Showing papers in "Journal of Microencapsulation in 1985"
TL;DR: The development of microparticulate food particles for marine suspension-feeders is discussed with respect to the difficulties of nutrient delivery in the aquatic environment and to feeding and digestion in crustacea and bivalve molluscs.
Abstract: The development of microparticulate food particles for marine suspension-feeders is discussed with respect to the difficulties of nutrient delivery in the aquatic environment and to feeding and digestion in Crustacea and bivalve molluscs. Loss of nutrients from particles suspended in seawater must be minimized by either trapping nutrients in gel particles or by encapsulation of the nutrients within impermeable walls. The gel matrix or capsule wall must be readily broken down by the animal so as to release the trapped dietary components.
65 citations
TL;DR: Not all of the adriamycin is released from the microspheres over 20 h; as biodegradation occurs in vivo after 24 h the amount of drug remaining in the system at 20 h is likely to be principally released by degradation of the protein matrix in vivo.
Abstract: Release of adriamycin from albumin and haemoglobin microspheres has been determined in vitro using a flow through system. Release from cross-linked albumin microspheres is controlled by the percentage of glutaraldehyde used but release profiles of spheres of 23, 41 and 60 μm diameter were virtually superimposable. Not all of the adriamycin is released from the microspheres over 20 h; as biodegradation occurs in vivo after 24 h the amount of drug remaining in the system at 20 h is likely to be principally released by degradation of the protein matrix in vivo. Estimates of the retained adriamycin vary from 16–26 per cent for albumin (n = 3) and 30 per cent for haemoglobin (n = 1).
26 citations
TL;DR: The results showed that rosin and rosin-glycerol intermediates with acid values of 122, 105 and 55 had excellent moisture protection properties and could be used for delayed release of drug.
Abstract: Rosin esters were prepared by heating rosin with glycerol and intermediate reaction products with different acid values were withdrawn. Salicylic acid granules were encapsulated using a 10 per cent solution of rosin esters in acetone. The coated microcapsules were evaluated for moisture absorption, flow properties and dissolution studies. The results showed that rosin and rosin-glycerol intermediates with acid values of 122, 105 and 55 had excellent moisture protection properties. Dissolution studies showed that these could be used for delayed release of drug.
25 citations
TL;DR: Eudragit retard microcapsules were prepared using an improved non-solvent addition phase separation process with tetrahydrofuran as the solvent and gave apparent first-order release profiles, confirmed by regression procedures.
Abstract: Eudragit retard microcapsules were prepared using an improved non-solvent addition phase separation process with tetrahydrofuran as the solvent. The evolution of microcapsule wall formation was studied by direct methodology. Eudragit coacervation was effected by progressive uptake of tetrahydrofuran by the non-solvent cyclohexane in the presence of a protective colloid, polyisobu tylene (PIB). The core materials had a higher affinity for the acrylic that the PIB phase, thus ensuring encapsulation. Microcapsule batch reproducibility depended mainly on the variation in particle size distribution of the recrystallized core material. All batches gave apparent first-order release profiles, confirmed by regression procedures. The release rate was decreased by raising the wall/core ratio, holding constant concentration of either the wall polymer or the core material. Increase in the non-solvent addition rate elevated the release rate, probably due to structural changes in the microcapsule wall. The veloc...
24 citations
TL;DR: Electrophoresis and gelatin adsorption studies revealed that cores onto which a large amount of gelatin has been adsorbed before coacervation can be encapsulated.
Abstract: Microencapsulation by way of simple coacervation by gelatin was examined. Five kinds of core material and six kinds of coacervation-inducing agent (CIA) were chosen and the encapsulability of each combination was studied. Some core materials are easily encapsulated, others are difficult to encapsulate, and some show a dependency of encapsulability on the CIA. Electrophoresis and gelatin adsorption studies revealed that encapsulation by way of simple coacervation by gelatin is caused by the affinity between core and coacervate resulting from gelatin adsorption on the core surface. These studies further revealed that cores onto which a large amount of gelatin has been adsorbed before coacervation can be encapsulated.
20 citations
TL;DR: The data indicate that the diffusion of the dissolution medium and dissolved drug through the ethylcellulose wall of the microcapsules is the rate-limiting step before dialysis, which implies that the release rate of the drug from dosage form significantly determined the absorption in the GI tract.
Abstract: Two types of coacervation-inducing agents (EVA, PIB) and three cooling rates (0.01998, 0.03482 and 0.06725d`C/min) affecting the preparation, micromeritic and drug release properties of bleomycin hydrochloride microcapsules were investigated. Particle size distribution of microcapsules induced by EVA significantly depended on the cooling rate, but that induced by PIB was independent of the cooling rate. Higher viscosity of PIB led to a smaller particle size of microcapsules than when EVA was used. The surface topography of the microcapsules for both types of coacervation-inducing agents was obviously different. We found that the release behaviour of bleomycin hydrochloride from the microcapsules also depended on the type of coacervation-inducing agent and the cooling rate. In general, the slower the cooling rate the more prolonged the release of the drug. Higuchi matrix model was followed for bleomycin hydro chloride released from the microcapsules. T50 of both types of microcapsules decreased wit...
20 citations
TL;DR: Control release behaviour from microcapsules was successfully investigated by using encapsulated anhydrous sodium sulphate (ASS) particles, and applying the Higuchi model to the estimation of the effective diffusion coefficient of ASS through the composite wall.
Abstract: Coacervation in polystyrene (PS)-cyclohexane solution induced by the lowering of temperature was utilized to investigate the fundamental problems involved in the microencapsulation procedure. Polydispersity of PS played a vital role in determining variables at the critical state of phase separation, such as the composition of coacervate (dense) and lean phases. This also depended on temperature. Observations revealed that microcapsules of glass beads consist of a wall with a thin film of PS covered with a thick shell of talc. Poor utilization of PS may limit practical applications of this system unless effective measures are taken for the recovery of unutilized PS. Controlled release behaviour from microcapsules was successfully investigated by using encapsulated anhydrous sodium sulphate (ASS) particles, and applying the Higuchi model to the estimation of the effective diffusion coefficient of ASS through the composite wall. The values of diffusion coefficient decreased from an order of 10(-7) to 10(-8) cm/s by lowering the encapsulation temperature.
18 citations
TL;DR: The microcapsule suspension showed prolongation of miosis and an improved bioavailability when compared with a standard eye dosage form.
Abstract: Poly(lactic acid) microcapsules of pilocarpine hydrochloride were prepared and evaluated by measuring a miotic effect in rabbits. The microcapsule suspension showed prolongation of miosis and an improved a when compared with a standard eye dosage form.
15 citations
TL;DR: The Eudragit E 100 polymer did not give better bioavailability than ethylcellulose as a coating polymer on bacampicillin microcapsules, but when stimulated intestinal fluid was adjusted to have an ionic strength similar to intestinal fluid, a better in vitro-in vivo correlation was obtained.
Abstract: Bacampicillin hydrochloride has been microencapsulated to mask its very bitter taste. The objective of the study was to compare the in vitro release and bioavailability of bacampicillin hydrochloride from microcapsules coated with two principally different polymers: a water-insoluble polymer, ethylcellulose, and an acid-soluble polymer, Eudragit E 100. The last mentioned was supposed to have advantages from a bioavailability point of view since this polymer should dissolve rapidly upon reaching the stomach. In vitro release studies were performed in different types of media by using a flow-through cell technique and USP paddle apparatus. The in vivo study was performed on 20 healthy volunteers taking single 400 mg doses of the drug in the two microcapsule suspensions and a reference tablet according to a randomized cross-over design. When standard dissolution fluids were used, the Eudragit E 100-coated microcapsules revealed very rapid dissolution but were greatly dependent on buffer concentration and ionic strength. The ethylcellulose-coated microcapsules released the drug much more slowly than Eudragit E 100 when using standard dissolution fluids. They were also affected by buffer concentration and ionic strength. The reference tablet had a significantly higher bioavailability than the two microcapsule suspensions. In vitro-in vivo correlation was not obtained when using standard dissolution fluids according to USP. However when stimulated intestinal fluid was adjusted to have an ionic strength similar to intestinal fluid, a better in vitro-in vivo correlation was obtained. The Eudragit E 100 polymer did not give better bioavailability than ethylcellulose as a coating polymer on bacampicillin microcapsules.
12 citations
TL;DR: The potential for microencapsulation of viable Brevibacterium linens with methionine or cysteine in milkfat to produce sulphur compounds was examined and numbers inside capsules increased about three-fold during 48 h at 26 degrees C under anaerobic conditions before a slow decline.
Abstract: The potential for microencapsulation of viable Brevibacterium linens with methionine or cysteine in milkfat to produce sulphur compounds was examined in this study. More than 80 per cent of B. linens cells were encapsulated and then numbers inside capsules increased about three-fold during 48 h at 26 degrees C under anaerobic conditions before a slow decline. Most of micro-organisms (7 x 10(7)/ml) were still viable in the capsules after 15 days. More than 90 per cent of cysteine and methionine were encapsulated and 90, 80 and 60 per cent of the encapsulated amino acids were maintained in the capsules at 4, 12 and 26 degrees C, respectively, after 24 h. Most of the cysteine was oxidized to cystine during microencapsulation but still available to micro-organisms whereas methionine remained in the reduced form. Partition coefficients of methionine and cysteine to milkfat were 0.117 and 0.275, respectively, indicating that most of these substrates would be available to cells of B. linens in the capsules.
10 citations
TL;DR: The higher concentration of EVA causing a thick, compact wall lead to an effective prolongation of drug release and might be used as a protective colloid to prevent aggregation of the microcapsules.
Abstract: The effect of concentration of ethylene-vinyl acetate (EVA) copolymer, used as a coacervation-inducing agent, on the preparation of ethylcellulose microcapsules was studied with theophylline as the core material. The influence of EVA concentration on the micromeritic properties of the microcapsules and their drug release behaviour were investigated. Particle size distribution of the microcapsules obtained was dependent on the amount of EVA copolymer. As the EVA concentration increased the quantity of larger particles was reduced and that of the smaller particles was increased. Thus EVA might be used as a protective colloid to prevent aggregation of the microcapsules. The porosity of the microcapsules decreased with respect to EVA concentration, but the wall thickness of the microcapsules showed a corresponding increase. Zero-order release kinetics, from the resulting microcapsules in the initial dissolution phase was obtained. The apparent zero-order release rate in the initial steady-state decrea...
TL;DR: The location of the liposomes in the brain after rectal administration shows that the brain-blood barrier can be overcome successfully by this method, and the risk of embolism and hypersensitivity, strict control of sterility and some other undesirable effects can be avoided.
Abstract: Bangham-type liposomes, undergoing freeze-thawing cycles, were detected electron microscopically in the brain, liver and spleen of experimental animals 24 h after rectal administration. This novel approach has several important advantages over intravenous, intraperitoneal and other usual means of adminis tration of liposome drug-entrapped treatment and diagnostics for human application. The location of the liposomes in the brain after rectal administration shows that the brain-blood barrier can be overcome successfully by this method. Moreover, the risk of embolism and hypersensitivity, strict control of sterility and some other undesirable effects can be avoided. The possible role of rectal administration in the development of liposome drug-entrapped treatment and diagnostics is discussed.
TL;DR: Permeations of a fluorescent probe entrapped in the inner aqueous phase of a large nylon capsule membrane corked with phosphatidylethanolamine bilayers were reversibly controlled by the phase transition of bilayers, the ambient pH change, and the addition of Ca2+/EDTA from outside.
Abstract: Permeations of a fluorescent probe entrapped in the inner aqueous phase of a large nylon capsule membrane corked with phosphatidylethanolamine bilayers were reversibly controlled by (i) the phase transition of bilayers, (ii) the ambient pH change, and (iii) the addition of Ca2+ /EDTA from outside. Their signal-receptive permeation control could be reproduced repeatedly without damaging corking bilayers, in contrast to that of liposomal membranes.
TL;DR: It is shown that the electro-neutral form of L(+)-ascorbic acid diffuses faster across the membranes than the anionic form by about two orders of magnitude.
Abstract: The transmembrane diffusion of L(+)-ascorbic acid has been studied by means of 1H-n.m.r. spectroscopy using small unilamellar DPPC vesicles as a model system. It is shown that the electro-neutral form of L(+)-ascorbic acid diffuses faster across the membranes than the anionic form by about two orders of magnitude. The diffusion is influenced by a molecular interaction between L(+)-ascorbate and the membrane surface and depends also on the fluidity of the membrane. The calculated permeation coefficients of neutral L(+)-ascorbic acid are between 6 x 10(-10) and 3 x 10(-8) cm s-1 (35-52 degrees C).
TL;DR: The potential of albumin (bovine serum) microspheres as delivery systems for haematoporphyrin and/or its zinc derivative was probed at the molecular level and a model assuming the microsphere-bound drug is distributed into two pools, differing in their drug-microsphere affinities, was found to account well for the equilibria data.
Abstract: The potential of albumin (bovine serum) microspheres as delivery systems for haematoporphyrin and/or its zinc derivative was probed at the molecular level. The microspheres, prepared by heat denaturation, were stable to detergents and organic solvents but could be degraded by proteolytic enzymes. Drug loading was either by encapsulation during microsphere formation or by binding to preformed microspheres. The efficiency of encapsulation was found to depend on the initial drug/protein ratio with a saturable pattern. Binding of both drugs, or each alone, indicated the presence of two types of affinities of each drug to the microspheres. The leakage (release) of drug(s) from the microspheres into the aqueous medium over a period of several hours showed biphasic behaviour for each type of preparation, bound and encapsulated, for one or both drugs A model assuming the microsphere-bound drug is distributed into two pools, differing in their drug-microsphere affinities, with no interference between the t...
TL;DR: In vitro dissolution characteristics ofEthylcellulose-walled microcapsules of 4-sulphonamidophenoxyacetic acid and Higuchi-type kinetics seem to describe the release of the major part of the drug more adequately.
Abstract: Ethylcellulose-walled microcapsules of 4-sulphonamidophenoxyacetic acid were prepared and their in vitro dissolution characteristics were investigated. Different release kinetics must be applied according to the respective average particle size and wall content values of the microcapsule fractions. The 'dissolution model' appears to fit better with small thin-walled microcapsules whereas, for larger thicker-walled microcapsules, Higuchi-type kinetics seem to describe the release of the major part of the drug more adequately.
TL;DR: Rosin-glycerol esters have been used as microencapsulating materials and a quantitative correlation has been observed between the physico-chemical properties, i.e. acid value and moisture affinity, and the release characteristics from the encapsulated drug.
Abstract: Rosin-glycerol esters have been used as microencapsulating materials. A quantitative correlation has been observed between the physico-chemical properties, i.e. acid value and moisture affinity, and the release characteristics from the encapsulated drug.
TL;DR: The phase diagram of the system ethyl cellulose-chloroform-ethane diol has been studied and the differing phase regions determined and the effect of temperature of these regions is recorded.
Abstract: The phase diagram of the system ethyl cellulose-chloroform-ethane diol has been studied and the differing phase regions determined. The effect of temperature of these regions is recorded. The phase diagram is used to determine the optimal conditions for the preparation of microcapsules with a phenobarbitone core and the size distribution of the microcapsules is recorded.
TL;DR: A mechanistic model for vesicle formation is described to provide a clear understanding of the events occurring during the encapsulation stages and stability studies show that less than 4 per cent of the original enzyme leaks from the vesicles over a 250 day period upon storage at 4 degrees C.
Abstract: Large unilamellar lipid vesicles are prepared by a detergent dialysis procedure using β-D-octylglucoside as the detergent. This procedure is nondenaturing and allows for the encapsulation of sensitive biological molecules. Vesicles prepared with the composition of 2 mol phosphatidylcholine and 1 mol cholesterol have a mean diameter of 200nm and allow for the encapsulation of ISO molecules of alkaline phosphatase per vesicle without loss of activity. Stability studies show that less than 4 per cent of the original enzyme leaks from the vesicles over a 250 day period upon storage at 4°C. A mechanistic model for vesicle formation is described to provide a clear understanding of the events occurring during the encapsulation stages.
TL;DR: The results indicate that the cytochrome c liposome association did not provide efficient protection of this substrate from the subcellular reduction, suggesting that some CDP-diglycerides were entrapped by liposomal membranes and were not available to sub cellular membranes as substrates.
Abstract: The effect of adding small unilamellar lecithin liposomes, prepared in the presence of cytidine-diphosphoryl-1,2-diglycerides (CDP-diglycerides) or cytochrome c, on microsomal biosynthesis of phosphatidylinositol and NADPH-cytochrome c reduction and on mitochondrial biosynthesis of polyglycerophos-phatides and succinate-cytochrome c reduction was studied in isolated guinea-pig liver subcellular membranes. Both microsomal biosynthesis of phosphatidylinositol and mitochondrial biosynthesis of phosphatidylglycerol were significantly reduced when CDP-diglycerides associated with liposomes were used, suggesting that some CDP-diglycerides were entrapped by liposomal membranes and were not available to subcellular membranes as substrates. The degree of decrease in phospholipid biosynthesis depended on the membrane and the nature of fatty acids in CDP-diglycerides. The composition of mitochondrial polyglycerophosphatides synthesized in the presence of CDP-diglycerides-liposomes was also affected in respec...
TL;DR: Within various organic solvent based coating systems examined, one containing cellacephate and hydrogenated castor oil as cofilm formers was found to produce microcapsules of sodium salicylate by pan coating with optimum enteric properties, as determined by in vitro evaluation by scanning electron microscopy and dissolution studies.
Abstract: Within various organic solvent based coating systems examined, one containing cellacephate and hydrogenated castor oil as cofilm formers was found to produce microcapsules of sodium salicylate by pan coating with optimum enteric properties, as determined by in vitro evaluation by scanning electron microscopy and dissolution studies. Scintiscans showed that such microcapsules packed in an outer hard gelatin capsule shell lodged temporarily in the oesophagus and tended to form aggregates on liberation in the stomach of the dog. Because of their rapid clearance from the stomach, single dosage with these microcapsules only prolonged appearance of the plasma peak by about 1.5 h in comparison to a conventional form. The microcapsules showed no decrease in bioavailability and only slight faecal blood loss during acute toxicity testing for gastrointestinal bleeding.
TL;DR: It was found that core particle encapsulability can be improved by recrystallization from aqueous solution of an ionic polymer and the electrostatic attractive force between gelatin molecules in solution and a polymer attached to the core particle cause gelatin adsorption on the core surface to result in a great improvement in encapsULability.
Abstract: In microencapsulation by way of simple coacervation by gelatin, some core materials are encapsulated easily, whilst others are difficult to encapsulate or show an encapsulability dependent on the coacervation-inducing agent. The treatment of core materials to improve encapsulability was studied. It was found that core particle encapsulability can be improved by recrystallization from aqueous solution of an ionic polymer. Electrophoresis, microscopical observation and pH dependency of encapsulability of recrystallized cores revealed that the electrostatic attractive force between gelatin molecules in solution and a polymer attached to the core particle cause gelatin adsorption on the core surface to result in a great improvement in encapsulability.
TL;DR: This procedure was adapted for unilamellar vesicles by modifying the second step of the procedure to allow the localization of any item within the unilAMEllar liposome compartments.
Abstract: A procedure has been carried out previously to separate the aqueous phase and the lipidic lamellae from multilamellar liposomes (Bakouche and Gerlier, Analyt. Biochem.,1983, 130, 379). This procedure consisted in multiple short bursts of sonication at a temperature below the transition temperature (Tm) of the lowest melting component followed by an ultracentrifugation. The aqueous phase and the lipidic lamellae were recovered in the supernatant and in the pellet respectively. This procedure was adapted for unilamellar vesicles by modifying the second step of the procedure. A suspension of unilamellar liposomes containing 5,6-carboxyfluorescein (5,6-CF) as a probe for the aqueous phase was disrupted by sonication at low temperature. After gel nitration on to a Sephadex G100 column, the phospholipid bilayers were readily separated from the aqueous probe 5,6-CF. Such a procedure should allow the localization of any item within the unilamellar liposome compartments.