Home About us Contact
|
Home About us Contact | ||
|
|
||
Polymeric Microspheres (polymeric + microsphere)
Selected AbstractsInfluence of Processing Temperature on Microcellular Injection-Moulded Wood,Polypropylene CompositesMACROMOLECULAR MATERIALS & ENGINEERING, Issue 10 2006Andrzej K. Bledzki Abstract Summary: Microcellular wood fibre reinforced polymer materials are significant because of their possibility to reduce the density of automotive components through microcellular structure, process and product part advantages, and as a new development with bio-fibre strengthened plastics. Soft wood fibre reinforced PP composites in box part and panel shape were prepared by an injection moulding process. Polymeric microspheres as a chemical foaming agent (endothermic) were used to produce the microcellular composites. The influence of injection moulding processing temperature on the microcellular structure and properties (tensile and flexural properties, notched charpy impact strength) was investigated by varying the temperature over the 150,170,°C, 160,180,°C and 170,190,°C. A comparative study of cell morphology, weight reduction and mechanical properties was conducted between box part and panel. Microcell morphology, cell size, shape and distribution were investigated using scanning electron micrographs. The results indicated that the lower processing temperature should be below the range of 170,190,°C and processing temperature at 160,180,°C, where the composites showed finer cellular structure compared to other processing temperatures. The mechanical properties did not differ with the variation of processing temperature regardless of composite types (box part or panel). Cellular structure changes in the box part were found considering near or far from injecting point. Microcellular injection-moulded box part (geometry: 150,×,100,×,70 mm3 in size) of soft wood fibre,PP composites. [source] Preparation and adsorption characteristic of polymeric microsphere with strong adsorbability for creatinineJOURNAL OF BIOCHEMICAL AND MOLECULAR TOXICOLOGY, Issue 3 2008Baojiao Gao Abstract Cross-linking terpolymer microspheres (HEMA/NVP/MBA; it can also be designated as HEMA/NVP because HEMA and NVP are main components) with an average diameter of 180 µm, were prepared via inverse suspension copolymerization by using 2-hydroxyethyl methacrylate (HEMA) and N -vinylpyrrolidone (NVP) as monomers and N,N,-methylene bisacrylamide (MBA) as cross-linked agent. The microsphere HEMA/NVP was chemically modified with 3,5-dinitrobenzoyl chloride (DNBC), and the functional microsphere DNBZ-HEMA/NVP, on which a great number of 3,5-dinitrobenzoate group (DNBZ) were bound, was obtained. The functional microsphere DNBZ-HEMA/NVP were characterized with FTIR and the chemical analysis method. The adsorption characteristics and mechanism of the absorption of DNBZ-HEMA/NVP for creatine was mainly studied. The results of static adsorption experiments show that the functional microsphere DNBZ-HEMA/NVP has very strong adsorption ability for creatinine, and the saturated adsorption amount is 25 mg/g. The adsorption capacity of the functional microsphere DNBZ-HEMA/NVP for creatinine is enhanced 20 times as against unmodified microsphere HEMA/NVP. The adsorption capacity is smaller, at lower and higher pH, and has a maximum as pH 8.5. The higher the salinity of the medium, the smaller the adsorption capacity. The adsorption capacity decreases with increasing temperature. The study results show that the adsorption of the microsphere DNBZ-HEMA/NVP for creatinine is ascribed to a chemical adsorption by driving of electrostatic interaction. © 2008 Wiley Periodicals, Inc. J Biochem Mol Toxicol 22:166,174, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20221 [source] Genetically engineered Pseudomonas: a factory of new bioplastics with broad applicationsENVIRONMENTAL MICROBIOLOGY, Issue 10 2001Elías R. Olivera Summary New bioplastics containing aromatic or mixtures of aliphatic and aromatic monomers have been obtained using genetically engineered strains of Pseudomonas putida. The mutation (,) or deletion (,) of some of the genes involved in the ,-oxidation pathway (fadA,, fadB,,fadA or ,fad,BA mutants) elicits a strong intracellular accumulation of unusual homo- or co-polymers that dramatically alter the morphology of these bacteria, as more than 90% of the cytoplasm is occupied by these macromolecules. The introduction of a blockade in the ,-oxidation pathway, or in other related catabolic routes, has allowed the synthesis of polymers other than those accumulated in the wild type (with regard to both monomer size and relative percentage), the accumulation of certain intermediates that are rapidly catabolized in the wild type and the accumulation in the culture broths of end catabolites that, as in the case of phenylacetic acid, phenylbutyric acid, trans -cinnamic acid or their derivatives, have important medical or pharmaceutical applications (antitumoral, analgesic, radiopotentiators, chemopreventive or antihelmintic). Furthermore, using one of these polyesters (poly 3-hydroxy-6-phenylhexanoate), we obtained polymeric microspheres that could be used as drug vehicles. [source] Uniform Polymeric Hollow Microcapsules with Controlled Doping Levels Fabricated under Nonreactive Conditions,ADVANCED MATERIALS, Issue 8 2007K. Wygladacz A chemically nonreactive method for the fabrication of uniform core/shell fluorescent polymeric microspheres (see figure) is demonstrated with a flow apparatus. Various dyes and labeled proteins are doped into the appropriate particle phases, and an early example of chemical sensing is demonstrated. [source] Solvent/non-solvent sintering: A novel route to create porous microsphere scaffolds for tissue regenerationJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2008Justin L. Brown Abstract Solvent/non-solvent sintering creates porous polymeric microsphere scaffolds suitable for tissue engineering purposes with control over the resulting porosity, average pore diameter, and mechanical properties. Five different biodegradable biocompatible polyphosphazenes exhibiting glass transition temperatures from ,8 to 41°C and poly (lactide- co -glycolide), (PLAGA) a degradable polymer used in a number of biomedical settings, were examined to study the versatility of the process and benchmark the process to heat sintering. Parameters such as: solvent/non-solvent sintering solution composition and submersion time effect the sintering process. PLAGA microsphere scaffolds fabricated with solvent/non-solvent sintering exhibited an interconnected porosity and pore size of 31.9% and 179.1 ,m, respectively which was analogous to that of conventional heat sintered PLAGA microsphere scaffolds. Biodegradable polyphosphazene microsphere scaffolds exhibited a maximum interconnected porosity of 37.6% and a maximum compressive modulus of 94.3 MPa. Solvent/non-solvent sintering is an effective strategy for sintering polymeric microspheres, with a broad spectrum of glass transition temperatures, under ambient conditions making it an excellent fabrication route for developing tissue engineering scaffolds and drug delivery vehicles. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008 [source] Preparation of polymer-supported polyethylene glycol and phase-transfer catalytic activity in benzoate synthesisAICHE JOURNAL, Issue 3 2010Baojiao Gao Abstract The crosslinked polymeric microspheres (GMA/MMA) of glycyl methacrylate (GMA) and methyl methacrylate (MMA) were prepared by suspension polymerization. Polyethylene glycol (PEG) was grafted on GMA/MMA microsphers via the ring-opening reaction of the epoxy groups on the surfaces of GMA/MMA microspheres, forming a polymer-supported triphase catalyst, PEG-GMA/MMA. The Phase-transfer catalytic activity of PEG-GMA/MMA microspheres was evaluated using the esterification reaction of n -chlorobutane in organic phase and benzoic acid in water phase as a model system. The effects of various factors on the phase transfer catalysis reaction of liquid,solid,liquid were investigated. The experimental results show that the PEG-GMA/MMA microspheres are an effective and stable triphase catalyst for the esterification reaction carried out between oil phase and water phase. The polarity of the organic solvent, the ratio of oil phase volume to water phase volume and the density of the grafted PEG on PEG-GMA/MMA microspheres affect the reaction rate greatly. For this investigated system, the solvent with high polarity is appropriate, an adequate volume ratio of oil phase to water phase is 2:1, and the optimal PEG density on the polymeric microspheres is 15 g/100 g. Triphase catalysts offer many advantages associated with heterogeneous catalysts such as easy separation from the reaction mixture and reusability. The activity of PEG-GMA/MMA microspheres is not nearly decreased after reusing of 10 recycles. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Feasibility study of aerosolized prostaglandin E1 microspheres as a noninvasive therapy for pulmonary arterial hypertensionJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 4 2010Vivek Gupta Abstract This study was designed to test the feasibility of polymeric microspheres as an inhalable carrier for prostaglandin E1 (PGE1) for treatment of pulmonary arterial hypertension. Poly(lactic- co -glycolic acid) (PLGA) microspheres were prepared by a double emulsion,solvent evaporation method. Six different microspheric formulations were prepared using two different blends of PLGA (50:50 and 85:15) and varying concentrations of polyvinyl alcohol (PVA) in the external aqueous phase (EAP). The particles were characterized for morphology, size, aerodynamic diameter, entrapment efficiency, release patterns, and metabolic stability. Pulmonary absorption was studied in a rat model, and safety of the formulations was evaluated by measuring cytotoxicity in Calu-3 cells and assessing injury markers in bronchoalveolar lavage (BAL) fluid. Both actual particle size and aerodynamic diameter of the formulations decreased with increasing PVA concentration. The mass median aerodynamic diameter of the particles was within the respirable range. Entrapment efficiency increased with increasing PVA concentration; PLGA 85:15 showed better entrapment due to hydrophobic interactions with the drug. Compared to intravenously administered PGE1, microspheres prepared with PLGA 85:15 produced a 160-fold increase in the half-life of PGE1 following pulmonary administration. Although plain PGE1 showed rapid degradation in rat lung homogenate, PGE1 entrapped in the particles remained intact for about 8,h. Optimized formulations were demonstrated to be safe, based on analysis of cytotoxicity and lung-injury markers in BAL fluid. Overall, the data suggest that microspheric PGE1 formulations have the potential to be used as a noninvasive and controlled-release alternative to the current medications used for treatment of pulmonary arterial hypertension that are administered by continuous infusion or require multiple inhalations. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 1774,1789, 2010 [source] Hydrophobic ion pairing of isoniazid using a prodrug approachJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 6 2002Huiyu Zhou Abstract Inhalation therapy for infectious lung diseases, such as tuberculosis, is currently being explored, with microspheres being used to target alveolar macrophages. One method of drug encapsulation into polymeric microspheres to form hydrophobic ion-paired (HIP) complexes, and then coprecipitate the complex and polymer using supercritical fluid methodology. For the potent antituberculosis drug, isoniazid (isonicotinic acid hydrazide, INH), to be used in this fashion, it was modified into an ionizable form suitable for HIP. The charged prodrug, sodium isoniazid methanesulfonate (Na,INHMS), was then ion paired with hydrophobic cations, such as alkyltrimethylammonium or tetraalkylammonium. The logarithms of the apparent partition coefficients (log P,) of various HIP complexes of INHMS display a roughly linear relationship with the numbers of carbon atoms in the organic counterions. The water solubility of the tetraheptylammonium,INHMS complex is about 220-fold lower than that of Na,INHMS, while the solubility in dichloromethane exceeds 10 mg/mL, which is sufficient for microencapsulation of the drug into poly(lactide) microspheres. The actual logarithm of the dichloromethane/water partition coefficient (log P) for tetraheptylammonium,INHMS is 1.55, compared to a value of ,,1.8 for the sodium salt of INHMS. The dissolution kinetics of the tetraheptylammonium,INHMS complex in 0.9% aqueous solutions of NaCl was also investigated. Dissolution of tetraheptylammonium,INHMS exhibited a first-order time constant of about 0.28 min,1, followed by a slower reverse ion exchange process to form Na,INHMS. The half-life of this HIP complex is on the order of 30 min, making the enhanced transport of the drug across biological barriers possible. This work represents the first use of a prodrug approach to introduce functionality that would allow HIP complex formation for a neutral molecule. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91:1502,1511, 2002 [source] Improvement of peripheral nerve regeneration in acellular nerve grafts with local release of nerve growth factorMICROSURGERY, Issue 4 2009Hailong Yu M.D. Previous studies have demonstrated the potential of growth factors in peripheral nerve regeneration. A method was developed for sustained delivery of nerve growth factor (NGF) for nerve repair with acellular nerve grafts to augment peripheral nerve regeneration. NGF-containing polymeric microspheres were fixed with fibrin glue around chemically extracted acellular nerve grafts for prolonged, site-specific delivery of NGF. A total of 52 Wister rats were randomly divided into four groups for treatment: autografting, NGF-treated acellular grafting, acellular grafting alone, and acellular grafting with fibrin glue. The model of a 10-mm sciatic nerve with a 10-mm gap was used to assess nerve regeneration. At the 2nd week after nerve repair, the length of axonal regeneration was longer with NGF-treated acellular grafting than acellular grafting alone and acellular grafting with fibrin glue, but shorter than autografting (P < 0.05). Sixteen weeks after nerve repair, nerve regeneration was assessed functionally and histomorphometrically. The percentage tension of the triceps surae muscles in the autograft group was 85.33 ± 5.59%, significantly higher than that of NGF-treated group, acellular graft group and fibrin-glue group, at 69.79 ± 5.31%, 64.46 ± 8.48%, and 63.35 ± 6.40%, respectively (P < 0.05). The ratio of conserved muscle-mass was greater in the NGF-treated group (53.73 ± 4.56%) than in the acellular graft (46.37 ± 5.68%) and fibrin glue groups (45.78 ± 7.14%) but lower than in the autograft group (62.54 ± 8.25%) (P < 0.05). Image analysis on histological observation revealed axonal diameter, axon number, and myelin thickness better with NGF-treated acellular grafting than with acellular grafting alone and acellular grafting with fibrin glue (P < 0.05). There were no significant differences between NGF-treated acellular grafting and autografting. This method of sustained site-specific delivery of NGF can enhance peripheral nerve regeneration across short nerve gaps repaired with acellular nerve grafts. © 2009 Wiley-Liss, Inc. Microsurgery, 2009. [source] Preparation and characterization of self-dispersible polymeric microspheres,POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 7-8 2006Ke Min Abstract Monodispersed OEGMA/St polymeric particles were prepared through soap-free emulsion polymerization, then surface modification was conducted by atom transfer radical polymerization (ATRP), and nano-size hairy shell of OEGMA/St particles were obtained. By hydrolysis, the grafting chains of the hairy particles were successfully cut down from the core particles. Through gel permeation chromatography (GPC) and transmission electron microscopy (TEM) measurements, the density of grafting chains was calculated. Experimental results showed that the hairy shell on the surface of the particles could dramatically improve the particles dispersibility in organic solvents. Copyright © 2006 John Wiley & Sons, Ltd. [source] Relationship between morphology structure and composition of polycaprolactone/Poly(ethylene oxide)/Polylactide copolymeric microspheresPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 9 2002Guangming Li Abstract A novel tri-component copolymer, polycaprolactone/poly(ethylene oxide)/polylactide (PCEL) was synthesized. The effect of the chemical composition on physical properties was investigated by using NMR, differential scanning calorimetry (DSC) and X-ray diffraction. Both the soft segment poly(ethylene oxide) (PEO) and polycaprolactone (PCL) could enhance the mobility of polymer chains and decrease the crystallizability of the copolymers. The polymeric microspheres, which are of interest for drug delivery systems, were prepared using an emulsification-solvent evaporation technique. By scanning electron microscopy (SEM) and atomic force microscopy (AFM), the surface morphology of the microspheres was studied. It was found that the presence of PEO segment could improve the hydrophilicity of the copolymers and the morphology of the polymeric microspheres could be altered by adjusting the chemical composition. The accumulation of PEO segments on the outer surface of the polymeric microspheres was proven by X-ray photoelectron spectroscopy (XPS). It had also been proven that the PCL segment could facilitate the movement of PEO segment to the outer surface. Copyright © 2002 John Wiley & Sons, Ltd. [source] | |||||||||||||