Bone structure: from angstroms to microns. (33/221)

Bone has a complex hierarchical structure, which despite much investigation, is still not well understood. Here we bring together pieces of this complicated puzzle, albeit from different sources, to present a tentative overview of bone structure. The basic building blocks are the extremely small plate-shaped crystals of carbonate apatite, just hundreds of angstroms long and wide and some 20-30 A thick. They are arranged in parallel layers within the collagenous framework. At the next hierarchical level these mineral-filled collagen fibrils are ordered into arrays in which the fibril axes and the crystal layers are all organized into a 3-dimensional structure that makes up a single layer or lamella of bone a few microns thick. The orientations of the collagen fibrils and the crystal layers in alternating lamellae of rat bone differ such that in the thinner lamellae, the fibrils and the crystal layers are parallel to the lamellar boundaries. In the thicker lamellae the fibrils are parallel to the boundary, but the crystal layers are rotated out of the plane of the boundary. In many bones these alternating lamellae are organized into even larger ordered structures to produce what is truly a remarkably ordered material, all the way from the molecular scale to the macroscopic product.  (+info)

Preparation and properties of nano-sized calcium fluoride for dental applications. (34/221)

OBJECTIVES: The aim of the present study was to prepare nano-sized calcium fluoride (CaF(2)) that could be used as a labile F reservoir for more effective F regimens and as an agent for use in the reduction of dentin permeability. METHODS: Nano-sized CaF(2) powders were prepared using a spray-drying system with a two-liquid nozzle. The properties of the nano-CaF(2) were studied and the effectiveness of a fluoride (F) rinse with nano-CaF(2) as the F source was evaluated. The thermodynamic solubility product of the nano-CaF(2) solution was determined by equilibrating the nanosample in solutions presaturated with respect to macro-CaF(2). Reactivity of the nano-CaF(2) was assessed by its reaction with dicalcium phosphate dehydrate (DCPD). F deposition by 13.2 mmol/L F rinse with the nano-CaF(2) as the F source was determined using a previously published in vitro model. RESULTS: X-ray diffraction (XRD) analysis showed pattern of low crystalline CaF(2). BET measurements showed that the nano-CaF(2) had a surface area of 46.3m(2)/g, corresponding to a particle size of 41nm. Transmission electron microscopy (TEM) examinations indicated that the nano-CaF(2) contained clusters comprising particles of (10-15) nm in size. The nano-CaF(2) displayed much higher solubility and reactivity than its macro-counterpart. The CaF(2) ion activity product (IAP) of the solution in equilibrium with the nano-CaF(2) was (1.52+/-0.05)x10(-10), which was nearly four times greater than the K(sp) (3.9 x 10(-11)) for CaF(2). The reaction of DCPD with nano-CaF(2) resulted in more F-containing apatitic materials compared to the reaction with macro-CaF(2). The F deposition by the nano-CaF(2) rinse was (2.2+/-0.3)mug/cm(2) (n=5), which was significantly (p<0.001) greater than that ((0.31+/-0.06)mug/cm(2)) produced by the NaF solution. SIGNIFICANCE: The nano-CaF(2) can be used as an effective anticaries agent in increasing the labile F concentration in oral fluid and thus enhance the tooth remineralization. It can also be very useful in the treatment for the reduction of dentin permeability.  (+info)

Extraosseous calcification. Evidence for abnormal pyrophosphate metabolism in uremia. (35/221)

The inorganic constituents and crystalline features of extraosseous calcium-phosphate deposits obtained from dialyzed uremic and hypercalcemic patients were studied. Visceral calcification (heart, lung, and kidney) in hypercalcemic patients exhibited either an amorphous or apatitic X-ray diffraction pattern. Uremic visceral calcification consistently gave an amorphous diffraction pattern. Although the calcium content of uremic and hypercalcemic visceral deposits was similar, other inorganic constituents were different. The mean pyrophosphate was 11 +/- 11.8 and magnesium 4.91 +/- 3.86 mg/g in the uremic group as compared to 0.92 +/- 0.24 and 1.36 +/- 1.26 mg/g in the hypercalcemic group (P less than 0.025). After incineration hypercalcemic visceral deposits having an amorphous diffraction pattern were found to generate pyrophosphate supporting the presence of brushite in these deposits. The small amount of pyrophosphate in apatitic deposits from both uremic and hypercalcemic patients actually decreased after incineration and the pyrophosphate content of uremic visceral deposits was unchanged by incineration. It is concluded that in hypercalcemic patients the initial visceral deposit is brushite which is subsequently transformed to apatite. Arterial and tumoral calcium-phosphate deposits in uremic patients were also apatite. Uremic visceral calcium-phosphate deposits are an unique mineral high in magnesium with approximately 30% of the phosphorus present as pyrophosphate. The high pyrophosphate content of these deposits could alter their crystalline structure and prevent the transformation to apatite. The infrared features, high magnesium content of the deposit, and resistance of pyrophosphate in the deposit to hydrolysis by pyrophosphatase suggests that the pyrophosphate may be deposited as the magnesium salt.  (+info)

Successful treatment of Corynebacterium urealyticum encrusted cystitis: a case report and literature review. (36/221)

Encrusted cystitis is a very rare chronic inflammatory disease of the bladder characterized by precipitation and incrustation of phosphate and ammonium-magnesium salts on the vescical mucosa, caused by urinary infection due to urolithic microorganisms. Corynebacterium urealyticum or Corynebacterium group D2, a multiple antibiotic-resistant urea-splitting bacterium, is the most frequently incriminated aetiology. We report a case of a 57-year-old man affected by systemic erythematosus lupus with a long history of dysuria and suprapubic pain who underwent percutaneous nephrostomy drainage with urethral stenting for lupoid obstructive uropathy. Before the diagnosis of encrusted cystitis by Corynebacterium urealyticum was established, the patient underwent five cystoscopies to remove the plaques and multiple unsuccessful antibiotic treatment courses. Eventually the infection was definitively cured after a two-week course with intramuscular teicoplanin.  (+info)

Effect of ionic activity products on the structure and composition of mineral self assembled on three-dimensional poly(lactide-co-glycolide) scaffolds. (37/221)

A biomimetic approach involving the self-assembly of mineral within the pores of three-dimensional porous polymer scaffolds is a promising strategy to integrate advantages of inorganic and organic phases into a single material for hard tissue engineering. Such a material enhances the ability of progenitor cells to differentiate down an osteoblast lineage in vitro and in vivo, compared with polymer scaffolds. The mechanisms regulating mineral formation in this one-step process, however, are poorly understood, especially the effects of ionic activity products (IP) of the mineralizing solution and incubation time. The aims of this study were to define the structure and composition of mineral formed within the pores of biodegradable polymer scaffolds as a function of IP and time. Three-dimensional poly(lactide-co-glycolide) scaffolds were fabricated by solvent casting/particulate leaching and incubated for 4-16 days in six variants of simulated body fluid whose IPs were varied by adjusting ionic concentrations. Scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy demonstrated the formation of carbonated apatite with sub-micrometer sized crystals that grew into spherical globules extending out of the scaffold pore surfaces. As IP increased, more mineral grew on the scaffold pore surfaces, but the apatite became less crystalline and the Ca/P molar ratio decreased from 1.63 +/- 0.005 to 1.51 +/- 0.002. Since morphology, composition, and structure of mineral are factors that affect cell function, this study demonstrates that the IP of the mineralizing solution is an important modulator of material properties, potentially leading to enhanced control of cell function.  (+info)

Amorphous calcium phosphate/urethane methacrylate resin composites. I. Physicochemical characterization. (38/221)

Urethane dimethacrylate (UDMA), an oligomeric poly(ethylene glycol) extended UDMA (PEG-U) and a blend of UDMA/PEG-U were chosen as model systems for introducing both hydrophobic and hydrophilic segments and a range of compliances in their derived polymers. Experimental composites based on these three resins with amorphous calcium phosphate (ACP) as the filler phase were polymerized and evaluated for mechanical strength and ion release profiles in different aqueous media. Strength of all composites decreased upon immersion in saline (pH = 7.4). Both polymer matrix composition and the pH of the liquid environment strongly affected the ion release kinetics. In saline, the UDMA/PEG-U composite showed a sustained release for at least 350 h. The initially high ion release of the PEG-U composites decreased after 72 h, seemingly due to the mineral re-deposition at the composite surface. Internal conversion from ACP to poorly crystallized apatite could be observed by X-ray diffraction. In various lactic acid (LA) environments (initial pH = 5.1) ion release kinetics was much more complex. In LA medium without thymol and/or carboxymethylcellulose, as a result of unfavorable changes in the internal calcium/phosphate ion stoichiometry, the ion release rate greatly increased but without observable conversion of ACP to apatite.  (+info)

Bioactive apatite coating on titanium using an alternate soaking process. (39/221)

We developed a novel apatite coating method that consisted of two-step of chemical treatment: a combined pretreatment of concentrated acid etching and alkaline treatment, followed by alternate soaking. In this study, the effects of the number of reaction cycles, solution temperature, and soaking time on apatite deposition on titanium surface using alternate soaking were investigated. Results revealed that the deposited amount of apatite mainly depended on the number of reaction cycles, and was independent of solution temperature and soaking time. Characterization results revealed that apatite formation using alternate soaking basically depended on ion exchange and adsorption on the pretreated surface. Further, apatite coating using alternate soaking on a 200-grid titanium mesh confirmed that this coating method was applicable for substrates with complicated shapes.  (+info)

High performance DNA nano-carriers of carbonate apatite: multiple factors in regulation of particle synthesis and transfection efficiency. (40/221)

Increasing attention is being paid on synthetic DNA delivery systems considering some potential life-threatening effects of viral particles, for development of gene-based nanomedicine in the 21st century. In the current nonviral approaches, most of the efforts have been engaged with organic macromolecules like lipids, polymers, and peptides, but comparatively fewer attempts were made to evaluate the potential of inorganic materials for gene delivery. We recently reported that biodegradable nanoparticles of carbonate apatite are highly efficient in transfecting a wide variety of mammalian cells. Here we show that a number of parameters actively regulate synthesis of the nanoparticles and their subsequent transfection efficacy. Development of "supersaturation", which is the prerequisite for generation of such particles, could be easily modulated by reactant concentrations, pH of the buffered solution, and incubation temperatures, enabling us to establish a flexible particle generation process for highly productive trans-gene delivery. Carbonate incorporation into the particles have been proposed for generating nano-size particles resulting in cellular uptake of huge amount of plasmid DNA as well as endosome destabilization facilitating significant release of DNA from the endosomes.  (+info)