Niosomes

Niosomes

(Targeted
drug delivery systems)

Niosomes

       Medication
is  encapsulated in a  vesicle

       Composed
of a bilayer  of non-ionic surface  active agents

       They
are vesicles composed of non-ionic surfactants

       Biodegradable,
relatively nontoxic, more stable and 
inexpensive

       Used
as an alternative to liposomes

Advantages of niosomes

       These
are very small in size -nanometric scale

       Structurally
similar to liposomes, but offer several advantages over them

       Niosomes
greatly increase transdermal drug delivery and 
also in targeted drug delivery

       Hydrophilic,
lipophilic and amphiphilic drugs can be accommodated in the vesicular moieties

       Act
as a depot to release the drug slowly and offer
a controlled release

       Increase
the stability of the entrapped drug

       Handling
and storage of                surfactants
do not require any special conditions

       Enhance
the skin penetration of drugs

Structure of niosomes

Ø  Niosomes
are microscopic  lamellar structures

Ø  Formed
on the admixture of  non-ionic surfactant
of the alkyl or dialkyl polyglycerol ether class and cholesterol with subsequent
hydration in aqueous media

         
Niosomes may be unilamellar or multilamellar
depending  on the method used to
prepare them

         
The hydrophilic ends are exposed on the outside
and inside  of the vesicle, while the hydrophobic chains face each  other within the bilayer

Methods of preparation

  1. Ether
    injection method

  2. Film
    hydration method

  3. Reverse
    phase evaporation

  4. The
    “Bubble” method

  5. Micro
    fluidization

  6. Sonication

1. Ether injection method

       In
this method a solution of niosomal ingredients in ether is  slowly injected into an aqueous medium at
high  temperature

       A
mixture of surfactant and cholesterol (150 μmol) is  dissolved in ether (20 ml)

       Injected
into an aqueous phase (4 ml) using a 14- gauge 
needle syringe at the rate of approximately 0.25ml/min

       The
aqueous phase is preheated to 600C during the injection  of the ether solution

       This
causes evaporation of ether leading to the formation of  single layered vesicles

       The
particle size of niosomes formed can range b/w 50μm  and 1000μm

Advantage

      Niosomes
prepared by ether injection method have better 
entrapment efficiency than those prepared by the film or  sonication

Disadvantage

      Small
amount of residual ether  frequently
remains in the  final product and is
difficult to remove

2. Film hydration method

         
Vesicle-forming agents such as the surfactant
and cholesterol are dissolved in a volatile organic solvent such  as diethyl ether, chloroform, or methanol in
a round bottom  flask

         
The organic solvent is evaporated under reduced pressure  using a rotary evaporator

         
A thin film of solid mixture remains deposited
on the walls of the flask

         
The dried surfactant layer is rehydrated with
the aqueous  phase at normal temperature
with gentle agitation to yield 
unilamellar niosomes or smaller niosomes using sonication,  technique

3. Reverse phase evaporation
technique

         
In this method, cholesterol and surfactant (1:1
ratio) are  dissolved in a mixture of
ether and chloroform

         
An aqueous phase containing the drug to be loaded
is added to this

         
Mixture is sonicated at 40C- 50C
until a clear gel is formed

         
Phosphate buffered saline (PBS) is added to it Sonicated

         
The temperature is raised to 400C and
the organic phase is  removed under
reduced pressure

         
A viscous niosome suspension is obtained

         
Diluted with PBS and heated on a water bath at
600C for  10min to yield
niosomes

4. The Bubble method

         
This method allows the preparation of niosomes without the use of organic solvent

         
The niosomes are prepared in a bubbling unit,
which consists of a round bottom flask with three necks

         
The flask is positioned in a water temperature

         
In the first neck water – cooled reflux is
positioned

         
In the second neck thermometer is fixed

         
The third neck is used to bubble nitrogen gas
into the mixture

         
A dispersion of cholesterol and surfactant in a
buffer (pH 7.4) is  taken in the flask
and maintained at 700C

         
The dispersion is then mixed with shear
homogenizer

         
Nitrogen gas is immediately bubbled into it at 700C
to yield  niosomes

5. Sonication

         
The aqueous phase is added into the mixture of  surfactant and cholesterol in a scintillation
vial

         
Homogenized using a sonic probe

         
The resultant vesicles are of small unilamellar (SUV)
type  niosomes

         
The SUV type niosomes are larger than SUV
liposomes

6. Micro fluidization

         
This is a recent technique to prepare small MLVS

       
 A
microfludizer is used to pump the fluid at a very high  pressure (10,000 psi) through a 5 mm screen

         
It is then forced along defined micro channels,
which direct  two streams of fluid to
collide together at right angles,  there
by affecting a very efficient transfer of energy

         
The lipids/surfactants can be introduced  fluidizer

         
The fluid collected can be recycled until vesicles
are obtained

Separation of
free/unentrapped drug

Dialysis

The aqueous niosomal dispersion is dialyzed in a dialysis
tubing against phosphate buffer or normal saline or glucose solution.

Gel Filtration

The unentrapped drug is removed by gel filtration of
niosomal dispersion through a Sephadex-G-50 column and elution with phosphate
buffered saline or normal saline.

Centrifugation

The niosomal suspension is centrifuged and the supernatant
is separated. The pellet is washed and then resuspended to obtain a niosomal
suspension free from unentrapped drug

Evaluation of niosomes

1. Entrappment efficiency

Entrapment efficiency = Amount entrapped / Total
amount added x 10

2. Vesicle Size

Laser Light Scattering method

3. Particle size analysis

Scanning Electron Microscopy (SEM)

4. Bilayer formation

Polarised Light Microscope

5. Number of lamellae

Nuclear Magnetic Resonance (NMR) spectroscopy

6.In vitro Release Study

7. In vivo Release Study

Scanning Electron Microscopy

Polarised Light Microscope

Applications

         
Anti-neoplastic treatment

         
Treatment of Leishmaniasis

         
Delivery of peptide drugs

         
Used in studying immune response

         
Niosomes as carriers for haemoglobin

         
Transdermal drug delivery systems

Summary

  1. Niosomes
    are vesicular systems in which the medication is encapsulated in a vesicle
    composed of a bilayer of non-ionic 
    surface active agents

2.       The
methods of preparation include Ether injection method, Film hydration method,
Reverse phase evaporation, The  “Bubble”
method, Micro fluidization, Sonication

3.       Niosomes
can be characterized for Entrapment efficiency, Vesicle Size, Particle size, Bilayer
formation, Number of  lamellae, In vitro
and In vivo release study

 

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