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PubMed1993

Enzymatic cleavage of disaccharide side groups in insoluble synthetic polymers: a new method for specific delivery of drugs to the colon.

A series of water-insoluble acrylic polymers containing disaccharide side groups were synthesized and evaluated in vitro. A cellobiose-derived monomer, 4-O-beta-D-glucopyranosyl-1-methacrylamido-1-deoxy-D-glucitol, was prepared and copolymerized with methacrylic acid. Two different modes of polymerization were used to give two products, P-1 and P-2. A homopolymer, P-3, was also synthesized using the same method as P-2. The degradation of the disaccharide side groups in these polymers and the monomer was evaluated by incubation with beta-glucosidase and measurement of the amount of glucose cleaved. It was found that the degradation rate increased in those polymers possessing lower contents of the disaccharide side groups (i.e. higher content of methacrylic acid). Scanning electron microscopy (SEM) observations of cross-sectioned slabs of P-1 visualized the degradation of the polymer. The enzymatic reaction caused a porous structure to be formed. The increased porosity may be used for the specific release of drugs into organs that contain large amounts of beta-glucosidases, such as the human colon.

Carbohydrate Sequence↗
PubMed2004

Compression of pellets coated with various aqueous polymer dispersions.

Pellets coated with a new aqueous polyvinyl acetate dispersion, Kollicoat SR 30 D, could be compressed into tablets without rupture of the coating providing unchanged release profiles. In contrast, the compression of pellets coated with the ethylcellulose dispersion, Aquacoat ECD 30, resulted in rupture of the coating and an increase in drug release. Plasticizer-free Kollicoat SR coatings were too brittle and ruptured during compression. The addition of only 10% w/w triethyl citrate as plasticizer improved the flexibility of the films significantly and allowed compaction of the pellets. The drug release was almost independent of the compression force and the pellet content of the tablets. The inclusion of various tabletting excipients slightly affected the drug release, primarily because of a different disintegration rate of the tablets. The core size of the starting pellets had no influence on the drug release. Pellets coated with the enteric polymer dispersion Kollicoat 30 D MAE 30 DP [poly(methacrylic acid, ethyl acrylate) 1:1] lost their enteric properties after compression because of the brittle properties of this enteric polymer. Coating of pellets with a mixture of Kollicoat MAE 30 DP and Kollicoat EMM 30 D [poly(ethyl acrylate, methyl methacrylate) 2:1] at a ratio of 70/30 and compaction of the pellets resulted in sufficient enteric properties.

Acrylic Resins↗
PubMed1998

The use of 13C solid state NMR to elucidate physico-chemical association in Eudragit RS100 microencapsulated acyl esters of salicylic acid.

A series of homogeneous Eudragit RS100 matrix microspheres containing molecularly dispersed acylated esterified homologues of salicylic acid, (acetylsalicylic acid, valerylsalicylic acid, or caprylsalicylic acid) were prepared in order to investigate the effect of encapsulation on solid-state orientation of the encapsulated molecule. Electrostatic association of the drug with the charged quaternary residues in the polymer may be responsible for the previously observed stability of acetylsalicylic acid (ASA) in aqueous swollen ASA-loaded Eudragit RS100 microspheres. Evaluation of the 13C nuclear magnetic resonance spectra for evidence of structural association of the incorporated probe molecules indicated that alteration of the microenvironment of the incorporated solutes had occurred. For instance, increasing the aliphatic character of the acyl side chain resulted in an increase in the upfield shift of the acyl bearing aromatic ring carbon, (C2), in the incorporated probe molecule as compared to the unincorporated probe molecule. Similarly, a downfield perturbation in the chemical shift of the free acid bearing aromatic ring carbon, (C1), was also observed. This microenvironment electrostatic shielding in the proximity of the ester carbonyl is attributed to an increase in the association of the probe molecule with the polymer subunits. Thereby, it is postulated that the matrix incorporated probe molecule is essentially shielded from hydrolytic attack until it is liberated into the external aqueous environment.

Acrylic Resins↗
PubMed2003

Studies in preparation and evaluation of pH-independent sustained-release matrix tablets of verapamil HCl using directly compressible Eudragits.

The objective of the present study was to investigate the impact of formulation factors on the properties of a 12h modified-release formulation of verapamil HCl. A 2(3) full factorial design was employed to investigate the influence of amount of Eudragit RS PO/RL PO (X1, a matrixing agent), HPMC K4M (X2, an auxiliary matrixing agent cum binder) and PEG 4000 (X3, channelling agent cum plasticizer). The tablets were prepared by direct compression and they were evaluated for in vitro dissolution studies in 0.1 N HCl. The time required for 90% of the drug release (t90) and similarity factor (f2) were used as responses for the selection of most appropriate batches. Swelling and fluid penetration studies were carried out in 0.1 N HCl. Time required for 90% of the drug release (t90) was calculated by using an appropriate kinetic model for each batch. An ideal drug release profile (i.e., 25% in the first hour and a constant drug release thereafter) was considered as a reference release profile for calculation of f2. Multiple regression analysis was adopted to evolve refined models for t90. The required release pattern was shown by batches containing a low level of Eudragit RS PO/RL PO (30% w/w), low level of HPMC K4M (10% w/w), and high level of PEG 4000 (15% w/w). Response surface plots are shown for t90. These formulations showed slower drug release in alkaline medium (pH 7.2). Succinic acid and KH2PO4 were incorporated in the matrix in order to obtain pH-independent drug release. Swelling of tablets and fluid penetration in the matrix were found to be influenced by the selected independent variables. This study demonstrates that the desired drug release pattern can be obtained by adopting a systematic formulation approach.

Biological Availability↗
PubMed1999

Interfacial micromorphology and tensile bond strength of dentin bonding systems after NaOCl treatment.

PURPOSE: The objective of this study was to test the hypothesis that NaOCl treatment of acid-etched dentin would not lower the tensile bond strength of adhesive resins, but would eliminate the hybrid layer. MATERIALS AND METHODS: One hundred twenty teeth and three different bonding agents were used for SEM- and CLSM-visualization of the dentin-composite interface and for bond strength measurements. After etching with phosphoric acid, 75 dentin samples were pretreated with 10% NaOCl. The other 75 samples were etched only with phosphoric acid and were kept as controls. Composite was bonded to the pretreated surfaces with a bonding resin. RESULTS: NaOCl-treated samples: hybrid layers were not visible, but resin tags and resin penetration through lateral branches of tubules were prominent. Layers of unfilled resin were not apparent for Gluma CPS and Prime & Bond 2.1. Hypochlorite treatment of acid-etched dentin resulted in reduced bond strengths for specimens bonded with Syntac and Gluma CPS, but such treatment increased bond strength for Prime & Bond 2.1 bonded specimens. CONCLUSION: The removal of the collagen layer with NaOCl can enhance or decrease bond strengths, depending on the bonding agent used.

Composite Resins↗
PubMed2003

Poly(2-alkylacrylic acid) polymers deliver molecules to the cytosol by pH-sensitive disruption of endosomal vesicles.

The permeability barrier posed by cell membranes represents a challenge for the delivery of hydrophilic molecules into cells. We previously proposed that poly(2-alkylacrylic acid)s are endocytosed by cells into acidified vesicles and are there triggered by low pH to disrupt membranes and release the contents of endosomes/lysosomes to the cytosol. If this hypothesis is correct, these polymers could be valuable in drug-delivery applications. The present paper reports functional comparisons of a family of three poly(2-alkylacrylic acid)s. Poly(2-propylacrylic acid) (PPAA), poly(2-ethylacrylic acid) (PEAA) and poly(2-methylacrylic acid) (PMAA) were compared in red-blood-cell haemolysis assays and in a lipoplex (liposome-DNA complex) assay. We also directly examined the ability of these polymers to disrupt endosomes and lysosomes in cultured human cells. Our results show that: (i) unlike membrane-disruptive peptides, the endosomal-disruptive ability of poly(2-alkylacrylic acid)s cannot necessarily be predicted from their haemolytic activity at low pH, (ii) PPAA (but not PEAA or PMAA) potently facilitates gene transfection by cationic lipoplexes and (iii) endocytosed poly(2-alkylacrylic acid)s are triggered by luminal acidification to selectively disrupt endosomes (not lysosomes) and release their contents to the cytosol. These results will facilitate the rational design of future endosomal-disrupting polymers for drug delivery.

Biological Assay↗
PubMed1999

Use of acryclic and metacrylic acid derivatives as sustained release matrices for theophylline hydrate tablets.

Carbopol 941, an acrylic acid polymer and "Eudragit L100-55, a metacylic acid polymer, were compared as sustained release matrix devices for theophylline hydrate tablets. The theophylline tablets containing 0 to 30% of either of the polymer were prepared using the direct compression method. In vitro drug release studies were carried out in 0.1 N HCl, simulated gastric fluid without pepsin (SGF) and simulated intestinal fluid without pancreatin (SIF). A relatively prolonged release of theophylline from the two polymer matrices for an 8 hr-release period was detected. At 20% w/w and in 0.1 N HCl there were no significant drug releases from the two matrices within the first 2 hrs; after this period, carbopol 941 exerted a more retardant effect on drug releases. At 30% w/w, release rate from Eudragit L100-55 was faster for a 6 hr period with a steady state release maintained at 50% for 4 hrs. The rates of theophylline release from the matrices depended on the pH of the dissolution media and on the properties of the two matrices. While drug release from Carbopol 941 was faster in acidic media, faster release occurred from Eudragit L100-55 in alkaline medium. Drug release kinetics from the two matrices was of a general mixed order, but the first order and the diffusion-controlled mechanism were occurring simultaneously. We can conclude that carbopol 941 can be considered a better-sustained release matrix in directly compressed theophylline tablets comparing with Eudragit L100-55.

Acrylates↗
PubMed2000

In vitro evaluation of two adhesive systems used with compomer filling materials.

AIM: To evaluate and compare the in-vitro shear bond strength, microleakage and dentine-restorative interface of a self-etching/self-priming dentine bonding agent with a three-component dentine-bonding agent. METHOD: For shear bond strength (SBS) testing 30 non-carious human molars were used of which 15 were tested with Non-Rinse Conditioner (NRC)/Prime&Bond NT (PBNT) and Dyract AP and 15 were tested with Scotchbond Multi-Purpose Plus (SBMP) and F2000. For the microleakage evaluation cavity preparations were made on the facial surfaces of 30 non-carious human premolars of which 15 were restored with NRC and PBNT with Dyract AP and 15 were restored with SBMP and F2000. The dentine-restorative interface was examined through a confocal scanning laser microscope (CSLM). RESULTS: The mean SBS of PBNT and SBMP were 12.8 and 18.1 MPa, respectively. The microleakage scores showed NRC/PBNT leaked on the dentine side in 13 of the 15 specimens examined. On the enamel side two of the 15 specimens showed microleakage. With SBMP no microleakage was observed on either enamel or dentine sides. The CSLM images show clear resin tag and hybrid layer formation for both the materials examined although SBMP showed better and deeper penetration into the dentine with longer resin tags. SBMP showed resin tags measuring about 150 mm while the hybrid layer measured about 5 mm. The length of the resin tags as well as the thickness of the hybrid layer for PBNT were 20 mm Pounds and 2 mm Pounds, respectively. CONCLUSIONS: The acid-etch technique of SBMP produced higher bond strength and no microleakage when compared with the self-etching/self-priming 'non-rinse technique' of NRC with PBNT. Thus it can only be speculated that SBMP should be the superior in the clinical situation.

Compomers↗
PubMed2007

In vitro and in vivo confocal Raman study of human skin hydration: assessment of a new moisturizing agent, pMPC.

The hydration capacities of a biomimetic polymer, 2-methacryloyloxethylphosphorylcholine polymer (pMPC), alone and microencapsulated, in association with another well known hydrating polymer, Hyaluronic acid, were investigated in vitro on skin models and in vivo on volunteers by using confocal Raman microspectroscopy. The hydration impact and the relative water content in the Stratum corneum were calculated from the Raman spectra using the OH (water)/CH3 (protein) ratio. Moreover, the follow-up of the presence of pMPC through the Stratum corneum was possible with confocal Raman microspectroscopy, using a characteristic vibration of pMPC, different from that of the encapsulating material. From our in vitro measurements, the improved hydration of the Stratum corneum was confirmed by the use of the encapsulated form of pMPC, which was higher when combined with Hyaluronic acid. On the basis of these in vitro findings, we validated this trend in in vivo measurements on 26 volunteers, and found a good correlation with the in vitro results. Mechanical and ultrastructural studies have been carried out to demonstrate the positive effects of the pMPC on the Stratum corneum function, namely the interaction with lamellar lipids and the plasticizing effects, which are both supposed to spell out the moisturizing effect. This study demonstrates the efficiency of a original hydrating agent, pMPC, entrapped with Hyaluronic acid in a new type of microcapsules by the use of a novel tool developed for both in vitro and in vivo approaches. This indicates a new step to evaluate and improve new moisturizers in response to the cosmetics or dermatologic demands.

Adult↗
PubMed1986

Surface discoloration of restorative resins in relation to surface softening and oral hygiene.

Restorative resins are susceptible to softening caused by organic acids produced in plaque. Consequently, plaque-covered resin restorations may be liable to pronounced surface staining. In the clinical part of the study a relationship between surface staining and local oral hygiene was demonstrated. This may be explained by the results from the laboratory part of the study, in which a relationship between surface staining and softening was found.

Bisphenol A-Glycidyl Methacrylate↗
PubMed2002

Comparison of antibacterial activity of simplified adhesive systems.

PURPOSE: To determine and compare the intrinsic antibacterial activity of commercially available simplified adhesive systems. MATERIALS AND METHODS: The antibacterial activity of five self-etching/priming one-step adhesives and three priming/bonding adhesives against Streptococcus mutans, Lactobacillus casei, and Actinomyces viscosus was assessed by the agar disc-diffusion test and determination of the minimum inhibitory/bactericidal concentration (MIC/MBC). Twenty microl of each adhesive was impregnated into a paper disc and placed on an agar plate inoculated with a bacterial suspension, with or without light-irradiation. The size of inhibition zones produced around the specimens was measured after 48 hours of incubation. The MIC values were measured by serial microdilution assays, visually examining the growth of bacteria after incubation with each adhesive for 24-48 hours. The subcultures were made on BHI agar plates from the wells showing no visible growth of bacteria, and the MBC values were determined based on production of colonies. Two primers in two-step self-etching systems and an experimental primer containing chlorhexidine were tested for reference. The results of disc-diffusion tests were analyzed by ANOVA and Fisher's PLSD test. RESULTS: The size of inhibition zones produced by adhesives varied among the brands. None of the available commercial adhesives showed significant inhibition against all three of the bacterial species tested. Light-irradiation reduced the size of inhibition zones for a few materials, but a similar trend to the effectiveness of non-irradiated specimens was observed. The antibacterial activity of commercial products determined in terms of MIC/MBC values were different from the results by disc-diffusion tests. The self-etching adhesives with low pH were not necessarily more effective than priming/bonding solutions, and no significant relationships between the acidity and antibacterial effects were found. Compared with commercial products, an experimental primer containing chlorhexidine produced significantly larger inhibition zones against all species (P < 0.05) and exhibited greater bacteriostatic/bactericidal activity, demonstrating lower MIC/MBC values.

Actinomyces viscosus↗
PubMedDate not supplied

Design and development of multiparticulate system for targeted drug delivery to colon.

A multiparticulate system combining pH-sensitive property and specific biodegradability for colon-targeted delivery of metronidazole has been investigated. Cross-linked chitosan microspheres were prepared from an emulsion system using liquid paraffin as the external phase and solution of chitosan in acetic acid as the disperse phase. The multiparticulate system was prepared by coating cross-linked chitosan microspheres exploiting Eudragit L-100 and S-100 as pH-sensitive polymers. Morphology and surface characteristics of the formulations were determined by scanning electron microscopy. Particle size of the chitosan microspheres was determined by optical microscopy while that of coated microspheres was determined by particle size analyzer. In vitro drug-release studies were performed in conditions simulating stomach-to-colon transit in presence and absence of rat caecal contents. The size of the microspheres was small and they were efficiently microencapsulated within Eudragit microspheres, forming a multireservoir system. By coating the microspheres with Eudragit pH-dependant release profiles were obtained. No release was observed at acidic pH; however, when it reached the pH where Eudragit starts solublizing there was continuous release of drug from the formulation. Further, the release of drug was found to be higher in the presence of rat caecal contents, indicating the susceptibility of chitosan matrix to colonic enzymes released from rat caecal contents.

Animals↗
PubMed2004

Bond strength and micro morphology of a self-etching primer versus a standard adhesive system with varying etching times in primary teeth.

AIMS: These were to firstly evaluate the shear bond strength of a composite resin to primary dental enamel treated with a standard adhesive system but with varying phosphoric acid etching times along with a self-etching prime, secondly to analyse the etching patterns using SEM. METHODS: Forty primary molars were used. In the first three groups, following acid etching, a layer of Prime & Bond NT adhesive was employed, and in group 4 the self-etching adhesive system (Prompt-L-Pop) was used. A composite cylinder (Spectrum, Denstply, Germany) was then applied. After processing of the samples, the teeth were subjected to shear stress using an Instrom universal machine. The study of primary enamel morphology after etching for different time periods and using different etching systems was carried out with a scanning electron microscope. STATISTICS: Data were analysed using one way ANOVA, followed by Scheffé, test to determine differences between groups. RESULTS: In the groups subjected to acid etching for 5 and 15 seconds significant differences were recorded versus the self-etching group (p<0.0001). Regarding the SEM study of primary enamel morphology, there was predominately a clear and marked type 2 etching pattern. CONCLUSIONS: Longer acid etching times for primary enamel do not appear necessary, as 15 seconds suffice to obtain retentive etching patterns, and the bonding strengths obtained with the traditional etching technique followed by two-step adhesive application are sufficient to ensure good composite resin bonding to the enamel surface. However, the self-etching adhesive system employed yields less than optimum bonding strength to primary enamel surfaces.

Composite Resins↗
PubMed1980

Enzymatic addition of modified cytosine nucleotides to DNA. Methacrylate polymerization by an azo pyrimidine.

An azo pyrimidine that induces the polymerization of 1-glyceryl methacrylate has been prepared. 1-Glyceryl methacrylate contains substituent glycol groups for binding heavy atoms for subsequent electron microscopic studies. Oxodation of 1-methyl N4-ureidocytosine (compound 1A) with N-bromosuccinimide produced 4-aminocarbonylazo-2-pyrimidinone (compound 2A). This orange compound shows a broad peak (lambda max = 349 nm) in its ultraviolet absorption spectrum. Mixing compound 2A with mildly acidic aqueous solutions of 1-glyceryl methacrylate (pH 3.6) resulted in polymerization of the methacrylate. Under these conditions, the ester 1-glyceryl methacrylate does not hydrolyze appreciably as judged by oxidation of the glycol groups with NaIO4 and spectrophotometric analysis of the HCHO liberated using Schiff's reagent. Attachment of azo nucleotides to the 3'-terminus of DNA was achieved in two steps. First, N4-ureidocytosine deoxynucleotides were enzymatically added to single strand DNA primers using calf thymus terminal deoxynucleotidyl transferase, Co2+, and N4-ureido-2'-deoxycytidine 5'-triphosphate (prepared by the HSO3--catalyzed transamination reaction of dCTP with semicarbazide). Second, these modified nucleotides were oxidized with N-bromosuccinimide to produce DNA that contained azo pyrimidine nucleotides at its 3'-end (azoDNA). Upon adding acid to the azoDNA, the azo nucleotides decomposed. If these nucleotides induce methacrylate polymerization upon decomposition as did compound 2A, it may be possible to mark the location of DNA termini in situ for electron microscopy by attaching heavy atoms to the poly(1-glyceryl methacrylate) formed. Such studies may elucidate the nature and location of the ends of the eukaryotic chromosomal DNA molecule in both chromosomes and interphase nuclei.

Acrylic Resins↗
PubMed2006

Preparation and evaluation of Eudragit S 100 microspheres as pH-sensitive release preparations for piroxicam and theophylline using the emulsion-solvent evaporation method.

Microencapsulation of the anti-inflammatory drug piroxicam and the anti-asthmatic drug theophylline was investigated as a means of controlling drug release and minimizing or eliminating local side effects. Microspheres of both drugs that are different in the chemical nature and size were successfully encapsulated at a theoretical loading of 25% with the pH sensitive Eudragit S 100 polymer using the emulsion-solvent evaporation method. Solvent composition, stirring rate and the volume of the external phase were adjusted to obtain reproducible, uniform and spherical microspheres. The size distribution of microsphere batches generally ranged from 125-500 microm with geometric means close to 300 microm. Optical light microscopy was used to identify the microsphere shape. Drug loading was determined by completely dissolving the microspheres in an alkaline borate buffer at pH 10. In vitro dissolution studies were carried out on the microspheres at 37 degrees C (+/-0.5 degrees C) at 100 rpm with USP Dissolution Apparatus II using the procedure for enteric-coated products at two successive different pH media (1.2 and 6.5). Both preparations exhibited an initial rapid release in the acidic medium with theophylline showing a larger increase in the amount released during this stage. The drug release was sustained for both preparations at pH 6.5 with theophylline microspheres, showing more extended release. Drug release rate kinetics followed a Higuchi spherical matrix model for both microsphere preparations.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1990

A 3-year evaluation of Gluma and Gluma/Scotchbond for restoration of cervical erosions.

Gluma and Gluma/Scotchbond were used in cervical abrasion/erosion lesions mediating a bond between a resinous restorative material and dentin. The lesions were restored without acid etching of enamel and without use of an intermediary layer of an enamel bonding agent. 142 restorations were placed. The restorations were evaluated clinically using the USPHS-system at the baseline and every half year during a 3-yr period. After 36 months the Gluma and Gluma/Scotchbond restorations showed a 14.3% and 7.4% cumulative loss of retention respectively. No secondary caries was observed during the evaluation period.

Adult↗
PubMed1990

[Visible-light initiator system using thiobarbituric acid derivatives with methyl substituent].

Seven 2-thiobarbituric acid derivatives with methyl substituents were synthesized. Experimental visible-light curing resins were prepared using these compounds as a reducing agent in the dl-camphorquinone (CQ)-reducing agent initiator system. The effects of methyl substitution for thiobarbituric acid on initiation behavior of CQ-thiobarbituric acid initiator system were examined by analysis of polymerization of triethylene glycol dimethacrylate (3 G) in DSC and depth of cure. The solubility of thiobarbituric acid derivatives in 3 G was markedly changed by the introduction of the methyl group. Although the methyl group substitution at position 1 (3) in thiobarbituric acid improved the solubility of the acid in 3 G, it did not enhance the initiation ability. Maximum exothermic rate, time at maximum exothermic peak, amount of insufficiently polymerized layer and depth of cure were significantly improved by the introduction of one methyl group at the position 5. Thus the initiation ability was enhanced by the substitution. However, the introduction of two methyl groups at position 5 did not promote polymerization, but the inhibitory effect became apparent as the concentration of the reducing agent was increased.

Composite Resins↗
PubMed2004

Hydrophilic chain length dependence of the ionic amphiphilic polymer monolayer structure at the air/water interface.

Detailed analysis of an interesting poly(methacrylic acid) (PMAA) brush structure in water of a diblock copolymer [(Et(2)SB(m)-b-(MMA)(n), where Et(2)SB is diethylsilacyclobutane] monolayer reported previously was performed by X-ray and neutron reflectometry and indicated that the hydrophilic layer formed with a relatively long PMAA chain is not a simple layer but is divided into two layers, that is, a "carpet"-like dense PMAA layer near the hydrophobic layer and a polyelectrolyte brush layer. The hydrophilic chain length dependence of the diblock copolymer monolayer was analyzed using m:n = 30:x polymer samples, especially of the PMAA double layer structure. With the increase in PMAA chain length in polymer samples, a carpet layer is mainly formed up to n approximately 50. With further increase in the PMAA chain length beyond n approximately 50, a well-defined brush layer appears. On the other hand, the variation in hydrophobic layer thickness with methacrylic acid unit is minimum at the critical PMAA length, that is, n approximately 50 under a constant surface pressure condition. It is strongly suggested that the two discrete layers contribute differently to surface pressure. Furthermore, from the comprehensive viewpoint, the major factor for brush formation was clarified not to be the absolute length of the PMAA chain, but the ratio of PEt(2)SB and PMAA chain length is an important factor.

Air↗