MICROENCAPSULATION

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INTRODUCTION :

INTRODUCTION Since life began, nature has been using the envelopment of systems for their protection or for providing a particular reaction space, the enveloping wall displaying additional specific membrane functions . The technique of microencapsulation aims at immobilizing gases, liquids or solids in an envelope. The result is a core contained in a capsule ranging from the nanometer to the millimeter scale.

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The technique of microencapsulation aims at immobilizing gases, liquids or solids in an envelope . The result is a core contained in a capsule ranging from the nanometer to the millimeter scale. Today , it is the mechanism utilized by approximately 65 percent of all sustained release system .hundred of drugs have been microencapsulated and used as sustained release systems.

Microencapsulation :

Microencapsulation Microencapsulation is the process by which individual particles or droplets of an active material (the core) are isolated by being surrounded with a coating (the shell) to produce capsules in the micrometer to millimetre range, known as microcapsules . These microcapsules release their contents at a later time by means appropriate to the application .

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Figure: Ca- Alg -coated, microspheres (450-1100) micrometers

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Many different active materials have been successfully encapsulated using a variety of coatings including gelatin, cellulose, polyethylene glycol and waxes. Figure : Microencapsulation layers

Reasons for encapsulation :

Reasons for encapsulation The reasons for microencapsulation are countless. In some cases, the core must be isolated from its surroundings, as in isolating vitamins from the deteriorating effects of oxygen , retarding evaporation of a volatile core . Improving the handling properties of a sticky material, or isolating a reactive core from chemical attack.

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In other cases, the objective is not to isolate the core completely but to control the rate at which it leaves the microcapsule, as in the controlled release of drugs or pesticides. The problem may be as simple as masking the taste or odor of the core, or as complex as increasing the selectivity of an adsorption or extraction process.

LITERATURE REVIEW :

LITERATURE REVIEW H. E. Feustel , et.al “Simplified numerical description of latent storage characteristics for phase change wallboard. Indoor Environmental Program, Energy and Environment Division Lawrence Berkely Laboratory University of California.” J Kelly Kissock . et.al “Testing and simulation of phase change wallboard for thermal storage in buildings”. In proceedings of the 1998 International Solar Energy Conference, 14 - 17, June, Albuquerque, Morehouse J M and Hogan R E(Eds. ) ASME, New York

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J. Kosny , et.al “Energy Benefits of Application of Massive Walls in Residential Buildings”. DOE,ASHRAE, ORNL Conference -Thermal Envelopes VIII, Clear Water, Florida - Dec. 2001. Zhang , Meng et.al "Development of a Thermally Enhanced Frame Wall With Phase- Change Materials for On-Peak Air Conditioning Demand Reduction and Energy Savings in Residential Buildings." International Journal of Energy Research. Vol. 29, No. 9, (2005) pp . 795-809.

METHODS OF PREPARATION :

METHODS OF PREPARATION

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Microencapsulation process Particle size [ μm ] Extrusion 250–2500 Spray-drying 5–5000 Fluid bed coating 20–1500 Rotating disk 5–1500 Coacervation 2–1200 Solvent evaporation 0.5–1000 Phase separation 0.5–1000 In-situ polymerization 0.5–1100 Interfacial polymerization 0.5–1000 Miniemulsion 0.1–0.5 Sol-gel encapsulation 2–20 Layer-by-layer (LBL) assembly 0.02–20

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Chemical processes Physical processes Physico -chemical Physicomechanical • Suspension, dispersion • Coacervation • Spray-drying and emulsion • Layer-by-layer • Multiple nozzle spraying polymerization (L-B-L) assembly • Fluid-bed coating • Polycondensation • Sol-gel encapsulation • Centrifugal techniques • Supercritical CO2-assisted • Vacuum encapsulation microencapsulation • Electrostaticencapsulation 1.Chemical Methods In-situ processes such as emulsion,suspension , precipitation or dispersion polymerization and interfacial polycondensations are the most important chemical techniques used for microencapsulation.

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Emulsion stabilisation is a technique based on single or double emulsions. Since many biopolymers are generally water-soluble, two systems can be distinguished when biopolymers are used as wall material . (A) Hydrophilic active ingredients : Single water-in-oil (W/O)-emulsions are employed if the active ingredient is water-soluble. In this case an aqueous biopolymer solution containing the active ingredient is emulsified in a hydrophobic phase like vegetable oil or organic solvent . When the desired droplet size is obtained, the matrix material is stabilized by crosslinking . Then, the oil phase is removed by washing with solvents like hexane and the particles are isolated. The particles can either be dried to obtain a powder, or used as a slurry.

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(B) Hydrophobic active ingredients : Double oil-water-oil (O/W/O)-emulsions can be used if the active ingredient is hydrophobic. The active ingredient is first added to an oil phase. This oil phase is then emulsified in the aqueous biopolymer phase to form an O/W-emulsion. Then the O/W-emulsion is added to a hydrophobic phase to form the double O/W/O-emulsion. Common challenge with emulsion stabilisation for hydrophobic ingredients is retention of the core ; often losses occur during the encapsulation process.

2.Physico-Chemical Processes Coacervation:

2.Physico-Chemical Processes Coacervation (A) Complex coacervation Complex coacervation is carried out by mixing two oppositely charged polymers in a solvent (usually water); The three basic steps in complex coacervation are: preparation of the emulsion. encapsulation of the core. stabilization of the encapsulated particle.

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(B) Encapsulation by Polyelectrolyte Multilayer Layer by layer (L-B-L) electrostatic assembly of electrically charged particles has attracted much attention due to its enormous potential in multilayered thin film preparations with a wide range of electrical, magnetic and optical properties. Polyelectrolyte multilayers are the most widely studied examples of L-B-L assembly, and are prepared by sequentially immersing a substrate in positively and negatively charged polyelectrolyte solutions in a cyclic procedure.

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The most widely used methods are as follows: (A) Rapid expansion of supercritical solution (RESS)

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(B) Gas anti-solvent (GAS)

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(C) Particles from gas-saturated solution (PGSS) This process is carried out by mixing core and shell materials in supercritical fluid at high pressure. During this process supercritical fluid penetrates the shell material, causing swelling. When the mixture is heated above the glass transition temperature , the polymer liquefies. Upon releasing the pressure, the shell material is allowed to deposit onto the active ingredient. When the pressure is released, the microparticles shrink and return to their original shape and entrap the ingredients.

3. Physico-Mechanical Processes:

3. Physico -Mechanical Processes (A) Extrusion Extruders are thermo-mechanical mixers that consist of one or more screws in a barrel.Extrusion technology was initially applied in the plastics processing area and after years of development and application, it has become a well-elaborated tool with technical solutions available for other fields like the pharmaceutical industry (for the production of controlled release formulations). The basic idea behind encapsulation using extrusion is to create a molten mass in which the active agents (either liquids or solids), are dispersed or dissolved. Upon cooling, this mass will solidify, thereby entrapping the active components.

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Schematic representation of an extruder for encapsulation Schematic representation of an extruder for encapsulation

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(B) Spray-Drying Microencapsulation by spray-drying is a low-cost commercial process which is mostly used for the encapsulation of fragrances, oils and flavors. Core particles are dispersed in a polymer solution and sprayed into a hot chamber. The shell material solidifies onto the core particles as the solvent evaporates such that the microcapsules obtained are of polynuclear or matrix type.

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(C) Fluidized-Bed Technology

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With the high demand for encapsulated materials in the global market, fluid-bed coaters have become more popular. They are used for encapsulating solid or porous particles with optimal heat exchange the liquid coating is sprayed onto the particles and the rapid evaporation helps in the formation of an outer layer on the particles. The thickness and formulations of the coating can be obtained as desired. (a) Top spray; ( b) bottom spray; (c) tangential spray.

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(D) Vibration technology This technology is based on an ancient principle (Lord Rayleigh, in the late 19th century) which shown that a laminar liquid jet breaks up into equally sized droplets by a superimposed vibration. The parameters are the frequency, the velocity of the jet and the nozzle diameter. To guarantee the production of uniform beads or capsules and to avoid large size distributions due to coalescence effects during the flight, the droplets pass through an electrostatic field to be charged. As a result these droplets don’t hit each other during the flight and will be spread over a larger surface of the gelation bath thus resulting in monodisperse beads.

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0,1 up to 3 mm.

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(E) JetCutter technology The JetCutter is a simple technology for bead production that meets the requirement of producing monodisperse beads originating from low up to high viscous fluids with a high throughput `

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Capsules diameter – 10-120 micrometers

RELEASE METHODS :

RELEASE METHODS Even when the aim of a microencapsulation application is the isolation of the core from its surrounding, the wall must be ruptured at the time of use. Many walls are ruptured easily by pressure or shear stress, as in the case of breaking dye particles during writing to form a copy. Capsule contents may be released by melting the wall, or dissolving it under particular conditions, as in the case of an enteric drug coating . In other systems, the wall is broken by solvent action, enzyme attack, chemical reaction, hydrolysis , or slow disintegration.

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APPLICATIONS OF MICROENCAPSULATION

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Chemistry Printing & recording Carbonless paper Adhesives Pigments and fillers Catalysts Agriculture Fungicide - herbicide Insect repellent Biopesticide Pigments and fillers Artificial insemination Food & feed Aromas Probiotics Unsaturated oil Enzyme food processing aminoacid for cow Medecine & Pharmacy & vetinary Controle release Taste masking Vectorisation Artificial organs single dose treatment Biotechnology & environment Continuous reactor Shear protection Reactor oxygenation Bioprobes Consumer & diversified cosmetics detergents (enzymes) sanitary (active, aromas) The applications of micro-encapsulation are numerous. The ones mentioned below are some of the most common ones. Carbonless copy paper Scratch-n-sniff Flavors and essences Pesticides and herbicides Pharmaceuticals Textiles Adhesives Visual indicators Thermochromic dyes Phase change materials

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Beverage production Protection of molecules from other compounds Drug delivery Encapsulation of Oil Before encapsulation After encapsulation

Current research in the Preventative Health Flagship:

Current research in the Preventative Health Flagship At Food Science Australia, the Preventative Health Flagship’s microencapsulation team is building on its strategy of developing new and innovative encapsulant material from natural food ingredients and testing their release properties to enable the potential targeted delivery of bioactives at different sites in the gastrointestinal tract. The encapsulant system has been modifi ed and can now deliver bioactives targeted to release in the colon. Preventative Health researchers have successfully microencapsulated omega-3 oils and probiotics . Work is also focussed on encapsulating combinations of water and lipid-soluble bioactives . Storage stability trials, in vitro and in vivo testing of selected formulations are also underway

CONCLUSION :

CONCLUSION Microencapsulation technology can protect active materials against environment, stabilize them, prevent or suppress volatilization. Microencapsulation technology can provide new forms andfeatures , thus, it can create whole new fields of applications. Drug delivery has become increasingly important mainly due to the awareness of the difficulties associated with a variety of old and new drugs Of the many polymeric drug delivery systems, biodegradable polymers have been used widely as drug delivery systems because of their biocompatibility and biodegradability.

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Microencapsulation is a powerful technique to achieve targeted delivery and on-demand release of different active ingredients. Some examples of the new technologies include micro- and nano-encapsulation through self-assembly, stimuli responsive capsules, unique capsule structure formation through microfluidics and novel capsule materials. . The resulting microparticles may offer the ability to improve the stability of therapeutic agents against hydrolytic or enzymatic degradation, to augment the therapeutic effect by releasing the drug into the specific site, and to sustain the therapeutic effect in the target site. Many synthetic and natural biodegradable polymers present exciting opportunities in tailor-making the microparticle formulations for long-term drug release with specific release rates.

REFRENCES :

REFRENCES 1. Z.W. Wicks, Jr., F.N. Jones, S.P. Pappas, Organic Coatings: Science and Technology Vol. I , John Wiley & Sons, Inc., New York, 1992 , Chapter 1 2. R. Lambourne , in: Paints and Surface Coatings , Theory and Practice (Eds. R. Lambourne , T.A. Strivens ), 2nd edn . ChemTech Pub. Inc., 1999 , Chapter 1. 3. J.V. Koleske , in: Encyclopedia of Analytical Chemistry (Ed. R.A. Meyers), John Wiley & Sons Ltd., Chichester , 2000 , Chapter 4.