Single On Purpose: Redefine Everything. Find Yourself First. John Kim. Gundry, MD. Permission to Dream Chris Gardner. Asmitha Lisma. RiTu RAj. Jagannath Jena. Charan Thota. Nasla Nasar. Anitta Kattukkaren. Show More. Views Total views. Actions Shares. No notes for slide. Ppt microencapsulation 1. Pharm Under the guidance of Mrs. Associate Professor, Department of Pharmaceutics. The product obtained by this process is called as microcapsules. Eg: Ofloxacin. Eg: Eprazinone.
Eg: Vit. Eg: NaCl. Eg: Methyl salicylate. Eg: Aspirin and Chlorpheniramine maleate. Disadvantages of Microencapsulation. B Coating Material: Inert substance which coats on core with desired thickness. Water insoluble resins Ethyl cellulose, Polyethylene. Waxes and lipids Paraffin, Carnauba, Beeswax. Enteric resins Shellac, Zein. A Air Suspension Wurster Method Within the coating chamber, particles are suspended on an upward moving air stream. Spraying of coating material on the air suspended particles.
The cyclic process is repeated depending upon purpose of microencapsulation. Air stream serves to dry the product. B Pan Coating The particles are tumbled in a pan while the coating material is applied slowly as solution or atomized spray to the core.
To remove the coating solvent, warm air is passed over the coated materials or dusting of talc is done. C Coacervation Phase Separation: Simple coacervation Complex coacervation A desolvation agent is added for phase separation It involves complexation between two oppositely charged polymers. Prepare enteric-coated dosage forms selectively absorbed in the intestine rather than the stomach. It can be used to mask the taste of bitter drugs. To reduce gastric irritation.
Nitrofurantoin, Used to aid in the addition of oily medicines to tableted dosage forms. The non-flowable multicomponent solid mixture of niacin, riboflavin, and thiamine hydrochloride and iron phosphate may be encapsulated and made directly into tablets. Peppermint oil, Methyl salicylate. Such as fumigants, herbicides, insecticides and pesticides. This expansion results in a decrease in pressure within the chamber. Figure 5: Factors influencing encapsulation efficiency A lower molecular weight polymer had a higher solubility in methylene chloride than a higher molecular weight polymer.
End- capped polymers, which were more hydrophobic than non-end-capped polymers of the same molecular weight and component ratio, were more soluble in methylene chloride. Diffusion of drugs into the continuous phase mostly occurred during the first 10 minutes of emulsification; therefore, as the time the polymer phase stayed in the non-solidified semi-solid state was extended, encapsulation efficiency became relatively low.
Particle size and bulk density also varied according to the polymer. Since polymers having higher solubilities in methylene chloride stayed longer in the semi-solid state, the dispersed phase became more concentrated before it completely solidified, resulting in denser microparticles. Johansen et al. A similar explanation as above applies to this observation: Hydrophilic PLGA is relatively less soluble in the solvent, methylene chloride, and precipitates more quickly than the end-capped one.
High solidification rate might have increased the encapsulation efficiency. On the other hand, the authors attribute the increase to the enhanced interaction between PLGA and the protein through hydrogen bonding and polar interactions Walter et al The hydrophilicity of the polymer enhanced the stability of the primary emulsion, and it contributed to such an increase. Methylene chloride is more soluble in water than chloroform or benzene.
The significance of solubility of the organic solvent in water was also confirmed by the fact that the addition of water-miscible co-solvents such as acetone, methanol, ethyl acetate, or dimethyl sulfoxide DMSO , contributed to increase of the encapsulation efficiency. Knowing that the methanol is a non-solvent for PLA and a water-miscible solvent, it can be assumed that methanol played a dual function in facilitating the polymer precipitation: First, the presence of methanol in the dispersed phase decreased the polymer solubility in the dispersed phase Jeyanthi et al.
Second, as a water-miscible solvent, methanol facilitated diffusion of water into the dispersed phase. In order to explain the low encapsulation efficiency obtained with benzene, the authors mention that the benzene required a larger amount of water non-solvent than methylene chloride for precipitation of the polymer, and the drug was lost due to the delayed solidification.
However, given that benzene is a poorer solvent than methylene chloride for a PLA polymer, this argument does not agree with the widely spread idea that a poor solvent requires a smaller amount of non-solvent to precipitate a polymer. In fact, there could have been a better explanation if they had considered that the delayed solidification was due to the low solubility of benzene in water: As a poor solvent for a PLA polymer, benzene requires only a small amount of non-solvent for complete solidification of the polymer.
However, since benzene can dissolve only a tiny fraction of water, it takes much longer to uptake water into the dispersed phase. That is, while solubility of a polymer in an organic solvent governs the quantity of a nonsolvent required in precipitating a polymer, solubility of the organic solvent in the non-solvent limits diffusion of the non-solvent into the polymer phase.
Thus, when a cosolvent system is involved, both solubility of a polymer in a solvent and solubility of the solvent in a non-solvent participate in determining the solidification rate of the dispersed phase. Here, the authors used a co-solvent system, varying the ratio of the component solvents. Encapsulation efficiency increased, and initial burst decreased as the volume fraction of DMSO in the co-solvent system increased.
Particle size increased, and density of the microparticle matrix decreased with increasing DMSO. Overall, these results indicate that the presence of DMSO increased the hydrophilicity of the solvent system and allowed fast extraction of the solvent into the continuous phase, which led to higher encapsulation efficiency and larger particle size. Concentration of the polymer Encapsulation efficiency increases with increasing polymer concentration Mehta et al. For example, the encapsulation efficiency increased from High viscosity and fast solidification of the dispersed phase contributed to reducing porosity of the microparticles as well Schlicher et al.
The contribution of a high polymer concentration to the encapsulation efficiency can be interpreted in two ways. First, when highly concentrated, the polymer precipitates faster on the surface of the dispersed phase and prevents drug diffusion across the phase boundary Rafati et al.
Second, the high concentration increases viscosity of the solution and delays the drug diffusion within the polymer droplets Bodmeier and McGinity, It is likely that a large volume of continuous phase provides a high concentration gradient of the organic solvent across the phase boundary by diluting the solvent, leading to fast solidification of the microparticles. A relevant observation is described in the literature Sah, In this example, which utilized ethyl acetate as a solvent, the formation of microparticles was dependent on the volume of the continuous phase.
When 8 mL of PLGA solution o was poured into 20 or 50 mL of water phase w , the polymer solution was well disintegrated into dispersed droplets.
On the other hand, when the continuous phase was 80 mL or more, the microspheres hardened quickly and formed irregular precipitates.
This is because the large volume of continuous phase provided nearly a sink condition for ethyl acetate and extracted the solvent instantly. Due to the fast solidification of the polymer, particle size increased with increasing volume of the continuous phase.
This apparent discrepancy can be explained by the fact that low bulk density Mehta et al. The rate of solvent removal can be controlled by the temperature ramp or the evaporation temperature in the former and by the volume of the dilution medium in the latter.
PLGA microparticles containing salmon calcitonin sCT were prepared by emulsification, followed by different solvent removal processes Mehta et al. The microparticles that resulted from this process had a hollow core and a porous wall. The core size and wall thickness were dependent on the temperature ramp. It is believed that the hollow core was due to the rapid expansion of methylene chloride entrapped within the solidified microparticles.
In controlled extraction of the solvent, the solvent was removed gradually and slowly by dilution of the continuous phase, which left the microparticles in the soft state for a longer period of time. The resulting microparticles showed a highly porous honeycomb- like internal structure without a hollow core.
In the later study, it was noted that the porosity was a function of the amount of water diffused into the dispersed phase from the continuous phase, which could only be allowed before the dispersed phase solidified completely Li et al.
In other words, the high porosity of the microparticles was due to the slow solidification of the microparticles. Close suggestions Search Search. User Settings. Skip carousel. Carousel Previous. Carousel Next.
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Did you find this document useful? Is this content inappropriate? Report this Document. Flag for inappropriate content. Download now. Save Save 4- microencapsulation. Original Title: 4- microencapsulation. Related titles. Carousel Previous Carousel Next. Jump to Page. Search inside document. Microencapsulation Microencapsulation is a means of applying thin uniform coatings to microparticles of solids dispersion or droplets of liquids.
The stabilization of core materials 2. The control of release or availability of core materials 3. Separation of chemically reactive ingredients within a tablet or powder mixture.
The stabilization of core materials Examples: Microencapsulation of certain vitamins to retard degradative losses. The control of release or availability of core materials Controlled release from microencapsulated products are used for prolonged action or sustained-release formulations Example: The application of varied amounts of an ethyl cellulose coating to aspirin using coacervation phase-separation encapsulation techniques, where release of aspirin is accomplished by leaching or diffusion mechanism from the inert, pH-insensitive ethvl cellulose coating.
Step 3 Rigidizing the coating, By thermal , cross-linking formaldehyde , or desolvation techniques, to form a self-sustaining microcapsule. As sodium sulfate. Solvent evaporation This method of microencapsulation is the most widely used due to: 1. Simple technique. Microcapsules add many functional benefits particularly in skin care and treatment products include : Acting as controlled release vehicles Offering stabilization of materials that would otherwise be unstable.
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