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At least 397 records · Page 22Linked to original sources
PubMed2000

Behavior of human osteoblastic cells on stoichiometric hydroxyapatite and type A carbonate apatite: role of surface energy.

To determine the role of physicochemical characteristics of the surface of dense ceramics on osteoconduction, we studied the proliferation and differentiation of human trabecular (HT) osteoblastic cells, extracellular collagenous matrix production, and biologic apatite formation on stoichiometric hydroxyapatite (HA) and type A carbonate apatite (CA). The surface physicochemical characteristics (composition, roughness) of HA and CA carefully were determined by Fourier-transformed infrared, X-ray photoelectron, and Raman spectroscopies, and by FTIR microscopy, before and after cell culture. On both HA and CA substrates, HT cells attached, proliferated, and differentiated. Cell proliferation did not differ on HA and CA. However, the initial cell attachment and spreading of HT cells were much lower on CA compared to HA. Physicochemical and biologic analyses showed that collagenous synthesis by HT cells after 6 weeks of culture also was lower on CA than on HA. Quantitative histologic analysis confirmed that the collagenous matrix production was lower on CA than on HA. Measurement of wettability showed that the polar interaction energy with water was significantly lower on CA than on HA. The lower cell attachment and collagen production on CA compared to HA clearly were related to the low affinity of HT cells for the CA surface. This study shows that the surface energy of the biomaterial greatly influences the initial cell attachment and spreading of human osteoblastic cells at the surface and affects collagenous matrix deposition on the biomaterial. This suggests that the enhancement of polar components of the surface of dense biomaterials may improve osteoblastic cell attachment and, thereby, osteoconduction.

Apatites↗
PubMed2005

A bio-recognition device developed onto nano-crystals of carbonate apatite for cell-targeted gene delivery.

The DNA delivery to mammalian cells is an essential tool for analyzing gene structure, regulation, and function. The approach holds great promise for the further development of gene therapy techniques and DNA vaccination strategies to treat and control diseases. Here, we report on the establishment of a cell-specific gene delivery and expression system by physical adsorption of a cell-recognition molecule on the nano-crystal surface of carbonate apatite. As a model, DNA/nano-particles were successfully coated with asialofetuin to facilitate uptake by hepatocyte-derived cell lines through the asialoglycoprotein receptor (ASGPr) and albumin to prevent non-specific interactions of the particles with cell-surface. The resulting composite particles with dual surface properties could accelerate DNA uptake and enhance expression to a notable extent. Nano-particles coated with transferrin in the same manner dramatically enhanced transgene expression in the corresponding receptor-bearing cells and thus our newly developed strategy represents a universal phenomenon for anchoring a bio-recognition macromolecule on the apatite crystal surface for targeted gene delivery, having immediate applications in basic research laboratories and great promise for gene therapy.

Animals↗
PubMed2002

Synthesis of functionally graded MgCO3 apatite accelerating osteoblast adhesion.

As a means of improving the biological properties of materials for use as bone substitutes, functionally graded carbonate apatite containing Mg, FGMgCO3Ap, was synthesized at 60 degrees C and pH 7.4 using a gradient magnesium supply system. X-ray diffraction analysis of FGMgCO3Ap showed a poorly crystallized apatitic pattern, similar to that of human bone. ESCA analysis clearly showed the negative gradient distribution in Mg1s intensity (atomic concentration) of magnesium from the crystal surface toward the inner core. When the FGMgCO3Ap crystals were mixed with collagen, the resulting FGMgCO3Ap-collagen composite, irradiated with UV light for 4 h, retained their features in the saline solution. After washing away the nonadhesive cells, a cell adhesion assay showed that the optical density of the FGMgCO3Ap-collagen composite was higher than that of the CO3Ap-collagen composite. SEM observation showed that the osteoblast-like cells adhered well to the surface of the FGMgCO3Ap-collagen composite. Staining with hematoxylin-eosin and alizarin red confirmed the existence of a great many more cells and a thicker extracellular matrix layer on the FGMgCO3Ap-collagen composite than on the CO3Ap-collagen composite. This result demonstrated the acceleration effect of magnesium ions on osteoblast adhesion on the FGMgCO3Ap-collagen composite.

Animals↗
PubMed1995

Pyrolysis-gas chromatography of carbonate apatites used for sintering.

Gas chromatography was employed to quasi-continuously determine the amount of carbon dioxide that evolved from carbonate apatite specimens during sintering. Assuming that the carbonate in the specimens decomposed to carbon dioxide on a mole-for-mole basis, the determination of the carbon dioxide evolved allowed for the determination of the amount of carbonate that remained in the specimens during different stages of sintering. Previously, this measurement could be carried out only after sintering was completed. Comparison of data obtained from specimens compacted isostatically at 600 MPa for sintering with powder specimens indicated that the amount of carbonate remaining in the sintered apatite mass strongly depended on heating rates, heating temperatures, and holding-time intervals.

Apatites↗
PubMed2003

In vitro and in vivo degradation of biomimetic octacalcium phosphate and carbonate apatite coatings on titanium implants.

Calcium phosphate (Ca-P) coatings have been applied onto titanium alloys prosthesis to combine the srength of metals with the bioactivity of Ca-P. It has been clearly shown in many publications that Ca-P coating accelerates bone formation around the implant. However, longevity of the Ca-P coating for an optimal bone apposition onto the prosthesis remains controversial. Biomimetic bone-like carbonate apatite (BCA) and Octacalcium Phosphate (OCP) coatings were deposited on Ti6Al4V samples to evaluate their in vitro and in vivo dissolution properties. The coated plates were soaked in alpha-MEM for 1, 2, and 4 weeks, and they were analyzed by Back Scattering Electron Microscopy (BSEM) and by Fourier Transform Infra Red spectroscopy (FTIR). Identical coated plates were implanted subcutaneously in Wistar rats for similar periods. BSEM, FTIR, and histomorphometry were performed on the explants. In vitro and in vivo, a carbonate apatite (CA) formed onto OCP and BCA coatings via a dissolution-precipitation process. In vitro, both coatings dissolved overtime, whereas in vivo BCA calcified and OCP partially dissolved after 1 week. Thereafter, OCP remained stable. This different in vivo behavior can be attributed to (1) different organic compounds that might prevent or enhance Ca-P dissolution, (2) a greater reactivity of OCP due to its large open structure, or (3) different thermodynamic stability between OCP and BCA phases. These structural and compositional differences promote either the progressive loss or calcification of the Ca-P coating and might lead to different osseointegration of coated implants.

Alloys↗
PubMed2003

Calcium and phosphate adsorption as initial steps of apatite nucleation on sol-gel-prepared titania surface.

Titania powders have been prepared by the sol-gel route from Ti (IV) ethoxide under acidic conditions. Adsorption experiments of calcium and phosphate ions on gel-derived titania suspensions were performed to suggest a likely initial step of apatite growth on its surface. Experiments were performed as a function of time and pH at 37 degrees C with and without NaCl present in the suspensions. Also, zeta (zeta) potential experiments were performed to determine the kind of calcium adsorption. Results suggest that, apparently, calcium and phosphate adsorption can act as two different initial steps for apatite growth.

Adsorption↗
PubMed2003

Calcium-deficient apatite: a first in vivo study concerning bone ingrowth.

Biphasic calcium phosphate (BCP) materials are increasingly used to restore bone loss in surgery. Calcium-deficient apatites (CDA), the precursors of BCP, are closer in structure to biological apatites and can be associated with therapeutic agents to form drug-delivery systems. The purpose of this first in vivo study of CDA was to evaluate the osteoconductive properties of two composites, consisting of 40-80 microm granules carried by a cellulose-derived polymer, used to fill critical size bone defects in rabbit femoral ends. Animals were sacrificed 2 or 3 weeks after implantation. Histomorphometric analysis of scanning electron microscopy implant surface files was performed using gray level threshold that distinguish between bone or materials (white) and noncalcified tissue (black). Quantitative results for new bone formation showed no significant differences between the composites or the implantation periods. However, nearly all of the CDA disappeared early while supporting more extensive bone colonization than biphasic calcium phosphates implanted in the same conditions.

Animals↗
PubMed2004

In vivo evaluation of a biomimetic apatite coating grown on titanium surfaces.

Osteoconductive mineral coatings represent an established technology for enhancing the integration of orthopedic implants with living bone. However, current coatings have limitations related to fabrication methods, attachment strength to metal substrates, and in vivo performance. Low temperature biomimetic growth is a coating technique wherein the device to be coated is immersed in a meta-stable saturated solution of the coating constituents and growth of the coating is then allowed to proceed on the surface of the device. This study focused on the in vivo evaluation of a biomimetic apatite coating fabricated under these conditions. The experiment was designed to specifically test the amount of bone ingrowth into the coated channels versus the uncoated channels of an established bone chamber system, with emphasis placed on the amount of bone present on the coupon surface. Three types of measurements were taken on each channel: linear ingrowth %, area ingrowth %, and continuous bone apposition %. The experiments demonstrated that under controlled conditions, the apatite coating appears to resorb in 8 weeks and did stimulate early osseointegration with the metal surface with a reduction in fibrous tissue encapsulation. This coating may, therefore, be useful in facilitating early bone ingrowth into porous surfaces without the potential for coating debris, macrophage infiltration, fibrous tissue encapsulation, and eventual coating failure as may occur with current plasma-sprayed hydroxapatite coating techniques.

Animals↗
PubMed2004

Apatite formation in the reaction-setting mixture of Ca(OH)2--KH2PO4 system.

Development of a new calcium phosphate cement (CPC) system as an alternative to that commonly used, basically consisting of tetracalcium phosphate and dicalcium phosphate self-setting mixtures, could be of interest in achieving special properties of the product. Powder mixtures of Ca(OH)(2) and KH(2)PO(4) were studied to assess their potential for the precipitation of apatite-like phase with the use of potassium phosphate salt solution as the cement liquid. X-ray diffraction and infrared (IR) spectroscopy studies and pH and setting time measurements were performed. The set cement was revealed to consist of a low crystalline carbonate-substituted apatite-like phase. The setting time of the cement was about 5 min. Its dissolution in distilled water led to an increase in solution pH to about 11.5, the pH slowly decreasing to 10.2 at day 10. The results showed the cement to be of an increased carbonate substitution ability compared to the tetracalcium phosphate-dicalcium phosphate anhydrous cement.

Apatites↗
PubMed2005

Evaluation of calcium titanate as apatite growth promoter.

Calcium titanate (CaTiO(3), perovskite) has been used to determine its apatite nucleation ability and propose a possible nucleation initial step. Measurements of calcium leaching from the calcium titanate surface and phosphate adsorption experiments were carried out separately by using commercial calcium titanate suspensions at room temperature. Adsorption behaviour determined by zeta potential measurements shows that phosphate is strongly adsorbed on the calcium titanate surface. It was found that the higher the pH, the higher the Ca present on the calcium titanate surface, but phosphate adsorption followed this trend only up to pH 7.4. Results suggest that phosphate ions are not adsorbed only on Ca sites but also on TiO(2) groups sites of the surface, formed after calcium leaching from the surface. When both ions are simultaneously added in a modified simulated body fluid containing calcium titanate, at 37 degrees C, apatite growth occurs on its surface after 1 week of immersion.

Adsorption↗
PubMed2004

FTIR study of carbonate loss from carbonated apatites in the wide temperature range.

The mineral constituent of bone tissue is a carbonate-substituted apatite (CHA). The thermal stability of the CHA has been revealed to depend on the substitution type and degree, although relatively little is known about this behavior. The aim of this study was to investigate the carbonate loss from synthetic CHAs in equilibrium conditions in a wide temperature range. An approach based on FTIR spectroscopy of condensed gas phase was applied to evaluate the CO and CO2 release with increasing temperature. Four different CHAs were studied, which were prepared by either precipitation from solution or the solid-state interaction. The samples differ from each other by the substitution degree. In one of the samples calcium was partially substituted by magnesium. Decomposition was shown to start at surprisingly low temperature, about 400 degrees C, and the CO content increases monotonously with the increase of temperature. The CO2 content goes through a maximum due to its decomposition into carbon monoxide and oxygen, the temperature of this maximum being strongly dependent on the chemical synthesis route. Therefore, control of the sintering atmosphere with respect to the CO2/CO ratio is needed when preparing the carbonated apatite bioceramics.

Apatites↗
PubMed1994

Proton-induced physicochemical calcium release from ceramic apatite disks.

When bone is cultured in acid medium there is net calcium efflux (JCa) and proton influx (JH) relative to the mineral. The acid medium appears to induce physicochemical mineral dissolution as well as cell-mediated bone resorption. To determine the independent effect of acid medium on physicochemical dissolution, we utilized cell-free synthetic ceramic apatite (CAP) disks, which contain carbonate (5.5%) in an apatite structure chemically similar to mammalian bone. CAP disks were cultured in control (Ctl, pH approximately equal to 7.44) or acid (Met, pH approximately equal to 7.11) medium for 48 h and compared to similarly treated neonatal (4-6 days old) mouse calvariae. Medium was changed and analyzed at 3, 24, and 48 h. At 3, 24, and 48 h there was significantly greater JCa from the CAP disks and calvariae incubated in Met compared to Ctl; over the entire 48 h time period there was a greater progressive increase in JCa from the CAP disks than the calvariae incubated in Met. There was no significant JCa at 3, 24, or 48 h from CAP disks or calvariae incubated in Ctl. At 3 h there was significantly greater JH into the CAP disks and calvariae incubated in Met compared to Ctl; JH was greater into the CAP disks than the calvariae. Utilizing a synthetic model of bone mineral we demonstrated that acid medium induces physicochemical calcium efflux and proton influx relative to the mineral.

Animals↗
PubMed1993

Influence of disodium (1-hydroxythylidene) diphosphonate on bonding between glass-ceramics containing apatite and wollastonite and mature male rabbit bone.

It has been reported that bioactive glass-ceramics containing crystalline oxy- and fluoroapatite [Ca10(PO4)6(O,F2) and wollastonite (CaSiO3), chemical composition: MgO 4.6, CaO 44.9, SiO2 34.2, P2O5 16.3, CaF2 0.5 in weight ratio] bond to bone tissue through the formation of an apatite (a calcium and phosphorus-rich layer) on the ceramic surface. In this study, the influence of disodium (1-hydroxythylidene) diphosphonate (DHTD) on the bonding between bone and glass-ceramics containing apatite and wollastonite was investigated. Rectangular ceramic plates (15 mm x 10 mm x 2 mm, abraded with #2000 alumina powder) were implanted into the tibial bone of mature male rabbits. DHTD was administered daily by subcutaneous injection to groups 1-5: group 1-4 at doses of 20, 5.0, 1.0, and 0.1 mg/kg body wt/day for 8 weeks; and group 5 at a dose of 5 mg/kg body wt/day for 4 weeks. Group 6 was given injections of saline as a control. At 8 weeks after implantation, the rabbits were killed. The tibiae containing the ceramics were dissected out and used for a detachment test. The failure load, when an implant became detached from the bone, or when the bone itself broke, was measured. The failure loads for groups 1-6 were 0 kg, 0 kg, 8.08 +/- 2.43 kg, 7.28 +/- 2.07 kg, 5.56 +/- 1.63 kg, and 6.38 +/- 1.30 kg, respectively. Ceramic bonding to bone tissue was inhibited by a higher dose of DHTD (groups 1 and 2).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Experimental animal investigation of bone regeneration with collagen-apatite.

Multicentric osteoregeneration is a new principle of osteoinduction [31a] which can be realized with the combination of collagen and fine dispersed hydroxyapatite ceramic particles (Collapat). This was histomorphometrically proved in the present study involving 14 rabbits with 28 6-mm-wide bore holes in the distal femoral condyles. With Collapat, an average of 5 times more new bone was regenerated than in the control defects without implant. The Wilcoxon matched-pairs signed-ranks test proved the positive effect of the implant Collapat on osteoregeneration with a significance of P less than 0.0001. At sites of Collapat insertion bone regeneration begins in the 2nd week, reaches its climax in the 3rd week, and is completed after the 4th week. in the course of development the histological picture is typified by a lively bone remodeling. Bone formation can be recognized in direct contact to the apatite granules. Foreign body or allergic reactions are not observed. Remodeling of the bone is not hindered by the slowly resorbable apatite granules. About 250 human implantations have been performed in our hospital since 1979, with good results and no negative effects.

Animals↗
PubMed1983

Synthetic apatites containing Na, Mg, and CO3 and their comparison with tooth enamel mineral.

Apatites containing Na, Mg, and CO3 in amounts occurring in tooth enamel mineral were synthesized by precipitation from aqueous solutions. The X-ray diffraction patterns showed only apatitic reflections, which were somewhat broader than those of enamel. X-ray Guinier photographs resulted in diffuse reflections from which the lattice parameters could not be determined. The infrared (IR) absorption spectrum of the synthetic samples was practically identical with that of tooth enamel. However, after heating the samples for 1/2 h at a temperature between 300 and 600 degrees C, no absorption peak was found at 2340 cm-1 as in the IR spectrum of tooth enamel after heating.

Apatites↗
PubMed1980

Is there a "citrate-apatite" in biological calcified systems?

An apatite containing citrate ions has been synthesized. Measurements of specific surface, as well as Ca/P ratio, infrared, X-ray, and calcination data are all consistent with the idea that citrate ion substitutes for PO4(3-) ion on the apatitic surface.

Apatites↗
PubMed1987

Transmission electron microscopy of lattice planes in human alveolar bone apatite crystals.

Periodic fringes corresponding to six different lattice planes have been observed in apatite crystals of human normal alveolar bone by transmission electron microscopy. Three of these sets of fringes have spacings less than 3.5 A corresponding to the Scherzer resolution of the microscope used. The (0002) lattice plane of hydroxyapatite of 3.4 A d-spacings, the (2111) lattice plane with a d-spacing of 2.81 A, and the (3030) lattice plane with a d-spacing of 2.72 A have been identified. The (0002) and (2121) lattice planes have been observed for the first time in bone microcrystals. Some of the crystals studied were characterized by a mean width/thickness ratio of 6.91, typical of platelike habit, whereas observations of crystals aligned along the (1210) and (1211) directions showed a needlelike habit. The mean length of the bone apatite crystals was 470 A. A dark line similar to the one observed in enamel and dentine crystals was also seen. The bone microcrystals observed have shown a high sensitivity to beam damage.

Adolescent↗