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Constant composition dissolution of mixed phases II. Selective dissolution of calcium phosphates
Abstract
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.
... This may be achieved through surface modifications, and the deposition of hydroxyapatite [Ca10(PO4)6(OH)2, HA] coatings on Ti substrates is generally applied. HA has become one of the most widely used biomedical materials because of its similar properties to bone [6,7]. Therefore, the strategies of coating Ti implants with HA coatings may combine the good mechanical properties of Ti with the excellent bioactivity of HA. ...
... Biological apatite is defined as nonstoichiometric apatite with various substitutions of other metallic ions for calcium ions. The incorporation of some elements, such as silicon and strontium, into the apatite crystal lattice could significantly improve the physicochemical and biological performances of HA [7][8][9][10][11]. ...
... The degradation of HA coatings is affected by the chemical composition, crystallinity, particle size, Ca/P ratio, preparation conditions, density and extent of ionic substitutions into the apatite lattice [38][39][40]. According to XRD, FTIR SEM and EDX results, the incorporation of lanthanum led to formation of uniform, crack-free La-HA coatings with enhanced crystallity, which contributed to the measured lower degradation rate of the La-HA coating [7,41]. The sustained release of incorporated ions, calcium and phosphate around the implant surface promotes the growth of the bone by increasing local supersaturation [42]. ...
Titanium (Ti) has been widely used in clinical applications for its excellent biocompatibility and mechanical properties. However, the bioinertness of the surface of Ti has motivated researchers to improve the physicochemical and biological properties of the implants through various surface modifications, such as coatings. For this purpose, we prepared a novel bioactive material, a lanthanum-incorporated hydroxyapatite (La-HA) coating, using a dip-coating technique with a La-HA sol along with post-heat treatment. The XRD, FTIR and EDX results presented in this paper confirmed that lanthanum was successfully incorporated into the structure of HA. The La-HA coating was composed of rod-like particles which densely compacted together without microcracks. The results of the interfacial shear strength test indicated that the incorporation of lanthanum increased the bonding strength of the HA coating. The mass loss ratios under acidic conditions (pH = 5.5) suggested that the La-HA coatings have better acid resistance. The cytocompatibility of the La-HA coating was also revealed by the relative activity of alkaline phosphatase, cellular morphology and cell proliferation assay in vitro. The present study suggested that La-HA coated on Ti has promising potential for applications in the development of a new type of bioactive coating for metal implants.
... Such formulations have superior in vivo resorbability, as opposed to conventional apatitic cements. The scientific basis behind this development can be clearly explained by the dissolution data published by Tang et al. 11 Relying on the experimental solubility values of some of the calcium phosphate phases recently reported by Tang et al., 11 it is seen that DCPD has a dissolution rate of 4.26 ϫ 10 Ϫ4 mol⅐m Ϫ2 ⅐min Ϫ1 at a pH value of 5.5, and this rate is only about 3.4 times greater than that of Ca 3 (PO 4 ) 2 (i.e., 1.26 ϫ 10 Ϫ4 ). To compare these, the dissolution rate for carbonated apatite was reported by the same researchers 11 to be 1.42 ϫ 10 Ϫ6 . ...
... Such formulations have superior in vivo resorbability, as opposed to conventional apatitic cements. The scientific basis behind this development can be clearly explained by the dissolution data published by Tang et al. 11 Relying on the experimental solubility values of some of the calcium phosphate phases recently reported by Tang et al., 11 it is seen that DCPD has a dissolution rate of 4.26 ϫ 10 Ϫ4 mol⅐m Ϫ2 ⅐min Ϫ1 at a pH value of 5.5, and this rate is only about 3.4 times greater than that of Ca 3 (PO 4 ) 2 (i.e., 1.26 ϫ 10 Ϫ4 ). To compare these, the dissolution rate for carbonated apatite was reported by the same researchers 11 to be 1.42 ϫ 10 Ϫ6 . ...
... The scientific basis behind this development can be clearly explained by the dissolution data published by Tang et al. 11 Relying on the experimental solubility values of some of the calcium phosphate phases recently reported by Tang et al., 11 it is seen that DCPD has a dissolution rate of 4.26 ϫ 10 Ϫ4 mol⅐m Ϫ2 ⅐min Ϫ1 at a pH value of 5.5, and this rate is only about 3.4 times greater than that of Ca 3 (PO 4 ) 2 (i.e., 1.26 ϫ 10 Ϫ4 ). To compare these, the dissolution rate for carbonated apatite was reported by the same researchers 11 to be 1.42 ϫ 10 Ϫ6 . ...
The aim of this paper is to develop a robust chemical process to synthesize Na- and K-doped brushite (DCPD: dicalcium phosphate dihydrate, CaHPO4·2H2O), a potential starting material for bone substitutes. The powders were synthesized by using sodium phosphate and potassium phosphate and aqueous solutions containing calcium chloride at room temperature, followed by drying at 37°C. DCPD powders thus formed were found to contain 460 ppm K and 945 ppm Na. On calcination in air, these powders readily transformed into monetite (DCPA: dicalcium phosphate anhydrous, CaHPO4) first, and then into Ca2P2O7 (calcium pyrophosphate). Na- and K-doped DCPD powders were shown to completely transform, in less than 1 week, into poorly crystalline carbonated apatite on immersion in an acellular simulated/synthetic body fluid (SBF) solution at 37°C. The Tris (i.e., tris(hydroxymethyl)aminomethane) buffered SBF solution used in this study had a carbonate ion concentration of 27 mM equal to that of human plasma. DCPD powders of this study displayed a notable apatite-inducing ability. This finding suggests the use of these DCPD powders as the starting materials for potential bone substitutes, which can be easily manufactured in aqueous solutions friendly to living tissues, at temperatures between room temperature and 37°C.
... For example, citric acid significantly inhibited the dissolution of HA, but had little influence on the dissolution of DCPD at 37 °C (pH = 5.50). 38 The applications of DCPD in the biomedical, food, and many other fields face the challenge of precise control of crystalline structure and properties due to various possible phase transformations of 'active' DCPD in presence of different additives and physiological environments. For example, DCPD can transform into DCPA (CaHPO4) at temperature above ~ 80 °C. 4 This transformation is accompanied by structural changes 39 and decrease in volume (~ 11%) 40 . ...
... The acidic condition was demonstrated to be favorable for the dissolution of DCPD. 38 To investigate the dissolution of DCPD with and without the addition of LAC, we put the above-mentioned three samples, DCPD-S (from SBF), DCPD-D (from DPBS), DCPD-C (commercial reference) in water at ambient conditions. As shown in Figure S30, in absence of LAC, turbidity was not observed in water after 24 h and 48 h, which could be understood with the very low solubility of DCPD in water (~ 0.088 g/L) at 25 °C 3, 4 . ...
The ubiquitous mineralization of calcium phosphate (CaP) facilitates biological organisms to produce hierarchically structured minerals. The coordination number and strength of Ca2+ ions with phosphate species, oxygen-containing additives, and solvent molecules played a crucial role in tuning nucleation processes and surface stability of CaP under the simulated body fluid (SBF) or aqueous solutions upon the addition of oligomeric lactic acid (LACn, n=1, 8) and changing pH values. As revealed by ab initio molecular dynamics (AIMD), density functional theory (DFT), and molecular dynamics (MD) simulations as well as high-throughput experimentation (HTE), the binding of LAC molecules with Ca2+ ions and phosphate species could stabilize both pre-nucleation clusters and brushite (DCPD, CaHPO4·2H2O) surface through intermolecular electrostatic and hydrogen bonding interactions. When the concentration of Ca2+ ions ([Ca2+]) is very low, the amount of the formed precipitation decreased with the addition of LAC based on UV-Vis spectroscopic analysis due to the reduced chance for the LAC capped Ca2+ ions to coordinate with phosphates and the increased solubility in acid solution. With the increasing [Ca2+] concentration, the kinetically stable DCPD precipitation was obtained with high Ca2+ coordination number and low surface energy. Morphologies of DCPD precipitation are in plate, needle, or rod, depending on the initial pH values that tuned by adding NH3·H2O, HCl, or CH3COOH. The prepared samples at pH ≈ 7.4 with different Ca/P ratios exhibited negative zeta potential values, which were correlated with the surface electrostatic potential distributions and potential biological applications.
... For example, citric acid significantly inhibited the dissolution of HA but had little influence on the dissolution of DCPD at 37°C (pH = 5.50). 38 The applications of DCPD in the biomedical, food, and many other fields face the challenge of precise control of crystalline structure and properties due to various possible phase transformations of ″active″ DCPD in the presence of different additives and physiological environments. For example, DCPD can transform into DCPA (CaHPO 4 ) at temperatures above ∼80°C. ...
... The acidic condition was demonstrated to be favorable for the dissolution of DCPD. 38 To investigate the dissolution of DCPD with and without the addition of LAC, we put the above-mentioned three samplesDCPD-S (from SBF), DCPD-D (from DPBS), and DCPD-C (commercial reference)in water at ambient conditions. As shown in Figure S30, in the absence of LAC, turbidity was not observed in water after 24 and 48 h, which could be understood with the very low solubility of DCPD in water (∼0.088 ...
... For example, citric acid significantly inhibited the dissolution of HA, but had little influence on the dissolution of DCPD at 37 °C (pH = 5.50). 38 The applications of DCPD in the biomedical, food, and many other fields face the challenge of precise control of crystalline structure and properties due to various possible phase transformations of 'active' DCPD in presence of different additives and physiological environments. For example, DCPD can transform into DCPA (CaHPO4) at temperature above ~ 80 °C. 4 This transformation is accompanied by structural changes 39 and decrease in volume (~ 11%) 40 . ...
... The acidic condition was demonstrated to be favorable for the dissolution of DCPD. 38 To investigate the dissolution of DCPD with and without the addition of LAC, we put the above-mentioned three samples, DCPD-S (from SBF), DCPD-D (from DPBS), DCPD-C (commercial reference) in water at ambient conditions. As shown in Figure S30, in absence of LAC, turbidity was not observed in water after 24 h and 48 h, which could be understood with the very low solubility of DCPD in water (~ 0.088 g/L) at 25 °C 3, 4 . ...
The ubiquitous mineralization of calcium phosphate (CaP) facilitates biological organisms to produce hierarchically structured minerals. The coordination number and strength of Ca2+ ions with phosphate species, oxygen-containing additives, and solvent molecules played a crucial role in tuning nucleation processes and surface stability of CaP under the simulated body fluid (SBF) or aqueous solutions upon the addition of oligomeric lactic acid (LACn, n=1, 8) and changing pH values. As revealed by ab initio molecular dynamics (AIMD), density functional theory (DFT), and molecular dynamics (MD) simulations as well as high-throughput experimentation (HTE), the binding of LAC molecules with Ca2+ ions and phosphate species could stabilize both pre-nucleation clusters and brushite (DCPD, CaHPO4·2H2O) surface through intermolecular electrostatic and hydrogen bonding interactions. When the concentration of Ca2+ ions ([Ca2+]) is very low, the amount of the formed precipitation decreased with the addition of LAC based on UV-Vis spectroscopic analysis due to the reduced chance for the LAC capped Ca2+ ions to coordinate with phosphates and the increased solubility in acid solution. With the increasing [Ca2+] concentration, the kinetically stable DCPD precipitation was obtained with high Ca2+ coordination number and low surface energy. Morphologies of DCPD precipitation are in plate, needle, or rod, depending on the initial pH values that tuned by adding NH3·H2O, HCl, or CH3COOH. The prepared samples at pH ≈ 7.4 with different Ca/P ratios exhibited negative zeta potential values, which were correlated with the surface electrostatic potential distributions and potential biological applications.
... Recently, dicalcium phosphate anhydrate (DCPA; CaHPO 4 ) and dicalcium phosphate dihydrate (DCPD; CaHPO 4 Á2H 2 O) also have received attention due to their favorable osteoinductive and bioresorbable properties. Dicalcium phosphates are one of the fastest resorbable CaP materials with the re-sorption rate of DCPD at a pH of 5.5 being approximately three times and three hundred times faster than that of TCP and carbonated HAp, respectively (Tang et al., 2003). Dissolution or re-sorption of a hard tissue scaffold is required for allowing simultaneous replacement with new bone tissues, and finally for obtaining complete repair without remnant of the artificial substitutes. ...
... Dissolution or re-sorption of a hard tissue scaffold is required for allowing simultaneous replacement with new bone tissues, and finally for obtaining complete repair without remnant of the artificial substitutes. Osteoinductivity is another key property as it plays a critical role in curing large size bone defects (Habibovic et al., 2006(Habibovic et al., , 2008Tang et al., 2003). ...
Electrospun nanofibers have attracted increasing interest as a tissue-engineering scaffold. This can be attributed to the relative simplicity and cost-effectiveness of the electrospinning process for the creation of nanofibrous structures that have unique characteristics that are favorable for tissue regeneration. The topography of the electrospun nanofibrous scaffolds resembles that of the natural extracellular matrix of human tissues. The ultra-high surface area to volume ratio and 3D interconnected porosity of the scaffolds enhance cell attachment and proliferation. Various materials including biodegradable, nondegradable, and natural polymers have been electrospun into randomly oriented or aligned fibers, thus providing many mechanisms for the tuning of degradation rates, mechanical properties, and biological response of the scaffolds for specific tissue applications. This chapter introduces recent advancement and discoveries of electrospinning technology for tissue regeneration applications with a focus on surface and structural modification of nanofiber matrix. Recent in vitro and in vivo assessment of electrospun nanofibrous scaffolds are also discussed in relation to soft and hard tissue regeneration.
... In contrast, groundwater samples from the Lehstenbach catchment showed pH values between 4 and 7. More complex dissolution experiments at different pH ranges and using different experimental conditions are described by Guidry and McKenzie (2003), Tang et al. (2003), Valsami-Jones et al. (1998), andJahnke (1984). Although these experiments tend to provide quantitative information about the dissolution rates of different minerals, Casey et al. (1993) point out that the appropriate level of comparison of field and laboratory weathering is at the scale of reactivity trends and not at that of quantitative similarity in reaction rates. ...
... However, the dissolution rate of apatite is pH dependent and is at its minimum at circumneutral pH, corresponding to the range of pH 5-7 in the waters in the Lehstenbach catchment (Wu and Forsling, 1995;Valsami-Jones et al., 1998;Guidry and McKenzie, 2003). Although the dissolution rate of apatite depends also on factors such as the distance from equilibrium (Guidry and McKenzie, 2003), the carbonate content (Jahnke, 1984) and the presence of weak acids (Tang et al., 2003), the dissolution rate of apatite is always higher than those of silicate minerals (feldspars, biotite), but lower than those of carbonates (calcite, dolomite). ...
From a biogeochemical perspective, catchments can be regarded as reactors that transform the input of various substances via precipitation, deposition, or human activities as they pass through soils and aquifers towards receiving streams. Understanding and modeling the variability of solute concentration in catchment waters require the identification of prevailing processes, determining their respective contributions to the observed transformation of substances, their interplay with hydrological processes, and the determination of anthropogenic impacts. However, numerous biogeochemical processes often interact in a highly non-linear way and vary on temporal and spatial scales, resulting in temporally and spatially varying water chemistry in catchments. This is particularly true for riparian wetlands. Processes in this catchment area often superimpose the influence of the hill slope (and largest) area of the catchment on surface water quality. Accordingly, the first part of this thesis (Study 1 and 2), focuses on the temporal and spatial variability of biogeochemical processes at the catchment scale. Therefore, the first aim was to identify the prevailing biogeochemical processes which affect the quality of catchment waters in two forested granitic catchments. Based on these results, (i) the long-term behavior of these processes was determined (Study 1) and (ii) hot spots of these processes at the catchment scale along different flow paths were identified (Study 2). The second part (Study 3) focuses on the interplay between hydrological and biogeochemical processes in a riparian wetland, with the aim of systematically tracing back the temporal patterns of stream water chemistry to different biogeochemical processes and antecedent hydrological boundary conditions in the wetland. The third part (Study 4 and 5) focuses on weathering processes with the goal (i) of identifying the mineralogical sources of the groundwater’s buffer capacity against acid atmospheric deposition in a forested granitic catchment and (ii) determining the mineralogical sources of the high cation loads in surface water, induced by intensive agricultural activities in two agricultural granitic catchments. To reach these aims, multivariate statistical methods of dimensionality reduction (linear Principal Component Analysis, non-linear Isometric Feature Mapping), a low-pass filtering of time-series, a Cluster analysis, and major and trace element ratios and strontium isotopes were used. A small number of biogeochemical process bundles explained 94% and 89% of the variance of the data set in Study 1 and 2, respectively. In Study 1, redox and topsoil processes, road salt and sulfate contamination were identified as predominating processes influencing water chemistry in the respective catchments. Low-pass filtered time series of component scores revealed a different long-term behavior at different sampling sites in both catchments, which could be traced back to the fraction of wetland area in the respective subcatchments as well as by the varying thickness of the regolith. Study 2 revealed that the upper 1 m topsoil layer could be considered as a biogeochemical hot spot for redox processes, acid-induced podsolization, and weathering processes along different flow paths. Up to 97% of the biogeochemical transformation of the chemical composition of soil solution, groundwater and stream water in the Lehstenbach catchment was restricted to this soil layer representing less than 2% of the catchment’s regolith. Wetland stream water, mobilized in the topsoil layer being considered a biogeochemical hot spot, showed a highly dynamic temporal pattern of component scores. Study 3 revealed four different types of wetland stream water chemical status, depending on the interplay between discharge dynamics, biological activity, and the water table position in the wetland. The sequence of different stream water types roughly followed a seasonal pattern, albeit being heavily modified by the respective hydrological boundary conditions for different years. Extended periods of low groundwater level in the second half of the growing season drastically changed the chemical boundary conditions, becoming evident in a drastic reoxidation of reduced species like sulfides and corresponding effects. Weathering processes are one of the predominating biogeochemical process bundles influencing water chemistry in forested catchments. Study 4 showed that the mineralogical sources of the groundwater’s buffer capacity against acid atmospheric deposition were dominated by the release of base cations from apatite dissolution, preferential cation release from feldspars and biotite, and feldspars weathering. In Study 5, determining the mineralogical sources of the high cation loads in surface water induced by intensive agricultural activities revealed a dominant manure contribution in the topsoil, and enhanced mineral dissolution (plagioclase and biotite) by fertilizer application in subsoils, becoming the unique source of base cations in the saprolite. Stream water chemistry differed from that of soil water, suggesting that stream water chemistry was dominated by elements issued from enhanced mineral and rock weathering. Soil acidification induced by agriculture allows the mobilization of cations stored in soil layers, enhances the rock weathering and accelerates plagioclase dissolution, which can highly influence stream water quality. Numerous biogeochemical, hydrological, and anthropogenic processes were found to interact with each other, mostly with non-linear patterns, influencing catchment water chemistry. The integral approach used in this thesis would be a useful prerequisite to develop accurate and parsimonious models commonly used for water management purposes by distinguishing between short- term and long-term shifts, reducing the number of processes to the predominating ones ultimately to be included in the model, focusing on hot spots and including spatial patterns where necessary and appropriate.
... Moreover, with the resorption rate faster than that of carbonated apatite and beta-tricalcium phosphate, DCPs are one of the fastest resorbable CaP materials. [19] Hence, a bioactive dicalcium phosphate anhydrate/multi-(amino acid) (DCPA/MAA) composite was fabricated to fit these characteristics. 25 In this study, we introduced DCPA into MAA to synthesize DCPA/MAA composite in situ polymerization. ...
... Coll: QC: Initial peaks. As compared with the MAA copolymer, however, the intensity of two 5 diffraction peaks in the composite dramatically declined, which is confirmed from observed characteristic peaks at diffracted angles (2θ) 19.75 and 23.57, respectively. ...
This study aims to evaluate in vitro degradability and osteoblast biocompatibility of dicalcium phosphate anhydrate/multi-(amino acid) (DCPA/MAA) composites prepared by in situ polymerization method. The results revealed that the composites could be slowly degraded in PBS solution, with weight loss of 9.5 ± 0.2 wt.% compared with 12.2 ± 0.2 wt.% of MAA copolymer after eight weeks, and the changes of pH value were in the range of 7.18-7.4 and stabilized at 7.24. In addition, the compressive strength of the composite decreased from 98 to 62 MPa while that of MAA copolymer from 117 to 86 MPa. Furthermore, with non-toxicity demonstrated by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide assay, the addition of DCPA to the MAA copolymer evidenced an enhancement of osteoblast differentiation and attachment compared with pure MAA materials regarding to alkaline phosphatase activity as well as initial cell adhesion. The results indicated that the DCPA/MAA scaffolds with good osteoblast biocompatibility, degradability, and sufficient strength had promising potential application in bone tissue engineering.
... [50][51][52] The dissolution rate of calcite at pH 5 is around 3 9 10 À6 mol·m −2 ·s -1 , whereas the same value for aragonite is about half of this, 1.3 9 10 À6 mol·m −2 ·s -1 . [50][51][52] To compare directly, the dissolution rate for brushite (in water) was reported by Tang et al. 53 to be 7.1 9 10 À6 mol·m −2 ·s -1 at pH 5.5 and RT. What happens within the first 15-16 min shown in Fig. 4(a) can best be explained by the below equations, 54 i.e., the affinity of CaCO 3 to steal a proton from the dissolved ammonium dihydrogen phosphate playing a key role; ...
... 56 If the solution pH in this crystallization system remains over the narrow range of 5.44-5.74 for about 24 h [see Fig. 4(a)] and if over this pH range brushite has a significant dissolution rate, 53 would it be possible to see at least some evidence of dissolution-reprecipitation processes on the formed brushite crystals? The answer was positive and almost all the high magnification SEM photomicrographs captured in this study were showing submicron spikes, nanothick sheets or dissolution spots as the one reproduced in Fig. 4(b) (for the composition of sample-1). ...
Conventional flat plate‐shaped brushite, dicalcium phosphate dihydrate, CaHPO4·2H2O), produced by reacting Ca‐chloride and alkali phosphate salt solutions, were found to undergo a maturation process (changing their Ca/P molar ratio from 0.8 to the theoretical value of 1) similar to those seen in biological apatites. Water lily (WL)‐shaped brushite crystals were produced in nonstirred aqueous solutions at room temperature in 24 h, by using precipitated calcite and NH4H2PO4 as the starting chemicals. The hydrothermal transformation of WL‐type brushite into octacalcium phosphate (OCP) or Ca‐deficient hydroxyapatite (CDHA) was tested at 37°C by using four different biomineralization solutions, including Tris‐buffered SBF (synthetic body fluid) and sodium lactate‐buffered SBF solutions. All four solutions used in this study consumed the starting brushite in 1 week and caused transformation into a biphasic mixture of nanocrystalline OCP and CDHA of high surface area. WL‐type brushite crystals when synthesized in the presence of small amounts of Zn2+ ions resulted in the formation of, for the first time, spherical micro‐granules of brushite. Synthesis of brushite in spherical form was difficult prior to this study.
... In contrast, groundwater samples from the Lehstenbach catchment showed pH values between 4 and 7. More complex dissolution experiments at different pH ranges and using different experimental conditions are described by Guidry and McKenzie (2003), Tang et al. (2003), Valsami-Jones et al. (1998, and Jahnke (1984). Although these experiments tend to provide quantitative information about the dissolution rates of different min- erals, Casey et al. (1993) point out that the appropriate level of comparison of field and laboratory weathering is at the scale of reactivity trends and not at that of quantitative similarity in reaction rates. ...
... However, the dissolution rate of apatite is pH dependent and is at its minimum at circumneutral pH, corresponding to the range of pH 5–7 in the waters in the Lehstenbach catchment (Wu and Forsling, 1995; Valsami-Jones et al., 1998; Guidry and McKenzie, 2003). Although the dissolution rate of apatite depends also on factors such as the distance from equilibrium (Guidry and McKenzie, 2003), the carbonate content (Jahnke, 1984) and the presence of weak acids (Tang et al., 2003), the dissolution rate of apatite is always higher than those of silicate minerals (feldspars, biotite), but lower than those of carbonates (calcite, dolomite). Based on Sr isotope and element ratios, the influence of apatite could not be distinguished from dolomite as a base cation source (Figs. 4 and 6). ...
The role of different minerals in base cation release and thus the increase of buffering capacity of groundwater against acid deposition is controversially discussed in the literature. The ⁸⁷Sr/⁸⁶Sr ratios and base cation concentration were investigated in whole rock leachates, mineral separates, precipitation, soil solution, groundwater and stream water samples in the Lehstenbach catchment (Germany) to identify the weathering sequence of the granite bedrock. Three different approaches were followed in parallel. It was assumed that the contribution of different minerals to base cation supply of the groundwater with increasing weathering intensity would be observed by investigating (1) unweathered rock leachates, deep groundwater and shallow groundwater, (2) groundwater samples from new groundwater wells, reflecting the initial weathering of the drilled bedrock, and groundwater from wells that were drilled in 1988, (3) stream water during baseflow, dominated by deep groundwater, and stream water during high flow, being predominantly shallow groundwater. Whereas the first approach yielded consistent patterns, there was some evidence that groundwater from the new wells initially reflected contamination by the filter gravel rather than cation release in an initial stage of weathering. Time series samples of stream water and groundwater solute concentrations and isotope ratios turned out to reflect varying fractions of soil water and precipitation water at baseflow and high flow conditions rather than varying contributions of different minerals that prevail at different stages of granite weathering.
... While the long-term dynamics of geogenic Ca-P are relatively well quantified (Walker and Syers 1976; Crews et al. 1995; Vitousek and Farrington 1997; Hedin et al. 2003), limited information is available on the time required for transformation of biogenic Ca-P. Since biogenic Ca-P structurally differs from geogenic Ca-P (Rao et al. 2000; Tang et al., 2003a), different dynamics can be expected. This study has, as objectives, to determine the transformation characteristics of biogenic Ca-P over a long period of time stretching from centennial to millennial time scales and to compare the transformation dynamics between biogenic Ca-P from this study and geogenic Ca-P as modeled by Walker and Syers (1976). ...
... Therefore, highly weathered, acid soils of the humid tropical environment in the central Amazon may have accelerated dissolution and weathering rates of Ca-P in soil. Dissolution rates of Ca-P compounds also depend on species, source, or crystal structure of the compound itself (Tang et al. 2003a). Comparing different phosphorites from western India, Rao et al. (2000) found that constituents and porosity of the initial substrate and physio-chemical conditions at the time of their formation were responsible for differences in macroscopic characteristics of phosphorites . ...
Background, aim, and scope
Changes in bioavailability of phosphorus (P) during pedogenesis and ecosystem development have been shown for geogenic calcium phosphate (Ca-P). However, very little is known about long-term changes of biogenic Ca-P in soil.
Materials and methods
Long-term transformation characteristics of biogenic Ca-P were examined using anthropogenic soils along a chronosequence from centennial to millennial time scales.
Results and discussion
Phosphorus fractionation of Anthrosols resulted in overall consistency with the Walker and Syers model of geogenic Ca-P transformation during pedogenesis. The biogenic Ca-P (e.g., animal and fish bones) disappeared to 3% of total P within the first ca. 2,000 years of soil development. This change concurred with increases in P adsorbed on metal-oxides surfaces, organic P, and occluded P at different pedogenic time. Phosphorus K-edge X-ray absorption near-edge structure (XANES) spectroscopy revealed that the crystalline and therefore thermodynamically most stable biogenic Ca-P was transformed into more soluble forms of Ca-P over time. While crystalline hydroxyapatite (34% of total P) dominated Ca-P species after about 600–1,000 years, β-tricalcium phosphate increased to 16% of total P after 900–1,100 years, after which both Ca-P species disappeared. Iron-associated P was observable concurrently with Ca-P disappearance. Soluble P and organic P determined by XANES maintained relatively constant (58–65%) across the time scale studied.
Conclusions
Disappearance of crystalline biogenic Ca-P on a time scale of a few thousand years appears to be ten times faster than that of geogenic Ca-P.
... MCP would therefore, if found on Mars, be an indicator of low-water rock ratios. Brushite has also been reported to dissolve 3-4 orders of magnitude more rapidly than fluorapatite [211], and the presence of brushite would therefore also indicate extremely low-water rock conditions. Similar to secondary calcium phosphates such as MCP and brushite, Mg phosphates such as newberyite are very soluble, with their presence in meteorites [212] similarly indicating low-water conditions. ...
This paper reviews the phosphate phases in meteorites and those measured by landed spacecraft, what they reveal about past igneous and aqueous conditions on Mars, and important implications for potential prebiotic chemistry, past habitability, and potential biosignatures that could be detected in samples returned from Mars. A review of the 378 martian meteorites as of 2023 indicate that of the two most common phosphate minerals in Mars meteorites, merrillite and apatites, the apatite composition is largely F- and Cl-rich, with shergottites containing more OH. The phosphate concentrations examined across multiple missions show a relatively narrow range of phosphate, with higher concentrations observed in the Mount Sharp Group in Gale crater and Wishstone at Gusev crater and lower concentrations observed at Jezero crater floor and Jezero fan. Possible secondary phosphates detected on Mars, including Fe phosphates at Jezero crater and Gusev crater and Ca- and Al-bearing secondary phosphates, temperatures of formation of secondary phases and their dissolution rates and solubilities are reviewed and summarized. Despite this wealth of information about phosphates on Mars, due to their fine scale and relatively low concentrations, Mars Sample Return is needed to better understand phosphate and its implications for the igneous, aqueous, and astrobiological history of Mars.
... Calcium phosphates as inorganic materials can provide cell-binding sites, helping cells to adhere to their surface and release ionic species, which can promote cell proliferation, differentiation, and extracellular matrix mineralization [32]. In our study, β-TCP was added into the chitosan hydrogel instead of hydroxyapatite because (1) β-TCP resorbs faster than hydroxyapatite and it can be gradually resorbed by the body, whilst hydroxyapatite remains in the body for a longer period [33,34], and hence, β-TCP has advantages in some applications such as drug delivery compared to hydroxyapatite; (2) β-TCP is often used where rapid bone regeneration is required, but hydroxyapatite is used when long-term structural support is needed [35]. The successful β-TCP/chitosan mixture hydrogels were confirmed with the XRD and FTIR results, and the presence of β-TCP did not inhibit the gelation progress. ...
The current treatment for periodontitis is aimed at resolving gingival inflammation, whilst complete periodontal tissue regeneration is not predictable, and it represents a therapeutic challenge. Injectable biomaterials hold tremendous potential in dental tissue regeneration. This study aimed to investigate the ability of an injectable thermosensitive β-tricalcium phosphate (β-TCP) and chitosan-based hydrogel to carry cells and promote periodontal tissue regeneration. In this study, different concentrations of β-TCP-loaded chitosan hydrogels were prepared (0%, 2%, 4%, or 6% β-TCP, 10% β-glycerol phosphate, and 1.5% chitosan). The characteristics of the hydrogels were tested using rheology, a scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), degradation, and biological analyses. The new biomaterial showed a sol–gel transformation ability at body temperature and exhibited excellent chemical and physical characteristics, whilst the existence of β-TCP enhanced the structure and the properties of the hydrogels. The SEM confirmed the three-dimensional networks of the hydrogels, and the typical rheological properties of strong gel were observed. The EDX and XRD validated the successful incorporation of β-TCP, and similar patterns between different groups were found in terms of the FTIR spectra. The stable structure of the hydrogels under 100 °C was confirmed via DSC. Biological tests such as Alamar Blue assay and Live/Dead staining confirmed the remarkable biocompatibility of the hydrogels with pre-osteoblast MC3T3-E1 and human gingival fibroblast (HGF) cells for 14 days, and the results were validated with confocal imaging. This preliminary study shows great promise for the application of the β-TCP-loaded thermosensitive chitosan hydrogels as a scaffold in periodontal bone and soft tissue repair.
... The underlying idea is an advanced adsorption and enrichment of modified peptides into the pellicle layers and onto the enamel surfaces [160]. As a result, these proteins or modified peptides reduce the amount of enamel dissolution areas [160,[166][167][168]. Additionally, these adsorbed proteins or peptides limit the acid transfer from biofilm communities onto the hydroxyapatite surface and vice versa, reducing the dissolution and diffusion of calcium and phosphate ions into the oral cavity [160,169]. ...
Background:
Bioadhesion and surface interactions on enamel are of essential relevance for initiation, progression and prevention of caries and erosions. Salivary proteins on and within initial carious and erosive lesions can facilitate or aggravate de- and remineralization. This applies for the pellicle layer, the subsurface pellicle and for proteins within initial carious lesions. Little is known about these proteinaceous structures related to initial caries and erosion. Accordingly, there is a considerable demand for an understanding of the underlying processes occurring at the interface between the tooth surface and the oral cavity in order to develop novel agents that limit and modulate caries and erosion. Objectives and findings: The present paper depicts the current knowledge of the processes occurring at the interface of the tooth surface and the oral fluids. Proteinaceous layers on dental hard tissues can prevent or aggravate demineralization processes, whereas proteins within initial erosive or carious lesions might hinder remineralization considerably and restrict the entry of ions into lesions.
Conclusions:
Despite the fact that organic-inorganic surface interactions are of essential relevance for de- and remineralization processes at the tooth surface, there is limited knowledge on these clinically relevant phenomena. Accordingly, intensive research is necessary to develop new approaches in preventive dentistry.
... DR9-RR14 peptide adsorbed onto the enamel may potentially be controlling the caries process by limiting the formation of enamel dissolution foci [30][31][32]. By doing so, this peptide reduces the diffusion of acids from the biofilm to the enamel mineral, or limits the transport of the dissolved dental mineral ions into the culture medium, as previously observed when the AEP was formed from total saliva [12]. ...
Engineering of the acquired enamel pellicle using salivary peptides has been shown to be a promising anticaries strategy. However, the mechanisms by which these peptides protect teeth against tooth decay are not fully understood. In this study, we evaluated the effect of the engineered salivary peptides DR9-DR9 and DR9-RR14 on enamel demineralization in two experimental conditions: (1) adsorbed onto the enamel surface forming the AEP, and (2) forming the AEP combined with their use to treat the biofilms 2×/day, using a validated cariogenic Streptococcus mutans in vitro biofilm model. Biofilms were grown for 144 h on enamel slabs and then collected to determine the bacterial viability (CFU/biofilm) and biofilm mass (mg protein/biofilm), and to extract cellular/extracellular proteins, which were characterized by mass spectrometry. The culture medium was changed 2×/day to fresh medium, and pH (indicator of biofilm acidogenicity) and calcium concentration (indicator of demineralization) was determined in used medium. DR9-RR14 peptide significantly reduced enamel demineralization (p < 0.0001) in both experimental conditions. However, this peptide did not have a significant effect on biofilm biomass (p > 0.05) nor did it modulate the expression of cellular and extracellular bacterial proteins involved in biofilm cariogenicity. These findings suggest that DR9-RR14 may control caries development mainly by a physicochemical mechanism.
... 4 The precipitation and dissolution hydroxyapatite crystal is a controlled process regulated by either crystal growth within the crystal nuclei or due to the activity of salivary peptides that alter the HAP surface energy. 5 Kosoric et al. studied the effectiveness of protein on HAP aggregation which also depends on degree of saturation, low HAP porosity and protein concentration. Hence found bovine albumin to be potent against demineralization. ...
Objective: The aim of this study was to analyze the effect of salivary proteins (statherin and histatin-1) on demineralized enamel surface and to study changes in texture, magnitude and direction of crystallites and changes in prismatic structure of enamel respectively. Material & Methods: Synchrotron x-ray diffraction technique to determine the variation in degree of crystal orientation (texture). Incisors were demineralized and sectioned to 300-500 microns, rinsed with salivary protein solutions of statherin and histatin separately and in combination with short and full-lengths. A beam spot size of 20μm × 20μm was used to obtain 2D diffraction patterns to distinguish orientation of crystallites. Results: The contour maps as well as the SEM analysis present similar surface properties of the sample treated with STN-21 and the controlled PBS sample. Therefore, STN-21 was found potent in preventing demineralization and restoring surface enamel texture followed by STN-21+HTN-21 and STN43+HTN38. HTN-21 and HTN-38 showed similar demineralization pattern as the controlled demineralized sample. Conclusion: Ranking of demineralization among samples was found to be controlled demineralized > HTN-21 = HTN-38 > STN-43+HTN-38 > STN-21+HTN-21 > STN-21. Developing STN-21 as a therapeutic against dental caries and erosion. Keywords: Enamel, Demineralization, salivary proteins.
... β-TCP has the same composition as α-TCP but with a different lattice structure, resulting in slightly reduced degradability and favorable bioresorption but poorer bioactivity [20]. Therefore, many clinical bone filling materials are composed of a biphasic combination of HA and β-TCP [21,22]. ...
Oyster shells are rich in calcium, and thus, the potential use of waste shells is in the production of calcium phosphate (CaP) minerals for osteopathic biomedical applications, such as scaffolds for bone regeneration. Implanted scaffolds should stimulate the differentiation of induced pluripotent stem cells (iPSCs) into osteoblasts. In this study, oyster shells were used to produce nano-grade hydroxyapatite (HA) powder by the liquid-phase precipitation. Then, biphasic CaP (BCP) bioceramics with two different phase ratios were obtained by the foaming of HA nanopowders and sintering by two different two-stage heat treatment processes. The different sintering conditions yielded differences in structure and morphology of the BCPs, as determined by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Brunauer–Emmett–Teller (BET) surface area analysis. We then set out to determine which of these materials were most biocompatible, by co-culturing with iPSCs and examining the gene expression in molecular pathways involved in self-renewal and differentiation of iPSCs. We found that sintering for a shorter time at higher temperatures gave higher expression levels of markers for proliferation and (early) differentiation of the osteoblast. The differences in biocompatibility may be related to a more hierarchical pore structure (micropores within macropores) obtained with briefer, high-temperature sintering.
... This report demonstrated that the thermal treatment of the iron ore with phosphorus presenting as fluoroapatite prior to thermal treatment resulted in the phosphorus presenting as a new phase, rhenanite (CaNaPO 4 ), which appears to selectively reside outside the metallic iron. Rhenanite (CaNaPO 4 ) is reported to possess a high solubility [272][273][274]. the phosphorus removal rate from the ore, which was attributed to the low solubility of both the crystalline and the amorphous grattarolaite in the sulfuric acid used in their study. In contrast, upon heating the iron ore to temperatures > 800 °C (Figure 2), they [37] reported high phosphorus removal rates (≥ 80%). ...
With the present rates of iron ore consumption, currently unusable, high-phosphorus iron ore deposits are likely to be the iron ores of the future as higher-grade iron ore reserves are depleted. Consequently, the design and timely development of environmentally-benign processes for the simultaneous beneficiation of high-phosphorus iron ores and phosphorus recovery, currently a technological challenge, might soon become a sustainability challenge. To stimulate interest in this area, phosphorus adsorption and association in iron oxides/hydroxyoxides, and current efforts at its removal, have been reviewed. The important properties of the most relevant crystalline phosphate phases in iron ores are highlighted, and insights provided on plausible routes for the development of sustainable phosphorus recovery solutions from high-phosphorus iron ores. Leveraging literature information from geochemical investigations into phosphorus distribution, speciation, and mobility in various natural systems, key knowledge gaps that are vital for the development of sustainable phosphorus removal/recovery strategies and important factors (white spaces) not yet adequately taken into consideration in current phosphorus removal/recovery solutions are highlighted, and the need for their integration in the development of future phosphorus removal/recovery solutions, as well as their plausible impacts on phosphorus removal/recovery, are put into perspective.
... In certain circumstances of drug delivery applications, tri-calcium phosphates (TCP) presents the more ideal composition compared with other calcium phosphates. Tri-calcium phosphate has been extensively studied for use as bone grafts [87][88][89][90] and for drug delivery systems [91][92][93][94] owing to appropriate dissolution rate [95][96][97]. The hydrothermal conversion from calcium carbonate exoskeletons to TCP would require a ratio between calcium and phosphorus of 1.5. ...
During the past two decades, a number of materials and devices have been utilised in drug delivery applications. A range of biomaterials with different morphologies and pore sizes are currently utilised. For any given biomaterial or bioceramic, having an adequate control of the chemical composition as well as the critical pore sizes is important in terms of controlling the effectiveness when used to deliver drugs locally. In comparison to all currently known and used biomaterials, given the fact that it possesses chemical similarity to human bone, and most importantly its dissolution characteristics which allow for bone regeneration and growth, calcium phosphate holds a special consideration. Moreover, due to their interconnected pore structure, marine materials such as shells and coral exoskeletons show potential for applications in drug delivery due to their easy conversion to calcium phosphates with controllable dissolution rates. This chapter covers a range of current methods used specifically for natural materials that can be converted to calcium phosphates and mixed with polymeric materials as thin film or nanostructured drug, genes, protein and range of delivery and as anticancer chemotherapeutic devices.
... To control the rate of solubility, BCPs are used. BCP is a combination of HAp and b-TCP (Tang et al., 2003). Depending on the carrier chemical composition, the adsorbed amount of a drug can be controlled. ...
The disadvantages of systemic drug therapy are that only a small fraction of any given dose actually reaches the surgical site, producing low-therapeutic tissue levels. An alternative approach is based on the use of implantable delivery tools, able to release the active substance in a controlled way. Biocompatibility, bioactivity, and osteoconductivity are the main driving forces of calcium phosphate biomaterials, promoting their application as bone substitutes. At the same time, multimodal porous structure and interconnectivity of pores make them promising candidates for site-specific drug delivery. The use of porous hydroxyapatite as a drug delivery system could result in a dual effect: the ability to interact with the bone tissues at the same time ensuring increased drug efficiency, controlled release, and site-specific delivery.
... Different dissolution tests of calcium phosphates have been carried out under various conditions using either continuous or discontinuous measurement techniques. The continuous measurement techniques include the constant composition method [24][25][26], the constant pH method [27] and other methods using electrodes [28]. The discontinuous measurement techniques include pharmacopoeia methods such as the BP (British Pharmacopoeia) and USP (United States Pharmacopeia) methods and other intermittent sampling-and-analysis methods [29,30]. ...
A potential standard method for measuring the relative dissolution rate to estimate the resorbability of calcium-phosphate-based ceramics is proposed. Tricalcium phosphate (TCP), magnesium-substituted TCP (MgTCP) and zinc-substituted TCP (ZnTCP) were dissolved in a buffer solution free of calcium and phosphate ions at pH 4.0, 5.5 or 7.3 at nine research centers. Relative values of the initial dissolution rate (relative dissolution rates) were in good agreement among the centers. The relative dissolution rate coincided with the relative volume of resorption pits of ZnTCP in vitro. The relative dissolution rate coincided with the relative resorbed volume in vivo in the case of comparison between microporous MgTCPs with different Mg contents and similar porosity. However, the relative dissolution rate was in poor agreement with the relative resorbed volume in vivo in the case of comparison between microporous TCP and MgTCP due to the superimposition of the Mg-mediated decrease in TCP solubility on the Mg-mediated increase in the amount of resorption. An unambiguous conclusion could not be made as to whether the relative dissolution rate is predictive of the relative resorbed volume in vivo in the case of comparison between TCPs with different porosity. The relative dissolution rate may be useful for predicting the relative amount of resorption for calcium-phosphate-based ceramics having different solubility under the condition that the differences in the materials compared have little impact on the resorption process such as the number and activity of resorbing cells.
Copyright © 2015. Published by Elsevier Ltd.
... 6H 2 O (0·4575g), CaCl 2 (0·417 g) and Na 2 SO 4 (0·1065 g) in Deionized water. (11,12) The solution was buffered at pH 7.4 with tris (hydroxyl methyl) Amino methane (CH 2 OH) 3 CNH 2 and 1M Hydrochloric acid at 36·5 ±1 • C. ...
The bone grafts were prepared using nanohydroxyapatite (nanoHAP) with the extracts of AV and mixed with beta tricalcium phosphate (βTCP) in a ratio of 60:40. The formed BCP was then conjugated with CH to form the bone graft. The Phytochemicals of AV imparts an anti-inflammatory and wound healing property to the bonegraft in addition to its osteoconductivity. The bone graft was subjected to various conventional characterization techniques like FTIR, XRD, SEM, UV spectrophotometric analysis, compression and tensile strength to reveal its chemical composition, surface morphology and mechanical strength. The UV spectrophotometric analysis and SEM images revealed the mineral deposition on the bone graft after immersing in SBF, thereby increasing its ossification property. FTIR and XRD revealed the presence of BCP with nano HAP crystals and Chitosan in the graft. Compression and tensile strength of the graft showed that the graft can be used in non–load bearing areas. In this study, a bone graft was synthesized using a novel technique of introducing the extracts of AV in the graft along with BCP and CH. The results revealed that the bone graft can be used as an Osteoconductive material for various biomedical applications.
... It is widely accepted that β-TCP can be resorbed in vivo and we may initially expect there would be ions dissolved from the β-TCP, which would affect gene expression. This dissolution from HA or β-TCP was observed in a number of studies when Ca and P free solutions were used [22][23][24][25][26]. Figure 5 shows the morphology of 10T1/2 cells on HA, α-TCP and β-TCP revealed by SEM. ...
In this study, we used a pluripotent mesenchymal stem cell (MSC) model, C3H/10T1/2, to evaluate three calcium phosphate (CaP) materials, namely the hydroxyapatite (HA), α-tricalcium phosphate (α-TCP) and β-tricalcium phosphate (β-TCP). 10T1/2 cell was chosen as it has advantages over its counterparts in terms of ease of maintenance, free of ethical concerns and also more reproducible results. ALP a enzymatic assay, RT-qPCR b , DAPI c staining and SEM d were employed to assess the osteoinductivity of these materials. A good reference material which also acts as a scientific control e is necessary for comparisons of results from different experimental batches and hence other materials such as titanium, Nunclon TM plastic surface, BD Falcon TM plastic surface and gold coated porous HA were also tested. The results show that ceramics induce a more sustained osteo-differentiation state as compared with plastics. Inductivity was found to be acting in descending order of strength with HA > β-TCP > α-TCP, which is reversed in terms of their impact on proliferation rate (HA TCP) and in vivo osteoinductivity in terms of incidence and quality of bone described previously (HA > -TCP >α-TCP). These confirm the suitability of using 10T1/2 cells in cell culture assay of osteoinductivity.
... Kilian et al. [10] showed that nonsintered HA could even be phagocytized and dissolved by macrophages and osteoclasts, while sintered ceramics were not degraded and remained at the site of implantation for years following the surgery. The β-TCP, on the other hand, has a significantly high solubility [11,12] and typically fades away from the defect site even before the completion of new bone formation. An ideal skeletal repair implant should readily take part in the bone remodeling processes, and also allow for the direct anchorage by the bony tissues surrounding it (osteoconduction) [13]. ...
Hydroxyapatite (HA) was prepared by co-precipitation of calcium chloride and phosphoric acid while β-TCP was prepared using ammonium hydrogen phosphate and calcium chloride. The wet powders from both preparations were centrifuged, sonicated, autoclaved and calcinated to produce nanoparticles. They were characterized by SEM, XRD and FTIR. Green and sintered disc of both samples were also prepared. The hydroxyapatite nanoparticles were of rod shape structure with dimension of 65±1.0 nm for length and 25±1.0 nm for width while β-TCP was larger with dimension of 200±10 nm for length and 100±10 nm for width. The hardness of sintered hydroxyapatite disc was found to be stronger than the sintered β-TCP.
... In order to obtain the superstructures similar to those natural biominerals, many efforts have been devoted to study the biomineralization processes. Recently, formation of biominerals with sophisticated superstructures from calcium carbonate [4], nano-hydroxyapatite (nano-HAP) [5][6][7], and barium sulfate [8] has been observed. Generally controlled by organic template molecules, these biominerals show exquisite morphologies, structures, and functional values. ...
Calcium carbonate particles with a novel bowknot-like superstructure were fabricated in the presence of poly(sodium 4-styrene sulfate) (PSS) and under the assistance of ultrasonication during the initial reaction stage. X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), selected area electron diffraction (SAED), and field-emission scanning electron microscopy (FE-SEM) equipped with energy-dispersive X-ray (EDX) were used to characterize the particles. Results demonstrated that the bowknot-like calcium carbonate particles were mainly composed of amorphous calcium carbonate (ACC) and some amounts of calcite and vaterite. Ultrasound irradiation associated with the presence of PSS affects the mesoscale crystallization, resulting in stepwise growth of the earlier bundles to the bowknot. Morphology evolution and dissolution of the bowknot particle were observed in different media, confirming that PSS and Ca(2+) ions in the solutions could accelerate and resist the transformation process, respectively. In the presence of PSS, ACC prefers to transform into vaterite.
... It is widely accepted that β-TCP can be resorbed in vivo and we may initially expect there would be ions dissolved from the β-TCP, which would affect gene expression. This dissolution from HA or β-TCP was observed in a number of studies when Ca and P free solutions were used [22][23][24][25][26]. Figure 5 shows the morphology of 10T1/2 cells on HA, α-TCP and β-TCP revealed by SEM. ...
In this study, we used a pluripotent mesenchymal stem cell (MSC) model, C3H/10T1/2, to evaluate three calcium phos-phate (CaP) materials, namely the hydroxyapatite (HA), α-tricalcium phosphate (α-TCP) and β-tricalcium phosphate (β-TCP). 10T1/2 cell was chosen as it has advantages over its counterparts in terms of ease of maintenance, free of ethical concerns and also more reproducible results. ALP a enzymatic assay, RT-qPCR b , DAPI c staining and SEM d were employed to assess the osteoinductivity of these materials. A good reference material which also acts as a scientific control e is necessary for comparisons of results from different experimental batches and hence other materials such as titanium, Nunclon TM plastic surface, BD Falcon TM plastic surface and gold coated porous HA were also tested. The results show that ceramics induce a more sustained osteo-differentiation state as compared with plastics. Inductivity was found to be acting in descending order of strength with HA > β-TCP > α-TCP, which is reversed in terms of their impact on proliferation rate (HA < TCP). This is also consistent with the results observed in SBF f study in terms of cal-cium phosphate precipitate area coverage (HA > TCP) and in vivo osteoinductivity in terms of incidence and quality of bone described previously (HA > -TCP >α-TCP). These confirm the suitability of using 10T1/2 cells in cell culture assay of osteoinductivity.
... DCPD'nin oda sıcaklığında ve pH değeri 5.5 olan su-bazlı bir çözeltideki çözünme hızı 4.26x10 -4 mol⋅m -2 ⋅min -1 iken, aynı koşullarda insan kemik minerali olan KEHA'in çözünme hızı ise 1.42x10 -6 mol⋅m -2 ⋅min -1 olarak ölçülmüştür [3]. [4]. ...
Brushite (DCPD, CaHPO<sub>4</sub>·2H<sub>2</sub>O, dicalcium phosphate dihydrate) and octacalcium phosphate (OCP, Ca<sub>8</sub>(HPO<sub>4</sub>)<sub>2</sub>(PO<sub>4</sub>)<sub>4</sub>·5H<sub>2</sub>O) are two important biomineralization phases of the musculoskeletal system of living vertebrates which respectively crystallize in the very first instants of hard tissue formation accompanied by calcification, and then transform into the so-called bone mineral named as calcium-deficient hydroxyapatite (CDHA, Ca<sub>10-x</sub>(HPO<sub>4</sub>)<sub>x</sub>(PO<sub>4</sub>)<sub>6-x</sub>(OH)<sub>2-x</sub>). The utilization of these two phases in the surgical treatment of bone defects and voids has lately been the focus of interest of a significant number of research projects. Although the synthesis of DCPD is quite easy and reproducible, the same cannot be said for that of OCP. Biomineralization solutions which use DCPD as the starting material and can allow the economical transformation of DCPD into OCP have been developed in this study. This paper explains the preparation conditions of these solutions and elucidates the X-ray diffraction and infrared spectroscopy data of the phases formed.
Bone defects are common and are associated with a significant burden of disease threatening the health of many people around the globe. Since the last decade, data obtained from case studies have demonstrated that 20% of patients who experience an osteoporotic hip break are unable to endure the primary year after medical treatment. Many similar cases suggest that there is a huge requirement for better treatment of unhealthy and broken bones. Human bone comprises of about 70% of calcium phosphate (CaP) mineral, therefore CaPs are possible alternative materials to fix a broken bone. CaP is broadly utilized for bone fixation because of its bioactive properties like osteoinductivity, osteoconductivity, and biodegradability. Therefore, examination of these properties and the impact of their different affecting factors are crucial for balancing CaP during the fabrication procedure to maximally fulfill required clinical prerequisites. The aim of this chapter is to highlight the systems behind the CaP-assisted bone development in the initial phase, specifically as a biocompatible bone graft substitute. In this study, the latest developments in the biological properties of CaP biomaterials, including hydroxyapatite (HA), tricalcium phosphate (TCP), and biphasic CaP (BCP), have been summarized. Moreover, recent advances on how their properties are altered by different factors are reviewed. Finally, perspectives regarding future developments of CaP materials are provided.
Marine structures, biogenic materials, and biomimetic approaches applied to the fabrication of advanced biomaterials and implants are used to address the shortcomings of existing scaffold designs that are biologically un-responsive throughout the regeneration process and lack necessary versatility. Bioactive ceramics converted from biostructures or natural marine-based materials such as corals, sea urchin, sponges and shells are being designed into functional scaffolds that can adapt and evolve to changing environment during regeneration process. They can regulate cell responses at nanostructured surfaces, and as modules for self-assembling by the patient’s own cells and as smart devices that possess tissue specific homing capabilities. These natural structures can be converted to bioactive ceramics such as hydroxyapatite to assist osseointegration. This chapter covers biomimicry, evolution of marine structures, and their specific use and current research on natural materials such as coral, sponge, sea urchin, sponge nacre, and foraminifera as models and raw materials for bioactive bone scaffolding materials and tissue engineering.
Phosphate amendment has shown promise for enhancing uranium immobilization. The mechanism of the enhancement however has remained unclear with contrasting observations under different geochemical conditions. A dual-domain reactive transport model (RTM) is developed here based on batch and column experimental data to understand the mechanisms and to explore the effectiveness of enhanced U(VI) immobilization under variable geochemical and flow conditions. Modeling results indicate that under low U(VI) conditions in natural waters, phosphate addition promotes immobilization through the formation of U(VI)-phosphate ternary surface complexes and the precipitation of calcium phosphate, both decreasing the concentrations of mobile U(VI)-Ca-CO3 aqueous complexes. This contrasts with previously proposed hypotheses attributing the enhancement to U(VI)-phosphate precipitation under high U(VI) experimental conditions. Sensitivity analysis shows that phosphate is effective under relatively low Ca (< 0.1 mM) and total inorganic carbon (TIC) (< 0.5 mM) conditions, where > 60% of U(VI) still remains on sediments after 113 residence times of flushing with low phosphate solutions (< 0.1 mM). Under high Ca or TIC conditions, a similar level of U(VI) immobilization can be achieved only when the phosphate concentration is higher than Ca or TIC concentrations. Compared to the strong geochemical effects, flow conditions have limited impacts on U(VI) immobilization. These results explain contrasting observations on the effectiveness of phosphate amendment and offer capabilities to extrapolate observations to other environmental conditions.
Phase transformations are important processes during mineral formation in both in vivo and in vitro model systems and macromolecules are influential in regulating the mineralization processes. Calcium phosphate mineralized alginate hydrogels are potential candidates for hard tissue engineering applications and transformation of the resorbable calcium phosphate phases to apatitic bone mineral in vivo enhances the success of these composite materials. Here, the transformation of brushite to hydroxyapatite (HA) and the effects of alginate additives on this process are studied by the investigation of supersaturation profiles with HA-seeded and unseeded experiments. This experimental design allows for detailed kinetic interpretation of the transformation reactions and deduction of information on the nucleation stage of HA by evaluating the results of seeded and unseeded experiments together. In the experimental conditions of this work, transformation was controlled by HA growth until the point of near complete brushite dissolution where the growth and dissolution rates were balanced. The presence of alginate additives at low concentration were not highly influential on transformation rates during the growth dominated region but their retardant effect became more pronounced as the dissolution and growth rates reached an equilibrium where both reactions were effective on transformation kinetics. Decoupling of seeded and unseeded transformation experiments suggested that alginate additives retard HA nucleation and this was most evident in the presence of G-block oligomers.
Currently there is an urgent need to develop an appropriate slow drug delivery system to sustain the local and targeted release of the drug to increase therapeutic efficacy while reducing side effects. In this study, a novel drug delivery system by means of hydrothermally converting marine exoskeletons to β-tricalcium phosphate was investigated. The in vitro dissolution of key chemical compositional elements and the release of drugs such as simvastatin and antibiotics were measured. Coating of these Foraminifera shells with an apatitic bone cement material reduced the dissolution rate by 50 % compared with control samples. This study shows the potential applications of marine structure-derived calcium phosphates as efficient local drug delivery systems.
Brushite (dicalcium phosphate dihydrate, DCPD, CaHPO4·2H2O) and whitlockite [WH, Ca9Mg(HPO4)(PO4)6] are usually found in the mammalian metabolism in the form of diverse pathological calcifications, dental calculi, urinary tract stones, salivary gland deposits, cardiovascular or pulmonary calcified deposits, and even as prostate or cartilage calcifications. The hydrothermal transformation of synthetic brushite crystals into single-phase whitlockite, octacalcium phosphate, or apatitic calcium phosphate was observed over the time period of 1 to 21 d and at 37°C, 70°C, and 115°C in nonstirred physiologically relevant solutions developed for this work. The strong influence of the physiologically relevant ions such as Mg2+ and HCO3− on hydrothermal transformations is exposed. The formation of the nanoglobules and nanofibrils of X-ray amorphous calcium phosphate or Mg-doped calcium phosphate on the surfaces of brushite crystals are observed for the first time in biomimetic solutions containing 10 mm Mg2+ and/or 27 mm HCO3−. The experimental conditions leading to the formation of such nanofibrils on brushite crystal surfaces are also found to stop the further transformation of brushite into any other calcium phosphate (CaP) phases even at high solution temperatures. Samples were characterized by scanning electron microscopy and powder X-ray diffraction.
IntroductionExperimental ProcedureResults and DiscussionConclusions
Acknowledgments
Biphasic rhenanite ((β-NaCaPO4)-apatitic calcium phosphate biomaterials for skeletal repair were prepared by using a one-pot, solution-based synthesis procedure at the physiological pH of 7.4, followed by low-temperature (300° to 600°C) calcination in air for 6 hours. Calcination was for the sole purpose of crystallization. An aqueous solution of Ca(NO3)2.4H20 was rapidly added to a solution of Na2HP04 and NaHC03 at room temperature. followed by immediate filtration of gel-like, poorlycrystallized precursor precipitates from the mother liquors of pH 7.4. Freeze-dried precursors were found to be nanosize with an average particle size of 45 nm and surface area of ca. 125 m2/g Upon calcination in air, precursor powders crystallized into biphasic (60% HA-40% rhenanite) biomaterials, while retaining their submicron particle sizes and high surface areas. Phase-pure rhenanite powders were also synthesized by solid-state reactive firing. Rhenanite is a high solubility sodium calcium phosphate phase. Samples were characterized by XRD, FTIR. SEM. ICP-AES. TG, DTA. DSC, and BET surface area measurements.
The formation of iron carbonate films, or by converting carbonate to magnetite at higher temperatures, are important means used to control the rate of corrosion in the oil and gas industry. The FeCO 3 film can slow the corrosion process by covering up the steel surface and preventing the diffusion of corrosive species to the pipe surface. On the other hand, the excessive build up of iron carbonate salt in the oilfield production line can be a major issue, particularly, in the absence of effective inhibitors. The growth and thickness of the film depend upon the kinetics of precipitation and crystal growth of iron carbonate. In such kinetic studies, it is important to keep these parameters constant. This work was intended to study the kinetics of crystal growth of mixed calcium-ferrous carbonate salts at constant experimental conditions. In this study all the parameters are well controlled. A special experimental design is used to keep the initial concentrations, pH (7.1), temperature (31 and 48°C), pressure (1 atm), and ionic strength (0.5 M) constant during the course of the experiment. The composition of calcium-ferrous carbonate salt that formed was determined. The mass flux of crystal growth was also investigated and found to be constant.
An electroless, room temperature solution growth method of depositing 50 to 150 μm thick, well-crystallized brushite (CaHPO4 · 2H2O, DCPD, dicalcium phosphate dihydrate) layers on the surface of an implantable medical device, such as a titanium alloy (Ti-6Al-4V) substrate, was developed. High ionic strength (189 to 609 mM) solutions with a Ca/P molar ratio of 2.50 and a pH value between 4.70 and 6.10 were prepared by dissolving appropriate quantities of CaCl2 · 2H2O, NaH 2PO4, NaHCO3, and NaCl in deionized water. Surface-etched Ti-6Al-4V substrates were simply soaked in the solutions from 24 to 72 hours at room temperature. Elongated CaHPO4 · 2H 2O crystals were in-situ-grown on the entire surfaces of the etched Ti-6Al-4V substrates.
Mysteries surrounding the most important mineral for the vertebrate biology, hydroxyapatite, are many. Perhaps the Greek root of its name, , meaning ‘to deceive’ and given to its mineral form by the early gem collectors who confused it with more precious stones, is still applicable today, though in a different connotation, descriptive of a number of physicochemical peculiarities exhibited by it. Comparable to water as the epitome of peculiarities in the realm of liquids, hydroxyapatite can serve as a paradigm for peculiarities in the world of solids. Ten of the peculiar properties of hydroxyapatite are sketched in this review piece, ranging from (i) the crystal lattice flexibility to (ii) notorious surface layer instability to (iii) finite piezoelectricity, pyroelectricity and conductivity to protons to (iv) accelerated growth and improved osteoconductivity in the electromagnetic fields to (v) high nucleation rate at low supersaturations and low crystal growth rate at high supersaturations to (vi) higher bioactivity and resorbability of biological apatite compared to the synthetic ones, and beyond. An attempt has been made to explain this array of curious characteristics by referring to a particular element of the crystal structure of hydroxyapatite: the hydroxyl ion channel extending in the direction of the c-axis, through a crystallographic column created by the overlapping calcium ion triangles.
This study reports the microwave-assisted synthesis and characterization of nHAp (nano-hydroxyapatite)-alumina composites. The crystalline phase and interaction of alumina with nHAp was analyzed using X-ray diffraction (XRD) and Raman microscopy analysis, respectively. High resolution transmission electron microscopy (HRTEM) micrographs exhibit morphological changes of nHAp composites with increasing alumina concentrations. Microhardness studies reveal the enhanced mechanical strength of nHAp10 and nHAp20 nanocomposites than pure nHAp. In vitro bioactivity of the nanocomposites was studied by immersing samples in simulated body fluid (Hank's solution) for 21days. The surface of biomineralized samples were analyzed using field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX). Hemolytic assay revealed acceptable compatibility for varying concentrations of all the samples. Cell proliferation assay was systematically investigated for 1day and 3days on Saos-2 osteoblast-like cell lines and it was found that nHAp nanocomposites improved the proliferation.
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Brushite (CaHPO4·2H2O, dicalcium phosphate dihydrate) is known to be the precursor to the mineralized portion (HA: calcium hydroxyapatite, Ca10(PO4)6(OH)2) of hard tissues in the biological crystallization processes. In other words, it can be readily asserted that there must be a point of equilibrium (within the three-dimensional pH, temperature and concentration space) between brushite and hydroxyapatite phases in physiological solutions. While brushite is acidic, hydroxyapatite is a basic phase. It is also known that mixtures which contain these phases, in appropriate mixing ratios, could undergo a neutralization reaction in aqueous solutions at the human body temperature of 36.5°C. Based on these facts, it would be possible to produce bone cements, for orthopedic applications, from the biphasic powder mixtures of brushite and apatite. The feasability of synthesizing these biphasic powder mixtures in variable phase ratios have been tested, for the first time in this study, by using a single-step chemical precipitation process. This paper explains this novel process and analyzes the X-ray diffraction and infrared spectroscopy data obtained from these powders.
Significant interest has been in examining calcium phosphate ceramics, specifically β-tricalcium phosphate (β-TCP) (Ca3(PO4)2) and synthetic hydroxyapatite (HA) (Ca10(PO4)6(OH)2), in composites and more recently, in fibrous composites formed using the electrospinning technique for bone tissue engineering applications. Calcium phosphate ceramics are sought because they can be bone bioactive, which means an apatite forms on their surface that facilitates bonding to bone tissue, and are osteoconductive. However, studies examining the bioactivity of electrospun composites containing calcium phosphates and their corresponding osteogenic activity have been limited. In this study, electrospun composites consisting of (20/80) HA/TCP nanoceramics and poly (ϵ-caprolactone) (PCL) were fabricated. Solvent and solvent combinations were evaluated to form scaffolds with a maximum concentration and dispersion of ceramic and pore sizes large enough for cell infiltration and tissue growth. PCL was dissolved in either methylene chloride (Composite-MC) or a combination of methylene chloride (80%) and dimethylformamide (20%; Composite-MC + DMF). Composites were evaluated in vitro for degradation, apatite formation, and osteogenic differentiation of human mesenchymal stem cells (MSCs) with an emphasis on temporal gene expression of osteogenic markers and the pluripotent gene Sox-2. Apatite formation and the osteogenic differentiation was the greatest for Composite-MC as determined by gene expression, protein production and biochemical markers, even without the presence of osteoinductive factors in the media, in comparison to Composite-MC + DMF and unfilled PCL mats. Sox-2 levels also reduced over time. The results of this study demonstrate that the solvent or solvent combination used in preparing the electrospun composite mats plays a critical role in determining their bioactivity which may, in turn, affect cell behavior. Biotechnol. Biotechnol. Bioeng. 2014;111: 1000–1017.
This study investigated the hydrothermal transformation of brushite (dicalcium phosphate dihydrate, DCPD, CaHPO4·2H2O) into octacalcium phosphate (OCP, Ca8(HPO4)2(PO4)4·5H2O) in seven different newly developed biomineralization media, all inspired from the commercial DMEM solutions, over the temperature range of 36.5°C to 90°C with aging times varying between 1h and 6days. DCPD powders used in this study were synthesized in our laboratory by using a wet-chemical technique. DCPD was found to transform into OCP in the Ca2+, Mg2+, Na+, K+, HCO3−, Cl− and H2PO4− containing aqueous biomineralization media in less than 72h at 36.5°C, without stirring. The same medium was able to convert DCPD into OCP in about 2h at 75–80°C, again without a need for stirring. Samples were characterized by using powder X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM).
Marine cyanobacteria have evolved phosphate uptake systems to live where P is limiting. Ultimately, P derives from apatite in rocks but little is known about apatite solubilization by cyanobacteria. Fluorapatite (FAP) was added to a P-free culture medium with and without Anabaena, as well as in cell-free supernatant to test reports that the cyanobacterium Anabaena PCC 7120 enhances the dissolution of fluorapatite (FAP). Anabaena, a fresh-water organism, is an analogue to harder-to-grow marine cyanobacteria. The initial abiotic release rate ratios (Ca/P) are significantly higher than the similar stoichiometric ratio of apatite. The majority of the “missing” P in abiotic experiments is sorbed to precipitates formed from Fe added as a nutrient to the culture medium. In contrast to literature reports, Ca release from FAP in the presence of Anabaena or culture supernatant was lower than abiotic release. However, Anabaena cultures aggregate and cells attach to the FAP when P-limited. Adhesion is explained by surface charge rather than P content because significant adhesion on boehmite occurred in similar experiments. X-ray photoelectron spectroscopic (XPS) analysis of the FAP surface after incubation with Anabaena is consistent with sorbed proteins that promote adhesion. These released polymers are also inferred to complex with Ca during dissolution, contributing to nucleation of Ca-P precipitates in experiments with cells or supernatant. These experiments emphasize that for Anabaena growing under P-limited conditions, polymeric material is important for cellular adhesion to mineral particles and for the concentration of phosphate as Ca-or Fe-complexes or nanoparticles.
Eight dissolution models of calcium apatites (both fluorapatite and hydroxyapatite) in acids were drawn from the published literature, analyzed and discussed. Major limitations and drawbacks of the models were conversed in details. The models were shown to deal with different aspects of apatite dissolution phenomenon and none of them was able to describe the dissolution process in general. Therefore, an attempt to combine the findings obtained by different researchers was performed which resulted in creation of the general description of apatite dissolution in acids. For this purpose, eight dissolution models were assumed to complement each other and provide the correct description of the specific aspects of apatite dissolution. The general description considers all possible dissolution stages involved and points out to some missing and unclear phenomena to be experimentally studied and verified in future. This creates a new methodological approach to investigate reaction mechanisms based on sets of affine data, obtained by various research groups under dissimilar experimental conditions.
The fundamental building blocks of hierarchically structured bone tissue are mineralized collagen fibrils with calcium phosphate nanocrystals that are biologically "engineered" through biomineralization. In this study, we demonstrate an original invention of dicalcium phosphate anhydrate (DCPA)/poly(lactic acid) (PLA) composite nanofibers, which mimics the mineralized collagen fibrils via biomimetic in-situ synthesis and electrospinning for hard tissue regenerative medicines. The interaction of the Ca(2+) ions and the carbonyl groups in the PLA provides nucleation sites for DCPA during the in-situ synthesis process. This resulted in the improved dispersion of DCPA nanocrystallites in the intra-nanoporous PLA nanofibers through electrospinning, compared to the severely agglomerated clusters of DCPA nanoparticles fabricated by conventional mechanical blending/electrospinning methods. The addition of poly(ethylene glycol) (PEG), as a co-polymer source, generated more stable and efficient electrospun jets and aided in the electrospinability of the PLA nanofibers incorporating the nanocrystallites. It is expected that the uniformly distributed DCPA nanocrystallites and its unique nanocomposite fibrous topography will enhance the biological performance and the structural stability of the scaffolds used for hard tissue reconstruction and regeneration.
Due to a great chemical similarity with the biological calcified tissues, many calcium orthophosphates possess remarkable biocompatibility and bioactivity. Materials scientists use this property extensively to construct artificial bone grafts that are either entirely made of or only surface-coated with the biologically relevant calcium orthophosphates. Porous scaffolds made of calcium orthophosphates are very promising tools for tissue engineering applications. A comprehensive overview of calcium orthophosphates, this book highlights their importance and biomedical uses.
Experimental data for alteration of synthetic Martian basalts at pH = 0–1 indicate that chemical fractionations at low pH are vastly different from those observed during terrestrial weathering. Rock surface analyses from Gusev crater are well described by the relationships apparent from low-pH experimental alteration data. A model for rock surface alteration is developed, which indicates that a leached alteration zone is present on rock surfaces at Gusev. This zone is not chemically fractionated to a large degree from the underlying rock interior, indicating that the rock surface alteration process has occurred at low water to rock ratio. The geochemistry of natural rock surfaces analyzed by APXS is consistent with a mixture between adhering soil/dust and the leached alteration zone. The chemistry of rock surfaces analyzed after brushing with the RAT is largely representative of the leached alteration zone. The chemistry of rock surfaces analyzed after grinding with the RAT is largely representative of the interior of the rock, relatively unaffected by the alteration process occurring at the rock surface. Elemental measurements from the Spirit, Opportunity, Pathfinder, and Viking 1 landing sites indicate that soil chemistry from widely separated locations is consistent with the low-pH, low water to rock ratio alteration relationships developed for Gusev rocks. Soils are affected principally by mobility of Fe and Mg, consistent with alteration of olivine-bearing basalt and subsequent precipitation of Fe- and Mg-bearing secondary minerals as the primary control on soil geochemistry.
Brushite (DCPD: CaHPO42H2O) powders were chemically synthesized by using Na- and K-phosphate and calcium chloride-containing aqueous solutions at RT, followed by drying at 37°C. DCPD powders thus formed were found to contain 460 ppm K. and 945 ppm Na. Upon calcining in air these powders readily transformed into CaHPO4 (monetite) first, and then into Ca2P2O7. Na- and K-doped DCPD powders were shown to completely transform, in less than 1 week, into poorly crystalline carbonated apatite upon immersion in an acellular SBF solution at 37°C. This finding suggests the use of these DCPD powders as potential bone-substitute materials, which can be easily manufactured in aqueous solutions friendly to living tissues at temperatures between RT and 37°C.
Sintered β-tricalcium phosphate (β-TCP, β-Ca3(PO4)2) and Zn-doped (600, 4100, and 10100 ppm) β-TCP samples were prepared by using an aqueous chemical synthesis technique, followed by the calcination of pressed powders at 1000°C in air. Precursor powders of the synthesis process were Ca-deficient nanoapatites (i.e., Ca/P molar ratio varying from 1.49 to 1.51) with rod-like but agglomerated particles of 50 ran length and 20 nm thickness. In vitro culture tests performed by mouse osteoblast-like cells showed that β-TCP doped with 4100 ppm Zn had the highest cell viability and alkaline phosphatase (ALP) activity values over a range of 0 to 1 wt% Zn. The sample surface roughness, measured by non-contact profilometry, was also found to have an effect on the Live/Dead cell counts, and the highest cell viability recorded in this study corresponded to the surfaces with the least roughness.
The salivary protein statherin is an inhibitor of spontaneous and secondary precipitation of hydroxyapatite (HAp). It is also
detected in enamel pellicle. The N-terminal region of statherin is involved in its adsorption onto tooth surfaces, and, calcium
binding. A peptide (StN21) was designed with a 21 amino acid sequence identical to the N-terminus of statherin. The aim was
to measure the effect of StN21 on the rate of mineral loss in a model system for dental caries and erosion using HAp subjected
to artificial carious and erosive conditions. StN21 was synthesised using Fmoc chemistry. A surface of each HAp block was
exposed to solution containing StN21 at concentrations 9.4–376μmolL−1 (in phosphate buffer) for 24h. Controls were HAp exposed to buffer only, and HAp exposed to lysozyme. Demineralising solution
(0.1molL−1 acetic acid, pH 4.5, 1.0mmolL−1 calcium and 0.6mmolL−1 phosphate) was circulated past the HAp blocks at 0.4mLmin-1 to mimic carious and erosive conditions. Scanning microradiography was used to measure the rate of mineral loss for demineralisation
periods of 3weeks. The rate of mineral loss of the samples exposed to StN21 was reduced by ∼40% compared to the controls,
but no dependence on the concentration of StN21 was observed at the concentrations used. StN21 has been shown to be a potent
and stable peptide that has potential as a preventive/therapeutic agent in the treatment of enamel erosion and dental caries.
Octacalcium phosphate (OCP) is proving to be an important intermediary in the formation of tooth and bone mineral and various pathological calcifications. Before this mineral can form, its solubility product must be exceeded. Thus, a knowledge of its precise values under various conditions is required for a basic understanding of calcification processes. The methodology suitable for measuring the solubility of metastable phases was developed and used to determine the negative logarithms of the solubility products of OCP, pKsp(OCP), at 4, 4.8, 6, 18, 23.5, and 37°C. This methodology includes (1) the use of high solid-to-liquid ratio, 10 mg/mL, to minimize the effects of hydrolysis, (2) frequent sampling during equilibration to detect possible effects of hydrolysis, (3) equilibration from supersaturation and from undersaturation, and (4) equilibration in the absence and presence of a CO2-containing atmosphere. The effects of (1) the use of different ionic models, (2) OCP hydrolysis, and (3) differences in equilibrium constants on the apparent pKsp(OCP) values are described; the latter two contribute significantly to the differences in pKsp(OCP).
The control of crystal formation has been developed to a remarkable degree by many organisms. Oriented nucleation, control over crystal morphology, formation of unique composites of proteins and single crystals, and the production of ordered multicrystal arrays, are all well within the realm of biological capability. Understanding the control and design principles in biomineralization is a fascinating subject that may well contribute to the improved fabrication of synthetic materials on the one hand, and to the solution of many serious pathological problems involving mineralization, on the other.
Present-day state of the art in crystal growth is reflected in the recent 6 - volume handbook of crystal growth1). The reviews2)3), and the proceedings of ICCG also cover specific features of recent developments. Therefore, here, we restrict ourselves to selected topics in growth kinetics from the melt (Sec. 2) and solution (Sec. 3), as it can be seen by crystal growers.
The solubility product of octacalcium phosphate [Ca4H(PO4)3 · 2.5H 2O] has been determined in the system Ca(OH)2-H3PO 4KNO3-H2O at 37°C in experiments involving a range of hydrodynamics, ionic strength, and equilibration time. A value of pK so= 49.3 ± 0.2 was obtained for three different solid preparations by considering activity coefficients and ion-pair corrections.
The applicability of the dual constant composition (DCC) method, using two ion-specific electrodes, is investigated for studies of the dissolution rates of mixed phases of octacalcium phosphate and tricalcium phosphate. The DCC dissolution of these crystals is compared with the results of parallel constant composition (CC) investigations using a single-ion probe. The DCC dissolution rates were also independent of which electrodes (pH or pCa) controlled the titrant additions. This provides experimental confirmation that, in the concomitant dissolution of hypothetical BA and BC salts (e.g., octacalcium phosphate and tricalcium phosphate), the rate data for each salt can be calculated from the titrant addition curves in the same undersaturated solutions.
Recent advances in the study of Biomineralization serve as a reminder of the intrinsic breadth and scope of Inorganic Chemistry at a time when Inorganic Chemistry in the UK is under threat of fragmentation. It is demonstrated that the study of biominerals from a chemical perspective has resulted in new structural and synthetic challenges, novel concepts such as molecular recognition at inorganic-organic interfaces, and the opportunity to develop a biomimetic approach to the crystal engineering of inorganic materials.
The mechanisms of adsorption of impurities during the growth of bulk crystals are surveyed. The impurities considered are foreign substances deliberately added to or inherently present in a growth medium. After a brief introduction to different growth models, the nature of impurities and types of impurity effects on growth kinetics, adsorption of impurities on F faces at relatively low and high impurity concentrations is first discussed. Here mechanisms of adsorption at kinks in steps and surface terrace in the presence of low concentrations of one impurity and two competitive impurities are presented. Then the concepts of adsorption of impurities involving the formation of two-dimensional impurity layer and three-dimensional impurity clusters as growth promotors on a growing face are developed. Thereafter the mechanism of adsorption of impurities on S and K faces and the determination of the adsorption mechanism on a growing face from the kinetic data are discussed. Finally, impurity effects on surface morphology of bulk crystals, and growth morphodroms of alkali halides are briefly reviewed.
Octacalcium phosphate (OCP) is regarded as an important biomineralization precursor during the formation of hydroxyapatite. In the present work, the kinetics of dissolution of OCP has been studied at 37-degrees-C over a range of undersaturations using the constant composition method. The kinetics data are analyzed in terms of recent crystal growth theories using a nonlinear least-squares procedure. A rate equation is derived for a spiral dissolution following a detachment-desorption-volume diffusion mechanism at very low kink densities. Volume diffusion appears to provide little resistance to OCP dissolution compared with processes occurring at the crystal surface. It is suggested that the ions detached from the crystal steps undergo surface diffusion before escaping into the bulk solution.
The crystallization of the calcium phosphate phases from metastable supersaturated solutions upon seeding with highly crystalline and well-characterized seed material has been studied using a constant solution composition method. The activities of all ionic species in solution were maintained constant by the simultaneous addition of reagent solutions containing calcium, phosphate, and hydroxyl ions, controlled by a specific ion electrode. In solutions of low calcium phosphate concentration, supersaturated only with respect to the thermodynamically most stable hydroxylapatite (HAP), macroscopic amounts of this phase could be grown on HAP seed material without the formation of a precursor phase. These low rates of crystallization at a pH of 7.40 were measured with a precision hitherto unattainable. The influence of supersaturation, seed concentration, and the presence of fluoride ion has been investigated.
The kinetics of crystallization of dicalcium phosphate dihydrate (DCPD) has been studied by following the changes in calcium, phosphate, and hydrogen ion concentrations when stable, supersaturated solutions are inoculated with seed crystals of the salt. After a brief initial surge, the rate of growth of the crystals follows an equation that is second order with respect to concentration, ([Ca 2+][HPO 42-]), over a wide range of calcium/phosphate ratios suggesting a predominantly surface reaction controlled process. Experiments at 15, 25, and 37° have been made in supersaturated solutions over a range of calcium and phosphate concentrations and the energy of activation corresponding to the crystal growth process is 10.5 kcal mol -1. Addition of sodium pyrophosphate to the supersaturated solutions has a striking inhibitory influence upon the rate of crystal growth of DCPD. The effect is analyzed in terms of adsorption, following the Langmuir isotherm, of pyrophosphate ions at the available crystal growth sites.
Selected topics that may be of interest for both crystal-structure and crystal-growth communities are overviewed. The growth of protein crystals, along with that of some other compounds, is one of the topics, and recent insights into related phenomena are considered as examples of applications of general principles. The relationship between crystal growth shape and structure is reviewed and an attempt to introduce semiquantitative characterization of binding for proteins is made. The concept of kinks for complex structures is briefly discussed. Even at sufficiently low supersaturations, the fluctuation of steps may not be sufficient to implement the Gibbs-Thomson law if the kink density is low enough. Subsurface ordering of liquids and growth of rough interfaces from melts is discussed. Crystals growing in microgravity from solution should be more perfect if they preferentially trap stress-inducing impurities, thus creating an impurity-depleted zone around themselves. Evidently, such a zone is developed only around the crystals growing in the absence of convection. Under terrestrial conditions, the self-purified depleted zone is destroyed by convection, the crystal traps more impurity and grows stressed. The stress relief causes mosaicity. In systems containing stress-inducing but poorly trapped impurities, the crystals grown in the absence of convection should be worse than those of their terrestrial counterparts.
Recent constant composition dissolution studies of sparingly soluble calcium phosphates have revealed an interesting and unusual behavior in that the rates decreased, eventually resulting in effective suppression, even though the solutions remained undersaturated. Contrary to traditional theories of dissolution, these experimental results indicated the importance of not only the particle size on the dissolution rate but also the participation of critical phenomena. In these theories, it is assumed that when the dissolution reactions are initiated, they continue spontaneously until all solid phase has disappeared. In terms of these mechanisms, there are no critical phenomena in the dissolution mechanism. Although the crystal size decreases during dissolution, when the reaction is controlled by polypitting (formation and growth of pits), the edge free energy increases at the very first stage due to the creation of pits and dissolution steps. The constant composition experimental results demonstrate the development of surface roughness as the dissolution steps are formed, implying an increase of the total edge length during the reactions. In an exactly analogous mechanism to crystal growth, the participation of critical conditions involving dissolution steps is a possibility. In contrast to crystal growth, dissolution is a process of size reduction and, when the particle size is sufficiently reduced, critical phenomena become important so that the influence of size must be taken into consideration. This paper proposes such a model for dissolution reactions, and although these unusual phenomena probably apply to all mineral phases, they are more evident for sparingly soluble electrolytes in which the critical conditions are attained much more readily.
A new method is described for studying, reproducibly, the kinetics of crystallization of minerals under conditions of constant solution composition even at very low supersaturations. For calcium phosphates the method provides direct evidence for octacalcium phosphate as the precursor to hydroxyapatite precipitation at physiological pH.
- L J Shyu
- L Perez
- S J Zawachi
- J C Heughebaert
- G H Nancollas
L.J. Shyu, L. Perez, S.J. Zawachi, J.C. Heughebaert, G.H. Nancollas,
J. Dent. Res. 62 (1982) 398.
- A A Chernov
- H Komatsu
A.A. Chernov, H. Komatsu, in: J.P. van der Eerden, O.S.L. Bruinsma
(Eds.), Science and Technology of Crystal Growth, Kluwer Academic,
Dordrecht, 1995, p. 67.
- W Wu
- R Tang
- M Hass
- G H Nancollas
W. Wu, R. Tang, M. Hass, G.H. Nancollas, J. Colloid Interface Sci. 244
(2001) 347.
- S Mann
S. Mann, J. Chem. Soc. Dalton Trans. (1993) 1.
- R W Marshall
- G H Nancollas
R.W. Marshall, G.H. Nancollas, J. Phys. Chem. 73 (1969) 3838.
- S Brunauer
- P H Emmett
- E Teller
S. Brunauer, P.H. Emmett, E. Teller, J. Am. Chem. Soc. 60 (1938)
309.
- K Sangwal
- Prog
- Cryst
K. Sangwal, Prog. Cryst. Growth Charact. 32 (1996) 3.
- P Koutsoukos
- Z Amjad
- M B Tomson
- G H Nancollas
P. Koutsoukos, Z. Amjad, M.B. Tomson, G.H. Nancollas, J. Am.
Chem. Soc. 102 (1980) 1553.
- S Mann
S. Mann, Struct. Bonding 54 (1983) 125.
- R Tang
- G H Nancollas
R. Tang, G.H. Nancollas, J. Cryst. Growth 212 (2000) 261.
- L Addadi
- S Weiner
L. Addadi, S. Weiner, Angew. Chem. Int. Ed. Engl. 31 (1992) 153.
- R Tang
- G H Nancollas
- C A Orme
R. Tang, G.H. Nancollas, C.A. Orme, J. Am. Chem. Soc. 123 (2001)
5437.
- M B Tomson
- G H Nancollas
M.B. Tomson, G.H. Nancollas, Science 200 (1978) 1059.
Handbook of Crystal Growth, North-Holland
- D T J Hurle
D.T.J. Hurle, Handbook of Crystal Growth, North-Holland, Amsterdam, 1993.
- J Zhang
- G H Nancollas
J. Zhang, G.H. Nancollas, J. Phys. Chem. 96 (1992) 5478.
- W E Brown
- J R Lehr
- J P Smith
- A W Frazier
W.E. Brown, J.R. Lehr, J.P. Smith, A.W. Frazier, J. Am. Chem. Soc. 79
(1957) 5318.
- M S Tung
- N Eidelman
- B Sieck
- W E Brown
M.S. Tung, N. Eidelman, B. Sieck, W.E. Brown, J. Res. Natl. Bur.
Stand. 93 (1988) 613.
- B M Tomson
- J B Barone
B.M. Tomson, J.B. Barone, G.H. Nancollas, At. Absorpt. Newsl. 16
(1977) 117.
- Brown