A new method of preparing monocored water-loaded microcapsules using interfacial polymer deposition process

Use of thermodynamic parameters for design of double-walled microsphere fabrication methods

Double-walled microspheres (DWMS), with drug localized to the particle core, present a promising route for control of drug release rates, for example, by varying the degradation rate or erosion mechanism of the polymer used to form the shell or the thickness of the shell. DWMS are often difficult to fabricate, however. Thermodynamic descriptions for polymer-polymer immiscibility, drug distribution between phases and polymer-solution spreading coefficient provide predictions of appropriate solvents and polymer concentrations for efficiently producing well-formed DWMS. As an example, thermodynamic parameters for a polyphosphoester/poly(D,L-lactide-co-glycolide) (PLG) DWMS system, encapsulating piroxicam, have been calculated and the predictions tested experimentally. Appropriate choices of solvents and initial polymer concentrations resulted in DWMS with the desired polyphosphoester shells and piroxicam located selectively in PLG cores.

In vitro degradation of polyanhydride/polyester core-shell double-wall microspheres

Double-wall microspheres (DWMS), comprising distinct polymer core and shell phases, are useful and interesting for controlled-release drug delivery. In particular, the presence of a surface-eroding polymer core may be expected to limit water penetration and, therefore, delay degradation of the core phase and drug release. In this study, solid microspheres and DWMS were fabricated using a surface-eroding polymer (poly[1,6-bis(p-carboxyphenoxy)hexane]; PCPH) and a bulk-eroding polymer (poly(D,L-lactide-co-glycolide); PLG). Erosion of the particles was observed by optical and electron microscopy, while polymer degradation was followed by gel permeation chromatography, during incubation in buffer at 37 degrees C. Degradation and erosion were very different depending on which polymer formed the particle shell. Nevertheless, the relatively thin (approximately 5 microm) PCPH shells could not prevent water penetration, and the PLG cores completely eroded by 6 weeks of incubation.

Preparation and characterization of biodegradable poly(l-lactide)/poly(ethylene glycol) microcapsules containing erythromycin by emulsion solvent evaporation technique

In this work, the producing of a biodegradable poly(l-lactide) (PLA)/poly(ethylene glycol) (PEG) microcapsule by emulsion solvent evaporation method was investigated. The effect of PEG segments added to the PLA microcapsules on the degradation, size distribution, and release behavior was studied. According to the results, PLA/PEG copolymer was more hydrophilic than PLA homopolymer, and with lower glass transition temperature. The surface of PLA/PEG microcapsules was not as smooth as that of PLA microcapsules, the mean diameters of prepared PLA and PLA/PEG microcapsules were 40 and 57 microm, respectively. And spherical forms were observed by the image analyzer and the scanning electron microscope (SEM). Drug release from microcapsules was affected by the properties of PLA/PEG copolymers determined by UV-vis spectra. It was found that the drug release rates of the microcapsules were significantly increased with adding of PEG, which explained by increasing hydrophilic groups.

Biodegradable poly(lactic acid) and poly(lactide-co-glycolide) microcapsules: problems associated with preparative techniques and release properties

Poly(lactic acid) [PLA] and its co-polymers with glycolic acid [PLCG] have been known to be biodegradable and histocompatible for the past 20 years. Their physico-chemical and biological properties have been found suitable, in many instances, for sustaining drug release in vivo for days or months. Several dosage forms for parenteral administration have been investigated using these polymers and a microencapsulation technique is chosen frequently for its unique properties. There are a limited number of published papers concerning preparation and characterization of PLA or PLCG microcapsules, possibly because of commercial unavailability and difficulties in the synthesis of reproducible batches of these polymers. However, microcapsules can be made using different traditional and non-traditional techniques containing core materials ranging from biological proteins to synthetic drugs. An attempt is made here to review problems associated with the different microencapsulation techniques using PLA or PLCG. In vivo and in vitro drug release from these microcapsules is also reviewed.

Permeability of ethylcellulose microcapsules towards phenobarbital

Inward permeation from the surrounding medium of phenobarbital through the wall of water-loaded ethylcellulose microcapsules was investigated as a function of capsule size under the conditions of constant total capsule volume and constant total capsule surface area. The experimental data obtained were analysed in terms of capsule wall density and drug partition coefficient. The drug permeability coefficients calculated according to an equation derived from Fick's first law of diffusion were found to increase with decreasing capsule size in both constant total capsule volume and constant total capsule surface area experiments. The wall density and the drug partition coefficient also exhibited the same trend. Based on these findings, it was concluded that the drug permeation through ethylcellulose microcapsule membrane occurs predominantly by a solution-diffusion mechanism.