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It is also defined as a process in which solids, liquids, or gases are enveloped in a membrane that may be impermeable or semi-permeable. The particle size of the microcapsules is ranging from 5-500, even extended up to 2000 microns depending on the material to be encapsulated, type of coating material, core to coat ratio and methods of preparation. Microcapsules belong to “reservoir” system . Slide 3: Applications of microcapsules: 1- Sustained action of drug. Size of capsules. Type of coating material. Thickness of coating materials. Permeability of the drug through the coat. Eg: ferrous sulfate MC, increasing coating material produces sustained action over 24hr. 2- Masking the disagreable taste and odor. Eg; erythromycine, chroramphenicole. Slide 4: 3- Stabilization of oxygen and moisture sensitive drugs. eg: vitamine A. Time (days) Percent potency remaining 100% Encapsulated Vit A Uncapsulated vit A Slide 5: 4- separation of the incompatible drugs. Eg: Aspirine+chloramphenicol SA Days Uncapsulated Aspirin Aspirine+chloram. MC of aspirine +chloram Slide 6: 5- Reducing side effect. Eg: NSAI when given orally. 6- Converting liquids to solids. Eg: cod liver oil. 7- Other uses: Immunoisolation(coating of single cell or tissues). Slide 7: Drawbacks of microcapsulation: 1- Incomplete coating. 2- Inadequate stability of sensitive materials. 3- Nonreproducible and unstable release. 4- Economic limitations. Slide 8: Methods of Microencapsulation: Spray drying. Spray congealing. Coaservation phase separation. Electrostatic spraying. Interfacial polymerization. Air suspension. Slide 9: 1- Spray Drying and Spray congealing: Rapid evaporation of the solvent from the droplets producing a free flowing particles.eg: ibuprofin, indomethacine. Spray congealing: the drug suspension in melted coat (fat or wax)then quickly cooed. Slide 10: Coascervation – phase separation: Coascervation: is flocculation or separation of liquids from solution containing colloidal solute, under the influence of different factors such as temp., pH adjustment, addition of electrolyte or solvents, and initiation of chemical reactions. Simple coascervation: Addition of electrolyte to produce salting-out of two phases effect thus meaning the formation of two phases, rich and poor in colloidal polymer aggregates. COACERVATION / PHASE SEPARATION : COACERVATION / PHASE SEPARATION 1.Formation of three immiscible phase 2.Deposition of coating 3.Rigidization of coating. Slide 12: Air suspension (Wurster process): This method involves the dispersing of solid, particulate core materials in a supporting air stream and then spray coating of the air suspending particles. Eg: carbazochrome sodium sulphonate. Slide 13: Core and coat Materials Microcapsules consist of two important parts: core and coat materials. The Core materials: They include active constituents which are either water soluble or insoluble with or without additives ( surfactant, retardants….etc) Slide 14: The Coating materials: The wall forming materials which are chemically compatible and non reactive with the core materials should provide a cohesive membrane with desired coating properties such as flexibility, solubility, permeability, strength and stability. Slide 15: eg: on coating materials, gelatin, gum arabic, cellulose derivatives, acrylic polymer and waxes. Application of coat depends on: - physico chemical properties of the drug. type pf product desired. Ehtyl cellulose is used to prepare sustained released MC. Eg: ascorbic acid. Release of drug from microcapsules : Release of drug from microcapsules The release of drug from microcapsule involves many steps according to the following equation: RT = r1+r2+r3 Where: r1: the rate at which the solvent penetrates the wall materials. r2: rate at which the drug dissolves. r3: the rate at which the dissolved drug penetrates the wall. Slide 17: r1 r2 r3 Drug Polymer membrane Drug release from microcapsules Factors affecting release of drugs : Factors affecting release of drugs pH pH during preparation may affect the properties of membrane. Solubility of drug in different pH dissolution media. Hardening agents (cross linking agents) Kinetic of drug release depends on cross liking method and type of cross linking agent. Slide 19: Effect of stirring speed: high stirring speed leads to smaller capsules size = high surface area. *Drug loading and colloidal polymer. ratios of core to coat. type of polymer *Additives: Surfactants, lubricants, bulking agents….etc. Dosage forms : Dosage forms Mainly microcapsules are filled in hard gelatin capsules or compressed as tablets. Gels and suspensions. Eg: ibuprofen, metronidazole tab. Fenbid ® (ibuprofen) Tablets and gel You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.