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PubMed1992

Kinetics of hydroxyapatite dissolution in acetic, lactic, and phosphoric acid solutions.

The present study was undertaken in an attempt to relate the kinetics of hydroxyapatite dissolution to solution parameters, under experimental conditions relevant to the dental caries process. Thus, the dissolution of hydroxyapatite was studied in acetic, lactic, and dilute phosphoric acid solutions having initial pH values from 4 to 6. Rates of dissolution and the corresponding degree of saturation with respect to hydroxyapatite were determined at various times throughout the dissolution process. Rates of dissolution of all solutions were found to decrease with increasing degree of solution saturation and were greater in solutions with lower initial values of pH. However, rates of dissolution in partially saturated phosphoric acid solutions (without added organic acid) were at least one order of magnitude lower than those observed in the organic acid buffers with the same initial pH, over the same range of saturation values. The data obtained are consistent with a surface-controlled dissolution model in which the rate of dissolution is dependent upon the degree of saturation and the sum of the activities of the acidic species in solution, i.e., phosphoric and organic acids. These results suggest that in order to assess the cariogenic potential of a given medium (e.g., plaque fluid), one must determine both the degree of saturation with respect to the dissolving mineral and the activities of acidic species in solution.

Acetates↗
PubMed1986

Coralline hydroxyapatite bone graft substitutes in a canine metaphyseal defect model: radiographic-biomechanical correlation.

Radiographic and biomechanical assessment of a new type of bone graft substitute derived from reef-building sea coral was performed in a canine metaphyseal defect model. Blocks of this material and autogenous iliac crest graft were implanted, respectively, into the right and left proximal tibial metaphyses of eight dogs. Qualitative and quantitative radiographic evaluation was performed in the immediate postoperative period and at 6 months after surgery. Biomechanical testing was carried out on all grafts following harvest at 6 months, as well as on nonimplanted coralline hydroxyapatite and autogenous iliac cancellous bone. In contrast to autografts, incorporation of coralline implants was characterized by predictable osseous growth and apposition with preservation of intrinsic architecture. Greater percent increase in radiographic density, higher ultimate compressive strength, and lower stiffness with incorporation were documented advantages of coralline hydroxyapatite over autogenous graft. Densitometric measurements correlated moderately with strength for both types of graft material (r = -0.65). These promising results have important implications to the clinical application of coralline hydroxyapatite bone graft substitutes as an alternative to autogenous grafting.

Absorptiometry, Photon↗
PubMed1977

The role of synthetic and bone extracted Ca-phospholipid-PO4 complexes in hydroxyapatite formation.

The calcium-phospholipid-phosphate (Ca-PL-PO4) complex isolated from young bone has been shown to initiate hydroxyapatite formation from a metastable calcium phosphate solution. The action of the complex was compared to that of the acidic phospholipids: phosphatidyl serine, phosphatidyl inositol and phosphatidic acid. These phospholipids first remove calcium, and a small amount of phosphate from the metastable solution forming a material similar to the complex isolated from bone, and then form hydroxyapatite. The rate of hydroxyapatite proliferation, once phosphatidyl serine and phosphatidyl inositol are converted to Ca-PL-PO4 complexes, is the same as the rate observed for comparable weights of the complex isolated from bone. It is suggested that the complex isolated from bone was formed in a manner similar to the complexes in our in vitro experiments. Finally, our evidence supports the possibility that a similar complex is responsible for the initial mineralization in matrix vesicles.

Bone Development↗
PubMed1981

Ion displacement following the adsorption of anionic macromolecules on hydroxyapatite.

Certain small anionic molecules displace phosphate ions from the hydroxyapatite crystal hydration layer on adsorption. This follows the interaction of negatively charged groups with calcium ions in the crystal surface. The present study examines ion-exchange processes occurring during the adsorption of anionic macromolecules and attempts to determine the role of coulombic forces in the process. Various natural and synthetic polyanionic substances were added to a buffered hydroxyapatite slurry and adsorption measured by solution depletion. Calcium and phosphate ion displacement or uptake by apatite was determined after accounting for polymer-bound ions. Carboxymethylcellulose and a polyacrylamide sample in which 54% of amide groups had been hydrolyzed to carboxyl were adsorbed in the lowest amounts, but both caused consistent rises in the bulk solution phosphate level. Crude bovine submaxillary mucin and a polyacrylamide sample in which 28% of amide groups had been hydrolyzed were adsorbed in greater amounts but caused little or no phosphate displacement. In no case was there a stoichiometric relation between carboxyl adsorbed and phosphate displaced. The polyacrylamide samples also displaced Ca ions into the bulk solution, whereas the other macromolecules caused a decrease in solution Ca concentration. These results provide some evidence for the operation of an ion-exchange mechanism in the adsorption of polyanions on hydroxyapatite but do not exclude the involvement of other mechanisms, especially in the case of salivary mucin.

Adsorption↗
PubMed1987

EXAFS study of structural disorder in carbonate-containing hydroxyapatites.

A structural characterization of pure hydroxyapatite and partially carbonated hydroxyapatites has been performed using EXAFS spectroscopy, X-ray diffraction, and infrared spectroscopy. Our findings show that marked structural changes within the hydroxyapatite unit cell accompany the substitution of the phosphate anion. Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy has shown that the incorporation of carbonate into the phosphate site alters the structural geometry beyond the nearest neighbor oxygen coordination to calcium in a manner consistent with an increase in structural disorder. The nearest neighbor coordination to calcium is not detectably affected by the presence of carbonate.

Durapatite↗
PubMed2004

Effects of vascular endothelial cell growth factor on fibrovascular ingrowth into rabbits hydroxyapatite orbital implant.

The effects of different concentrations of vascular endothelial cell growth factor (VEGF) on the fibrovascular ingrowth into rabbits hydroxyapatite orbital implant were investigated. Twelve New Zealand white rabbits were divided into 3 groups and received hydroxyapatite orbital implant surgery in their right eyes. Before and after the operation, the implants were treated with 10 ng/ml VEGF, 100 ng/ml VEGF, or normal saline as control group. The animals received technetium bones scan at 2, 4, and 6 weeks postoperatively. The mean radioactivity counts within region of interest (ROI) of the surgery eye (R) and the non-surgery eye (L) in the same animal were tested, and the R/L ratios were calculated. The implants were harvested at 6th weeks and examined histopathologically. The results showed that at second week, there was no significant difference in mean R/L ratios between VEGF group and control group (F=2.83, P=0.111); At 4th week (F=7.728, P=0.011) and 6th week (F=7.831, P=0.011) postoperatively, the mean ratios in VEGF groups were significantly higher than that in control group. At 6th week postoperatively, the fibrovascularization rates in VEGF groups were higher than in control group significantly (F=8.711, P=0.008). It was suggested that VEGF could promote the fibrovascular ingrowth into hydroxyapatite orbital implant, thus might shorten the time required for complete vascularization of the HA orbital implant.

Animals↗
PubMed2006

Synthesis of a potentially bioactive, hydroxyapatite-nucleating molecule.

A human phosphophoryn (PP) cDNA was previously cloned from immature root apex total RNA in our laboratory. This cDNA comprises 2,364 bp, encoding 788 amino acids. More than 80% of the sequences are arranged as (DSS)(n) (n = 1-16), DS, and NSS motifs. We hypothesize that the capability of PP to bind Ca(2+) and nucleate hydroxyapatite may depend on these repeated sequences. Two polypeptides were synthesized based on the human PP cDNA sequence to test the hypothesis. One polypeptide has the amino acid sequence DDPNSSDESNGNDD (synthetic polypeptide 1, SP1), which is from the N-terminal end of PP; the other polypeptide, DSKSDSSKSESDSS (synthetic polypeptide 2, SP2), is the PP repeated sequence motif. Phosphorylation of the polypeptides was accomplished by reacting them with adenosine triphosphate and casein kinases I and II. The ability of these molecules to cause mineralization was tested in a steady-state agarose gel system. The results show that phosphorylated SP2 (P-SP2) precipitated approximately 60% of the total Ca + PO(4) precipitated by PP. P-SP1 precipitated about 23% of that precipitated by PP and was similar to the amount precipitated in the control gel, that is, without added peptides. Transmission electron microscopy and X-ray diffraction analysis showed that the precipitate formed in the P-SP2-containing gel was hydroxyapatite. The capability of P-SP2 to nucleate Ca + PO(4) and precipitate hydroxyapatite is a result of the repeated sequence motif, which contains a high percentage of phosphorylated serine. This molecule could be used in the repair and regeneration of dental tissue.

Adenosine Triphosphate↗
PubMed2006

Clinical manifestations and pathogenesis of hydroxyapatite crystal deposition in juvenile dermatomyositis.

Pathologic deposition of mineral in the form of bone-like hydroxyapatite is a frequent occurrence in juvenile dermatomyositis (JDM) and other connective tissue diseases. Although the sizes of the mineral crystals in JDM are similar to those in bone, there is much more mineral in the deposits than there is in bone. Bone matrix proteins also accumulate associated with the deposits. The reasons for the formation of these deposits are not known. It is our hypothesis that persistent inflammation is a component of JDM and other hydroxyapatite deposition diseases. Other contributing factors are genetic, environmental, and physical chemical. This paper discusses the influence of inflammation on the deposition of hydroxyapatite, with emphasis on the clinical and environmental factors that may facilitate the formation of calcific deposits in JDM.

Adolescent↗
PubMed1985

The effects of basic and acidic synthetic polypeptides on the adherence of the oral bacteria, Streptococcus mutans and Streptococcus sanguis, to hydroxyapatite.

Two basic and two acidic synthetic polypeptides that bind strongly to hydroxyapatite at neutral pH were tested to determine their influence on adsorption of two Streptococcus mutans and two Streptococcus sanguis strains to hydroxyapatite. The adsorption of the strains was significantly enhanced or reduced by the basic and acidic agents, respectively. Study of acidic polypeptides provided evidence of competition between the polypeptides and the bacterial cells for hydroxyapatite adsorption sites.

Adsorption↗
PubMed1979

Hydroxyapatite chromatography of short single-stranded DNA.

Short single-stranded segments of calf thymus DNA were obtained by random cleavage with DNAase I. After treatment with various concentrations of DNAase I, fragment sizes were estimated using the ratio of total to terminal phosphorus. DNA populations ranging from 4--180 bases were obtained. Fragments with lengths up to 1140 were generated by shearing in a Virtis homogenizer. The hydroxyapatite elution profiles of sized populations were determined by elution with phosphate gradients. A curve relating elution molarities to single-strand chain length was 'biphasic', with the elution molarity being extremely sensitive to chain lengths below 50 nucleotides but much less sensitive to chain lengths above 100 nucleotides. These results show that single-stranded fragments below 50 nucleotides elute from hydroxyapatite appreciably before high molecular-weight denatured DNA using phosphate gradients. This is an important consideration when using hydroxyapatite to fractionate DNA populations which contain short single strands.

Animals↗
PubMed1993

Identification of the adsorbing site of lysozyme onto the hydroxyapatite surface using hydrogen exchange and 1H NMR.

The lysozyme-hydroxyapatite interaction was studied by measuring individual hydrogen-deuterium (H-D) exchange rates of amide protons. The H-D exchange reaction was initiated by transferring the lysozyme adsorbed on hydroxyapatite powder from H2O into D2O. After various H-D exchange time periods (pH 7.0, 25 degrees C), the complex was dissociated and the remaining hydrogen label was determined by 2D NMR analysis. The H-D exchange rate of amide protons of residues 9, 11, 13, and 83 was slowed in the hydroxyapatite-lysozyme complex compared with free lysozyme. Residues 9, 11 and 13 positioned at the back of the active site would be the location of the binding site.

Adsorption↗
PubMed1992

High-performance hydroxyapatite chromatography of integral membrane proteins and water-soluble proteins in complex with sodium dodecyl sulphate.

Integral membrane proteins from human erythrocytes were fractionated in the presence of sodium dodecyl sulphate (SDS) on four types of high-performance hydroxyapatite columns. A column of 2-microns sintered hydroxyapatite beads from Asahi Optical (Tokyo, Japan) gave the best resolution. With this column, glycophorin was eluted early in a gradient of increasing sodium phosphate buffer concentration, the glucose transporter was eluted later in two zones, one of which contained this protein alone, and the anion transporter was eluted last. Water-soluble proteins applied in complex with SDS also separated reasonably well upon elution. The water-soluble proteins and the membrane proteins were all eluted mainly in the order of increasing polypeptide length, but with considerable individual variation. SDS-polypeptide complexes are probably adsorbed onto hydroxyapatite by the interaction of positively charged amino acid side groups with phosphate ions (at P-sites) and of negatively charged amino acid side groups and polypeptide-bound dodecyl sulphate anions with calcium ions (at C-sites). As a rule, the number of charged side groups and dodecyl sulphate anions, and thus the number of binding sites, increases with the polypeptide chain length, which explains the general order of release of the polypeptides.

Amino Acids↗
PubMed1992

The advantages of coated titanium implants prepared by radiofrequency sputtering from hydroxyapatite.

The method used to apply hydroxyapatite to implant surfaces may affect the thickness and ultimately the physical properties of the coating. This study investigated and compared the healing rates of bone around commercially pure titanium implants and titanium implants sputter-coated from a hydroxyapatite target. Forty-five sputter-coated implants and an equal number of noncoated titanium implants were placed into 15 partially edentulated dog mandibles. The implants were removed at three time periods and were evaluated mechanically and histologically. A multiple analysis of variance indicated that the interface bond strength was statistically greater (p less than 0.01) for the sputter-coated implants. Histologic analysis of the bone-implant interface demonstrated that coated implants had nearly twice the percentage of direct bone contact compared with noncoated implants. The results indicate that implants sputter-coated from a hydroxyapatite target will accelerate the healing of bone at the implant interface.

Animals↗
PubMed1981

Adsorptive bonding to hydroxyapatite I: adsorption of anthranilic acid - the effect of solvents. Search for surface bonding groups for coupling agents to teeth.

A study was initiated to explore the nature of surface-active groups of model compounds that might cause chemisorption of comonomers used in the polymerization of dental resins on hydroxyapatite (the main constituent of bone) and thus effect a strong and durable bond between the resins and hard tooth tissues. In an effort to accomplish this objective, adsorption of anthranilic acid on hydroxyapatite was studied from three solvents: 95% aq. ethanol, dimethyl sulphoxide and methylene chloride. The adsorption is reversible from the first two solvents and the isotherms follow Langmuir plots. Adsorption is irreversible from methylene chloride; a constant amount of adsorbate is removed from different solutions above a certain threshold concentration but all adsorbate is removed from solutions below this threshold concentration. The saturation amounts obtained from the two Langmuir plots and the maximum irreversibly adsorbed amount in the above three solvents are 11.4, 6.0 and 17.2 mmol/100 g, respectively. These, together with the surface area (41.0 m2/g; BET, N2) of the hydroxyapatite, yield the effective molecular areas of 60, 114, and 40 A2, respectively. These areas can be matched, on geometrical considerations, with areas of 60, 110, and 40 A2 of the model adsorbate molecule rotating about; (i) its centre, lying flat on the surface, (ii) its carboxyl group at 45 degrees to the surface, and (iii) the carboxyl group in an upright position, respectively.

Adsorption↗
PubMed1989

Solubilization of hydroxyapatite crystals by murine bone cells, macrophages and fibroblasts.

Calcium phosphate ceramic is widely used as implant material. It is made up of hydroxyapatite, beta-tricalcium phosphate or various combinations of both. In the present study, we use an in vitro model to examine the role of cell-mediated resorption of calcium phosphate ceramic implant material. We compare the abilities of two sequential enzymatic released populations of bone cells from murine calvaria (Population II and Population V), macrophages and dermal fibroblasts to solubilize 45Ca-labelled hydroxyapatite crystals. These crystals were incubated with each of the cell types for 24 h in the presence or absence of parathyroid hormone, prostaglandin E2, calcitonin, and 1,25-dihydroxyvitamin D3. The amount of cell-mediated hydroxyapatite solubilization was determined by measuring the radioactivity in an aliquot of the supernatant after centrifugation. Using dermal fibroblasts as a baseline, relative abilities of macrophages, Population II and Population V to degrade crystals were 10.5, 5 and 2 times that of fibroblasts. Crystal-cell contact was required. While none of the bone resorption agents tested had any effect on this process, crystal dissolution by bone cells was inhibited by two lysosomotropic agents, NH4Cl and chloroquine.

Ammonium Chloride↗
PubMed1990

Preliminary studies on the phenomenological behaviour of osteoblasts cultured on hydroxyapatite ceramics.

SEM was used to investigate the phenomenological behaviour of osteoblasts towards sintered hydroxyapatite. The osteoblasts were seeded on to porous and dense hydroxyapatite and cultured for 4 to 28 d. They attached and adhered on to the hydroxyapatite surfaces, proliferated and secreted extracellular matrix. No signs of toxicity embarrassment were apparent. It is argued that cell phenomenology seems to be a prerequisite to morphogenesis, and on this premise it is speculated that surface-reactive bone replacement materials owe their compatibility to the ability of their surfaces to interact favourably with the peptides involved in osteomorphogenesis and bone repair.

Animals↗
PubMed1991

Crystallographic behaviour of fluoridated hydroxyapatites containing Mg2+ and CO3(2-) ions.

Fluoridated hydroxyapatites containing small amounts of magnesium and carbonate ions were synthesized at 80 and 60 degrees C to examine their inhibiting properties regarding apatite crystal growth, in contrast to the promoting action of fluoride. The shortening of a-axis and c-axis dimensions of the apatite crystals, as revealed by X-ray diffraction analysis, suggested that both magnesium and carbonate ions were substituted into the apatite crystals. The a-axis dimensions also decreased with the degree of fluoridation. The infrared spectra due to CO3(2-) ions at 875 cm-1 were shifted with increasing fluoride content. The overall crystallinity was inhibited in comparison with that of Mg and CO3-free fluoridated hydroxyapatites, but recovered considerably with increased fluoride content. The apparent solubility of the apatites at pH 4.0 and 37 degrees C was higher than that of Mg and CO3-free fluoridated hydroxyapatites at lower fluoride contents, but gradually approached the latter at higher fluoride content. After 1 month's incubation, dicalcium phosphate dihydrate was formed from fluoride-free Mg-CO3 apatite synthesized at 60 degrees C.

Carbonates↗
PubMed1992

Osteoblasts on hydroxyapatite, alumina and bone surfaces in vitro: morphology during the first 2 h of attachment.

The morphological responses of individual osteoblasts as they attached and spread on hydroxyapatite, bovine bone, alumina with rough and polished surfaces, and tissue culture polystyrene in vitro were examined with scanning electron microscopy. Depending on the surface tested two different morphological sequences were observed during 2 h of adhesion. On alumina, both rough and smooth, bone, and tissue culture polystyrene the cells were round after 0.5 h, and spread radially during the next 1.5 h until they were almost flat, with a nuclear bulge. On hydroxyapatite, however, the cells were flat and circular at 0.5 h, and the edge of the cytoplasm was hardly discernable. This morphology did not change much during the subsequent 1.5 h. The observed cellular morphological response may be related to the bioreactivity of hydroxyapatite.

Aluminum Oxide↗