Expanded versatility of microcapsules prepared by interfacial polymerization.
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Capsules↗
Biomedical subjects
J W McGinity
Publications and source records attributed to J W McGinity.
Polylactic acid microspheres containing quinidine base and quinidine sulphate prepared by the solvent evaporation technique. I. Methods and morphology.
D,1-polylactic acid (PLA) microspheres containing the antiarrhythmic drug, quinidine, were prepared by the solvent evaporation method. The drug was present as either the base or as the sulphate salt. A slight modification in the process resulted in high yields of free-flowing, non-aggregated microspheres. The successful entrapment of drug within the microspheres was highly dependent on drug solubility in the aqueous phase. Diffusion and drug loss to the aqueous phase was minimized by adjusting the pH of the aqueous phase to minimal drug solubility. Saturation of the aqueous phase with drug further improved the payload of the microspheres. The appearance of the microsphere surface depended on the pH of the aqueous phase, the electrolyte concentration, and the type and amount of drug present. Structural changes and erosion of the polymer were observed at high pH-values.
Hydrogen-Ion Concentration↗
Polylactic acid microspheres containing quinidine base and quinidine sulphate prepared by the solvent evaporation technique. II. Some process parameters influencing the preparation and properties of microspheres.
D,L-polylactic acid (PLA) microspheres containing quinidine base and quinidine sulphate were prepared by the solvent evaporation method. The present study was carried out to examine how various process parameters in the aqueous phase influenced the preparation and properties of PLA-microspheres. The amount of drug that could be incorporated into the microspheres depended primarily on the solubility of the drug in the aqueous phase and the precipitation of PLA at the droplet surface. The drug content was found to be influenced by the organic solvent: aqueous phase ratio, the temperature of the aqueous phase, and the amount of emulsifying agent. Time-dependent pH-change studies in the aqueous phase showed that polymer precipitation at the outer surface of the microspheres, and drug loss due to partitioning, occurred rapidly. A partition method for increasing the payload of drug in the microspheres was developed by incorporating drug in both the aqueous and the organic phases. Using this method, drug could be loaded into the microspheres independent of the pH of the aqueous media. The partition method circumvented the surface degradation observed with PLA microspheres prepared at high pH values of the aqueous phase. This method may prove useful for the entrapment of water-soluble drugs.
Hydrogen-Ion Concentration↗
Polylactic acid microspheres containing quinidine base and quinidine sulphate prepared by the solvent evaporation method. III. Morphology of the microspheres during dissolution studies.
Poly(dl-lactide) (PLA) microspheres containing quinidine or quinidine sulphate were prepared by the emulsification-solvent evaporation technique. The in vitro release profile of quinidine or quinidine sulphate from the microspheres was characterized by three phases: a lag time, a rapid release phase (burst), and a slow release phase. Drug release was studied as a function of the ionic strength of the dissolution medium, to demonstrate the importance of the water imbition into the microspheres which induced the drug release. The lag time increased with increasing ionic strength. The microspheres stayed intact during the dissolution study as shown by scanning electron microscopy (SEM). Disintegration of microspheres which was initially observed was an artifact introduced during the SEM procedure. The high vacuum applied either during the coating of the microspheres with gold-palladium or during the actual observation in the scanning electron microscope caused the microspheres to collapse or rupture.
Chemical Phenomena↗
Preparation of multi-phase microspheres of poly(D,L-lactic acid) and poly(D,L-lactic-co-glycolic acid) containing a W/O emulsion by a multiple emulsion solvent evaporation technique.
Multi-phase microspheres of poly(D,L-lactic acid) (PLA) or poly(D,L-lactic-co-glycolic acid) (PLGA) containing a water-in-oil (W/O) emulsion were prepared by a multiple emulsion solvent evaporation technique. Acetonitrile was used as the solvent for the polymers and light mineral oil as the dispersion medium for the encapsulation procedure. Process and formulation parameters to optimize the microencapsulation of a W/O emulsion containing water-soluble drugs were investigated. Drug loading efficiencies of 80-100 per cent were obtained under specific preparative conditions. The drug loading efficiency in the microspheres was dependent upon the ratio of the W/O emulsion to polymer and the concentration of surfactant in the mineral oil. Compared to conventional microspheres, in which fine drug particles are homogeneously dispersed in the polymer beads, the multi-phase microspheres permit the higher encapsulation efficiency of water-soluble drugs and eliminate partitioning into the polymer-acetonitrile phase which results in low encapsulation efficiency with conventional solvent evaporation techniques.
Acetonitriles↗
Properties of multiphase microspheres of poly(D,L-lactic-co-glycolic acid) prepared by a potentiometric dispersion technique.
Multiphase microspheres of poly(D,L-lactic-co-glycolic acid) (PLGA) were prepared by a multiple emulsion potentiometric dispersion technique. Water-soluble compounds were dissolved in the aqueous phase (W) and emulsified in soybean oil (O) to form a stable emulsion. This primary emulsion was dispersed in a solution of PLGA and acetonitrile (O) to form a W/O/O emulsion. The W/O/O emulsion was then dispersed in a hardening solution of light mineral oil (O) using a potentiometric dispersion technique to produce microspheres of the W/O/O/O type with a very narrow and selective size distribution. The size of the microspheres was controlled by varying the internal diameter of the conductive infusion tube or by the variation of voltage applied to the conductive tube. Particle size analysis revealed a particle size distribution of 1-50 microns for microspheres made by this method as compared to a distribution of 50-500 microns for microspheres made by conventional agitation methods. Chlorpheniramine maleate was encapsulated with a loading efficiency of 88.9% with the potentiometric method as compared with a loading efficiency of 74.3% for the agitation method.
Chemistry, Pharmaceutical↗
Properties of multiphase microspheres of poly(dl-lactic acid) or poly(dl-lactic-co-glycolic acid) produced by mechanical agitation, sonication, or potentiometric dispersion.
The effect of processing techniques on the molecular weight of the polymer in biodegradable microspheres of poly(dl-lactic acid) (PLA) and poly(dl-lactic-co-glycolic acid) (PLGA) was investigated. Multiphase microspheres were produced by conventional agitation, potentiometric dispersion, or sonication. Gel permeation chromatography was used to determine the molecular weight of the polymer before and after processing. Polymer in microspheres of PLA produced by sonication experienced a 21% decrease in molecular weight of the polymer after 90 s of sonication, while microspheres made by potentiometric dispersion or mechanical agitation exhibited insignificant changes in molecular weight. Microspheres produced by potentiometric dispersion were found to have a more narrow particle size distribution compared to the other methods. A decrease in the internal diameter of the infusion tube used to produce multiphase microspheres by the potentiometric dispersion method was found to decrease the mean particle size of the resultant microspheres. Two surfactants were investigated at varied levels for utilization in the continuous phase, and particle size analysis revealed that increased surfactant levels caused an increase in the mean particle size of microspheres containing BSA produced by potentiometric dispersion. This phenomenon was attributed to an increase in conductivity of the continuous phase as the surfactant level was increased.
Chemistry, Pharmaceutical↗
Changes in brain pH, PO2, PCO2, cerebral blood flow, and blood gases induced by a hyperosmolar oxyreplete hemosubstitute during cardiopulmonary bypass.
Eleven goats (mean weight, 69 +/- 16 kg) underwent 5 hrs of normothermic nonpulsatile cardiopulmonary bypass (CPB) using as priming fluid either a Ringer's based crystalloid priming solution (CP, n = 5) of a hyperosmolar oxyreplete hemosubstitute (HS, n = 6). The HS contained 20% w/v perfluorocarbon (perfluorodecalin), its osmolarity was 800-900 mOsm/1, and the administered dose of perfluorocarbon was 30-50 ml/kg. Otherwise, the experimental procedure was identical for both groups. PaCO2 was maintained above 35 mmHg and blood flow rate at 65 ml/kg. Brain tissue pH, PO2, and PCO2, cerebral blood flow (CBF), arterial and venous blood gases, and other systemic variables were monitored. During CPB, PVO2 and brain tissue PO2 were increased significantly in the HS group. The CBF per kilogram of weight also was significantly higher in the HS group. Metabolic acidosis developed in both groups and, surprisingly, brain tissue pH and pHV were lower in the HS group. The mean values of PVCO2 and brain tissue PCO2 indicate that brain tissue hypercapnia also occurred in both groups. The HS provided long-term stability and compatibility with electrolytes, and did not cause major complications or allergic reactions during CPB. Perfluorocarbon based HSs improve tissue oxygenation, eliminate the risk of infection due to homologous transfusions, do not require blood type matching, have a shelf life longer than that of blood, and, therefore, they can be an important factor in diminishing the incidence of complications after CPB.
Animals↗