liposomes Flashcards

1
Q

how are liposomes and niosomes different?

A

lipid is a vesicle forming amphiphiles= liposome
surfactant is a vesicle-forming amphiphiles= niosomes
polar group with, mainly two alkyl chains

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2
Q

what are the different types of liposomes and niosomes in drug delivery formed by amphiphiles in aqueous media?

A

micelle and rod-like micelle
bilayered and inverse micelles
hexagonal 1 and 2
lamellar

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3
Q

how many layers can a liposome have?

A

up to 3

it can have bilayers of phospholipids which alternate with aqueous compartments

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4
Q

what is the definition of liposomes and niosomes?

A

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.

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5
Q

what are liposomes?

A

artificially manufactured vesicles, made from glycolipids, phospholipids (e.g., phosphatidylcholine) and cholesterol.

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6
Q

what are cubosomes?

A

self-assembled nanostructured particles that formed in aqueous lipid and surfactant systems.

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7
Q

what are niosomes?

A

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.

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8
Q

what are some of the applications of liposomes and niosomes in drug delivery?

A

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

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9
Q

how are liposomes and niosomes classified?

A

they are classified according to size and number of membranes

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10
Q

what are the classifications of liposomes and niosomes?

A

Multi-Lamellar Large Vesicles (MLVs)
Small Uni-lamellar Vesicles (SUVs)
Large Uni-lamellar Vesicles (LUVs)

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11
Q

how does vessicle size vary? how big is the membrane layer?

A

20 nm up to few nm

Membrane (Lipid bilayer) thickness is about 4 nm

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12
Q

what affects the size of liposomes and niosomes?

A

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.

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13
Q

what are MLVs?

A

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.

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14
Q

how are liposomes and niosomes manufactured?

A

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

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15
Q

what can be repeated in the manufacturing process to enhance the drug entrapment?

A

dehydration/ rehydration

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16
Q

why are MLVs rehydrated at a lipid film at temperatures above the phase transition temp?

A

to transit from a gel phase into the liquid crystalline phase

17
Q

what happens below the phase transition temperature?

A

celow Tci.e. gel phase, the lipid chains are ordered and the polar head groups are slightly hydrated; no vesicles are formed.

18
Q

what happens above the phase transition temperature?

A

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.

19
Q

what is the phase transition temperature of phosphatidycholine containing liposomes?

A

is below room temperature; stable delivery systems.

20
Q

what is the phase transition temperature of dipalmitoyl-phosphatidyl-choline containing liposomes?

A

is just above the temperature of the skin; suitable for dermal products and cosmetics

21
Q

how would you make the drug release retarded?

A

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

22
Q

how would you make the drug release quick?

A

Lipophilic drugs located within the bilayer structure of liposomes

23
Q

what are MLVs cleared by?

A

phagocytosis cells (RES).

24
Q

what are SUVs?

A

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.

25
Q

what limits the amount of drug that can be entrapped in SUV?

A

the small inner cavity volume

26
Q

what can SUV’s be useful for and why?

A

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.

27
Q

what are LUVs?

A

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.

28
Q

why would a phospholipid or non-ionic surfactant be mixed with amphiphilic or lipophilic compounds?

A

in order to change the physicochemical properties of the vesicles.

29
Q

what does cholesterol modulate?

A

modulates the rheological properties of the bilayer. It increases the membrane fluidity, it reduces the membrane permeability.

30
Q

when will charged liposomes be formed ?

A

if amphiphilic lipids (is added to phospholipid)

31
Q

what does use of synthetic products or natural phospholipids with fatty acid chains do ?

A

and degrees of saturation:-An increase in the degree of saturation increased membrane rigidity and thus decreased membrane fluidity

32
Q

what does an increase in the acyl chain length do?

A

increased bilayer thickness, which might be useful in modified release systems.

33
Q

what does the head group of a lipid determine?

A

determines the charge of the vesicles. A negative charge results in surface hydration.