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Biodegradable polymers degrade within the body as
a result of natural biological processes.
They are broken down into biologically acceptable
molecules that are metabolized and removed from the
body via normal metabolic pathways.
Ideal Characteristics Of Polymers In
Biodegradable Delivery System
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BULK EROSION SURFACE EROSION
The degradation is primarily the process of chain cleavage
leading to a reduction in molecular weight. On the other hand,
erosion is the sum of all processes leading to the loss of mass
from a polymer matrix.
The degradation of the polymer can be through either bulk
erosion (as in poly(α-hydroxy esters)) or surface erosion (as
in polyanhydrides, poly(orthoesters)).
Generally Hydrophobic Polymers degraded by these
Bulk Erosion : In this process
hydrolysis occurs throughout
the bulk of the polymer. The
matrix can disintegrate before
drug depletion, and a large
burst in rate of drug delivery
can take place.
Surface Erosion: In a surface
erosion process hydrolysis of
the polymer is confined to the
outer surface, and the interior
of the matrix remains
Type I Erosion
It is evident with water-soluble
to form a three-dimensional
Erosion can occur by
cleavage of cross-links
(type IA) or cleavage of
polymer backbone (type
Type II Erosion
It occurs with polymers that
were earlier water-insoluble
but converted to water-soluble
forms by hydrolysis, ionization
or protonation of a pendant
Type III Erosion
High molecular weight, water-insoluble
converted to small, water-soluble
molecules by a
hydrolytic cleavage of labile
bonds in the polymer
Factors Influence the Degradation Behavior
Chemical Structure and Chemical Composition
Presence of Low Mw Compounds (monomer, oligomers,
solvents, plasticizers, etc)
Presence of Ionic Groups
Presence of Chain Defects
Morphology (crystallinity, presence of microstructure,
orientation and residue stress)
Processing methods & Conditions
Method of Sterilization
Site of Implantation
Physiochemical Factors (shape, size)
Mechanism of Hydrolysis (enzymes vs water)
♦ Aliphatic Poly (ester)s
Poly (glycolic acid) (PGA)
Poly (lactic acid) (PLA)
Poly (ß-malic acid)
♦ Poly (ortho esters)
♦ Poly (amino) Acids and
Pseudopoly (amino) Acids
POLY (GLYCOLIC ACID) ---(--O—C-CH2---)n
POLY (LACTIC ACID) --(--O---C—CH---)n
POLY (CAPROLACTONE) --(--O—C---(CH2)5---)n
First polymers used in medicine dated back to 1954.
Most commercialized class of Polymers
ex : ADRIAMYCIN®
Bio compatible & Bio resorbable
Synthesis & Co polymerisation can be easily done
t ½ ranges from weeks (PLA) to years (PCL).
APPLICATIONS : (1) Sutures, ligatures etc.
(2) DECAPEPTYL ® , LUPRON DEPOT ®
DEGRADATION IS MAINLY BY
Esterase, pronase, bromelain
R—COO---R1 + H2O R—COOH + R1 –OH
• Fungi – ‘ FUSARIUM MONILIFORMAE’
• YEAST- ‘CRYPTOCOCCUS’
POLY PHOSPHO ESTERS
--(--P---O---R---O--)-- Poly (Phosphate )
--(--P---O---R---O--)-- Poly (Phosphonate)
Highly Adjustable properties
High Mol.wt gives good strength
Get degraded within 6 months
T1/2 is from 2 to 4 months..
Degradation products – phosphates & alcohol.
Paclitaxel, Cisplatin, Plasmid DNA.
Sterilisation & stability
Highly susceptible to hydrolysis in open air.
Should be stored in a desiccators.
Sterilization only by gamma irradiation.
• Two carboxylic groups at each end
• High Degradation rate
• Degrade by Surface Erosion
• Aromatic P.A’s are slower degrading
• Copolymerisation can control degradation rate
• Biological tests in Rabbits proved them Non-mutagenic
APPLICATIONS : 1) Peptides for osteomylites.
2) Protiens for brain tumour.
Mostly they degrade by Surface Erosion (S.E)
Their t1/2 is less than 30 days.
Due to S.E. proportion of drug released alters with
Primary amine containing drugs react at pH 7.2.
The above reaction is not seen below pH 5.0.
They are ideal when action is required for 1 week
They have more application as parentrals.
A polyolefin is a polymer produced from a simple olefin (also
called an alkene with the general formula CnH2n) as a
Carbon Chain based Polymers.
They contain Double & Triple bonds extensively.
Presence of substituents like cyanoacryl groups enhance
Introduction of vinyl group makes them more stable
ex : Teflon
1) Sutures, catheters, implants.
2) Membrane barrier for drugs.
A polyamide is a polymer containing monomers of amides
joined by peptide bonds.
These are generally called as ‘NYLONS’.
They are generally slow degrading.
By Introduction of copolymers like ‘L-Aspartic Acid', nearly
40% of polymer Is degraded within 1 week.
Mainly degraded In vivo by Non-specific ‘Amidases’
They are more stable when compared to other Polymers.
• Haemofiltration Membranes.
• Dressings, sutures etc.
Play an essential role in Formulation of CDDS.
Patient compliance is improved.
Help in adjusting duration of action of drug.
Most of them are Inert.
Copolymerisation can be done.
Drug release cannot be 100% predicted.
These are the polymers obtained from natural resources, and
are generally non-toxic.
Ex : DEXTRAN
ADVANTAGES : 1) Readily & Abundantly Available.
2) Comparatively Inexpensive.
3) Non toxic products.
4) Modified to get semi synthetic forms.
• It is a major plasma protein component.
• It accounts for more than 55% of total protein in
• It is used to design particulate drug delivery systems.
Factors Affecting Drug Release From Albumin
• Physicochemical properties and the concentration of the
• Interaction between the drug and the albumin matrix.
• Size and density of microspheres.
• Nature and degree of cross-linking.
• Presence of the enzymes and pH in the environment.
• Albumin micro-spheres are used to deliver drugs like
Insulin, Sulphadiazene, 5-fluorouracil, Prednisolone etc.
• It is mainly used in chemotherapy, to achieve high local
drug concentration for relatively longer time.
It is a major structural protein in animals
It is used as sutures ,Dressings, etc.
Readily isolated & purified in large quantities.
Can be processed in variety of forms .
Chance of antigenic response.
Variability in drug release kinetics.
Poor mechanical strength.
• Since the use of organic solvents and high temperature
is not required even viable bacteria and viruses can be
• It protects the antigens and the vaccines against
degradation in GIT.
• It acts as an adjuvant.
• Alginates are particularly used as carriers of peptides
and other sensitive drug molecules since particulate
carriers can be easily prepared in aqueous solution at
• Alginate micro-spheres are efficiently used for oral
delivery of vaccines.
• Dextran is a complex branched polysaccharide made of many
glucose molecules joined into chains of varying lengths.
• It consists of α-D-1,6-glucose-linked glucan with side-chains
linked to the backbone of Polymer.
• Mol.wt ranges from 1000 to 2,00,000 Daltons
• Enzymes from moulds such as ‘PENCILLIUM’ degrade it.
1) Replacement of Blood loss.
2) Thrombosis Prophylaxis.
3) Improvement of Rheology.
• It consists of B-1-4 linked 2 amino-2-deoxy gluco –pyranose
• Commercially manufactured by N-deacetylation of Chitin
which is obtained from Mollusc shells.
• It is soluble only in acidic pH i.e. when amino group is
• Thereby it readily adheres to bio membranes.
• It is degraded mainly by Glycosidases & lysozymes.
Free availability, Biocompatibility, Biodegradability
Bioadhesive, unique properties.
e.g. Poly (N-alkyl substututed acrylamides)
Electrically and Chemically
e.g. PEG & Poly(methacrylic acid)
(PMMA), collagen, Poly(pyrrole)
pH Sensitive polymers
e.g. Poly(2-ethylacrylic acid) (PEAA)