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:
• 1^st 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.
• 2^nd 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