PubMed · 9891337
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
E C Liao, L I Zon. 1999. Simple sequence-length polymorphism analysis.. https://doi.org/10.1016/s0091-679x(08)61900-7
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
Besides parenteral delivery, polymeric nanoparticles have been used for oral drug delivery. In this study, model polymeric nanoparticles (aqueous colloidal polymer dispersions: Eudragit(R) RL 30D, L 30D, NE 30D, or Aquacoat(R)) with different physicochemical properties were incorporated into various solid dosage forms (granules, tablets, pellets or films). The compatibility of the nanoparticles with commonly used tabletting excipients and the redispersibility of the nanoparticles after contact of the solid dosage forms with aqueous media were investigated. Ideally, the nanoparticles should be released from the solid dosage forms with their original properties. The addition of polymeric binders (e.g. polyvinylpyrrolidone, Na carboxymethylcellulose or hydroxypropyl methylcellulose) to the aqueous nanoparticle dispersions prior to wet granulation resulted in phase separation (depletion or bridging flocculation) for many nanoparticle/binder systems. Two critical parameters for the complete redispersibility/release of the nanoparticles with the original particle size properties from the solid dosage forms were a (1) high minimum film formation temperature (MFT) of the polymer dispersion and (2) a good wettability of the dried polymeric nanoparticles. Nanoparticle dispersions with a low MFT were not redispersible, they coalesced into larger agglomerates/films during the drying step. Contact angle measurements correlated well with the redispersibility of the nanoparticles, with ethylcellulose particles having high contact angles and poor redispersibility and Eudragit(R) RL, a polymer stabilized with quaternary ammonium groups, having low contact angles and good redispersibility.
Controlled-release (CR) matrix tablets of ibuprofen (IBF) and Carbopol(R) 934P, and blended mixture of Carbopol(R) 934P and 971P resins, at different drug to polymers ratios, were prepared by the direct compression method. The investigation focuses on the influence of the proportion of the matrix material, and several co-excipients (lactose, microcrystalline cellulose (MCC), and starch) on the mechanism and release rate of the drug from the tablets. In vitro drug release in pH 7.2 phosphate buffer solution appears to occur both by diffusion and a swelling-controlled mechanism, exhibiting either anomalous or Case II type transport. The release process could be described by plotting the fraction released versus time and fitting data to the simple exponential model: Mt/Minfinity=ktn. The release kinetics were modified when the blended mixtures of Carbopol(R) 934P and 971P resins were used as the matrix materials. In general, all of the co-excipients, used in this study, enhanced the release rate of IBF. However, lactose demonstrated slower and more linear release behavior as compared to microcrystalline cellulose or starch. The dissolution T50 and T90 values for the three co-excipients were in the order of lactose>microcrystalline cellulose>starch.
The separation of macromolecules such as polymers and DNA by means of electrophoresis, gel permeation chromatography or filtration exploits size-dependent differences in the time it takes for the molecules to migrate through a random porous network. Transport through the gel matrices, which usually consist of full swollen crosslinked polymers, depends on the relative size of the macromolecule compared with the pore radius. Sufficiently small molecules are thought to adopt an approximately spherical conformation when diffusing through the gel matrix, whereas larger ones are forced to migrate in a snake-like fashion. Molecules of intermediate size, however, can get temporarily trapped in the largest pores of the matrix, where the molecule can extend and thus maximize its conformational entropy. This 'entropic trapping' is thought to increase the dependence of diffusion rate on molecular size. Here we report the direct experimental verification of this phenomenon. Bragg diffraction from a hydrogel containing a periodic array of monodisperse water voids confirms that polymers of different weights partition between the hydrogel matrix and the water voids according to the predictions of the entropic trapping theory. Our approach might also lead to the design of improved separation media based on entropic trapping.