Coacervation Phase Separation

Coacervation-phase separation is a method to use a coacervation-inducing agent to reach the coacervation-phase separation during/after the solvent evaporation to form the microcapsules or the nanocapsules. The coating can be controlled by changing the parameters during the process, so that the drug content, particle size distribution, biomedical properties, etc. of the microcapsules/nanocapsules can be controlled. This procedure has been employed widely for preparation of microcapsules/nanocapsules for drug release.

Terbutaline sulphate microcapsules were prepared by coacervation-phase separation induced by the solvent evaporation technique [472-474]. The cellulose acetate phthalate was employed as coating material alone and in combination with ethyl cellulose. The prepared microcapsules were evaluated for their drug content, particle size distribution (microscopic method), flow properties, bulk density, and in vitro dissolution. Propranolol hydrochloride microcapsules were prepared by the coacervation-phase separation induced by the solvent evaporation technique [475].

Microcapsules of phenylpropanolamine HCl were prepared by three techniques, viz. coacervation-phase separation, air suspension, and pan coating, using different polymers and/or waxes as wall-forming materials [476].

Microcapsules were prepared from naproxen and ethylcel-lulose by coacervation phase separation, using polyisobuty-lene as a coacervation-inducing agent [477]. The micrometric properties of the microcapsules and dissolution behavior were examined. Using polyisobutylene at different concentrations, the release of naproxen during an in vitro dissolution test from 60 to 90% was regulated. The microcapsules were aggregates of individually coated naproxen crystals clustered together.

Using ethylcellulose and cellulose triacetate as co-wall materials, sustained release microcapsules of theophylline were prepared. The solid drug dispersed in the cellulose triacetate matrices was first prepared by solvent evaporation; then the matrices were microencapsulated by means of coacervation-phase separation of ethylcellulose from toluene solution on addition of petroleum ether [478].

Phenytoin sodium was microencapsulated with ethylcellu-lose by a coacervation-phase separation method from ethyl acetate solution to develop a prolonged release dosage form of phenytoin [479].

Microcapsules of phenylpropanolamine (PPA) hydrochlo-ride with core:wall ratios of 1:1, 2:1, and 1:2 were prepared by the coacervation-phase separation method, using ethylcellulose as the coating material [480]. Two batches of PPA • HCl powder with different particle sizes were used as the core material. The different sizes of microcapsules were separated using a range of standard sieves. The effects of drug particle size, the media pH, and the core:wall ratio on the dissolution kinetics were evaluated kinetically.

The preparation of lipid vesicles using simple coac-ervation was described [481]. The optimal coacervation conditions for the formation of lipid vesicles by the triangular phase diagram of the lipid-alcohol-water system were examined. Four different alcohols (methanol, ethanol, «-propanol, and 2-propanol) were used as a lipid solvent, and deionized, distilled water was used as a poor solvent for the lipids. The lamellarity and size homogeneity of the resulting lipid vesicles were observed using a specific fixation technique with malachite green. The majority of vesicles formed by methanol as a lipid solvent appeared to be large and unilamellar, ranging from 100 to 1000 nm in diameter.

Surfactant precipitation is one method of separating and concentrating surfactant for reuse from a subsurface surfactant-based remediation process. The dialkyldiphenylether disulfonates was shown to be very effective in this application as one class of surfactant [482]. The precipitation and coacervation phase boundaries for a surfactant mixture, which was primarily didecyldiphenylether disulfonate as a function of concentration of added NaCl and KCl, were reported [482].

Nicardipine hydrochloride (N.HCl) microcapsules were prepared by means of the coacervation phase separation technique using ethylcellulose as a coating material [483, 484]. Micromeritic investigations were carried out on nicardipine hydrochloride, ethylcellulose, and nicardipine hydrochloride microcapsules in order to standardize the microcapsule product and to optimize the pilot production of dosage forms prepared with these microcapsules.

Ketorolac tromethamine is a nonsteroidal drug with potent analgesic and anti-inflammatory activity and is absorbed rapidly [T-max (1.0 h) with an efficiency >87%] following oral and intramuscular administration. Microcapsules of the ketorolac tromethamine were prepared by means of the coacervation-phase separation technique induced by the addition of nonsolvent, and release rates from microcapsules were studied [485]. Eudragit S100 was used as the coating material.

Nitrofurantoin, a synthetic bactericidal drug, was encapsulated with Eudragit RS 100 polymer by a coacervation phase separation technique using variable proportions of poly-isobutylene (0% to 3%) as a protective colloid [486]. The in vitro release experiments were carried our over the entire pH range of the gastrointestinal tract, the data obtained from the dissolution profiles were compared in light of different kinetic models, and the regression coefficients were compared. The in vivo studies were performed on female human volunteers.

Rhizobacteria-containing polymer microparticles were prepared using either a complex coacervation-phase separation method or a spray-drying technique [487]. The microparticles obtained were characterized with regard to their particle size distribution, morphology, and bacterial content. Long-term bacterial survival within the micropar-ticles stored under controlled conditions (relative humidity and temperature) was investigated.

The aspirin-impregnated microspheres of chitosan/poly (acrylic acid) copolymer were produced in order to evaluate the release characteristics as a function of pH, simulating the fluids in the gastrointestinal tract [488]. Chitosan micro-spheres were obtained by the coacervation-phase separation method, induced by the addition of a nonsolvent (NaOH 2.0 M solution). The microspheres were cross-linked with glutaraldehyde, reduced with sodium cianoborohydride, and grafted with poly(acrylic acid).

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