Industrial Pharmacy Lecture 8 PDF

 INTRODUCTION Defination Microencapsulation is a process by which very tiny droplets or particles of liquid or solid material are surrounded or coated with a continuous film of polymeric material. Microencapsulation may be defined as the process of surrounding or envelo...

 INTRODUCTION Defination Microencapsulation is a process by which very tiny droplets or particles of liquid or solid material are surrounded or coated with a continuous film of polymeric material. Microencapsulation may be defined as the process of surrounding or enveloping one substance within another substance on a very small scale, yielding capsules ranging from less than one micron to several hundred microns in size." It is mean of applying thin coating to small particle of solid or droplet of liquid & dispersion. Microencapsulation is a process by which solids, Liquids or even gases may be enclosed in microscopic particles by formation of thin coatings of wall material around the substances. Particle size: 50-5000 micron. 2 phases: a) Core material b) Coating material The product obtained by this process is called as micro particles, microcapsules, microsphere, coated granules, pellets.. Particles having diameter between 3 - 800µm are known as micro particles or microcapsules or microspheres. Particles larger than 1000µm are known as Macroparticles.  A well designed controlled drug delivery system - can overcome some of the problems of conventional therapy. - enhance the therapeutic efficacy of a given drug. To obtain maximum therapeutic efficacy, drug is to be delivered: -to the target tissue -in the optimal amount -in the right period of time there by causing little toxicity and minimal side effects. One such approach is using microspheres as carriers for drugs. Microspheres are characteristically free flowing powders. consisting of proteins or synthetic polymers. biodegradable in nature.  REASONS FOR MICROENCAPSULATION 1. To protect reactive substances from the environment. 2. To convert liquid active components into a dry solid system. 3. To separate incompatible components for functional reasons. 4. To protect the immediate environment of the microcapsules from the active components. 5. Isolation of core from its surroundings, as in isolating vitamins from the effects of oxygen. 6. evaporation of a volatile core. 8. isolating a reactive core from chemical attack. 9. for safe handling of the toxic materials. 10. to get targeted release of the drug. 11. To control release of the active components for delayed (timed) release or long-acting (sustained) release. 12. The problem may be as simple as masking the taste or odor of the core. 13. To Increase of bioavailability. 14. Protects the GIT from irritant effects of the drug. Fundamental Consideration/Formulation considerations Generally Micro particles consist of two components a) Core material The solid core can be mixture of active constituents, stabilizers, diluents, excipients and release-rate retardants or accelerators. b) Coat or wall or shell material Compatible, non reactive with core material Provide desired coating properties like strength, flexibility. impermeability, optical properties, non hygroscopicity, tasteless and stable  Core Material The material to be coated. It may be liquid or solid or gas. Liquid core may be dissolved or dispersed material. Composition of core material: Drug or active constituent Additive like diluents Stabilizers  Coating Material Inert substance which coats on core with desired thickness. Composition of coating: Inert polymer Plasticizer Coloring agent Resins, waxes and lipids Release rate enhancers or retardants ROLE OF POLYMERS: Polymers are substances of high molecular weight made up by repeating monomer units. Polymer molecules may be linear or branched, and separate linear or branched chains may be joined by crosslinks. Polymers are used widely in pharmaceutical systems as adjuvants, coating materials and, a components of controlled and site- specific drug delivery systems  Coating Material Properties 1. Stabilization of core material. 2. Inert toward active ingredients. 3. Controlled release under specific conditions. 4. Film-forming, tasteless, stable. 5. Non-hygroscopic, no high viscosity, economical. 6. Soluble in an aqueous media or solvent, or melting. 7. The coating can be flexible, thin, etc. Coat thickness Depends on: The coating to core ratio The particle size (surface area ) of the core material  Advantages of Microencapsulation 1. To Increase of bioavailability 2. To alter the drug release 3. To improve the patient’s compliance 4. To produce a targeted drug delivery 5. To reduce the reactivity of the core in relation to the outside environment 6. To decrease evaporation rate of the core material. 7. To convert liquid to solid form & To mask the core taste.  Disadvantages of Microencapsulation 1. Microencapsulation techniques are of high cost. 2. Different dosage forms like tablets, capsules, lozenges can not be encapsulated by single microencapsulation process. 3. Coating may not be uniform this can effect release pattern of a drug in the body. 4. Possible cross reaction between core and shell material. 5. Difficulties to achieve continuous and uniform film. 6. Shelf life of hygroscopicity drugs is reduced. MICROENCAPSULATION TECHNIQUES 1. Air suspension techniques 2. Co-acervation process 3. Solvent evaporation 4. Pan coating 5. Polymerization 6. Spray-drying & congealing  Air suspension techniques It consist of dispersing the solid particulate core material in supporting air stream and being coated with coating material (usually polymeric solution) In this, the fine core materials are suspended in a vertical current of air and sprayed with the coating material After evaporation of solvent, a layer of encapsulating material is deposited on core Gives improved control and flexibility as compared to pan coating.  During each pass through the coating zone, the core material receives an increment of coating material. The cyclic process is repeated, p several hundred times during processing, depending on the purpose of microencapsulation the coating thickness desired. The supporting air stream also serves to dry the product while it is being encapsulated. Drying rates are related to the volume temperature of the supporting air stream. Disadvantage Agglomeration of the particles to some larger size is normally achieved. variables for efficient, effective encapsulation by air suspension techniques: 1.Density, surface area, melting point, solubility, friability, volatility, Crystallinity and flow-ability of core the core material. 2.Coating material concentration (or melting point if not a solution). 3.Coating material application rate. 4. Volume of air required to support and fluidizes the core material. 5. Amount of coating material required. Co-acervation process Steps of co-acervation phase separation process: 1. Preparation of the dispersion of core material into homogeneous coating polymer solution. 2. Desolvation or co-acervation of the polymer molecules (this results in formation of three immiscible phase i.e. polymer rich phase, solvent phase and dispersed phase). 3. Deposition of coating polymer on the core material. 4. Hardening of the coating. Step 1: Preparation of dispersion In the first step, we have to prepare a dispersion. The dispersion is called a suspension if the dispersed phase is solid. So Here, in this case, we are going to deposit coating material, on the surface of fine solid particles The dispersion is called emulsion if core material is liquid. So Here, in this case, we are going to deposite coating material on the surface of the liquid droplet.  Step 2: Co-acervation or desolvation of polymer molecules In the second step, polymer molecules from the solution are desolvated or co-acervated. Co-acervation is different from crystallization or precipitation or flocculation. According to the nature of the polymer, various changes such as a change in temperature or change in pH can reduce the solubility of the polymer. As a result of this, a large amount of polymer would separate out in a new phase This polymer-rich phase is called as a co-acervate, in which polymer remains in the amorphous liquid state. Methods of achieving co-acervation A. Change in temperature. B. Addition of incompatible polymer. C. Addition of non-solvent D. Addition of salt F. Polymer-polymer interaction Step 3: Deposition of polymer on core In this step, co-acervated polymeric molecules are deposited on the surface of core materials and form a thin film.  Step 4:Hardening of the coat Hardening of the coat material can be accomplished by multiple ways including: (desolvation, change in pH, reduction in temperature, crosslinking or gelation etc). Solvent evaporation (chemical proceess) Pan coating  POLYMERIZATION Spray-drying & congealing Microencapsulation by spray-drying is a low-cost commercial process which is mostly used for the encapsulation of fragrances, oils and flavors. Steps: 1- Core particles are dispersed in a polymer solution and sprayed into a hot chamber. 2- The shell material solidifies at the core particles as the solvent evaporates. - The microcapsules obtained as matrix type.  Spray Drying is the most commonly used encapsulation method in the food industry. The process is economical and flexible uses equipment that is readily available, and produces particles of good quality. The process involves three basic steps: Preparation of a dispersion or emulsion to be processed Homogenization of the dispersion and Atomization of the mass into the drying chamber. Spray dried ingredients typically have a very small particle size (generally less than 100µm) which makes them highly soluble. Typical shell materials include gum acacia, modified starch and mixtures. Other polysaccharides like alginate, carboxymethylcellulose and other gum. Proteins, soy proteins, can be used as the wall material in spray drying.  APPLICATION OF MICROENCAPSULATION TECHNIQUES Application Taste masking e.g. acetaminophen. Sustain release e.g. aspirin Conversion of liquid to solid e.g. clofibrate Odor masking e.g. castor oil Reducing gastric irritation e.g. phenylbutazone. Stabilization to oxidation e.g. vitamin  CONCLUSION 1.protection and masking. 2.reduced dissolution rate. 3.Easy of handling. 4.spatial targeting of the active ingredient. 5.This approach facilitates accurate delivery of small quantities of potent drugs 6.reduced drug concentrations at sites other than the target organ or tissue and protection of labile compounds before and after administration.