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PubMedDate not supplied

The relation between swelling properties and cross-linking of hydrogels designed for colon-specific drug delivery.

Copolymers of 2-hydroxyethyl methacrylate (HEMA) and methacrylic acid (MAA)-based hydrogels containing 5% and 10% of a cross-linking agent were studied as drug delivery systems. Terephthalic acid was covalently linked with HEMA, abbreviated as CA (cross-linking agent). Free radical cross-linking copolymerization of HEMA and methacrylic acid (MAA) in three different molar ratios, mixed with a particulate 3, 3-azobis (6-hydroxy benzoic acid) (ABHB) as an azo derivative of 5-aminosalicylic acid with the various ratios CA as cross-linking agent were carried out with using 2, 2, Azobisisobutyronitrile as initiator at the temperature range 60-70 degrees C. The compositions of the cross-linked three-dimensional polymers were determined by FTIR spectroscopy. Glass transition temperature of the network polymers was determined calorimetrically. The hydrolysis of drug-polymer conjugates was carried out in cellophane membrane dialysis bags containing an aqueous buffer solution (pH 7.4 and pH 1) at 37 degrees C. The drug-release profiles indicate that the amount of drug release depends on its degree of swelling and cross-linking.

Azo Compounds↗
PubMed1995

A sensitive procedure for the quantitation of free and N-(2-hydroxypropyl) methacrylamide polymer-bound doxorubicin (PK1) and some of its metabolites, 13-dihydrodoxorubicin, 13-dihydrodoxorubicinone and doxorubicinone, in human plasma and urine by reversed-phase HPLC with fluorimetric detection.

A high-performance liquid chromatographic assay has been developed and validated for the determination in plasma and urine of doxorubicin (DXR) and some of its metabolites released in vivo from an N-(2-hydroxypropyl)methacrylamide (HPMA) polymer containing DXR linked through its aminosugar moiety to the polymer via an oligopeptide spacer (PK1). The method also allows measurement of the DXR still bound to the polymer. Following addition of two internal standards, the free compounds were extracted twice with isopropanol-chloroform (25:75, v/v). The first extraction was performed at physiological pH and the second after buffering at pH 8.4, in order to extract the aglycones and the glycosides, respectively. Determination of total DXR (polymer-bound plus free DXR) was performed, after quantitative acid hydrolysis to release doxorubicinone from free or polymer-bound DXR, by extraction with the same solvent mixture at pH 7.4. In both cases the organic phase was evaporated to dryness; the compounds were then separated by reversed-phase high-performance liquid chromatography (HPLC) under isocratic conditions and quantitated by fluorimetric detection. In the chromatograms all the analytes appeared to be separated at the baseline and no interference from blank human plasma and urine was observed. The suitability of the method for in vivo samples was checked by the analysis of plasma and urine samples obtained from a cancer patient who had received a single intravenous dose of the test compound.

Blood↗
PubMed1999

Shear bond strengths of one-bottle adhesives to moist enamel.

PURPOSE: This study evaluated bond strengths of six one-bottle bonding agents and a control (primer plus unfilled resin) to moist enamel. MATERIALS AND METHODS: One-hundred and five bovine teeth were randomly assigned to seven groups of 15. Enamel was etched for 15 seconds with 35% phosphoric acid. Etched enamel was rinsed, and excess water was blotted with tissue paper. Following application of the adhesive, composite resin was bonded using a gelatin capsule technique. Shear bond strengths to enamel were determined using a universal testing machine (Instron Corp., Canton, Massachusetts). RESULTS: Mean bond strengths ranged from 21.9 MPa for OptiBond Solo (Kerr Corp., Orange, California) to 29.6 MPa for Prime & Bond 2.1 (Dentsply/Caulk, Milford, Delaware). Prime & Bond 2.1 had a significantly higher mean bond strength than the other adhesives. CLINICAL SIGNIFICANCE: The results of this study suggest that all of the one-bottle systems tested should provide clinically acceptable bonding to moist enamel.

Animals↗
PubMed1991

Hydrostatic intrapulpal pressure and bond strength of bonding systems.

The purpose of this study was to evaluate the effect of intra-pulpal pressure on shear bond strength of three light-cured glass-ionomer cements (GC lining cement, Vitrabond, and Zionomer) and four dentin bonding agents [Gluma/Scotchbond, Scotchbond 2, MBL, and Clearfil Photo Bond]. Buccal dentin surfaces were prepared just below the DEJ by means of a diamond bur. Dentin treatments were made for Zionomer (Zionomer conditioner), Scotchbond 2 (Scotchprep), MBL (10-3 solution), Clearfil PB (H3PO4), GC lining cement (Polyacrylic acid), and Gluma/Scotchbond (EDTA). Resin composites were inserted into tubes, positioned on dentin, cured, tested after five min or 24 h, and compared with samples bonded and stored under an intra-pulpal pressure of 36 cm of saline. After 24 h in superficial dentin, intrapulpal pressure reduced the bond strength only in MBL, Scotchbond 2, and Zionomer. Clearfil PB bond strength was increased, while Vitrabond, GC lining cement, and Gluma/Scotchbond were unaffected by the presence of pulpal pressure. However, in deep dentin, Scotchbond 2 and Clearfil PB shear bond strengths were significantly reduced by storage in the presence of 36-cm H2O pulpal pressure. Only Vitrabond remained unaffected by pulpal pressure in deep dentin.

Composite Resins↗
PubMed1987

Glycol methacrylate embedding in histotechnology: the hematoxylin-eosin stain as a method for assessing the stability of glycol methacrylate sections.

Glycol methacrylate (GMA) samples containing inhibitor in the range of 200-300 ppm were included in a standard embedding mixture. The pH of the GMA samples was measured as a 10% solution of the sample in distilled water. The acidity of GMA due to methacrylic acid causes background staining of sections after basic dyes. The concentration of GMA and the amount of impurities such as methacrylic acid (MA) and ethylene glycol dimethacrylate (EDMA) were measured by gas chromatography. Distinct variations in purity were found among five samples of GMA. Sections derived from GMA samples containing more than 2% EDMA showed few, if any, minifolds after staining with hematoxylin and eosin and were more stable in alcoholic and basic solutions; sections from purer GMA showed minifolds and were less stable. Addition of crosslinkers, EDMA or triethylene glycol dimethacrylate (TEDMA) prevented these artifacts. Crosslinkers clearly influence dimensional changes in sections. Addition of crosslinkers to GMA samples containing minimal amounts of MA improved the results. The possibility of obtaining a high quality GMA embedding medium is discussed.

Acrylates↗
PubMed1991

Fibrinolytic behaviour of streptokinase-immobilized poly(methacrylic acid-g-ethylene oxide).

Streptokinase was immobilized on poly(methacrylic acid-g-ethylene oxide) surfaces by means of a modified coupling reagent method. The surfaces were activated with a carbodiimide to form an O-acyl isourea derivative, which, upon addition of the enzyme, condensed to form the corresponding amide. The quantity of enzyme immobilized on the surface increased as the reaction time with carbodiimide and streptokinase increased. The fibrinolytic activity of the immobilized enzyme systems was measured by a clot lysis assay. The dynamics of fibrin clot lysis was investigated for a period of up to 500 min. The lysis reaction mechanism was found to approximate a first-order fibrin degradation. In addition, the kinetic rate constant was found to increase with increasing immobilized enzyme content.

Drug Carriers↗
PubMed2004

Improvement of protein loading and modulation of protein release from poly(lactide-co-glycolide) microspheres by complexation of proteins with polyanions.

A novel method was proposed to incorporate and modulate protein release from poly(lactide-co-glycolide) (PLGA) microspheres by a modified w/o/w emulsion solvent evaporation technique with poly(methacrylic acid) (PMAA)/insulin complex suspension as the inner aqueous phase instead of the neat protein solution. It was found that a reversible, water-insoluble complex could be formed between PMAA and insulin by electrostatic interactions. A great increase in insulin entrapment efficiency was observed as the PMAA/insulin complex was adopted to prepare PLGA microspheres. A large number of the complex particles adsorbed at the surface of the microspheres, resulting in the more rapid insulin release. The complexation and microencapsulation processes have little effect on insulin bioactivity, which was revealed by examination of the plasma glucose levels of the diabetic rats administrated with the microspheres.

Animals↗
PubMed1983

Polymer analogs of 3-chloro-4-benzyloxyphenylacetic acid and their pharmacological activity.

Polymer analogs of 3-chloro-4-benzyloxy-phenylacetic acid (BPh) were prepared, representing esters of BPh with three polymer alcohols: poly(vinyl alcohol) (P-I), poly(2-hydroxyethyl methacrylate) (P-II), and poly(2,3-dihydroxypropyl methacrylate) (P-III). Their anti-inflammatory activity was determined by testing their inhibitory effect on the growth of edema in the hind legs of rats. The relative activities of the esters P-I-BPh and P-II-BPh with respect to that of BPh are 0.06 and 0.10, respectively. In the case of P-III-BPh the activity is stronger (0.37), probably owing to the easier release of BPh from P-III-BPh due to hydrolysis. No prolonged effect of BPh polymeric esters could be achieved.

Animals↗
PubMed1998

Conjugates of monoclonal antibodies with polyelectrolyte complexes-- an attempt to make an artificial chaperone.

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) from rabbit muscle is a tetrameric enzyme. Inactivation of GAPDH at 50 degreesC or in the presence of 4 M urea proceeds via formation of inactive dimers followed by their aggregation. Antibodies (clone 6C5) were selected which bind specifically inactive dimers but not native tetramers. The simplified model of chaperone action when the inactive misfolded forms are removed from the reaction media preventing aggregation was developed using antibodies in combination with polyelectrolyte complexes. The antibodies were coupled covalently to polyanionic component of the complex, poly(methacrylic) acid. The treatment of inactivated GAPDH with this conjugate followed by its precipitation after equimolar addition of polycation, poly-(N-ethyl-4-vinylpyridinium) bromide, resulted in a significant increase in the specific activity of GAPDH. The restoration of specific activity was more complete in the experiments with lower GAPDH concentration and in the samples with lower inactivation degree, conditions where aggregation is less pronounced. Some aggregates are formed at high inactivation degree and high GAPDH concentration and observed as an increase in the solution turbidity. They could be removed by centrifugation. Antibody/polyelectrolyte complex treatment followed by centrifugation to remove insoluble aggregates resulted in nearly complete restoration of enzyme specific activity.

Animals↗
PubMed1976

Polymer-ceramic composite for tooth-root implant.

A new polymer-ceramic composite suitable for tooth-root implants has been developed in this study. This material exhibited the desirable combination of good mechanical properties, controlled porosity, and ease of processing. A thermal processing technique was utilized to polymerize acrylic acid (AA) in the presence of either 0.3 or 0.05 mu alumina particles. Porosity and pore size distribution were influenced by the alumina particle size and the processing technique. For a 50 vol % AA solution, the composite had an average compressive strength of 18,000 psi and 38% porosity when 0.3 mu filler particles were used. In comparison, the 0.05 mu alumina-filled composite had an average compressive strength of 28,000 psi with a 15% porosity. Data on the physical and structural characteristics of the composite are presented in this study. Based on these results, the composite material shows good potential for use in tooth-root implants as well as other orthopedic implant applications.

Absorption↗
PubMed1986

Bonding to porcelain and gold.

To test the effectiveness of bonding orthodontic attachments to porcelain, edgewise brackets were bonded to 160 lower incisor, porcelain denture teeth by means of two different resin systems and three different porcelain bonding agents. Bonding to porcelain was found to be not only effective, but the use of a porcelain primer before bonding resulted in shear strengths comparable to those achieved with conventional acid-etch enamel bonding when the same resin was used. Roughening the porcelain surface and bonding with a heavily filled resin without a porcelain primer provided shear strengths (30.6 lbs) comparable to conventional acid-etch enamel bonding with a lightly filled resin (28.8 lbs). Roughening the porcelain surface before bonding, adding porcelain primers, and using highly filled resins all added significantly to bond strength, but caused a progressively greater risk of porcelain fracture during debonding. One of three methods to polish porcelain completely restored a roughened porcelain surface to its former appearance. The porcelain bonding primers failed to provide a significant increase in bond strength when bonding to gold. However, a roughened gold surface bonded with a heavily filled resin provided shear strengths (27.3 lbs). comparable to conventional acid-etch enamel bonding by means of a lightly filled resin (28.8 lbs). The use of a highly filled resin on an intact, glazed porcelain surface without using a porcelain primer may provide sufficient bond strength clinically. If more bond strength is needed, the use of Reliance porcelain primer on an intact glaze is preferable to Ormco porcelain primer or Fusion. Still greater bond strength can be developed by roughening the porcelain surface before application of a primer and use of a highly filled resin. The potential for porcelain fracture in debonding, however, is much increased and it is questionable whether bond strengths of this magnitude are required clinically.

Bisphenol A-Glycidyl Methacrylate↗
PubMed2005

Fluorescence probe studies on the complexation between poly(methacrylic acid) and poly(N, N-diethylacrylamide).

The complexation between poly(methacrylic acid) (PMAA) and poly(N, N-diethylacrylamide) (PDEAM) in aqueous phase was studied by UV-vis and fluorescence probe techniques. It was demonstrated that the complexation of PMAA with PDEAM occurs within a pH range of 1-6.5 and along with the complexation, the conformation of PMAA changed from a hypercoiled to a loose coiled form. The complex ratio between the two polymers is 1:1 (PMAA:PDEAM, in monomer unit). Salt effect studies showed that the complexation occurred due to formation of hydrogen bonds between the two polymers. Based upon these conclusions and the "compact micelle-like structure" for PMAA at low pH, a "ladder" model was proposed for the structure of PMAA-PDEAM complex formed at low pH.

Acrylamides↗
PubMed2002

Surface modification of polycaprolactone with poly(methacrylic acid) and gelatin covalent immobilization for promoting its cytocompatibility.

Polycaprolactone (PCL) membrane was modified by grafting copolymerization of methacrylic acid (MAA) initiated under UV light. The covalent immobilization of gelatin on PCL-g-PMAA surface was consequently performed by using condensing agent, 1-ethyl-3-(3-dimethylamino propyl) carbodiimide hydrochloride. The occurrence of grafting copolymerization of PMAA and further immobilization of gelatin was confirmed by ATR-FTIR and X-ray photoelectron spectroscopy characterizations. The existence of carboxyl groups grafted on PCL surface was verified quantitatively by absorbance spectroscopy where rhodamine 6G was employed to react with carboxyl groups to generate an absorbance at 512 nm. The endothelial cell culture proved that the PCL membrane slightly modified with suitable amount of PMAA or gelatin had better cytocompatibility than control PCL or PCL membrane heavily modified with PMAA or gelatin.

Biocompatible Materials↗
PubMed2007

Anion- and cation-exchange MicroHPLC utilizing poly(methacrylates)-coated monolithic silica capillary columns.

A novel method was developed for the preparation of highly efficient anion- and cation-exchange microHPLC columns using an on-column polymerization of methacrylates having amine or sulfonic acid functional groups onto monolithic silica capillary columns modified with 3-methacryloxypropyltriethoxysilane as the anchor groups. The chromatographic evaluation of the columns using nucleic acids, nucleotides, and inorganic anions as samples showed the characteristics of the ion-exchange-type stationary phases. These columns exhibited higher separation efficiency when compared with the conventional particle-packed columns. A capillary column for the simultaneous anion- and cation-exchange separation could be prepared by a step-by-step functionalization. The advantages of this column preparation will include: (1) no need of column packing; (2) no need of the preparation of silane reagents possessing anion- and cation-exchange functionalities; (3) the amount of immobilized polymer could be controlled by changing polymerization conditions. These columns should be suitable for the separation of biologically active compounds by the microHPLC modes.

Anion Exchange Resins↗
PubMed1980

Controlled slow release of chemotherapeutic drugs for cancer from matrices prepared by radiation polymerization at low temperatures.

The vinyl polymer-chemotherapeutic agent composites of various shapes (rod, tablet, membrane, microsphere, and powder) were prepared by radiation polymerization at low temperatures for the purpose of durable controlled slow release of drugs from implanted matrices. Bleomycin hydrochloric acid, mitomycin C, and 5-fluorouracil were tested as chemotherapeutic drugs entrapped in poly(diethylene glycol dimethacrylate) including a small quantity of a polymer such as poly(styrene), poly(vinyl formal), poly(vinyl acetate), poly(methyl methacrylate) on polyethylene glycol No. 600. The release rates from the matrices depended much on the kind of polymer, drug, and monomer concentration in polymerization and also on the shape of the composite. The release of these drugs from polymer matrices obeyed the diffusion-controlled release mechanism based on Higuchi's equation and was durable for more than thirty days. It was found that the release rate can be controlled easily by design of the shapes and structures of the polymer matrices.

Antineoplastic Agents↗
PubMed2005

An oral delivery device based on self-folding hydrogels.

A self-folding miniature device has been developed to provide enhanced mucoadhesion, drug protection, and targeted unidirectional delivery. The main part of the device is a finger like bilayered structure composed of two bonded layers. One is a pH-sensitive hydrogel based on crosslinked poly(methyacrylic acid) (PMAA) that swells significantly when in contact with body fluids, while the other is a non-swelling layer based on poly(hydroxyethyl methacrylate) (PHEMA). A mucoadhesive drug layer is attached on the bilayer. Thus, the self-folding device first attaches to the mucus and then curls into the mucus due to the different swelling of the bilayered structure, leading to enhanced mucoadhesion. The non-swelling PHEMA layer can also serve as a diffusion barrier, minimizing any drug leakage in the intestine. The resulting unidirectional release provides improved drug transport through the mucosal epithelium. The functionality of this device is successfully demonstrated in vitro using a porcine small intestine.

Adhesives↗
PubMedDate not supplied

Influence of two dentin bonding systems on the demineralization of the root surface.

It has been assumed that dentin adhesives can prevent root surface caries. The aim of this study was to determine the caries-protective effect of two different dentin bonding systems on the demineralization of root surfaces in vitro. The root surfaces of 60 freshly extracted caries-free human molars were thoroughly cleaned and polished, thereby removing the cementum. The teeth were then coated with acid-resistant nail varnish, exposing two rectangular windows of 6 mm2 each. One window served as an untreated control, while the other window was treated with a dentin bonding system. The specimens were distributed among the following experimental groups--Group 1: Syntac, Heliobond (no air thinning); Group 2: Syntac, Heliobond (as recommended); Group 3: Syntac, without Heliobond; Group 4: Prime & Bond 2.0 (no air drying); Group 5: Prime & Bond 2.0 (as recommended); Group 6: Prime & Bond 2.0 (dentin pretreated with 36% phosphoric acid). Subsequently, all specimens were demineralized for 6 days with acidified gel (HEC, pH 4.8, 37 degrees C). From each tooth, three dentinal slabs were cut perpendicular to the polished surface of the windows. The slabs were ground to a thickness of 80 microns and imbibed with water. The depth of the respective demineralized areas was determined using a polarized light microscope. All control specimens exhibited lesions with a mean depth of 67 microns. In Groups 2, 3, and 5 the lesion depth was reduced significantly, while in Groups 1, 4, and 6 no lesions could be detected. It was concluded that the demineralization of the root surface can be impeded by application of the dentin adhesives tested.

Acrylates↗
PubMed1998

Design of microencapsulated chitosan microspheres for colonic drug delivery.

Among the different approaches to achieve colon-selective drug delivery, the use of polymers, specifically biodegraded by colonic bacteria, holds great promise. In this work a new system which combines specific biodegradability and pH-dependent release is presented. The system consists of chitosan (CS) microcores entrapped within acrylic microspheres. Sodium diclofenac (SD), used as a model drug, was efficiently entrapped within CS microcores using spray-drying and then microencapsulated into Eudragit L-100 and Eudragit S-100 using an oil-in-oil solvent evaporation method. The size of the CS microcores was small (1.8-2.9 microns) and they were encapsulated within Eudragit microspheres (size between 152 and 233 microns) forming a multireservoir system. Even though CS dissolves very fast in acidic media, at pH 7.4, SD release from CS microcores was delayed, the release rate being adjustable (50% dissolved within 30-120 min) by changing the CS molecular weight (MW) or the type of CS salt. Furthermore, by coating the CS microcores with Eudragit, perfect pH-dependent release profiles were attained. No release was observed at acidic pHs, however, when reaching the Eudragit pH solubility, a continuous release for a variable time (8-12 h) was achieved. A combined mechanism of release is proposed, which considers the dissolution of the Eudragit coating, the swelling of the CS microcores and the dissolution of SD and its further diffusion through the CS gel cores. In addition, infrared (IR) spectra revealed that there was an ionic interaction between the amine groups of CS and the carboxyl groups of Eudragit, which provided the system with a new element for controlling the release. In conclusion, this work presents new approaches for the modification of CS as well as a new system with a great potential for colonic drug delivery.

Chitin↗