the cells on the composite showed a similar trend to that on the pure apatites, although slight down-regulations were observed, implying that the FHA-ZrO(2) 50:50 composite retains the osteoblastic functionality and traits of the pure HA ceramics to a high degree. This finding, in conjunction with the considerable improvements in mechanical properties, supports the extended use of this composite for hard tissue applications.

Biocompatible Materials↗

PubMed2005

Fabrication and characteristics of bioactive sodium titanate/titania graded film on NiTi shape memory alloy.

A bioactive sodium titanate/titania graded film was formed in situ on NiTi shape memory alloy (SMA) by oxidizing in H(2)O(2) solution and subsequent NaOH treatment and characterized by scanning electron microscopy, Raman spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy (XPS). The bioactivity of the film was investigated using a simulated body fluid (SBF) soaking test. A titania (TiO(2)) layer was first found on NiTi substrate after oxidized in H(2)O(2) solution, and then a porous sodium titanate (Na(2)TiO(3))/titania film with many Ti--OH groups and a trace of Ni(2)O(3) was formed by the reaction of partial TiO(2) phase with NaOH solution. After immersion in SBF for 12 h, apatite was observed to nucleate and grow on the film. With longer soaking time, more apatite appeared on its surface but our control experiments didn't reveal any apatite formation on the chemically polished NiTi SMA, which indicates the bioactivity of NiTi implants could be improved by the formation of the bioactive film. Moreover, XPS depth profiles of O, Ni, Ti, and Na show the bioactive film possesses a smooth graded interface structure to NiTi substrate, which is in favor of sufficient mechanical stability of apatite layer by subsequent deposition in SBF.

Biocompatible Materials↗

PubMed2006

Crystallochemistry, textural properties, and in vitro biocompatibility of different silicon-doped calcium phosphates.

Three silicon-doped calcium phosphates (Si-CaPs) were synthesized by heating precipitated silicon-doped apatite via different thermal treatments. Temperatures of 700 degrees C, 900 degrees C, and 1100 degrees C led to an apatite-glass biphasic material, nanocrystalline Si-doped apatite (SiHA), and Si-doped apatite-alpha tricalcium phosphate biphasic material, respectively. Structure, microstructure, textural properties, and chemical differences were determined for the three bioceramics. Biocompatibility tests were carried out by seeding osteblast-like cells onto the three substrates. Si-CaP treated at 700 degrees C and 900 degrees C led to Ca decrease in the culture media, partially impeding the cell proliferation over them. However, the proliferation capability is restored when additional culture medium is added. Finally, cytotoxicity results indicated that cell damage is much lower in osteblast-like cells seeded onto SiHA and SiHA-alpha tricalcium phosphate samples than in plastic culture control.

Biocompatible Materials↗

PubMed1987

The calcium-buffering phase of bone mineral: some clues to its form and formation.

Devitalized, neonatal, rat calvariae incubated in a buffered solution release Ca2+ and Pi during the first day into the medium until levels reach 1.2 mM and 2.6 mM, respectively. Thereafter levels gradually decrease to stabilize by the fifth day at 0.5 mM and 2 mM. Comparison of these solubility changes with those of known calcium phosphate salts suggests that calvarial solubility is controlled by a mixture of impure, soluble, apatite precursors, which at cell death transform to an impure apatite. Increasing concentrations of Mg2+ increased the rate of Ca2+ release and, at 3 mM, stabilized Ca2+ by the fifth day at 0.9 mM. Decreasing the pH from 7.4 to 7.2 produced similar solubility changes as did the addition of citrate at 0.3 mM, phosphocitrate at 0.3 mM, ATP at 0.1 mM, and the bisphosphonate, HEBP, at 0.1 mM. Osteocalcin did not increase calvarial solubility but was able to slow the rate of calcium phosphate phase transition if present at the time of in vitro crystal formation. Phosphocitrate and HEBP were also more effective when present during in vitro crystal formation. HEBP was most effective when present during biological crystal formation, as shown by the increased solubility of devitalized calvariae removed after in vivo administration of HEBP. In vivo manipulations of osteoclast activity produced changes in plasma calcium which correlated with the solubility of the corresponding calvariae after removal and devitalization. Low milk intake increased calvarial solubility. Increasing doses of 1,25(OH)2D3 increased plasma calcium and calvarial solubility, both of which were reversed by injection of acetazolamide. It was concluded from this survey of devitalized bone solubility that calcium exchange between bone and body fluids can buffer calcium homeostasis in the young rat. The exchange is passive. The active components appear to be osteoblastic formation of soluble apatite precursors and their stabilizers and, in reverse, osteoclastic transformation of apatite to precursors by H2CO3 secretion.

Acetazolamide↗

PubMed1979

Potassium permanganate induced calcergy: a model to study the effects of drugs on hydroxyapatite crystal deposition.

Hydroxyapatite crystal deposition is thought to play a role in the inflammatory episodes of osteoarthritis. A plaque of hydroxyapatite crystals was produced by local subcutaneous injection of a potassium permanganate solution. Transmission electron microscopy with X-ray energy spectroscopy was used to identify the crystal deposits as hydroxyapatite. The effects of dexamethasone, indomethacin, ethane 1-hydroxy-1, 1-diphosphonate (EHDP) and dichloromethylene diposphonate (Cl2MDP) on the development of the apatite plaque was studied. EHDP strongly inhibited the apatite deposition. Cl2MDP slowed the natural resorption of the apatite plaque. Dexamethasone and indomethacin failed to affect the crystal deposition process. The results suggest that EHDP could inhibit crystal deposition in the osteoarthritic joint and that Cl2MDP might have a role in slowing apatite crystal shedding from osteoarthritic cartilage and so reduce the synovitis seen in Osteoarthritis.

Animals↗

PubMed1993

Characterization of the mineralization process in cultures of rabbit growth plate chondrocytes.

The present study was undertaken to investigate the mineralization process in chondrocyte cultures. Chondrocytes were isolated from the growth plate of ribs of 4-week-old rabbits. The nature and properties of mineral crystals precipitated in chondrocyte cultures were compared with those of crystals formed in the hypertrophic zone and bone of rabbit rib growth plates in vivo. The chondrocytes were maintained at high density on type II collagen-coated dishes in Eagle's medium, alpha-modification, with 10% fetal bovine serum and 50 micrograms/ml of ascorbic acid. These cells differentiated into hypertrophic cells 10 days after seeding and produced alkaline phosphatase and 1,25-dihydroxyvitamin D3 receptors on Days 30-70 at levels as high as those in the lower hypertrophic zone in vivo. Mineralization was initiated between Days 20 and 30 and advanced progressively throughout the culture period. However, mineralization was suppressed by the addition of parathyroid hormone (2 x 10(-8) M) or by the presence of fibroblasts. Examination by electron microscopy and Fourier transform infrared (FTIR) spectroscopy verified that mineralized nodules formed in vitro were composed of small apatite crystals. Importantly, FTIR spectral features of the apatite crystals (e.g., the prominent PO4 bands at 1125 and 1032 cm-1) were similar to those of cartilage apatites formed in vivo and differed markedly from those of carbonated bone apatites. These results suggest that growth plate chondrocytes cultured on collagen-coated dishes are an appropriate model for studies on cartilage mineralization.

Alkaline Phosphatase↗

PubMed1999

Use of Dicalcium Phosphate Dihydrate as a Probe in an Approach for Accurate Calculations of Solution Equilibria in Buffered Calcium Phosphate Systems.

Both synthetic and biological carbonated apatites have been shown to possess metastable equilibrium solubility (MES) distributions. Investigation of their MES behavior requires accurate knowledge of the activities of the relevant ions over a range of solution compositions. This in turn requires that the activity coefficients for these ions and the stability constants for the various solution complexes be accurately known. Since the solubility of dicalcium phosphate dihydrate (DCPD) can be easily determined, it can be used as a probe to study the appropriateness of proposed sets of stability constants and activity coefficients. In the present study, the solubility of DCPD was determined in acetate buffer solutions at pHs ranging from 4.5 to 6.5 and this allowed for the determination and evaluation of the stability constants of the NaHPO(-)(4), CaHPO(0)(4), CaH(2)PO(+)(4), and CaAc(+) complexes. The activity coefficients were calculated by a modification of the extended Debye-Hückel method and also by Bockris and Reddy's method, in which the activity of water and the hydration numbers of ions are also considered. The solution conditions were controlled to simulate the dissolution media used for the determination of MES distributions of apatites in our laboratory. Both methods of activity coefficient determination gave very consistent DCPD solubility product (K(DCPD)) values, and values for the stability constants of the relevant complexes determined using the two methods were close to each other. This approach of determining the stability constants under a set of conditions similar to those in apatite dissolution studies offers an effective set of parameters which, though not necessarily always exactly correct in absolute terms, are internally consistent and should allow for the quantitative characterization of the MES behavior of apatites. Copyright 1999 Academic Press.

Journal Article↗