Microencapsulation involves innovative techniques to coat a drug or active agent in small capsules, achieving protection, controlled release, or other therapeutic objectives.
This encapsulation can significantly impact the pharmacokinetics and biodistribution of the encapsulated agent.
Below are various microencapsulation methods, each with unique processes, advantages, and limitations:
1) Spray Drying
Process:
The core material is dispersed into a polymer solution to form an emulsion or suspension.
This mixture is sprayed into a chamber with hot air.
As the droplets travel down, the solvent evaporates, leaving behind solid microcapsules.
Advantages:
Fast process, scalable for large-scale production.
High encapsulation efficiency.
Limitations:
High temperatures can degrade heat-sensitive drugs.
2) Coacervation (Phase Separation)
Process:
Polymer separates from the solution and surrounds the active ingredient.
Separation can be induced through temperature, pH changes, or adding a non-solvent.
Advantages:
Suitable for heat-sensitive drugs since high temperatures aren’t used.
Limitations:
Achieving a uniform coating can be challenging and often requires post-processing to solidify the shell.
3) Pan Coating
Process:
Core materials are placed in a rotating pan, and polymer is sprayed onto them.
The pan’s rotation coats particles with layers of polymer.
Advantages:
Widely used, especially in food and confectionery industries.
Limitations:
Slower process and may not be suitable for very tiny particles.
4) Liposome Encapsulation
Process:
Drug is trapped within lipid vesicles or liposomes, with a lipid bilayer that can entrap both hydrophilic and hydrophobic drugs.
Advantages:
Effective for drugs unstable in gastrointestinal conditions.
Liposomes can be functionalized for targeted delivery.
Limitations:
Liposomes can be unstable and may have a short shelf-life.
5) Solvent Evaporation
Process:
Drug and polymer are dissolved in a volatile organic solvent and emulsified into an aqueous phase.
As the solvent evaporates, microcapsules form.
Advantages:
Suitable for various drugs and polymers.
Limitations:
Residual solvents may remain, potentially problematic for internal drug delivery.
6) Polymer-Polymer Incompatibility
Process:
Two incompatible polymers are used.
The drug is dissolved or dispersed in one polymer solution, then emulsified into a second polymer solution. Microcapsules form as the solvent is removed.
Advantages:
Useful when a drug is incompatible with other polymers.
Limitations:
Requires careful selection of incompatible polymers.
7) Ionic Gelation or Complex Coacervation
Process:
Interaction between a polymer and an ionic cross-linking agent, often with biopolymers like chitosan.
Advantages:
Mild conditions, suitable for heat-sensitive drugs.
Limitations:
May need post-processing to ensure stability.
8) Emulsion Technique of Microencapsulation Methods
Process:
Oil-in-water (o/w) or water-in-oil (w/o) emulsion is formed, with the drug in one phase and the polymer in the other.
As the polymer solvent is removed, the polymer precipitates around the drug droplets or particles.
Advantages:
Versatile, usable for both hydrophilic and hydrophobic drugs.
Limitations:
Achieving a stable emulsion can be challenging.