Preparation Of Calcium Phosphate Research Articles

In vitro degradation studies of calcium phosphate glass ceramics prepared by controlled crystallization

Calcium phosphate glass ceramics with incorporation of small additions of two nucleating agents, MgO and K 2O were prepared in the metaphosphate and pyrophosphate region, using an appropriate two-step heat treatment of controlled crystallization defined by differential thermal analysis results. Identification and quantification of crystalline phases precipitated from the calcium phosphate glass were performed using X-ray diffraction and Rietveld analysis. The β-Ca 2P 2O 7 (β-DCP), KCa(PO 3) 3, β-Ca(PO 3) 2 and Ca 4P 6O 19 phases were detected in the glass ceramics. In order to evaluate the degradation of the glass ceramics prepared, degradation studies were carried out during 42 days in Tris-HCl solution at 37 °C, pH 7.4, using granules in the range of 355–415 μm. The materials presented a weight loss ranging up to 12%. The ions leached during the immersion mainly originated from the KCa(PO 3) 3 phase, probably due to the presence of K + ion in the calcium metaphosphate, and the residual glassy phase. The structural changes at the surface of materials during degradation have been analyzed by Fourier transform infrared spectroscopy and X-ray diffraction. Results showed that significant surface changes occurred with immersion time, with the decrease of KCa(PO 3) 3, β-Ca 2P 2O 7 and β-Ca(PO 3) 2 phases occurring at different periods of immersion. This study has demonstrated an easy way to prepared calcium phosphate materials with specific calcium phosphate phases and crystallization, and therefore specific degradation rates.

Hydrothermal method for preparing calcium phosphate monoliths

A new hydrothermal route for preparing biphasic calcium phosphate monoliths is proposed. Firstly, a slurry of b-tricalcium phosphate/ortho-phosphoric acid (b-TCP/H3PO4) is cast into the desired final shape and size to obtain a block composed of dicalcium phosphate dihydrate (DCPD) and b-TCP. This block is then treated in 1.0 M Na2HPO4 at 60 °C in order to hydrolyze the DCPD into Ca10-x(HPO4)x(PO4) 6-x(OH)2-x (CDHA) and Ca8H2(PO4)6 .5H2O (OCP). The result is a monolithic piece which preserves the initial shape and size, but which is composed instead of CDHA, OCP, and b-TCP. During the initial stage, when the pH is slightly alkaline, the product of DCPD hydrolysis is CDHA. However, when a neutral or slightly acidic pH is reached OCP is formed. Test samples processed by this method showed complete conversion of DCPD into CDHA and OCP after 112 h of hydrolysis, and with a compressive strength of 16.2 MPa, similar to cancellous bone.

Investigation of Bone Formation using Non-Crystalline Calcium Phosphate Glass in Beagle Dogs

Investigation of Bone Formation using Non-Crystalline Calcium Phosphate Glass in Beagle Dogs

Proteins incorporated into biomimetically prepared calcium phosphate coatings modulate their mechanical strength and dissolution rate

In a previous investigation, we demonstrated that when bovine serum albumin (BSA) is biomimetically co-precipitated with Ca 2+ and PO 4 3− ions upon titanium-alloy implants, it becomes incorporated into the crystal lattice and is not merely deposited on its surface. Moreover, the protein elicited a change in crystal structure from an octacalcium phosphate type to a carbonated apatite one, which bears a closer resemblance to natural bone mineral. In the present study, we investigated the dissolution rate and mechanical strength of such BSA-containing coatings as a function of protein concentration within the bathing medium (10 ng/ml to 1.0 mg/ml). BSA-containing coatings released Ca 2+ ions more slowly (5 ppm/min) than did non-BSA-containing ones (10 ppm/min), but this rate did not change as a function of protein concentration within the bathing medium. In contrast, the strength of coatings increased almost linearly as a function of protein concentration within the bathing medium, indicating that BSA incorporated into the crystal lattice enhances its mechanical strength in a concentration-dependent manner.

Calcium Effects on Phosphorus Absorption: Implications for the Prevention and Co-Therapy of Osteoporosis

Objective: To evaluate the effect of calcium intake on absorption of dietary phosphorus, with special reference to typical calcium intakes and to those likely to be encountered in prevention and treatment of osteoporosis.Setting: Two academic health sciences centers; inpatient metabolic research unit.Methods: Evaluation of calcium and phosphorus balance data obtained in two data sets, the first, 543 studies of healthy women aged 35–65, and the second, 93 men and women aged 19–78; development of multiple regression models predicting fecal phosphorus (the complement of net absorbed phosphorus); data from the two centers analyzed separately as a check on the consistency of the findings.Results: Mean net absorption of phosphorus was 60.3% (±18.1) for data set 1 and 53.0% (±9.4) for data set 2. Just two variables, fecal calcium and diet phosphorus, were positively and independently associated with fecal phosphorus. These variables explained 73% of the variance in fecal phosphorus in data set 1 and 33% in data set 2. Fecal calcium alone explained the lion’s share of the relationship. The coefficients of the fecal calcium term in the models fitted to the data were 0.332 ± 0.022 and 0.155 ± 0.039, for data sets 1 and 2, respectively. Adjusting for the relationship between fecal calcium and calcium intake and using the parameters of the larger data set, it follows that each increase in calcium intake of 0.5 g (12.5 mmol) decreases phosphorus absorption by 0.166 g (5.4 mmol).Conclusions: As calcium intake increases without a corresponding increase in phosphorus intake, phosphorus absorption falls and the risk of phosphorus insufficiency rises. Intakes with high Ca:P ratios can occur with use of supplements or food fortificants consisting of non-phosphate calcium salts. Older patients with osteoporosis treated with current generation bone active agents should receive at least some of their calcium co-therapy in the form of a calcium phosphate preparation.

Structure development and crystallization behaviour of PP/nanoparticulate composite

The structure development and crystallization behaviour of polypropylene (PP) containing nanoparticles of calcium phosphate prepared by a new route based on matrix mediated control of growth and morphology was investigated by X-ray diffraction (XRD), optical microscopy and DSC techniques. The results obtained were compared with that of PP containing conventionally prepared calcium phosphate (CaP0). Both nanoparticle filled PP as well as CaP0 filled PP crystallized in monoclinic α crystalline phase. However, considerable changes were observed in the relative intensities of the XRD peaks, especially the peak II (040 reflection), in the case of PP filled with nanosize calcium phosphate. The isothermal crystallization curves showed dramatic increase of crystallization rate and decrease in t1/2 value for PP/nanoparticulate composites resulting in a rapid decrease in the ultimate spherulite size as compared to PP/CaP0 samples. The nucleating efficiency was found to be dependent on the particle size as inverse exponential power law. These results were further confirmed by DSC analysis. The optical transparency of the PP/nanoparticle composites was found to be much higher than that containing conventional CaP0 for the same concentrations and this could be associated with the reduction in the PP crystallite size.

Hydroxyapatite cement: an alternative for craniofacial skeletal contour refinements

Hydroxyapatite cement is a calcium phosphate preparation composed of tetracalcium phosphate and dicalcium phosphate anhydrous powders. When mixed with water it isothermically forms a paste which can easily be shaped intraoperatively. This mixture sets in approximately 15-20 min and converts into water insoluble, nonceramic, microporous hydroxyapatite in 4 h. This biomaterial was used to correct either congenital or traumatic craniofacial contour irregularities or deficiencies in 20 patients. On follow-up there was only one patient who required repeat surgery for further correction, there were no other complications. The good cosmetic results, the ease of operation, the pliability of the cement paste allowing precise moulding during application, the short operation time and the avoidance of a donor site makes hydroxyapatite cement an attractive material for treating craniofacial contour defects. Careful long term follow-up is necessary to establish its safety and reliability.

Preparation of calcium phosphate coating on porous tantalum

Preparation of calcium phosphate coating on porous tantalum

A Study on the Thermal Properties of Dibasic Calcium Hydrogen Phosphate and Monobasic Calcium Phosphate.

Dibasic calcium hydrogen phosphate (CaHPO 4 . 2H 2 O) and monobasic calcium phosphate (Ca(H 2 PO 4 ) 2 ° H 2 O) are usually mixed with calcium carbonate or phosphoric acid as the raw material to prepare calcium phosphate glass by melting. In this work, the dehydration mechanisms and the activation energies of dehydration of CaHPO 4 . 2H 2 O and Ca(H 2 PO 4 ) 2 . H 2 O are investigated using nonisothermal TA technique and X-ray powder diffraction patterns.

A simple method to prepare calcium phosphate coatings on Ti6Al4V.

A two-step chemical treatment followed by immersion in a supersaturated calcification solution (SCS) was found to be a simple way to prepare calcium phosphate (Ca-P) coatings on Ti6Al4V. The Ca-P deposition on the treated metallic surfaces could be accelerated by employing a pre-calcification (Pre-Ca) procedure prior to immersion in SCS. The two-step treatment was performed by etching the metallic plates with a mixture of HCl and H2SO4 followed by ageing in boiling diluted NaOH solution at 140 degrees C. Pre-Ca was carried out by incubating the two-step treated plates in Na2HPO4 solution and then in saturated Ca(OH)2 solution. The formation of a bioactive microporous surface oxide layer on Ti6Al4V by the two-step treatment was most probably responsible for the induction of Ca-P precipitation. The deposition rates and compositions of Ca-P coatings in two different SCSs were investigated by means of scanning electron microscopy, X-ray diffraction and infrared spectrophotometry.

Rapid association of unconjugated bilirubin with amorphous calcium phosphate.

The association of unconjugated bilirubin (UCB) with amorphous calcium phosphate was studied in vitro. To this end UCB, solubilized in different micellar bile salt solutions, was incubated with freshly prepared calcium phosphate precipitate. It was demonstrated that amorphous calcium phosphate (ACP) rapidly binds and precipitates UCB in a dose-dependent way. The results indicate that binding of UCB to ACP is specific: binding to barium phosphate was negligible and addition of low amounts of Mg2+ before formation of the calcium phosphate precipitate (Ca:Mg = 5:1) inhibited binding by 80%. Free Ca2+ stimulated binding, whereas free phosphate ions inhibited binding of UCB in taurocholate solutions and to a lesser extent in glycocholate solutions. The apparent affinity of UCB for amorphous calcium phosphate was different in the various bile salt solutions. Binding of UCB decreased at pH > 8.5 in taurocholate solutions, but not in glycocholate solutions where binding of UCB was constant from pH 7.5-10.5. We propose a model in which UCB directly binds to amorphous calcium phosphate in the presence of bile salts that weakly interact with ACP, like taurocholate. In the presence of bile salts that strongly interact with ACP, such as glycochenodeoxycholate, binding of UCB may also occur via the bile salt. In conditions of unconjugated hyperbilirubinemia, such as the Crigler-Najjar syndrome, neonatal jaundice, and in the Gunn rat, considerable amounts of UCB diffuse across the intestinal mucosa. Binding of UCB to calcium phosphate in the intestine may stimulate its excretion and thereby constitute a relevant mechanism of excretion.

Chloride- and alkali-containing calcium phosphates as basic materials to prepare calcium phosphate cements

Combinations of an alkali-containing calcium phosphate-like rhenanite, sodium whitlockite or calcium potassium phosphate and a chloride-containing calcium phosphate-like spodiosite or chloroapatite with or without additions of other calcium phosphates like monocalcium phosphate monohydrate, dicalcium phosphate or dicalcium phosphate dihydrate were made and mixed with water into pastes. The setting time of these pastes was determined. After soaking for a day in Ringer's solution at 37°C the compressive strength and the diametral tensile strength were determined. Two of the combinations tried in this study resulted in the formation of cements at room temperature. One cement was of the type dicalcium phosphate, whereas the other gave octocalcium phosphate as the solid reaction product. The byproducts formed were an aqueous solution of NaCl and one of K 2HPO 4, respectively. Applications for bone repair and augmentation are envisaged. Biomaterials (1994) 15, (12) 1019–1023

Hydroxyapatite Cement: I. Basic Chemistry and Histologic Properties

Hydroxyapatite cement is a unique calcium phosphate preparation that can be shaped intraoperatively and sets in vivo to an implant composed of microporous hydroxyapatite. The histologic response to this cement was evaluated by implanting disks made of this material within the heads of nine cats. Three sets of 12 hydroxyapatite cement disks were produced containing 0%, 10%, and 20% macropores by volume, respectively. The disks were implanted subcutaneously, intramuscularly, above the periosteum of the skull, and directly onto the surface of the calvarium. Each macropore percentage was represented in each tissue plane, and animals were killed up to 9 months postoperatively. There were no toxic reactions, implants extruded, or wound infections. Histologic examination of the implant-soft-tissue interfaces revealed a transient inflammatory response without foreign body reaction. The disks were resorbed over time in direct proportion to their macropore content (surface areas) in all groups except for those disks placed directly onto the surface of the calvarium below the periosteum. In this group, numerous foci of bone formed at the skull-implant interface, with variable replacement of the deep surface of these implants by bone. Implant replacement by bone is postulated to occur through a combination of implant resorption coupled with osteoconduction. Based on these properties, hydroxyapatite cement may prove useful when applied to the reconstruction of non-stress-bearing skeletal tissue.

Phosphopeptide dissociation from micellar calcium phosphate preparations does not induce crystallinity

Phosphopeptide dissociation from micellar calcium phosphate preparations does not induce crystallinity

The EXAFS spectra of poorly crystalline calcium phosphate preparations from heated milk

The EXAFS spectra of poorly crystalline calcium phosphate preparations from heated milk

Comparative chemistry of amorphous and apatitic calcium phosphate preparations

Unwashed samples of amorphous calcium phosphate (ACP) contain an irreplaceable labile fraction, rich in acid phosphate and low in Ca/P ratio, which is irreversibly lost during the washing process. Native ACP precipitated in the pH range 6.6–10.6 varied in Ca/P molar ratio from 1.18 to 1.50 and in HPO42−/total P from 33.0% to 10.1%. At pH 7.40, native ACP had a Ca/P molar ratio of 1.36±0.02 and contained 22.8 (±2.2)% HPO42−. Unwashed precipitate data could not be attributed to either trapped supernatant Ca2+ and HPO42− or extraneous Na+, Cl−, and CO32−. The amorphous calcium phosphates are recognized as a class of salts having variable chemical but identical glass-like, physicochemical properties. Non-crystalline CaHPO4·xH2O may also be an ACP, especially during early formative stages. At physiological pH, ACP transforms to small platy crystals containing large amounts of readily-replaceable acid phosphate. Washing this surface layer produced chemical alterations in the resultant crystals; unwashed crystals had poorly-crystalline apatitic diffraction patterns but exhibited poorly-resolved infrared spectra intermediate between apatite and octacalcium phosphate. Structural explanations for all these phenomena are discussed, and revised bone and cartilage amorphous/crystalline mineral compositions have been re-calculated.

Thermochemical studies on amorphous calcium phosphate.

Previous studies have indicated that synthetically-precipitated amorphous calcium phosphate, even though not a periodically regular structure, possesses a chemically definable local unit of structure. The present paper is a report of thermochemical studies performed to more clearly define this local chemical unit. Upon ignition in the absence of water, freezedried amorphous calcium phosphate preparations converted into crystalline α-and/or β-tricalcium phosphates. At temperatures just below the crystallization point, the amorphous calcium phosphate became almost completely dehydrated. Additionally, pyrophosphate production at these subcrystallization temperatures was very low. From these data, it appears that water in amorphous calcium phosphate does not exist in combination with the P2O5 component as acid phosphate but retains its molecular identity, suggesting, together with previously reported chemical data, that amorphous calcium phosphate when formed under specific chemical conditions is a hydrated tricalcium phosphate.

Assorption patterns of enterovirus ribonucleic acid : I. Methods of preparation of calcium phosphate

Fractionation of infectious poliovirus RNA on calcium phosphate columns is described. The RNA was extracted from type I poliovirus, strain Brunhilde. Three fractions were obtained. A description is given of the methods of preparing calcium phosphated on which such fractionations can be achieved.

Preparation of calcium phosphate for protein chromatography

Simple procedures are described for the preparation of a relatively neutral and of a basic calcium phosphate for column chromatography of proteins.