Microparticulate Drug Delivery System Biology Essay

Published: Last Edited:

This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.

Microspheres are defined as spherical polymeric particles with size ranging from to 1 to 100 µm. There are two subtypes of microparticles. Microcapsules are vesicular systems in which the drug molecules are surrounded by a membrane . Microspheres are matrix system in which the drug molecules are dispersed throughout the particle. Basically microparticles are used mainly for parentral administration.

A well designed controlled drug delivery systems can overcome the problems of conventional theraphy and enhance the therapeutic efficacy of a given drug . For obtaining maximum therapeutic efficacy , it is necessary to deliver the agent to the target tissue , there by causing little toxicity and minimize side effects. In a sustained and controlled release fashion there are so many targeting approaches used for delivering a therapeutic substance to the target site. One of the major approach is using microspheres as a carrier system for drugs.

The term microcapsule should be used for reservoir type devices whereas microspheres are monolithic or matrix type microparticles. The particles can be embedded within a polymeric matrix in either a solid aggregate state or a molecular dispersion to form microspheres. The particles can be coated by a solidified polymeric envelope to form microcapsules.

The process involves the spray coating of pellets, spheres ,granules ,beads , powder or tablets held in suspension by column of air. The fluid bed processing equipment used is multifunctional and may be used in preparing microspheres . The items to be coated are fed into a vertical cylinder and are supported by a column of air that enters from the bottom of the cylinder . Within the air stream , the solid rotate both vertically and horizontally . As the coating solution enters the system from the bottom , it is rapidly placed on the suspended ,rotating solids with roundings coats being applied in less than an hour with assistance of warm air blasts released in the chamber.

Coacervation Phase Seperation

It is one of the method of microencapsulation of solid or liquid drugs that has wide commercial application for instance , in the manufacture of sustained release dosage forms . The material to be encapsulated available as fine powders, preferably micronized or as an immiscible liquid . It is dispersed in the polymer solution prior to cooacervation and must therefore be insoluble in the liquid medium. The precipitant liquid is added with continuous stirring . The coacervates droplets form mainly around the core particles which acts as nuclei, because even prior to addition of precipitants , the solid surfaces are coated with a layer of adsorbed polymer . Stirring is maintained to prevent the coacervate droplets which engulf the core particles from coalescing . The coacervate phase must be fliud enough to wrap completely around the core particles but viscous enough to avoid being sheared off the surface of particles during stirring .

Fig No. 3: Schematic Representation of Coacervation Process


The centrifugation method is a unique modification of simple extrusion technique of producing microspheres. The simple extrusion method utilizes a device consisting of tow concentric tubes containing aligned fluid nozzles. The liquid material to be coated is extruded through nozzle of the inner tube into the coating fluid contained in the outer tube.

Intially the fluid extrudes as rod surrounded by the coating fluid ,but the rod ultimately breaks up into droplets which are then immersed in coating fluid to the extruded droplets pass through nozzle orifice of the outer tube , the coating fluid forms a surface coat which encases the extruded particle .Spherically shaped particles are formed by surface tension of liquid .By suitable means the formed coat is converted to more rigid structure . Hardening baths are usually employed for the process. These bath are designed according to the coating material used. Bath may be non solvent to the coating material whereas in still other cases only a decrease in temperature is needed to harden the coat.

This process is primarily employed to prepare microcapsule of liquid. Thus the coating fluid is immiscible with the liquid to be encapsulated. The capsule size can be controlled by varying such factors as the orifice size, the rotational speed ,flow rate of fluid to be encapsulated. The centrifugation method is capable of producing microspheres in 100-200 µm range .

Spray drying

The application of spray drying process to the production of microspheres has been found to be useful for a variety of materials and can be employed to encapsulate both liquids and solids. In the case of liquid, fluid to be coated is first emulsified. The film - forming coating material is contained in the continuous phase of emulsion and the fluid to be coated becomes the dispersed phase .The emulsion is subjected to the spray drying process and the solvent constituting the continuous phase is removed. The film former is thus deposited upon the surface of dispersed particles .The resulting product is a free flowing powder like material containing the encapsulated liquid. The same procedure is followed to produce coated solids. Solvent removal during the spray drying process deposits the coating material on the surface of solid particles .

Fig No. 4: Microencapsulation technique by spray drying

Emulsion Solvent evaporation

The emulsion solvent evaporation technique also called as emulsion hardening has been widely used to prepare microspheres for controlled drug release .This technique involves dispersion of drug in an organic polymer solution followed by emulsification of polymer solution in water. After continuous stirring the solvent evaporates and drug containing rigid polymer microspheres are formed.

Interfacial Polymerization

The interfacial polycondensation or polymerization technique has been applied to the microencapsulation of various liquids. Particulate solids can be suspended in the liquid so the microencapsulated particle contains both solids and liquids. The process consist of bringing 2 reactants together at the interface of the dispersed phase and continuous phase in emulsion system This interfacial polymerization reactions produces a continuous film of the formed polymer around the dispersed phase. The recovery of the microspheres from the continuous phase can be accomplished by spray drying , flash evaporation, filtration or other separation technique. The various polymer coating materials which have been utilized to prepare microspheres include polyamides ,polyurethanes, polysulfonamides , polyesters, polycarbonates and polysulfonates. The particle size of the product created by this method varies in accordance with particle diameter of the dispersed phase .Therefore particles varying greatly in size ,from approximately 3 to 200 micrometer in diameter can be prepared .

Applications of microencapsulation

This technology have been used widely in the design of controlled release and sustained release dosage forms.

The bitter taste of drugs like paracetamol, nitrofurantoin can be minimized by using this technique.

To reduce gastric and other GI tract irritations,s the drugs have been microencapsulated

eg . Sustained release aspirin preparations have been reported to cause significantly less GI bleeding than conventional preparations.

For easy handling and storage purpose , liquid can be converted to pseudo solid.

eg:- Eprazinone.

Hygroscopic properties of materials can be reduced by microencapsulation eg:- NaCl.

To reduce the odor and volatility, the substances can be microencapsulated . eg:-CCl4

To provide protection to the core material against atmospheric effects microencapsulation technique has been employed eg:- Vit A.

Separation of incompatible substances has been achieved by encapsulation .
















Aliphatic polyesters

Poly-malic acid

Poly-glycolic acid

Poly-hydroxyl butyrate

Poly-lactic acid

Cross linked proteins and Hydrogels

Poly Vinyl Alcohol(PVA)

Cross linked Poly Vinyl Pyrollidone (PVP)


Hydroxy Propyl Methyl Cellulose(HPMC)

Ethyl cellulose


Cellulose acetate

Polyethyl Vinyl Acetate(PVA)

Poly Ether Urethane(PEU)




Microspheres are defined as spherical polymeric particles with size ranging from to 1 to 100 µm. There are two subtypes of microparticles. Microcapsules are vesicular systems in which the drug molecules are surrounded by a membrane . Microspheres are matrix system in which the drug molecules are dispersed throughout the particle. Basically microparticles are used mainly for parentral administration.

Aceclofenac is a Non Steroidal Anti Inflammatory Drug (NSAID ) which is a phenyl acetic acid derivative . It shows effective anti inflammatory effect and analgesic properties . It is mainly used in rheumatoid arthritis, osteo arthritis and ankylosing spondylitis.

After oral administration, it is rapidly and effectively absorbed with 100% bioavailability. But its biological half- life is only 3-4 hours . Therefore it requires multiple dosing of drug for maintaining therapeutic effect throughout the day .The normal dose of aceclofenac is 100mg b.i.d. The frequent adverse side effects occurring with aceclofenac are GI disturbances , GI bleeding and peptic ulceration .

The short half -life and multiple dose administration makes aceclofenac a good candidate for the formulation of delayed release microspheres. The main aim of the study was to formulate the delayed release microspheres of aceclofenac . In the present study emulsion solvent evaporation technique has been adopted to formulate the delayed release dosage forms. The preparation and invitro evaluation of aceclofenac microspheres using seven different polymers were carried out in the following stages.

Standard graph of aceclofenac

Preparation of microspheres by emulsion slovent evaporation technique

Compatibility studies

Micrometric properties

Morphology of microspheres (SEM)

Drug entrapment efficiency or incorporation efficiency

Percentage yield

Invitro drug release