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At least 217 records · Page 12Linked to original sources

PubMed1998

Siliceous tablets in the larval shells of apatitic discinid brachiopods

The marine bivalved Brachiopoda are abundant throughout the geological record and have apatitic (CaPO4-rich) or calcitic (CaCO3-rich) shells. Vesicles covering the larval valves of living apatitic-shelled discinids contain tablets of silica. The tablets are cemented into close-packed mosaics by spherular apatite in glycosaminoglycans. They are usually lost as vesicles degrade but leave imprints on the underlying apatitic shell. Similar imprints ornament larval surfaces of some of the earliest Paleozoic apatitic-shelled brachiopods and may also be indicators of siliceous biomineralization.

Journal Article↗

PubMed2004

Biocompatibility of composite membrane consisting of oriented needle-like apatite and biodegradable copolymer with soft and hard tissues in rats.

The purpose of this study was to evaluate histologically the reaction of soft and hard tissues in rats toward a composite membrane consisting of oriented needle-like apatite crystals and biodegradable copolymer. Histological findings regarding the soft tissue reaction showed that the membrane with or without apatite was covered by fibrous connective tissue at four weeks after implantation. In the case of hard tissue, the defect in dura mater--which was covered with an apatite-containing membrane--was fully filled with new bone at four weeks after implantation. As for the membrane without apatite, there was some indication of a granulation tissue reaction around the membrane. These results suggested that the biodegradable composite membrane containing oriented needle-like apatite had excellent biocompatibility with both soft and hard tissues.

Absorbable Implants↗

PubMed1992

Interaction of bile salts with calcium hydroxyapatite: inhibitors of apatite formation exhibit high-affinity premicellar binding.

Of the major human bile salts, only the glycine-conjugated dihydroxy species prevent the transformation of amorphous calcium phosphate to calcium hydroxyapatite, a component of gallstones; we have proposed that this inhibition occurs by competition between the bile salt and HPO4(2-) anions for binding site on the apatite crystal embryo. Now we show that the binding affinity of bile salts to fully mature hydroxyapatite has the following order: glycine-conjugated dihydroxy salts > taurine-conjugated dihydroxy salts > glycocholate approximately taurocholate. Glycine-conjugated dihydroxy bile salts bound with high affinity as "premicellar" aggregates, but the remaining species appeared to bind as a wider range of aggregate sizes. Glycochenodeoxycholate binding was decreased as the pH increased from 6.6 to 9.8 and the apatite surface charge reversed from net positive to net negative. Binding was competitively inhibited by HPO4(2-), but not by H2PO4-. Ca2+ promoted the binding of glycochenodeoxycholate, taurochenodeoxycholate and glycocholate, and for the latter two bile salts the increase was associated with enhanced "premicellar" binding. The binding of taurocholate was not influenced by Ca2+. When either glycocholate or taurocholate was mixed with glycochenodeoxycholate, mixed aggregates were formed that had a lower affinity for apatite than had pure glycochenodeoxycholate aggregates. Because only glycine-conjugated dihydroxy bile salts inhibit apatite formation, these results suggest that inhibition depends on high-affinity "premicellar" bile salt-apatite binding.

Anions↗

PubMed2003

[Investigation of tissue reaction of apatite cement implants impregnated with vancomycin].

Investigation of biocompatibility degree of apatite cement as a carrier of antibiotic--vancomycin was the purpose of the experimental study. Investigation of local reactions of muscular tissue was carried out on 18 rats of Wistar type, by implanting samples of apatite cement with vancomycin in the dorsal muscles. Sections of the animals and microscopic investigations were made 7, 14, 30, 90, 180 and 270 days after the implantation. Investigation of local reactions of bone tissue were carried out on 12 rabbits of New Zealand breed, by implanting the investigated samples into the femoral bone in the region of trochanter. Macroscopic, radiological and microscopic investigations were carried out 1, 3, 6 and 9 months after the surgery. The obtained results of the investigations from muscular and bone tissue, were compared to the investigations in analogical tissues of apatite cement without the medication. In macro- and microscopic investigations in the early period inflammatory reaction of muscles was noticed to be stronger around the samples with vancomycin, in comparison to the control implant. In the later period there was no inflammatory reaction and a thin fibrous connective tissue surrounded the implant and a histological picture was similar, as in cases of an implant without the antibiotic. The local reaction of bone tissue both in the control and in the investigated group (apatite cement with vancomycin) was similar. In the early period the proliferation of rich cellular connective tissue, was noticed. In the later period starting from the 3rd month, formation of young bone tissue was noticed and only locally there were focuses of fibrous tissue. The process observed after splitting of the tested materials into bone tissue, was very similar to healing processes after long bone fraction. The carried out investigations showed, that tissue reaction after implantation of apatite cement and its composite with vancomycin, was very similar and showed a high degree of tissue biocompatibility.

Animals↗

PubMed1994

Bone formation under the influence of bone morphogenetic protein/self-setting apatite cement composite as a delivery system.

Self-setting apatite cement (apatite cement) with a phase of hydroxyapatite (HAP) was employed as a delivery system for bone morphogenetic protein (BMP). A composite of BMP and apatite cement (BMP/HAP composite) was implanted both in thigh muscle and surgically created defect of a critical size of 5 mm, which is a size that does not heal spontaneously in the femur of mice, to evaluate its osteogenetic potential as an augmentation and reconstructive material for clinical usage. The histological and immunohistochemical assessment of proteoglycans reiterated osteogenesis in the muscle tissue. On day 14 postimplantation of BMP/HAP composite, chondroid tissue was formed in the muscle, and HAP particles were seen in newly formed chondroid tissue. On the 21st day, endo-chondral ossification had occurred, however, small HAP particles remained in the newly formed bone, i.e., HAP particles and newly formed osseous tissues coexisted in a central area. BMP/HAP composite was incorporated by newly formed osseous tissue in the experimented animals. HAP particle found in BMP/HAP composite implanted into the bone defect was resorbed and replaced by osseous tissue. The apatite cement was proved to have advantages for its shaping as well as collapsing properties, and thus, apatite cement containing BMP is suggested as a favorable augmentation material in clinical usage for delivery system of BMP.

Animals↗

PubMed1996

Quantitative assessment of apatite formation via a biomimetic method using quartz crystal microbalance.

Quantitative assessment of hydroxyapatite formation on a gold surface via the biomimetic method, composed of a nucleation step in a simulated body fluid (SBF) containing glass powders and a subsequent apatite growth step in glass powder-free SBF, was made using a quartz crystal microbalance (QCM) technique. The frequency change of the QCM linearly increased with increasing soaking time, and largely depended on the nucleation period. The growth rates, defined as daily increase in thickness, increased monotonicly with an increasing nucleation period of up to 96 h, thereafter being constant at 2.0 microns/day. The growth rate of the apatite layer increased with increasing temperature of the SBF: 0.9, 2.0, and 3.8 microns/day at 25, 37, and 50 degrees C, respectively. The Arrhenius-type activation energy for the growth of apatite was 47.3 kJ/mol. The QCM method was found to be a very powerful tool for quantitative, in situ measurement of precipitation and growth of apatite in real time.

Apatites↗

PubMed1997

Bonding strength of bonelike apatite layer to Ti metal substrate.

Our previous study showed that titanium metal forms a bonelike apatite layer on its surface in simulated body fluid when it was subjected to NaOH and heat treatments to form a sodium titanate hydrogel or amorphous sodium titanate surface layer. In the present study, bonding strength of the apatite layer formed on the titanium metals to the substrates were examined under tensile stress, in comparison with those of the apatite layers formed on Bioglass 45S5-type glass, dense sintered hydroxyapatite, and glass-ceramic A-W, which are already clinically used. The NaOH-treated titanium metals showed higher bonding strength of the apatite layer to the substrates, which was maximized by heat treatments at 500 and 600 degrees C, than all the examined bioactive ceramics. It is believed that bioactive metals thus obtained are useful as bone substitutes, even under load-bearing conditions.

Apatites↗

PubMed1998

Influence of magnesium substitution on a collagen-apatite biomaterial on the production of a calcifying matrix by human osteoblasts.

The induction of a calcifying matrix is of great interest in the restoration of bone defects. In a previous in vitro study we demonstrated that a collagen sponge constituted of type I collagen fibrils, chondroitin sulfates, and hydroxyapatite crystals induces an earlier and a more abundant synthesis of a new extracellular calcifying matrix than do other biomaterials such as collagen or hydroxyapatite alone. Bone mineral contains various amounts of magnesium ions, either adsorbed at the surface of apatite crystals or incorporated inside the crystal structure. Magnesium is known to reduce the degradation rate of tricalcium phosphate ceramics and to influence the crystallization of mineral substance. Thus we evaluated two sponges modified with different substituted apatites. The substituted low magnesium-containing apatite sample decreased the osteoinductive properties of the sponge whereas the substituted high magnesium-containing apatite sample had a toxic effect on bone cells and prevented the formation of any extracellular matrix. Such a toxic effect can be explained by the presence of large numbers of magnesium ions released into the culture medium even though at physiological level magnesium is able to promote bone mineralization and to control the growth of hydroxyapatite crystals. Thus collagen sponges containing hydroxyapatite remain one of the most appropriately evaluated biomaterials used for the restoration of periodontal pockets and bone defects.

Apatites↗

PubMed1999

Transmission electron microscopic study of interface between bioactive bone cement and bone: comparison of apatite and wollastonite containing glass-ceramic filler with hydroxyapatite and beta-tricalcium phosphate fillers.

We developed a bioactive bone cement that consists of apatite and wollastonite containing glass-ceramic (AW-GC) powder and bisphenol-a-glycidyl methacrylate (Bis-GMA) based resin. In this study, we made three types of cement (designated AWC, HAC, and TCPC) consisting of either AW-GC, hydroxyapatite (HA), or beta-tricalcium phosphate (beta-TCP) powder as the inorganic filler and Bis-GMA based resin as the organic matrix. These cements were implanted into rat tibiae and cured in situ. Specimens were prepared 1, 2, 4, and 8 weeks after the operation and observed using transmission electron microscopy. Each of the bone cements was in direct contact with the bone. In AWC-implanted tibiae, the uncured surface layer of Bis-GMA based resin was completely filled with newly formed bone-like tissue 2 weeks after implantation. The AW-GC particles were surrounded by bone and were in contact with bone through an apatite layer. No intervening soft tissue was seen. In HAC-implanted tibiae, it took 4 weeks for the uncured layer to completely fill with newly formed bonelike tissue. The HA particles were also in contact with bone through an apatite layer. In TCPC-implanted tibiae, it took 8 weeks for the uncured layer to fill with newly formed bone-like tissue. The new bone that formed on the TCPC was not as dense as that on the AWC or HAC, and an intervening apatite layer was not evident. Results indicated that AWC had higher bioactivity than either HAC or TCPC.

Animals↗

PubMed1999

Role of fibronectin during biological apatite crystal nucleation: ultrastructural characterization.

The role of adhesion molecules like osteopontin and bone sialoprotein, both containing the Arg-Gly-Asp sequence have been shown to have a role in mineral formation, whereas fibronectin (FN), another adhesive protein, was never studied during the mineralization processes. The formation and maturation of biological apatite crystals are under matrix control, and one of the roles of specific crystal proteins is to control the nucleation and growth of biological apatite during the mineralization process (promotion or inhibition). In the case of calcium phosphate ceramic used as a bone substitute, a dissolution-precipitation process occurs after implantation before the bone ingrowth and bone mineralization. The early precipitation consists of common biological apatite crystals. These crystals are the result of secondary nucleation and a heteroepitaxic growth process on synthetic residual crystals. In in vivo studies, hydroxyapatite crystals were implanted subcutaneously into mice for 1 or 2 weeks. Fibronectin immunogold labeling of the newly formed crystals on surfaces of high-resolution transmission electron microscopy sections of retrieved implants revealed the close association of these precipitated crystals with FN. In in vitro experiments using a solution of human FN incubated in the presence of calcium phosphate crystals, we obtained apatite crystal precipitation. The fibronectin network observed in high-resolution transmission electron microscopy showed numerous clusters of very small particles (1 nm in diameter and 2 nm in length), whereas the same experiment realized as control on albumin revealed no crystal precipitation. These results demonstrate for the first time the role of FN in early biological crystal nucleation. This process could have important biological significance in accounting for ectopic calcification, primary nucleation in calcified tissue, and bone ingrowth on calcium phosphate ceramics.

Animals↗

PubMed2000

Apatite growth on calcium adsorbed surface of wet flocculated silica particles immersed in a modified simulated body fluid.

An alternative method for the calcium phosphate apatite formation onto the surface of flocculated pure silica particles is reported, in an attempt to understand the possible mechanism for the apatite formation. A stable silica sol was flocculated by adding calcium ions in aqueous solution. The wet flocks were resuspended in a basic aqueous solution containing a calcium salt, trying to allow the absorption of calcium ions onto the silica surface through a hydrogen ion exchange. The as-prepared materials were immersed in a modified simulated body fluid at different temperatures (37 and 90 degrees C) and silica concentrations. It was found that these factors have a strong influence on the apatite formation. The apatite formation was confirmed by (31)P MAS-NMR, FT-Raman, XRD, and TEM.

Adsorption↗

PubMed2000

Analysis of apatite layers on glass-ceramic particulate using FTIR and FT-Raman spectroscopy.

A nucleation and crystallization schedule was adapted to produce 40% crystalline Bioglass ceramic particulates. These particles were placed in a dynamic environment in a simulated physiologic solution (SBF-9) for time periods ranging from 10 min to 7 days. Fourier transform Raman spectroscopy (FT-Raman) and infrared spectroscopy (FTIR) were used to analyze the apatite layer formation on the particulates. FTIR determined that amorphous apatite formation took place within 2 h, with the appearance of crystalline apatite in 14 h. The vibrational frequencies obtained through FT-Raman were equivalent to those obtained using FTIR. These analyses showed that a fully crystallized apatite layer was present on the particulate after 3 days of exposure in SBF solution. These findings are consistent with those associated with amorphous Bioglass particles.

Apatites↗

PubMed1981

Erosive arthritis associated with apatite crystal deposition.

Apatite crystals can be associated with erosive arthritis. This report describes 3 such patients, 2 of whom had idiopathic apatite crystal deposition and 1 who had apatite related to renal failure and chronic dialysis. Diagnosis was delayed for several years in 1 patient. Roentgenograms showed calcifications in all patients. Synovial fluid had non-birefringent chunks and globules suggestive of apatite. Diagnosis was established by electron microscopy in all 3 patients with verified by x-ray diffraction in 2.

Apatites↗

PubMed1984

Difference of bond bonding behavior among surface active glasses and sintered apatite.

Three types of surface active glasses and sintered apatite were implanted in femurs of rabbits for 8 and 16 weeks and subjected to the push-out test to measure the bone bonding strength. The apatite surface layers of these materials, which were formed under in vitro treatment, were studied using IR, NMR, and AES. The difference in the bonding strength among these materials was shown statistically. The results of in vitro experiments explained the differences. It was concluded that the crystal chemistry and formation rate of the surface apatite layer significantly influenced the bonding strength. Materials that formed a surface apatite layer having a bone-like crystal chemistry and fast formation rate showed high bone bonding strength.

Animals↗

PubMed1987

SEM-EPMA observation of three types of apatite-containing glass-ceramics implanted in bone: the variance of a Ca-P-rich layer.

The progressive changes of a Ca-P-rich layer between bone and three types of apatite-containing glass-ceramics of the same chemical composition: MgO 4.6, CaO 44.9, SiO2 34.2, P2O5 16.3, CaF2 0.5 (in weight ratio) were examined. Plates (15 mm X 10 mm X 2 mm, mirror surface) containing apatite (35 wt%) (designated A-GC), apatite (35 wt%) and wollastonite (40 wt%) (designated A.W-GC), and apatite (20 wt%), wollastonite (55 wt%), and whitlockite (15 wt%) (designated A.W.CP-GC) were prepared. They were implanted into the tibia of mature male rabbits for 5 days, 10 days, 20 days, 30 days, 60 days, 6 months, and 12 months. All three types of glass-ceramics showed direct bonding to the bone 30 days after implantation. It was observed by SEM-EPMA 30 days after implantation that Si and Mg content decreased, P content increased, and Ca content did not change across the reactive zone from the glass-ceramics to bone. The level of P and Si in the A.W.CP-GC changed five days after implantation. In A.W-GC and A-GC, a little change in P and Si levels was observed between 10 and 20 days after implantation. The width of reactive zone was narrowest with A-GC, wider with A.W-GC, and widest with A.W.CP-GC. The dissolution of glass-ceramics stopped 6 months after implantation. This phenomenon shows that the glass-ceramics may be suitable for clinical use.

Animals↗

PubMed2004

Comparative study of the in vitro apatite-forming ability of poly(epsilon-caprolactone)-silica sol-gels using three osteoconductivity tests (static, dynamic, and alternate soaking process).

The in vitro apatite-forming ability of poly(epsilon-caprolactone) (70 wt %)-silica sol-gels, with hydroxyl and triethoxysilane end-groups with potential use in bone repair have been assessed using static and dynamic osteoconductivity tests. Diffuse reflectance infrared spectroscopy, scanning electron microscopy, and microanalysis techniques were used to observe and characterize precipitates formed on the material's surface. An apatite layer was observed to form on both of the composites' surface. However, variations were observed according to the test method used, in accordance with other studies on bioactive ceramics. A third method, the "alternate soaking process" (ASP) was developed to provide rapid results and quantify the amount of calcium-containing precipitates formed on the surface of potentially "bioactive" materials. The results presented here show that for a material to be bioactive and have the ability to form a precipitate containing calcium and phosphate ions, levels of calcium ions measured by a complexometric assay should be significantly higher than the level of 5 microg/cm(2). This level of calcium ions was obtained after 20 ASP cycles for the hydroxyl and triethoxysilane end-capped poly(epsilon-caprolactone) samples that did not form precipitates on their surfaces even after >50 ASP cycles. For the two sol-gel silica composites containing approximately 70% hydroxyl and triethoxysilane poly(epsilon-caprolactone), there was no significant difference in the amount of calcium-containing precipitate as observed using the in vitro apatite-forming ability tests suggesting that polymer end-group modification is not detrimental to the apatite-forming ability of such composites.

Apatites↗

PubMed2004

Effect of wollastonite ceramics and bioactive glass on the formation of a bonelike apatite layer on a cobalt base alloy.

A biomimetic method was used to promote a bioactive surface on a cobalt base alloy (ASTM F-75). The metallic substrates were alkali treated and some of the samples were subsequently heat treated. The treated samples were immersed in simulated body fluid (SBF) on granular particles of either bioactive glass or wollastonite. For comparative purposes, no bioactive system was used in some tests. Three different methods were used for the immersion of the samples in SBF: 1) 21 days in SBF, 2) 21 days in 1.5 SBF, and 3) 7 days in SBF followed by 14 days in 1.5 SBF (re-immersion method). A bonelike apatite layer was formed on all the samples placed on wollastonite and bioactive glass particles. The morphology of the apatite layer formed by using the re-immersion method and wollastonite closely resembled the existing bioactive systems. No apatite layer was observed on the samples treated without bioactive material and soaked for 21 days in SBF or 1.5 SBF, apart from the substrates treated by using the re-immersion method. The heat treatment delayed the apatite formation in all the cases studied.

Alloys↗

PubMed2005

Adherent apatite coating on titanium substrate using chemical deposition.

Plasma-sprayed "HA" coatings on commercial orthopedic and dental implants consist of mixtures of calcium phosphate phases, predominantly a crystalline calcium phosphate phase, hydroxyapatite (HA) and an amorphous calcium phosphate (ACP) with varying HA/ACP ratios. Alternatives to the plasma-spray method are being explored because of some of its disadvantages. The purpose of this study was to deposit an adherent apatite coating on titanium substrate using a two-step method. First, titanium substrates were immersed in acidic solution of calcium phosphate resulting in the deposition of a monetite (CaHPO4) coating. Second, the monetite crystals were transformed to apatite by hydrolysis in NaOH solution. Composition and morphology of the initial and final coatings were identified using X-ray diffraction (XRD), Scanning Electron Microscopy, and Energy Dispersive Spectroscopy (EDS). The final coating was porous and the apatite crystals were agglomerated and followed the outline of the large monetite crystals. EDS revealed the presence of calcium and phosphorous elements on the titanium substrate after removing the coating using tensile or scratching tests. The average tensile bond of the coating was 5.2 MPa and cohesion failures were observed more frequently than adhesion failures. The coating adhesion measured using scratch test with a 200-microm-radius stylus was 13.1N. Images from the scratch tracks demonstrated that the coating materials were squashed without fracturing inside and/or at the border of the tracks until the failure point of the coating. In conclusion, this study showed the potential of a chemical deposition method for depositing a coating consisting of either monetite or apatite. This method has the advantage of producing a coating with homogenous composition on even implants of complex geometry or porosity. This method involves low temperatures and, therefore, can allow the incorporation of growth factors or biogenic molecules.

Apatites↗