Effect of capsule size on permeability of gelatin-acacia microcapsules toward sodium chloride

Nimesulide PLA microspheres as a potential sustained release system for the treatment of inflammatory diseases

Polylactic acid (PLA-L) microspheres were prepared as a biodegradable polymeric carrier for a non-steroidal anti-inflammatory drug, nimesulide. The preparation of this system was performed by the classical emulsion solvent-evaporation method. Size analysis of the microparticulate system showed that unloaded and loaded nimesulide-PLA microspheres had average diameters of about 42.9 nm and 2.1 microm, respectively. Scanning electron microscopy (SEM) of loaded and unloaded microsphere samples showed that the particles shape were perfectly spherical, the loading efficiency of nimesulide in PLA microspheres was 70%; Thus, the microparticle system evaluated in this work showed the potential to act as a sustained release system for nimesulide: in vitro dissolution profiles showed the PLA-L microparticles were able to sustain the release of the drug for a considerable period of time (28.7% within 108 h).

Release characteristics of an azo dye from poly(ureaurethane) microcapsules

The time course for the transfer of azo dyes from the microcapsule core of dioctylphthalate to the dispersing medium of methanol through a poly(ureaurethane) (PUU) membrane was measured for various average size microcapsules with a size distribution. The dye release curves are represented by a stretched exponential function C(t)=C(eq)[1-exp [-(t/tau(eff))(alpha)]], where C(t) is the concentration of the dye in methanol, C(eq) that at the equilibrium state, and t the time. The exponent alpha decreased by increasing the variance of the size distribution of microcapsules. The effective time constant tau(eff) was expressed by tau(eff)=c(0)<R(2)>/kappa(alpha), where <R(2)> and kappa(alpha) are the mean square of microcapsule radius and a correction for the size distribution, respectively. The characteristic proportional constant, c(0), was determined as 2.6+/-0.2 min/microm(2). From the value of the constant, the diffusion coefficient of the azo dye in the PUU membrane was evaluated as 2.6 x 10(-12) cm(2)/s.

Permeability to solutes of polyamide capsules with different chemical compositions

The permeability of nylon capsule membranes with different chemical compositions to solutes was studied at different temperatures. The rate of solute permeation through the membrane decreased with increasing hydrophobicity of the membrane in the temperature range of 293-323 K. Increase in the size of permeant molecules caused a decreased in their rate of permeation through all capsule membranes at all temperatures studied. Higher permeation rates were observed for all permeants at higher temperatures. The activation energy of permeation was evaluated for the permeants from the Arrhenius plots of their permeation data. From the values of activation energy evaluated the solute permeation through the nylon capsule membranes was demonstrated to proceed by a pore mechanism.

Preparation and characterization of polylactic acid microspheres containing water-soluble dyes using a novel w/o/w emulsion solvent evaporation method

Polylactic acid (PLA) microspheres containing soluble dyes as water-soluble model compounds were prepared using the water-in-oil-in-water (w/o/w) emulsion solvent evaporation method. Addition of electrolytes such as NaCl or CaCl2 into the external aqueous phase significantly improved brilliant blue (BB) entrapment efficiency compared to the case of no additives. NaCl was the most effective for obtaining high entrapment efficiency (80-90% of theoretical BB content). The average diameter of the obtained microspheres was in the region of 10-20 microns in all cases. PLA microspheres containing 5 and 10% (w/w) BB exhibited the so-called burst release. The release rate decreased with decrease in the internal aqueous droplet volume in the preparation process. In particular, with PLA microspheres containing 5% (w/w) BB, those prepared with the smallest internal droplet volume (63 microliter), the initial burst release was reduced significantly, and 50% (w/w) of the loaded BB remained in the microspheres for 7 days.

Sustained-release dosage form of nitrofurantoin. Part 1. Preparation of microcapsules and in vitro release kinetics

A new sustained-release dosage form of nitrofurantoin as microcapsules was prepared by carboxymethylcellulose-aluminium sulphate simple coacervation technique. In vitro release studies for microcapsules and their formulated hard gelatin capsule and tablet forms were performed. Release rates were studied as functions of core: wall ratios and the particle sizes of the microcapsules. Dissolution tests of microcapsules and their dosage forms were studied in simulated gastric and intestinal media without enzyme using the USP XXI basket method. Release data were examined kinetically and the ideal kinetic models were estimated for drug release. In addition, optical and electron scanning microscopic works were carried out on the microcapsules.

Influence of total surface area of core material on yield of deposited coacervate

Influence of total surface area of core material on yield of deposited coacervate was evaluated. A simple coacervation method was employed solvent-evaporation method were used as a model core substance. A mixed polymer system--aqueous solution of gelatin and potassium salt of cellulose acetate phthalate--was used as a wall material. A sodium sulphate solution acted as a desolvating agent. Results obtained clearly show an opposite effect of the size of core material and derived total surface area on the yield of attached coacervate. While keeping the amount of core material constant, the amount of deposited coacervate increased both with the decreased size of core particles (increased total surface area), and increased concentration of desolvating agent. The proportion of wall material gradually increases with the increased concentration of sodium sulphate solution in the range from 1 to 9 per cent of the weight of microcapsules. Analysis of variance was used for the evaluation of obtained data.

Preparation of microcapsules from complex coacervation of Gantrez-gelatin. II. In vitro dissolution of nitrofurantoin microcapsules

Nitrofurantoin crystals were encapsulated in a Gantrez-gelatin complex coacervation system. The encapsulation process was reproducible and inexpensive and the microcapsules were free flowing and directly compressible into tablets. In vitro release of nitrofurantoin from Gantrez-gelatin microcapsules was studied as a function of the core:coat ratio, the molecular weight of Gantrez and the particle size of the microcapsules. The release of the drug was significantly reduced using G149-gelatin microcapsules of core:coat ratio of 1:2. Release data were examined kinetically and were found to follow a diffusion-controlled model. In vitro release of the drug from the microcapsules filled in capsules and compressed into tablets confirmed the efficiency of the encapsulation process for preparing prolonged release formulations.

Preparation of microcapsules from complex coacervation of Gantrez-gelatin. I. Development of the technique

Trials to induce complex coacervation between two grades Gantrez-AN polymer (G-AN), and Type A gelatin were made. Physical parameters influencing the coacervation process were studied. Maximum coacervation was attained when the pH of the gelatin solution was at 6.8. Increasing the molecular weight of Gantrez decreased the ratio of combination of both polymers. The ratio for optimum coacervation was 1:4 for Gantrez-AN 119-gelatin system and 2:3 for Gantrez-AN 149-gelatin system with total colloid concentration of 2.5 g per cent w/v in both cases. High stirring speed gave almost spherical uniform coacervates. Recovery of the product as water-insoluble discrete units required the use of formaldehyde and isopropanol for coacervate denaturation and flocculation, respectively.

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.

In vitro drug release from egg albumin microcapsules

The in vitro release of phenacetin from microcapsules prepared using egg albumin as the membrane material was investigated. It was shown by scanning electron microscopy that the albumin microcapsules have nonsmooth surfaces. The amount of phenacetin released is proportional to the square root of time up to 50-70% drug release. Increases in the albumin concentration and 1-vinyl-2-pyrrolidinone polymer content in the aqueous phases used in the microcapsule preparation have an effect on matrix porosity and channel tortuosity in the matrix of albumin microcapsules. The in vitro release rate was found to decrease with increasing albumin concentration and 1-vinyl-2-pyrrolidinone polymer content in the aqueous phases. The in vitro release rate per unit area also decreased with decreasing capsule size.

Volume of water-filled pores in the ethyl cellulose membrane and the permeability of microcapsules

The volume fraction of the water-filled pores in the microcapsule membranes was calculated and the values from 0.55 to 2.5% were obtained. Differential scanning calorimetry of aqueous suspensions of microcapsules showed no structured water present in the ethyl cellulose membranes. The temperature effect on the apparent diffusion coefficient of a drug was investigated and the apparent activation energy of diffusion was calculated.