characteristics such as biocompatibility, drug compatibility, suitable biodegradation kinetics, suitable mechanical properties, and ease of processing [16, 17]. In the
last two decades, a wide variety of synthetic biodegradable polymers have been
used to create therapeutic delivery devices for drugs and genes due to their
biocompatibility and biodegradability [18]. Several synthetic biodegradable and
biocompatible polymers have been approved by the US FDA for drug delivery
devices. While different aspects of polymeric devices have been reviewed in detail
elsewhere, this article summarizes the more recent successful evidence for applying
polymeric materials and tools to various health complications like cardiovascular
disease, cancer, and immunological problems.
3 Biodegradation in Polymers
The term ‘biodegradation’ defines the gradual breakdown of a material by certain
biological activity [19]. Biodegradable polymers have the tendency to degrade into
smaller molecules and by-products under a controlled mechanism; the degradation
products are then easily eliminated from the body through metabolic pathways.
The use of biodegradable polymeric devices in drug delivery applications requires
the polymer to be able to degrade under physiological conditions. Knowledge of the
degradation mechanisms, degradation kinetics, evolution of mechanical properties,
and identification of the degradation products of biomaterials are the basic
requirements in selecting and designing polymeric materials for specific
applications. Depending on the mode of degradation, polymeric biomaterials are
classified into hydrolytically and enzymatically degradable polymers. Most of the
naturally occurring polymers undergo enzymatic degradation. Hydrolytically
degradable polymers contain chemical bonds such as esters, orthoesters,
anhydrides, carbonates, amides, urethanes, ureas, etc. that are susceptible to hydrolysis [5]. The following processes and mechanisms play an important role in the
degradation of polymeric materials.
3.1 Oxidation
Polymers degrade in the body fluids and tissues by chemical and/or enzymatic
oxidation. It is well known that during the inflammatory response to foreign
materials, inflammatory cells particularly leukocytes and macrophages produce
highly reactive oxygen-containing species such as superoxide (O 2
À ) hydrogen
peroxide (H 2 O 2 ), nitric oxide (NO), and hypochlorous acid (HOCl) [20, 21]. The
oxidative effect of these reactive oxygen species causes polymer chain scission and
ultimately contributes towards the degradation of polymeric materials. Superoxides
accelerate the degradation of aliphatic polyesters by the cleavage of ester bonds
through nucleophilic attack of O 2
À [22].
172
S.K. Pandey et al.
last two decades, a wide variety of synthetic biodegradable polymers have been
used to create therapeutic delivery devices for drugs and genes due to their
biocompatibility and biodegradability [18]. Several synthetic biodegradable and
biocompatible polymers have been approved by the US FDA for drug delivery
devices. While different aspects of polymeric devices have been reviewed in detail
elsewhere, this article summarizes the more recent successful evidence for applying
polymeric materials and tools to various health complications like cardiovascular
disease, cancer, and immunological problems.
3 Biodegradation in Polymers
The term ‘biodegradation’ defines the gradual breakdown of a material by certain
biological activity [19]. Biodegradable polymers have the tendency to degrade into
smaller molecules and by-products under a controlled mechanism; the degradation
products are then easily eliminated from the body through metabolic pathways.
The use of biodegradable polymeric devices in drug delivery applications requires
the polymer to be able to degrade under physiological conditions. Knowledge of the
degradation mechanisms, degradation kinetics, evolution of mechanical properties,
and identification of the degradation products of biomaterials are the basic
requirements in selecting and designing polymeric materials for specific
applications. Depending on the mode of degradation, polymeric biomaterials are
classified into hydrolytically and enzymatically degradable polymers. Most of the
naturally occurring polymers undergo enzymatic degradation. Hydrolytically
degradable polymers contain chemical bonds such as esters, orthoesters,
anhydrides, carbonates, amides, urethanes, ureas, etc. that are susceptible to hydrolysis [5]. The following processes and mechanisms play an important role in the
degradation of polymeric materials.
3.1 Oxidation
Polymers degrade in the body fluids and tissues by chemical and/or enzymatic
oxidation. It is well known that during the inflammatory response to foreign
materials, inflammatory cells particularly leukocytes and macrophages produce
highly reactive oxygen-containing species such as superoxide (O 2
À ) hydrogen
peroxide (H 2 O 2 ), nitric oxide (NO), and hypochlorous acid (HOCl) [20, 21]. The
oxidative effect of these reactive oxygen species causes polymer chain scission and
ultimately contributes towards the degradation of polymeric materials. Superoxides
accelerate the degradation of aliphatic polyesters by the cleavage of ester bonds
through nucleophilic attack of O 2
À [22].
172
S.K. Pandey et al.