Helga Füredi-Milhofer

Morphological and phase changes in calcium oxalate crystals grown in the presence of sodium diisooctyl sulfosuccinate

Calcium oxalate was crystallized in the presence of the anionic surfactant dioctyl sulphosuccinate, AOT, and the phase composition of the precipitates (by X-ray diffraction powder patterns and thermal analysis) and their crystal growth morphology (by scanning electron microscopy and electron diffraction) were determined. In the control systems and in the presence of low concentrations of AOT (below the critical micellar concentration, CMC) calcium oxalate monohydrate (CaC2O4 · H2O, COM) was the dominant crystal phase. Crystals grown in the presence of C(AOT)> 0.75 CMC were thinner and more elongated than in the controls, indicating preferential adsorption of the surfactant at the 1¯01 and {010} crystal faces. When the AOT concentration exceeded the critical micellar concentration, the morphological changes in COM crystals became more intense and the composition of the precipitates abruptly changed to mixtures of COM and calcium oxalate dihydrate (CaC2O4 · (2 + x)H2O, x < 0.5;COD) with a COM/COD ratio up to 50 wt%. The morphology of the COD crystals was mostly unaffected. The phase change was attributed to preferential adsorption of AOT — in the form of surface aggregates — at the crystal faces of COM with the consequence of strong inhibition of nucleation and crystal growth of this crystal type and growth of the kinetically less favored COD crystals.

Precipitation of calcium oxalates from high ionic strength solutions: V. The influence of precipitation conditions and some additives on the nucleating phase

The influence of precipitation conditions (temperature, initial reactant concentrations and the mode of stirring) and some additives (glutamic acid (Glu), ornitine (Orn), tryptophan (Trp) and phosphate (PO4) on the morphology and composition of calcium oxalate initially pricipitating from high ionic strength solutions was investigated. The type of calcium oxalate hydrate formed strongly depends on the stirring conditions, e.g. the hydrodynamics of the system. Magnetic stirring promoted the formation of calcium oxalate trihydrate (COT), while in mechanically stirred and unstirred systems mixtures of calcium oxalate monohydrate (COM) calcium oxalate dihydrate (COD) and COT appeared. At a temperature of > 300 K significant transformation of metastable COT and COD into the thermodynamically stable form, COM, occurred within 1 h. All investigated aminoacids influenced the nucleation of the solid phase promoting the formation of mixtures of COM and COT in systems in which COT only was normally formed. Urinary concentrations of phosphate ions (PO4) did not change the nature of the solid phase.

Biomimetic organic-inorganic nanocomposite coatings for titanium implants.

A new class of organic-inorganic nanocomposites, to be used as coatings for surface enhancement of metal implants for bone replacement and repair, has been prepared by a biomimetic three-step procedure: (1) embedding amorphous calcium phosphate (ACP) particles between organic polyelectrolyte multilayers (PE MLs), (2) in situ transformation of ACP to octacalcium phospate (OCP) and/or poorly crystalline apatite nanocrystals by immersion of the material into a metastable calcifying solution (MCS) and (3) deposition of a final PE ML. The organic polyelectrolytes used were poly-L-glutamic acid and poly-L-lysine. The nanocomposites obtained by each successive step were characterized by scanning electron microscopy, energy dispersive X-ray analysis (EDS), and XRD, and their suitability as coatings for metal implants was examined by mechanical and in vitro biological tests. Coatings obtained by the first deposition step are mechanically unstable and therefore not suitable. During the second step, upon immersion into MCS, ACP particles were transformed into crystalline calcium phosphate, with large platelike OCP crystals as the top layer. After phase transformation, the nanocomposite was strongly attached to the titanium, but the top layer did not promote cell proliferation. However, when the coating was topped with an additional PE ML (step 3), smoother surfaces were obtained, which facilitated cell adhesion and proliferation as shown by in vitro biological tests using primary human osteoblasts (HO) directly seeded onto the nanocomposites. In fact, cell proliferation on nanocomposites with top PE MLs was far superior than on any of the individual components and was equivalent to proliferation on the golden standard (plastic).

Crystallization from microemulsions : a novel method for the preparation of new crystal forms of aspartame

Solubilization and crystallization of the artificial sweetener aspartame (APM), in water/isooctane microemulsions stabilized with sodium diisooctyl sulfosuccinate (AOT) has been investigated. The amount of aspartame that could be solubilized depended primarily on the amount of surfactant and on the temperature. The maximum AOT/aspartame molar ratio at the w/o interface is shown to be 6.2 at 25°C. It was concluded that the dipeptide is located at the w/o interface interspersed between surfactant molecules and that it acts as a cosurfactant. A new crystal form, APM III, was obtained by cooling of hot w/isooctane/AOT microemulsions containing solubilized aspartame. The new crystal form exhibits a distinct X-ray diffraction powder pattern, as well as changes in the FTIR spectra, thermogravimetric and DSC patterns. H-NMR spectra of APM III dissolved in D 2 O were identical to the spectrum of commercial aspartame recorded under the same conditions. The new crystal form has greatly improved dissolution kinetics.

INTERACTIONS OF ORGANIC ADDITIVES WITH IONIC CRYSTAL HYDRATES: THE IMPORTANCE OF THE HYDRATED LAYER

The interactions of two groups of hydrated model crystals, calcium hydrogenphosphate dihydrate (DCPD) vs. octacalcium phosphate (OCP) and calcium oxalate monohydrate (COM) vs. calcium oxalate dihydrate (COD) with different organic additives are considered. DCPD precipitates as platelet-like crystals with the dominant faces shielded by hydrated layers and charged lateral faces. In the second system COM has charged surfaces, while all faces of COD are covered with layers containing water molecules. The organic molecules tested include negatively charged, flexible and rigid small and macromolecules (glutamic and aspartic acid, citrate, hexaammonium polyphosphate, phytate and polyaspartate) and anionic surfactants (sodium dodecyl sulphate, SDS, sodium diisooctyl sulfosuccinate, AOT, sodium cholate NaC and disodium oleoamido PEG-2 sulfosuccinate, PEG). Two types of effects have been demonstrated: (1) Effect on crystal growth morphology: Flexible organic molecules with high charge density and anionic surfactant...

Influence of some aminoacids on the spontaneous precipitation of calcium oxalate from high ionic strength solutions

Kinetics of spontaneous batch precipitation of calcium oxalate from high ionic strength (0.3 mol dm-3) solutions, at pH = 6.50±0.05 and 298K, was followed by size distribution and thermogravimetric analysis, X-ray diffraction and optical microscopy. The effect of glutamic acid, ornithine or tryptophan on nucleation, crystal growth and aggregation was investigated in a wide range of concentrations, including that of physiological significance. The investigated aminoacids affected the nucleation of the solid phase. Their influence on growth and aggregation of crystals depended on the type and the concentration of aminoacid used. Results are interpreted in terms of critical time and supersaturation when crystal growth or aggregation commences, control mechanism of crystal growth and/or aggregation and the effect of aggregation on the rate of crystal growth.

Polyelectrolyte Multilayer-Calcium Phosphate Composite Coatings for Metal Implants

The preparation of organic-inorganic composite coatings with the purpose to increase the bioactivity of bioinert metal implants was investigated. As substrates, glass plates and rough titanium surfaces (Ti-SLA) were employed. The method comprises the deposition of polyelectrolyte multilayers (PEMLs) followed by immersion of the coated substrate into a calcifying solution of low supersaturation (MCS). Single or mixed PEMLs were constructed from poly-L-lysine (PLL) alternating with poly-L-glutamate, (PGA), poly-L-aspartate (PAA), and/or chondroitin sulfate (CS). ATR-FTIR spectra reveal that (PLL/PGA)10 multilayers and mixed multilayers with a (PLL/PGA)5 base contain intermolecular β-sheet structures, which are absent in pure (PLL/PAA)10 and (PLL/CS)10 assemblies. All PEML coatings had a grainy topography with aggregate sizes and size distributions increasing in the order: (PLL/PGA)n < (PLL/PAA)n < (PLL/CS)n. In mixed multilayers with a (PLL/PGA)n base and a (PLL/PAA)n or (PLL/CS)n top, the aggregate sizes were greatly reduced. The PEMLs promoted calcium phosphate nucleation and early crystal growth, the intensity of the effect depending on the composition of the terminal layer(s) of the polymer. In contrast, crystal morphology and structure depended on the supersaturation, pH, and ionic strength of the MCS, rather than on the composition of the organic matrix. Crystals grown on both uncoated and coated substrates were mostly platelets of calcium deficient carbonate apatite, with the Ca/P ratio depending on the precipitation conditions.

Preparation of a partially calcified gelatin membrane as a model for a soft-to-hard tissue interface.

Cartilage and/or bone tissue engineering is a very challenging area in modern medicine. Since cartilage is an avascular tissue with limited capacity for self-repair, using scaffolds provides a promising option for the repair of severe cartilage damage caused by trauma, age-related degeneration, and/or diseases. Our aim in this study was to design a model for a functional biomedical membrane to form the interface between a cartilage-forming scaffold and bone. To realize such a membrane gelatin gels containing calcium or phosphate ions were exposed from one side to a solution of the other constituent ion (i.e., a sodium phosphate solution was allowed to diffuse into a calcium-containing gel and vice versa). The partially calcified gels were analyzed by XRD, ATR-FTIR spectra, E-SEM, and EDX. Thus, we confirmed the existence of a gradient of crystals, with a dense top layer, extending several micrometers into the gel. XRD spectra and Ca/P atomic ratios confirmed the existence of calcium deficient apatites. The effect of different experimental parameters on the calcification process within the gelatin membranes has been elucidated. It was shown that increasing the gelatin concentration from 5 wt % to 10 wt % retards calcification. A similar effect was observed when glycerol, which is frequently used as plasticizer, was added to the system. With increasing calcium concentration within the organic matrix, the quantity and density of calcium phosphate crystals over/within the gel increased. The possible explanations for the above phenomena are discussed.

Bone Mineral Density Loss in Patients with Urolithiasis: A Follow-Up Study

BACKGROUND Recurrent calcium urolithiasis is often associated with disorders of calcium metabolism. The purpose of this investigation was to assess bone mineral content (BMC) and bone mineral density (BMD) over a period of 1 year in patients with urolithiasis and to determine the factors that could have influenced the changes in bone density during that period. METHODS The patient group comprised 34 men aged 41.2 plus minus 7.9 years with recurrent urolithiasis. A wide spectrum of biochemical measurements was performed. Bone mineral density (g/cm(2)), bone mineral content (BMC), and bone area (BA) were measured twice during a period of 1 year at the lumbar spine (L2-L4), femoral neck, Ward triangle, and trochanter, using dual energy absorptiometry. Patient results were compared to those obtained from 30 healthy male controls of a comparable age group. RESULTS Nine patients were hypercalciuric, while the majority of the remaining metabolic parameters were within the reference values. Bone mineral content and bone areas at all regions were lower in patients comparing to controls, but not significantly. The greatest annual reduction of BMD was noticed at Ward triangle (-5.70% in patients and -2.36% in controls), followed by femoral neck (-4.06% patients, -2.03% controls) and trochanter (-3.06% patients, -1.39% controls). There was no significant decrease of the BMD of the spine. Analyzing the influence of age, body mass index (BMI), metabolic parameters, and dietary calcium intake on the annual reduction of bone density, we found that age, hyperuricosuria, and calcium intake were significantly associated with bone loss in that time period. CONCLUSIONS Bone mass reduction in patients with urolithiasis over a 1-year period did not differ significantly from that in controls and was principally related to age, hyperuricosuria, and calcium dietary restriction but not to increased calcium excretion.

Precipitation diagrams and solubility of uric acid dihydrate

The solubility of uric acid dihydrate (UA·2H2O) and the precipitation of UA·2H2O and anhydrous uric acid (UA) from solutions containing sodium hydroxide and hydrochloric acid have been investigated. For the solubility studies, crystals of pure UA·2H2O were prepared and equilibrated with water and with solutions of HCl or NaOH for 60 min or 20 h, respectively. The equilibrium pH (pH = 2–6.25) and uric acid concentration were determined. For the precipitation experiments, commercial UA was dissolved in NaOH in a 1:1.1 molar ratio and UA·2H2O and/or UA were precipitated with hydrochloric acid. The precipitates and/or supernatants were examined 24 h after sample preparation. The results are represented in the form of tables, precipitation diagrams and “chemical potential” diagrams. Solubility measurements with 60 min equilibration times yielded the solubility products of UA·2H2O, Ksp(298 K) = (0.926 ± 0.025) × 10-9 mol2 dm-6 and Ksp(310 K) = (2.25 ± 0.05) × 10-9 mol2 dm-6 and the first dissociation constants of uric acid, K1(298 K) = (2.45 ± 0.07) × 10-6 mol dm-3 and K1(310 K) = (3.63 ± 0.08) × 10-6 mol dm-3. Precipitation diagrams show that under the given experimental conditions, at 298 K, UA·2H2O is stable for 24 h while at 310 K this was true only for precipitates formed from solutions of high supersaturations. At lower supersaturations, mixtures of UA·2H2O and UA formed. Consequently, while the Ksp value determined from precipitation data obtained at 298 K (Ksp = 1.04 × 10-9 mol2 dm-6) was consistent with the respective solubility product, the 310 K precipitation boundary yielded an ion activity product, AP, the value of which fulfills the conditions Ksp(UA) < AP < Ksp (UA·2H2O). Similar ion activity products were obtained from solubility measurements in pure water at 20 h equilibration time.