Biodegradable Polymer: Introduction

Definition: A polymer that are degradable in-vivo, either by enzymatically or non-enzymatically, to produce biocompatible or nontoxic by-products.
Biodegradation: A natural process by which organic chemicals are converted to simpler compound through elemental cycles such as the carbon, nitrogen and Sulphur cycles.
  • Microorganism plays a central role in the biodegradation process.
  • Bio degradation occur in two steps:
    • 1st step From Fragmentation of the polymer into lower molecules:
      • By abiotic reaction i.e. oxidation, photo degradation, hydrolysis.
      • By biotic reaction i.e. degradation by microorganism.
    • 2nd step: Bio Assimilation of the polymer fragments
  • Biodegradability of the polymer depends on
    • Its origin & chemical structure & also environmental condition
  • Biodegradable polymers are capable of being cleaved into biocompatible by-product through chemical or enzyme catalyzed hydrolysis
  • Advantages of Biodegradable polymer:
    • Provide constant controlled rate for long time
    • Metabolized by-product is non-toxic and easily remove by body extraction
    • Dose dumping not exhibit
    • No surgical removal of implanted device
    • It can be used for targeted drug delivery
  • Disadvantages of Biodegradable polymer:
    • Burst effect at initial dose
  • Mechanism of drug release from Biodegradable polymer:
    • This polymer degrades within body as a result of natural biological process.
    • Most biodegradable polymer degrades through hydrolysis process.
    • Biodegradable polymer undergo degradation in four steps
      • Hydration
      • Strength loss
      • Loss of mass Integrity
      • Mass loss
    • Hydration:
      • It is variable in rate, degree and is dependent upon the nature of polymer.
      • In this step, disruption of Vander Waal’s bond or hydrogen bond is broken.
    • Strength loss
      • In this step, the covalent bond is broken.
      • The strength loss rate is dependent upon the temperature, pH and degree of crystallinity. 
      • More crystalline species may be expected to maintain their strength for longer period of time compare to those of amorphous.
    • Loss of mass Integrity
      • In this step more and more covalent bond is broken and polymer is degraded to a molecular weight level.
      • This step is more important in degradation.
    • Mass loss:
      • This step involves the complete removal of Polymer from the tissue.
      • It occurs either by solubilization of small units or by phagocytes
      • Sometime the polymer mass may be removed from site, without actual reduction in their length, thought  solubilization that involve side chain modification
  • Factors affecting Biodegradation of polymer:
    • Chemical structure
    • Chemical decomposition
    • Present of ionic groups
    • Molecular weight
    • Morphology
    • Site of implantation
    • Mechanism of hydrolysis
    • Hydrophilicity
  • Classification of biodegradable polymers:
  • Natural polymer: 
    • Guar gum, Acacia, Karaya, Tragacanth, Xanthan, Albumin, pectin, starch, gellen etc.
    • Prime advantage include biodegradation in natural products, easy availability, absense of toxicity and antigenicity
    • Albumin micro spheres have been employed to deliver many drugs like hematoprophyrin, sulphadiazine, and prednisolone, 5-flurouracil
  • Semisynthetic polymer:
    • Cellulose derivatives:
      • Cellulose is insoluble in water and most commom solvents
      • Have poor solubility
      • Chemically modified cellulose have a good properties, 
      • It include; CMC, MC, HEC, HPMC etc
    • Collagen:
      • Have good biocompatibility, low toxicity, degradation on implantation and gelling ability
    • Gelatin:
      • It has been employed as matrix and coating material.
      • It offers advantage like low antigen profile ,poor binding to drug, low temp
      • So reduce to chances of drug degradation
    • Chitin and chitosan:
      • Chitosan has been administered as excipients for oral drug formulations.
      • It is used as direct tableting agent, mask bitter taste, disinyegrant & for coating.
      • Have good mucoadhesive, antimicrobial and controlled release properties
    • Dextran:
      • Synthesized from sucrose by certain lactic acid bacteria.
    • Alginate:
      • Alginate micro spheres have been used for oral delivery of vaccines.
      • They protect antigen/vaccine against degradation in G.I.T.
      • Have good gelling ability
    • Fibrinogen, Hyaluronic acid, Cyclodextrin

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