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PubMed2005

[The preparation, structure evaluation and preliminary application of biomimetic biphasic calcium phosphate scaffold].

OBJECTIVE: To fabricate biomimetic biphasic calcium phosphate BCP ceramic scaffolds using three-dimensional (3D) gel-lamination technology and evaluated their structure with 3D parameters and related method. METHODS: Series two-dimensional images of femoral head's specimen of dogs were obtained by micro-computed tomography (Micro-CT). According to these images, porous biomimetic biphasic calcium phosphate (BCP) ceramic scaffolds with oriented trabecular structure were fabricated by three-dimensional (3D) gel-lamination technology. And then, the three-dimensional structure of the scaffolds were reconstructed by computer according to Micro-CT images of these scaffolds and evaluated by three-dimensional parameters. These parameters included bone volume fraction (BVF, BV/TV), bone surface/bone volume (BS/BV) ratio, trabecular thickness (Tb.Th), trabecular number (Tb.N), trabecular spacing (Tb.Sp) and structure model index (SMI). The biomechanical properties and biocompatibility of these scaffolds were also evaluated in the study. Six scaffolds, which were combined with BMCs (bone mesenchymal cells, BMCs), were planted into the bone defect of six dogs' femoral head respectively. RESULTS: There was no significant difference between trabecular samples and BCP scaffolds in BV/TV, Tb.Th, Tb.N, and Tb.Pf (P > 0.05). The trabecular system of the scaffold, which had some orientation, represented plate-like model. With a micro-porous porosity of 62%, the average compressive modulus and ultimate strength along the axis of the scaffolds reached (464.0 +/- 36.0) MPa and (5.6 +/- 0.8) MPa respectively. The results of animal test indicated that the trabeculae of these scaffolds were covered by a layer of new bone after 10 weeks of operation. CONCLUSION: Porous BCP scaffolds have been produced with oriented microarchitectural features designed to facilitate vascular invasion and cellular attachment and with initial mechanical properties comparable to those of trabecular bone.

Animals↗
PubMed1983

ESR spectra of VO2+ ions adsorbed on calcium phosphates.

The ESR spectra of oxovanadium(IV) ions, (VO2+), adsorbed on hydroxyapatite(OHAp), fluorhydroxyapatite(FHAp), Mg-containing tricalcium phosphate(Mg-TCP), .octacalcium phosphate (OCP), dicalcium phosphate dihydrate (DCPD), and amorphous calcium phosphate(ACP) were measured at room temperature. The ESR parameters of VO2+ adsorbed on these compounds were slightly different from one another and accordingly, the ESR technique by use of VO2+ was useful for an analysis of the calcium phosphates precipitated from supersaturated solutions. The ESR parameters of VO2+ adsorbed on ACP and Mg-TCP were found to be very similar to each other, suggesting that ACP and TCP resemble each other in the structure of their crystal surfaces.

Adsorption↗
PubMed1992

Toxicity of silica-containing calcium phosphate glasses demonstrated in mice.

Suspensions of calcium phosphate glass containing various concentrations of silica (glass composition (moles): 100 Ca(PO3)2 to x SiO2,x = 0, 5, 10, 15 or 40) dispersed in normal saline were injected intraperitoneally into C57BL/6 mice to determine the mortality within 30 days. The mortality was 0/10, 3/10, 9/10, 10/10 and 10/10 at x = 0, 5, 10, 15 and 40 mol of silica, respectively. By means of inductively coupled plasma analysis, the amount of dissolved silica (Si4+) in water at 37 degrees C from the calcium phosphate glass depended on the amount of silica in the glasses. The mortality of mice was directly proportional to the silica content of the glass injected intraperitoneally. These results clearly show that the dissolved silica (Si4+) from the glass, monomeric or low molecular silicic anion, is highly toxic. The SiO2 component in biomaterials has toxic potential when dissolved in the body.

Animals↗
PubMed2004

Calcium phosphates and glass composite coatings on zirconia for enhanced biocompatibility.

Calcium phosphates (CaP) and phosphate-based glass (P-glass, xCaO-(0.55-x) Na(2)O-0.45P(2)O(5) composition) composite coatings were obtained on a strong ZrO(2) to improve biocompatibility, the mechanical strength and biological activity. Hydroxyapatite (HA) and P-glass mixed powder slurries were coated on the ZrO(2) substrate, and subsequently heat-treated to obtain CaP- and P-glass composite coatings. The effects of glass composition (x=0.3, 0.4, 0.5 mol), mixing ratio of glass to HA (30%, 40%, 50% wt/wt), and heat treatment temperature (800 degrees C, 900 degrees C, 1000 degrees C) on the coating properties were investigated. After heat treatment, additional calcium phosphates, i.e., dicalcium phosphate (DCP) and tricalcium phosphate (TCP), were crystallized, resulting in the formation of triphasic calcium phosphates (HA-TCP-DCP) surrounded by a glass phase. The relative amounts of the crystalline phases varied with coating variables. The higher heat treatment temperature and glass amount, and the lower CaO content in the glass composition rendered the composite coatings to retain the higher amounts of TCP and DCP while the initial HA decreased. These appearance of additional crystalline phases and reduction of HA amount were attributed to the combined effects, i.e., the melting-crystallization of P-glass and the reaction between glass liquid phase and HA powder during thermal treatment. As a result of the glass phase in the composite coatings, their microstructures became much denser when compared to the pure HA coating. In particular, a completely dense structure was obtained at coating conditions with large amount of glass addition (50 wt%) at the glass composition of lower CaO content (0.3 mol CaO), and the following heat treatment above 800 degrees C for 2h. As a result, the adhesion strengths of the composite coating layers were significantly improved when compared to the pure HA coating. The highest strength of the composite coating was approximately 40 MPa, an improvement of approximately 80% with respect to the pure HA coating. The composite coatings showed much higher dissolution rates than the pure HA coating due to the newly formed crystallines (TCP and DCP) and the remaining glass phase. The osteoblast-like cells grew and spread actively on the composite coating samples. The proliferation numbers and alkaline phosphate (ALP) activities of the cells on the composite coatings were improved by approximately 30-40% when compared to Thermanox control and ZrO(2) substrate, and were comparable to the pure HA coating. These findings suggested that the CaP and P-glass composites are potentially useful for hard tissue coating system, due to their morphological and mechanical integrity, enhanced bioactivity, and favorable responses to the osteoblast-like cells.

Adhesiveness↗
PubMedDate not supplied

Anticariogenic complexes of amorphous calcium phosphate stabilized by casein phosphopeptides: a review.

Using laboratory, animal, and human in situ caries models, investigators have shown that casein phosphopeptide amorphous calcium phosphate complexes (CPP-ACP) exhibit an anticariogenic activity. The casein phosphopeptides (CPP) are produced from a tryptic digest of the milk protein casein by aggregation with calcium phosphate and purification by ultrafiltration. The CPP have a remarkable ability to stabilize calcium phosphate in solution and substantially increase the level of calcium phosphate in dental plaque. Through their multiple phosphoseryl residues, the CPP bind to forming clusters of amorphous calcium phosphate (ACP) in metastable solution, preventing their growth to the critical size required for nucleation and precipitation. The proposed mechanism of anticariogenicity for the CPP-ACP is that they localize ACP in dental plaque, which buffers the free calcium and phosphate lon activities, thereby helping to maintain a state of supersaturation with respect to tooth enamel depressing demineralization and enhancing remineralization. The CPP-ACP, unlike fluoride, can be added to sugar-containing foods and therefore have commercial potential as an additive to foods as well as to toothpastes and mouthwashes for the control of dental caries.

Amino Acid Sequence↗
PubMed2005

Fabrication of hybrid nanocapsules by calcium phosphate mineralization of shell cross-linked polymer micelles and nanocages.

Self-assembled shell cross-linked poly(acrylic acid-b-isoprene) (PAA78-b-PI97) micelles or cross-linked PAA nanocages in aqueous solution were used as templates for the preparation of novel polymer-inorganic nanocapsules. The hybrid nanostructures were typically 50-70 nm in diameter and consisted of spherical polymer nanoparticles or nanocages enclosed within a continuous 10-20 nm thick surface layer of amorphous calcium phosphate. Nucleation of calcium phosphate specifically in association with the polymer nanoparticles was facilitated by low supersaturation levels and by sequestration of Ca2+ ions within the carboxylate-rich PAA domains prior to addition of HPO4(2-). Modifications in ionic concentrations were used to control the calcium phosphate surface layer thickness and prepare mineralized cross-linked PAA-b-PI micelles with variable shell permeability. The permeability of beta-carotene into the hydrophobic PI core of mineralized shell cross-linked PAA-b-PI micelles was reduced by approximately 50 or 100% respectively for hybrid nanostructures enclosed within 10 or 20 nm thick calcium phosphate layers. Our results suggest that calcium phosphate-polymer cross-linked nanocapsules could have potential applications as pH-responsive biocompatible hybrid nanostructures for use in applications such as drug delivery, bioimaging, and therapeutics.

Biocompatible Materials↗
PubMed1987

Chemical synthesis of phosphoseryl-phosphoserine, a partial analogue of human salivary statherin, a protein inhibitor of calcium phosphate precipitation in human saliva.

Human salivary secretions are supersaturated with respect to basic calcium phosphates but spontaneous precipitation of these salts from saliva, or surface-induced precipitation of calcium phosphates onto dental enamel, does not normally occur. This unexpected stability has been attributed to the inhibitory activities of two kinds of salivary phosphoproteins: statherin and the acidic, proline-rich phosphoproteins (PRP). Investigation of the structure-function relationships of statherin, the most potent inhibitor of primary (spontaneous) and secondary (seeded) precipitation of calcium phosphate salts in human saliva has been limited to studies of peptide segments obtained from the native peptide by specific proteolysis. Solid phase peptide synthesis (SPPS) is a useful and potentially more flexible alternative. Phosphoserine residues (positions 2 & 3) play critically important roles in the precipitation-inhibition activities of statherin, but SPP synthesis of these phosphorylated peptides is precluded because of the instability of phosphoserine residues in the presence of HF. Thus, this peptide was synthesized by solution-phase methods. The dipeptide possessed substantial inhibitory activity in assays for inhibition of both primary and secondary precipitation of calcium phosphate salts, but was not as active as either N-terminal tryptic hexapeptide of statherin or intact statherin. Syntheses of other model phosphorylated peptides are underway to expand the structure-function relationships.

Calcium Phosphates↗
PubMed2004

Dynamic study of calcium phosphate formation on porous HA/TCP ceramics.

Bone-like apatite formation on porous calcium phosphate ceramics was investigated in static simulated body fluid (SBF) and dynamic SBF at different flowing rates. The results of a 14-day immersion in static SBF showed that the formation of bone-like apatite occurred both on the surface and in the pores of the samples. When SBF flow at the physiological flow rate in muscle (2 ml/100 ml min1), bone-like apatite could be detected only in internal surface of the pores of samples. The result that bone-like apatite formation could only be found in the pores when SBF flown at physiological flow rate was consistent with that of porous calcium phosphate ceramics implanted in vivo: osteoinduction was only detected inside the pores of the porous calcium phosphate ceramics. This result implicates that the bone-like apatite may play an important role in the osteoinduction of Ca-P materials. The dynamic model used in this study may be better than usually used static immersion model in imitating the physiological condition of bone-like apatite formation. Dynamic SBF method is very useful to understand bone-like apatite formation in vivo and the mechanism of ectopic bone formation in calcium phosphate ceramics.

Biomimetic Materials↗
PubMed2005

Dynamic study of calcium phosphate formation on porous HA/TCP ceramics.

Bone-like apatite formation on porous calcium phosphate ceramics was investigated in static simulated body fluid (SBF) and dynamic SBF at different flowing rates. The results of a 14-day immersion in static SBF showed that the formation of bone-like apatite occurred both on the surface and in the pores of the samples. When SBF flowed at the physiological flow rate in muscle (2 ml/100 ml.min), bone-like apatite could be detected only in internal surface of the pores of samples. The result that bone-like apatite formation could only be found in the pores when SBF flowed at physiological flow rate was consistent with that of porous calcium phosphate ceramics implanted in vivo: osteoinduction was only detected inside the pores of the porous calcium phosphate ceramics. This result implicates that the bone-like apatite may play an important role in the osteoinduction of Ca-P materials. The dynamic model used in this study may be better than usually used static immersion model in imitating the physiological condition of bone-like apatite formation. Dynamic SBF method is very useful to understand bone-like apatite formation in vivo and the mechanism of ectopic bone formation in calcium phosphate ceramics.

Apatites↗
PubMed1998

Osteoinduction by calcium phosphate biomaterials.

Different materials were implanted in muscles of dogs to study the osteoinduction of calcium phosphate biomaterials. Bone formation was only seen in calcium phosphate biomaterials with micropores, and could be found in hydroxyapatite (HA) ceramic, tricalcium phosphate/hydroxyapatite ceramic (BCP), beta-TCP ceramic and calcium phosphate cement. The osteoinductive potential was different in different materials. The results indicate that osteoinduction can be a property of calcium phosphate biomaterials when they exhibit specific chemical and structural characteristics.

Journal Article↗
PubMed2000

Chemical transformation of some biologically relevant calcium phosphates in aqueous media during a steam sterilization.

The purpose of this study was to investigate the effect of steam sterilization on some biologically relevant calcium phosphates: CaHPO4 . 2H2O (DCPD), calcium deficient apatite (CDA) and biphasic calcium phosphate (BCP). Suspensions of 0.2 g of each calcium phosphate compound with 5.0 ml of deionized water were prepared and steam sterilized in an autoclave (20 min at 121 degrees C). After sterilization the suspensions were filtered and the dried solids characterized with scanning electron microscopy, IR-spectroscopy and X-ray diffraction. The pH and calcium concentrations of the filtrates were determined with ion selective electrodes. Similar measurements were made with the same samples which were not sterilized. The sterilization procedure was found to result in the dehydration of DCPD and hydration of calcium oxide incorporated into the BCP. Solution pH was observed to change from 7.3 to 5.5 for the solutions in equilibrium with DCPD and from 8.5 to 10.6 for those in equilibrium with BCP. Minor changes both with the solid and liquid phases were found to occur during the steam sterilization of CDA. These results indicate that steam sterilization may have different effects on different calcium phosphate suspensions: it can result in dehydration of DCPD, fast hydration for CaO in BCP, but no significant effect on CDA.

Journal Article↗
PubMed1998

Interface potential of calcium phosphate in simulated body fluid.

Calcium phosphate ceramics are used in the substitution of injured or damaged bones. Nevertheless, the behaviour of these materials, and in particular, the mechanisms guiding their interface response in physiological environment is still unknown. This work describes the construction of hydroxyapatite and tricalcium phosphate electrodes used to determine the interface potential behaviour of these materials in a simulated body fluid, in a pH range corresponding to the variation observed in human body injuries, at ambient and physiological temperatures. These measurements are associated with the adsorption/desorption of ions from the materials. The results show that hydroxyapatite and tricalcium phosphate have similar behaviour in that they reach an interface potential equilibrium state faster when the solution pH is decreased and the temperature increased. This behaviour may be attributed to their ability to form a calcium-rich layer and is relevant to their quality as implantable materials.

Body Fluids↗
PubMed1986

[The shoulder in basic calcium phosphate microcrystal deposit disease].

Basic calcium phosphate (BCP) crystal deposition can lead to periarticular collections associated with typical radiographic findings, most frequently observed in the shoulder. Moreover, these deposits may be revealed in other articular sites (i.e., wrist, hand, foot, elbow, hip, etc.). Initially, the calcium deposits may appear poorly defined (cloudlike); afterwards, they may reveal different patterns (linear, triangular or circular areas), changing in size, configuration and site. Adjacent bone may be normal, although osteoporosis, cystic lesions and reactive sclerosis are reported. The radiographic appearance of calcifications will depend upon the exact location of the deposits in the specific tendon of the rotator cuff, the adjacent bursae and the soft tissues.

Adult↗
PubMed2001

Transforming growth factor-beta1 incorporated in calcium phosphate cement stimulates osteotransductivity in rat calvarial bone defects.

Bone regeneration of the alveolar crest around dental implants is an important factor in the success of implant use. Calcium phosphate cement can be used as a bone substitute and applied clinically as a paste to fill micro- and macroscopic bone defects. We have shown earlier that the intermixing of the recombinant human transforming growth factor-beta1 (rhTGF-beta1) in hardening calcium phosphate cement stimulated osteoblastic differentiation of rat primary bone cells in vitro. The aim of the present study was to examine whether the similar enrichment with rhTGF-beta1 affects the replacement of calcium phosphate cement by bone (osteotransduction) in calvarial critical size defects (csd) of adult rats. Two bone defects of 5 mm diameter were created bilaterally in each skull of 10 adult male rats. Both defects were filled with 53 mg of calcium phosphate cement without rhTGF-beta1 (control) at one side, and with 10 or 20 ng rhTGF-beta1 at the other side. After 8 weeks, defects with surrounding skull were analysed histologically and histomorphometrically. The addition of rhTGF-beta1 in the cement increased the amount of bone in rat skull defects. This finding coincidences with our in vitro observations, that intermixing of rhTGF-beta1 in calcium phosphate cement stimulates bone cell differentiation. Addition of rhTGF-beta1 stimulated bone formation as indicated by an increased bone volume of 50% and an increased bone/cement contact of 65%, in comparison to control defects with cement without rhTGF-beta1. In addition, rhTGF-beta1 reduced the remaining volume of cement, by 11% at 10 ng rhTGF-beta1, and by 20% at 20 ng rhTGF-beta1 in the cement. Defect closure was not affected. We conclude that the intermixing of rhTGF-beta1 in a fast-setting calcium phosphate cement stimulates bone growth and the osteotransduction of the cement. For bone regeneration procedures around endosseous implants, calcium phosphate cement with rhTGF-beta1 might be an appropriate combination for early osseointegration and implant use.

Animals↗
PubMed2006

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

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

Biocompatible Materials↗
PubMed2004

An equilibrium thermodynamic model of the sequestration of calcium phosphate by casein micelles and its application to the calculation of the partition of salts in milk.

An equilibrium thermodynamic model of the interaction of calcium, phosphate and casein in milk is described in which the micellar calcium phosphate is assumed to be in the form of calcium phosphate nanoclusters. A generalized empirical formula for the nanocluster is used to define the molar ratios of small ions (Ca, Mg, P(i) and citrate) to a casein phosphorylated sequence (phosphate centre, PC). From this model, a method of calculating the partition of milk salts into diffusible and non-diffusible fractions is obtained. No arbitrary assumptions are made, no fitting of adjustable parameters is done and the PCs in the caseins are defined by inspection of their primary structures. In addition to the salt partition, the mole fractions of the individual caseins not complexed to the calcium phosphate through one or more of their PCs are computed and a generic stability rule for milks is derived. The use of the model is illustrated by calculations of the partition of salts in a standard milk and by comparison with experimental data on the partition of salts in the milk of individual cows. The generic stability rule is applied to the individual milks to determine whether the micellar calcium phosphate is thermodynamically stable. According to the calculations, compositions that might lead to pathological calcification in the lumen of the mammary gland were seldom found in primiparous healthy cows in early or mid lactation but occurred more often in multiparous animals, in late lactation and during mastitic infection.

Animals↗
PubMed1977

In vitro adsorption of doxorubicin hydrochloride on insoluble calcium phosphate.

The adsorption of doxorubicin hydrochloride, a potent antitumor agent, on solid tribasic calcium phosphate was studied in vitro. A Langmuir adsorption isotherm at pH 7.4 and the maximum adsorption capacity of tribasic calcium phosphate were established. Tribasic calcium phosphate was chosen as a model for solid bone samples, which are stained with doxorubicin in patients who have received long-term doxorubicin therapy.

Adsorption↗