Download Why Biodegradable Polymer

Basic Concept of Biodegradable Polymer
Course : ACCE-522
M. Sc. Final Year
Special Course
Polymer
• The term "polymer" derives from the ancient Greek word polus, meaning
"many, much" and meros, meaning "parts", and refers to a molecule whose
structure is composed of multiple repeating units.
• A polymer is a large molecule (macromolecules) composed of many repeated
subunits, known as monomers. monomers can be linked together in various
ways to give linear, branched and cross linked polymers etc…….
History
The polymer is a big term and bears a great significant that was used since 1833 by Jons
Jacob Berzelius. Further it was elaborated in 1866 by Berthelot. But it was Hermann
Staudinger, in the year 1920, which was the first to propose the concept of polymers in the
sense we use today. It lead to the Nobel Prize in 1953 for his work which is at the base of all
science of macromolecules.
History
Because of the inconveniences as well as environmental concerns that occur due to synthetic
polymers, considerable interest in being focused on the development of biodegradable polymers so
that, they would mix themselves with soil after their applications being over. For ecological balance,
the development of biodegradable polymers is one of the leading edges of research in polymer
science for biomedical, agricultural and domestic uses.
Biodegradable polymers have a long history and since many are natural products, the precise
timeline of their discovery and use cannot be accurately traced. The concept of synthetic
biodegradable plastics and polymers was first introduced in the 1980s. In 1992, an international
meeting was called where leaders in biodegradable polymers met to discuss a definition, standard,
and testing protocol for biodegradable polymers.
Biodegradable polymers
Biodegradable polymers are those polymers that are degradable due to the enzymatic action of
living organisms or because of the natural processes of the environment and thus ultimately are
consumed by the living body or mix with the environment without creating any kind of adverse
effects. Actually in general, all of the natural polymers can be considered as biodegradable. So if
the structural feature of a natural polymer that makes it biodegradable could be introduced in a
synthetic polymer then it could possibly be turned into a biodegradable polymer. Generally
polymers containing hetero-linkage on their backbone are biodegradable.
“Every resource made by nature returns to nature”
Biodegradable polymers
Biodegradable polymers are a specific type of polymer that breaks down after its intended
purpose to result in natural byproducts such as gases (CO2, N2), water, biomass, and inorganic salts.
These polymers are found both naturally and synthetically made, and largely consist
of ester, amide, and ether functional groups. Their properties and breakdown mechanism are
determined by their exact structure. These polymers are often synthesized by condensation
reactions, ring opening polymerization, and metal catalysts. There are vast examples and
applications of biodegradable polymers.
Biodegradable polymers
• Biodegradable polymers are defined as polymers comprised of monomers linked to one
another through functional groups and have unstable links in the backbone.
• They are broken down into biologically acceptable molecules that are metabolized and
removed from the body via normal metabolic pathways.
FACTORS AFFECTING BIODEGRADATION OF POLYMERS
 Morphological factors
•
Shape & size
•
Variation of diffusion coefficient and mechanical stresses
 Chemical factors
•
Chemical structure & composition
•
Presence of ionic group and configuration structure
•
Molecular weight and presence of low molecular weight compounds
 Physical factors
•
Processing condition
•
Sterilization process
Why Biodegradable Polymer ?
Synthetic biodegradable polymer are preferred more than the natural biodegradable polymer
because they are free of immunogenicity & their physicochemical properties are more predictable
& reproducible
POLYMERIC MATERIAL
DEGRADATION TIME
Cotton rags
1-5 months
Paper
2-5 months
Rope
3-14 months
Orange peels
6 months
Wool socks
1 to 5 years
Cigarette butts
1 to 12 years
Plastic coated paper milk cartons
5 years
Plastic bags
10 to 20 years
Nylon fabric
30 to 40 years
Aluminum cans
80 to 100 years
Plastic 6-pack holder rings
450 years
Glass bottles
1 million years
Plastic bottles
May be never
Classification
Biodegradable polymers can be classified in three categories:
A: BASED ON ORIGIN
Natural origin : Collagen, Albumin, Casein, etc.
Semi-synthetic polymers : Gelatin, Dextran , Chitin, Alginate, Chitosan , etc.
Synthetic polymers : Aliphatic polyesters : PGA, PLA,PCL, etc.
Polyphosphoesters , polyanhydrides , polyphosphazenes, polyaminoacids
B. BASED ON ENVIORNMENTAL FACTORS:
Thermosensitive polymer: Polyacrylamide , etc.
Electrically and chemically controlled: Poly(pyrrole), collagen, etc.
pH sensitive polymer: poly (2-ethylacrylic acid), etc.
C. MISCELLANEOUS:
Polymeric phospholipids, Polyethyleneamine, Polyamidoamine, PEG
Synthetic biodegradable polymers
1) Aliphatic poly(esters)
• These are prepared by ring opening and polymerization of cyclic ester.
• Aliphatic polyesters include:
a) POLY (GLYCOLIC ACID)
b) POLY (LACTIC ACID)
c)POLY (CAPROLACTONE)
POLY (GLYCOLIC ACID)
POLY (LACTIC ACID)
---(--O—C-CH2---)n
--(--O---C—CH---)n
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a) POLYGLYCOLIC ACID
Polyglycolide or Polyglycolic acid (PGA) is a biodegradable, thermoplastic polymer and the
simplest linear, aliphatic polyester.
• It is a tough fibre-forming polymer.
• Due to its hydrolytic instability its use has been limited.
• It has a glass transition elevated degree of temperature between 35-40 C., crystallinity,
around 45.
• Its melting point is in the range 55%, thus resulting in of 225-230 C. insolubility in water.
• polyglycolide is degraded by hydrolysis, and broken down by certain enzymes.
•
– Applications
–
Used to deliver drugs in the form of microspheres, implants etc.,
–
Examples of drugs delivered include steroid hormones, antibiotics, anti cancer agents etc.,
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b) POLYLACTIC ACID
• Polylactic acid or polylactide (PLA) is a thermoplastic aliphatic polyester derived from
renewable resources, such as corn starch, tapioca products (roots, chips or starch) or
sugarcane.
•
It can biodegrade under certain conditions, such as the presence of oxygen, and is
difficult to recycle.
• Highly crystalline, high melting point, low solubility.
• Bacterial fermentation is used to produce lactic acid from corn starch or cane sugar.
 APPLICATIONS
• PLA is used in the preparation of sutures or orthopaedic devices.
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c) POLYCAPROLACTONE
• Polycaprolactone (PCL) is a biodegradable polyester.
• It has a low melting point of around 60 C.
•
It has a glass transition temperature of about ­60 C.
• slower degradation rate than PLA.
• It remains active as long as a year for drug delivery.
 Applications:
Drug delivery applications of PCL includes:
- Cyclosporin in the form of nanoparticles
- Ciprofloxacin in the form of dental implants
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2) Poly anhydrides
–
–
–
–
–
–
–
–
Highly reactive and hydrolytically unstable.
Degrade by surface degradation without the need for catalysts.
Aliphatic (CH2 in backbone and side chains) polyanhydrides degrade within days.
Aromatic (benzene ring as the side chain) polyanhydrides degrade over several
years.
Excellent biocompatibility.
Drug loaded devices prepared by compression molding or microencapsulation.
Suitable for short term drug delivery.
Used for vaccination and localized tumor therapy.
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3) polyphosphazenes
• Its hydrolytic stability/instability is determined by change in side group attached to
macromolecular backbone.
• Used in the construction of soft tissue prosthesis, tissue like coatings, as material for
blood vessel prosthesis.
• Used for immobilization of antigen or enzyme.
• Use for drug delivery under investigation
• Based on side chain these are of 3 types:
– Hydrophobic phosphazenes
– Hydrophilic phosphazenes
– Amphiphilic phosphazenes
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4) Polyaminoacids
– Aminoacid side-chains offer sites for drug attachment.
– Low-level systemic toxicity owing to their similarity to naturally occurring amino
acids.
– Investigated as suture materials.
– Artificial skin subtitutes .
– Limited applicability as biomaterials due to limited solubility and processibility .
– Drug delivery (difficult to predict drug release rate due to swelling)
– Polymers containing more than three or more amino acids may trigger antigenic
response.
– Tyrosine derived polycarbonates developed as high-strength degradable
orthopaedic implants.
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Natural biodegradable polymers
• Natural polymers are an attractive class of biodegradable polymers as they are:
– Derived from natural sources
– Easily available
– Relatively cheap
eg:
Albumin
Collagen
Dextran
Gelatin
Pectin,
starch etc.,
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1) Collagen
•
Collagen is the most widely found protein in mammals and is the major provider of
strength to tissue.
The number of biomedical applications in which collagen have been utilized is too high;
it not only has been explored for use in various types of surgery, cosmetics, and drug
delivery, but also in bioprosthetic implants and tissue engineering of multiple organs
as well.
•
It is used as sutures ,Dressings, etc.
•
Disadvantages
 Poor dimensional stability. Variability in drug release kinetics.
 Poor mechanical strength.
Applications:
• Majorly used in optical drug delivery system
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2) Albumin
It is a major plasma protein component.
It accounts for more than 55% of total protein in human plasma.
It is used to design particulate drug delivery systems.
Applications:
•
Albumin micro-spheres are used to deliver drugs like Insulin, Sulphadiazene, 5fluorouracil, Prednisolone etc.
•
It is mainly used in chemotherapy, to achieve high local drug concentration for
relatively longer time.
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3) Dextran
• 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.
Its Mol.wt ranges from 1000 to 2,00,000 Daltons.
Applications:
• Used for colonic delivery of drug in the form of gels.
4) GELATIN
• Gelatin is a mixture of peptides and proteins produced by partial hydrolysis of collagen,
extracted from the boiled bones, connective tissues, organs and some intestines of animals.
Gelatin is an irreversible hydrolyzed form of collagen, Physicochemical properties depends on
the source of collagen, extraction method and thermal degradation.
 Applications:
 Employed as coating material.
 Gelatin micropellets are used for oral controlled delivery of drugs.
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Classification
Advantages of Biodegradable Polymers
• Localized delivery of drug
• Sustained delivery of drug
• Stabilization of drug
• Decrease in dosing frequency
• Reduce side effects
• Improved patient compliance
• Controllable degradation rate
Application
• Polymer system for gene therapy.
• Biodegradable polymer for optical, tissue engineering, vascular, orthopedic, skin
adhesive & surgical glues.
• Bio degradable drug system for therapeutic agents such as anti tumor, antipsychotic
agent, anti-inflammatory agent.
• Polymeric materials are used in and on soil to improve aeration, and promote plant
growth and health.
• Many biomaterials, especially heart valve replacements and blood vessels, are made of
polymers like Dacron, Teflon and polyurethane.
Thank you all