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PubMed1996

Hydroxyapatite coated external fixation pins: an experimental study.

A sheep model was developed for the implantation of 84 bicylindrical stainless steel external fixation pins. One-half of the pins were coated with hydroxyapatite, and the rest remained uncoated. A set of 6 pins with the same coating was implanted in the lateral side of the left tibias of 14 sheep, the final insertion torque was measured, and a monolateral external fixator was assembled on the pins. The medial tibial middiaphysis then was exposed and a 5-mm resection osteotomy was done. Sheep were euthanized 6 weeks after surgery, radiographs were taken, and the initial extraction torque was measured on 4 pins from each sheep. Undecalcified sectioning and histologic and histomorphometric analyses were done on the remaining 2 pins. Radiographic pin tract rarefaction was significantly lower in the hydroxyapatite coated pins compared with the uncoated pins. Group average insertion torque was 960 +/- 959 Nmm in the hydroxyapatite coated pins and 709 +/- 585 Nmm in the uncoated pins. Group average initial extraction torque was 1485 +/- 1308 Nmm and 298 +/- 373 Nmm, respectively. Bone pin contact was 85.7% +/- 8.9% and 50.3% +/- 20.4%, respectively, in hydroxyapatite coated and uncoated pins. Bone between the threads was 95.6% +/- 5.7% and 80% +/- 8.7%, respectively, in hydroxyapatite coated and uncoated pins. Hydroxyapatite coating was effective for improving the bone-to-pin interface.

Animals↗
PubMed1997

Biomechanical, scanning electron microscopy, and microhardness analyses of the bone-pin interface in hydroxyapatite coated versus uncoated pins.

OBJECTIVE: To evaluate the bone-pin interface in hydroxyapatite coated versus uncoated pins. DESIGN: Eighty-four bicylindrical stainless steel external fixation pins were implanted in a test group of 14 sheep. One-half of the pins were coated with hydroxyapatite and the rest remained uncoated. INTERVENTION: Six coated pins were implanted in the left tibia of seven sheep, and six uncoated pins were implanted in the left tibia of the other seven sheep. In all sheep, the right tibia was left intact. During pin implantation, the final insertion torque was measured, and a linear external fixator was mounted on the pins. Then the medial tibial mid-diaphysis was exposed and a 5-mm resection osteotomy was performed. The sheep were killed six weeks after surgery. MAIN OUTCOME MEASURES: The extraction torque was measured on four pins removed from each sheep. Radiographic pin tract rarefaction was measured on all the pins. Two pins from each sheep were used for histologic, scanning electron microscopy (SEM), and microhardness analysis. Histomorphometric analysis was carried out on the SEM specimens at x 36 magnification. RESULTS: Radiographic pin tract rarefaction was significantly lower in the hydroxyapatite coated pins than in the uncoated pins (P < 0.001). Group average insertion torque was 960 +/- 959 N/mm in the hydroxyapatite coated pins, and 709 +/- 585 N/mm in the uncoated pins (p = not significant). Group average extraction torque was 1485 +/- 1308 N/mm and 298 +/- 373 N/mm, respectively (p = 0.0001). Histomorphometric analysis showed that the group average bone-pin contact was 50.7 +/- 16.9% in the hydroxyapatite coated pins and 27.6 +/- 7.1% in the uncoated pins (p < 0.01). Microhardness analysis showed that bone tissue close to the pins was softer than bone tissue far from them. CONCLUSION: Hydroxyapatite coating is an effective method of refining the bone-pin interface and may improve the clinical results of the external fixation technique.

Animals↗
PubMed1999

In vivo evaluation of coralline hydroxyapatite and direct current electrical stimulation in lumbar spinal fusion.

STUDY DESIGN: An animal model of posterolateral intertransverse process lumbar spinal fusion using autologous bone, coralline hydroxyapatite, and/or direct current electrical stimulation. OBJECTIVES: To evaluate the effect of an osteoconductive bone graft substitute and direct-current electrical stimulation on the rate of pseudarthrosis in a rabbit spinal fusion model. SUMMARY OF BACKGROUND DATA: Conventional techniques for the surgical treatment of degenerative conditions in the lumbar spine have a substantial failure rate and associated morbidity. Bone graft substitutes and electrical stimulation are alternative techniques to enhance fusion rates and limit the morbidity associated with posterolateral intertransverse process fusion using autologous iliac crest bone graft. METHODS: Fifty-three adult female New Zealand White rabbits underwent single-level lumbar posterolateral intertransverse process fusion. Animals were assigned to one of four groups using either autologous bone (Group I), coralline hydroxyapatite with autologous bone marrow aspirate (Group II), coralline hydroxyapatite with a 40-microA implantable direct current electrical stimulator and bone marrow aspirate (Group III), or coralline hydroxyapatite with a 100-microA implantable direct current electrical stimulator and bone marrow aspirate (Group IV). Animals were killed at 8 weeks, and fused motion segments were subjected to manual palpation, mechanical testing, and radiographic and histologic analysis to assess the fusion mass. RESULTS: Successful fusion was achieved in 57% (8/14) of animals in Group I, 25% (3/12) in Group II, 50% (6/12) in Group III, and 87% (13/15) in Group IV. Mean stiffness and ultimate load to failure were significantly higher in Group IV than in all other groups (P < 0.05). Histologic analysis demonstrated a qualitative increase in fusion mass in Group IV versus all other groups. CONCLUSIONS: Direct-current electrical stimulation increased fusion rates in a dose-dependent manner in a rabbit spinal fusion model. Coralline hydroxyapatite is an osteoconductive bone graft substitute, and thus requires an osteoinductive stimulus to ensure reliable fusion rates. Furthermore, coralline hydroxyapatite and direct current electrical stimulation can be used together to increase fusion rates in a rabbit spinal fusion model while avoiding the morbidity associated with harvesting iliac crest bone.

Animals↗
PubMed2005

The efficacy of hydroxyapatite composite impregnated with amphotericin B.

We investigated the efficacy of local biodegradable composites composed of hydroxyapatite-plaster of paris and either chitosan or alginate binder impregnated with amphotericin B. Antifungal activity was tested for Candida albicans using a modified disc diffusion technique for 6 weeks and compared with similarly impregnated polymethylmethacrylate. The physicochemical properties of each preparation were evaluated using scanning electron microscopy and Fourier transform infrared spectroscopy. The antifungal activity of amphotericin B eluted from the hydroxyapatite composites was significantly greater than the polymethylmethacrylate after 7 days. The hydroxyapatite composites and the polymethylmethacrylate system sustained their antifungal activity for at least 1 month. However, after 5 weeks, the antifungal activities of the polymethylmethacrylate systems rapidly lessened, while the hydroxyapatite composites sustained their activities at a much higher level. We found no difference in antifungal activity between the hydroxyapatite composite using either the chitosan or alginate binder. Scanning electron microscopy and Fourier transform infrared spectroscopy revealed the drug release profile. The hydroxyapatite composites impregnated with amphotericin B showed superior antifungal efficacy over those loaded in polymethylmethacrylate in an in vitro study, but additional in vivo research is needed to confirm this result.

Absorbable Implants↗
PubMed1992

Influence of dichloromethylene bisphosphonate on the in vitro phagocytosis of hydroxyapatite particles by rat peritoneal exudate cells: an electron microscopic and chemiluminescence study.

Transmission electron microscopy and standard chemiluminescence assays were used to investigate the in vivo effect of dichloromethylene bisphosphonate (clodronate) on the phagocytosis of pure hydroxyapatite particles by rat peritoneal macrophages and the production of chemiluminescence by the peritoneal exudate cells. Hydroxyapatite (control) and a hydroxyapatite/clodronate suspension (28 mumol clodronate per gram of hydroxyapatite, experimental) were injected into the peritoneum of rats, the clodronate dose being 10 micrograms/kg. Macrophages were harvested at 12, 24, 48, and 96 hours after injection and the particle phagocytosis was assessed by transmission electron microscopy. Hydroxyapatite alone was completely phagocytosed by 24 hours and hydroxyapatite reacted with clodronate was completely phagocytosed by 48 hours. From 48 hours onwards hydroxyapatite particle dissolution was observed in the phagosomes of cells in the two groups. At 48 hours the chemiluminescence produced by the peritoneal exudate cells was also measured. Clodronate and clodronate/hydroxyapatite enhanced cell activity on subsequent challenge with phorbol myristate acetate or zymosan. Clodronate seemed to exhibit an inhibitory effect on the phagocytic activity and an enhancement of the chemiluminescence production by the cells in this model, indicating that it was modifying the inflammatory cell response.

Animals↗
PubMed2002

Inorganic-organic polymer hybrid scaffold for tissue engineering--II: partial enzymatic degradation of hydroxyapatite-chitosan hybrid.

This article describes the preparation of porous chitosan, a hydroxyapatite hybrid, by partial enzymatic degradation. Two enzymes, chitosanase and lysozyme, were selected to hydrolyze a chitosan-reinforced matrix and create pores within the chitosan-hydroxyapatite composite. The degree of enzymatic hydrolysis of the chitosan-hydroxyapatite composite was determined by measuring the % weight loss of the chitosan matrix and the hydroxyapatite component. Hydroxyapatite loss from the chitosan matrix increased with the degree of enzymatic hydrolysis of the chitosan-reinforced matrix. After hydrolysis, the composite was further characterized by FTIR. Quantitative analysis revealed a decrease in the characteristic pyranose ring peak (1072 cm(-1)), compared with Po4(2-) (1110 cm(-1)), showing that the chitosan matrices were enzymatically hydrolyzed. The surface of the porous chitosan-hydroxyapatite composite, prepared by controlling enzymatic hydrolysis, was also observed by SEM.

Chitin↗
PubMed1991

Glycochenodeoxycholic acid inhibits calcium phosphate precipitation in vitro by preventing the transformation of amorphous calcium phosphate to calcium hydroxyapatite.

Calcium hydroxyapatite can be a significant component of black pigment gallstones. Diverse molecules that bind calcium phosphate inhibit hydroxyapatite precipitation. Because glycine-conjugated bile acids, but not their taurine counterparts, bind calcium phosphate, we studied whether glycochenodeoxycholic acid inhibits calcium hydroxyapatite formation. Glycochenodeoxycholic acid (2 mM) totally inhibited transformation of amorphous calcium phosphate microprecipitates to macroscopic crystalline calcium hydroxyapatite. This inhibition was not mediated by decreased Ca2+ activity. Taurocholic acid (2-12 mM) did not affect hydroxyapatite formation, but antagonized glycochenodeoxycholic acid. Both amorphous and crystalline precipitates contained a surface fraction relatively rich in phosphate. The surface phosphate content was diminish by increasing glycochenodeoxycholic acid concentrations, and this relationship was interpreted as competition between bile acid and HPO4(-4) for binding sites on the calcium phosphate surface. A phosphate-rich crystal surface was associated with rapid transition from amorphous to crystalline states. These results indicate that glycochenodeoxycholic acid prevents transformation of amorphous calcium phosphate to crystalline hydroxyapatite by competitively inhibiting the accumulation of phosphate on the crystal embryo surface.

Calcium↗
PubMed1987

Clinical evaluation of porous and nonporous hydroxyapatite in the treatment of human periodontal bony defects.

The purpose of this study was to investigate the effectiveness of a synthetic nonporous hydroxyapatite graft material (OrthoMatrix HA-500), a porous replamineform hydroxyapatite graft material (Interpore 200), and a debrided control with respect to defect fill. Twelve adult patients having periodontitis and three similar angular osseous defects as verified by radiographic analysis and clinical probe depths greater than or equal to 5 mm were selected. Clinical parameters gathered prior to surgical intervention and at identified postoperative visits included plaque index, probing depth, and standardized radiographic examination. Customized acrylic stents were used as fixed reference guides for the insertion of endodontic silver points to the base of each defect during both initial and 6-month reentry surgeries. A total of 36 defects were randomly assigned to one of three treatment modalities such that 12 defects received OrthoMatrix HA-500, 12 received Interpore 200, and 12 served as debrided controls. Comparison of nonporous hydroxyapatite, porous replamineform hydroxyapatite, and debrided control treatment modalities revealed a statistically significant improvement (P less than 0.05) in the mean per cent of defect resolved in only those sites treated with nonporous hydroxyapatite. Similar positive trends were seen in the sites treated with nonporous hydroxyapatite for mean reentry defect depth and mean defect fill although these were not statistically significant (P greater than 0.05). No other significant differences were noted.

Adult↗
PubMed1989

Porous hydroxyapatite grafts in chronic subcrestal periodontal defects in rhesus monkeys: a histological investigation.

The purpose of this investigation was to evaluate the histologic response to replamineform (porous) hydroxyapatite grafts in chronically inflamed, surgically created, periodontal pockets in Rhesus monkeys. Forty-eight subcrestal defects were surgically created in 8 Rhesus monkeys. Orthodontic wires were adapted to the base of the defects and left in place for 8 weeks. The defects were randomly assigned a treatment modality so that 8 granular porous and 8 block porous hydroxyapatite grafts were done. Eight sites were left as unoperated controls. Twenty-four contralateral sham-operated sites were treated by open curettage. Histometric measurements of the length of regenerated connective tissue attachment were recorded. Block hydroxyapatite, granular hydroxyapatite, and sham-operated sites exhibited similar amounts of regenerated connective tissue attachment, which was significantly greater than that which occurred in unoperated controls. Newly formed bone was observed within the porous channels of the hydroxyapatite grafts as well as in direct apposition on the surface of implant particles. New bone, cementum, and periodontal ligament was observed in grafted sites and in defects treated by open curettage. In some instances healing occurred by means of a long junctional epithelium. Histology confirmed that unoperated defects remained as unhealed, inflamed periodontal pockets. The results of this study suggest that porous hydroxyapatite grafts have the potential to regenerate the attachment apparatus in primates.

Alveolar Process↗
PubMed1991

Early clinical results of hydroxyapatite-coated total hip arthroplasty.

A retrospective clinical and radiographic review of 25 conventional cementless total hip replacements (THRs) and 25 cementless hydroxyapatite-coated THRs was performed to evaluate early postoperative results. The hydroxyapatite-coated group had a higher incidence of pain-free arthroplasties compared with the standard cementless group (72% v 44%, P = .045) at the 2-month postoperative evaluation. At the 6-month evaluation, 76% of hydroxyapatite-coated THRs were pain-free compared with 52% of conventional cementless THRs, although the statistical significance disappears (P greater than .05). No differences between groups existed in the 6-month Harris hip scores, average motion, use of external support, Trendelenberg gait, postoperative implant radiolucent lines. Adding a 50- to 75-mug hydroxyapatite coating to a proximal one-third porous femoral prosthesis and porous surface acetabular cup improved the early clinical results in cementless THR. Whether this improvement in pain scores reflects a more stable cementless prosthesis via increased rates and amount of osseus ingrowth or adjunctive bone hydroxyapatite chemical bonding remains unanswered. Long-term follow-up of femoral subsidence and THR revision is needed to indicate the durability and success of hydroxyapatite coating.

Adult↗
PubMedDate not supplied

Mandibular bone response to plasma-sprayed coatings of hydroxyapatite.

Sintered hydroxyapatite ceramic particles can be applied as a coating on a titanium substrate using a plasma-spraying technique. The biological and mechanical properties of implants with such a coating were studied in the mandible of a dog. The results indicated that a very strong and direct bonding between the hydroxyapatite coating and the mandibular bone developed. The shear strength of the bone/ceramic interface was higher than the interfacial strength between ceramic and titanium substrate. From the radiologic, macroscopic, and microscopic observations it was concluded that the biological properties of plasma-sprayed coatings of hydroxyapatite are the same as those of sintered hydroxyapatite ceramic. As a result of mechanical failure of the coherence of the hydroxyapatite particles at the outer layer of the coating, free particles of hydroxyapatite were observed in the surrounding bone tissue.

Alveolar Process↗
PubMed1989

The hydroxyapatite-binding regions of a rat salivary glycoprotein.

The regions of a salivary sulphated glycoprotein which are involved in its attachment to hydroxyapatite (Biogel HTP) have been characterised. The sulphated glycoprotein, a 35S-labelled preparation from mixed palatal and buccal minor gland secretions of the rat was bound onto hydroxyapatite and the resultant glycoprotein-hydroxyapatite complex was sequentially digested with pronase E and alpha-L-fucosidase, a treatment which released 86.8% +/- 1.7% of the radioactivity of the initially bound glycoprotein. The fragments which remained attached to the hydroxyapatite after enzymic digestion were fractionated on Sephadex G-25 and analysed for carbohydrate and amino acid components. A range of amino acids were detected which could reflect both glycosylated and non-glycosylated-binding regions. Sialic acid, although considered to be involved in the attachment process was not detected in any of the fragments remaining after enzymic digestion, a finding which provides indirect evidence that the enzymically liberated products do not subsequently re-attach to the hydroxyapatite surface. The notable feature of the fractions with average Mr estimated at 1000 or less is the high proportion of N-acetylhexosamine and N-acetylgalactosamine. It is apparent that the hexosamine residues, which normally bear the ester sulphate moieties of sulphated glycoproteins, play an important role in the attachment of sulphated glycoproteins to hydroxyapatite.

Amino Acids↗
PubMed1989

Interaction of human salivary mucins with hydroxyapatite.

The interactions between hydroxyapatite (HAP) and several types of mucins (human whole salivary mucins, HWSM; ovine submandibular mucin, OSM; porcine gastric mucin, PGM) were compared using a quantitative assay. Of these mucins, HWSM displayed by far the highest binding to hydroxyapatite, followed by PGM and OSM, respectively. HWSM binding to hydroxyapatite was measured at pH 6.3 and 7.0. Data obtained appeared to fit empirically the Langmuirian adsorption isotherm. Apparent affinity constant (K-value) and maximum binding capacity (N-value), derived from these isotherms, indicated that upon lowering the pH the K-value increased from 0.7 to 0.8 ml/mg and the N-value from 2,050 to 2,640 micrograms/m2 hydroxyapatite. The pH-dependence of the HWSM-HAP interaction, measured over a large pH-range, at a fixed concentration of HWSM, indicated a two- to three-fold increase in binding upon lowering the pH from 7.5 to 5.5 At pH 5.5 the presence of HWSM induced an increased solubilization of hydroxyapatite, as deduced from the amounts of Ca2+ and phosphate-ions released. Addition of Ca2+ - and Mg2+ -ions (1mM) resulted in a decrease, both of HWSM binding and of the hydroxyapatite solubilization. These effects were more pronounced at the lower pH-values (pH less than 6.0).

Adsorption↗
PubMed1988

Calcium-acidic phospholipid-phosphate complexes in human hydroxyapatite-containing pathologic deposits.

The deposition of calcium-containing crystals in tissues is due to a combination of factors: elevation in the concentrations of precipitating ions, formation of specific nucleators, and removal of macromolecules that inhibit crystal deposition. This study tested the hypothesis that calcium acidic phospholipid phosphate complexes, which promote hydroxyapatite deposition both in vitro and in vivo, are associated only with hydroxyapatite deposits, and furthermore, that the presence of these complexes is associated with all such hydroxyapatite deposits. Lipid analysis of 76 surgical specimens containing evidence of pathologic calcification (35 hydroxyapatite, 35 calcium pyrophosphate dihydrate, and 6 containing other crystalline materials) had mean complexed acidic phospholipid contents of 8.7, 1, and 0.012, (microgram/mg demineralized dry weight) respectively. Tissues that contained larger, more perfect hydroxyapatite crystals based on x-ray diffraction analyses, had a higher complexed acidic phospholipid content (7.5 +/- 4 micrograms/mg demineralized dry weight, N = 16) than tissues with poorly crystallized hydroxyapatite (3.9 +/- 2 micrograms/mg, N = 11). Histologically, tissues containing larger crystals were characterized by cell or tissue necrosis. Poorly crystalline deposits were found in tissues showing little or no evidence of cell necrosis or tissue degeneration.

Calcinosis↗
PubMed1982

Phosphoprotein inhibition of hydroxyapatite dissolution.

A chromatography column containing hydroxyapatite beads was used to study the effect of different proteins on the rate of hydroxyapatite dissolution. The four phosphoproteins tested (phosvitin, alpha sl-casein, beta-casein and kappa-casein) markedly reduced the rate of hydroxyapatite dissolution. Three nonphosphorylated proteins had a relatively smaller effect. The effect of the protein in reducing the hydroxyapatite dissolution rate has been attributed to protein binding to the surface of hydroxyapatite. The reduction in dissolution rate, expressed as the change in nmol calcium released per min per nmol of phosphoprotein bound to hydroxyapatite, increased with increasing number of phosphoserine residues of the protein. The results are consistent with the proposition that phosphoproteins have a regulatory role in mineralization processes and could provide a mechanism by which dietary and salivary phosphoproteins exert an anticariogenic effect.

Animals↗
PubMed1994

Heterogeneous Mg-containing hydroxyapatites.

Two different Mg-containing hydroxyapatites, H-MgAp and Mg-HAp, were synthesized at 80 degrees C and pH 7.4. For H-MgAp, the calcium solution was supplied in the first half of the synthesis period and the calcium solution containing magnesium was supplied in the second half. For Mg-HAp, the order of supply was reversed. The X-ray diffraction patterns of H-MgAp and Mg-HAp differed slightly from each other. The (002) reflection of both patterns shifted towards a higher angle. The chemical compositions, especially the Mg contents, of the two apatites were almost the same as each other; and the Mg contents were half of that of homogeneous MgHAp synthesized with continuous supply of Mg at the same concentration. However, their crystal shapes were quite different, with H-MgAp appearing plate-like and Mg-HAp needlelike. In a solubility experiment, Mg-HAp was more soluble than H-MgAp. These results suggest that two different heterogeneous Mg-containing hydroxyapatites may be formed: hydroxyapatite covered with Mg-containing hydroxyapatite, and Mg-containing hydroxyapatite covered with hydroxyapatite.

Crystallography, X-Ray↗
PubMed1997

Solubility product of OH-carbonated hydroxyapatite.

Information on the solubility of OH-carbonated hydroxyapatite, Ca10(PO4)6(CO3)x(OH)2-2x, previously has not been available. In the present study the solubility product (Ksp) of OH-carbonated hydroxyapatite was measured in a 0.1 M acetic acid and sodium acetate buffer solution in a pH range of 4.0-5.8 at a CO2 partial pressure of 10(-3.52) atm. The equilibrium solubility increased with the increase of carbonate content. The Ksp values decreased with the decrease of pH. For example, Ksps were 10(-119), 10(-123), and 10(-130) for pure hydroxyapatite at pH 4.9, 4.5, and 4.1, respectively. The decrease of Ksp was not accounted for by calcium-carbonate complexation. Ksp measured at isoelectric points (L) was expressed as pL = 118.65 - 0.47316 x (CO2 wt%)2.4176. From this formula, the L values were calculated for pure and fully carbonated hydroxyapatite as 10(-118.7) and 10(102.8), respectively. The L value for pure hydroxyapatite agreed with values measured under carbonate-free conditions. Therefore, the L values were regarded as the Ksp for OH-carbonated hydroxyapatite excluding errors arising from carbonate contamination in the solution.

Air Pressure↗
PubMed1999

Enrichment of low abundance proteins of Escherichia coli by hydroxyapatite chromatography.

Visualization of low-copy-number gene products is essential for the detection of novel drug targets by differential protein expression studies. We investigated the enrichment of low-abundance proteins of Escherichia coli by hydroxyapatite chromatography. The proteins of the various pools collected from a ceramic hydroxyapatite column were analyzed by two-dimensional electrophoresis and identified by matrix-assisted laser desorption ionization mass spectrometry. Approximately 800 spots corresponding to 296 different proteins were identified in the hydroxyapatite eluate. About 130 proteins that had not been detected in the two-dimensional gels of the total extract were identified. Hydroxyapatite chromatography enriched low-abundance but also major components of the E. coli protein extract. In particular, it enriched many low-molecular-mass proteins, such as cold-shock proteins. The proteins bound to the hydroxyapatite matrix belong to several classes, including enzymes with various catalytic activities, heat- and cold-shock proteins and many hypothetical and novel proteins with yet unknown functions. The results include a list of the proteins enriched by hydroxyapatite chromatography and a two-dimensional map of the enriched proteins. They may be useful in the design of protein purification pathways using master purification steps and in the search for novel drug targets.

Bacterial Proteins↗