liposomes Flashcards
how are liposomes and niosomes different?
lipid is a vesicle forming amphiphiles= liposome
surfactant is a vesicle-forming amphiphiles= niosomes
polar group with, mainly two alkyl chains
what are the different types of liposomes and niosomes in drug delivery formed by amphiphiles in aqueous media?
micelle and rod-like micelle
bilayered and inverse micelles
hexagonal 1 and 2
lamellar
how many layers can a liposome have?
up to 3
it can have bilayers of phospholipids which alternate with aqueous compartments
what is the definition of liposomes and niosomes?
They are Vesicles which are:spherical self-assembled particles suspended in an aqueous phase.
Liquid crystals, closed bilayers consist of amphiphilic compounds, phospholipids or surfactants in aqueous media Dispersed colloidal particles
Forms of liquid crystals: Lamellar; hexagonal and cubic liquid crystals. The dispersed colloidal units are termed accordingly as liposomes, hexasomes and cubosomes.
what are liposomes?
artificially manufactured vesicles, made from glycolipids, phospholipids (e.g., phosphatidylcholine) and cholesterol.
what are cubosomes?
self-assembled nanostructured particles that formed in aqueous lipid and surfactant systems.
what are niosomes?
artificially made vesicles, consist of mixtures of non-ionic surfactants (e.g., Spans®), cholesterol and a co-surfactant (e.g., dialkylethers of polyoxyethylene, Brij®, Cremophor®). Niosomes are stable and less toxic than liposomes.
what are some of the applications of liposomes and niosomes in drug delivery?
Used as biodegradable and biocompatible drug carrier
to enhance drug potency
to reduce drug toxicity
They used for delivery of cytotoxic drugs and vaccines by injections
Transdermal drug delivery
Pulmonary drug delivery
how are liposomes and niosomes classified?
they are classified according to size and number of membranes
what are the classifications of liposomes and niosomes?
Multi-Lamellar Large Vesicles (MLVs)
Small Uni-lamellar Vesicles (SUVs)
Large Uni-lamellar Vesicles (LUVs)
how does vessicle size vary? how big is the membrane layer?
20 nm up to few nm
Membrane (Lipid bilayer) thickness is about 4 nm
what affects the size of liposomes and niosomes?
The rate of uptake by the reticuloendo the lialsystem (RES) for elimination increases with increasing size.
Liposomes, niosomes and cubosomes for systemic drug delivery should be of small size; the upper size limit for a long systemic circulation is 150–200 nm.
But, the small liquid crystals will have small inner cavity and hence small amount of encapsulated drug. Accordingly,
for therapeutic use a balance between size and loading efficiency must be found.
what are MLVs?
Multi-lamellar large vesicles consist of a number of concentric lipid bilayers, which are separated from each other by the aqueous medium in which the vesicles are suspended.
The size of these vesicles is between 0.1 and 10 μm.
Due to their large size they are of limited use in drug delivery, but they are used as membrane models.
how are liposomes and niosomes manufactured?
1 phospholipid or non-ionic surfactant are dissolved in an organic solvent
2 evaporation of solvent- rotary evaporator
3 thin mixed lipid film will form at the surface of the evaporation vessel
4 rehydration: aq buffer solution containing the dissolved drug is added and the vessel is shook at temp above the phase transition temp
5 multi-lamellar vesicles will form and a suspension containing the vesicles in aq liquid are formed
6- ultrasound/ pressure filtration and dialysis
7- UVLS in aq medium
what can be repeated in the manufacturing process to enhance the drug entrapment?
dehydration/ rehydration
why are MLVs rehydrated at a lipid film at temperatures above the phase transition temp?
to transit from a gel phase into the liquid crystalline phase
what happens below the phase transition temperature?
celow Tci.e. gel phase, the lipid chains are ordered and the polar head groups are slightly hydrated; no vesicles are formed.
what happens above the phase transition temperature?
above Tci.e. liquid crystalline phase, lipid chains have gained a liquid-like mobility, and their polar head groups are fully hydrated; vesicles are formed.
what is the phase transition temperature of phosphatidycholine containing liposomes?
is below room temperature; stable delivery systems.
what is the phase transition temperature of dipalmitoyl-phosphatidyl-choline containing liposomes?
is just above the temperature of the skin; suitable for dermal products and cosmetics
how would you make the drug release retarded?
Hydrophilic drugs are loaded between the lipid bilayers and in the inner cavity. The molecules must pass through each bilayer in order to be released from the vesicle
how would you make the drug release quick?
Lipophilic drugs located within the bilayer structure of liposomes
what are MLVs cleared by?
phagocytosis cells (RES).
what are SUVs?
Have a size: 20-50 nm; a large membrane curvature AND high membrane tension.
Hence, SUVs are thermodynamically unstable; SUVs tend to fuse into larger entities thermodynamically more stable.
Number of lipids molecules in the inner cavity is nearly half of that in the outer lipid bilayer membrane.
what limits the amount of drug that can be entrapped in SUV?
the small inner cavity volume
what can SUV’s be useful for and why?
SUVs can pass through the gaps between the endothelial cells of blood capillaries and hence they can be used for drug targeting into tissues, for example, tumour tissues.
what are LUVs?
Large Uni-lamellar Vesicles (LUVs)
Have a size above 50 nm;
membranes are free of tension,
vesicles show no tendency for fusion into larger vesicles,
better storage stability compared to small uni-lamellar vesicles.
LUVs have a larger inner cavity i.e. an increased aqueous inner volume. Hence, there will be a balance between entrapped hydrophilic drug (s) and the amount of lipids required to form these vesicles.
why would a phospholipid or non-ionic surfactant be mixed with amphiphilic or lipophilic compounds?
in order to change the physicochemical properties of the vesicles.
what does cholesterol modulate?
modulates the rheological properties of the bilayer. It increases the membrane fluidity, it reduces the membrane permeability.
when will charged liposomes be formed ?
if amphiphilic lipids (is added to phospholipid)
what does use of synthetic products or natural phospholipids with fatty acid chains do ?
and degrees of saturation:-An increase in the degree of saturation increased membrane rigidity and thus decreased membrane fluidity
what does an increase in the acyl chain length do?
increased bilayer thickness, which might be useful in modified release systems.
what does the head group of a lipid determine?
determines the charge of the vesicles. A negative charge results in surface hydration.
