BIODEGRADABLE POLYMERS

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					            A seminar on

USE OF BIODEGRADABLE POLYMERS IN




                     By
CONTENTS

 INTRODUCTION
 CONTROLLED DRUG RELEASE DEVICES
 POLYMER DEGRADATION AND EROSION
 DRUG RELEASE MECHANISMS
 CLASSIFICATION
 APPLICATIONS
 CONCLUSION
 REFERENCES
INTRODUCTION


§ DEFINITIONS
 POLYMERS : These are referred to as macromolecules of high
  molecular weight, comprising of repeating units of small molecules,
  the monomers.

 BIODEGRADABLE POLYMERS : These can be defined as
  polymers comprised of monomers linked to one another through
  functional groups and have unstable linkages in the backbone. They
  are biologically degraded or eroded by enzymes introduced in vitro
  or generated by surrounding living cells or by non-enzymatic
  processes into oligomers or monomers that can be metobolized or
  excreted.
Introduction Contd.,

♠ Polymers first developed in search for biodegradable suture
  materials have been proven to be useful and successful for
  long-term drug delivery applications.

♠ Biodegradable polymers are highly desirable in these
  situations because they degrade in the body to biologically
  inert and compatible molecules.

♠ By incorporating drugs in biodegradable polymers, dosage
  forms that release the drug over a prolong length of time can
  be prepared in variety of shapes and sizes.
Advantages
* No surgical procedures are needed after completion of dosage
  regime since the remaining polymer will degrade and get cleared by
  the body.

*   As a result, biodegradable polymers offer a novel approach for
    developing sustained release drug delivery systems that are simple
    and convenient to patient.

* In addition to eliminating the necessity of removal, the key
  advantages (Leong, 1991) that polymeric drug delivery products
  can offer are;
* Localized delivery of drug, sustained delivery of drug,
  stabilization of the drug, release rate which is less dependent
  of the drug properties and steadier release rate with time.
               POLYMER DEGRADATION

 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.

  Degradation Schemes
 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
  mechanisms.

    Enzymatic degradation
    Hydrolysis
Contd.,

 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
  essentially unchanged.
      Factors Influence the Degradation Behavior
 Chemical Structure and Chemical Composition
 Molecular Weight
 Presence of Low Mw Compounds (monomer, oligomers,
  solvents, plasticizers, etc)
 Presence of Ionic Groups
 Presence of Chain Defects
 Configurational Structure
 Morphology (crystallinity, presence of microstructure,
  orientation and residue stress)
 Processing methods & Conditions
 Method of Sterilization
 Storage History
 Site of Implantation
 Absorbed Compounds
 Physiochemical Factors (shape, size)
 Mechanism of Hydrolysis (enzymes vs water)
    Erosion Mechanisms



1
Contd.,

  Type I Erosion
 It is evident with water-
  soluble polymers cross-
  linked to form a three-
  dimensional network.

 Erosion can occur by
  cleavage of cross-links
  (type IA) or cleavage of
  the water-soluble
  polymer backbone (type
  IB)
Contd.,

           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
            group.

           Type III Erosion
           High molecular weight, water-
            insoluble macromolecules are
            converted to small, water-
            soluble molecules by a
            hydrolytic cleavage of labile
            bonds in the polymer
            backbone.
          DRUG RELEASE MECHANISMS

 Drug release from biodegradable polymers can occur by any
  one of three basic mechanisms, shown schematically in
  Figures (a), (b), and (c).
 In the (a), the drug covalently attached to the polymer
  backbone and is released as its attachment to the backbone
  cleaves by hydrolysis of bond A.
Contd.,




 In this mechanism, the active agent is contained in a core
  surrounded by a bioerodible rate-controlling membrane, which
  provides a constant rate of drug release from a reservoir-type
  device, with erodibility, which results in bioerosion and makes
  surgical removal of the drug-depleted device unnecessary.
Contd.,




 In this mechanism, the drug is homogeneously dispersed in a
  polymer and drug release from this monolith is controlled by
  diffusion, by a combination of diffusion and erosion, or by
  erosion.
     Classification of Biodegradable Polymers
1.   Natural Polymers And Modified Natural Polymers

 Proteins : Collagen
              Albumin
              Casein
              Gelatin
              Fibrinogen

 Polysaccharides :
               Chitin and Chitosan,
               Dextran, Alginate,
               Calcium Pectinate,
               Cellulose, Inulin,
               Starch, Hyaluronic acid
                    2. SYNTHETIC POLYMERS

                               ♦ Polyphosphazenes
♦ Aliphatic Poly (ester)s
                                 Hydrophilic
                                 Hydrophobic
  Poly (glycolic acid) (PGA)
                                 Insoluble Surface-active
  Poly (lactic acid) (PLA)
                                 Insoluble biodegradable
  Poly (ε-caprolactone)
                                 Imidazolyl derivatives
  Poly (para-dioxanone)
                                 Glyceryl derivatives
  Poly (hydroxybutyrate)
                                 Glucosyl derivatives
  Poly (ß-malic acid)
                               ♦ Poly (amino) Acids and
♦ Polyphosphoesters              Pseudopoly (amino) Acids
                                 Poly-L-glutamic acid
♦ Polyanhydrides                 Poly-L-Lysine (PLL)
                                 Hydroxyproline-derived
♦ Poly (ortho esters)            Polyesters
                                 Tyrosine-derived poly
                                 (iminocarbonates)
                                          Contd.,

3. ENVIRONMENTALLY                                4. MISCELLANEOUS POLYMERS
   RESPONSIVE POLYMERS

 Thermosensitive Polymers                           Polymeric Phospholipids
    e.g. Poly (N-alkyl substututed acrylamides)      Polyethyleneimine
 Electrically and Chemically                        Polyamidoamine
  Controlled Polymers                                Polyethylene Glycol
     e.g. PEG & Poly(methacrylic acid)
      (PMMA), collagen, Poly(pyrrole)

     pH Sensitive polymers
    e.g. Poly(2-ethylacrylic acid) (PEAA)

 Azopolymers
Polyesters
BIODEGRADATION PROFILES
Contd.,
 The environmentally responsive polymers alter their structure and
  physical properties in response to external signals.

 The signals employed for modulation of polymer profile are
  temperature, current, chemical and photomodulation.

 These are useful for designing drug delivery systems that release the
  incorporated drug only when it is placed in an appropriate biological
  environment.
Contd.,
APPLICATIONS
Collagen Based Delivery Systems
Drug Delivery Applications of Lactide/Glycolide
                  Polymers
Drug Delivery Applications of PCL-based Polymers
Drug Delivery Applications of Poly(phospho ester)s

				
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