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At least 19 recordsLinked to original sources

PubMed2005

Reduced platelet adhesion to titanium metal coated with apatite, albumin-apatite composite or laminin-apatite composite.

Titanium metal coated with apatite (HA-Ti), albumin-apatite composite (AA-Ti) or laminin-apatite composite (LA-Ti) was prepared by the immersion of NaOH- and heat-treated titanium metal in a calcium phosphate solution, or one supplemented with albumin or laminin. Platelet adhesion to the obtained materials under flow conditions was investigated in real time using a cone- and plate-type viscometer and fluorescence labeled platelets. Adhesion and activation of the platelets on the HA-Ti, AA-Ti and LA-Ti were definitely suppressed as compared with those on untreated titanium metal with a mirror surface. Furthermore, the numbers of platelets adhered to AA-Ti and LA-Ti are smaller than those adhered to HA-Ti, although the differences were not statistically significant. These findings suggest that HA-Ti, AA-Ti and LA-Ti, especially AA-Ti and LA-Ti, would exhibit thromboresistance that is superior to commercially pure titanium metal in terms of platelet adhesion.

Adult↗

PubMed1989

[Self-setting apatite cement. 8. Dissolution and remineralization behavior of 45Ca-apatite cement].

Self-setting apatite cement hardens into a mass of single phase apatite when mixed with diluted phosphoric acid. Structurally this mass consists of two types of apatite, i.e. the seed apatite used as a setting accelerator and the matrix apatite formed afterward in the reaction of dicalcium phosphate dihydrate (DCPD) and tetracalcium phosphate (Te-CP). To investigate the dissolution behavior of self-setting apatite cement in detail, two types of 45Ca labeled apatite cement were prepared. In one, the seed apatite was labeled with 45Ca (45Ca-HAp cement) and in the other the matrix apatite was labeled with 45Ca through use of 45Ca-DCPD (45Ca-DCPD cement). Solubility, estimated from the concentration of 45Ca released in 1 mM of organic acid (e.q. acetic, lactic, or citric acid) with initial pH adjusted to 4.0 at 37 degrees C, was approximately zero for 45Ca-HAp cement, whereas the solubility of 45Ca-DCPD cement was approximately the same as unlabeled cements used so far. This finding suggests that dissolution of the matrix apatite governs dissolution of the set cement, though comparison of X-ray diffraction patterns and electron micrographs of the seed apatite and apatite in the set cement showed no essential difference in crystallinity and crystal shape. The fact that the matrix apatite was formed by enveloping the seed apatite may account for the preferential dissolution of matrix apatite. In synthetic saliva labeled with 45Ca having a degree of supersaturation with respect to apatite comparable to rest saliva, 45Ca concentration in solution decreased once the cement pellet was introduced.(ABSTRACT TRUNCATED AT 250 WORDS)

Apatites↗

PubMed1999

Apatite formation on/in hydrogel matrices using an alternate soaking process: II. Effect of swelling ratios of poly(vinyl alcohol) hydrogel matrices on apatite formation.

In our previous study, we reported a novel method of apatite formation on/in a three-dimensional hydrogel matrix. Using this method, bone-like apatite could be formed on/in the hydrogel matrix under normal conditions in vitro. A poly(vinyl alcohol) (PVA) gel was used as a model matrix. The method consists of two steps: first, water is transformed in a PVA gel with a CaCl2/Tris-HCl aqueous solution (pH 7.4) and second, the gel is soaked in a Na2HPO4 aqueous solution. In the present study, we report a detailed study of the effects of the swelling ratios of PVA gels on apatite formation. Cross-sectional observations and gravimetric measurements of PVA gels with various swelling ratios were done. The amount of apatite formed on/in PVA gels increased almost linearly with an increase in the reaction cycles. The rates of apatite formation on/in PVA gels largely depended on the swelling ratios, which were approximately 0.48, 0.61, 1.28, and 1.55 mg per cycle for swelling ratios of 4.1, 10.4, 16.8, and 30.1, respectively. The apatite content in PVA-apatite composites that was obtained by this method also increased with an increase of the reaction cycles. After six reaction cycles, a PVA gel with a high swelling ratio contains approximately 70 wt% of formed apatite in the composite. On the other hand, a gel with a low swelling ratio contains about 15 wt% of formed apatite in the composite. Cross-sectional views of the PVA gels after each cycle showed that apatite crystals were formed, not only on the surface of the gel but also within it after fifteen reaction cycles. The hydrogel-apatite composites that were obtained using an alternative soaking process will be useful as not only bone substitute materials but also as soft tissue adhesive materials.

Apatites↗

PubMed1976

[Studies on the application of apatite to dental materials. (I) --Apatite ceramics-- (author's transl)].

Apatite ceramics is composed of hydroxyapatite [Ca10(PO4)6(OH)2] sintered at high temperature. It is known that hydroxyapatite is the main component of bone and tooth minerals. There are two synthetic methods for the apatite powder. One is so called wet synthetic method: Synthesis by the reaction of Ca++ and PO4--- in the aqueous solution of approximately pH 7.0, the other is dry method: Synthesis by the solid state reaction at high temperature. The apatite powder stable below 1400 degrees C was prepared by the latter method in this work. After passing through a sieve, this powder was cold-pressed and then sintered at 1000 degrees C to 1300 degrees C in air. Biological apatite powders were also perpared as a reference. It was found that any apatite ceramics having porosity in the range of 5 to 50% could be obtained under the various sintering conditions. Compressive strength of these apatite ceramics increased with the reduction of the porosity, and those with porosity less than 20% were more than 100 kg/cm2. Vickers hardness was measured. This result showed the same tendency as that of compressibility. Hardness of the apatite ceramics with 90% relative density was almost the same or more as that of enamel. Solubility of the synthetic apatite powder in distilled water and aqueous solution of lactic acid (pH 4.0) was nearly the same as biological apatites. The dissolution rate decreased with the reduction of porosity of the ceramics. It was certified that hot pressing technique was extremely effective to obtain high density ceramics (more than 95% of density) and thus low parosity apatite ceramics. From the facts as described above, it is understood that sintered pure hydroxy-apatite is an excellent ceramics of high mechanical strength.

Apatites↗

PubMed1987

Chemical implant fixation using hydroxyl-apatite coatings. The development of a human total hip prosthesis for chemical fixation to bone using hydroxyl-apatite coatings on titanium substrates.

Sintered hydroxyl-apatite implants form very tight bonds with living bone but are susceptible to fatigue failure. Plasma-sprayed apatite coatings on titanium substrates overcome the fatigue problem. The static tensile substrate bond strength of the apatite coating is in excess of 85 megapascals (MPa) (12,000 psi). In a plug implant study designed to discount mechanical retention, a bone bonding shear strength of 64 MPa (9280 psi) was achieved, comparable to the strength of cortical bone. Histologic sections confirm the close bonding between apatite coating and living bone. In a canine total hip arthroplasty study, the apatite-coated implants proved far superior to the uncoated controls. Uncoated prostheses were surrounded by fibrous tissue and were easily extracted from the femur at any postoperative time. The apatite-coated implants were rigidly fixed within three weeks with demonstrable bone formation up to the implant surface. Bony defects up to 2 mm in depth were filled with bone within six weeks. The hypothetical mechanism of bone bonding is chemical. Hydroxyl-apatite coatings permit an implant fixation far superior to current methods using either cemented or cementless techniques. The plan is to study a human total hip prosthesis with hydroxyl-apatite coating for chemical fixation to bone.

Animals↗

PubMed1998

Apatite-organic polymer composites prepared by a biomimetic process: improvement in adhesion of the apatite layer to the substrate by ultraviolet irradiation.

A dense and uniform layer of highly bioactive apatite can be formed in arbitrary thickness on any kind and shape of organic polymer substrates by the following biomimetic process. The substrate is first placed in contact with granular particles of CaO, SiO2-based glass soaked in a simulated body fluid with ion concentrations nearly equal to those of human blood plasma for forming apatite nuclei, and then soaked in another fluid highly supersaturated with respect to the apatite for making the apatite nuclei grow. In the present study, the polymer substrates were pretreated with ultraviolet (UV) light, and then subjected to the biomimetic process described above. By UV irradiation, the induction period for the apatite nucleation of poly(ethylene terephthalate) (PET), poly-ether sulphone (PESF), polyethylene (PE), poly(methyl methacrylate) (PMMA) and polyamide 6 (N6) substrates were reduced form 24 h to 10 h. The adhesive strengths of the apatite layer to the substrates increased from 2.5-3.2 MPa to 4.5-6.0 MPa for PET, PESF and PMMA, and from about 1.0 MPa to 4.0-6.5 MPa for PE and N6 substrates. These results have been explained by assuming that silicate ions, which induce apatite nucleation, are easily adsorbed on the substrates due to the formation of polar groups, with an improved hydrophilic nature, on the polymer surfaces by UV irradiation.

Journal Article↗

PubMed1994

Osteoclastic resorption of apatite formed on apatite- and wollastonite-containing glass-ceramic by a simulated body fluid.

We immersed mirror-polished apatite- and wollastonite-containing glass-ceramic (A-W GC) disks in a simulated body fluid (SBF) for 5 days to form bonelike apatite on their surface. Neonatal rabbit bone cells were cultured on these or on plain A-W GC disks for 10, 24, and 48 h. We observed the substrates by scanning electron microscopy after treating them with pronase E plus EDTA to remove all cells except osteoclasts. Osteoclasts with a non-motile appearance formed no lacunae on the plain A-W GC, whereas on the bonelike apatite formed on A-W GC by the SBF, actively moving osteoclasts made many tracklike resorption lacunae. These were evident even after 10 h of culture and became more extensive after longer culture periods. The bonelike apatite was therefore a more suitable medium than plain A-W GC for maintaining osteoclast activity. This study demonstrated in vitro osteoclastic resorption of bonelike apatite formed on A-W GC by an SBF. It suggests that the apatite layer, through which a surface-active ceramic bonds to bone in vivo, can be resorbed by osteoclasts and subjected to bone remodeling.

Animals↗

PubMed1999

Apatite formation on/in hydrogel matrices using an alternate soaking process (III): effect of physico-chemical factors on apatite formation on/in poly(vinyl alcohol) hydrogel matrices.

The aim of this study is to clarify the physico-chemical factors which influence apatite formation on/in a hydrogel during a novel alternate soaking process. A poly(vinyl alcohol) (PVA) gel was used as a model matrix. The amount of apatite formed on/in PVA gels decreased with an increase in the reaction temperature during the same reaction cycles. This suggested that the equilibrium swelling ratios decreased with increasing reaction temperatures; that is, the diffusion of calcium and phosphate ions reduced at high reaction temperature. However, the crystallinity of apatite formed on/in PVA gels was greater at higher reaction temperatures. The amount of apatite formed on/in PVA gels increased with an increase in the calcium and phosphate solution concentrations, and increased by shaking at the first three reaction cycles. A few influences could be observed when the solution volume was changed, however, the soaking order was not effective in this study. These results indicate that the amount of apatite formation on/in PVA gels can be controlled by changing the reaction temperature and the Ca- and P-solution concentrations, and that the crystallinity of apatite can be also changed by controlling the reaction temperatures.

Apatites↗

PubMed1990

[Specific physicochemical properties of apatites. 10. Fe-containing fluoridated apatites].

Fe-containing hydroxyapatites and fluoridated hydroxyapatites were synthesized at 80 degrees C and pH 7.4. Fe-containing hydroxyapatites became poorly crystallized with the increase of Fe2+ ions in the solution and a- and c-axis dimensions seemed to decrease slightly. The apparent solubility of Fe-containing hydroxyapatites decreased greatly with the increase of iron content in spite of the decrease in crystallinity. Fe-containing fluoridated apatites were less well crystallized than Fe-free fluoridated apatites. The Fe2+ uptake of fluoridated apatites was independent of fluoride concentration in the solution. a-Axis dimensions of Fe-containing fluoridated apatites decreased with the degree of fluoridation in addition to the decrease related to the substitution of Fe2+ ions. The apparent solubility of Fe-containing fluoridated apatites decreased more than that of Fe-free fluoridated apatites especially at a low fluoride content.

Apatites↗

PubMed2003

Apatite-forming ability of glass-ceramic apatite-wollastonite - polyethylene composites: effect of filler content.

The bioactivity of a range of glass-ceramic apatite-wollastonite (A-W) - polyethylene composites (AWPEXs) with glass-ceramic A-W volume percentages ranging from 10 to 50, has been investigated in an acellular simulated body fluid (SBF) with ion concentrations similar to those of human blood plasma. The formation of a biologically active apatite layer on the composite surface after immersion in SBF was demonstrated by thin-film X-ray diffraction (TF-XRD) and field-emission scanning electron microscopy (FE-SEM). An apatite layer was formed on all the composites, with the rate of formation increasing with an increase in glass-ceramic A-W percentage. For composites with glass-ceramic A-W filler contents >or=30 vol %, the apatite layer was formed within 12 h of immersion, which is a comparable time for apatite formation on monolithic glass-ceramic A-W. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) demonstrated that the apatite formation on AWPEX samples with 50 vol % filler content occurred in a manner similar to that seen on pure glass-ceramic A-W, in that the calcium, silicon, and magnesium ion concentrations increased and, conversely, a decrease was observed in the phosphate ion concentration. These results indicate that a suitable in vitro response was achieved on a composite incorporating particulate glass-ceramic A-W with a particularly favorable response being observed on the AWPEX sample with 50 vol % filler content.

Journal Article↗

PubMed1988

[Need for the differentiation of apatite and carbonate apatite].

With extensive analytical and clinical examinations it is shown that the proof of carbonate in apatite may allow no additional reference of an infection with urea-splitting bacteria. With certain analytical methods the presence of carbonate is demonstrable in each urinary calculus apatite phase. Carbonate-bearing apatite indeed is accompanied frequently with struvite, but may be occur also without an infection. Therefore, in the future it should be renounced on the differentiation of apatite and carbonate apatite in routine analyses of urinary calculi.

Apatites↗

PubMed2007

Transfer of apatite coating from porogens to scaffolds: uniform apatite coating within porous poly(DL-lactic-co-glycolic acid) scaffold in vitro.

Strategies to bone tissue engineering have focused on the use of synthetic or natural degradable materials as scaffolds for cell transplantation to guide bone regeneration. Biocompatibility, biodegradability, biomechanical integrity, and osteoconductivity are important requirements for the scaffold materials. This study explored a new approach of apatite coating to enhance the osteoconductivity of a synthetic degradable poly(DL-lactic-co-glycolic acid) (PLGA) scaffold. The new approach was developed to ensure a relatively uniform apatite coating on the interior pore surfaces deep inside a scaffold, even for a relatively thick scaffold with small pores. Apatite was first coated on the surface of paraffin spheres of the desirable sizes. The paraffin spheres were then molded to form a foam. PLGA/pyridine solution was cast into the interspaces among the paraffin spheres. After the paraffin spheres were dissolved and removed by cyclohexane, PLGA scaffold with controlled pore size, good interconnectivity and high porosity was obtained with apatite left on the pore surface uniformly throughout the whole scaffold. The scaffold and apatite coating were characterized using thermogravimetry analysis, scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffractometry.

Bone Regeneration↗

PubMed2006

Fabrication of biporous low-crystalline apatite based on mannitol dissolution from apatite cement.

Biporous (macro- and microporous) calcium phosphate gains much attention as a bone substitute material because of its large surface area and that it improves cell penetration. In the present study, we evaluated the feasibility of biporous, low-crystalline apatite based on dissolution of mannitol from self-setting apatite cement (Biopex). Mannitol--known as a biocompatible, easily dissolved monosaccharide alcohol--was recrystallized to obtain larger crystals. It was crushed with pestle and mortar, sieved to obtain crystals which passed through a 500-microm mesh but which remained against a 300-microm mesh, and then used as porogen. Although Biopex containing 60 wt% mannitol was not able to be taken out of the mold, addition of mannitol caused no initial setting inhibition to Biopex if the amount was 40 wt% or less. Similarly, transformation to apatitic product was confirmed when the apatite cement was immersed in 0.9% saline kept at 37 degrees C for seven days. The set mass became low-crystalline, biporous apatite with approximately 60% porosity.

Bone Substitutes↗

PubMed1993

Tissue response of apatite-filled resin cement and titanium-reinforced apatite dental implants in dogs.

Abutment and root portion divided two-piece dental implants were designed to modify the one-piece dense hydroxyapatite (D-HAP) implant. The initial placement of the root portion endosseously ensured an aseptic environment and physical stability for the implant during the bone healing period. The outer D-HAP shell of the root portion was fortified by an inner titanium cylinder and cemented with an adhesive resin cement containing 4-methacryloyoxyethyl trimellitate anhydride (4-META) and reinforced by fine apatite filler. Upon attaining integration of the bone and implant, the abutment was screwed and fixed into the screw hole of the root portion. The tissue response of both the apatite-filled resin cement and root portion of the two-piece implant was studied by animal canine experiments. Light and electron microscopic examination of specimens taken from experimental animal tissue showed bone contacted directly not only the exposed apatite filler at the surface of the apatite-filled resin cement, but also the resin portion. These findings of direct bone contact suggested that the tissue response of apatite-filled resin cement was approximately similar to the usual D-HAP. Because most of the surface of the outer D-HAP shell of the root portion came in contact with bone, it prevented the deposition of contamination on the D-HAP surface during the manufacturing procedures of the root portion.

Animals↗

PubMed2001

Dissolution of poorly crystalline apatite crystals by osteoclasts determined on artificial thin-film apatite.

Poorly crystalline apatite (PCA) crystals introduced into bone tissue should be stable for a definite period before they are dissolved as a result of a host response. In this report, the dissolution of PCA crystals by the action of osteoclasts was studied on artificial thin films. These consisted of PCA crystals having similar crystallographic properties to bone crystals which were developed for assaying the osteoclast activity in vitro. The dissolution of minerals by osteoclasts decreased along with the decreased amount of labile phosphate and hydrogen phosphate domains of apatite crystals, which were caused by the crystal maturation temperature. A profound effect on mineral dissolution by pH in the culture medium was also shown. Low acidity considerably increased mineral dissolution, whereas a slight alkalinity totally blocked mineral dissolution. There was little difference in the mineral dissolution behavior of osteoclasts near the physiologic pH. In addition, it was determined whether mineral dissolution by osteoclasts was dependent on the destruction of the organic matrix. Nocodazole was introduced to inhibit the secretion of hydrolytic enzymes, and acetazolamide was added to inhibit acid production by the osteoclasts. There was no significant change as a result of nocodazole addition on mineral dissolution or by the addition of acetazolamide on degradation of collagen. These results indicate that small changes in the physicochemical properties of apatite crystals can decrease resorption by osteoclasts, which can be highly activated at low pH. These results also suggest that mineral dissolution and organic degradation by osteoclasts are self-regulating.

Acetazolamide↗

PubMed1988

Effect of fluoride in the apatitic lattice on adsorption of enamel proteins onto calcium apatites.

The selective adsorption of enamel proteins onto crystalline calcium apatites having different specific surface areas and various degrees of fluoride substitution was investigated. The proteins were obtained from the outer (close to the ameloblast) layer of secretory enamel of porcine permanent incisors. The adsorption of the enamel proteins was not affected markedly by the variation of specific surface area of the hydroxyapatites used as adsorbents, but it was enhanced substantially with increasing fluoride content in the crystalline lattice. Through the use of SDS- and two-dimensional polyacrylamide gel electrophoresis, it was shown that the originally secreted amelogenin (25 kd) as well as 60-90-kd and 5-6-kd molecules adsorbed most selectively onto the hydroxyapatites and that additional moieties having 21-23-kd and 14-18-kd molecular masses commenced to adsorb onto the apatitic surfaces with increasing degrees of fluoride substitution in the lattice. In contrast, the 20-kd amelogenin, a product partially degraded from the 25-kd amelogenin, showed no significant adsorption, even onto the fluoridated apatites. These results suggest that the retention of proteinaceous matrix in the developing enamel might be affected by the nature of the forming crystals.

Adsorption↗

PubMed1990

[Apatite-collagen complex. Preparation of a new apatite-collagen complex].

A new apatite-collagen complex was prepared in calcium beta-glycerophosphate solutions at pH 8.50. For this preparation, reconstituted type I collagen was cross-linked with phosvitin in the presence of alkaline phosphatase by use of a cross-linking agent of dimethyl suberimidate. After two weeks of immersion in daily-renewed solution of calcium beta-glycerophosphate, the complex contained apatite approximately two times the modified collagen in weight. When viewed in a scanning electron microscope, needle-like crystals precipitated densely on the collagen fibrils. However, in some portion of the complex, dot-like precipitate was observed as well. X-ray diffraction and IR analyses of the complex suggested that the apatite precipitated on the collagen fibrils was very similar to bone mineral in two aspects, crystallinity and carbonate content.

Apatites↗

PubMed2003

Bonding strength of the apatite layer formed on glass-ceramic apatite-wollastonite-polyethylene composites.

Bioactive glass-ceramic apatite-wollastonite (A-W) has been incorporated into polyethylene in particulate form to create new bioactive composites for potential maxillofacial applications. The effects of varying the volume fraction of glass-ceramic A-W filler and the glass-ceramic A-W particle size were investigated by measuring the bonding strength of the bonelike apatite layer formed on the surface of glass-ceramic A-W-polyethylene composites. The bonding strength was evaluated via a modified ASTM C-333 standard in which a tensile stress was applied to the substrate and the strength of the bioactive layer was compared with that formed on commercially available hydroxyapatite-polyethylene composite samples, HAPEX. The composites demonstrated greater bonding strength with increased filler content and reduced filler particle size (maximum 6.9 +/- 0.5 MPa) and a marginally greater bonding strength as compared with HAPEX (2.8 +/- 0.5 MPa), when glass-ceramic A-W-polyethylene composite samples with the same filler content were tested. The higher bonding strength of the apatite layer formed on the A-W-polyethylene composite samples suggests that, in addition to maxillofacial applications, these composites might also be utilized in applications involving higher levels of load bearing.

Adhesiveness↗