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PubMedDate not supplied

Preparation and characteristics of microcapsules containing enoxacin by one continuous process of agglomeration and microencapsulation.

A novel microencapsulation technique was carried out with the phase separation of Eudragit RS from the wet spherical agglomeration (WSA) system by non-solvent addition. To elucidate the characteristics of microcapsules the spherical agglomerates containing enoxacin (ENX), lactose or Avicel which are different in their affinity to water (i.e. insoluble, soluble or absorbable properties, respectively), were prepared as core particles in an acetone/n-hexane mixture (volume ratio 3/7) by a WSA technique. The size of all kinds of spherical agglomerates was controlled by the amount of bridging liquid (ammonia water or distilled water) used. In the microencapsulation process encapsulation was performed efficiently at 400-600 rpm. Avicel agglomerates could be coated up to 30 per cent with Eudragit RS with less aggregation. Various additives were compared as additions into the system to avoid the aggregation of encapsulated particles. Addition of more than 3 per cent magnesium stearate based on the core weight in the system, before or at the same time as phase separation of Eudragit RS occurred, resulted in low aggregation of microcapsules for spherical agglomerates containing ENX or lactose. In formulating a water-absorbable excipient such as Avicel in the agglomerates of ENX, adding some 10 per cent Eudragit RS-dichloromethane solution into the WSA system, and using magnesium stearate as a protective agent, the resultant microcapsules could be obtained efficiently without aggregation, showing sustained release of ENX depending on coating level.

Acrylic Resins↗
PubMed2004

Electrostatic free energy of weakly charged macromolecules in solution and intermacromolecular complexes consisting of oppositely charged polymers.

When oppositely charged polyelectrolytes are mixed in water, attraction between oppositely charged groups may lead to the formation of polyelectrolyte complexes (associative phase separation, complex coacervation, interpolymer complexes). Theory is presented to describe the electrostatic free energy change when ionizable (annealed) (macro-)molecules form a macroscopic polyelectrolyte complex. The electrostatic free energy includes an electric term as well as a chemical term that is related to the dissociation of the ionic groups in the polymer. An example calculation for complexation of polyacid with polybase uses a cylindrical diffuse double layer model for free polymer in solution and electroneutrality within the complex and calculates the free energy of the system when the polymer is in solution or in a polyelectrolyte complex. Combined with a term for the nonelectrostatic free energy change upon complexation, a theoretical stability diagram is constructed that relates pH, salt concentration, and mixing ratio, which is in qualitative agreement with an experimental diagram obtained by Bungenberg de Jong (1949) for complex coacervation of arabic gum and gelatin. The theory furthermore explains the increased tendency toward phase separation when the polymer becomes more strongly charged and suggests that complexation of polyacid or polybase with zwitterionic polymer (e.g., protein) of the same charge sign (at the "wrong side" of the iso-electric point) may be due (in part) to an induced charge reversal of the protein.

Hydrogen-Ion Concentration↗
PubMedDate not supplied

Effect of manufacturing conditions on the formation of double-walled polymer microspheres.

This paper discusses the optimization of the solvent evaporation process to produce double-walled (DW) microspheres in a single-step. Five process variables were studied: polymer solution concentration, polymer weight ratio, polymer solution volume ratios, encapsulation temperature, and air flow rate across the top of the encapsulation vessel. The effects of these variables on the process efficiency (defined here as the percentage of microspheres with a DW configuration compared to the total number of microspheres) were examined. Total polymer concentrations of less than 20% (w/v) produced microspheres with high efficiency, with phase separation consistent across all size fractions in each batch. Changing the volume ratio of the two polymer solutions had no significant effect on the process efficiency. The weight ratio of the polymers greatly influenced the process efficiency, resulting in a low 63% efficiency for the 1:3 Poly-L-lactide (PLLA): Poly(carboxyphenoxypropane-co-sebacic)anhydride 20:80 (P(CPP:SA 20:80)) weight ratio and 0% for the 3:1 weight ratio. The 1:3 weight ratio also caused the polymers to reverse their orientation, although the efficiency for this switch was still relatively low. The temperature of the non-solvent bath affected the efficiency of certain pairs of polymers, but not all. The PLLA/Poly(lactide-co-glycolide) 50:50 (PLGA) pair was most sensitive to temperature, due to the chemical similarity of the two polymers which narrowed the range of acceptable conditions for encapsulation. Pairs of polymers which phase separated readily (e.g. polystyrene and PLLA) were the least sensitive to temperature changes. Process yield and size distribution show no clear trends with respect to air flow rate across the top of the reaction vessel. The efficiency of the process to produce DW microspheres increased and the process time decreased with increasing air flow across the surface of the encapsulation vessel.

Chemistry, Pharmaceutical↗
PubMed1990

Blood flow in microvascular networks. Experiments and simulation.

A theoretical model has been developed to simulate blood flow through large microcirculatory networks. The model takes into account the dependence of apparent viscosity of blood on vessel diameter and hematocrit (the Fahraeus-Lindqvist effect), the reduction of intravascular hematocrit relative to the inflow hematocrit of a vessel (the Fahraeus effect), and the disproportionate distribution of red blood cells and plasma at arteriolar bifurcations (phase separation). The model was used to simulate flow in three microvascular networks in the rat mesentery with 436,583, and 913 vessel segments, respectively, using experimental data (length, diameter, and topological organization) obtained from the same networks. Measurements of hematocrit and flow direction in all vessel segments of these networks tested the validity of model results. These tests demonstrate that the prediction of parameters for individual vessel segments in large networks exhibits a high degree of uncertainty; for example, the squared coefficient of correlation between predicted and measured hematocrit of single vessel segments ranges only between 0.15 and 0.33. In contrast, the simulation of integrated characteristics of the network hemodynamics, such as the mean segment hematocrit or the distribution of blood flow velocities, is very precise. In addition, the following conclusions were derived from the comparison of predicted and measured values: 1) The low capillary hematocrits found in mesenteric microcirculatory networks as well as their heterogeneity can be explained on the basis of the Fahraeus effect and phase-separation phenomena. 2) The apparent viscosity of blood in vessels of the investigated tissue with diameters less than 15 microns is substantially higher than expected compared with measurements in glass tubes with the same diameter.

Animals↗
PubMed2002

Molecular organization of cholesterol in polyunsaturated membranes: microdomain formation.

The molecular organization of cholesterol in phospholipid bilayers composed of 1,2-diarachidonylphosphatidylcholine (20:4-20:4PC), 1-stearoyl-2-arachidonylphosphatidylcholine (18:0-20:4PC), and 20:4-20:4PC/18:0-20:4PC (1/1 mol) was investigated by solid-state (2)H NMR and by low- and wide-angle x-ray diffraction (XRD). On the basis of distinct quadrupolar powder patterns arising from [3 alpha-(2)H(1)]cholesterol intercalated into the membrane and phase separated as solid, solubility chi(NMR)(chol) = 17 +/- 2 mol% and tilt angle alpha(0) = 25 +/- 1 degrees in 20:4-20:4PC were determined. The corresponding values in 18:0-20:4PC were chi (NMR)(chol) > or = 50 mol% and alpha(0) = 16 +/- 1 degrees. Cholesterol solubility determined by XRD was chi(NMR)(chol) = 15 +/- 2 mol% and chi(NMR)(chol) = 49 +/- 1 mol% for 20:4-20:4PC and 18:0-20:4PC, respectively. XRD experiments show that the solid sterol is monohydrate crystals presumably residing outside the bilayer. The (2)H NMR spectrum for equimolar [3 alpha-(2)H(1)]cholesterol added to mixed 20:4-20:4PC/18:0-20:4PC (1/1 mol) membranes is consistent with segregation of cholesterol into 20:4-20:4PC and 18:0-20:4PC microdomains of <160 A in size that preserve the molecular organization of sterol in the individual phospholipid constituents. Our results demonstrate unambiguously that cholesterol has low affinity to polyunsaturated fatty acids and support hypotheses of lateral phase separation of membrane constituents into sterol-poor/polyunsaturated fatty acid-rich and sterol-rich/saturated fatty acid-rich microdomains.

Cholesterol↗
PubMed2005

Formation of Liesegang patterns in the presence of an electric field.

The effects of an external electric field on the formation of Liesegang patterns are investigated. The patterns are assumed to emerge from a phase separation process in the wake of a diffusive reaction front. The dynamics is described by a Cahn-Hilliard equation with a moving source term representing the reaction zone, and the electric field enters through its effects on the properties of the reaction zone. We employ our previous results [I. Bena, F. Coppex, M. Droz, and Z. Rácz, J. Chem. Phys. 122, 024512 (2005)] on how the electric field changes both the motion of the front, as well as the amount of reaction product left behind the front, and our main conclusion is that the number of precipitation bands becomes finite in a finite electric field. The reason for the finiteness in case when the electric field drives the reagents towards the reaction zone is that the width of consecutive bands increases so that, beyond a distance l(+), the precipitation is continuous (plug is formed). In case of an electric field of opposite polarity, the bands emerge in a finite interval l(-), since the reaction product decreases with time and the conditions for phase separation cease to exist. We give estimates of l(+/-) in terms of measurable quantities and thus present an experimentally verifiable prediction of the "Cahn-Hilliard equation with a moving source" description of Liesegang phenomena.

Journal Article↗
PubMed1996

Effect of EO Chain Length of Dodecanol Ethoxylates (C12En) on the Complexation of C12En/SDS Mixed Micelles with an Oppositely Charged Polyelectrolyte

Turbidimetry, dynamic light scattering, and capillary electrophoresis were used to study the complexation of polydiallyldimethylammonium chloride (PDADMAC) with mixed micelles of sodium dodecyl sulfate (SDS) and dodecanol ethoxylates (C12En). The effect of EO chain length and its distribution was examined using various combinations of C12En (n = 4, 6, 8, 12). The results show that the onset of the complexation of PDADMAC with the mixed micelles is affected by the EO chain length of C12En: the mole fraction (Y) of SDS in the mixed micelle required to form the complex (Yc) increases with n. The effect of EO chain length on the onset of bulk phase separation shows the same trend. Although Yc varies with n, the electrophoretic mobility of mixed micelles with composition corresponding to Yc is independent of n. We propose that the effect of EO chain length has two aspects: (1) an increase in the average distance between bound polycation segments and the SDS sulfate groups, and (2) an increase in the distance between SDS head groups, which causes a decrease in the surface charge density (sigma) of the micelle. Therefore, the electrical potential at the mean locus of bound polymer segments, psi0, decreases with increasing n; in order for complexation to occur, this effect must be compensated for by a larger value of Y. Broader distributions of EO chain length lead to an increase in the range of Y over which the soluble complex is stable. We suggest that polycations initially bind to micelles which are rich in shorter EO chains and thus have higher "surface" potential, psi0. However, additional SDS may go preferentially into micelles rich in longer chains with lower psi0. This delays the formation of micelles which have sufficiently large psi0 to cause phase separation.

Journal Article↗
PubMed2005

Encapsulation of essential oils in zein nanospherical particles.

Three essential oils, oregano, red thyme, and cassia (100% pure oil), were encapsulated by phase separation into zein nanospheres. Topographical images indicated that the powders were made up of irregularly shaped particles ( approximately 50 mum) containing close-packed nanospheres. Approximately 31% of the oregano encapsulated particles had mean diameters greater than 100 nm compared to 19% for the zein alone particles. In vitro digestion of zein particles with pepsin at a concentration ratio of 10:1 was complete after 52 h in phosphate-citrate buffer, pH 3.5, at 37 degrees C by spectroscopic analysis. Nonenzymatic, aqueous in vitro release of essential oils from encapsulated zein particles was carried out in phosphate buffered saline at pH 7.4 and 37 degrees C. Release occurred at varying rates over 20 h probably from different locations within the closely packed nanospheres of different sizes. Gel electrophoresis SDS-PAGE of zein incubated with freeze-dried swine manure solids at 37 degrees C indicated that preformed microbial enzymes capable of digesting zein within minutes were present in the manure. Except for differences in size of nanospheres, no structural differences were resolved by several microscopic methods, suggesting that the oil and proteins phases were blended during phase separation.

Animals↗
PubMed1992

Hydroxypropyl cellulose/poly(ethylene glycol)-co-poly(propylene glycol) aqueous two-phase systems: system characterization and partition of cells and proteins.

Novel aqueous polymeric two-phase systems are described. These systems are formed by mixing hydroxypropyl cellulose (molecular mass 100,000, trade name Klucel L) with poly(ethylene glycol)-co-poly(propylene glycol) copolymer [molecular mass 6,500, poly(propylene glycol) content 50% w/w, trade name Pluronic P105], in a saline buffer. The phase diagram was measured and the interfacial tensions, phase separation times, and lower phase viscosities of three phase systems having constant Pluronic P105 concentration but varying in Klucel L concentration were determined. The partition behavior of a representative cell, bacterium, and protein and the affinity ligand-mediated alteration in the partition behavior of a protein from a yeast extract protein mixture were also characterized. The results suggest that Klucel L/Pluronic P105 phase systems may be cost-effective substitutes for, or complements to, existing aqueous polymeric phase systems. The physical characterization and representative partition data reported here should facilitate application of these new systems.

Cell Separation↗
PubMed1999

Phenotypic characterization of lith genes that determine susceptibility to cholesterol cholelithiasis in inbred mice. Pathophysiology Of biliary lipid secretion.

The inbred C57L strain but not the AKR strain of mice carry Lith genes that determine cholesterol gallstone susceptibility. When C57L mice are fed a lithogenic diet containing 15% fat, 1% cholesterol, and 0.5% cholic acid, gallbladder bile displays rapid cholesterol supersaturation, mucin gel accumulation, increases in hydrophobic bile salts, and rapid phase separation of solid and liquid crystals, all of which contribute to the high cholesterol gallstone prevalence rates (D. Q-H. Wang, B. Paigen, and M. C. Carey. J. Lipid Res. 1997. 38: 1395;-1411). We have now determined the hepatic secretion rates of biliary lipids in fasting male and female C57L and AKR mice and the intercross (C57L x AKR)F(1) before and at frequent intervals during feeding the lithogenic diet for 56 days. Bile flow and biliary lipid secretion rates were measured in the first hour of an acute bile fistula and circulating bile salt pool sizes were determined by the "washout" technique after cholecystectomy. Compared with AKR mice, we found that i) C57L and F(1) mice on chow displayed significantly higher secretion rates of all biliary lipids, and larger bile salt pool sizes, as well as higher bile salt-dependent and bile salt-independent flow rates; ii) the lithogenic diet further increased biliary cholesterol and lecithin outputs, but bile salt outputs remained constant. Biliary coupling of cholesterol to lecithin increased approximately 30%, setting the biophysical conditions necessary for cholesterol phase separation in the gallbladder; and iii) no gender differences in lipid secretion rates were noted but male mice exhibited significantly more hydrophobic bile salt pools than females. We conclude that in gallstone-susceptible mice, Lith genes determine increased outputs of all biliary lipids but promote cholesterol hypersecretion disproportionately to lecithin and bile salt outputs thereby inducing lithogenic bile formation.

Alleles↗
PubMed2001

Study of crystallization of endogenous surfactant in Eudragit NE30D-free films and its influence on drug-release properties of controlled-release diphenhydramine HCl pellets coated with Eudragit NE30D.

This study investigates the crystallization of the endogenous surfactant nonoxynol 100 in Eudragit NE30D-free films during storage and the influences of nonoxynol 100 on the dissolution of diphenhydramine hydrochloric acid (HCl) pellets coated with Eudragit NE30D before and after aging at ambient conditions. Polarizing light microscopy showed that when Eudragit NE30D-free films were stored at ambient conditions, off-white, flower-shaped crystals formed and increased in the polymer film as storage time increased. Also, x-ray diffraction showed polymer crystals in the aged free film. Thermogravimetric analysis showed no evidence of combined volatile molecules with the polymer molecules, and Fourier transformed infrared spectroscopy (FTIR) data suggested the same chemical composition of the polymer before and after phase separation. Further, from normal light microscopy, the appearance of the melting droplets in the polymer film indicated that the polymer molecules did not form the crystals. After the extraction of nonoxynol 100 by water, the free film formed by the water-extracted Eudragit NE30D was found free of the crystals after aging at the same conditions. The combination of the thermogravimetric analysis, FTIR, and microscopy showed that the origin of the crystals in dry Eudragit NE30D-free films came from nonoxynol 100, and not from the polymer molecules themselves. Monitoring by differential scanning calorimeter, it was found that the rates of crystallization of nonoxynol 100 were faster when the films were stored at 30 degrees C and 40 degrees C than when stored at ambient conditions and 45 degrees C. When stored at -5 degrees C, the crystallization rate was nearly zero. As the temperature got closer to melting temperature, the crystallization rate was very low because the system was in a thermodynamically disfavored state. The rate gradually increased and finally passed through a maximum as the crystallization temperature decreased. As the temperature kept decreasing, the crystallization rate became small again and eventually stopped because the system turned into a kinetically disfavored state. Because the phase transition of nonoxynol 100 in Eudragit NE30D occurred at ambient conditions, its influence on the dissolution of diphenhydramine HCl pellets coated with Eudragit NE30D was studied. Three different levels of nonoxynol 100 were used in Eudragit NE30D dispersions to make 3 different batches of Eudragit NE30D film-coated, controlled-release diphenhydramine HCl pellets. The results showed the dissolution rate increased as the level of nonoxynol 100 increased in the coating formula. Compared to the commonly used water-soluble additive human peripheral mononuclear cell, nonoxynol 100 was more effective in enhancing the dissolution of diphenhydramine HCl from pellets coated with Eudragit NE30D. Further study showed that the phase separation of the surfactant during aging tends to stabilize or slightly increase dissolution rates at higher surfactant levels.

Acrylates↗
PubMed2005

Development of acrylate-based monolithic stationary phases for electrochromatographic separations.

Organic monolithic stationary phases were synthesized in fused-silica capillaries. They were prepared by in situ polymerization under UV irradiation of various alkyl acrylates, 1,3-butanediol diacrylate, and 2-acrylamido-2-methyl-1-propanesulfonic acid in a ternary porogenic solvent. The resulting stationary phases were tested in CEC. The influence of UV irradiation energy on the resulting separative performances of the monoliths was studied. It was thus demonstrated that the use of hexyl acrylate rather than butyl acrylate and lauryl methacrylate gives highly efficient monoliths (more than 300 000 plates per meter) with optimized EOF. It was also confirmed that the mobile phase ionic strength may affect significantly the separation efficiency. The influence of the nature of the mobile phase organic modifier (ACN or methanol) on EOF, retention, efficiency, and selectivity was studied and differences were observed. Finally, the performances of monolithic stationary phases developed and optimized for CEC separations were evaluated in nanoLC.

Acrylates↗
PubMed2005

[Studies on chromatographic properties of 2,4,6-trinitrophenol-modified zirconia-magnesia stationary phase for the separation of fullerenes ].

A stationary phase for the separation of C60 and C70 was prepared by modifying zirconia-magnesia composites with 2,4,6-trinitrophenol. The modified composite was characterized by using elemental analysis, diffused reflectance Fourier transform infrared spectroscopy and specific surface area. The effects of the toluene content in toluene-cyclohexane mobile phase and the column temperature on the separation of C60 and C70 were examined. Meanwhile, the separation of fullerenes including 3% high fullerenes was investigated at the temperature of 348 K using pure toluene as the mobile phase. The results showed that the stationary phase of 2,4,6-trinitrophenol-modified zirconia-magnesia composite exhibits advantage in the separation of C60 and C70, and strong temperature dependence. The retention times of C60 and C70 and their separation factor on the stationary phase increase with the increase of the column temperature. The stationary phase is a potential packing material for separation of fullerenes in preparative scale.

Chromatography, High Pressure Liquid↗
PubMed2005

Effects of colloid polydispersity on the phase behavior of colloid-polymer mixtures.

We study theoretically the equilibrium phase behavior of a mixture of polydisperse hard-sphere colloids and monodisperse polymers, modeled using the Asakura-Oosawa model [S. Asakura and F. Oosawa, J. Chem. Phys. 22, 1255 (1954)] within the free volume approximation of H. N. W. Lekkerkerker, W. C. K. Poon, P. N. Pusey, A. Stroobants, and P. B. Warren [Europhys. Lett. 20, 559 (1992)]. We compute full phase diagrams in the plane of colloid and polymer volume fractions, using the moment free energy method. The intricate features of phase separation in pure polydisperse colloids combine with the appearance of polymer-induced gas-liquid coexistence to give a rich variety of phase diagram topologies as the polymer-colloid size ratio xi and the colloid polydispersity delta are varied. Quantitatively, we find that polydispersity disfavors fluid-solid against gas-liquid separation, causing a substantial lowering of the threshold value xi(c) above which stable two-phase gas-liquid coexistence appears. Phase splits involving two or more solids can occur already at low colloid concentration, where they may be kinetically accessible. We also analyze the strength of colloidal size fractionation. When a solid phase separates from a fluid, its polydispersity is reduced most strongly if the phase separation takes place at low colloid concentration and high polymer concentration, in agreement with experimental observations. For fractionation in gas-liquid coexistence we likewise find good agreement with experiment, as well as with perturbative theories for near-monodisperse systems.

Journal Article↗
PubMed2004

Memory effect of diethylamine mobile phase additive on chiral separations on polysaccharide stationary phases.

The existence of a memory effect for amine additives on polysaccharide chiral stationary phases has often been suggested, but not clearly demonstrated. Demonstration of this effect is made difficult by the uncertainty as to which analytes benefit from use of amine additives and, typically, an unclear history of column use. In this work, analytes were selected for differences in their behavior with and without additives. Columns were used with no prior history. A persistent memory effect was demonstrated on a CHIRALPAK AD-H column in hexane-based mobile phases. This effect was short-lived, with polar organic mobile phases. Memory was short-lived on a CHIRALCEL OJ-H column. Flushing with isopropanol was shown to remove most of the memory effect. Compounds expected to require amine additives on CHIRALCEL OD-H column did not. Acid treatment of the AD-H and OD-H columns changed their performance, which was subsequently restored by the incorporation of amine.

Chromatography, Liquid↗
PubMed1995

Macromolecular ionophores. 1. Chiral recognition properties of poly[(1-->6)-2,5-anhydro-D-glucitol] toward racemic amino acid ester.

The chiral recognition property of poly[(1-->6)-2,5-anhydro-3,4-di-O-alkyl-D-glucitol] (1) toward racemic RCH (CO2CH3)NH3+.PF6- (2.HPF6) has been studied using a transport system involving an aqueous source and receiving phases separated by a chloroform phase containing 1. Transport rates for aromatic guests 2a (R = Ph) and 2b (R = CH2Ph) were faster than those for aliphatic guests, 2c (R = CH(CH3)2) and 2d (R = CH2CH(CH3)2), using the polymer substituted with methyl groups (1a). The enantiomeric excess (e.e.) was 10.9% for 2a as a maximum value and decreased in the order of 2a > 2c > 2b = 2d. When the transport of 2a.HPF6 was carried out using the polymers with 3,4-di-O-methyl (1a), ethyl (1b), allyl (1c), and pentyl (1d) groups, the e.e. was 22.0% for 1d as a maximum value and increased in the order of 1a < 1b < 1c < 1d. The formation of a complex between 1a and 2a.HPF6 was confirmed by 1H and 13C NMR spectral measurements.

Amino Acids↗
PubMed1999

Aluminum Polyphosphate Nanoparticles: Preparation, Particle Size Determination, and Microchemistry.

Admixture of aluminum nitrate, sodium polyphosphate, and ammonium hydroxide solutions yields stable dispersions of hydrated aluminum polyphosphate particles within a broad reagent concentration range. These particles are formed by liquid-liquid phase separation, for which a phase diagram was calculated using suitable models for concentrated electrolyte solutions. Particle effective diameters range from a few nanometers to many hundreds and are fractionated by centrifugation. Particle electrophoretic mobility is very low and the hydration degree is high ( approximately 80% v/v). Dry nanoparticles (1- to 15-nm diameter as observed by TEM) as well as particle aggregates are obtained by lyophilization. Element (P, Al, and Na) mapping by ESI-TEM shows that particle aggregates have a core-and-shell morphology, with a higher content of P in the aggregate core and a higher Na content at the outer shell. Copyright 1999 Academic Press.

Journal Article↗