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PubMed2004

Dispersion properties of an alumina nanopowder using molecular, polyelectrolyte, and steric stabilization.

A commercial alumina nanopowder was characterized and its dispersion was studied using electrostatic, electrosteric, and steric surfactants. Citric acid was used as the electrosteric dispersant, ammonium polymethacrylic acid (Darvan C) as the electrosteric dispersant, and Hypermer KD-1 in alpha-terpineol as a purely steric system. Phase stability in water was examined by X-ray diffraction, and the surface chemistry was characterized by zeta potential and isoelectric points. Rheology measurements were used to study the impact of each dispersant type on maximum solids loading, with the maximum loading being achieved for the polyelectrolyte dispersant. Differences in maximum solids loading are related to the excluded volume of the particle separation distance induced by each stabilizing interaction.

Aluminum Oxide↗
PubMed1987

[Resistance and disintegration behavior of gastric juice-resistant drug products. 3. Pharmaceutical-technological and analytical studies of gastric juice-resistant commercial preparations].

Enteric coated commercial dosage forms often do not correspond with acid resistance and disintegration requirements of the Ph. Eur. About 15-20% of 181 tested samples disintegrate during acid resistance test or do not disintegrate in buffer solution pH = 6.8. The percentage was extremely high amongst enteric coated pancreatin or cardiac glycosides (about 30%) preparations. Storage conditions and time influence acid resistance and disintegration time. 80% of 34 products coated with celluloseacetate phthalate, hydroxypropylmethylcellulose phthalate or polymethacrylic acid ester did not change disintegration time after 2 years storage at 20 degrees C. After storage at 40 degrees C the number decreased to 40%. After 5 years at 20 degrees C number of products which were not stable increased.

Chemistry, Pharmaceutical↗
PubMed1996

A new method for permeabilization of the plasma membrane of cultured mammalian cells. IV. Structural requirement for high molecular weight polymers for potentiation of bleomycin cytotoxicity toward mammalian cells under conditions of vortex-stirring.

As we previously reported, the cytotoxicity of bleomycin (BLM) toward cultured mammalian cells was extraordinarily potentiated when the cells and BLM were vortex-stirred for a few seconds in the presence of high molecular weight polyacrylic acid (PAA). Cationic and nonionic polymers could not take the place of PAA in potentiating BLM cytotoxicity. The present study revealed that potentiation was sharply dependent on the molecular weight of PAA and a molecular weight of over 10(6) daltons seemed to be required. Copolymers of acrylic acid (AA) and acrylamide showed some potentiation which was relative to their AA content. It is worth noting that another type of anionic polymer, polymethacrylic acid, did not show any potentiating capacity at all. Polyacrylic sulfonate derivative showed a marginal capacity. The structural requirement for high molecular weight polymers for potentiation of BLM cytotoxicity was demonstrated by the increased uptake of Lucifer Yellow, a non-permeant material. In addition, the ability of permeabilization was not correlated with kinematic viscosity of anionic polymers.

Animals↗
PubMed1967

The equilibrium sedimentation of hyaluronic acid and of two synthetic polymers.

1. The method of equilibrium sedimentation has been investigated as an alternative to osmotic-pressure measurement for determining thermodynamic properties of polymer solutions at relatively high concentrations. 2. The simplifications that must be made in the theoretical treatment are discussed. 3. Measurements have been made on samples of polyethylene glycol, neutralized polymethacrylic acid and hyaluronic acid. With the first and third, values of the ;non-ideality coefficients' have been obtained that agree with those obtained from osmotic measurements on the same materials. 4. Evidence has been obtained of the presence in hyaluronic acid preparations of a fraction that has either a lower degree of thermodynamic non-ideality or a higher density increment than the bulk of the sample. This fraction is not protein.

Chemical Phenomena↗
PubMed1990

Immunological agglutination kinetics of latex particles with physically adsorbed antigens.

The influence of the properties of antigens and particles on the immunological agglutination kinetics of the antigen-coated latex particles was studied. Horse cytochrome c, hen egg-white lysozyme (HEL), bovine serum albumin (BSA), and Aspergillus sp. glucose oxidase were physically adsorbed onto the surfactant free latices of styrene-methacrylic acid (MAA) copolymer (P (S/MAA)) and polystyrene (PS). The initial rates of the immunological agglutination of these protein-coated particles initiated by the addition of antibodies were quantified by the absorbance change at a wavelength of 680 nm. The initial agglutination rates of the particles covered with smaller antigens were lower. This effect of the molecular size of antigens was larger in P(S/MAA), because small antigens are probably buried in the hydrous polymethacrylic acid layer on the surface of particles. Thus, both the molecular size of antigens and the surface properties of particles affect the sensitivity of the immunological agglutination. On the other hand, the dependence of the initial rate of the immunological agglutination on the ionic strength and pH was similar irrespective of antigen-particle systems. The initial agglutination rates were largest at an ionic strength of approximately 0.05 at pH 7.0 and decreased with increasing pH. This dependence of the sensitivity on the pH and ionic strength is attributed to the electrostatic interactions of particle-particle and antibody-particle.

Adsorption↗
PubMed2002

Molecular organization and dynamics of micellar phase of polyelectrolyte-surfactant complexes: ESR spin probe study.

Molecular dynamics and organization of the micellar phase of complexes of linear polyelectrolytes with ionogenic and non-ionogenic surfactants was studied by the ESR spin probe method. Complexes of polyacrylic acid (PAA) and sodium polystyrenesulfonate (PSS) with alkyltrimethylammonium bromides (ATAB), as well as complexes of poly-N,N'-dimethyldiallylammonium chloride (PDACL) with sodium dodecylsulfate (SDS) were studied. The micellar phase of such complexes is highly organized molecular system, molecular ordering of which near the polymeric chain is much higher than in the 'center' of the micelle, it depends on the polymer-detergent interaction, flexibility of polymeric chain and length of carbonic part of the detergent molecule. Complexes of polymethacrylic acid (PMAA) with non-ionic detergent (dodecyl-substituted polyethyleneglycol), show that the local mobility of surfactant in such complexes is significantly lower than in 'free' micelles and depends on the number of micellar particles participating in formation of complexes.

Acrylic Resins↗
PubMed1980

Insulin permeability of hydrophilic polyacrylate membranes.

The diffusive permeability of insulin in polyhydroxyethyl methacrylate (37.1% water), polyhydroxyethyl acrylate (51.8% water), polymethacrylic acid (67.5% water), and cuprophane PT-150 membranes was determined and correlated with the weight fraction of water in the membrane. Insulin diffusivity in the membranes was determined to be 1.0 x 10(-6) cm2/sec, which is in reasonable agreement with literature values for insulin diffusivity in water.

Acrylates↗
PubMed1984

Novel concept for a mucosal adhesive ointment.

Conventional adhesive ointments cause irritation to the mucous membranes. Therefore, a novel mucosal adhesive ointment based partly on neutralized polymethacrylic acid methyl ester was formulated. The flow curves of the ointment vehicle showed pseudoplastic properties. The rheological behavior as well as the adhesion on the mucosal membrane could be varied by the type and concentration of the polymer used and the base used for neutralization. During clinical studies, the ointment vehicle as well as a tretinoin (vitamin A acid) preparation for the treatment of lichen planus did not cause any local irritation or systemic side effects. Both vehicle and preparation were found to be pleasant for the patients to use. The new system of the mucosal adhesive ointment is not limited to the incorporation of tretinoin as the active agent; combined with other drugs the system could be applied to all types of mucosal membranes.

Adhesiveness↗
PubMed1975

Measurement of membrane potential and estimation of effective fixed-charge density in membranes.

Electrical potentials Em arising across cross-linked phenolsulfonate membrane separating NaCl solutions of molality M1 and M2 have been measured at 25 degrees C. These values of Em have been used in the Nernst equation to calculate values for the apparent transport number ti(app) for the counterion or the co-ion in the membrane. Values of ti(app) together with the limiting value for the cation transport number in the aqueous phase have been used in the equation developed by Kobatake and co-workers to evaluate the membrane permselectivity Ps as a function of external electrolyte concentration. With the help of the equation relating Ps to phiX, the effective fixed-charge density in the membrane (where phi is a constant, 0 less than phi less than 1, and X is the membrane stochiometric charge density and can be evaluated by chemical analysis of the membrane phase), values for phiX and phi have been determined. Values of phi were low in dilute solutions and increased with increase in the concentration of the external solution. Similar behavior was noted in the case of another membrane system, cross-linked polymethacrylic acid in contact with KOH solutions. On the other hand, the membrane system, "untreated" collodion in contact with KCl solutions, exhibited a behavior in which the values of phi, low in dilute solutions, increased and then decreased following a gradual increase in the external concentration. This slight divergence in its behavior was attributed to the heterogeneity of the collodion membrane structure. The reliability of this potentiometric method to estimate effective fixed-charge density in membranes has been discussed in relation to a similar but old method due to Teorell, Meyer and Sievers. Also the significance of the values derived for phi has been pointed out.

Evaluation Studies as Topic↗
PubMed1991

Clinical implications of resilient denture lining material research. Part II: Gelation and flow properties of tissue conditioners.

The clinical effectiveness of tissue conditioners and functional impression materials is influenced by their gelation and flow properties. Laboratory tests were previously conducted that simulated the conditions of clinical use to the extent possible on six commercial intraoral-gelling resilient denture liners. The liners were found to vary significantly in their gelation times and to flow throughout the 7-day study. Their initial flow after mixing was influenced most by the time of loading. While extrapolations to the clinical environment require caution, the results of this study imply that the dentist should (1) adapt clinical techniques to the gelation times of particular materials, (2) reduce the initial flow of some materials by delaying denture placement on the supporting mucosa, and (3) expect the materials to be effective tissue conditioners for at least 7 days.

Acrylic Resins↗
PubMed1991

In vivo fungal presence and growth on two resilient denture liners.

To determine whether two intraoral-setting resilient denture liners supported the in vivo presence or growth of oral commensal fungi, the liners were randomly placed in the mandibular complete dentures of 14 patients. Cytologic smears were made from the liner surfaces at 1 hour and 1, 2, 7, 14 and 30 days after intraoral placement. Yeast forms were observed in six patient trials of material A and in two trials of material B. Hyphae were observed in only one patient trial of material A and in two trials of material B. When yeast forms and hyphae findings were combined and were considered as indicative of fungal presence or growth, the prevalence up to 30 days was seven for material A and four for material B. Statistical analysis revealed no significant difference in the prevalence of fungal presence or growth between the two resilient denture liners tested.

Acrylic Resins↗
PubMed1996

Effects of acidic conditioners on dentine demineralization and dimension of hybrid layers.

OBJECTIVES: This study was aimed at investigating the relationships between dentine conditioning for different durations with different acids and (1) the resulting depth of dentinal demineralization and (2) the rebounding capacity of collapsed collagen due to primer and adhesive resin penetration. METHODS: Two commercial and four experimental acids were tested directly by light microscopic evaluation of the depth of decalcification of dentine, and indirectly by determination of the hybrid layer thickness and the total depth of demineralization effects on perpendicular sections through Gluma bonded composite resin specimens. RESULTS: Depths of demineralization increased by both acid concentrations and conditioning times following a logarithmic relationship. There was good agreement between the results of the direct and the indirect procedures. Thirty seconds' conditioning with 20% phosphoric-acid gel resulted in 10-microns hybrid layer thickness. This 20% compound was considered a suitable compromise as a uni-etch conditioner since 30-s etch duration also generated an effective enamel retentive pattern and at the same time a frosted enamel appearance for visual control of extent and efficacy of enamel conditioning.

Acid Etching, Dental↗
PubMed1997

The permeability of dental gloves following exposure to certain dental materials.

OBJECTIVES: This investigation sought to study the permeability of three commonly used clinical gloves when exposed to chemical agents. METHODS: A total of 35 gloves of each type were selected at random and were assigned to one of seven equally sized treatment groups. The effective barrier properties were investigated following treatment for 15 min with one of: acid etchant, Trim, cavity varnish, Hibiscrub, Hydrex and Vitremer using a dye permeability test. Following the chemical insult a 0.02% solution of erythrosine dye was introduced into each glove and the outer glove surface was washed with 10 ml of distilled water at intervals of 30, 60, 90 and 120 min. The percentage absorption of the collected washings, at 530 nm, was determined using a spectrophotometer. The results were compared with those values obtained from untreated gloves. RESULTS: Acid etchant and Hydrex had little effect on any of the gloves. Trim caused an increase in permeability of the vinyl gloves but had little or no effect upon those made of latex. Cavity varnish increased the permeability of both Biogel D and Tru-Touch but had no effect on Featherlite. The integrity of the latex gloves was diminished by Hibiscrub but little effect was observed in the case of the vinyl based glove. The permeability of all three gloves was increased by exposure to Vitremer liquid. CONCLUSIONS: Manufacturers should provide details of potential glove chemical interactions to assist dentists in glove selection.

Analysis of Variance↗
PubMed1990

Ceramic bracket bonding: a comparison of bond strength with polyacrylic acid and phosphoric acid enamel conditioning.

The purpose of this study was to compare in vitro shear bond strength with three different enamel surface preparations: (1) 37% phosphoric acid etch, (2) sulfated polyacrylic acid etch with removal of crystals by vigorous rinsing and (3) polyacrylic acid etch with crystal growth. Forty extracted human premolar teeth were divided into four groups of ten. Ceramic brackets were bonded to teeth in each of three groups. The fourth group used was bonded with metal brackets and a phosphoric acid enamel preparation. The same lightly filled resin cement was used for all groups. A shearing force was applied to the teeth. The results demonstrated that the shear force needed to debond with ceramic brackets was 21% greater than the shear force with metal brackets. The polyacrylic acid crystal growth group had shear bond strength values approximately one half as great as the phosphoric acid etch group when ceramic brackets were used. Bond failures in the phosphoric acid etch group were at the bracket/resin interface with the bulk of the resin remaining on the tooth compared with the polyacrylic acid crystal growth group in which the bond failure was at the enamel resin interface. Enamel fractures were not found when healthy nonrestored teeth were subjected to the shearing force. In a preliminary test using phosphoric acid etch and teeth with compromised enamel (large restorations involving three or more surfaces), half of the teeth fractured during debonding. The study demonstrated that a polyacrylic acid conditioning of the enamel surface produces different retentive surfaces, depending on the presence or absence of crystal growth.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid Etching, Dental↗
PubMed2005

Cartilage tissue engineering PLLA scaffold with surface immobilized collagen and basic fibroblast growth factor.

A previously reported "grafting and coating" method (J. Biomed. Mater. Res. (Appl. Biomater.) 63 (2002) 838) was modified and used to introduce stable collagen layer and incorporate basic fibroblast growth factor (bFGF) on PLLA scaffold surface to prepare tissue engineering scaffold with improved biocompatibility. To make the modification of the 3-D porous PLLA scaffold possible, grafting of polymethacrylic acid (PMAA) onto the PLLA surface was initiated by the -OOH/Fe2+ system instead of the UV light used in the former method. Water soluble carbodimmide chemistry was applied to graft collagen onto the PLLA scaffold surface, followed by physical coating of the collagen solution with or without basic fibroblast growth factor (bFGF). Surface modification of 2-D PLLA membrane was also done for fundamental understanding of the modification. The -COOH density on/in the PMAA grafted PLLA membrane/scaffold was measured by colorimetric method and the collagen content on/in the collagen immobilized PLLA membrane/scaffold was measured by ninhydrin method. Chondrocyte culturing on the collagen immobilized PLLA surfaces showed significantly improved cell spreading and growth. Incorporation of fibroblast growth factors in the collagen layer further enhanced the cell growth. This convenient and effective method can be used to prepare bioactive scaffolds with extra cellular matrix (ECM)-mimic composition for tissue engineering.

Animals↗
PubMed2005

A triclosan-containing compomer reduces Lactobacillus spp. predominant in advanced carious lesions.

OBJECTIVES: To assess the antimicrobial effect of acid etching or a triclosan-containing compomer on the cultivable microflora of incompletely excavated dentinal carious lesions. METHODS: Thirty detinal lesions were opened with a diamond burr. Subsequent to removal of the softened biomass a sample of dentin was taken from the cavity floor with a round bur. Ten cavities each were treated with 36% phosphoric acid (PH) for 15s, covered with a triclosan-containing compomer (TC) or received no treatment as control (CO). All lesions were restored with a compomer composite. Sampling was performed directly after etching in the PH group and at re-entry after 6 weeks in all groups. Aliquots were plated on blood agar and selective media for Lactobacilli (Rogosa) and mutans Streptococci (MSB). Cultures were incubated anaerobically for 7 days at 37 degrees C prior to quantitative assessment and biotyping of the isolates. RESULTS: Application of phosphoric acid resulted in initial reduction of the totally cultivable microflora (p=0.006). Evaluation of the total number of cultivable microflora after 6 weeks revealed no differences between the groups (p>0.05). Lactobacilli counts were significantly lower in the TC group compared to the PH and CO groups (p<0.05). No difference was detected between the PH and CO groups after 6 weeks. SIGNIFICANCE: Phosphoric acid initially reduces the number of microorganisms in carious dentin but not in the longer term. The experimental triclosan composite suppresses Lactobacilli species over a period of 6 weeks.

Acid Etching, Dental↗
PubMed2003

Dentin permeability: self-etching and one-bottle dentin bonding systems.

STATEMENT OF PROBLEM: There are many bonding systems available, with or without a prior acid etch. The mechanisms differ from system to system. Therefore it is important that the clinician know which are the most effective and which provide the best seal. PURPOSE: This study measured the infiltration of physiological saline solution across dentin after application of self-etching or 1-bottle dentin bonding systems. MATERIALS AND METHODS: Thirty-six extracted noncarious human third molars from patients 18 to 25 years old were used for this study. Dentin disks were cut from crown segments parallel to the occlusal surface at the incisal portion of the pulp cavity. The 36 disks, each 1 mm thick, were divided into 6 groups (n=6 per group), each of which received one of the following dentin bonding systems: Optibond Solo Plus and Excite, which have ethanol as the solvent; Prime & Bond NT, which has acetone as the solvent; Single Bond, which has a mixed solvent; and Clearfil SE Bond or Prompt L-Pop, both self-etching systems The hydraulic conductance, the volume of fluid transported across a known area of surface (0.28 cm(2)) per unit time under a unit pressure gradient (200 cm H(2)O), was analyzed for the self-etching and 1-bottle dentin bonding systems with the Flodec apparatus. Both sides of each specimen were etched with 36% phosphoric acid for 30 seconds. Measurements were made every 30 seconds for 15 minutes. The initial measurement served as the reference value for each specimen. The measurements were repeated when a smear layer had been formed and, finally, after one of the 6 bonding systems had been applied. The data were analyzed by use of analysis of variance and a posteriori tests (Fischer's PLSD, Duncan's new multiple range) with alpha=.05. RESULTS: The greatest mean reduction (40%, P<.05) in penetration was observed with the 4 products with conventional etching: Optibond Solo Plus, Single Bond, Excite, and Prime & Bond NT. The self-etching products were associated with reductions of 36% (Clearfil SE Bond) and 16% (Prompt L Pop). Standard deviations were high, 50% of the mean value, except for the Single Bond group (-42 +/- 13) and Prime & Bond NT (-41 +/- 14). CONCLUSION: Within the limitations of this study, the 4 bonding systems tested with a phosphoric acid before etching provided a greater decrease in dentin permeability than the 2 self-etching systems. The difference in permeability decrease was significant for Prompt L-Pop but not for Clearfil SE Bond.

Acetone↗