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Definition :

Definition “The term microcapsule is defined as a spherical particle with size less than 200 µm , containing a core substance .” Microspheres are spherical empty particles. The term microcapsules and microspheres are used synonymously. Some other related terms are microbeads and beads .

Microsphere images:

Microsphere images


ADVANTAGES OF MICROSPHERES Increased duration of action. First pass effect can de avoided. Improved protein and peptide drug delivery. Less side effects and increased therapeutic effect. Reduce toxicity. Ability to bind and release high concentration of drugs. Patient compliance is good. Method of preparations are simple Can be injected into the body using hypodermic needle.


DISADVANTAGES OF MICROSPHERES Removal once injected is difficult. Sometimes non-uniformity of drug content may result while preparation. Unknown toxicity of beads.

Microspheres :

Microspheres The microsphere are characteristically free flowing powders consisting of proteins or synthetic polymers , which are biodegradable in nature, and ideally having a particle size less than 200 µm . Solid biodegradable microspheres incorporating a drug dispersed or dissolved throughout particle matrix have the potential for the controlled release of drug. These carriers received much attention not only for prolonged release but also for the targeting of the anticancer drugs to the tumour.

Classification of polymers:

S ynthetic polymers Natural polymers Non biodegradable materials Acrolin Epoxy polymers Biodegradable Lactides and glycolydes polyanhydrides Proteins Albumins Gelatin Collagen Carbohydrates Starch Agarose Chitosan Chemically modified carbohydrates Poly(acryl) dextran Poly(acryl)starch Classification of polymers


PREREQUISITES FOR IDEAL MICROPARTICULATE CARRIERS The material utilized for the preparation of microparticulates should ideally fulfil the following prerequisites : Longer duration of action Control of content release Increase of therapeutic efficiency Protection of drug Reduction of toxicity Biocompatibility Sterilizability Relative stability Water solubility or dispersability Bioresorbability Targetability Polyvalent


GENERAL METHODS OF PREPARATION The microspheres can be prepared by using several techniques but the choice of the technique mainly depends on the nature of the polymer used, the drug , the intended use and the duration of therapy . The method of preparation and its choice are equivocally determined by some formulation and technology related factors as mentioned below: The particle size requirement. The drug or the protein should not be adversely affected by the process. Reproducibility of the release profile and the method. No stability problem There should be no toxic products associated with the final product. Synthetic polymers are now materials of choice for the controlled release as well as targeted micro particulate carriers .

Slide 10:

Methods used for the manufacture of microspheres are Single emulsion technique Double emulsion technique Phase separation coacervation Spray drying and spray congealing 5. Solvent extraction method 6. Air suspension method

Single Emulsion Technique :

Single Emulsion Technique The microparticulate carriers of natural polymers, i.e. those of proteins and carbohydrates are prepared by single emulsion technique. The natural polymers are dissolved or dispersed in aqueous medium followed by dispersion in the non-aqueous medium e.g., oil. In the second step of preparation, cross linking of the dispersed globule is carried out. The cross-linking can be achieved either by means of heat or by using the chemical cross linkers.

Slide 12:

The chemical cross-linking agents used include glutaraldehyde , formaldehyde, terephthaloyl chloride, diacid chloride, etc. Cross-linking by heat is affected by adding the dispersion to previously heated oil. Heat denaturation is however, not suitable for the thermolabile drugs while the chemical cross-linking suffers disadvantage of excessive exposure of active ingredient to chemicals if added at the time of preparation

Single emulsion technique:

Single emulsion technique

Double emulsion technique:

Double emulsion technique Double emulsion method of microspheres preparation involves the formation of the multiple emulsions or the double emulsion of type w/o/w and is best suited to the water-soluble drugs, peptides, proteins and the vaccines. This method can be used with both the natural as well as the synthetic polymers . The aqueous protein solution is dispersed in a lipophilic organic continuous phase. This protein solution may contain the active constituents.

Slide 15:

The continuous phase is generally consisted of the polymer solution that eventually encapsulates the protein contained in dispersed aqueous phase . The primary emulsion is then subjected to homogenization or sonication before adding to aqueous polyvinyl alcohol solution. This results in the formation of double emulsion . The emulsion is then subjected to solvent removal by solvent evaporation or solvent extraction process. The solvent evaporation is carried out by maintaining emulsion at reduced pressure or by stirring the emulsion so that the organic phase evaporate

Slide 16:

Then the emulsion is added to larger quantity of water into which organic phase diffuses out. The solid microspheres are obtained by subsequent filtration and washing . A number of hydrophilic drugs like leutinizing hormone releasing hormone(LH-RH) agonist, vaccines, protein/ peptides are incorporated into microspheres using this method.

Double emulsion technique:

Double emulsion technique

Phase Separation Coacervation Technique :

Phase Separation Coacervation Technique Phase separation method is specially designed for preparing the reservoir type of the system to encapsulate water soluble drugs e.g. peptides, proteins. Some of the preparations are of matrix type particularly, when the drug is hydrophobic in nature e.g. steroids. In matrix type device, the drug or the protein is soluble in the polymer phase. The process is based on the principle of decreasing the solubility of the polymer in the organic phase to affect the formation of the polymer rich phase called the ‘ coacervates .’

Slide 19:

In this technique the polymer is first dissolved in a suitable solvent and then drug is dispersed by making its aqueous solution, if hydrophilic or dissolved in the polymer solution itself, if hydrophobic. Phase separation is then accomplished by changing the solution conditions by using any of the method mentioned. Salt addition Non-solvent addition Addition of in-compatible polymer Change in p H The process is carried out under continuous stirring to control the size of the microparticles.

Coecervation phase separation :

Coecervation phase separation

Spray Drying and Spray Congealing :

Spray Drying and Spray Congealing Spray drying and spray congealing methods are based on drying of the mist of the polymer and drug in the air. Depending upon the removal of the solvent or the cooling of the solution , the two processes are named spray drying and the spray congealing respectively. The polymer is first dissolved in a suitable volatile organic solvent such as dichloromethane, acetone, etc.

Slide 22:

The drug in the solid form is then dispersed in the polymer solution under high-speed homogenization . This dispersion is then atomized in a stream of hot air . The atomization leads to the formation of the small droplets or the fine mist from which the solvent evaporates instantaneously leading the formation of the microspheres in a size range 1-100 um . Microparticles are separated from the hot air by means of the cyclone separator while the traces of solvent are removed by vacuum drying.

Slide 23:

One of the major advantages of the process is feasibility of operation under aseptic conditions. The two processes are rapid, requiring single stage operation, suitable for both batch and bulk manufacturing. These techniques have been used to encapsulate a large number of the drugs. The spray drying process is used to encapsulate various penicillins .


It involves the removal of the organic phase by the extraction of the organic solvent. eg: removal of the water miscible organic solvent like isopropanol Organic phase removed by extraction with water, this process decreases the hardening time for the microsphers. The drug or protein is added directly to the polymer organic solution. THE RATE OF SOLVENT REMOVAL BY EXTRATION METHOD DEPENDS ON 1.Temperature of water 2.Ratio of emulsion volume to the water 3.Solubility profile of the polymer SOLVENT EXTRATION

Slide 25:

Dale E. wurster’s process consist of dispersing the solid particulate core material in a supporting air stream(helps to dry the product while being encapsulated) in the coating chamber of Wurster’s air suspension encapsulation unit and spray coating of the suspended particles with coating material(polymer solution). The recirculating flow of the particle through the coating zone helps them to get an increment of coating material. The recirculation is continued to full fill the purpose of encapsulation, desired coating material thickness and the through encapsulation of the core material . The coatings can be applied in the form of solvent solution,aqueous solution,emulsion,dispersion or as hot melts. This method is mainly applicable for solid core materials however liquids can also be encapsulated(using solid sorbents). AIR SUSPENSION METHOD

Slide 26:

PROCESSING VARIABLES TO BE CONSIDERED FOR EFFECTIVE AND EFFICIENT ENCAPSULATION 1.Density,surface area,solubility,friability,melting point,volatility,crystallinity and flowability of 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 or fluidize the core material. 5.Amount of coating material required. 6.Inlet and outlet operating temperatures.

Slide 27:



REFERENCES Advanced in controlled and novel drug delivery, By N.K.Jain Theory and practice of Industrial Pharmacy by Lachman&Lieberman . Internet Targeted $ Controlled drug delivery system- S.P.Vyas $ R .K.KHAR

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