The document discusses the stability aspects of liposomes. It notes that liposome stability can be classified as physical, chemical, or biological. Physical stability is determined by factors like particle size, lipid composition, and aggregation/fusion of liposomes. Chemical stability depends on the oxidation and hydrolysis of lipids over time. Biological stability relates to how liposomes interact with plasma components. Several methods to improve liposome stability are discussed, such as controlling size and lamellarity, lipid selection, drug loading techniques, lyophilization, and antioxidant addition. Other vesicle types like niosomes and transfersomes are also summarized briefly in terms of their composition, uses, and stability issues.

1. Stability Aspects of Liposomes
PREPARED BY : HARNISHA PATEL
SEMESTER :3
MPHARM(PHARMACEUTICS)

2.  Stability testing - the primary tool used to assess expiration dating and storage conditions for
pharmaceutical products.
 Protocols used for stability testing in the industry are derived from the recommendations of the
International Conference on Harmonization (ICH).
 These guidelines were developed as a cooperative effort between regulatory agencies and industry
officials from Europe, Japan, and United States.
 Liposomes have been extensively investigated for drug delivery, drug targeting, controlled release and
enhancing solubility.
 Major Limitation:
INSTABILITY of LIPOSOMES.

3. CLASSIFICATION OF STABILITY OF LIPOSOMES:
 Liposome stability can be subdivided into physical, chemical and biological stabilities, which are all
inter-related.
 The shelf-life stability of liposomes is determined by :
(1). Physical Stability:
 By optimizing the size distribution, pH and ionic strength, the addition of antioxidants and chelating
agents.
 Stable liquid liposomes.
 Physical processes such as aggregation/flocculation and fusion/coalescence that affect the shelf life of
liposomes.
 Loss of liposome associated drug and changes in size.

4. A). Aggregation/flocculation
 Formation of larger units of liposomal material;
these units are still composed of individual
liposomes.
 Reversible. e.g. by applying mild shears forces,
by changing the temperature.
 The presence of aggregation can accelerate the
process of coalescence of liposomes, which
indicates that new colloidal structures are
formed.
 There is no reduction of surface in aggregation
the small particles retain their identity.
 Aggregation moves as a single unit.
B). Coalescence/fusion:
 Irreversible process; the original liposomes
cannot be retrieved.
 A colloidal dispersion is often
thermodynamically unstable.
 The central feature = the total surface area is
reduced in the coarsening process of unstable
liposome dispersion.
 After small particles coalescence, only the new
larger particle remains.

5. MECHANISM OF FUSION & AGGREGATION:
 Loosely packed head groups and tightly packed alkyl chains in the outer layer with the opposite
arrangement in the inner layer of the bilayer.
 Thermodynamically unstable state
 which favors aggregation and/or fusion of the vesicles
 Instability

6. (2). Chemical stability
 As phospholipids form the backbone of the bilayer their chemical stability is important.
 Two types of chemical degradation reactions can affect the performance of phospholipid bilayers:
 A).Hydrolysis of the ester bonds linking the fatty acids to the glycerol backbone and
 B).Peroxidation of unsaturated acyl chains (if present).
 The oxidation and hydrolysis of lipids may lead to
the appearance of short-chain lipids and then soluble
derivatives will form in the membrane, resulting
in the decrease of the quality of liposome products.

7. C). Biological stability:
 Depends on :
1).The presence of agents such as proteins that interact with liposomes upon application to the subject
2).Administration route.
 Strategies used to enhance biological stability of liposomes will improve liposome-mediated drug
delivery by increasing circulation time in the blood stream.
 Incorporating steric stability, e.g. the incorporation of PEG into liposomes has shown to increase the
liposomal biological stability towards plasma components.

8. A COMPARISON BETWEEN VESICULAR
DRUG DELIVERY SYSTEM & STABILITY
ISSUES

9. LIPOSOMES:
 For drug delivery , Unilamellar( diameter 50
– 150 nm) are used. Larger liposomes are
rapidly removed from the blood circulation.
 Liposomes may increase the solubility of
insoluble drugs(1000X).
 In the small intestine, liposomes are digested
in the presence of bile and enzymes. The
drug is liberated and further solubilized in
bile and digested lipids.
 Efficient carriers for drugs, diagnostics,
vaccines, nutrients and other bioactive
agents.
STABILITY ISSUES:
 The physical instability causes fusion &
aggregation.
 Chemical instability indicates
hydrolysis and oxidation of lipids.
 Liposomes in plasma are prone to
aggregation and exhibit leakage
 The destabilization of liposomes is due
to the lipid exchange between the
liposomes and HDLs

10. NIOSOMES:
 Niosomes are formed of cholesterol and
nonionic surfactants with or without
incorporation of cholesterol or other lipids.
 Stabilized due to cholesterol and small
amount of anionic surfactant such as dicetyl
phosphate.
 Higher chemical stability of the surfactants
than that of phospholipids, which are
present in liposomes.
 Due to the presence of ester bond,
phospholipids are easily hydrolysed.
STABILITY ISSUES:
 Only chemical stability.
 Stability problems such as physical
stability of fusion, aggregation,
sedimentation and leakage on storage.

11. ETHOSOMES:
 Noninvasive carriers that enable
drugs to reach the deep skin layers
and/or the systemic circulation.
 They are composed mainly of
phospholipids, high concentration of
ethanol and water (disturbance of
skin lipid bilayer & ability to
penetrate the stratum corneum)
 High patient compliance due to
semisolid form (gel or cream) rather
than Iontophoresis and
Phonophoresis
STABILITY ISSUES:
 Ethosomes are used for transdermal
drug delivery which can provide
better skin permeation and stability
than liposomes.
 It improves entrapment of drug.
 Overall good stability.

12. TRANSFERSOMES:
 Capable of non-invasive
transdermal delivery of low & high
molecular weight drugs.
 Ultradeformable (ultraflexible) lipid
aggregates, which are able to
penetrate the mammalian skin intact.
 Incorporation of "edge activators“
such as sodium cholate, sodium
deoxycholate, span 80 and Tween
80. flexibility and allows to
change their membrane composition
locally and reversibly & they
penetrate into narrow pore.
STABILITY ISSUES:
 Chemically unstable because they
are prone to oxidatation.
 Purity of natural phospholipids is
criterion for stability.

13. HERBOSOMES / PHYTOSOMES:
 Water soluble phytoconstituents are
poorly absorbed due to their large
molecular size by passive diffusion.
 Due to their poor lipid solubility
limiting their ability to pass across
the lipid‐rich biological membranes,
resulting in poor bioavailability.
 Herbosomes enhance the absorption
of active, its dose requirement is
reduced.
STABILITY ISSUES:
 Chemical bonds are formed between
phosphatidylcholine molecule and
phytoconstituent.
 So the herbosomes show better
stability profile with appreciable
drug entrapment.

14. SPHINGOSOMES:
 Liposomal phospholipid can undergo
chemical degradation such as
oxidation and hydrolysis.
 The hydrolysis may be avoided by
use of lipid which contains ether or
amide linkage instead of ester
linkage (sphingolipid).
STABILITY ISSUES:
 Sphingolipid are used for the
preparation of stable liposomes known
as sphingosomes.
 Higher cost of sphingolipids hinders
the preparation and use of these
vesicular systems.
 They show better stability as compared
to liposomes BUT they have low
entrapment efficacy.

15. CUBOSOMES:
 Discrete, sub micron nanostructured
particles of bicontinuous cubic liquid
crystalline phase.
 Produced by high-energy dispersion of
bulk cubic phase, followed by colloidal
stabilization using polymeric surfactants.
STABILITY ISSUES:
 Cubosomes posses the simple
production procedure and have
better chemico-physical stability.
 They are the good option with many
advantages over liposomes,
 But manufacturing of cubosomes on
a large scale has difficulty because
of their viscosity.

16. METHODS FOR ENHANCEMENT OF STABILITY:
 Maximum encapsulation efficiency and absence of drug leakage is achieved only when the physical ,
chemical , biological stability of liposomes is enhanced.
 Depends on the number of factors :
1). Control of particle size and lamellarity
2). Lipid composition
3). Method of drug loading
4). Prodrug Approach
5). Lyophilization
6). Prevention from oxidation and hydrolysis
7). Pro-vesicular Drug Delivery
8). Electro steric stabilization
9). Layersome
10).Ufosomes

17. 1). CONTROL OF PARTICLE SIZE & LAMELLARITY:
 Change in particle size affect targeting , RES uptake & efficacy.
 Aggregation and fusion are observed with particle size < 20 nm due to excessive high stress curvature.
 The lamellarity of liposomes influences encapsulation efficiency, the efflux rate of drug.
 Particle size and lamellarity depends on the method of manufacturing.
 Ex. liposomes prepared by the combinations of some lipids on storage at 4 and 25°C over 6-month
period large unilamellar vesicles (REV) proved to be superior than multilamellar liposomes (MLV) and
dehydration/rehydration liposomes (DRV) systems as far as physical stability was concerned.

18. 2).LIPID COMPOSITION:
 Permeability and stability of liposomes are influenced by the rigidity/stiffness of the lipid bilayer.
 Selection of lipid depends on the phase transition temperature of lipids, which depends on fatty acid
side chains, degree of unsaturation, chain length and polar head groups.
 Lipids with long acyl chain length are most commonly used because high phase transition temperature.
 This can be achieved by combinations of lipids or incorporation of another substances such as
cholesterol , provides more rigidity to those phospholipids and therefore prevent liposome aggregation.
 Charge on the liposomes determines the in vivo stability.
 A). Liposomes with neutral charge & positive charge containing phosphatidylcholine are the most
stable
 B). Stability of negatively charged liposomes is depended on their composition.

19. 3).METHOD OF DRUG LAODING:
 Drug loading methods involves passive and active loading.
A).Passive loading includes mechanical dispersion, solvent dispersion and detergent solubilization.
B).Remote or active loading method load drug molecules into preformed vesicles by using pH gradient and
potential difference across liposomal membranes.
 Active loading give the greater encapsulation efficiency , ethanol addition to preformed liposomes is an
effective method to achieve efficient pH gradient-dependent loading of liposomes

20. 4).PRODRUG:
 Physical properties of drug play a role in the stability.
 Problems like poor entrapment efficiency & physical - chemical instability are associated with the
liposomal entrapment of drug molecules.
 Lipophilic character of prodrug improves the interaction with lipid bilayers, favoring the absorption
through the lipid barriers of skin.
 Liposomes work as a lipophilic carrier which is able to deliver drug near to the cell surface.
 Lipid composition is also equally responsible for stability of liposomes along with partition behavior of
drug.

21. 5).LYOPHILIZATION:
 The problems related to lipid oxidation and hydrolysis during shelf life of the liposomal product can
be reduced by the storage of liposomal dispersion in the dry state.
 Freeze-drying (Lyophilization) is used as an effective approach to render liposomes stable without
compromising their physical state or encapsulation capacity.
 But without appropriate stabilizers will again lead to fusion of vesicles. Cryoprotectants, including
saccharides (e.g. sucrose,trehalose, and lactose) are used.
MECHANISM:
 Aggregation of liposomes could be prevented by the formation of stable boundaries between the
vesicles.
 Cryoprotectants form these stable boundaries due to their ability to replace the bound water around
the bilayer via interaction with the polar region of the lipid head group (water replacement
hypothesis).

22. 6).Prevention from oxidation and hydrolysis:
 Numbers of factors are responsible for chemical instability of liposomes like pH, ionic strength and
exposure to oxygen.
 To prevent it:
a).Minimize use of unsaturated lipids
b).Use of argon or nitrogen environment to minimize the exposure to oxygen
c).Use of antioxidants like α-tochopherols, beta hydroxy toluene (BHT)
d).Use of light resistant container for the storage of liposomal formulations.
e).Cholesterol also protect liposomal lipids by reducing lipid bilayer hydration.

23. 7).Pro-vesicular Drug Delivery:
Pro vesicular drug delivery developed to overcome the stability problems associated with
aqueous vesicular dispersions.
They are solid carriers of drug containing liposomes.

24. LIPOSOMES:
 Unilamellar or multilamellar
 spheroid structures composed of
lipid molecules, often
phospholipids.
 They show controlled release and
increased solubility.
 But have tendency to aggregate or
fuse,
 Susceptible to hydrolysis or
oxidation.
PROLIPOSOMES:
 an alternative forms to conventional
liposomal formulation
 Composed of water soluble porous
powder as a carrier phospholipids.
 Drugs is dissolved in organic
solvent. Lipid and drug are coated on
to a soluble carrier to form free-
flowing granular material.
 Show controlled release, better
stability, ease of handling and
increased solubility.

25. NIOSOMES:
 Non-ionic surfactant based multilamellar
or unilamellar vesicles,
 Aqueous solution of solute is entirely
enclosed by a membrane of surfactant
macro-molecules as bilayers.
 They are cheap and chemically stable but
possess problems related to physical
stability such as fusion, aggregation,
sedimentation and leakage on storage.
PRONIOSOMES:
 approach minimizes the problems
associated with niosomes as it is a dry
and free flowing product which is more
stable during sterilization and storage.
 Ease of transfer, distribution,
measuring and storage make it a
versatile delivery system.
 Proniosomes are water-soluble carrier
particles that are coated with
surfactant.

26. 8).ELECTROSTERIC STABILIZATION:
 Steric stabilization can be achieved by covering the surface with an adsorbed layer of long, bulky
molecules to prevent the aggregation of the liposomes.
 The electrostatic repulsion can be obtained by increasing the charge of a surface by lowering the ionic
strength or addition of charged molecules on the bilayer.
 Liposomes coated with ligands, such as PEG, polyvinyl alcohol, poloxamer , stearylamine , block
copolymers have shown increase in the liposome stability.
 Polymer coating done by interfacial polycondensation.
 The release of drug from polymer-coated vesicles is retarded due to the effective double barrier
produced by the polymeric coat

27. 9).LAYERSOME:
 The layer-by-layer coating concept is one of the strategies used for the preparation or the
stabilization of nanosystems.
 The layersomes are conventional liposomes coated with one or multiple layers of biocompatible
polyelectrolytes in order to stabilise their structure.
 The formulation strategy is based on an alternative coating procedure of positive and negative
polymers on initially charged small liposomes.
 Drawback of liposome : their instability during storage or in biological media which is related to
surface properties.
 This surface modification stabilize the structure of the liposomes and lead to stable drug delivery
systems.

28. 10).UFOSOMES:
 Unsaturated fatty acid liposomes.
 It is colloidal suspensions of closed lipid bilayers that are composed of fatty acids and their ionized
species (soap).
 Fatty acid vesicles = the nonionized neutral form : the ionized form (the negatively charged soap).
 The ratio of nonionized neutral form and the ionized form is critical for the vesicle stability.
 Ufosome membranes are much more stable in comparison to liposomes.

29.  Future prospective for betterment of vesicular delivery:
Type of Vesicle Description
Aquasomes Three layered compositions with ceramics carbon , nanocrystalline particulate
core coated with, glassy cellobiose.
Specific targeting and molecular shielding.
Cryptosmes Surface coat composed of polyoxoyethylene derivative.
Capable of ligand mediated drug targeting.
Discomes Niosomes solublized with non ionic surfactant solutions
Emulsomes Lipid vesicles consisted of microscopic lipid assembly with apolar core.

30. Enzymosomes Liposomal constructs ,
to provide a mini bioenvironmental in which enzymes are covalently immobilized
or coupled to the surface of liposomes.
Targeted delivery to tumor cell.
Genosomes Artificial macromolecular complexes for gene transfer
Virosomes Liposomes spiked with virus glycoprotein
Vesosomes Multiple compartments of the vesosomes give better protection to the interior
contents in serum
Proteosomes High molecular weight multi-submit enzyme complexes with catalytic activity