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PubMed2003

Physical parameters of hydroxyapatite adsorption and effect on candidacidal activity of histatins.

Histatins 1, 3 and 5 are the major members of a histidine-rich protein family present in human salivary secretions. These proteins are distinct from many salivary proteins in their high positive charge density at neutral pH, and their antibacterial and antifungal properties. In this study, the hydroxyapatite adsorption characteristics of histatin 1, containing a single phosphoserine residue, recombinantly expressed histatin 1, native histatin 3, synthetic histatin 5 and an internal 12-residue sequence of histatin 5 were investigated. A Langmuir-type model was used to analyse the adsorption. A comparison of the affinities and binding sites of phosphorylated and recombinant histatin 1 provided an estimate of the positive influence of the single phosphoseryl group on mineral adsorption. Furthermore, an apparent correlation was shown to exist between peptide chain length and the number of binding sites. The influence of histatin 5 adsorption on its anticandidal activity was also investigated by performing Candida albicans killing assays with histatin 5 and histatin 5/hydroxyapatite suspensions. A decrease in killing activity was observed with the increase of hydroxyapatite present. The results suggest that the anticandidal properties of histatin 5 could be impaired by the conformations resulting from mineral adsorption, or that putative cellular receptors necessary for candidacidal activity are inaccessible when histatin 5 is adsorbed on hydroxyapatite.

Adsorption↗
PubMed1998

Adsorption of human lysozyme onto hydroxyapatite. Identification of its adsorbing site using site-directed mutagenesis.

To elucidate hydroxyapatite-protein interaction, mutant human lysozymes in which the surface charge was modified by site-directed mutagenesis were used. Five mutant human lysozymes (K1A, K13A, K33A, R10A, R14A) were expressed in yeast. The chromatographic behavior of these lysozymes was studied with a HPLC hydroxyapatite column. Elution molarities of K1A and R14A mutants were greatly lowered. While Lys-13 and Arg-10 are located around Lys-1 and Arg-14, K13A and R10A mutants bound onto hydroxyapatite stronger than K1A and R14A mutants. In combination with an X-ray crystal structure of human lysozyme, it is concluded that the adsorbing site of human lysozyme is at the back of the active site and that Arg-14, Lys-1, Arg-10 and Lys-13 play important roles in binding.

Adsorption↗
PubMedDate not supplied

Complications in motility PEG placement for hydroxyapatite orbital implant in anophthalmic socket.

PURPOSE: In a retrospective study, we evaluated the complications in using the motility peg system (nonsleeved and sleeved) for hydroxyapatite orbital implants in an anophthalmic socket. METHODS: Drilling for motility peg placement was performed in 265 patients with hydroxyapatite implantation: nonsleeved peg system (n = 191), sleeved peg system (n = 74). A statistical analysis was performed using the chi-square test. RESULTS: Extrusion rates were significantly lower in the sleeved peg system (10.8%) compared to the nonsleeved peg system (27.2%) (P =.005). The other complications related to motility peg placement were granulation tissue overgrowth (4.2%), hydroxyapatite exposure around peg head (3.0%), and decentered peg (1.9%). CONCLUSIONS: To minimize peg extrusion, the sleeved peg was better than the nonsleeved peg for use in primary motility peg placement.

Adult↗
PubMed2006

Results of a 2-year multicenter trial of endoscopic treatment of vesicoureteral reflux with synthetic calcium hydroxyapatite.

PURPOSE: With no FDA approved material available for endoscopic treatment of vesicoureteral reflux, in 2001 we began a prospective multicenter trial of synthetic calcium hydroxyapatite as a subureteral bulking agent in children with traditional indications for surgical repair. MATERIALS AND METHODS: A total of 98 patients (155 ureters) with grades II to IV reflux were enrolled at 10 sites in the United States to obtain 86 patients with completed protocol end points at 3 months. Of the 86 patients 74 underwent renal and bladder ultrasonography, blood count and serum chemistry analysis, and VCUG at 1 year. A total of 46 patients (47%) completed 2-year study end points, including VCUG. RESULTS: At 1 and 2 years 24 of the 74 patients (32%) were cured. Ureteral cure rates were 46% and 40% at 1 and 2 years, respectively. With 35 patients treated and 85% compliance with the required 2-year VCUG the primary center achieved 2-year cure rates of 66% of patients and 72% of ureters. CONCLUSIONS: Synthetic calcium hydroxyapatite is a safe, durable and effective material for endoscopic treatment of VUR. Increased experience with the injection of synthetic calcium hydroxyapatite yields improved results.

Adolescent↗
PubMed1996

Influence of particle size of hydroxyapatite as a capping agent on cell proliferation of cultured fibroblasts.

The influence of particle size of biomaterials on cell reaction and cell proliferation was studied by means of coculturing fibroblasts with calcium phosphate ceramics. Both dense and porous hydroxyapatite ceramics obtained under different sintering conditions were selected, and two particle sizes of 300 and 40 micrometers were used to examine cell reaction. The four materials were each cocultured with dental pulp-derived fibroblasts for 7 days. Cell reaction was observed by phase-contrast microscopy and scanning electron microscopy. Cell proliferation was measured by counting the number of trypsinized cells in 7-day-old culture. On the seventh day, the dense 300-micrometer particles of hydroxyapatite were completely covered by cultured cells that had proliferated on the dish surface. On the other hand, the porous and dense 40-micrometer particles were captured or gathered by the cultured cells, which seemed not to proliferate. The porous 300-micrometer particles were accompanied by numerous small broken pieces on the dish surface, and the cells proliferated only around the large particles. From these results, the dense 300-micrometer particles of hydroxyapatite can be considered the most appropriate biomaterial.

Biocompatible Materials↗
PubMed2001

Kinetics of hydroxyapatite precipitation at pH 10 to 11.

The mechanism and kinetics of hydroxyapatite (HAP) precipitation from aqueous solution at the conditions of pH 10-11 and at calcium ion concentrations of more than 0.5 mol/l were investigated. The results show that the reaction undergoes the following process: transferring from octacalcium phosphate (OCP) to amorphous calcium phosphate (ACP) rapidly, and then from ACP to calcium-deficient hydroxyapatite (DAP) and HAP. DAP was the non-stoichiometric material that ACP converts to HAP. Reaction temperature greatly affects the reaction rate of the conversion from ACP to HAP. It takes about 24 h to form pure-phase HAP at 25 degrees C while it takes only 5 min at 60 degrees C. The temperature also has a great deal of influence on the particle size and morphology of precipitated hydroxyapatite. The reaction of transformation from ACP to DAP was second order and the activation energy was 95 kJ/mol (22.7 kCal/mol) and therefore it was inferred that the conversion reaction was a surface control process.

Calcium Phosphates↗
PubMed2001

Mechanochemical synthesis of nanocrystalline hydroxyapatite from CaO and CaHPO4.

Ceramic hydroxyapatite phase was triggered to occur by high-energy mechanical activation of a dry powder mixture of calcium oxide (CaO) and anhydrous calcium hydrogen phosphate (CaHPO4). A singe-phase hydroxyapatite of high crystallinity was realised by >20 h of mechanical activation without further thermal treatment at high temperatures. The resulting hydroxyapatite powder exhibits an average particle size of approximately 25 nm and a specific surface area of 76.06 m2/g, as measured by multi-point BET technique. It was sintered to a density of 98.20% theoretical density at 1200 degrees C for 2 h.

Calcium Compounds↗
PubMed2001

Influence of residual stress on bonding strength and fracture of plasma-sprayed hydroxyapatite coatings on Ti-6Al-4V substrate.

Six hydroxyapatite coatings (HACs) were plasma sprayed on Ti-6Al-4V substrates by varying the substrate temperatures and the cooling conditions. This study is aimed not only to measure the residual stress of HACs under various conditions, but also to assess the influence of residual stress in HACs on their bonding strength. The residual stress and bonding strength were measured by XRD "sin2 psi" technique and standard adhesion test (ASTM C-633), respectively. The result of the study clearly established the relationship between bonding strength and residual stress. The arguments leading to the above conclusion were discussed in detail. Fractographic analysis indicated that fracture of the system occurred mainly inside the hydroxyapatite coating under lower residual stress; as residual stress increased, fracture tended to occur more easily along the crucial HA-Ti alloy substrate interface. A mechanism was presented for the relationships between residual stress, fracture behaviour and bonding strength for the plasma-sprayed hydroxyapatite coatings on Ti-6Al-4V substrate.

Alloys↗
PubMed2001

Influence of thickness on the properties of hydroxyapatite coatings deposited by KrF laser ablation.

The growth of hydroxyapatite coatings obtained by KrF excimer laser ablation and their adhesion to a titanium alloy substrate were studied by producing coatings with thicknesses ranging from 170 nm up to 1.5 microm, as a result of different deposition times. The morphology of the coatings consists of grain-like particles and also droplets. During growth the grain-like particles grow in size, partially masking the droplets, and a columnar structure is developed. The thinnest film is mainly composed of amorphous calcium phosphate. The coating 350nm thick already contains hydroxyapatite, whereas thicker coatings present some alpha tricalcium phosphate in addition to hydroxyapatite. The resulting coating to substrate adhesion was evaluated through the scratch test technique. Coatings fail under the scratch test by spallating laterally from the diamond tip and the failure load increases as thickness decreases, until not adhesive but cohesive failure for the thinnest coating is observed.

Alloys↗
PubMed2002

The ultrastructure of the plasma-sprayed hydroxyapatite-bone interface predisposing to bone bonding.

The deposition of biological apatite and subsequent formation of bone on hydroxyapatite implants depends on the partial dissolution of the implant surface and the reprecipitation of carbonated apatite from the biological milieu. Previous investigations in vitro have shown that the degree of dissolution and reprecipitation decreases as the coating crystallinity increases. These findings prompted the current study of the effects of coating crystallinity on the mechanism of bone bonding. The process of mineralization of bone associated with a hydroxyapatite coating was compared to the normal process of ossification. Plasma-sprayed hydroxyapatite (PSHA) coated titanium alloy (6% Al-4% V) rods as received and annealed for 0.7 h at 600 degrees C in air to increase the coating crystallinity were implanted in the proximal and distal femora and proximal tibiae of adult mongrel dogs for 3 h, 3 and 10 days. Bony sites containing the implant were prepared for ultramicrotomy and transmission electron microscopy using an anhydrous embedding procedure: fixation in ethylene glycol and embedment in Spurr's resin. The results demonstrated the precipitation of biological apatite crystallites on non-annealed PSHA coatings in vivo within 3 h of implantation. After 3 and 10 days there were differences in the ultrastructure of the mineral phase on the surfaces of non-annealed and annealed surfaces. Observations showed that there was little difference in the mechanism of mineralization of bone associated with HA-coated prostheses and the normal process of ossification.

Alloys↗
PubMed2003

Bonding efficacy of polyalkenoic acids to hydroxyapatite, enamel and dentin.

Previously, we introduced a methodology to determine the chemical bonding potential of polyalkenoic acids to mineralized tissues through quantification of the degree of ionic bond formation between the carboxyl groups of a polyalkenoic acid with calcium of hydroxyapatite. In a continuation of that study, we now investigated in how far the chemical bonding potential to synthetic hydroxyapatite is influenced by the molecular structure of the polyalkenoic acid and if this also may affect the self-adhesiveness to enamel and dentin. X-ray photoelectron spectroscopy and inductively coupled plasma atomic emission spectrometry were used to quantitatively analyze the chemical bonding efficacy of a polyalkenoic acid consisting of acrylic acid units (PAA) to synthetic hydroxyapatite (HAp) in comparison to the chemical bonding potential of the previously investigated synthesized polyalkenoic acid (s-PA) co-polymer consisting of 90w/w% acrylic and 10w/w% maleic acid units. In addition, the analysis was carried out for enamel and dentin samples. PAA revealed a significantly lower bonding effectiveness with only half of its carboxyl groups bonded to HAp versus about two-third of the carboxyl groups of s-PA. The difference in bonding potential was confirmed by the considerably lower adhesiveness of PAA to enamel and dentin as compared to that of s-PA The present findings indicate that the molecular structure of the polyalkenoic acid significantly influences the chemical bonding efficacy to Hap-based substrates.

Acrylic Resins↗
PubMed2004

Studies on the microspheres comprised of reconstituted collagen and hydroxyapatite.

Microspheres comprised of hydroxyapatite particles, dispersed in reconstituted fibrous collagen, were prepared and characterized. The hydroxyapatite particles distributed evenly throughout the collagen matrix of the microsphere. Diameters of the reconstituted collagen fibers ranged from 30 to 90 nm, and exhibited a regular banding pattern with cross-striation of 50-60 nm under transmission electron microscope, suggesting that the reconstitution of collagen was not hindered by the hydroxyapatite particulates. When osteoblast cells isolated from newborn rat calvaria were seeded and cultured on the microspheres, the cell density increased from 2x10(4) to 3.2x10(4)cells/cm(2) in 8 days. Von Kossa staining exhibited spotty accumulation of mineral deposits on microspheres indicating matrix mineralization of the cultured cells. Analyses by electron microscopy and confocal microscopy showed that the osteoblast cells spread and attached to the microsphere via focal adhesion, while F-actin and DNA staining demonstrated the presence of stress fibers; moreover, mitotic cells could be observed. Together, these results indicate that osteoblast cells are capable of proliferating, differentiating and mineralizing in the matrix of the microspheres, and suggest that the microspheric composite is a potential grafting material for future clinical applications.

Animals↗
PubMed1997

Investigation of the dissolution of the bioceramic hydroxyapatite in the presence of titanium ions using ToF-SIMS and XPS.

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) analyses have been used to investigate the dissolution of hydroxyapatite in the presence of titanium chloride suggesting the substitution of titanium ions for calcium in the hydroxyapatite structure. The surface analytical data suggest that titanium was incorporated within the solid phase as titanium phosphate. Comparison of relative ion intensities in the ToF-SIMS spectra reveals changes in the composition of the surface chemistry of hydroxyapatite. These relative ion intensities show that the maximum surface uptake of titanium occurred at a solution concentration of 500 ppm titanium chloride for a time of incubation of 30 min. These data correlate with that obtained using XPS highlighting the semi-quantitative information which ToF-SIMS can provide.

Biocompatible Materials↗
PubMed1997

Effect of pH on protein adsorption to hydroxyapatite and tricalcium phosphate ceramics.

Calcium phosphate ceramics used for clinical applications vary considerably in their phase composition. A range of hydroxyapatite and tricalcium phosphate powders, some of which are used in plasma-sprayed coatings for metal prostheses, were found to leach substances which change the pH of water and cell culture medium. The adsorption of serum proteins from cell culture medium to the same hydroxyapatite and tricalcium phosphate ceramics was compared by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and individual bands identified by enhanced chemiluminescence immunodetection and gas chromatography sequencing. The iron transport protein transferrin showed distinct differences in adsorption to a variety of hydroxyapatite and tricalcium phosphate powders, with higher concentrations of transferrin adsorbed to powders which caused no change or a drop in the pH of cell culture medium or water. Transferrin was also adsorbed to Biotal HA 120 in greater concentrations at a lower pH than it was at a higher pH. These preliminary studies show that pH changes brought about by the leaching of soluble ions may have an effect on protein adsorption.

Adsorption↗
PubMed1997

Rietveld analysis and Fourier maps of hydroxyapatite.

Rietveld analysis was applied to the X-ray powder diffraction data of well-crystallized hydroxyapatites synthesized at 80 degrees C and pH 7.4. The least-squares refinement program adopted for Rietveld analysis showed good pattern fitting with the calculated profile. The a- and c-axis dimensions, a-0.943046 + 0.000126 nm and c-0.687485 +/- 0.000104 nm, were obtained and compared with the data estimated from a single peak. The lattice dimensions obtained by Rietveld analysis were much closer to the values of a single crystal, a = 0.9432 nm and c-0.6881nm. Fourier analysis was also performed. The maps of electron densities expressed the existing possibility of each atom composing hydroxyapatite in the crystal structure. In particular, columnar calcium and screw-axis calcium were clearly revealed. These data agreed well with the computer graphics model of hydroxyapatite reported previously.

Computer Simulation↗
PubMed1999

Effect of powder grinding on hydroxyapatite formation in a polymeric calcium phosphate cement prepared from tetracalcium phosphate and poly(methyl vinyl ether-maleic acid).

The primary aim of this study was to determine if cements based on poly(methyl vinyl ether-maleic acid) (PMVE-Ma) and tetracalcium phosphate resulted in hydroxyapatite formation. In addition, the mechanical strength of this type of polymeric calcium phosphate cement was evaluated. Cements were prepared by mixing, in a powder/liquid mass ratio of 3.0, an aqueous solution of PMVE-Ma (mass fraction = 25%) and tetracalcium phosphate powders ground for various periods of time. The tetracalcium phosphate powders and set cements were characterized by means of X-ray powder diffraction and scanning electron microscopy. Mechanical strengths of the cements were tested 24 h after mixing. Prolonged grinding of tetracalcium phosphate powder decreased particle size and/or crystallite size and increased lattice distortion. This enhanced the reactivity of the tetracalcium phosphate powder and elevated the extent of crosslinking between PMVE-Ma molecules, resulting in improved mechanical strength. Hydroxyapatite formation was detected in the cement prepared with the most finely ground tetracalcium phosphate powder. The conversion of residual tetracalcium phosphate particles to more thermodynamically stable hydroxyapatite crystals will reduce the solubility of the polymeric cement and increase its biocompatibility.

Calcium Phosphates↗
PubMed1999

Transformation of modified brushite to hydroxyapatite in aqueous solution: effects of potassium substitution.

Brushite (dicalcium phosphate dihydrate, DCPD, CaHPO4 x 2H2O) was deposited electrolytically from calcium dihydrogen phosphate solution with and without potassium chloride (KCl) as a supporting electrolyte. The kinetics of brushite transformation to hydroxyapatite (HA, Ca5(PO4)3OH) in the presence of calcium and protein free, aqueous body fluid (Hank's balanced salt solution, HBSS) was investigated. We present evidence that the deposition of brushite in a KCl-supported electrochemical bath yields a modified brushite where some of the calcium is substituted by potassium. Transformation of both normal (i.e. potassium free) and modified brushite to hydroxyapatite upon exposure to calcium and protein-free aqueous fluid (HBSS) was followed by reflectance Fourier Transform Infrared (FTIR) spectroscopy and X-ray diffraction (XRD) techniques. Changes in the morphology of the coatings were studied using scanning electron microscopy (SEM). Results indicate that modified brushite undergoes faster transformation to hydroxyapatite in HBSS in comparison to normal brushite. Our results show that the presence of potassium ions in the brushite not only favors the formation of different intermediate phases but also alters transformation rates to HA.

Calcium Phosphates↗
PubMed2001

Spontaneous loosening of hydroxyapatite peg sleeves.

OBJECTIVE: To report a new complication associated with pegging hydroxyapatite orbital implants: spontaneous loosening of the sleeve. DESIGN: Retrospective noncomparative case series. PARTICIPANTS: Four patients ranging in age from 38 to 60 years participated. METHODS: Four patients are described who successfully received hydroxyapatite orbital implants with motility peg and sleeve systems. In each case spontaneous loosening of the sleeve developed. MAIN OUTCOME MEASURE: Clinical and surgical outcomes were assessed. RESULTS: Three patients had the peg and sleeve removed followed by repair of the peg hole, and one patient had placement of a larger diameter peg and sleeve system. All patients did well. CONCLUSIONS: Problems have been reported when motility coupling pegs are used with hydroxyapatite orbital implants. Spontaneous loosening of the sleeve is another potential complication to discuss with the patient considering an implant peg.

Adult↗