418
other hand, the lipophilic drug is dispersed or dissolved in a polymer solution in an
organic solvent. This technique is well known for the preparation of PNPs but
employing it for the preparation of lipid NPs is quite innovative [42, 43]. SLNs of
cyclosporine were prepared by this technique [44]. This technique prevents partitioning out of the drug into the disperse phase. Moreover, it is a feasible and accessible technique that does not require a solvent [42]. Its only disadvantages are the
residual solvent content particularly when the organic solvent is employed as a
hardening agent.
Polymerization Technique
This method includes the fabrication of NPs by the monomer’s polymerization in an
external phase. The polymerization method can be subdivided as stated below:
Emulsion Polymerization Method
A scalable and rapid technique for the production of NPs. Based on the characteristics of the external phase employed, it can be further characterized as: continuous
aqueous phase method and continuous organic phase method.
Continuous Organic Phase Method
It includes the diffusion of monomer’s solution into an inverse microemulsion/
emulsion or in a monomer’s non-solvent. This method involves employing toxic
organic solvents, initiators, and monomers which need to be removed from NPs so
it is not a popular technique. Therefore, other techniques have gained more attention
because it is a laborious process.
Aqueous Continuous Phase Technique
This technique uses water as a continuous phase and also to dissolve the monomer.
This method does not need the use of the emulsifier/surfactants. Numerous
approaches are employed at the beginning of the polymerization reaction. In the
continuous phase, initiation begins on the collision between the initiator (free radical/an ion) and the dissolved monomer molecule. While the polymerization can be
started by strong visible light or ultraviolet or high-energy radiation (γ-radiation).
Polymerization initiates through the anionic polymerization mechanism on the collision between the monomer molecules and radicals. Phase separation happens and
NPs are formed before or after the polymerization process termination. It is an easily scalable and the fastest method for the preparation of NPs. The disadvantages of
Z. Iqbal et al.
other hand, the lipophilic drug is dispersed or dissolved in a polymer solution in an
organic solvent. This technique is well known for the preparation of PNPs but
employing it for the preparation of lipid NPs is quite innovative [42, 43]. SLNs of
cyclosporine were prepared by this technique [44]. This technique prevents partitioning out of the drug into the disperse phase. Moreover, it is a feasible and accessible technique that does not require a solvent [42]. Its only disadvantages are the
residual solvent content particularly when the organic solvent is employed as a
hardening agent.
Polymerization Technique
This method includes the fabrication of NPs by the monomer’s polymerization in an
external phase. The polymerization method can be subdivided as stated below:
Emulsion Polymerization Method
A scalable and rapid technique for the production of NPs. Based on the characteristics of the external phase employed, it can be further characterized as: continuous
aqueous phase method and continuous organic phase method.
Continuous Organic Phase Method
It includes the diffusion of monomer’s solution into an inverse microemulsion/
emulsion or in a monomer’s non-solvent. This method involves employing toxic
organic solvents, initiators, and monomers which need to be removed from NPs so
it is not a popular technique. Therefore, other techniques have gained more attention
because it is a laborious process.
Aqueous Continuous Phase Technique
This technique uses water as a continuous phase and also to dissolve the monomer.
This method does not need the use of the emulsifier/surfactants. Numerous
approaches are employed at the beginning of the polymerization reaction. In the
continuous phase, initiation begins on the collision between the initiator (free radical/an ion) and the dissolved monomer molecule. While the polymerization can be
started by strong visible light or ultraviolet or high-energy radiation (γ-radiation).
Polymerization initiates through the anionic polymerization mechanism on the collision between the monomer molecules and radicals. Phase separation happens and
NPs are formed before or after the polymerization process termination. It is an easily scalable and the fastest method for the preparation of NPs. The disadvantages of
Z. Iqbal et al.