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POLYMER SCIENCE

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POLYMER SCIENCE By: Prof. Dr. Basavaraj K. Nanjwade M. Pharm., Ph.D KLE University s College of Pharmacy BELGAUM -590010, Karnataka, India Cell: 00919742431000 – PowerPoint PPT presentation

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Title: POLYMER SCIENCE


1
POLYMER SCIENCE
  • By
  • Prof. Dr. Basavaraj K. Nanjwade M. Pharm., Ph.D
  • KLE Universitys College of Pharmacy
  • BELGAUM -590010, Karnataka, India
  • Cell 00919742431000
  • Cell No bknanjwade_at_yahoo.co.in

2
CONTENTS
  • INTRODUCTION TO POLYMERS
  • CLASSIFICATION OF POLYMERS
  • GENERAL MECHANISM OF DRUG RELEASE
  • APPLICATION IN CONVENTIONAL DOSGAE FORMS
  • APPLICATIONS IN CONTROLLED DRUG DELIVERY
  • BIODEGRADABLE POLYMERS
  • NATURAL POLYMERS
  • REFERENCESS

1
3
INTRODUCTION
  • A polymer is a very large molecule in which one
    or two small units is repeated over and over
    again
  • The small repeating units are known as
    monomers
  • Imagine that a monomer can be represented by
    the letter A. Then a polymer made of that monomer
    would have the structure
  • -A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-
    A-A-A

2
4
  • In another kind of polymer, two different
    monomers might be involved
  • If the letters A and B represent those
    monomers, then the polymer could be represented
    as
  • -A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-
    B-A-B-A
  • A polymer with two different monomers is
    known as a copolymer.

3
5
Chemistry of the polymers
  • Polymers are organic, chain molecules
  • They can, vary from a few hundreds to thousands
    of atoms long.
  • There are three classes of polymers that we will
    consider-
  • Thermo-plastic - Flexible linear chains
  • Thermosetting - Rigid 3-D network
  • Elastomeric - Linear cross-linked chains

4
6
THERMOPLASTICS
  • In simple thermoplastic polymers, the chains are
    bound to each other by weaker Van der Waals
    forces and mechanical entanglement.
  • Therefore, the chains are relatively strong, but
    it is relatively easy to slide and rotate the
    chains over each other.

5
7
ELASTOMERS
  • Common elastomers are made from highly coiled,
    linear polymer chains.
  • In their natural condition, elastomers behave in
    a similar manner to thermoplastics (viscoelastic)
  • i.e. applying a force causes the chains to
    uncoil and stretch, but they also slide past each
    other causing permanent deformation.
  • This can be prevented by cross-linking the
    polymer chains

6
8
  • Polymers can be represented by
  • 3-D solid models
  • 3-D space models
  • 2-D models

7
9
MOLECULAR STRUCTURE
  • The mechanical properties are also governed by
    the structure of the polymer chains.
  • They can be
  • Linear
    Network (3D)
  • Branched
  • Cross-linked

8
10
POLYMER MOLECULES
  • Before we discuss how the polymer chain molecules
    are formed, we need to cover some definitions
  • The ethylene monomer looks like
  • The polyethylene molecule looks like

9
11
  • Polyethylene is built up from repeat units or
    mers.
  • Ethylene has an unsaturated bond. (the double
    bond can be broken to form two single bonds)
  • The functionality of a repeat unit is the number
    of sites at which new molecules can be attached.

10
12
MOLECULAR WEIGHT
  • When polymers are fabricated, there will always
    be a distribution of chain lengths.
  • The properties of polymers depend heavily on the
    molecule length.
  • There are two ways to calculate the average
    molecular weight
  • 1 Number Average Molecular Weight
  • 2. Weight Average Molecular Weight

11
13
  • Number Average Molecular Weight
  • Mn S Xi Mi
  • Where, xi number of chains in the ith weight
    range
  • Mi the middle of the ith weight
    range
  • Weight Average Molecular Weight
  • Mw S Wi Mi
  • Where, wi weight fraction of chains in the ith
    range
  • Mi the middle of the ith weight
    range

12
14
MOLECULAR SHAPE
  • The mechanical properties of a polymer are
    dictated in part by the shape of the chain.
  • Although we often represent polymer chains as
    being straight,
  • They rarely are.

13
15
Contd
  • The carbon carbon bonds in simple polymers form
    angles of 109º

14
16
15
17
POLYMER CRYSTALLINITY
  • Thermoplastic polymers go through a series of
    changes with changes in temperature. (Similar to
    ceramic glasses)
  • In their solid form they can be semi-crystalline
    or amorphous (glassy).

16
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17
19
CRYSTALLINE THERMOPLASTIC
  • The ability of a polymer to crystallize is
    affected by
  • Complexity of the chain Crystallization is
    easiest for simple polymers (e.g. polyethylene)
    and harder for complex polymers (e.g. with large
    side groups, branches, etc.)
  • Cooling rate Slow cooling allows more time for
    the chains to align
  • Annealing Heating to just below the melting
    temperature can allow chains to align and form
    crystals
  • Degree of Polymerization It is harder to
    crystallize longer chains
  • 5. Deformation Slow deformation between Tg and
    Tm can straighten the chains allowing them to get
    closer together.

18
20
  • CLASSIFICATION POLYMERS
  • ON BASIS OF INTERACTION WITH WATER
  • Non-biodegradable hydrophobic Polymers
  • E.g. polyvinyl chloride, polyethylene vinyl
    acetate
  • Soluble Polymers E.g. HPMC, PEG
  • Hydrogels E.g. Polyvinyl
    pyrrolidine
  • BASED ON POLYMERISATION METHOD
  • Addition Polymers E.g. Alkane Polymers
  • Condensation polymers E.g. Polysterene and
    Polyamide
  • Rearrangement polymers
  • BASED ON POLYMERIZATION MECHANISM
  • Chain Polymerization
  • Step growth Polymerization

19
21
Contd.
  • BASED ON CHEMICAL STRUCTURE
  • Activated C-C Polymer
  • Polyamides, polyurethanes
  • Polyesters, polycarbonates
  • Polyacetals, Polyketals, Polyorthoesters
  • Inorganic polymers
  • Natural polymers
  • BASED ON OCCURRENCE
  • Natural polymers E.g. 1. Proteins-collagen,
    keratin, albumin, 2. carbohydrates- starch,
    cellulose
  • Synthetic polymers E.g. Polyesters, polyamides

20
22
Contd.
  • BASED ON BIO-STABILITY
  • Bio-degradable
  • Non Bio-degradable

21
23
CHARACTERISTICS OF AN IDEAL POLYMER
  • Should be versatile and possess a wide range of
    mechanical, physical, chemical properties
  • Should be non-toxic and have good mechanical
    strength and should be easily administered
  • Should be inexpensive
  • Should be easy to fabricate
  • Should be inert to host tissue and compatible
    with environment

22
24
CRITERIA FOLLOWED IN POLYMER SELECTION
  • The polymer should be soluble and easy to
    synthesis
  • It should have finite molecular weight
  • It should be compatible with biological
    environment
  • It should be biodegradable
  • It should provide good drug polymer linkage

23
25
GENERAL MECHANISM OF DRUG RELEASE FROM POLYMER
  • There are three primary mechanisms by which
    active agents can be released from a delivery
    system namely,
  • Diffusion, degradation, and swelling followed by
    diffusion
  • Any or all of these mechanisms may occur in a
    given release system
  • Diffusion occurs when a drug or other active
    agent passes through the polymer that forms the
    controlled-release device. The diffusion can
    occur on a macroscopic scale as through pores in
    the polymer matrix or on a molecular level, by
    passing between polymer chains

24
26

Drug release from typical matrix release system
25
27
  • For the reservoir systems the drug delivery rate
    can remain fairly constant.
  • In this design, a reservoir whether solid drug,
    dilute solution, or highly concentrated drug
    solution within a polymer matrix is surrounded by
    a film or membrane of a rate-controlling
    material.
  • The only structure effectively limiting the
    release of the drug is the polymer layer
    surrounding the reservoir.
  • This polymer coating is uniform and of a
    nonchanging thickness, the diffusion rate of the
    active agent can be kept fairly stable throughout
    the lifetime of the delivery system. The system
    shown in Figure a is representative of an
    implantable or oral reservoir delivery system,
    whereas the system shown in b.

26
28
                                     Drug
delivery from typical reservoir devices (a)
implantable or oral systems, and (b) transdermal
systems.

27
29

28
30
ENVIRONMENTALLY RESPONSIVE SYSTEM
  • It is also possible for a drug delivery system to
    be designed so that it is incapable of releasing
    its agent or agents until it is placed in an
    appropriate biological environment.
  • Controlled release systems are initially dry and,
    when placed in the body, will absorb water or
    other body fluids and swell,
  • The swelling increases the aqueous solvent
    content within the formulation as well as the
    polymer mesh size, enabling the drug to diffuse
    through the swollen network into the external
    environment.

29
31
  • Examples of these types of devices are shown in
    Figures a and b for reservoir and matrix systems.
  • Most of the materials used in swelling-controlled
    release systems are based on hydrogels, which are
    polymers that will swell without dissolving when
    placed in water or other biological fluids. These
    hydrogels can absorb a great deal of fluid and,
    at equilibrium, typically comprise 6090 fluid
    and only 1030 polymer.

30
32

Drug delivery from (a) reservoir and (b) matrix
swelling-controlled release systems.
31
33
32
34
33
35
APPLICATIONS
  • The pharmaceutical applications of polymers
    range from their use as binders in tablets
  • Viscosity and flow controlling agents in liquids,
    suspensions and emulsions
  • Polymers are also used as film coatings to
    disguise the unpleasant taste of a drug, to
    enhance drug stability and to modify drug release
    characteristics.

34
36
Applications in Conventional Dosage Forms
  • Tablets
  • - As binders
  • - To mask unpleasant taste
  • - For enteric coated tablets
  • Liquids
  • - Viscosity enhancers
  • - For controlling the flow
  • Semisolids
  • - In the gel preparation
  • - In ointments
  • In transdermal Patches

35
37
Applications In Controlled Drug Delivery
  • Reservoir Systems
  • - Ocusert System
  • - Progestasert System
  • - Reservoir Designed Transdermal Patches
  • Matrix Systems
  • Swelling Controlled Release Systems
  • Biodegradable Systems
  • Osmotically controlled Drug Delivery

36
38
  • BIO DEGARADABLE POLYMERS

37
39
BIO DEGRADABLE POLYMER
  • Biodegradable polymers can be classified in two
  • Natural biodegradable polymer
  • Synthetic 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

38
40
FACTORS AFFECTING BIODEGRADATION OF POLYMERS
  • PHYSICAL FACTORS
  • Shape size
  • Variation of diffusion coefficient
  • Mechanical stresses
  • CHEMICAL FACTORS
  • Chemical structure composition
  • Presence of ionic group
  • Distribution of repeat units in multimers
  • configuration structure
  • Molecular weight
  • Morphology
  • Presence of low molecular weight compounds

39
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CONTD
  • Processing condition
  • Annealing
  • Site of implantation
  • Sterilization process
  • PHYSICOCHEMICAL FACTORS
  • Ion exchange
  • Ionic strength
  • pH

40
42
ADVANTAGES OF BIODEGRADABLE POLYMERS IN DRUG
DELEVERY
  • Localized delivery of drug
  • Sustained delivery of drug
  • Stabilization of drug
  • Decrease in dosing frequency
  • Reduce side effects
  • Improved patient compliance
  • Controllable degradation rate

41
43
ROLE OF POLYMER IN DRUG DELIVERY
  • The polymer can protect the drug from the
    physiological environment hence improve its
    stability in vivo.
  • Most biodegradable polymer are designed to
    degrade within the body as a result of hydrolysis
    of polymer chain into biologically acceptable
    progressively small compounds.
  • TYPES OF POLYMER DRUG DELIVERY SYSTEM
  • MICRO PARTICLES These have been used to
    deliver therapeutic
    agents like doxycycline.
  • NANO PARTICLES delivery drugs like
    doxorubicin, cyclosporine, paclitaxel, 5-
    fluorouracil etc

42
44
  • POLYMERIC MICELLES used to deliver therapeutic
    agents.
  • HYDRO GELS these are currently studies as
    controlled release carriers of proteins
    peptides.
  • POLYMER MORPHOLOGY
  • The polymer matrix can be formulated as
    either micro/nano-spheres, gel, film or an
    extruded shape.
  • The shape of polymer can be important in drug
    release kinetics.

43
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Application
  • For specific site drug delivery- anti tumour
    agent
  • Polymer system for gene therapy
  • Bio degradable polymer for ocular, non- viral
    DNA, tissue engineering, vascular, orthopaedic,
    skin adhesive surgical glues.
  • Bio degradable drug system for therapeutic agents
    such as anti tumor, antipsychotic agent,
    anti-inflammatory agent and biomacro molecules
    such as proteins, peptides and nucleic acids

44
46
BIO DEGRADABLE POLYMERS FOR ADVANCE DRUG DELIVERY
  • Polymers play an vital role in both conventional
    as well as novel drug delivery. Among them , the
    use of bio degradable polymer has been success
    fully carried out.
  • Early studies on the use of biodegradable suture
    demonstrated that these polymers were non- toxic
    biodegradable.
  • By incorporating drug into biodegradable polymer
    whether natural or synthetic, dosage forms that
    release the drug in predesigned manner over
    prolong time

45
47
DRUG RELEASE MECHANISM
  • The release of drugs from the erodible polymers
    occurs basically by three mechanisms,
  • The drug is attached to the polymeric backbone by
    a labile bond, this bond has a higher reactivity
    toward hydrolysis than the polymer reactivity to
    break down.
  • The drug is in the core surrounded by a
    biodegradable rate controlling membrane. This is
    a reservoir type device that provides erodibility
    to eliminate surgical removal of the
    drug-depleted device.
  • a homogeneously dispersed drug in the
    biodegradable polymer. The drug is released by
    erosion, diffusion, or a combination of both.

46
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Schematic representation of drug release
mechanisms In mechanism 1, drug is released by
hydrolysis of polymeric bond. In mechanism 2,
drug release is controlled by biodegradable
membrane. In mechanism 3, drug is released by
erosion, diffusion, or a combination of both
47
49
POLYMER EROSION MECHANISM
  • The term 'biodegradation' is limited to the
    description of chemical processes (chemical
    changes that alter either the molecular weight or
    solubility of the polymer)
  • Bioerosion' may be restricted to refer to
    physical processes that result in weight loss of
    a polymer device.
  • The erosion of polymers basically takes place by
    two methods-
  • Chemical erosion
  • Physical erosion

48
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CHEMICAL EROSION
  • There are three general chemical mechanisms that
    cause bioerosion
  • The degradation of water-soluble macromolecules
    that are crosslinked to form three-dimensional
    network.
  • As long as crosslinks remain intact, the
    network is intact and is insoluble.
  • Degradation in these systems can occur
    either at crosslinks to form soluble backbone
    polymeric chains (type IA) or at the main chain
    to form water-soluble fragments (type IB).
    Generally, degradation of type IA polymers
    provide high molecular weight, water-soluble
    fragments, while degradation of type IB polymers
    provide low molecular weight, water soluble
    oligomers and monomers

49
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  • The dissolution of water-insoluble macromolecules
    with side groups that are converted to
    water-soluble polymers as a result of ionization,
    protonation or hydrolysis of the groups. With
    this mechanism the polymer does not degrade and
    its molecular weight remains essentially
    unchanged. E.g. cellulose acetate
  • The degradation of insoluble polymers with labile
    bonds. Hydrolysis of labile bonds causes scission
    of the polymer backbone, thereby forming low
    molecular weight, water-soluble molecules. E.g.
    poly (lactic acid), poly (glycolic acid)
  • The three mechanisms described are not
    mutually exclusive combinations of them can
    occur.

51
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PHYSICAL EROSION
  • The physical erosion mechanisms can be
    characterized as heterogeneous or homogeneous.
  • In heterogeneous erosion, also called as surface
    erosion, the polymer erodes only at the surface,
    and maintains its physical integrity as it
    degrades. As a result drug kinetics are
    predictable, and zero order release kinetics can
    be obtained by applying the appropriate geometry.
    Crystalline regions exclude water. Therefore
    highly crystalline polymers tend to undergo
    heterogeneous erosion. E.g polyanhydrides

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  • Homogeneous erosion, means the hydrolysis occurs
    at even rate throughout the polymeric matrix.
    Generally these polymers tend to be more
    hydrophilic than those exhibiting surface
    erosion. As a result, water penetrates the
    polymeric matrix and increases the rate of
    diffusion. In homogeneous erosion, there is loss
    of integrity of the polymer matrix. E.g poly
    lactic acid

53
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  • Natural polymers
  • Polymers are very common in nature
  • some of the most widespread naturally occurring
    substances are polymers Starch and cellulose are
    examples
  • Green plants have the ability to take the simple
    sugar known as glucose and make very long chains
    containing many glucose units
  • These long chains are molecules of starch or
    cellulose
  • If we assign the symbol G to stand for a
    glucose molecule, then starch or cellulose can be
    represented as
  • -G-G-G-G-G-G-G-G-G-G-G-G-G-G-G-G-G-G-G-G-G-G-G-G-G
    -G-G-

54
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NATURAL POLYMERS
  • Natural polymers remains the primary choice of
    formulator because
  • - They are natural products of living organism
  • - Readily available
  • - Relatively inexpensive
  • - Capable of chemical modification
  • Moreover, it satisfies most of the ideal
    requirements of polymers.
  • But the only and major difficulty is the batch-
    to-batch reproducibility and purity of the sample.

55
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  • Examples
  • 1) Proteins
  • - Collagen Found from animal tissue.
  • Used in absorbable sutures, sponge wound
    dressing, as drug delivery vehicles
  • - Albumin Obtained by fabrication of blood
    from healthy donor.
  • Used as carriers in nanocapsules
    microspheres
  • - Gelatin A natural water soluble polymer
  • Used in capsule shells and also as coating
    material in microencapsulation.

56
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  • 2) Polysaccharides
  • - Starch Usually derivatised by introducing
    acrylic
  • groups before manufactured int
    microspheres.
  • Also used as binders.
  • - Cellulose
  • Naturally occuring linear polysaccharide. It
    is insoluble in water but solubility can be
    obtained by substituting -OH group.
  • Na-CMC is used as thickner, suspending
    agent, and film formers.
  • 3) DNA RNA
  • They are the structural unit of our body. DNA
    is the blueprint that determines everything of
    our body.

57
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CURRENTLY AVAILABLE POLYMERS FOR CONTROLLED
RELEASE
  • Diffusion controlled systems
  • Solvent activated systems
  • Chemically controlled systems
  • Magnetically controlled systems

58
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DIFFUSION CONTROLLED SYSTEM 
  • Reservoir type
  • Shape spherical, cylindrical, disk-like
  • Core powdered or liquid forms
  • Properties of the drug and the polymer
    diffusion rate and release rate into the
    bloodstream
  • Problems removal of the system, accidental
    rupture
  • Matrix type
  • Uniform distribution and uniform release rate
  • No danger of drug dumping

59
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SOLVENT ACTIVATED SYSTEM
  • Osmotically controlled system
  • Semipermeable membrane
  • Osmotic pressure decrease concentration gradient
  • Inward movement of fluid out of the device
    through a small orifice
  • Swelling controlled system
  • Hydrophilic macromolecules cross-linked to form a
    three-dimensional network
  • Permeability for solute at a controlled rate as
    the polymer swells
  •  

60
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CHEMICALLY CONTROLLED SYSTEMS
  • Pendant-chain system
  • Drug chemically linked to the backbone
  • Chemical hydrolysis or enzymatic cleavage
  • Linked directly or via a spacer group
  • Bioerodable or biodegradable system
  • Drug uniformly dispersed
  • Slow released as the polymer disintegrates
  • No removal from the body
  • Irrespective of solubility of drug in water
  •   

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MAGNETICALLY CONTROLLED SYSTEMS
  • Cancer chemotherapy
  • Selective targeting of antitumor agents
  • Minimizing toxicity
  • Magnetically responsive drug carrier systems
  • Albumin and magnetic microspheres
  • High efficiency for in vivo targeting
  • Controllable release of drug at the microvascular
    level
  •   

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RECENTLY DEVELOPED MARKETED FORMULATIONS
  • Medisorb
  • Microencapsulation by PLA, PGA, PLGA
  • Drug release week to one year
  • Alzamer
  • Bioerodible polymer release at a
    controlled rate
  • Chronic disease, contraception, topical
    therapy

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USE OF FEW POLYMERS IN DRUG DELIVERY
  • Poly(L-lactic acid) for release of progesterone,
    estradiol, dexamethasone
  • Copolymer of gluconic acid and ethyl-L-glutamte
    as bioerodible monolithic device
  • PLA, PGA, PLGA for parenteral administration of
    polypeptide
  • Sustained release (weeks or months)
  •  Orahesive sodium carboxymethyl cellulose,
    Pectin, gelatin
  • Orabase blend in a polymethylene/mineral oil
    base  

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REFERENCES
  • Novel drug delivery systems Y.W.Chien Dekker
    50
  • Bioadhesive drug delivery system
  • Dekker 98
  • Encyclopedia of controlled drug delivery systems.
  • www.google.com

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ANY QUERIES?
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Y
O
U
T
K
N
A
H
Cell No 00919742431000 E-mailbknanjwade_at_yahoo.co
.in
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