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Release Behavior (release + behavior)
Kinds of Release Behavior Selected AbstractsSynthesis, Characterization and Drug Release Behavior of pH-Responsive O-carboxymethyl Chitosan-graft-poly(N-vinylpyrrolidone) Hydrogel Beads,ADVANCED ENGINEERING MATERIALS, Issue 12 2009Liwei Ma In this work, the carboxymethyl chitosan (CMCTS) grafted poly(N-vinylpyrrolidone) (PVP) copolymers were synthesized. The hydrogel beads containing VB2 were prepared from the copolymers by an ionic crosslinked. The experimental results shown that VB2 drug release rate from those beads decreased with the increasing grafting percentage, crosslinker concentration and pH value of the medium. Besides, the beads have the better control ability for releasing of model drug than CMCTS does. [source] Structural Evolution and Copper-Ion Release Behavior of Cu-pHEMA Hybrids Synthesized In Situ,ADVANCED ENGINEERING MATERIALS, Issue 11 2009Yen-Yu Liu Abstract A novel Cu-pHEMA hybrid was successfully prepared by in situ photopolymerization of 2-hydroxyethyl methacrylate (HEMA) monomer in the presence of Cu(II) copper ions, following an in situ chemical reduction. Experimental observations indicate that intermolecular interactions such as the coupling force and hydrogen bonding between the Cu and the hydroxyl groups further stabilize the hybrid structure to a considerable extent. Localization of the metallic copper particles within the pHEMA network structure as a result of those intermolecular interactions gives rise to the formation of discretely distributed nanocrystallites with particle sizes ranging from 5 to 25,nm in diameter. A crystallographic change of the Cu nanophase from an amorphous-like to a crystalline structure is observed as the H2O:HEMA molar ratio increases, upon synthesis, accompanied with an increase in the particle size. A relatively slow and sustained release of the Cu (in the form of cupric ions) from the hybrids was measured for a time period of about 10 days, which also illustrates a Cu(II)-induced proliferation of the endothelial cells over a relatively small range of release rate of the Cu from the hybrids. Such a new type of Cu-loaded hybrid hydrogel is expected to be compatible and may be considered as a candidate biomaterial for biomedical/therapeutic uses. [source] Encapsulation and/or Release Behavior of Bovine Serum Albumin within and from Polylactide-Grafted Dextran MicrospheresMACROMOLECULAR BIOSCIENCE, Issue 4 2004Tatsuro Ouchi Abstract Summary: Polylactide (PLA)-grafted dextran (Dex- graft -PLA) of various contents of sugar units was synthesized by anionic polymerization of L -lactide (L -LA) using the alkoxide of partially trimethylsilylated dextran (TMSDex) and subsequently removing the trimethylsilyl (TMS) groups. The copolymer showed different solubility from L -LA homopolymer with increasing the content of sugar units. We prepared bovine serum albumin (BSA)-loaded microspheres (MS)s according to a water-in-oil-in-water emulsion-solvent evaporation/extraction method using methylene chloride/DMSO as an organic cosolvent. MSs prepared from Dex- graft -PLA [MS(Dex- graft -PLA)s] exhibited higher loading efficiency of BSA than MSs prepared from PLLA [MS(PLLA)s]. The in vitro release rate of BSA from MS(Dex- graft -PLA) was faster than that from MS(PLLA). BSA released from MS(Dex- graft -PLA) maintained the secondary structure of native BSA to a great extent, compared with BSA released from MS(PLLA). Confocal fluorescence images of the differential interference micrographs over the fluorescence images of MS(PLLA) and MS(Dex- graft -PLA). [source] Electrospun PEG,PLA nanofibrous membrane for sustained release of hydrophilic antibioticsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2010Xiuling Xu Abstract Reported in this study is the successful incorporation of a hydrophilic antibiotic drug, tetracycline hydrochloride (TCH), into electrospun PEG,PLA nanofibrous membrane without loss of its bioactivity. Degradation behavior of the copolymer was studied in vitro. Release behavior of TCH from the electrospun membrane and antimicrobial effects of the TCH-loaded membrane against Staphylococcus aureus culture were investigated. The medicated nanofibrous membrane demonstrated sustained release of TCH over 6 days and was found to be effective in inhibiting growth of S. aureus. In addition, increasing the antibiotic drug content in the electrospun membranes was found to enhance the anti-bacterial effectiveness of the medicated fiber mats. And the combination of mechanical barriers provided by the electrospun biodegradable nanofibrous membranes and their capability of local sustained delivery of antibiotics made these membranes more useful in biomedical applications, particularly as new wound dressings for ulcers caused by diabetes or other diseases, and to provide a better means of treatment for these malignant wounds and ulcers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Release behavior of freeze-dried alginate beads containing poly(N -isopropylacrylamide) copolymersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Jae-Hyung Choi Abstract Beads composed of alginate, poly(N -isopropylacrylamide) (PNIPAM), the copolymers of N -isopropylacrylamide and methacrylic acid (P(NIPAM- co -MAA)), and the copolymers of N -isopropylacrylamide, methacrylic acid, and octadecyl acrylate (P(NIPAM- co -MAA- co -ODA)), were prepared by dropping the polymer solutions into CaCl2 solution. The beads were freeze-dried and the release of blue dextran entrapped in the beads was observed in distilled water with time and pH. The degree of release was in the order of alginate bead < alginate/PNIPAM bead , alginate/P(NIPAM- co -MAA) bead < alginate/P(NIPAM- co -MAA- co -ODA) bead. On the other hand, swelling ratios reached steady state within 20 min, and the values were 200,800 depending on the bead composition. The degree of swelling showed the same order as that of release. Among the beads, only alginate/P(NIPAM- co -MAA- co -ODA) bead exhibited pH-dependent release. At acidic condition, inter- and intraelectrostatic repulsion is weak and P(NIPAM- co -MAA- co -ODA) could readily be assembled into an aggregate due to the prevailing hydrophobic interaction of ODA. Thus, it could block the pore of bead matrix, leading to a suppressed release. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Monodisperse Mesoporous Silica Spheres Inside a Bioactive Macroporous Glass,Ceramic Scaffold,ADVANCED ENGINEERING MATERIALS, Issue 7 2010Renato Mortera In the field of bone tissue engineering, monosized MCM-41 spheres have been incorporated inside a bioactive glass,ceramic macroporous scaffold belonging to the SiO2CaOK2O (SCK) system so obtaining a multiscale hierarchical composite. The MCM-41-SCK system was prepared by dipping the glass,ceramic scaffold into the MCM-41 synthesis solution and was characterized by means of XRD, micro-XRD, N2 sorption and scanning electron microscopy. The MCM-41 spheres inside the scaffold are highly uniform in diameter, as those synthesized in powder form. The adsorption capacity of the composite toward ibuprofen is three times higher than that of the MCM-41-free scaffold, because of the presence of the ordered mesoporous silica. Also the release behavior in SBF at 37,°C is strongly affected by the presence of MCM-41 inside the scaffold macropores. [source] Fabrication and Drug Delivery of Ultrathin Mesoporous Bioactive Glass Hollow FibersADVANCED FUNCTIONAL MATERIALS, Issue 9 2010Youliang Hong Abstract Ultrathin mesoporous bioactive glass hollow fibers (MBGHFs) fabricated using an electrospinning technique and combined with a phase-separation-induced agent, poly(ethylene oxide) (PEO), are described. The rapid solvent evaporation during electrospinning and the PEO-induced phase separation process demonstrated play vital roles in the formation of ultrathin bioactive glass fibers with hollow cores and mesoporous walls. Immersing the MBGHFs in simulated body fluid rapidly results in the development of a layer of enamel-like apatite mesocrystals at the fiber surfaces and apatite nanocrystals inside the hollow cores. Drug loading and release experiments indicate that the drug loading capacity and drug release behavior of the MBGHFs strongly depends on the fiber length. MBGHFs with fiber length >50,µm can become excellent carriers for drug delivery. The shortening of the fiber length reduces drug loading amounts and accelerates drug release. The MBGHFs reported here with sophisticated structure, high bioactivity, and good drug delivery capability can be a promising scaffold for hard tissue repair and wound healing when organized into 3D macroporous membranes. [source] Smart Hydrogels Co-switched by Hydrogen Bonds and ,,, Stacking for Continuously Regulated Controlled-Release SystemADVANCED FUNCTIONAL MATERIALS, Issue 4 2010Fang Li Abstract A series of hydrogels with continuously regulatable release behavior can be achieved by incorporating hydrogen bonding and ,,, stacking co-switches in polymers. A poly(nitrophenyl methacrylate- co -methacrylic acid) hydrogel (NPMAAHG) for control over drug release is fabricated by copolymerizing 4-nitrophenyl methacrylate and methacrylic acid using ethylene glycol dimethacrylate as a crosslinker. The carboxylic acid groups and nitrylphenyl groups form hydrogen bonds and ,,, stacking interactions, respectively, which act as switches to control the release of guest molecules from the polymers. As revealed by the simulated gastrointestinal tract drug release experiments, the as-synthesized NPMAAHG hydrogels can be regulated to release only 4.7% of drugs after 3,h in a simulated stomach and nearly 92.6% within 43,h in the whole digestive tract. The relation between the release kinetics and structures and the mechanism of the smart release control are analyzed in terms of diffusion exponent, swelling interface number, drug diffusion coefficient, and velocity of the swelling interface in detail. The results reveal that the release of guest molecules from the hydrogels can be continuously regulated for systemic administration by controlling the ratio of the hydrophilic hydrogen bonds and the hydrophobic ,,, stacking switches. [source] Protein-Release Behavior of Self-Assembled PEG,, -Cyclodextrin/PEG,Cholesterol HydrogelsADVANCED FUNCTIONAL MATERIALS, Issue 18 2009Frank van de Manakker Abstract This paper reports on the degradation and protein release behavior of a self-assembled hydrogel system composed of , -cyclodextrin- (,CD) and cholesterol-derivatized 8-arm star-shaped poly(ethylene glycol) (PEG8). By mixing ,CD- and cholesterol-derivatized PEG8 (molecular weights 10, 20 and 40 kDa) in aqueous solution, hydrogels with different rheological properties are formed. It is shown that hydrogel degradation is mainly the result of surface erosion, which depends on the network swelling stresses and initial crosslink density of the gels. This degradation mechanism, which is hardly observed for other water-absorbing polymer networks, leads to a quantitative and nearly zero-order release of entrapped proteins. This system therefore offers great potential for protein delivery. [source] Nanogels of poly(acrylic acid): Uptake and release behavior with fluorescent oligothiophene-labeled bovine serum albuminJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010Simona Argentiere Abstract Nanometer-sized poly(acrylic acid) (PAA) hydrogels were synthesized by emulsion polymerization of methyl acrylate and subsequent acidic hydrolysis. The nanohydrogel was characterized by spectroscopic methods (FTIR and 1H-NMR) and scanning probe techniques, and their pH-dependent swelling behavior was studied by dynamic light scattering. To determine the suitability of PAA nanogels as pH-sensitive carriers for biomedical applications, uptake and release of an oligothiophene fluorophore and its albumin conjugated from PAA nanogels were investigated as a function of pH by absorption and photoluminescence measurements. It was observed that uptake and release processes of both the oligothiophene and its conjugate could be controlled by changing the pH of the external solution. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Controlled release of argatroban from PLA film,Effect of hydroxylesters as additives on enhancement of drug releaseJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Akira Mochizuki Abstract The aim of this study was to develop a drug eluting stent that prevents vein restenosis. For this, we selected argatroban as the study drug and poly(lactic acid) (PLA) as the matrix. To enhance the release of argatroban from PLA film, the addition of hydroxylesters (additives) was investigated. The additives investigated were diethyl tartrate (DET), diethyl malate (DEM), and triethyl citrate (TEC). Marked enhancement of drug release was observed in DET-added film, while TEC- or DEM-added film showed little enhancement. To clarify the effect of DET, the release profile based on the contents of the drug and DET in the film and the effect of alkyl chain length of tartrate were studied. Tartrates used were dimethyl, di- i -propyl, and di- n -butyl esters (DMT, DiPT, and DnBT, respectively), and the enhancement order was DMT , DET , DiPT , DBT , PLA alone. The reasons for enhancement were discussed from the viewpoint of drug release behavior, degradation of PLA, water uptake within the film, and SEM observations. It was concluded that enhancement of drug release was due to large amounts of water uptake within the film which resulted in the formation of open pores at its surface. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Characterization of pegylated copolymeric micelles and in vivo pharmacokinetics and biodistribution studiesJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2006Wen-Jen Lin Abstract The aim of this study was to evaluate the influence of pegylated copolymeric micelle carrier on the biodistribution of drug in rats. The copolymers were synthesized via a modified ring-opening copolymerization of lactone monomers (,-caprolactone, ,-valerolactone, L -lactide) and poly(ethylene glycol) (PEG10,000 and PEG4000). The molecular weights and the polydispersities of synthesized copolymers were in the range of 15,000,31,000 g/mol and 1.7,2.7, respectively. All of the pegylated amphiphilic copolymers were micelles formed with low CMC values in the range of 10,7,10,8M. The drug-loaded micelles were prepared via a dialysis method. The average particle size of micelles was around 150,200 nm. The cytotoxicity in terms of cell viability after treated with PCL,PEG, PVL,PEG, and PLA,PEG micelles was insignificant. PCL,PEG and PVL,PEG micelles without branch side chain in structures had higher drug loading than PLA,PEG micelles. In vitro release profiles indicated the release of indomethacin from these micelles exhibited a sustained release behavior. The similar phenomenon was also observed in vivo in rats. The pegylated copolymeric micelles not only decreased drug uptake by the liver and kidney, but also prolonged drug retention in the blood. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006 [source] Tobramycin and Gentamycin elution analysis between two in situ polymerizable orthopedic compositesJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2003M. DiCicco Abstract This research analyzed Tobramycin and Gentamycin elution characteristics for two antibiotic-impregnated bone composites: PMMA-based Simplex P® and the novel, hybrid, bioactive, CORTOSSÔ. Experimental results were correlated with composite hydrophilicity and antibiotic phase partitioning behaviors. The phase partitioning experiment was conducted to understand antibiotic solubility in aqueous environments. By comparing experimental results with calculated data, antibiotic release behavior was predicted. Total Tobramycin elution percentages from CORTOSS and Simplex P were 12.5 and 6.4%, respectively. Total Gentamycin elution percentages from CORTOSS and Simplex P were 6.95 and 10.17%, respectively. Phase partitioning data indicate 100% of Tobramycin remains in aqueous phases, being extremely hydrophilic. This is supported by its calculated theoretical value (log P = , 7.32). Results suggest that Tobramycin elution can be attributed to composite hydrophilicity as well as its high degree of hydrophilicity. Fifteen percent of Gentamycin distributes in hydrophobic phases (log P = , 4.22). Despite a lower Gentamycin hydrophilicity, its release was affected by its complexation with polar salts in the leaching buffer, thereby increasing its elution potential, making it appreciably water soluble. CORTOSS is more hydrophilic; therefore the migration of aqueous liquids into the polymer network of CORTOSS facilitates greater antibiotic elution compared with hydrophobic Simplex P. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 65B: 137,149, 2003 [source] Design and In vitro evaluation of a film-controlled dosage form self-converted from monolithic tablet in gastrointestinal environmentJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 11 2010Tingting Zhang Abstract The purpose of this study is to design an easily manufactured sustained drug delivery system, which can be converted to a film coated system during the dissolution process and then control the drug release according to near zero-order kinetics. Two kinds of pH-sensitive and oppositely charged hydrophilic polymers, chitosan and alginate, were physically mixed as the matrix. Slightly water-soluble drugs such as theophylline, aspirin, and acetaminophen were utilized as model drugs. In vitro drug release and swelling tests were undertaken in simulated gastrointestinal environments. The formation and properties of the film formed during the dissolution process were identified using different techniques. It was demonstrated that formation of the film was based on the interaction of the polymers on tablet surface with the change of system pH. In 0,4,h drug release depended on the intrinsic properties of the polymers, however, characteristics of the film played a leading role in controlling drug release after 4,h. By studying the ratio of relaxation over Fickian diffusion and relationship between tablets swelling and drug release, it was revealed that the film probably modified drug release behavior by limiting polymer erosion. The in vivo behavior of this hydrophilic matrix system will be investigated. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:4678,4690, 2010 [source] Binding and release studies of a cationic drug from a star-shaped four-arm poly(ethylene oxide)- b -poly(methacrylic acid)JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 2 2010E. He Abstract Star-shape polymers possess higher densities of terminal functional groups and three-dimensional tetrahedron structure that induce significantly different association and interactions with drug compared to linear structure of identical molecular weights. Four-arm poly(ethylene oxide)- b -poly(methacrylic acid) block copolymer was synthesized by atom transfer radical polymerization technique, and it self-assembled into core-shell micelles and extended unimers at low and high pH respectively. The negatively charged carboxylate groups on the polymer chains interacted with a cationic drug through electrostatic interaction forming polymer/drug complexes stabilized by biocompatible hydrophilic PEO segments. The hydrodynamic radius (Rh) of the polymeric aggregates and polymer/drug complexes ranged from 46 to 84,nm and 32 to 55,nm at pH of 4.6 and 8.0 respectively, making them suitable for drug delivery applications. The thermodynamic parameters and interactions between polymer and drug were determined by isothermal titration calorimetric technique. The electrostatic force, hydrogen bonding and hydrophobic interactions controlled the characteristics of polymer/drug formation and complexes when the molar ratios of drug and polymer were varied. Drug selective electrode system was used to measure the dynamic release of imipramine hydrochloride (IPH) from multi-arm PEO- b -PMAA star polymer. The release exponent n was greater than 0.5 indicating a non-Fickian type diffusion behavior, where the release behavior was dominated by chain relaxation induced by ion exchange that was dependent on pH. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:782,793, 2010 [source] Solid lipid microparticles produced by spray congealing: Influence of the atomizer on microparticle characteristics and mathematical modeling of the drug releaseJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 2 2010Nadia Passerini Abstract The first aim of the work was to evaluate the effect of atomizer design on the properties of solid lipid microparticles produced by spray congealing. Two different air atomizers have been employed: a conventional air pressure nozzle (APN) and a recently developed atomizer (wide pneumatic nozzle, WPN). Milled theophylline and Compritol® 888ATO were used to produce microparticles at drug-to-carrier ratios of 10:90, 20:80, and 30:70 using the two atomizers. The results showed that the application of different nozzles had significant impacts on the morphology, encapsulation efficiency, and drug release behavior of the microparticles. In contrast, the characteristics of the atomizer did not influence the physicochemical properties of the microparticles as differential scanning calorimetry, Hot Stage microscopy, X-ray powder diffraction, and Fourier transform infrared spectroscopy analysis demonstrated. The drug and the lipid carrier presented in their original crystalline forms in both WPN and APN systems. A second objective of this study was to develop a novel mathematical model for describing the dynamic process of drug release from the solid lipid microparticles. For WPN microparticles the model predicted the changes of the drug release behavior with particle size and drug loading, while for APN microparticles the model fitting was not as good as for the WPN systems, confirming the influence of the atomizer on the drug release behavior. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:916,931, 2010 [source] Multivariate modeling of encapsulation and release of an ionizable drug from polymer microspheresJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 12 2009Hagar I. Labouta Abstract In the formulation of polymer microspheres (MSs) loaded with verapamil hydrochloride (VRP), a low molecular weight ionizable drug, by W/O/W emulsification, the pH of the external aqueous phase proved to be a primary determinant of both IE and drug release behavior. Increasing the pH of the external aqueous phase enhanced IE (,100% at pH 8.4). This was associated with a considerable increase in initial release rate at pH 1.2. Two multivariate methods, factorial analysis (FA) and artificial neural network (ANN), were used to investigate the impact of the combined effect of the external phase pH and other parameters (polymer concentration and initial drug load) on MS characteristics; IE, initial drug release, MS size and yield. FA indicated that the external aqueous phase pH affected all responses, with a particularly strong correlation with IE in addition to a combined synergistic effect with polymer concentration on MS size. ANN showed better internal and external predictive ability of responses compared to FA. The ANN model developed in the study can be successfully used for multivariate modeling of the encapsulation and release of VRP and similar drug salts from hydrophobic polymer MSs prepared by multiple emulsification in addition to other MS characteristics. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:4603,4615, 2009 [source] Development and in vitro evaluation of a mucoadhesive vaginal delivery system for nystatinJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 2 2009Juliane Hombach Abstract The purpose of the present study was to design and evaluate a novel vaginal delivery system for nystatin based on mucoadhesive polymers. L -Cysteine and cysteamine, respectively, were covalently attached to poly(acrylic acid), and the two different thiolated polymers were evaluated in vitro regarding their swelling behavior, mucoadhesive properties and release behavior. Tablets comprising these thiolated polymers and nystatin demonstrated a high stability in vaginal fluid simulant pH 4.2 and an increase in weight by swelling whereas control tablets comprising unmodified poly(acrylic acid) disintegrated and dissolved. The mucoadhesion time of tablets on freshly excised bovine vaginal mucosa on a rotating cylinder and the total work of adhesion of gels and tablets increased significantly due to the formation of disulfide bonds between the thiolated polymer and cysteine rich subdomaines of the mucus layer. The drug nystatin was released more slowly out of thiomer tablets and gels than out of PAA control tablets and gels. Therefore these thiolated polymers are promising delivery systems for nystatin providing a prolonged residence time and a sustained drug release in vitro under physiological relevant conditions. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:555,564, 2009 [source] Drug release phenomena within a hydrophobic starch acetate matrix: FTIR mapping of tablets after in vitro dissolution testingJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 8 2008Jari Pajander Abstract The aim of this study was to assess the utility of Fourier transform infrared mapping to study the drug release phenomena within a hydrophobic matrix tablet. Starch acetate with a degree of substitution (2.7) was used as a hydrophobic matrix former. Anhydrous caffeine and riboflavin sodium phosphate were used as water soluble model drugs. The USP (XXVIII) paddle-method was selected as an in vitro dissolution test. Mapping of the diluted tablets' cross-section was performed by attenuated total reflection mode. Fourier transform infrared mapping can distinguish drug particles from the bulk matrix and it can be considered as a valuable method for obtaining both quantitative and qualitative information on drug release processes. The physicochemical properties of the drug compound strongly contribute to its release behavior when the USP paddle in vitro dissolution test is used. Mapping of the riboflavin product revealed a more homogenous matrix distribution due to its smaller particle size. Consequently, its dissolution release profile was more uniform than caffeine which possessed a wider particle size distribution and lower solubility. Mapping showed that caffeine became localized in the lower part of the tablet unlike riboflavin. The hydrodynamic conditions during the in vitro release test might contribute to this differentiation. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97: 3367,3378, 2008 [source] Novel colon-specific microspheres with highly dispersed hydroxycamptothecin cores: Their preparation, release behavior, and therapeutic efficiency against colonic cancerJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 12 2006Bin Lu Abstract To increase therapeutic efficiency of hydroxycamptothecin (HCPT) against colonic cancer and decrease its side-effects, highly dispersed HCPT was first incorporated in fast release microspheres. HCPT in the microspheres showed a solubility two times larger, and its cumulative release rate for 24 h in simulated colonic juice 140 times higher than that of free HCPT. The microspheres were then coated with a layer of Eudragit S100 by air suspension spray-drying method with a selfdesigned device to obtain colon-specific microspheres (HCPT,CSMS). The mean particle size of the microspheres was 200 µm before coating and 230 µm after coating. The in vitro cumulative release results for HCPT,CSMS in simulated gastric juice for 2 h, in simulated enteric juice for 4 h, and in simulated colonic juice for 18 h showed that over 60% of total HCPT released in simulated colonic juice in the initial 5 h. Animal tests with per os (po) administration showed that free HCPT was mainly absorbed in stomach and small intestine, while the HCPT in HCPT,CSMS was mainly delivered and absorbed in colon. po administration of HCPT,CSMS to nude mice with colonic cancer showed a cancer inhibition rate of 61.4% compared to 39.8% for free HCPT. © 2006 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 95:2619,2630, 2006 [source] Energy Release in Isothermally Stretched Silicate Glass fibersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2006Lasse Hornbøll Three types of silicate glass fibers are annealed, simultaneously stretched in the glass transition region for certain time lengths, then slowly cooled to room temperature under load, and subsequently scanned by differential scanning calorimetry (DSC). During the DSC scanning, a broad exothermic peak (representing energy release) occurs in the stretched fibers well below the glass transition temperature, while it does not occur in the non-stretched fibers. The peak indicates that mechanical stretching can result in an energy enhancement in the fibers. It also confirms that the energy released during reheating of the fibers formed using an industrial continuous fiber drawing process originates not only from thermal quenching but also from mechanical stretching. However, the mechanical stretching-induced energy is much lower than the thermal hyperquenching-induced energy in glass fibers. The effect of annealing temperature and time on the energy release behavior is discussed in terms of viscoelasticity. [source] Influence of Solute Charge and Hydrophobicity on Partitioning and Diffusion in a Genetically Engineered Silk-Elastin-Like Protein Polymer HydrogelMACROMOLECULAR BIOSCIENCE, Issue 10 2010Adam A. Dinerman Abstract The influence of solute hydrophobicity and charge on partitioning and diffusion in physically crosslinked networks of a genetically engineered SELP polymer was investigated. A series of fluorescent dyes were used to assess the impact of solute charge and hydrophobicity on release behavior. The mechanism of solute release from the SELP hydrogel appeared to vary as a function of dye hydrophobicity. The extent of FITC attachment to amine-terminated G4 dendrimers influenced SELP hydrogel partitioning more than dendrimer diffusion properties. Results suggest the possibility of controlling solute release from SELP hydrogels by modifying the hydrophobicity and surface charge of drugs and drug/polymer conjugates as well as the possibility of "designing-in" solute-specific interactions. [source] The Influence of Pendant Hydroxyl Groups on Enzymatic Degradation and Drug Delivery of Amphiphilic Poly[glycidol- block -(, -caprolactone)] CopolymersMACROMOLECULAR BIOSCIENCE, Issue 11 2009Jing Mao Abstract An amphiphilic diblock copolymer PG- b -PCL with well-controlled structure and pendant hydroxyl groups along hydrophilic block was synthesized by sequential anionic ring-opening polymerization. The micellization and drug release of PG- b -PCL copolymers using pyrene as a fluorescence probe were investigated for determining the influences of copolymer composition and lipase concentration on drug loading capacity and controlled release behavior. The biodegradation of PG- b -PCL copolymers was studied with microspheres as research samples. It has been concluded that the polar hydroxyl groups along each repeat unit of hydrophilic PG block in PG- b -PCL copolymer have great influences on drug encapsulation, drug release, and enzymatic degradation of micelles and microspheres. [source] Loading and Release of Ibuprofen in Multi- and Monofilament Surgical SuturesMACROMOLECULAR BIOSCIENCE, Issue 9 2006Raül Zurita Abstract Summary: The preparation of mono- and multifilament sutures incorporating ibuprofen as an anti-inflammatory agent is considered. Poly(p -dioxanone) monofilament samples can be loaded by a molecular diffusion process using a swelling agent such as dichloromethane. The mechanical properties have been measured and have not shown a significant change for the ibuprofen loaded samples in knot tensile assays. The kinetics of both the loading process and the release in a Sörensen's medium at 37,°C have been investigated. Diffusion coefficients have also been estimated from film and slab poly(p -dioxanone) samples containing ibuprofen and their release behavior compared to that shown by monofilaments. Release from a coating copolymer based on lactide, , -caprolactone and trimethylene carbonate (PLA/PCA/PTMC 10/60/30) has also been studied. This coating solubilizes ibuprofen molecules well and can be used for braided sutures or when a rapid dose of ibuprofen is preferred. [source] Loading of Bacterial Cellulose Aerogels with Bioactive Compounds by Antisolvent Precipitation with Supercritical Carbon DioxideMACROMOLECULAR SYMPOSIA, Issue 2 2010Emmerich Haimer Abstract Bacterial cellulose aerogels overcome the drawback of shrinking during preparation by drying with supercritical CO2. Thus, the pore network of these gels is fully accessible. These materials can be fully rewetted to 100% of its initial water content, without collapsing of the structure due to surface tension of the rewetting solvent. This rehydration property and the high pore volume of these material rendered bacterial cellulose aerogels very interesting as controlled release matrices. Supercritical CO2 drying, the method of choice for aerogel preparation, can simultaneously be used to precipitate solutes within the cellulose matrix and thus to load bacterial cellulose aerogels with active substances. This process, frequently termed supercritical antisolvent precipitation, is able to perform production of the actual aerogel and its loading in one single preparation step. In this work, the loading of a bacterial cellulose aerogel matrix with two model substances, namely dexpanthenol and L-ascorbic acid, and the release behavior from the matrix were studied. A mathematical release model was applied to model the interactions between the solutes and the cellulose matrix. The bacterial cellulose aerogels were easily equipped with the reagents by supercritical antisolvent precipitation. Loading isotherms as well as release kinetics indicated no specific interaction between matrix and loaded substances. Hence, loading and release can be controlled and predicted just by varying the thickness of the gel and the solute concentration in the loading bath. [source] Chitosan-Pectin Composite Gel Spheres: Effect of Some Formulation Variables on Drug ReleaseMACROMOLECULAR SYMPOSIA, Issue 1 2004Pornsak Sriamornsak Abstract Chitosan-pectin composite gel spheres were prepared by ionotropic gelation method. Pectin solution containing indomethacin, a model drug, was extruded into a mixture of chitosan and calcium chloride. The release behavior of indomethacin from composite gel spheres was investigated in-vitro. The influence of factors affecting release behavior, such as type of pectin, molecular weight of chitosan, cross-linking time and release medium, were discussed in this study. Adding chitosan into gelation medium could retard the release of indomethacin from gel spheres. The different type of pectin used demonstrated slightly different drug release profiles. The higher molecular weight of chitosan showed less indomethacin release than the lower one. The increased cross-linking time slowed the drug release from composite gel spheres. The release of indomethacin from composite gel spheres was also dependent on the release medium. The drug release was slower in tris buffer where no phosphate ions which can induce the precipitation of calcium phosphate. The results suggested that the composite gel spheres of pectin and chitosan could be used as a controlled release drug delivery carrier. [source] The shock and release behavior of an aerospace-grade cured aromatic amine epoxy resinPOLYMER COMPOSITES, Issue 10 2008P.J. Hazell Knowing the dynamic behavior of polymer materials that are used in the construction of fiber-reinforced composite materials is particularly important for such materials that are subjected to impact. In this work, we have conducted a number of plate-impact experiments on a commercially important aromatic amine epoxy resin that is used in the construction of carbon fiber composite materials. The measured Hugoniot in shock velocity,particle velocity space was Us = 2.65 + 1.55 up (,0 = 1.141 g/cc), and is similar to the measured Hugoniots of other resins presented by different researchers. We have also measured the longitudinal stress in the shocked material and shown, in common with other polymers, that above a threshold stress, an increase in shear strength with impact stress is observed. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers [source] Interpenetrating polymeric network hydrogels for potential gastrointestinal drug releasePOLYMER INTERNATIONAL, Issue 11 2007Sema Ekici Abstract New interpenetrating polymeric network (IPN) hydrogels based on chitosan (C), poly(N -vinyl pyrrolidone) (PVP) and poly(acrylic acid) (PAAc), crosslinked with glutaraldehyde (G) and N,N,-methylenebisacrylamide (MBA), were prepared and investigated for potential gastrointestinal drug delivery vehicles utilizing a model drug, amoxicillin. IPN hydrogels were synthesized by simultaneous polymerization/crosslinking of acrylic acid monomer in the presence of another polymer (C) and crosslinker (G, MBA). Three different concentrations of glutaraldehyde were used (0.5, 1.0 and 2.0 w/w) to control the overall porosity of the hydrogels, named C-P-AAc/0.5, C-P-AAc/1.0 and C-P-AAc/2.0, respectively. Spectroscopic and thermal analyses such as Fourier transform infrared spectroscopy, thermogravimetric analysis and thermomechanical analysis were performed for IPN characterization. Equilibrium swelling studies were conducted for pH and temperature response behavior. Swelling studies were also carried out in simulated gastric fluid of pH = 1.1 and simulated intestinal fluid of pH = 7.4 to investigate possible site-specific drug delivery. It was found that the release behavior of the drug from these IPN hydrogels was dependent on the pH of the medium and the proportion of crosslinker in the IPN. It was observed that amoxicillin release at pH = 7.4 was higher than at pH = 1.1. The analysis of the drug release showed that amoxicillin was released from these hydrogels through a non-Fickian diffusion mechanism. Copyright © 2007 Society of Chemical Industry [source] Modulation of dynamic release of vitamin B2 from a model pH-sensitive terpolymeric hydrogel systemPOLYMER INTERNATIONAL, Issue 12 2004Dr SK Bajpai Abstract Terpolymeric devices consisting of acrylamide, methacrylamide and acrylic acid were synthesized and the release of the model drug riboflavin from these devices was studied at the physiological temperature 37°C. The gels exhibit a sharp pH-dependent release behavior. The devices released nearly 42.2 ± 2.6% drug at pH 1.0 while nearly 95.3 ± 3.2% drug was released at pH 7.4. With increasing concentration of cross-linker in the gel, the drug released was found to decrease. Moreover, with low content of cross-linker a nearly zero-order profile was obtained. The size of the cylindrical devices also affected the release kinetics and a linear dependency was observed between t1/2 (ie, the time required for 50 % release) and the square of the diameter, thus supporting the Tanaka,Fillmore theory. The molar ratio of acrylamide and methacrylamide also affected the dynamic release of riboflavin. It was found that variation in transit time could also affect the drug-releasing capacity of the devices. Finally, the average and ,late-time' diffusion coefficients for the gels having different initial loads were also evaluated. Copyright © 2004 Society of Chemical Industry [source] Photopolymerization of alicyclic methacrylate hydrogels for controlled releasePOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 7 2009Jing Han Abstract Alicyclic hydroxy methacrylate monomer, o -hydroxycyclohexyl methacrylate (HCMA), was synthesized and characterized by Fourier transformed infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance spectroscopy (1H-NMR). Photopolymerization kinetics of HCMA was investigated via real-time infrared spectroscopy (RT-IR). Polymeric network hydrogels based on hydroxyethyl methacrylate (HEMA) and HCMA were prepared by using the photopolymerization technique. Mechanical strength, swelling characteristic, and controlled release behavior of hydrogels with various feed compositions were studied. Poly(HEMA-co-HCMA) hydrogel had higher storage modulus than that of poly(HEMA) hydrogel as investigated by dynamic mechanical analysis (DMA). Acid orange 8 was used as a model drug for the investigation of drug release behavior of copolymeric hydrogels. Results indicated that increase in HCMA ratio in hydrogel composition could reduce the swelling rate and prolong the release time. Scanning electron microscopy (SEM) was also utilized to study the surface morphology of hydrogels, and the results indicated that HCMA content influenced pore diameter on the hydrogel surface. Copyright © 2008 John Wiley & Sons, Ltd. 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