Micro Encapsulation

MICROENCAPSULATION

Microencapsulation:

Definition: It is the process by which individual particles

or droplets of solid or liquid material (the core) are

surrounded or coated with a continuous film of

polymeric material (the shell) to produce capsules in the

micrometer to millimetre range, known as

microcapsules.

Microencapsulation (Cont.):

Morphology of Microcapsules:

The morphology of microcapsules depends mainly on the core

material and the deposition process of the shell.

1- Mononuclear (core-shell) microcapsules contain the shell around

the core.

2- Polynuclear capsules have many cores enclosed within the shell.

3- Matrix encapsulation in which the core material is distributed

homogeneously into the shell material.

- In addition to these three basic morphologies, microcapsules can

also be mononuclear with multiple shells, or they may form clusters of

microcapsules.

Morphology of Microcapsules (Cont.):

Microencapsulation (Cont.):

Coating material properties:

•Stabilization of core material.

•Inert toward active ingredients.

•Controlled release under specific conditions.

•Film-forming, pliable, tasteless, stable.

•Non-hygroscopic, no high viscosity, economical.

•Soluble in an aqueous media or solvent, or melting.

•The coating can be flexible, brittle, hard, thin etc.

Microencapsulation (Cont.):

Coating materials:

Gums: Gum arabic, sodium alginate, carageenan.

Carbohydrates: Starch, dextran, sucrose

Celluloses: Carboxymethylcellulose, methycellulose.

Lipids: Bees wax, stearic acid, phospholipids.

Proteins: Gelatin, albumin.

Microencapsulation (Cont.):

Benefits of Microencapsulation:1- microorganism and enzyme immobilization.

- Enzymes have been encapsulated in cheeses to accelerate ripening

and flavor development.

The encapsulated enzymes are protected from low pH and high ionic

strength in the cheese.

• The encapsulation of microorganisms has been used to improve

stability of starter cultures.

Benefits of Microencapsulation (Cont.):

2-Protection against UV, heat, oxidation, acids, bases (e.g.colorants and vitamins).

e.g. Vitamin A / monosodium glutamate

appearance (white)

protection (water, T, ligth)

3- Improved shelf life due to preventing degradative reactions (dehydration, oxidation).

4-Masking of taste or odours.

5- Improved processing, texture and less wastage of ingredients.- Control of hygroscopy

- enhance flowability and dispersibility

- dust free powder

- enhance solubility

6-Handling liquids as solids

7-There is a growing demand for nutritious foods for

children which provides them with much needed

vitamins and minerals during the growing age.

Microencapsulation could deliver the much needed

ingredients in children friendly and tasty way.

8- Enhance visual aspect and marketing concept.

Benefits of Microencapsulation (Cont.):

Benefits of Microencapsulation (Cont.):

9- Carbonless copy paper was the first marketable product to employ

microcapsules. A coating of microencapsulated colorless ink is

applied to the top sheet of paper, and a developer is applied to

the subsequent sheet. When pressure is applied by writing, the

capsules break and the ink reacts with the developer to produce

the dark color of the copy.

Benefits of Microencapsulation (Cont.):

10-Today's textile industry makes use of microencapsulated materialsto enhance the properties of finished goods. One applicationincreasingly utilized is the incorporation of microencapsulatedphase change materials (PCMs).

Phase change materials absorb and release heat in response tochanges in environmental temperatures. When temperatures rise,the phase change material melts, absorbing excess heat, and feelscool. Conversely, as temperatures fall, the PCM releases heat as itsolidifies, and feels warm.

This property of microencapsulated phase change materials can beharnessed to increase the comfort level for users of sportsequipment, clothing, building materials, etc.

Benefits of Microencapsulation (Cont.):

11- Pesticides are encapsulated to be released over

time, allowing farmers to apply the pesticides less

amounts than requiring very highly concentrated and

toxic initial applications followed by repeated

applications to combat the loss of efficacy due to

leaching, evaporation, and degradation.

Benefits of Microencapsulation(Cont.):

12- Ingredients in foods are encapsulated for severalreasons.

Most flavorings are volatile; therefore encapsulation ofthese components extends the shelf-life of theseproducts.

Some ingredients are encapsulated to mask taste,such as nutrients added to fortify a product withoutcompromising the product’s intended taste.

Alternatively, flavors are sometimes encapsulated tolast longer, as in chewing gum.

Benefits of Microencapsulation(Cont.):

13- Controlled and targetted release of active ingredients.

Many varieties of both oral and injected pharmaceuticalformulations are microencapsulated to release over longer periodsof time or at certain locations in the body.

Aspirin, for example, can cause peptic ulcers and bleeding if dosesare introduced all at once. Therefore aspirin tablets are oftenproduced by compressing quantities of microcapsules that willgradually release the aspirin through their shells, decreasing risk ofstomach damage.

14- Microencapsulation allows mixing of incompatible compounds.

Microencapsulation

Technologies

Microencapsulation processes with their

relative particle size ranges.

Physico - Chemical

Processes

Physico - mechanical

Processes

Coacervation (2 – 1200 um) Spray-drying (5 – 5000 um)

Polymer-polymer incompatibility

(0.5 – 1000 um)

Fluidized- bed technology

(20 – 1500 um)

Solvent evaporation

(0.5 – 1000 um)

Pan coating (600 – 5000 um)

Encapsulation by supercritical

fluid

Spinning disc (5 – 1500 um)

Encapsulation by Polyelectrolyte

multilayer (0.02 – 20 um)

Co-extrusion

(250 – 2500 um)

Microencapsulation processes with their

relative particle size ranges (cont.).

Physico-Chemical

Processes (cont.)

Chemical Processes

Hydrogel microsphere Interfacial polymerization

(0.5 – 1000 um)

Phase Inversion (0.5—5.0 um) In situ polymerization

(0.5 – 1100 um)

Hot Melt (1—1000 um)

Microencapsulation Techniques (Cont.):

I. Physico-Chemical Processes:

1- Coacervation:

- Two methods for coacervation are available, namely

simple and complex processes.

-In simple coacervation, a desolvation agent is added for

phase separation.

- Whereas complex coacervation involves complexation

between two oppositely charged polymers.

1- Coacervation (Cont.):

Complex coacervation:1- First the core material (usually an oil) is dispersed into

a polymer solution (e.g., a cationic aqueous polymer,gelatin).

2- The second polymer (anionic, water soluble, gumarabic) solution is then added to the prepareddispersion.

3- Deposition of the shell material onto the core particlesoccurs when the two polymers form a complex.

4-This process is triggered by the addition of salt or bychanging the pH, temperature or by dilution of themedium.

1- Coacervation (Cont.):

5- Finally, the prepared microcapsules are stabilized by

crosslinking (with formaldehyde), desolvation or

thermal treatment.

Complex coacervation is used

to produce microcapsules containing

fragrant oils, liquid crystals, flavors,

dyes or inks as the core material.

Microencapsulation Techniques (Cont.):

2- Polymer-polymer incompatibility:

- Also called phase separation.

1- This method utilizes two polymers that are soluble ina common solvent, yet do not mix with one anotherin the solution.

2- The polymers form two separate phases, one rich inthe polymer intended to form the capsule walls, theother rich in the incompatible polymer meant toinduce the separation of the two phases. The secondpolymer is not intended to be part of the finishedmicrocapsule wall.

Microencapsulation Techniques (Cont.):

3- Solvent Evaporation:

- It is the most extensively used method of microencapsulation.

1-Prepare an aqueous solution of the drug (may contain a viscositybuilding or stabilizing agent)

2- Then added to an organic phase consisting of the polymersolution in solvents like dichloromethane or chloroform withvigorous stirring to form the primary water in oil emulsion.

3- This emulsion is then added to a large volume of water containingan emulsifier like PVA or PVP to form the multiple emulsion(w/o/w).

4- The double emulsion is then subjected to stirring until most of theorganic solvent evaporates, leaving solid microspheres.

5- The microspheres can then be washed and dried.

Microencapsulation Techniques (Cont.):

4- Polymer Encapsulation by Rapid Expansion ofSupercritical Fluids:

- Supercritical fluids are highly compressed gasses that

possess several properties of both liquids and gases.

- The most widely used being supercritical CO2 and

nitrous oxide (N2O).

- A small change in temperature or pressure causes a

large change in the density of supercritical fluids.

Polymer Encapsulation by Rapid Expansion of Supercritical Fluids (Cont.):

Steps:1-Supercritical fluid containing the active ingredient and the shell

material are maintained at high pressure and then released atatmospheric pressure through a small nozzle.

2-The sudden drop in pressure causes desolvation of the shellmaterial, which is then deposited around the active ingredient(core) and forms a coating layer.

-Different core materials such as pesticides, pigments, vitamins,flavors, and dyes are encapsulated using this method.

-A wide variety of shell materials e.g. paraffin wax and polyethyleneglycol are used for encapsulating core substances.

-The disadvantage of this process is that both the active ingredientand the shell material must be very soluble in supercritical fluids.

Microencapsulation by rapid expansion of

supercritical solutions

Microencapsulation

Techniques (Cont.):5- Hydrogel microspheres:

1- Microspheres made of gel-type polymers, such as alginate, are

produced by dissolving the polymer in an aqueous solution

2-Then, suspending the active ingredient in the mixture

3- Extruding through a precision device, producing micro droplets

4- Then fall into a hardening bath that is slowly stirred. The hardening

bath usually contain calcium chloride solution.

Advantage: The method involves an ―all-aqueous‖ system and avoids

residual solvents in microspheres.

The particle size of microspheres can be controlled by:

A- using various size extruders or B- by varying the polymer solution flow

rates.

Hydrogel microspheres

Microencapsulation Techniques (Cont.):

II Physical Processes:

1- Spray-Drying & spray-congealing :

- Microencapsulation by spray-drying is a low-cost commercialprocess which is mostly used for the encapsulation of fragrances,oils and flavors.

Steps:

1- Core particles are dispersed in a polymer solution and sprayed intoa hot chamber.

2- The shell material solidifies onto the core particles as the solventevaporates.

- The microcapsules obtained are of polynuclear or matrix type.

micro-encapsulation by spray-drying.

Spray drying

Microencapsulation Techniques (Cont.):

Spray-congealing:

- This technique can be accomplished with spray

drying equipment when the protective coating is

applied as a melt.

1- the core material is dispersed in a coating material

melt.

2- Coating solidification (and microencapsulation) is

accomplished by spraying the hot mixture into a cool

air stream.

- e.g. microencapsulation of vitamins with digestable

waxes for taste masking.

Microencapsulation Techniques (Cont.):

2- Fluidized-Bed Technology: - Different types of fluid-bed coaters include top spray, bottom

spray, and tangential spray.

- used for encapsulating solid or liquids absorbed into porousparticles.

Steps:1-Solid particles to be encapsulated are suspended on a jet of air

and then covered by a spray of liquid coating material.

2- The rapid evaporation of the solvent helps in the formation of anouter layer on the particles.

3- This process is continued until the desired thickness and weight is obtained.

Schematics of a fluid-bed coater.

(a) Top spray;

(b) bottom spray;

(c) tangential spray

Fluid-bed coater

Microencapsulation Techniques (Cont.):

3- Pan coating:1- Solid particles are mixed with a dry coating material.

2- The temperature is raised so that the coating material melts and

encloses the core particles, and then is solidified by cooling.

Or, the coating material can be gradually applied to core particles

tumbling in a vessel rather than being wholly mixed with the core

particles from the start of encapsulation.

Pan coating:

Microencapsulation Techniques (Cont.):

4- Co-Extrusion:

1- A dual fluid stream of liquid core and shell materials is

pumped through concentric tubes and forms droplets

under the influence of vibration.

2-The shell is then hardened by chemical cross linkings,

cooling, or solvent evaporation.

- Different types of extrusion nozzles have been

developed in order to optimize the process

Schematic presentation of the Co-extrusion process

Co-extrusion Process

Microencapsulation Techniques (Cont.):

5- Spinning Disk:

:Steps:1- Suspensions of core particles in liquid shell material are poured into

a rotating disc.

2- Due to the spinning action of the disc, the core particles become

coated with the shell material.

3- The coated particles are then cast from the edge of the disc by

centrifugal force.

4- After that the shell material is solidified by external means (usually

cooling).

- This technology is rapid, cost-effective, relatively simple and has

high production efficiencies.

Microencapsulation by spinning disc