Biodegradable Polymers

Biodegradable Polymers: 

Biodegradable polymers were intensely researched to help in the post-surgical treatment because they degrade in the body to biologically inert and compatible molecules. Due to this property biodegradable polymers offered a new approach in the development of Sustained release drug delivery systems.

Advantages of polymers as drug carriers are

Ø      Localized delivery of drug 

Ø      Stabilization of drug

Ø      Drug release rate is less dependable

Ø      Steadier release time 

Polymer degradation Mechanism:

Bioresorbable is the degradation mechanism of these polymers. They have its degradation by polymer being absorbed or excreted by living system. Following are few mechanisms which degrade or erode polymers like ionic groups, stress, storage, site of application, ADME of body towards polymers, sterilization, manufacturing process, presence of unwanted chain or molecule in polymer etc.

These are divides in mainly two mechanisms:

I.                    Chemical erosion

II.                 Physical erosion

Chemical erosion further divides in 3 sub mechanisms

1. Degradation of water soluble macromolecules are cross linked to form three-dimensional network
2. Dissolution of water insoluble macromolecules that are converted to water-soluble polymers as a result of ionization, protonation or hydrolysis of the groups.
3. 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.

  Physical erosion further divides in 2 sub mechanisms

1. 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 is predictable.
2. 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.

 Drug release mechanisms

1. Release of drug by hydrolysis of polymeric bond.
2. Release is controlled by biodegradable membrane.
3. Release by erosion, diffusion or a combination of both.

 Examples of such polymers available in the market

1. Zoladex® - supplied with goserelin acetate equivalent to 3.6 mg of goserelin.
2. Lupron depot® - is micro-sphere formulation based polymer.
3. Gliadel® wafer – contain Carmustine (Cancer  chemotherapeutic agnet)
4. Alzamer® depot technology – It is non-aqueous polymer solution for sustained delivery.