Microencapsulation

Microencapsulation is a process in which tiny particles or droplets are surrounded by a coating to give small capsules, of many useful properties. In general, it is used to incorporate food ingredients, enzymes, cells or other materials on a micro metric scale.

1. Microencapsulation is a means of applying thin uniform coatings to micro particles of solids dispersion or droplets of liquids. Microcapsules are small particles that contain an active agent (core material) surrounded by a shell or coating. Their diameters generally range from a few microns to a few millimeters. Microcapsules can have many different types and structures: Simple droplets of liquid core material surrounded by a spherical shell (Microcapsules) Irregularly-shaped particles containing small particles of solid core material dispersed in a continuous polymer shell matrix (microspheres).

2. Core Material : The core material is the material to be coated, which may be liquid or solid in nature. The composition of the core material can be varied: The liquid core can include dispersed and/or dissolved material. The solid core can be a mixture of active constituents, stabilizers, diluents, excipients , and release-rate retardants or accelerators.

3. Coating material : Be capable of forming a film that is cohesive with the core material Be chemically compatible and non-reactive with the core material Provide the desired coating properties, such as strength, flexibility, impermeability, optical properties, and stability. Coating material selected from natural and synthetic film-forming polymers like: - carboxy methyl cellulose - ethyl cellulose - cellulose acetate phthalate - poly vinyl alcohol - gelatin, gelatin- gum arabic - poly hydroxy cellulose - waxes - chitosan

4. Chemical Microencapsulation

5. Coacervation-Phase Separation : Coacervation is Colloidal phenomenon. It is coacervate is tiny spherical droplet. Coacervate means aggregation.

6. Step 1 : Formation of three phases

7. Step 2 : Coating of Polymer Around Core As soon as Polymer gets coaservated from solution it forms coating around core material and then it is rigidized with Physical OR Chemical means. The coaservation deposits around core particle by : Coalescence of many inviduals droplets around core. Single coaservate droplet may encompass ore or more particles.

8. Step 3 : Rigidization of Coat Essential to impart stability and protection from drug leaching from microcapsule.

9. Polymer-polymer incompatibility : This method utilizes two polymers that are soluble in a common solvent, yet do not mix with one another in the solution Polymer form two separate phases, one rich in polymer intended to form the capsules walls, the other rich in the incompability polymer meant to induce separation of the incompatible polymer meant to induce separation of the two phases. The second polymer is not intended to be part of the finished microcapsules wall.

10. Interfacial Polymerization : The process is based on formation by interfacial polymerization reaction of two monomer dissolve in an aqueous or organic phase. Two monomers in a polycondensation or polyaddition meet at interface and condensed polymer wall form instantaneously at the interface of the emulsion droplets. The degree of polymerization can be controlled by : Temperation Monomer concentration Composition of either phase Example of wall material : Polyamide, polyuria, polyurethane epoxy resin.

11. In-Situ Polymerization : In this process direct polymerization of single monomer unit is carried out on particle surface. E.g. : Cellulose fiber are encapsulated in polyethylene while immersed in dry toluene. Usual deposition rate are about 0.5 micro meter / min. Coating thickness ranges 0.2 to 0.75 micro meter Matrix is uniform even over sharp projections.

12. Mechanical Encapsulation

13. Air Suspension : Microencapsulation by air suspension techniques using Wurster Air Suspension Apparatus control panel coating chamber particles being treated process airflow air distribution plate nozzle for applying film coatings

14. Principle : The Wurster process consists of the dispersing of solid particulate core materials in a supporting air stream and the spray-coating of the air ­ suspended particles. Within the coating chamber, particles are suspended on an upward moving air stream as indicated in the drawing. The design of the chamber and its operating parameters provide a recirculating flow of the particles through the coating zone portion of the chamber, where a coating material, usually a polymer solution, is spray-applied to the moving particles. During each pass through the coating zone, the core material receives an increment of coating material. The cyclic process is repeated several times during processing, depending on the purpose of microencapsulation, the coating thickness desired. The air stream also serves to dry the product while it is being encapsulated.

15. Capability of air suspension : The process has the capability of applying coatings in the form of solvent solutions, aqueous solutions, emulsions, dispersions, or hot melts The coating material selection appears to be limited only in that the coating must form a cohesive bond with the core material. The process generally is applicable only to the encapsulation of solid core materials Particle size, The air suspension technique is applicable to both microencapsulation and macroencapsulation coating processes with particle size range 35-5000 µm

16. Fluidized bed coater solvent extraction : Fluidized bed coater has become more popular. They are used for encapsulating solid or porous particle with optimum heat exchange. The coating is spread on particle and the rapid evaporation helps in formation of an outer layer on the particles.

17. Top Spray : In this the Coating Material is sprayed downwards on the fkuid such that as the solid or porous particle move to the coating region become encapsulated. Increased encapsulation efficiency and prevention oil cluster formation. Bottom spray : This is also known as “ Wurster’s coater “. This technique uses coating chamber that having cylindrical nozzles and perforated bottom plate. The cylindrical nozzle is used for spraying coating material. As particle move upward through the perforated bottom plate and pass though nozzle area, they are encapsulated by coating material. Tangential Spray : It consist of rotating disc at the bottom of the coating chamber with same diameter as the chamber. During process the disc is raised to create gap between edge of chamber and disc. The tangential nozzle is placed above the rotating disc through which the coating material is released. The particle move through the gap into the spraying zone and are encapsulated.

18. Rotational Suspension Separation :

19. Extrusion and Spheronization : Dispersion of core material in molten carbohydrate mass. Extruded in dehydrating liquid for hardening. Spheronization. Separation & dyeing.

20. Spray Drying and Spray Congealing : The Spray dryer equipment components include :

21. Spray Drying and Spray Congealing : Microencapsulation is conducted by dispersing a core material in a coating solution, in which the coating substance is dissolved and in which the core material is insoluble, and then by atomizing the mixture into a heated air stream. Microencapsulation by spray-congealing can be accomplished with spray drying equipment when the coating is applied as a melt . General process variables and conditions are quite similar to those spray drying , except that the core material is dispersed in a coating material melt rather than a coating solution. Waxes, fatty acids polymers , alcohols, and sugars, which are solids at room temperature but meltable at reasonable temperatures, are applicable to spray-congealing techniques. Coating solidification (microencapsulation) is accomplished by spraying the hot mixture into a cool air stream

22. Solvent evaporation :

23. Solvent Evaporation Diagram :

24. Pan Coating : Pan Coating process is used for solid particles greater than 600 microns in size. The coating is applied as a solution, or as an atomized spray, to the desired solid core material in the coating pan. Warm air is passed over the coated materials as the coatings are being applied in the coating pans to remove the coating solvent. Final solvent removal is accomplished in a drying oven. The coating operation is repeated three times. Then coating followed by dusting with talc the microcapsules are rolled until drying, and the excess talc is removed by vacuum. The product is then screened through a 12­mesh screen

25. Pan Coating Diagram :

26. Means of handling liquid solid Example : Eprazonium

27. Taste makin g of bitter drugs : Eg. Aspirin, Ampicillin etc.

28. Protein Stability :

29. Other application :