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排序方式: 共有188条查询结果,搜索用时 15 毫秒
1.
The objectives of this study were to evaluate the physical structure and the release mechanisms of theophylline microspheres
made of Eudragit S 100 polymer as an enteric polymer, combined with a nonerodible polymer, Eudragit RL 100. In the preparation
process, polymer combinations (1:1) were dissolved in an organic solvent mixture composed of acetone and methanol at a specific
ratio containing a theoretical drug loading of approximately 15%. Two microsphere formulations (LS1 and LS2) were prepared
at two different total polymer concentrations (10% in LS1 and 12.7% in LS2). Dissolution studies were carried out using US
Pharmacopeia Dissolution Apparatus II in an acidic medium for 8 h and in an acidic medium (2 h) followed by a slightly basic-buffered
medium for 10 h. Both LS1 and LS2 microsphere formulations produced particles that were spherical in shape and had very narrow
size distributions with one size fraction comprising 70–80% of the yield. Scanning electron microscopy and quantitative Fourier
transform infrared were used for microsphere physical structure evaluation. Except for the absence of drug crystals, photomicrographs
of both LS microspheres after dissolution in pH 1.2 and 7.2 buffer solutions were similar to those before dissolution. Dissolution
results indicated the ability of LS microspheres to minimize drug release during the acid stage. However, in the slightly
basic medium that followed the acidic stage, the drug release was sustained and controlled in its kinetics and data fitted
to Peppas equation indicated a case II transport suggesting that the drug release is mainly through swelling/erosion mechanism. 相似文献
2.
Svetlana V. Shilova Grigory M. Mirgaleev Ksenia A. Romanova Yury G. Galyametdinov 《Biopolymers》2023,114(10):e23555
This work reports synthesis of pH-responsive alginate/chitosan hydrogel spheres with the average diameter of 2.0 ± 0.05 mm, which contain cefotaxime that is an antibiotic of the cefalosporine group. The spheres provided the cefotaxime encapsulation efficiency of 95 ± 1%. An in vitro release of cefotaxime from the spheres in the media that simulate human biological fluids in peroral delivery conditions was found to be a pH-dependent process. The analysis of cefotaxime release kinetics by the Korsmeyer–Peppas model revealed a non-Fickian mechanism of its diffusion, which may be related to intermolecular interactions occurring between the antibiotic and chitosan. Conductometry, UV spectroscopy, and IR spectroscopy were used to study complexation of chitosan with cefotaxime in aqueous media with varied pH, characterize the composition of the complexes, and calculate their stability constants. The composition of the cefotaxime–chitosan complexes was found to correspond to the 1.0:4.0 and 1.0:2.0 molar ratios of the components at pH 2.0 and 5.6, respectively. Quantum chemical modeling was used to evaluate energy characteristics of chitosan–cefotaxime complexation considering the influence of a solvent. 相似文献
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5.
Alterations in retinal blood flow can contribute to, or be a consequence of, ocular disease and visual dysfunction. Therefore, quantitation of altered perfusion can aid research into the mechanisms of retinal pathologies. Intravital video microscopy of fluorescent tracers can be used to measure vascular diameters and bloodstream velocities of the retinal vasculature, specifically the arterioles branching from the central retinal artery and of the venules leading into the central retinal vein. Blood flow rates can be calculated from the diameters and velocities, with the summation of arteriolar flow, and separately venular flow, providing values of total retinal blood flow. This paper and associated video describe the methods for applying this technique to mice, which includes 1) the preparation of the eye for intravital microscopy of the anesthetized animal, 2) the intravenous infusion of fluorescent microspheres to measure bloodstream velocity, 3) the intravenous infusion of a high molecular weight fluorescent dextran, to aid the microscopic visualization of the retinal microvasculature, 4) the use of a digital microscope camera to obtain videos of the perfused retina, and 5) the use of image processing software to analyze the video. The same techniques can be used for measuring retinal blood flow rates in rats. 相似文献
6.
Intravascular magnetomotive optical coherence tomography of targeted early‐stage atherosclerotic changes in ex vivo hyperlipidemic rabbit aortas 下载免费PDF全文
Jongsik Kim Adeel Ahmad Joanne Li Marina Marjanovic Eric J. Chaney Kenneth S. Suslick Stephen A. Boppart 《Journal of biophotonics》2016,9(1-2):109-116
We report the development of an intravascular magnetomotive optical coherence tomography (IV‐MM‐OCT) system used with targeted protein microspheres to detect early‐stage atherosclerotic fatty streaks/plaques. Magnetic microspheres (MSs) were injected in vivo in rabbits, and after 30 minutes of in vivo circulation, excised ex vivo rabbit aorta samples specimens were then imaged ex vivo with our prototype IV‐MM‐OCT system. The alternating magnetic field gradient was provided by a unique pair of external custom‐built electromagnetic coils that modulated the targeted magnetic MSs. The results showed a statistically significant MM‐OCT signal from the aorta samples specimens injected with targeted MSs.
7.
The mucoadhesive properties of chitosan microspheres prepared by different method were evaluated by studying the interaction
between mucin and microspheres in aqueous solution. The interaction was determined by the measurement of mucin adsorbed on
the microspheres. A strong interaction between chitosan microspheres and mucin was detected. The intensity of the interaction
was dependent upon the method of preparation of chitosan microspheres and the amount of mucin added. The extent of mucus adsorption
was proportional to the absolute values of the positive zeta potential of chitosan microspheres. The zeta potential in turn
was found to be dependent upon the method of preparation of microspheres. The adsorption of type III mucin (1% sialic acid
content) was interpreted using Freundlich or Langmuir adsorption isotherms. The values ofr
2 were greater for Langmuir isotherm as compared with Freundlich isotherm. The adsorption of a suspension of chitosan microspheres
in the rat small intestine indicated that chitosan microspheres prepared by tripolyphosphate cross-linking and emulsification
ionotropic gelation can be used as an excellent mucoadhesive delivery system. The microspheres prepared by glutaraldehyde
and thermal cross-linking showed good stability in HC1 as compared with microspheres prepared by tripolyphosphate and emulsification
ionotropic gelation. 相似文献
8.
The purpose of this research was to encapsulate superoxide dismutase (SOD) and catalase (CAT) in biodegradable microspheres
(MS) to obtain suitable sustained protein delivery. A modified water/oil/water double emulsion method was used for poly(D,L-lactide-co-glycolide)
(PLGA) and poly(D,L-lactide) PLA MS preparation co-encapsulating mannitol, trehalose, and PEG400 for protein stabilization.
Size, morphology, porosity, mass loss, mass balance, in vitro release and in vitro activity were assessed by using BCA protein
assay, scanning electron microscopy, BET surface area, and particle-sizing techniques. In vitro activity retention within
MS was evaluated by nicotinammide adenine dinucleotide oxidation and H2O2 consumption assays. SOD encapsulation efficiency resulted in 30% to 34% for PLAMS and up to 51% for PLGA MS, whereas CAT
encapsulation was 34% and 45% for PLGA and PLAMS, respectively. All MS were spherical with a smooth surface and low porosity.
Particle mean diameters ranged from 10 to 17 μm. CAT release was prolonged, but the results were incomplete for both PLA and
PLGA MS, whereas SOD was completely released from PLGA MS in a sustained manner after 2 months. CAT results were less stable
and showed a stronger interaction than SOD with the polymers. Mass loss and mass balance correlated well with the release
profiles. SOD and CAT in vitro activity was preserved in all the preparations, and SOD was better stabilized in PLGA MS. PLGA
MS can be useful for SOD delivery in its native form and is promising as a new depot system. 相似文献
9.
The purpose of this study was to investigate the effect of particle size, storage temperature, and duration of storage on
the physical stability and morphology of polylactic-co-glycolic acid (PLGA) nanospheres and microspheres. PLGA nanospheres
and microspheres containing the fluorescent dye, Bodipy, were prepared in varying sizes by controlling the method and degree
of agitation during the emulsification phase of preparation. Mean diameters of the particles were measured by dynamic light
scattering. To evaluate the effect of storage temperature and duration of storage on the extent of aggregation, nanospheres
and microspheres were stored at 4°C, 25°C, 37°C, and 50°C for 6 days and then monitored using both confocal and scanning electron
microscopy. The mean ±SD diameters of PLGA particles containing Bodipy were: 266.9±2.8, 351.6±1.8, 988.8±14.1, and 1865.9±67.0
nm. The extent of aggregation of the particulate delivery system decreased as the mean diameter increased, and increased as
the storage temperature increased. The maximum extent of aggregation was observed with the smallest (266 nm) nanospheres.
Microspheres did not aggregate. The aggregation of nanospheres was significantly reduced by introducing an additional evaporation
step during preparation, suggesting that migration of residual dichloromethane from within the nanospheres may have dissolved
the PLGA on the surface. The extent of aggregation of nanospheres increased as the temperature was increased from 4°C to 50°C,
and decreased as particle size increased. To avoid aggregation, PLGA nanospheres should be stored at 4°C. 相似文献
10.
This paper describes the formulation of a biodegradable microparticulate drug delivery system containing clodronate, a bisphosphonate
intended for the treatment of bone diseases. Microspheres were prepared with several poly(D,L-lactide-co-glycolide) (PLGA)
copolymers of various molecular weights and molar compositions and 1 poly(D,L-lactide) (PDLLA) homopolymer by a water-in-oil-in-water
(w/o/w) double emulsion solvent evaporation procedure. Critical process parameters and formulation variables (ie, addition
of stabilizing agents) were evaluated for their effect on drug encapsulation efficiency and clodronate release rate from microparticles
Well-formed clodronate-loaded microspheres were obtained for all polymers by selecting suitable process parameters (inner
water/oil volume ratio 1∶16, temperature-raising rate in the solvent evaporation step 1°C/min, 2% wt/vol NaCl in the external
aqueous phase). Good yields were obtained in all batches of clodronate microspheres (above 60%); drug encapsulation efficiencies
ranged between 49% and 75% depending on the polymer used. Clodronate release from all copolymer microspheres was completed
in about 48 hours, while those from PDLLA microspheres required about 20 days. The change of microsphere composition by adding
a surfactant such as Span 20 or a viscosing agent such as carboxymethylcellulose extended the long-term release up to 3 months.
Clodronate was successfully entrapped in PLGA and PDLLA microspheres, and drug release could be modulated from 48 hours up
to 3 months by suitable selection of polymer, composition, additives, and manufacturing conditions.
Published: July 11, 2001. 相似文献