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At least 793 records · Page 44Linked to original sources
PubMed2006

The phase behaviour of poly(styrene-co-methacrylic acid)/poly(2,6-dimethyl-1,4-phenylene oxide) by inverse gas chromatography.

The miscibility behaviour of blends of poly(styrene-co-methacrylic acide) (PSMA-12) containing 12% of methacrylic acid with poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) at five different compositions has been studied by inverse gas chromatography (IGC). The adequacy of two types of solvents (solvents and precipitants) has been tested in order to detect the glass transition temperature, T(g). A single T(g) has been observed in PSMA-12/PPO blends containing less than 67wt% of PPO. Two glass transition temperatures appeared, however, in blends containing higher PPO content. The polymer-polymer interaction parameters have been calculated in the molten state (260-280 degrees C), their values being in good agreement with the observed phase behaviour. Moreover, the methods proposed by Farooque-Deshpande and Huang for obtaining the true polymer-polymer interaction parameters have been compared. Finally, the ability of IGC in order to determine T(g)s has been extended to a ternary system, PSMA-12/PPO/EMV4P-8 poly(ethylmethacrylate-co-4-vinylpyridine) which, depending on the composition, gives a single, two and even three T(g)s.

Chromatography, Gas↗
PubMed2005

Preparation and characterization of intelligent core-shell nanoparticles based on poly(D,L-lactide)-g-poly(N-isopropyl acrylamide-co-methacrylic acid).

New thermo-responsive, pH-responsive, and biodegradable nanoparticles comprised of poly(D,L-lactide)-graft-poly(N-isopropyl acrylamide-co-methacrylic acid) (PLA-g-P(NIPAm-co-MAA)) were developed by grafting biodegradable poly(D,L-lactide) onto N-isopropyl acrylamide and methacrylic acid. A core-shell type nano-structure was formed with a hydrophilic outer shell and a hydrophobic inner core, which exhibited a phase transition temperature above 37 degrees C suitable for biomedical application. Upon heating above the phase transition temperature, PLA-g-P(NIPAm-co-MAA) nanoparticle showed a polarity increase of pyrene in either buffer solution or intra-hepato-carcinoma cells as determined by fluorescence measurement, indicating that the structure of nanoparticles caused leakages from outer shell copolymers aggregation and collapsed. The drug loading level of 5-fluorouracil (5-FU) encapsulated in the PLA-g-P(NIPAm-co-MAA) nanoparticles can be as high as 20%. The release of 5-FU from nanoparticles was strongly controlled by the pH in the aqueous solution. Based on these results, PLA-g-P(NIPAm-co-MAA) nanoparticles can be used as a drug carrier for intracellular delivery of anti-cancer drug.

Acrylamides↗
PubMed2006

Vaccination of mice against intestinal Trichinella spiralis infections by oral administration of antigens microencapsulated in methacrilic acid copolymers.

BALB/c and NIH mice have been successfully vaccinated against the intestinal nematode Trichinella spiralis by oral administration of crude larval extracts (CLE) and excretory-secretory (ES) products derived from first stage T. spiralis larvae (L1) encapsulated in microcapsules made of copolymers of the metacrylic acid (Eudragit L100). Oral vaccination stimulated the secretion of IFN-gamma and inhibited the secretion of IL-4 in spleen and mesenteric lymph nodes (MLN) of BALB/c mice. In vaccinated mice the proportion of CD4+ cells increased (p<0.05) in Peyer's patches (PP) and decreased (p<0.05) in spleen whereas the proportion of CD19+ cells decreased (p<0.05) in both PP and spleen, with regard to unvaccinated controls. No variation was evident for the proportion of CD8+ cells. Oral vaccination elevated the antigen-specific serum IgG1 and IgA (p<0.05) as well as the antigen-specific IgA response in MLN (p<0.05). It is concluded that this way of vaccination induced a concurrent Th1/ Th2 local and systemic responses that are protective and at the same time they may help balancing the strong Th2 response triggered by helminth infections.

Adjuvants, Immunologic↗
PubMed2004

Experimental study of attenuation properties of normoxic polymer gel dosimeters.

The change in linear attenuation coefficient with absorbed dose has been investigated for aqueous polyacrylamide, gelatine and tetrakis (PAGAT) and aqueous methacrylic acid, gelatine and tetrakis (MAGAT) normoxic polymer gel dosimeters using tetrakis (hydroxy methyl) phosphonium chloride as the antioxidant. The measured linear attenuation coefficient increased linearly with absorbed dose up to 15 Gy for PAGAT gels and 10 Gy for MAGAT gels. Computerized tomography (CT) numbers or Hounsfield units (H) were calculated from the linear attenuation coefficients and compared with values obtained using a CT scanner. Both calculated and measured CT numbers followed a similar pattern when fitted with a biexponential curve. The CT numbers obtained from linear attenuation measurements were found to be greater than that obtained with the CT scanner for both PAGAT and MAGAT polymer gels. The H-dose sensitivities of the MAGAT and PAGAT polymer gel dosimeters measured on a CT scanner were calculated to be (0.85 +/- 0.08) H Gy(-1) and (0.31 +/- 0.03) H Gy(-1), respectively. The H-dose sensitivities of the MAGAT and PAGAT polymer gel dosimeters from attenuation measurements were found to be (1.10 +/- 0.66) H Gy(-1) and (0.34 +/- 0.01) H Gy(-1), respectively.

Acrylic Resins↗
PubMed2004

Temperature and pH-responsive polymeric composite membranes for controlled delivery of proteins and peptides.

This work was focused on the investigation of temperature and pH-responsive polymeric composite membranes and their permeability to proteins and peptides in response to environmental stimuli. The composite membranes were prepared from nanoparticles of poly(N-isopropylacrylamide-co-methacrylic acid) of various NIPAAm:MAA ratios dispersed in a matrix of a hydrophobic polymer. N-Benzoyl-L-tyrosine ethyl ester HCl, momany peptide, Leuprolide, vitamin B(12), insulin, and lysozyme were used as model solutes. The morphology of the membranes was examined with SEM and permeation of the solutes was measured using side-by-side diffusion cells at varied temperatures and pH. Permeability of the solutes across the membranes increased with increasing temperature or particle concentration, while decreased with increasing pH and molecular size of the solutes. Membranes containing nanoparticles of more NIPAAm units exhibited higher thermal sensitivity, and those with higher MAA content showed more pH responsiveness, which was in line with the temperature and pH-responsive volume change of the nanoparticles. The change in permeability was quickly detected following the application of the stimuli. These results and partition study using vitamin B(12) supported the proposed gel-pore mechanism of solute permeation through these composite membranes.

Acrylamides↗
PubMedDate not supplied

Effect of rotary instrumentation on composite bond strength with simulated pulpal pressure.

This study evaluated the effect of cutting teeth with different types of burs at various speeds on shear bond strength using Prime and Bond NT (Dentsply/DeTrey). A simulated pulpal pressure of 25-mmHg, equivalent to 34 cmH2O, was created in a false pulpal chamber filled with distilled water and maintained for seven days. The human teeth were divided into six groups of 10 teeth each: fine grit straight fissure diamond bur in air rotor (DA), fine grit straight fissure diamond bur in micromotor (DM), crosscut fissure carbide bur in air rotor (CCA), crosscut fissure carbide bur in micromotor (CCM), plain fissure carbide bur in micromotor (CM) and #600-grit silicon carbide paper (SiC). The tooth surfaces in these groups were cut under copious air-water spray and treated with Prime and Bond NT after etching with 38% phosphoric acid. Composite restorations were then prepared with TPH spectrum (Dentsply/ DeTrey). After soaking in water at 37 degrees C for 24 hours, the specimens were loaded at a 45 degrees angle to their longitudinal axes by using a Z 010 Universal Testing Machine (Zwick), and shear bond strengths were determined at a crosshead speed of 2 mm/minute. All of the specimens were then observed under Stereomicroscope at 10x. Statistical analysis was made using one-way and two-way ANOVA and t-test (p < 0.05). The bond strengths achieved with a fine grit straight fissure diamond bur, a crosscut fissure carbide bur in air rotor and a crosscut fissure carbide bur in micromotor, were significantly higher than a fine grit straight fissure diamond bur, a plain fissure carbide bur and #600-grit silicon carbide abrasive paper in the micromotor. Therefore, selecting an appropriate bur and its speed may improve bonding for adhesive systems, although crosscut fissure carbide burs produced high bond strengths at either speed used.

Acrylic Resins↗
PubMed1987

Marginal adaptation of composite resin restorations placed with or without intermediate low-viscous resin. An SEM investigation.

The marginal adaptation to acid-etched enamel of a hybrid and a microfilled composite resin, placed with or without intermediate low-viscous resin, was investigated in vivo. Each of 37 patients received four class III test fillings, one with each filling technique. The evaluation was done with the use of SEM on replicas from the cavity margins, 1 week and 1 year after insertion of the fillings. The observed defects were marginal cracks or fractures, chip fractures, and enamel fractures. In the comparison of the size and volume of the marginal defects no significant differences were seen after 1 week between fillings of the same material placed with or without an intermediate resin. However, after 1 year the hybrid resin fillings with an intermediate resin showed significantly better adaptation than the ones without. No difference was found between the microfilled resin fillings. The hybrid resin fillings showed significantly better marginal adaptation than the microfilled resin fillings after 1 week. A further increase of the differences was observed after 1 year.

Adhesives↗
PubMed1999

One-year clinical evaluation of SureFil packable composite.

The purpose of this trial was to clinically evaluate SureFil high-density posterior composite for Class II restorations of permanent first and second molars. All teeth were restored in occlusion with the natural dentition. After cavity preparation, the enamel was etched for 15 seconds with 34% phosphoric acid. No liner/base material was used for the dentin. Two applications of Prime and Bond 2.1 were placed for adhesion to the exposed dentin and etched enamel. One coat of adhesive was cured for 10 seconds with a curing light, and one thin coat was spread with a gentle jet of air. The cavity was restored in 3-mm to 5-mm increments. Evaluation was assessed immediately after placement (baseline), and at 3 months, 6 months, 9 months, and 1 year for retention, leakage, marginal integrity, color stability, abrasive resistance, surface staining, surface texture, postoperative sensitivity, and secondary caries. The restorations were evaluated indirectly for wear using a modified USPHS and indirect cast comparison method. At baseline, 25 restorations were graded Alfa in all categories. At 3-, 6-, and 9-month recalls (N = 24), all restorations were graded Alfa in all categories. At the 1-year recall (N = 20), there were three Bravos for surface staining.

Adult↗
PubMed1999

Influence of neutron irradiation on Eudragit coated tablets: validation of neutron activation II.

The in vitro characteristics of enteric coated acetylsalicylic acid tablets and cores were compared before and after irradiation with thermal neutrons, 2, 4, 7 or 15 min at 1.1.1013 neutrons cm-2s-I. The irradiation procedure affected the coated formulation to a greater extent than the cores. Drug release from tablets was already affected after 2 min of exposure, whereas the cores showed no significant inhibition of release until after 15 min of irradiation, leading to the conclusion that the effects of irradiation were caused by a combination of changes both in the core and the coating. Both tablets and cores showed an increase in the disintegration time following irradiation. Scanning electron micrographs (SEM) of non-irradiated cores/tablets and cores/tablets irradiated for 15 min, showed clear differences in the structure of the surface. SEM of the tablets irradiated for 15 min, showed that the irradiation had caused the film to loosen from the core in several places. SEM of the cross-sections of both irradiated tablets and cores showed a partially melted surface above stacked layers with reduced porosity.

Acrylic Resins↗
PubMed1991

Effect of human saliva on surface degradation of composite resins.

The amount of methacrylic acid produced by incubation of the dimethacrylate ester TEGDMA in human whole saliva was measured. The conversion rate of TEGDMA was determined in stimulated saliva from dental students and in unstimulated saliva from both dental students and patients. The differences in mean conversion rate measured in the three groups were not statistically significant (P = 0.346). The mean conversion rate +/- SD for all saliva samples was 4.54 +/- 3.24 mumol MAA/L.h. The surface of BISGMA/TEGDMA-polymer specimens treated with porcine liver esterase in activities equivalent to those found in human saliva exhibited a lower Wallace microhardness than the surface of untreated specimens. Polymer specimens incubated in human saliva exhibited a similar reduction in the microhardness. The results demonstrated that enzymes in human saliva are capable of softening the surface of dimethacrylate polymers presumably by inducing a hydrolysis of methacrylate ester bonds. The mechanical removal of a surface layer softened by hydrolases will expose a new surface layer to enzymatic attack. The enzymatic softening may thus contribute to the in vivo wear of composite restorations.

Bisphenol A-Glycidyl Methacrylate↗
PubMed2005

Encapsulating live cells with water-soluble chitosan in physiological conditions.

A new class of microcapsules was prepared under physiological conditions by polyelectrolyte complexation between two oppositely-charged, water-soluble polymers. The microcapsules consisted of an inner core of half N-acetylated chitosan and an outer shell of methacrylic acid (MAA) (20.4%)-hydroxyethyl methacrylate (HEMA) (27.4%)-methyl methacrylate (MMA) (52.2%) (MAA-HEMA-MMA) terpolymer. Both 400 and 150 kDa half N-acetylated chitosans maintained good water solubility and supplied enough protonated amino groups to coacervate with terpolymer at pH 7.0-7.4, in contrast to other chitosan-based microcapsules which must be prepared at pH <6.5. The viscosity of half N-acetylated chitosan solutions between 80 and 3000 cPas allowed the formation of microcapsules with spherical shape. Molar mass, pH and concentration of half N-acetylated chitosan, and reaction time, influenced the morphology, thickness and porosity of the microcapsules. Microcapsules formed with high concentration of half N-acetylated chitosan exhibited improved mechanical stability, whereas microcapsules formed with low concentration of half N-acetylated chitosan exhibited good permeability. This 3D microenvironment has been configured to cultivate sensitive anchorage-dependent cells such as hepatocytes to maintain high level of functions.

Animals↗
PubMed2001

Formation of quasi-regular compact structure of poly(methacrylic acid) upon an interaction with alpha-chymotrypsin.

Structure and dynamic properties of free poly(methacrylic acid) (PMA) and PMA complexed with alpha-chymotrypsin (CT) were studied using the time resolved fluorescence anisotropy technique. We have found that the interaction of PMA with CT induces the formation of a quasi-regular structure of PMA. At a CT/PMA weight ratio of 4:1 the interaction with CT leads to formation of approximately four equal segments of polyelectrolyte, each binding one CT molecule and characterized by an independent rotational mobility. Increase of the CT/PMA weight ratio above 8:1 gives rise to the overall rotation of the whole enzyme-polyelectrolyte complex. In water-ethanol mixtures the mobility of PMA segments containing CT decreases and the structure of the complex becomes even more rigid due to enhancement of the electrostatic interaction between CT and PMA. Formation of the compact and quasi-regular structure of the complex is perhaps the main reason behind the enhancement of enzyme stability and suppression of enzyme aggregation in water-organic cosolvent mixtures.

Animals↗
PubMed2004

Preparation and characterisation of thiolated poly(methacrylic acid)-starch compositions.

The development of mucoadhesive polymer systems, which start swelling in the intestine after oral administration without an enteric coating, might be the key for drug delivery systems exhibiting a prolonged intestinal residence time. The preparation and characterisation of such polymeric excipients was therefore the aim of this study. A poly(methacrylic acid)-cysteine conjugate (thiolated PMAA) exhibiting 747.8+/-30.9 micromol thiol groups per gram polymer was co-precipitated with starch at pH 3. The resulting thiolated PMAA-starch composition consisting of 24% thiolated PMAA and 76% starch was lyophilised and analysed with regard to its swelling behaviour as well as to its cohesive and mucoadhesive properties. Results demonstrated that the thiolated PMAA-starch composition does not swell at all in a simulated gastric fluid. In contrast, a 4- and 6-fold increase in weight by water uptake was observed at pH 5 and 7, respectively. Disintegration studies demonstrated improved cohesive properties due to the immobilisation of thiol groups on PMAA, which are involved in the formation of stabilising inter- and/or intrachain disulfide bonds. Tensile studies demonstrated a total work of adhesion of 90.2+/-15.2 and 27.5+/-2.9 microJ for thiolated PMAA-starch and PMAA-starch, respectively. These results were confirmed by mucoadhesion studies utilising the rotating cylinder method. Thiolated PMAA-starch represents therefore a promising novel mucoadhesive excipient, which might provide a prolonged residence time of various delivery systems in the intestine.

Polymethacrylic Acids↗
PubMed2006

Release behaviour and biocompatibility of drug-loaded pH sensitive particles.

The purpose of this work was to investigate the physical properties of drug-loaded poly(methacrylic acid-g-ethylene glycol) {P(MAA-g-EG)} particles, their biocompatibility with the gastrointestinal tract of rats and also the effects of these particles on the tight junctions of the rat intestinal epithelium. Model drugs such as diltiazem HCl, diclofenac Na, ciprofloxacin HCl and isoniazid were used in this study. P(MAA-g-EG) particles were prepared by free radical solution polymerization of methacrylic acid (MAA) and poly(ethylene glycol) (PEG). The loading efficiency of the model drugs in the particles and in vitro release profiles were investigated in pH 7.4 phosphate buffer and in gradually pH changing buffers (pH 1.2, 5.8, 6.8 and 7.4). The stability of free particles and drug-loaded particles was established by Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC). In conclusion, P(MAA-g-EG) particles controlled the release rate of small molecular weight model drugs according to the pH of the medium. Stability of those particles loaded with drugs did not change in accelerated stability conditions. Histopathological results indicated that loading drugs to the particles prevented cell and tissue damage after 20 h. Free particles showed no change of tight junctions after 2 and 10 h. The results of TEM showed that increasing the amount of P(MAA-g-EG) particles from 100 to 385 mg clearly opened the tight junction, but with serious epithelial cell disruption.

Administration, Oral↗
PubMedDate not supplied

The influence of microencapsulation using Eudragit RS100 on the hydrolysis kinetics of acetylsalicylic acid.

Homogeneous Eudragit RS100 matrix microspheres containing molecularly dispersed acetylsalicylic acid (ASA) were prepared in order to investigate the effect of encapsulation on the decomposition rate of a hydrolytically susceptible drug. ASA-loaded microspheres of this non-eroding polymer matrix were analysed at predetermined time points following immersion of the microspheres in temperature controlled buffer systems at pH 1.2 or pH 12.1 at 30, 40 or 50 degrees C. The mass balance of the total amount of solutes (ASA and SA) initially located within the microsphere interior was equal to the sum of the amount of solutes remaining in the microsphere interior and the amount of solutes in the aqueous phase at any time during the course of the study. Each analysis involved the quantitation of four species; the drug and decomposition product, salicylic acid (SA), in both the microspheres phase and the external aqueous phase. A simple model system using first-order rate approximations for the concurrent Fickian diffusion and hydrolysis decomposition of the drug resulted in a multiexponential expression which adequately described the time-course profile of the drug. SA-loaded microspheres were used as a control under similar conditions to determine the magnitude of the contribution of microsphere phase hydrolysis of ASA to the overall rate of drug loss from the microspheres. Results indicated that microspheres phase hydrolysis of ASA was minimal. Even after 900 h of immersion in pH 12.1 buffer some ASA remained within the microsphere. It is postulated that the matrix incorporated drug is essentially shielded from hydrolytic attack until it is liberated into the external aqueous environment. Electrostatic association of the drug with the charged quaternary residues in the polymer along with the limiting availability of water within the microsphere may be responsible for the observed stability of ASA in aqueous swollen ASA-loaded Eudragit microspheres.

Acrylic Resins↗
PubMedDate not supplied

New class of ultrathin, highly cell-adhesion-resistant polyelectrolyte multilayers with micropatterning capabilities.

Hydrogen-bonded multilayers comprised of polyacrylamide (PAAm) and a weak polyelectrolyte, such as poly(acrylic acid) (PAA) or poly(methacrylic acid) (PMA), were investigated for their surface-cell interactions. The assembled films were lightly cross-linked thermally or photochemically in order to render them stable in a physiological environment. Both PAA/PAAm and PMA/PAAm multilayers were found to exhibit a high resistance to the adhesion (cytophobicity) of mammalian fibroblasts, even with only a single bilayer coating. Protein adsorption to the multilayers, as revealed by surface plasmon resonance measurements, was greatly reduced for fibronectin and serum-containing medium. In situ swelling experiments indicate that the H-bonded multilayers are hydrogellike coatings capable of a high level of swelling in buffered solution. Utilizing the H-bonding nature of these multilayers, we were able to micropattern the films to create more complex cell-resistant/-adhesive surfaces. The long-term stability of the cell-resistant multilayers was found to be exceptionally good even under conditions (pH 7.4, buffered solution) where a high degree of swelling takes place. No degradation of the micropatterned films was observed over a period of a month, during which time the multilayer coatings remained highly resistant to cell-adhesion.

Acrylic Resins↗
PubMed1996

Photodynamic crosslinking of proteins. I. Model studies using histidine- and lysine-containing N-(2-hydroxypropyl)methacrylamide copolymers.

One of the mechanisms by which cells might be damaged during the photodynamic therapy (PDT) of tumors is via the covalent crosslinking of proteins to proteins or to other molecules in the cell. It has been suggested that photodynamically generated singlet oxygen interacts with photo-oxidizable amino acid residues such as His, Cys, Trp and Tyr in one protein molecule to generate reactive species, which in turn interact non-photochemically with residues of these types or with free amino groups in another protein molecule to form a crosslink. In some cases, photochemically generated free radicals may be involved in crosslinking. This paper describes studies on the use of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers containing epsilon-aminocaproic acid side chains terminating in His (P-Acap-His) or Lys (P-Acap-Lys) as models for the photodynamic crosslinking of proteins. The model copolymer P-Acap-His had a weight-averaged molecular weight of about 22,000 and contained four to five His residues per copolymer molecule. The model copolymer P-Acap-Lys had a weight average molecular weight of about 18,000 and contained four to five Lys residues per copolymer molecule. The extent of photocrosslinking, as sensitized by rose bengal, was estimated by measuring the increase in the viscosity of model copolymer solution after various periods of illumination. The extent of intermolecular crosslinking was estimated from the changes in molecular weight distribution of samples before and at the end of illumination as determined by size exclusion chromatography. Photodynamic crosslinking occurred between P-Acap-His molecules and between P-Acap-His and P-Acap-Lys molecules. The higher the concentration of macromolecules in the solution, the higher is the yield of intermolecular crosslinking. Oxygen was necessary for crosslinking, and azide inhibition studies indicated the involvement of singlet oxygen.

Fluorescent Dyes↗
PubMed2004

Effect of sodium hypochlorite on dentin bonding in primary teeth.

PURPOSE: The aim of this study was to evaluate the effect of sodium hypochlorite (NaOCl) on the shear bond strength (SBS) using three bonding systems in primary dentin. MATERIALS AND METHODS: Forty-five sound extracted primary molars were selected. The crowns were longitudinally sectioned, embedded in polystyrene resin, and flattened until a dentin surface was reached. The samples were assigned to 6 groups (n = 15): G1, Single Bond (SB); G2, NaOCl + SB; G3, Prime & Bond 2.1 (PB); G4, NaOCl + PB; G5, Clearfil SE Bond (CSE); G6, NaOCl + CSE. All the adhesive systems were applied according to the manufacturers' instructions, except for the application of 10% NaOCl solution for 60 s in groups 2, 4 (after acid etching), and 6 (before applying adhesive system). The composite resin was placed in increments in a mold and light cured for 20 s. The samples were stored in distilled water at 37 degrees C for 24 h and submitted to SBS testing with a crosshead speed of 0.5 mm/min. The failure sites were observed with SEM. The data were treated with ANOVA and Tukey's tests (p < 0.05). RESULTS: There was no statistically significant difference between the groups with or without treatment of the substrate with NaOCl, regardless the material used. The SBS averages in MPa (+/-SD) were: G1: 15.8(1.9)a; G2: 14.6(1.3)a; G3: 10.2(0.7)a; G4: 9.9(0.2)a; G5: 13.3(1.2)a; and G6: 10.7(1.0)a. There was a statistically significant difference between the materials (SB > or = CSE > or = PB). Mixed failure was the failure type most frequently observed for all groups. CONCLUSION: Dentin surface treatment with NaOCl did not affect the resin-dentin bonding strength in primary teeth.

Acrylic Resins↗