Drug targeting is the ability of a therapeutic agent to act on desired site of action with little or no interaction with non target tissue. Niosomes are one of the best carriers for drug targeting. Niosomes are Microscopic lamellar structure formed on admixture of non ionic surfactant of the alkyl or dialkyl polyglycerol ether class and cholesterol with subsequent hydration in aqueous media. Niosomes can be SUV (Small Unilamellar Vesicles ), MLV (Multi lameller Vesicles) or LUV ( Large Unilamellar Vesicles). The method of preparation of noisome is based on liposome technology. The basic process of preparation is same like hydration by aqueous phase of the lipid phase which may be either a pure surfactant or mixture of surfactant or mixture of surfactant with cholesterol. Niosomes are important vehicle for drug delivery and being nonionic which is less toxic and improve the therapeutic index of drug by restricting action to target cells. Niosomes have shown good release profile and thus serve better option for drug delivery system.
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Niosome, Mutilamellar vesicle,
Target oriented drug delivery system are the areas of major interest in the modern pharmaceutical research. The selective drug delivery to the target tissue increases the therapeutic efficiency of the drug and decreases its undesirable effect of non target tissue. Niosomes are microscopic lamellar structure, one type of nonionic surfactant vesicle, admixture of nonionic surfactant of alkyl or dialkyl polyglycerol ether class and cholesterol with subsequent hydration in aqueous media.[1.14.2] The presence of the steroidal system (cholesterol) increase the Rigidity of the bilayer and important component of the cell membrane and its presence affects bilayer fluidity and permeability. This carrier system protect the drug molecule from the premature degradation and inactivation due to unwanted immunological and pharmacological effects.[1.4.4]. Niosomes and liposomes are equiactive in drug delivery potential and both increase drug efficiency as compared with that of free drug. Mostly niosomes are preferred over liposome because the former exhibit high chemical stability and economy.[1.21.4]. This article basically emphasize on the increasing interest of various inventor and researchers in nano size colloidal systems, specially highlighting the niosomal drug delivery system.
Niosomal dispersion in an aqueous phase can be emulsified in a non-aqueous phase to regulate the delivery rate of drug and administer normal vesicle in external non aqueous phase.
Niosomes possess an infrastructure consisting of hydrophilic, amphiphilic and lipophilic moieties together and as a result can accommodate drug molecule with a wide range of solubilities.
They improve oral bioavalability of poorly absorbed drugs and enhance skin penetration of niosomes.
They increase the therapeutic performance of the drug molecule by delayed clearance from the circulation, protecting the drug from biological environment and restricting effects to target cells.
The surfactant are biodegradable, biocompatible and non-immunogenic hence can be used safely in preparation of niosomes.
The vesicle may act as a depot, releasing the drug in a controlled manner.
They are osmotically active and stable, as well as they increase the stability of entrapped drug.
They can be made to reach the site of action by oral, parenteral as well as topical routes.
Such type of drug delivery system having high cost.
It has low solubilty and low stability.
Leakage and Fusion of encapsulated drug or molecules is seen.
It has short half-life.
Sometimes phospholipid undergoes oxidation and hydrolysis.
COMPONENTS OF NIOSOMES :
Mainly niosomes contains following types of components.
Non Ionic surfactants :
It having bilayer lattices in which the hydrophillic heads align facing aqueous bulk while the hydrophobic head having less contact with aqueous media.[1.4.4]
Following types of Nonionic surfactants are
Surfactant-I (MW-473) is C16 monoalkyl glycerol ether with average of three glycerol units.
Surfactant-II (MW-972) is diglycerol ether with average of the seven glycerol units.
Surfactant-III (MW-393) is ester linked surfactant other than alkyl glycerol, alkyl glycosides & alkyl ether bearing polyhydrixyl head group are also used in formulation of niosomes.[1.4.4-6-7]
Alkyl Esters: In this category Sorbitan esters are mostly preferred surfactant for preparation of niosomes.[1.4.8-9]. Vesicles which are prepared by the polyoxyethelyne sorbitan mono laurate are relatively soluble than other surfactant vesicles.[1.4.10]
Always on Time
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For e.g. Polyoxyethylene (polysorbate 60) has been utilized for encapsulation of Diclofenac sodium. A mixture of polyoxyethelene-10-steryl ether : glyceryl laurate : cholesterol (27:15:57) has been used in Transdernal delivery of cyclosporine-A. [1.4.4, 12]
Alkyl Amide : Galactoside and Glucoside have been utilized to produce niosomal vesicle [1.4.13]
Fatty acid and Amino acid Compounds : some long chain fatty acid and amino acid compounds have been utilized in some niosomal preparation. [1.4.14]
Steroids are important components of the cell membrane and their presence in membrane affect the bilayer fluidity and permeability.Cholesterol which is a steroid derivative and used in formulation of niosomes but may not show any role in the formation of bilayer.
Here cholesterol affect properties of niosomes like membrane permeability, Rigidity, encapsulation efficiency, ease of rehydration of freeze dried noisome and their toxicity. It prevent the vesicle aggregation by the inclusion of molecules which stabilize the system against the formation of aggregates by repulsive steric or electroststic forces that leads to the transition from the gel to liquid phase in noisome system. Hence the noisome becomes leaky.[1.4.15]
Charged Molecule :
To Increase the stability of noisome by electrostatic repulsion which prevents coalescence, some charged molecule are added to niosomes.
The negatively charged molecules [e.g. Diacetyl phosphate (DCP) and Phosphotidic acid.] and
The positively charged molecules [Stearylamine (STR) and staryl pyrimidium chloride] are use in niosomal preparation. These charged molecules are used to prevent aggregation of niosomes [1.4.1,16] . But 2.5 to 5 mol % concentration of charged molecules are tolerable because high concentration inhibit niosome formation.[1.4.1,17].
METHODS OF PREPARATION :
Hand Shaking Method (Thin Film Hydration Technique) [1.7.11](16)
The mixture of vesicle forming ingredients like surfactant and cholesterol are dissolved in volatile organic solvents like diethyl ether, chloroform or methanol in a Round bottom flask. The organic solvent is evaporated at room temperature (20Â°C) using rotoary evaporator leaving a thin layer of solid mixture on the wall of flask. The dried film can be rehydrated by aqueous phase at 0 to 60Â°C with gentle agitation, which will form typical mutilamellar noisome.
Fig.1 Hand Shaking Method
Ether Injection Method : [1.6.22] (17)
In this method niosomes are formed by introducing a solution of surfactant dissolved in diethyl ether into warm water maintained at 60Â°C. The surfactant mixture in ether is injected through 14- gauge niddle into an aqueous solution of material. Then ether will be vaporized leads to formation of single layered vesicle which has diameter from 50 to 1000 nm.
Sonication : (18)[1.6.23]
In this method an aliquot of drug solution in buffered is added to the surfactant or cholesterol mixture in a 10 ml glass vial. The mixture is probe sonicated at 60Â°C for 3 min. using a sonicator with a titanium probe to yield niosomes.
Reverse Phase Evaporation Techniques : [1.6.23](18)
In this method, surfactant and cholesterol are dissolved in a mixture of chloroform and ether.
An aqueous phase containing drug is added to this mixture and resulting two phase is sonicated at 4-5Â°C. The clear gel is formed which is further sonicated after the addition of a small amount of phosphate buffer saline. The organic phase is removed at 40Â°C under low pressure. Then resulting viscous noisome suspension is diluted with phosphate buffered saline and heated in a water bath at 60Â°C for 10 min to yield niosomes.
In this method, the mixture of cholesterol and diacetyl phosphate is prepared and then solvent is evaporated with the help of rotary vaccum evaporator to leave a thin film. The film is hydrated by aqueous drug solution and suspension thus obtained is extruded through the polycarbonate membrane having pore size 0.1 Âµm and then placed in series up to 8 passages to obtain uniform size niosomes.
Trans membrane pH gradient Drug uptake process (Remote loading):
In this method cholesterol and surfactant are dissolved in chloroform. The surfactant is evaporated under reduced pressure to get obtain thin film on the wall of round bottom flask. The film is then hydrated with 300 mM citric acid (pH 4.0) by vortex mixing. The multilamellar vesicle are frozen and thawed 3 times and then sonicated. To this niosomal suspension, aqueous solution containing 10 mg/ml of drug is added and vortexed. The pH of the sample is then raised to 7.0-7.2 with 1M dissolution phosphate. The mixture is then heated at 60°C for 10 min to give niosomes.
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Multiple Membrane Extrusion method: [1.17.13](22)
For controlling the size of niosome, this one is good method. In this method surfactant, cholesterol and diacetyl phosphate all are mixed in chloroform and form thin film by Evaporation. The film is then hydrated with aqueous drug solution and resultant suspension extruded through polycarbonate membranes which are placed in series for upto 8 passage.
Emulsion method: [1.14.26,27](23,24)
In this method the oil in water (o/w) emulsion is placed from an organic solution of surfactant, cholesterol and an aqueous solution of drug. Then the organic solvent is evaporated which leaving a thin film dispersed in aqueous phase.
Niosome preparation using Micelle :
Niosomes are formed from a mixed micellar solution by the use of Enzymes. A mixed micellar solution of C16G2, dicalcium hydrogen phosphate, polyoxyethylene sholesterol sebacetate diester (PCSD) converts to a niosome dispersion when incubated with esterase. PCSD is cleaved by esterase to yield polyoxyethylene, sebacic acid and cholesterol. Cholesterol in combination with C16G2 and DCP then yield C16G2 niosomes.
Active Trapping Method :[1.3](25)
In this method loading of drug after the formation of niosomes. The niosomes are prepared and then drug is loaded by maintaining pH gradient or ion gradient to facilitate uptake of drug into niosomes.
It has different advantage like 100% entrapment, Absence of leakage, High drug lipid ratio, Cost effective and suitability for labile drug.
The Bubble Method :[1.3] (26)
In this method niosomes are formed in one step without use of organic solvent. All components are dispersed in buffer and the dispersion is placed in a round bottom flask which is immersed in water bath with controlled temperature. The flask has three necks attached to water cooled reflux, thermometer and nitrogen supply. The dispersion is mixed with a shear homogenizer for 15 seconds and then bubbled with nitrogen in this assembly to form niosomes.
Microfluidization : [1.3](27)
In this method the two phase are allowed to interact at ultra high speed in micro channels in an interaction chamber. The high speed impingement and the enegy involved in this which leads to formation of uniformed small niosomes.
TYPES OF NIOSOMES:
The niosomes are calssified as function of the number of Bilayer ( e.g. SUV, MUV) or as a function of size (e.g. LUV,SUV) or as a function of the method of preparation (e.g. REV, DRV) There are mainly three types of niosomes [1.23.9]
Multi lamellar vesicles (MLV)
Large unilamellar vesicles (LUV)
Small unilammellar vesicles (SUV)
I . Multi lamellar Vesicles (MLV) :
It consists of a number of bilayer surrounding the aqueous lipid compartment separately. The approximate size of such vesicles are 0.5 to 10 Âµm diameter. MLV are most widely used niosomes. Which are simple to make and mechanically stable upon storage for long periods. These vesicle are mostly suited as drug carrier for Lipophillic compounds
II. Large Unilamellar Vesicles (LUV) :
Such types of Niosomes are high aqueous to lipid compartment ratio, so that large volume of Bio-active materials can be entrapped with a very economical use of membrane lipids.
III. Small Unilamellar Vesicles (SUV) :
such types of niosomes are mostly prepared from multi lamellar vesicles by sonication method, French press extrusion method or Homonization method . The size of small unilamellar vesicles are 0.025-0.05 Âµm diameter which are thermodynamically unstable and are susceptible to aggregation and fusion. Their entrapped volume is small and percentage entrapment of a aqueous solute is correspondingly low.
CHARACTERIZATION OF NIOSOMES:
Entrapment efficiency: [1.17.23](14)
After preparing niosomal dispersion, unentrapped drug is separated by Dialysis, Gel filteration or Centrifugation and the drug remained entrapped in noisome is determined by complete vesicle disruption using 50% n-propanol or 0.1% Triton X-100 and analyzing the resultant solution by appropriate assay method for the drug.
Entrapped efficiency(EE)= Amount entrapped total amount Ã- 100
Vesicle Diameter :
Niosomes are spherical and so their diameter can be determined by Light Microscopy, photon correlation microscopy and freeze fracture electron microscopy. Freeze thawing [1.17.24](15) is also applicable for such measurement.
In-vitro release : [1.17.24](15)
A method of in-vitro release rate study include the use of dialysis tubing. A dialysis sac is washed and soaked in distilled water. The vesicle suspension is pipette out into a bag made up of tubing and sealed. The bag containing the vesicle is placed in 200 ml of buffer solution in a 250 ml beaker with constant shaking at 25Â°C and 37Â°C. at various time interval s. The buffer is analyzed for the drug content by an appropriate assay method.
Bilayer Rigidity and Homogeneity:[1.9.7,8,9]
The Rigidity of bilayer affects biodistribution and biodegradation of niosomes. In homogeneity can occur both within niosome structure themselves and between niosomes in dispersion and could be identified via. p-NMR, Differntial scanning calorimertry (DSC) and Fourier transform infra-red spectroscopy (FT-IR) techniques. Now a day, fluorescence resonance energy transfer (FRET) are used to obtain deeper insight about the shape, size and structure of niosomes.
Vesicle charge can play important role in the behavior of niosomes in vivo and in vitro. Charged niosomes are more stable against aggregation and fusion than uncharged vesicle. In order to obtain an estimate of the surface potential, the zeta potential of individual niosomes can be measured by Microelectrophoresis. Another approach is the use of pH-sensitive fluorophores. Dynamic light scattering have been used to measure the zeta potential used now a days.
The niosomal formulation were subjected to stability by storing at 4C, 25C and 37C in thermostatic over for the period of three months. After one month, drug content of all the formulations were checked by method discussed previously in entrapped efficiency parameter.
Tissue Distribution or In vivo study:
This study is carried out by using suitable animal models like albino rats (100-150 gm). Mostly three groups are taken each group contain three animals (total 3*3=9). The first group is treated as control, in which free niosome without drug are injected. To the second group free drug is injected. The third group is treated by lyophilized niosome. After sacrificing the animals, different tissue like liver, lungs, spleen, heart and kidney are removed. After washing the tissue with phosphate buffer (pH-7.4) the organ are homogenized and centrifuged. The supernant is used for the determination of drug content using suitable method.[1.4.46] The surfactants with alkyl side chain length from C12-C18 are suitable for preparation of niosomes[1.24.8](33). Span series surfactant having HLB number of between 4 and 8 can form niosomal vesicle.[1.24.9](34)
Factor affecting physicochemical properties of niosomes:
Nature of Surfactants:
Types of surfactants affect encapsulation efficiency, toxicity and stability of niosomes. The surfactant used in formation of niosome must have hydrophilic head and hydrophobic tail. Hydrophobic tail consist of one or two alkyl or perfluoroalkyl groups or in some cases a single steroidal group [1.24.6](31) The ether type surfactants with single chain alkyl as hydrophobic tail is more toxic than corresponding dialkyl ether chain. The ester type surfactant are chemically less stable but less toxic than ether type surfactant.[1.24.7](32).
Table 1: Differnent types of Non-ionic surfactant
Type of Non-Ionic surfactant
Steryl alcohol, Cetyl alcohol Cetosteryl alcohol, oleyl alcohol
Glyceryl laurate, Polysorbates, Spans
Brij, Lauryl glucoside, Octyl glucoside, Nanoxylol-9
Structure of Surfactants:
The structure of surfactant affects the geometry of vesicle, which is related to critical packing parameter. Critical packing parameter (CPP) can be defined by following equestion.[1.21.20](35)
CPP = v / lc Ã- a0
Where, v = hydrophobic group volume
lc = the crical hydrophobic length,
a0 = the area of hydrophilic head group.
From the CPP value,type of miceller structure can be predicted.
If CPP < Â½ then formation of spherical micelles, If Â½ < CPP < 1 formation of bilayer micelles and If CPP > 1 formation of inverted micelles.
Temperature of hydration :
Hydration temperature affect the shape and size of the niosome. For ideal condition it should be above the gel to liquid phase transition temperature of system. Temperature change of niosomal system affects assembly of surfactant into vesicles and induces vesicle shape transformation.[1.21.21]
Nature of Encapsulated drug :
The physicochemical properties of encapsulated drug affect charge and rigidity of the niosome bilayer. Here drug interacts with surfactant head group and develops the charge which creates mutual repulsion between surfactant bilayer and hence increase vesicle size.[1.21.19](37) The aggregation of vesicle is prevented due to the charge which is developed on bilayer. In PEG (polyoxyethylene glycol) coated vesicle, some drug is entrapped in the long PEG chain, hence reducing the tendency to increase the size.[1.24.15](38)
Table 2: Effect of the Nature of Drugs on the formation of Niosomes
Nature of the Drugs
Leakage from vesicle
Improve transdermal delivery
Altered electrophoretic mobility, increase encapsulation property
Different additives are added along with surfactant and drug to form stable niosomes. Niosomes having number of morphologies, permeability and stability properties which can be altered by adding different additives. For e.g. Polyhedral niosomes formed from C16G2, the shape of these niosome remains unaffected by adding low amount of solulan C24(Cholesteryl poly-24-oxyethylene ether), which prevent aggregation due to development of steric hinderance.[1.21.22](39)
As a Carrier for drug delivery
Span 80, Cholesterol
Thin layer evaporation method
5- flurouracil (5-FU)
For Brain targeting
N-Palmitoyl glucosamine (NPG), Span 60, Cholesterol, Solulan C24
Probe sonication technique
Vasoactive intestinal peptides
To Improve Bioavalability
Cholesterol, Span 60, Span 20, Span 40, Dicetylphosphate(DCP)
Film hydration method
Span 40, Cholesterol, DCP
Solvent evaporation technique
To prolong the release time
Reverse phase evaporation method
Cholesterol, DCP and Tween 85 or pluronic F108
Reverse phase evaporation method