Synthesis of stabilized hydroxyapatite nanosuspensions for enamel caries remineralization.

BACKGROUND: The aim of this study was to develop and evaluate a method for synthesizing a stable suspension of hydroxyapatite nanoparticles and to test its efficacy for remineralizing carious enamel lesions. METHODS: Hydroxyapatite (HA) particles were synthesized using wet chemistry. Synthesized particles were introduced into a high-pressure homogenizer (5-10 homogenization passes at 15 000 psi) in the presence of different stabilizers. Size and distribution of the resultant particles were determined using dynamic light scattering (DLS). The morphology and composition of the nanoparticles were determined using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Subsequently, artificial lesions were treated with HA nanosuspension plus artificial saliva or a fluoride-containing artificial saliva only. Visual analysis and quantification of the lesion mineral density before and after remineralization were performed using microcomputed tomography. RESULTS: DLS and SEM results confirmed the formation of nonagglomerated HA nanoparticles (20-40 nm) following high-pressure homogenization treatment. Quantitative evaluation of the lesions showed that remineralization of the lesion with hydroxyapatite nanosuspension led to a significantly higher level of mineral gain compared to the control group (P < 0.05). CONCLUSION: High-pressure homogenization is an effective method for facile preparation of a stable suspension of hydroxyapatite nanoparticles. Treatment of artificial lesions with nonagglomerated spherical HA nanoparticles improves the remineralization of enamel lesion.

Antibiotic eluting clay mineral (Laponite®) for wound healing application: an in vitro study.

Different materials in form of sponge, hydrogel and film have been developed and formulated for treating and dressing burn wounds. In this study, the potential of Laponite, a gel forming clay, in combination with an antimicrobial agent (mafenide), as a wound dressing material was tested in vitro. Laponite/mafenide (Lap/Maf) hydrogel was formulated in three different ratios of Lap/Maf 1:1, 1:2, 1:3. Laponite/mafenide/alginate (Lap/Maf/Alg) film was also formulated by combining Lap/Maf gel (1:1) with alginate. Intercalation rate of mafenide into the layers of Laponite nanoparticles and physico-chemical properties, including wound dressing characteristics of materials were studied using various analytical methods. Furthermore, the degradation of materials and the release profile of mafenide were investigated in simulated wound exudates fluid and antibacterial effectiveness of the eluted mafenide was tested on a range of bacterial species. The cytotoxicity of materials was also evaluated in skin fibroblast culture. The results showed that mafenide molecules were intercalated between the nano-sized layers of Laponite. The eluted mafenide showed active antibacterial effects against all three tested bacteria. All intercalated mafenide released from Lap/Maf 1:1 and 1:2 gel formulations and nearly 80% release from 1:3 formulation during test period. No significant difference was observed in release profile of mafenide between Lap/Maf/Alg film and Lap/Maf formulations. Wound dressing tests on Lap/Maf/Alg film showed it is a breathable dressing and has capacity to absorb wound exudates. The study showed that prepared Lap/Maf composite has the potential to be used as an antibiotic eluting gel or film for wound healing application. Additionally, Laponite has shown benefits in wound healing processes by releasing Mg(2+) ions and thereby reducing the cytotoxic effect of mafenide on fibroblast cells.

A mini-review on novel intraperiodontal pocket drug delivery materials for the treatment of periodontal diseases.

Periodontal disease is defined as chronic inflammatory condition characterized by the destruction of the periodontal tissues causing loss of connective tissue attachment, loss of alveolar bone, and the formation of pathological pockets around the diseased teeth. The use of systemic antibiotics has been advocated for its treatment, but concerns emerged with respect to adverse drug reactions and its contribution to bacterial resistance. Thus local drug delivery devices have been developed that aim to deliver a high concentration of antimicrobial drugs directly to the affected site, while minimizing drug's systemic exposure. A burst release of antimicrobial agent from carrier, resulting in a short and inadequate exposure of bacteria residing in periodontal pocket to the agent, remains the main challenge of current local delivery systems for the treatment of periodontal disease. This review aims to investigate and compare different local antimicrobial delivery systems with regard to the treatment of periodontal disease.

BioWeld(®) Tube and surgical glue for experimental sutureless venous microanastomosis.

BACKGROUND: The medial wall of mammalian veins is generally thin and fragile compared with the thick muscle seen in arteries. This makes venous microanastomoses time consuming and challenging. This study aimed to determine the feasibility and effectiveness of using the BioWeld(®) Tube in conjunction with a surgical glue (butyl-2-cyanoacrylate) in performing sutureless venous microanastomoses. METHODS: The feasibility and effectiveness of microvascular anastomoses in a rabbit jugular vein model were investigated in six animals, using the BioWeld(®) Tube in conjunction with butyl-2-cyanoacrylate surgical glue. Patency and tissue repair mechanisms at the anastomotic site were assessed 1 week after the procedure. RESULTS: All anastomoses remained patent at 1 week. Muscle necrosis occurred only in areas where the tissue was subject to the fold-and-bond procedure. CONCLUSION: The study showed the feasibility and short-term effectiveness of the BioWeld(®) Tube in facilitating venous anastomoses.

Development of inhalable formulations of anti-inflammatory drugs to potentially treat smoke inhalation injury in burn victims.

Injury arising from smoke inhalation is a significant mortality risk in severe burned patients. Inflammatory processes are major contributors to the development of respiratory insufficiency owing to pulmonary oedema, formation of airway fibrin clots and hypoxaemia. Anti-inflammatory and anti-coagulant drugs such as heparin and pentoxifylline are currently systemically administered for the treatment of smoke inhalation. Delivery of these drugs in the form of inhalable particles could be an effective manner to achieve rapid targeted action for acceleration of the treatment. The study developed and characterised a series of spray-dried heparin and pentoxifylline dry powder formulations suitable for inhalation administration. Drug particles were co-spray-dried with leucine in varying ratios. Particle size analysis confirmed all powders (except 2%, w/w, pentoxifylline with 1%, w/w, leucine in spray-drying feed solution) had particle size in the optimal range (< or =5 microm) for deep lung drug deposition. Leucine supplementation dramatically altered heparin surface topography while pentoxifylline formulations were a mixture of elongated needles interspersed with wrinkly particles. Addition of leucine improved fine particle fraction of heparin and pentoxifylline. The study indicated manufacture of inhalable heparin and pentoxifylline was feasible and can potentially be an attractive delivery alternative to the more conventional systemic delivery route.

Laser-assisted end-to-end BioWeld anastomosis in an ovine model.

The BioWeld tube, an albumin-based exovascular stent, has been used for microsurgical anastomoses and compared to conventional sutures. The study presented investigated the potential of the BioWeld tube for vascular anastomosis in larger vessels. Laser-assisted BioWeld anastomoses were compared to conventional-sutured anatomoses of the carotid artery of Merino-x ewes. The BioWeld procedure resulted in 100% survival and 100% patency at 1 and 6 week post-operative periods, with no noticeable foreign body response. Sutured animals showed 100% survival and patency. The ischemic time for BioWeld anastomosis averaged 15 minutes compared with 10 minutes for sutures. This study indicates that the BioWeld tube is an easy to use anastomotic technique with equivalent success rates and comparable anastomotic times.

The influence of surface chemistry and topography on the contact guidance of MG63 osteoblast cells.

The purpose of the present study was to determine in vitro the effects of different surface topographies and chemistries of commercially pure titanium (cpTi) and diamond-like carbon (DLC) surfaces on osteoblast growth and attachment. Microgrooves (widths of 2, 4, 8 and 10 microm and a depth of 1.5-2 microm) were patterned onto silicon (Si) substrates using microlithography and reactive ion etching. The Si substrates were subsequently vapor coated with either cpTi or DLC coatings. All surfaces were characterized using atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and contact angle measurements. Using the MG63 Osteoblast-Like cell line, we determined cell viability, adhesion, and morphology on different substrates over a 3 day culture period. The results showed cpTi surfaces to be significantly more hydrophilic than DLC for groove sizes larger than 2 microm. Cell contact guidance was observed for all grooved samples in comparison to the unpatterned controls. The cell viability tests indicated a significantly greater cell number for 8 and 10 microm grooves on cpTi surfaces compared to other groove sizes. The cell adhesion study showed that the smaller groove sizes, as well as the unpatterned control groups, displayed better cell adhesion to the substrate.

Calcium phosphate fibres synthesized from a simulated body fluid.

The biomimetic coating method was used for fabricating calcium phosphate fibres for biomedical applications such as bone defect fillers. Natural cotton substrate was pre-treated with phosphorylation and a Ca(OH)2 saturated solution. The pre-treated samples were then soaked in simulated body fluid (SBF) of two different concentrations, 1.5 times and 5.0 times the ion concentration of blood plasma. The cotton was then burnt out via sintering of the ceramic coating at 950 degrees C, 1050 degrees C, 1150 degrees C, and 1250 degrees C. The results demonstrated that osteoblastic cells were able to cover the entire surface cotton fibres, and the cell coverage appeared to be independent of surface roughness and Ca/P ratio of fibres.

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.

Preparation of different forms of titanium oxide on titanium surface: effects on apatite deposition.

Methods of preparing different types of titanium oxide (TiO(2)) and their effects on apatite deposition and adhesion on titanium surfaces were investigated. Forty-eight commercially pure titanium (Ti) discs were divided into four groups (12 per group) and each group was subjected to the following treatments: Group 1, heat treatment at 750 degrees C; Group 2, oxidation in H(2)O(2) solution followed by heat treatment; Group 3, dipping in rutile/gelatin slurry; and Group 4, dipping in anatase/gelatin slurry. Surface-treated Ti discs were immersed in a supersaturated calcium phosphate solution to allow apatite deposition. Results showed that the percentage of area covered by deposited apatite was highest in Group 4 compared to the other groups. Apatite deposited on Ti discs pretreated in H(2)O(2) solution (Group 2) demonstrated the highest adhesion to the titanium substrate. Results from this study indicated that surface treatment method affects the type of TiO(2) layer formed (anatase or rutile) and affects apatite deposition and adhesion on the Ti surface.

Mechanical properties and microstructure of hypomineralised enamel of permanent teeth.

Isolated enamel defects are commonly seen in first permanent molar teeth but there has been little work on the physical and morphological composition of affected molars. The aim of this study was to determine the mechanical and morphological properties of hypomineralised first permanent molar teeth, utilising the Ultra-Micro-Indentation System (UMIS) and scanning electron microscope, respectively. Further investigations using Energy Dispersive X-ray Spectrometery (EDS), Back Scatter Electron (BSE) Imaging, and X-ray diffraction were employed to attempt to determine the chemical composition, mineral content and crystalline structure of the hypomineralised tissue, respectively, of eight first permanent molars with severe enamel hypomineralisation. The hardness and modulus of elasticity were found to be statistically significantly lower (0.53+/-0.31 and 14.49+/-7.56 GPa, respectively) than normal enamel (3.66+/-0.75 and 75.57+/-9.98 GPa, respectively). Although the fractured surface of the hypomineralised enamel was significantly more disorganised and the relative mineral content was reduced by approximately 5% in comparison to sound enamel, the mineral phase and Ca/P ratio was similar in hypomineralised and sound enamel. The dramatic reduction in the mechanical properties of first permanent molar teeth has ramifications when clinicians are choosing restorative materials to restore the defects. The reason for the dramatic reduction in mechanical properties of hypomineralised first permanent molar teeth is at present unknown.

Biphasic calcium phosphate bioceramics: preparation, properties and applications.

Biphasic calcium phosphate (BCP) bioceramics belong to a group of bone substitute biomaterials that consist of an intimate mixture of hydroxyapatite (HA), Ca(10)(PO(4))(6)(OH)(2), and beta-tricalcium phosphate (beta-TCP), Ca(3)(PO(4))(2), of varying HA/beta-TCP ratios. BCP is obtained when a synthetic or biologic calcium-deficient apatite is sintered at temperatures at and above 700 degrees C. Calcium deficiency depends on the method of preparation (precipitation, hydrolysis or mechanical mixture) including reaction pH and temperature. The HA/beta-TCP ratio is determined by the calcium deficiency of the unsintered apatite (the higher the deficiency, the lower the ratio) and the sintering temperature. Properties of BCP bioceramics relating to their medical applications include: macroporosity, microporosity, compressive strength, bioreactivity (associated with formation of carbonate hydroxyapatite on ceramic surfaces in vitro and in vivo), dissolution, and osteoconductivity. Due to the preferential dissolution of the beta-TCP component, the bioreactivity is inversely proportional to the HA/beta-TCP ratio. Hence, the bioreactivity of BCP bioceramics can be controlled by manipulating the composition (HA/beta-TCP ratio) and/or the crystallinity of the BCP. Currently, BCP bioceramics is recommended for use as an alternative or additive to autogeneous bone for orthopedic and dental applications. It is available in the form of particulates, blocks, customized designs for specific applications and as an injectible biomaterial in a polymer carrier. BCP ceramic can be used also as grit-blasting abrasive for grit-blasting to modify implant substrate surfaces. Exploratory studies demonstrate the potential uses of BCP ceramic as scaffold for tissue engineering, drug delivery system and carrier of growth factors.

Ultrastructural properties of bone mineral of control and tiludronate-treated osteoporotic rat.

Bisphosphonates have been widely used in the treatment of human bone pathologies including osteoporosis. In this case, bisphosphonates have been shown to reduce bone resorption, thereby increasing the mass and mechanical resistance of bone. Determining the effects of these molecules on the properties of the bone apatite crystals could provide a better insight into the mechanism of bisphosphonate/bone interaction. The aim of this study was to determine the ultrastructural effects of a third generation bisphosphonate (tiludronate) on the morphology, size, distribution, chemical composition, and structure of apatite crystals in bone (trabecular) in a rat osteoporotic model. Four groups of rats were studied: (1) sham operated, (2) untreated ovariectomized (OVX), (3) OVX rats which received 35 mg/kg of tiludronate, (4) OVX rats which received 160 mg/kg of tiludronate. The rats of groups 3 and 4 received tiludronate orally in 2 consecutive days every week for 1 year. Scanning electron microscopy (SEM), high and low resolution transmission electron microscopy (TEM), and electron microprobe analysis (EDX) were used for the ultrastructural characterization of the bone mineral. This study demonstrated that tiludronate slightly increased the width of bone apatite crystals without changing any other crystal characteristics.

Inhibition of apatite formation by vitronectin.

This study investigated the concentration-dependent effect of vitronectin (VN), a glycoprotein of the bone matrix, on apatite formation and growth. Precipitation trials in metastable solution and in a pH-controlled solution system showed an inhibition of apatite microcrystal formation by VN. In the presence of biphasic calcium-phosphate ceramic, transmission electron microscopy showed a reduction of precipitated microcrystal size: precipitates were significantly smaller than in ionic simulated body fluid without proteins or in the presence of type I collagen as a negative control. Moreover, the size of the precipitated microcrystals was reduced in a dose-dependent manner. Two indirect methods showed that calcium-phosphate precipitation was inhibited by VN. It would appear that VN prevents apatite formation by inhibiting the growth of apatite crystals rather than by secondary nucleation, as in the case of osteopontin, a bone-specific protein.

Characterization of the trabecular rat bone mineral: effect of ovariectomy and bisphosphonate treatment.

Bisphosphonates, potent inhibitors of bone resorption, have been used clinically to correct the continued loss of bone mass in osteoporosis and in other conditions. However, there has been some concern that long-term treatment with these compounds, as well as more recently developed drugs, may also decrease the rate of bone formation. Bisphosphonates, which are strongly bound to hydroxyapatite crystals, may alter the structure and reactivity of the crystals, interfere with new crystal nucleation and growth, as well as alter the short-range order of newly formed crystals. We have investigated the chemistry and structure of the solid calcium-phosphate mineral phase of lumbar vertebrae of ovariectomized, 6.5-month-old rats treated with bisphosphonates for 1 year after onset of osteopenia. Appropriate control groups were used for comparison. The techniques used to assess the mineral phase were chemical analyses, Fourier transform-infrared (FT-IR) and FT-Raman spectroscopy, FT-IR microspectroscopy, and phosphorus-31 magic-angle-sample spinning nuclear magnetic resonance spectroscopy ((31)P MAS NMR). The (31)P MAS NMR spectra of trabecular bone of lumbar vertebrae of control, ovariectomized, and treated animals were similar. However, there were several significant differences in the results obtained by FT-IR spectroscopy of the whole tissue samples, FT-IR microspectroscopy of sections of bone, and chemical analyses. For example, whereas chemical analyses demonstrated that the CO(3) content of the mineral phase of the ovariectomized animals was decreased compared with controls, FT-IR microspectroscopy of bone sections showed no changes in the relative CO(3) content, but some changes in the environment of the CO(3) groups. However, chemical analyses of the crystals, combined with data from all three spectroscopic methods and with data from serum analysis, did indicate small changes in the mineral phase after ovariectomy, corrected after treatment with bisphosphonates. In any event, the chemical and structural data in the present studies demonstrate that the bisphosphonate, tiludronate, does not significantly alter the mineral components of bone after 1 year of treatment during the course of which bone loss was reversed.

Crystal polymer interaction with new injectable bone substitute; SEM and Hr TEM study.

A composite constituted of calcium phosphate (CaP) granules and a hydrophilic polymer as a carrier (hydroxy-propyl-methyl cellulose, HPMC) was developed to be an injectable bone substitute (IBS, CNRS patent). IBS is a composite and not an ionic cement. The composite obtained is ready to use and sterile. Chemical interactions between organic and inorganic components appeared during the association of the two. The interactions of the CaP and the polymer have been studied using scanning electron microscopy (SEM), electron microprobe (EDX), and high-resolution transmission electron microscopy (HrTEM) SEM revealed a degradation of the granules into smaller particles while EDX was unable to show significant changes in the Ca/P ratio during aging of the composite. With Hr TEM, however, we observed hydrolysis (process of dissolution and precipitation) from the surface to about 13 nm into the HA crystals and occasional dissolution with precipitation of beta-TCP crystals. In HA, the first zone of interaction consisted of a single layer of small globular crystals of 2 to 3 nm in diameter. Numerous lattice patterns in all three axes could be observed. Under the globular crystals zone, the inter-reticular distances of the single crystals appeared enlarged by 1.2% (from 0.817 to 0.827 nm). The enlargement seems to correspond to diffusion of HPO(4) into the crystal lattice. In beta-TCP crystals, dissolution was observed to be several nanometers deep, but globular surface precipitation rarely was observed. With time or after steam sterilization, no changes were observed. These data demonstrate the strong interactions of the hydrophylic polymer with calcium phosphate, but only in the first several nanometers of thickness.

Ultrastructural properties of laser-irradiated and heat-treated dentin.

Previous studies using scanning electron microscopy and infrared absorption spectroscopy reported that laser irradiation causes compositional changes in enamel. The purpose of this study was to evaluate the ultrastructural and compositional changes in dentin caused by irradiation with a short-pulse laser (Q-switched Nd:YAG). The irradiated and non-irradiated areas of the lased dentin samples were investigated by scanning (SEM) and transmission electron microscopy (TEM), micro-micro electron diffraction, and electron microprobe analysis of dispersive energy (EDX). Heat-treated dentin was similarly investigated. This study demonstrated that laser irradiation resulted in the recrystallization of dentin apatite and in the formation of additional calcium phosphate phases consisting of magnesium-substituted beta-tricalcium phosphate, beta-TCMP, beta-(Ca,Mg)3(PO4)2, and tetracalcium phosphate, TetCP, Ca4(PO4)O. TEM analyses of the modified and unmodified zones of the irradiated areas showed two types of crystal populations: much larger crystals from the modified zone and crystals with size and morphology similar to those of dentin apatite in the unmodified zone. The morphology of crystals in the modified zones in the irradiated dentin resembled those of dentin sintered at 800 or 950 degrees C. In the irradiated areas (modified and unmodified zones), the Ca/P ratio was lower compared with that in the non-irradiated dentin. The Mg/Ca ratio in the modified zones was higher than that in the unmodified zones and in the non-irradiated dentin. In sintered dentin, the Mg/Ca ratio increased as a function of sintering temperature. The ultrastructural and compositional changes observed in laser-irradiated dentin may be attributed to high temperature and high pressure induced by microplasma during laser irradiation. These changes may alter the solubility of the irradiated dentin, making it less susceptible to acid dissolution or to the caries process.

Zinc effect on the in vitro formation of calcium phosphates: relevance to clinical inhibition of calculus formation.

PURPOSE: To determine the effect of zinc on the in vitro formation of calcium phosphates and its relevance to calculus inhibition. MATERIALS AND METHODS: Different types of calcium phosphate phases (amorphous calcium phosphate, ACP; dicalcium phosphate dihydrate, DCPD; octacalcium phosphate, OCP; and carbonate hydoxyapatite, CHA) were precipitated from solutions containing increasing concentrations of zinc (Zn) ions. The precipitates were characterized using x-ray diffraction, infrared absorption spectroscopy, and scanning electron microscopy. RESULTS: The presence of Zn ions affected the type and amount of calcium phosphate phases formed. Zn, even at concentrations as low as 0.1 mM/L, inhibited the crystal growth of DCPD, OCP and AP; and, at higher concentrations (0.5 mM to 2 mM/L), promoted the formation of amorphous calcium phosphate, ACP, or Zn-substituted tricalcium phosphate (beta-TCP) depending on the reaction pH and temperature.

Osteogenic potential in vitro of human bone marrow cells cultured on macroporous biphasic calcium phosphate ceramic.

Calcium phosphate ceramics are synthetic bone substitutes that promote bone formation by osteoconduction. However, they have shown an osteogenic potential in vivo in animal models when associated with bone marrow cells. In order to develop an osteogenic human "hybrid material," we studied the in vitro osteogenic potential of human bone marrow cells cultured on macroporous biphasic calcium phosphate (BCP) pellets in the presence of dexamethasone with or without 1alpha,25 dihydroxyvitamin D3. We were examining, in particular, their mesenchymal stem cell proliferation and hematopoietic potential. Osteogenic differentiation was evaluated in terms of alkaline phosphatase activity and immunological characterization of the extracellular matrix formed by these cells. The specimens were observed by scanning and transmission electron microscopy. Human mesenchymal stem cells proliferated on macroporous BCP ceramic, with a doubling time delayed at the beginning of the culture as compared to the cultures realized on plastic. These cells maintained a hematopoietic activity identical to that of cultures performed in plastic wells. The proliferating mesenchymal stem cells expressed an osteoblastic phenotype, as shown by alkaline phosphatase activity and the synthesis in ceramic macropores of an extracellular matrix composed of fibronectin, osteocalcin, and collagen I (but not collagen III). In addition, numerous microcrystals of apatite precipitated on the extracellular matrix, producing a mineralized fibrillar network within the ceramic not observed with cell cultures realized on plastic. These results demonstrate that human mesenchymal stem cells cultured on macroporous BCP ceramic express and conserve their osteoblastic phenotype even after one month of culture and that these osteogenic cells are able to form new bone matrix in a BCP ceramic in vitro.

Electron microscopy study of intrahepatic ultrasmall superparamagnetic iron oxide kinetics in the rat. Relation with magnetic resonance imaging.

Ultrasmall superparamagnetic iron oxide (USPIO) contrast agents for use in magnetic resonance imaging (MRI) are currently undergoing clinical evaluation. However, the images observed and the kinetic profiles obtained differ from one agent to another. In this study, BD IX rats received an intravenous penis injection of the USPIO contrast agents AMI-HS and AMI-227. A cytologic study of the liver was performed, and the data obtained were compared with those of MRI. Images acquired in light microscopy, transmission electron microscopy, microanalysis and electron diffraction provided data on the cell categories involved in the processing of these contrast agents, the importance and modalities of each category relative to this processing, and the modalities of agent elimination. AMI-HS was rapidly removed from the bloodstream by Kupffer's cells and hepatocytes and then eliminated through bile ducts. AMI-227 remained much longer in the blood compartment since it was processed very slowly by endothelial and Kuppfer's cells in the near absence of hepatocytic participation and thus of elimination by the bile ducts. These results allowed us to base our interpretation of MRI sequences on cytologic observations.