Calcium Phosphate Nucleation Research Articles

Heterogeneous nucleation of calcium phosphates on solid surfaces in aqueous solution.

The heterogeneous nucleation of calcium phosphates on solid surfaces of poly(methyl methacrylate) (PMMA), poly-(tetrafluoroethylene-co-hexafluoropropylene) (FEP), silicone rubber, mica, and radiofrequency glow discharge (RFGD)-treated PMMA, FEP, and silicone rubber has been studied in solutions supersaturated with respect to hydroxyapatite. The surface properties of the substrates were characterized by contact angle measurements. For the RFGD-treated surfaces, the Lifshitz-Van der Waals surface tension component changes very little, but the Lewis acid-base surface tension parameters vary greatly depending upon the materials. With scanning electron microscopy, nucleation of calcium phosphates was observed only on the surfaces: mica, RFGD-treated PMMA and FEP, with relatively high values of the Lewis base surface tension parameter. The more hydrophobic surfaces having low Lewis acid-base surface tensions, untreated PMMA and FEP, silicone rubber, and even RFGD-treated silicone rubber showed no nucleation.

Calcium phosphate nucleation on porous silicon: factors influencing kinetics in acellular simulated body fluids

A range of bio-ceramics can induce calcium phosphate nucleation in simulated body fluids over timescales of hours to days. Such in-vitro behaviour is well correlated with in-vivo bone and tissue bonding ability. We demonstrate and discuss here how the “bio-activity” of porous silicon films might be tailored by manipulation of layer microstructure, chemical composition, and surface electrical charge. The kinetics of in-vitro calcification can be accelerated to occur within hours, suggesting that silicon bio-chips might be developed that could rapidly bond in-vivo with living tissue and bone. Crown Copyright © 1997 Published by Elsevier Science S.A.

Promotion of calcification on carboxymethylchitin discs

A series of water-insoluble carboxymethylchitin (CM-chitin) discs of varying degrees of substitution (d.s.) has been investigated for their interaction with calcium phosphate. Discs of d.s. 0.03, 0.11, 0.14 and 0.23 were prepared by casting from solutions of CM-chitin in 90% formic acid. Calcium uptake and calcium phosphate nucleation were found to increase with the degree of substitution of the CM-chitin discs. The results suggest that water-insoluble CM-chitin may be useful as a platform for in vivo calcification.

In vivo calcium phosphate formation induced by sol—gel‐prepared silica

Implantation with plugs made of a porous sol-gel-prepared silica into the femurs of goats demonstrated that a calcium phosphate was formed both on the silica plugs and within the pores inside the silica plugs 12 weeks postoperatively. This observation indicates that a highly hydrated silica surface is effectively catalytic for calcium phosphate nucleation. Calcification can be triggered in physiologic solution under stimulation of the silica gel. A high level of silicon in the uncalcified osteoid region of young bone is thus thought to provide a number of SiOH groups for initiating calcium phosphate formation. Our results provide some information about the mechanism of calcium phosphate mineralization in higher animals. We believe that heterogeneous nucleation of apatite can be induced from metastable calcium phosphate solutions including physiologic fluids on those specific surfaces of materials, where there are abundant acidic OH groups.

Surface Induced Calcium Phosphate Nucleation and Growth

AbstractCalcium phosphate nucleation on colloidal oxide surfaces, such as TiO2, SiO2 and Al2MO3, has been studied as a model system to understand the role of surface chemistry on crystal nucleation kinetics and phase formation. The nucleation induction times have been measured using Constant Composition (CC) technique and calcium phosphate phases formation have been determined mainly by X-ray diffraction. The results indicated TiO2 not only significantly reduces the nucleation induction time and interfacial energy but also stimulates octacalcium phosphate formation over dicalcium phosphate dihydrate. SiO2 and Al2O3 have little effect on both nucleation kinetics and phase formation.

Dietary effects upon calcium oxalate urolithiasis risk.

An animal model involving rats fed with different diets (high protein, high carbohydrate, high lipid, high fiber and control balanced diet) was used to evaluate the dietary effects on the main oxalocalcic urolithogenic parameters. It was found that the inhibitory factors that prevent calcium oxalate stone formation (citrate and magnesium) were clearly more favorable in the group of rats fed with a balanced diet. However, factors favouring the heterogeneous calcium phosphate nucleation were also found in the balanced diet. On the other hand, factors facilitating the heterogeneous uric acid nucleation were found in rats treated with high protein, high lipid, high carbohydrate and high fiber diets. In conclusion it seems that the balanced diet appears to be the less lithogenic one.

Effects of Non-Collagenous Matrix Proteins, Fatty Acid Derivatives, Etc. on the Nucleation and Growth of Calcium Phosphate on Hydroxyapatite

ABSTRACTThe effects of various non-collagenous bone matrix bio-chemicals on the deposition of calcium phosphate on hydroxyapatite surfaces have been studied. Guanidine-HCI bone extract, guanidine-EDTA bone extract and phosphatidylserine all showed an overall inhibitory effect on calcification. Phosphoserine promoted secondary nucleation but hindered crystal growth. Serum albumin altered the lattice structure of the crystals, thus inducing a significant calcium deficiency. This structural change also resulted in a different fracture behaviour.

The mineralization of calcium phosphate on separated salivary protein films

In the oral environment, dental enamel becomes coated with a proteinaceous layer referred to as the acquired enamel pellicle. The role of this layer in controlling re- and de-mineralization of enamel and the formation of other calcium deposits is not yet completely understood. In this study, the constant composition kinetics technique has been coupled with a flow-through cell in order to investigate the ability of various salivary proteins to mineralize hydroxyapatite when immobilized as films. Purified proteins of amylase, statherin, the C-terminal octapeptide of statherin and the cystatins SA-I and SA-II were studied. Amylase induced the nucleation and growth of calcium phosphate more readily than either SA-I, statherin or the C-terminal statherin. However, surfaces in which SA-II was adsorbed did not appear to induce mineralization despite having film thicknesses similar to SA-I and amylase. The morphologies of the grown crystalline phases differed markedly with statherin films showing the best crystal definition.

Urolithiasis inhibitors and calculus nucleation

The possible inhibitors of heterogeneous nucleation were investigated. The effects of magnesium, pyrophosphate, citrate and Chondroitin Sulphate on calcium phosphate or uric acid heterogeneous nucleation of calcium oxalate were studied. It was found that whereas magnesium, pyrophosphate and citrate acted as effective inhibitors in the presence of calcium phosphate as heterogeneous nucleant, only chondroitin sulphate manifested important inhibitory effects when uric acid was the heterogeneous nucleant.

The effect of dissolved impurity on calcium phosphate nucleation in supersaturated medium

Using the example of amorphous calcium phosphate (ACP) precipitation, it was shown that molecules of dissolved impurities can cause nucleation in supersaturated aqueous solutions. Electron microscopy was used as the basic method of analysis. ACP was synthesized under the conditions of rapid reagent mixing at a pH of 10.80 in a wide range of initial reagent concentrations. Transmission electron microscopy indicates that ACP particles are spheroids with an average size of 27 nm, partially joined into larger aggregates. The particle size distribution function can be described by the Fokker-Planck equation, the solution of which is in good agreement with experimental data provided proportionality exists between the number of nucleation centers and the concentration of impurities introduced with the reagents. It can be concluded that the impurity molecules contained in the reagents present a basis for ACP particle formation.

Calcium phosphate nucleation and growth in solution

Calcium phosphate nucleation and growth in solution

Heterogeneous Nucleation of Calcium Phosphates. II. Inhibition by Cupric Ions.

Heterogeneous Nucleation of Calcium Phosphates. II. Inhibition by Cupric Ions.

Peptide inhibitors of calcium phosphate precipitation in the urine of normal and stone-forming men

Peptide fractions from normal and stone-forming human urines were isolated by ion-exchange and gel filtration and the ability of these fractions to inhibit the homogeneous nucleation of calcium phosphate from aqueous solution was examined, using a new quantitative precipitation test. Comparisons between urines from 8 normal male adults and 8 patients with frequently recurring, calcium-containing renal stones revealed a lower mean inhibitory activity in the stone-forming urines than in normal urine but there was a considerable overlap of values and the difference was significant only at the 5% level. No inhibitory activity could be demonstrated in normal or stone-forming urine when calcium oxalate was substituted for calcium phosphate in the precipitation test. The evidence for the existence of urinary inhibitors of calcium salt precipitation was examined and it was concluded that the absence of peptide inhibitors of homogeneous nucleation was not a primary cause of stone formation in our patients.

Nucleation of calcium phosphate from solution

A method of determining the stoichiometry of metastable phases from nucleation characteristics is described and is applied to calcium phosphate precipitation. The stoichiometric ratio [Ca]/[P] is shown to be 1.49 ± 0.02 in the pH range 7.0–9.1, indicating that it is not hydroxyapatite which normally forms first in the physiological pH region. Characterization of the product by radio isotopes and by infrared spectroscopy and electron diffraction confirms the stoichiometry and indicates that the calcium phosphate nucleated from solution at high pH is an amorphous or soft metastable material. Some biological implications of these findings are pointed out.

The nucleation of calcium phosphate from solution

Dicalcium phosphate was precipitated from homogeneous solution in the pH range 5–6 by using the hydrolysis of cyanate to control the precipitation process. Turbidimetric determination of the onset of precipitation enabled the critical supersaturation to be determined. In this region the average critical supersaturation ratio was found to be 2.3.

Mechanisms of calcification: role of collagen, polyphosphates, and phosphatase.

The nucleating properties of various collagens have been tested by determining quantitatively the minimum ion product, Ca times P, required to form calcium phosphate crystals. While most collagens require a product of 35 (mg%)2 or greater for calcium phosphate to precipitate, some collagens extracted from tendon induce mineralization at a product of 16 (mg%)2. Plasma ultrafiltrate contains one or more substances which increase this minimum ion product, and therefore inhibit calcium phosphate nucleation. These substances are inactivated by alkaline phosphatase. Finally, polyphosphates, both organic and inorganic, are highly inhibitory to calcium phosphate nucleation and precipitation. It is therefore suggested that at least two mechanisms may be necessary for a tissue to mineralize: 1) the formation of a nucleating collagen and 2) the presence of phosphatase for the local destruction of the inhibitor(s) present in plasma.