Microencapsulation

Microencapsulation

• Microencapsulation is the process by which tiny liquid droplets or solid particles are suspended or coated with a continuous film of polymeric material.
• Product known as: microcapsules
• Size : micrometer to millimeter (<1mm)

Mononuclear microcapsule

Parts of microcapsules:

1. Intrinsic part (inner): Core: contains active ingredient.

2. Extrinsic part (outer): Shell: comprises polymeric material.

• The shell protects the core from external atmospheres.
• Core material exists in the form of either a solid, liquid and gas.
• Core materials --> solutions, suspensions, emulsions.
• Core material and shell materials should be compatible with each other.

Morphology of microcapsules:

1. Mononuclear microcapsules: contain the shell around core.
2. polynuclear microcapsules: contain many cores within a shell.
3. Matrix microcapsules: core material is evenly distributed inside shell material. i.e. API (drug, core) is dispersed in shell (polymer).

polynunclear and matrix microcapsules

Different techniques used for microencapsulation:

Chemical processes: suspension, dispersion and emulsion polymerization, polycondensation.

Physico-chemical processes: 

Coacervation, layer-by-layer assembly, sol-gel encapsulation,

Supercritical CO2 assisted microencapsulation.

Physico-mechanical process: 

spray drying, multiple nozzle spraying, fluid-bed coating, centrifugal technique, vacuum encapsulation, electrostatic encapsulation.

Microencapsulation processes with their relative particle size ranges:

Microencapsulation process	Size (micrometer)
Extrusion	250-2500
Spray-drying	5-5000
Fluid bed coating	20-1500
Rotating disc	5-1500
Coacervation	2-1200
Solvent evaporation	0.5-1000
Phase separation	0.5-1000
in-situ polymerisation	0.5-1000
Interfacial polymerisation	0.5-1000
miniemulsion	0.1-0.5
Sole-gel encapsulation	2-20
Layer-by-layer assembly	0.02-20

Coating materials used in microencapsulation:

Class	Coating materials
Water soluble resins	Gelatin, gum arabic, starch, polyvinyl pyrrolidone, carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, arabinogalactan, polyvinyl alcohol, polyacrylic acid.
Water insoluble resins	Ethylcellulose, polyethylene, polymethacrylate, polyamide, poly(ethylene-vinyl acetate), cellulose nitrate, silicones, poly(lactide-co-glycolide)
Waxes and lipids	Paraffin, carnauba, spermaceti, beeswax, stearic acid, stearyl alcohol, glyceryl stearate.
Enteric resins	Shellac, cellulose acetate phthalate, zein.