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PubMed1999

Calcium phosphate bone cements for clinical applications. Part II: precipitate formation during setting reactions.

Calcium phosphate bone cements (CPBC) have been of great interest in medicine and dentistry due to their excellent biocompatibility and bone-repair properties. In this article, a review is presented of the scientific literature concerning precipitate formation during setting reactions of CPBCs. Firstly, the available information has been classified according to the intended final product or calcium phosphate formed during setting reactions. Taking the final product into account, a second classification has been made according to the calcium phosphates present in the original powder mixture. This is the most natural classification procedure because it is based on thermodynamic reasons supported by solubility diagrams for the calcium phosphate salts. By understanding the thermodynamics of calcium phosphate salts in an aqueous solution at room or body temperature it is possible to optimize the manufacturing technology involved in the production of CPBCs. Knowledge of the limitations of this thermodynamic approach opens up new possibilities in the search for CPBCs with better in vitro and in vivo properties for clinical applications.

Journal Article↗
PubMed2004

Strontium substituted calcium phosphate biphasic ceramics obtained by a powder precipitation method.

Strontium (Sr) substituted calcium phosphate ceramics were fabricated using a powder precipitation method. The Sr ions were added up to 8 mol % to replace the Ca ions during the powder preparation. Composition analysis showed that the added Sr was not fully incorporated within the as-precipitated apatite structure, presumably being washed out during the powder preparation. After calcination, the Sr containing powders were crystallized into apatite and tricalcium phosphate (TCP), that is, biphasic calcium phosphates were formed. The amount of TCP increased with increasing the Sr addition. The lattice parameters of the calcined powders increased gradually with Sr substitution in both the a- and c-axis. However, the obtained values deviated slightly from the calculated ones at higher Sr additions (>4%) due to the partial substitution of Sr ions. The microstructure of the sintered bodies changed with the Sr addition due to the formation of TCP. The Vickers hardness increased slightly from 5.2 to 5.5 MPa with increasing Sr addition, which was driven by the HA+TCP biphasic formation. The osteoblast-like cells cultured on the Sr-substituted biphasic sample spread and grew actively. The proliferation rate of the cells was higher in the samples containing more Sr. The alkaline phosphate activity of the cells was expressed to a higher degree with increasing Sr addition. These observations confirmed the enhanced cell viability and differentiation of the Sr-substituted biphasic calcium phosphate ceramics.

Alkaline Phosphatase↗
PubMed2000

Behavior in simulated body fluid of calcium phosphate coatings obtained by laser ablation.

Three types of calcium phosphate coatings onto titanium alloy substrates, deposited by the laser ablation technique, were immersed in a simulated body fluid in order to determine their behavior in conditions similar to the human blood plasma. Neither the hydroxyapatite coating nor the amorphous calcium phosphate coating do dissolve and the alpha-tricalcium phosphate phase of the coating of beta-tricalcium phosphate with minor alpha phase slightly dissolves. Precipitation of an apatitic phase is favored onto the hydroxyapatite coating and onto the coating of beta-tricalcium phosphate with minor alpha phase. Onto the titanium alloy substrate reference there is also precipitation but at larger induction times. However, onto the amorphous calcium phosphate coating no precipitate is formed.

Alloys↗
PubMed2005

[Study on the methods of promoting the injectability of calcium phosphate cement].

OBJECTIVE: To study the methods of promoting the injectability of calcium phosphate cement. METHODS: Evaluation methods of bone cements, injectability and methods of promoting injectability were reviewed by extensive investigating of latest literatures. RESULTS: It was very important to improve the injectability of calcium phosphate cement. Commonly used methods to evaluate the injectability included testing injectability coefficient, pushing force and injection pressure. Injectability of calcium phosphate cement were promoted by increasing liquid/solid ratio, modulating the component of solid or liquid phase, and adding various additives. CONCLUSION: Promoting the injectability of calcium phosphate cement is the clinical requirement.

Biocompatible Materials↗
PubMed1991

Relationship between metabolic acidosis and calcium phosphate urinary stone formation in women.

The relationship between the degree of metabolic acidosis and calcium phosphate stone formation was studied. Furthermore, the reasons why renal tubular acidosis (RTA) and primary hyperparathyroidism (PHPT) dominantly occur in women, and female stone formers more often produce calcium phosphate stone are discussed. Blood was slightly more acidotic in women than in men in both the urolithiasis and the control groups. Likewise, blood was significantly more acidotic and urinary pH significantly higher in patients with PHPT. Patients with RTA had severe metabolic acidosis, and urinary pH was highest among all groups. Calcium phosphate concentration was significantly higher in women than in men, and was also higher in patients with PHPT than in those with urolithiasis. All patients with RTA had pure calcium phosphate stones. The reasons why females are more acidotic and have more calcium phosphate in stones are suspected to be related to progesterone and urinary tract infection.

Acidosis, Renal Tubular↗
PubMed1997

The effects of calcium phosphate particles on the growth of osteoblasts.

With advances in ceramics technology, calcium phosphate bioceramics have been applied as bone substitutes for several decades. The focus of this work is to elucidate the biocompatibility of the particulates of various calcium phosphate cytotoxicities. Four different kinds of calcium phosphate powders, including beta-tricalcium phosphate (beta-TCP), hydroxyapatite (HA), beta-dicalcium pyrophosphate (beta-DCP), and sintered beta-dicalcium pyrophosphate (SDCP), were tested by osteoblast cell culture. The results were analyzed by cell count, concentration of transforming growth factor-beta 1 (TGF-beta 1), alkaline phosphatase (ALP), and prostaglandin E2 (PGE2) in culture media. The changes were most significant when osteoblasts were cultured with beta-TCP and HA bioceramics. The changes in cell population of the beta-TCP and HA were quite low in the first 3 days, then increased gradually toward the seventh day. The changes in TGF-beta 1 concentration in culture medium inversely related to the changes in cell population. The ALP titer in the culture media of the beta-TCP and HA were quite high in the first 3 days, then decreased rapidly between the third and seventh days. The concentrations of PGE2 in the culture media tested were quite high on the first day, decreased rapidly to the third day, and then gradually until the seventh day. The changes in the beta-DCP and SDCP were quite similar to those of HA and beta-TCP but much less significant. We conclude that HA and beta-TCP have an inhibitory effect on the growth of osteoblasts. The inhibitins effects of the HA and beta-TCP powders on the osteoblast cell cultures possibly are mediated by the increased synthesis of PGE2.

Alkaline Phosphatase↗
PubMed2003

In vivo evaluation of bone marrow stromal-derived osteoblasts-porous calcium phosphate ceramic composites as bone graft substitute for lumbar intervertebral spinal fusion.

STUDY DESIGN: Autogenous bone marrow stromal-derived osteoblasts-porous calcium phosphate ceramic composites were constructed in vitro under cell culture for 48 hours and implanted as a bone graft substitute for lumbar intervertebral spinal fusion in rabbits. OBJECTIVES: To evaluate the efficacy of autogenous bone marrow stromal-derived osteoblasts-porous calcium phosphate ceramic composites as an alternative to autogenous graft materials in a lumbar interbody spinal fusion model. SUMMARY OF BACKGROUND DATA: Bone marrow contains a population of rare progenitor cells capable of differentiating into bone, cartilage, muscle, tendon, and other connective tissues. These cells can be induced and differentiated into osteogenic osteoblasts with addition of osteogenic supplements. Combining bone marrow stromal-derived osteoblasts with porous ceramics gave rise to bone tissue in subcutaneous sites and repaired critical size segmental femoral defects. Little work has been done in the spine to assess fusion rates and associated biomechanical characteristics. METHODS: Five experimental groups were evaluated: sham operation (Group I); porous calcium phosphate ceramics alone (Group II); autogenous tricortical iliac crest (Group III); bone marrow stromal-derived osteoblasts-calcium phosphate ceramic composites (Group IV); bone marrow stromal-derived osteoblasts-calcium phosphate ceramic composites with rhBMP-2 (Group V). All rabbits were killed 12 weeks after surgery, and the spinal fusion segments underwent the evaluation of gross inspection, manual palpation, radiography, computed tomography, nondestructive biomechanical testing, and histologic analysis. RESULTS: Successful spinal fusion was achieved by manual palpation in 100% (6/6) of animals in Group IV and Group V, 66.7% (4/6) in Group III, 50% (3/6) in Group II, and 0% (0/6) in Group I. Radiographic studies showed that minimal disc height loss was observed with ceramic blocks than with autograft. Biomechanical testingconfirmed that spines from Group IV and Group V were statistically significantly stiffer in flexion, extension, left and right bending, and left and right torsion than Group III and Group II. Histologic analysis demonstrated a qualitative increase of bone formation in fusion mass in Group IV and Group V versus all other groups. The size of fusion mass and the stiffness of fusion segments were greatest in Group V. CONCLUSION: The results indicate that bone marrow stromal-derived osteoblasts-calcium phosphate ceramic composites may provide an alternative to autogenous graft materials for lumbar interbody spinal fusion. Adding recombinant human bone morphogenetic protein-2 into the composites may reinforce the biomechanical stiffness for spinal fusion segments. Porous calcium phosphate ceramics alone were not suitable as a bone graft substitute for lumbar interbody spinal fusion.

Animals↗
PubMed1993

Osseointegration of macroporous calcium phosphate ceramics having a different chemical composition.

Calcium phosphate macroporous ceramics are biocompatible for bone surgery. Their osseointegration is, however, sometimes very poor. To measure the effect of the calcium phosphate content of the ceramic on its osseointegration, macroporous ceramics, differing in their chemical composition, were implanted into sheep femurs. The ceramics were composed of different percentages of hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP). All other characteristics were the same. Results were assessed histologically with image analysis and showed significant differences in the amount of bone formed at the contact of the different ceramics. Ceramics containing beta-TCP induced better osseointegration than pure HA ceramics.

Animals↗
PubMed2001

Electron diffraction and high resolution transmission electron microscopy in the characterization of calcium phosphate precipitation from aqueous solutions under biomineralization conditions.

Calcium phosphate precipitation obtained from aqueous solutions at room and body temperature and pH 5.5-7.5 were investigated by high-resolution transmission electron microscopy (HRTEM), transmission electron diffraction, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Supersaturated solutions of calcium phosphates were prepared by different methods of mixing of the stock solutions: diffusion-controlled mixing in space, convection-controlled mixing on earth and forced mixing on earth and with typical physiological parameters (pH and temperature). Concentrations of the stock solutions, rate of solution mixing and duration of precipitation influence very strongly the chemical composition of the precipitation, the phase composition of individual crystals, their sizes, morphology and structure. Microdiffraction and HRTEM techniques showed an incontestable advantage on other techniques like SEM and XRD in the investigation of small particles and mixtures of calcium phosphates (hydroxyapatite and octacalcium phosphate) with different proportions.

Journal Article↗
PubMed1999

Porous calcium phosphate coating over phosphorylated chitosan film by a biomimetic method.

A porous calcium phosphate coating deposited on chitosan films was studied using scanning electron microscopy, energy-dispersive X-ray analysis, micro-Fourier transform infrared spectroscopy (micro-FTIR) and thin-film X-ray diffractometry (XRD). Chitosan films were first prepared by dissolving chitosan powder in dilute acetic acid and drying in a flat petri dish. The films were phosphorylated using urea and H3PO4 with the P content being 0.1-0.2 wt%. Phosphorylated films soaked in saturated Ca(OH)2 solution for 8 days led to the formation of a calcium phosphate precursor phase over the entire surface. This precursor phase stimulated the growth of a porous coating of calcium-deficient hydroxy apatite when immersed in 1.5 x SBF for more than 20 days. Phosphorylated films not treated with Ca(OH)2 did not show any calcium phosphate growth upon immersion in SBF solution. The precursor phase is thought to be octacalcium phosphate, which nucleates a HAP phase during SBF treatment. Initially, this treatment in SBF results in the formation of a single-layer calcium phosphate particles over the film surface. As immersion time in SBF increases, further nucleation and growth produce a porous HAP coating. The Ca/P ratio of the HAP coating is a function of SBF immersion time.

Absorptiometry, Photon↗
PubMed1997

Tissue response to fast-setting calcium phosphate cement in bone.

Fast-setting calcium phosphate cement (FSCPC) is a promising new bioactive cement with a significantly short setting time (approximately 5-6 min) compared to conventional calcium phosphate cement (c-CPC) (30-60 min) at physiologic temperatures. As a result of its ability to set quickly, it is applicable in surgical procedures where fast setting is required. In this study, FSCPC was implanted in rat tibiae to evaluate tissue response and biocompatibility. FSCPC was converted to hydroxyapatite (HAP) in bone faster than c-CPC in the first 6 h. By 24 h, significant amounts of both FSCPC and c-CPC had been converted to HAP. The conversion of FSCPC into HAP further proceeded gradually, reaching 100% within 8 weeks. Infrared spectroscopic analysis disclosed the deposition of B-type carbonate apatite, which is a biological apatite contained in human dentin or bone, on the surface of the FSCPC. Histologically, FSCPC showed a tissue response similar to that of c-CPC. A slight inflammatory reaction was observed in the soft tissue apposed to both cements in the early period, and new bone was formed along the surface of the FSCPC at the adjacent bone. However, no resorption of either cement by osteoclasts or macrophages was observed within 8 weeks. We conclude that FSCPC is superior to c-CPC in clinical applications in oral and maxillofacial, orthopedic, plastic, and reconstructive surgery, since it shows a faster setting time and higher mechanical strength in the early period that are required in these surgical procedures, as well as osteoconductivity and excellent biocompatibility similar to that of c-CPC.

Animals↗
PubMed1986

Biomaterial aspects of calcium phosphates. Properties and applications.

Biomaterials composed of calcium phosphate ceramics are receiving increasing attention as potential bone graft substitutes. These substances have proved to be the most biocompatible hard-tissue implant materials discovered. The mechanical and biologic properties of the calcium phosphates, as well as their present and future applications, are discussed.

Absorption↗
PubMed1990

Resolution-enhanced Fourier transform infrared spectroscopy study of the environment of phosphate ions in the early deposits of a solid phase of calcium-phosphate in bone and enamel, and their evolution with age. I: Investigations in the upsilon 4 PO4 domain.

In order to investigate the possible existence in biological and poorly crystalline synthetic apatites of local atomic organizations different from that of apatite, resolution-enhanced, Fourier transform infrared spectroscopy studies were carried out on chicken bone, pig enamel, and poorly crystalline synthetic apatites containing carbonate and HPO4(2-) groups. The spectra obtained were compared to those of synthetic well crystallized apatites (stoichiometric hydroxyapatite, HPO4(2-)-containing apatite, type B carbonate apatite) and nonapatitic calcium phosphates which have been suggested as precursors of the apatitic phase [octacalcium phosphate (OCP), brushite, and beta tricalcium phosphate and whitlockite]. The spectra of bone and enamel, as well as poorly crystalline, synthetic apatite in the upsilon 4 PO4 domain, exhibit, in addition to the three apatitic bands, three absorption bands that were shown to be independent of the organic matrix. Two low-wave number bands at 520-530 and 540-550 cm-1 are assigned to HPO4(2-). Reference to known calcium phosphates shows that bands in this domain also exist in HPO4(2-)-containing apatite, brushite, and OCP. However, the lack of specific absorption bands prevents a clear identification of these HPO4(2-) environments. The third absorption band (610-615 cm-1) is not related to HPO4(2-) or OH- ions. It appears to be due to a labile PO4(3-) environment which could not be identified with any phosphate environment existing in our reference samples, and thus seems specific of poorly crystalline apatites. Correlation of the variations in band intensities show that 610-615 cm-1 band is related to an absorption band at 560 cm-1 superimposed on an apatite band. All the nonapatitic phosphate environments were shown to decrease during aging of enamel, bone, and synthetic apatites. Moreover, EDTA etching show that the labile PO4(3-) environment exhibited a heterogeneous distribution in the insoluble precipitate.

Aging↗
PubMed2006

Increased remineralization of tooth enamel by milk containing added casein phosphopeptide-amorphous calcium phosphate.

Casein phosphopeptide amorphous calcium phosphate nano-complexes (CPP-ACP) in chewing gum, lozenges and mouthrinses have been shown to re-mineralize enamel subsurface lesions in human in situ experiments. The aim of this double-blind, randomized clinical study was to investigate the capacity of CPP-ACP added to bovine milk to re-mineralize enamel subsurface lesions in situ. Ten subjects drank milk containing either 2.0 or 5.0 g CPP-ACP/l or a control milk whilst wearing removable appliances with enamel slabs containing subsurface demineralized lesions. Each 200 ml milk sample was consumed once a day for each weekday over three consecutive weeks. After each treatment and one weeks rest the subjects crossed over to the other treatments. At the completion of the treatments the enamel slabs were removed and remineralization determined using microradiography and microdensitometry. The results demonstrated that all three milk samples re-mineralized enamel subsurface lesions. However, the milk samples containing CPP-ACP produced significantly greater remineralization than the control milk. The re-mineralizing effect of CPP-ACP in milk was dose-dependent with 2.0 and 5.0 g CPP-ACP/l producing an increase in mineral content of 70 and 148%, respectively, relative to the control milk. The differences in remineralization following exposure to the three milk samples were all statistically significant (P<0.001). In conclusion, this study shows that the addition of 2.0-5.0 g CPP-ACP/l to milk substantially increases its ability to re-mineralize enamel subsurface lesions.

Administration, Buccal↗
PubMed2001

Formation of macropores in calcium phosphate cement implants.

A calcium phosphate cement (CPC) was shown to harden at ambient temperatures and form hydroxyapatite as the only end-product. Animal study results showed that CPC resorbed slowly and was replaced by new bone. For some clinical applications, it would be desirable to have macropores built into the CPC implant to obtain a more rapid resorption and concomitant osseointegration of the implant. The present study investigated the feasibility of a new method for producing macropores in CPC. Sucrose granules, NaHCO3, and Na2HPO4 were sieved to obtain particle sizes in the range of 125 microm to 250 microm. The following mixtures of CPC powder (an equimolar mixture of tetracalcium phosphate, Ca4(PO4)2O, and dicalcium phosphate anhydrous, CaHPO4) and one of the above additive granules were prepared: control-no additive; mixture A-0.25 mass fraction of sucrose; mixture B-0.25 mass fraction of NaHCO3; mixture C-0.25 mass fraction of Na2HPO4, and mixture D-0.33 mass fraction of Na2HPO4. Cement samples were prepared by mixing 0.3 g of the above mixtures with 0.075 ml of the cement liquid (1 mol/l Na2HPO4). After hardening, the specimens were placed in water for 20 h at about 60 degrees C to completely dissolve the additive crystals. Well-formed macropores in the shapes of the entrapped crystals were observed by scanning electron microscope (SEM). The macroporosities (mean+/-standard deviation; n = 6) expressed as volume fraction in % were 0, 18.9 +/- 1.7, 26.9 +/- 1.6, 38.3 +/- 4.4 and 50.3 +/- 2.7 for the control, A, B, C and D, respectively. The diametral tensile strengths (mean+/-standard deviation; n = 3) expressed in MPa were 10.1 +/- 0.7, 3.7 +/- 0.3, 2.4 +/- 0.2, 1.5 +/- 0.5 and 0.4 +/- 0.1, respectively, for the five groups. The results showed that macropores can readily be formed in CPC implants with the use of water-soluble crystals. The mechanical strength of CPC decreased with increasing macroporosity.

Journal Article↗
PubMed2005

Corrosion behavior of titanium in the presence of calcium phosphate and serum proteins.

The effect of calcium phosphate surface deposit and the surface adsorption of the serum proteins, bovine serum albumin (BSA) and fibrinogen, on the corrosion resistance and electrochemical behavior of (cp)titanium in phosphate buffer saline solution (pH 7.4) was investigated at physiological temperature, 37 degrees C, using electrochemical impedance spectroscopy and dc electrochemical polarization techniques. The formation of calcium phosphate deposit on the Ti surface decreased both the corrosion rate at the open circuit potential (OCP) and the anodic reaction current in the high anodic potential range (>2.6 V). Addition of BSA significantly moved the OCP towards a more negative (cathodic) potential and inhibited the cathodic corrosion reaction, but did not significantly change the corrosion resistance at the OCP. Addition of fibrinogen showed a similar, but less pronounced effect than BSA. The possible mechanisms leading to these observed effects are discussed.

Biocompatible Materials↗
PubMed1996

Improved properties of amorphous calcium phosphate fillers in remineralizing resin composites.

OBJECTIVES: The rationale for this study was based on the hypothesis that the mechanical strength of methacrylate composites containing the bioactive filler, amorphous calcium phosphate, can be enhanced by synthesizing this filler in the presence of glass-forming agents. Specifically, this study was conducted to prepare composites with zirconia- and silica-modified amorphous calcium phosphate fillers, and to determine whether the remineralization potential from the release of calcium and phosphate ions and the mechanical properties of the corresponding methacrylate composites were enhanced. METHODS: The modified amorphous calcium phosphates were synthesized at pH 10.5 by mixing 800 mmol/L Ca(NO3)2 solutions and either 250 mmol/L zirconylchloride (ZrOCl2) or 4.4 mol/L tetraethoxysilane (TEOS) solutions with solutions containing 525 mmol/L Na2HPO4 and 11 mmol/L Na4P2O7. After washing and drying, the amorphous calcium phosphates were mixed with visible light-activated resins and photopolymerized to form composite disks that were then examined for their ability to release Ca2+ and total ionic phosphate (PO4(3-) + HPO4(2-) + H2PO4-, hereafter indicated as PO4) by immersion in HEPES-buffered (pH 7.4) saline at 37 degrees C. Solution ion concentrations were compared at regular intervals up to 265 h. Biaxial flexural strengths of the composites before and after immersion were compared, and significant differences were established by Student's test (p < 0.05). RESULTS: Both ZrOCl2- and TEOS-modified amorphous calcium phosphate composite disks released Ca2+ and PO4 ions at sustained levels requisite for remineralization to occur. The transformation of amorphous calcium phosphate into hydroxyapatite within the composites was also retarded, particularly in the case of amorphous calcium phosphate modified with ZrOCl2. Biaxial flexure strength values of composite disks showed that TEOS- and ZrOCl2-amorphous calcium phosphate-filled composites increased in strength by 33% and 21% before immersion and by 25% and 27% after immersion, respectively, compared to unmodified amorphous calcium phosphate composites (controls). All strength increases except TEOS after immersion were significant (p < 0.05). SIGNIFICANCE: Properly modified amorphous calcium phosphate fillers can be used to prepare bioactive composites with enhanced mechanical properties for more demanding dental applications without compromising their remineralizing potential.

Calcium↗