Polyamides, poly(amino acids), poly(alkyl cyanoacrylates), polyesters,
polyorthoesters, polyurethanes, and polyacrylamides have been used to develop
various drug-loaded systems. Among them, thermoplastic aliphatic polyesters like
poly(lactic acid) (PLA), poly(glycolic acid) (PGA), and especially their copolymer
poly(lactic-co-glycolic acid) (PLGA), have generated great interest due to their
excellent biocompatibility, bioresorbability, and biodegradability [3, 4]. The most
commonly and extensively used biodegradable polymers are PLA, PLGA, poly
(E-caprolactone) (PCL), chitosan, gelatin, and poly(alkyl cyanoacrylates), which
are usually polymerized through condensation or other conventional polymerization reactions. Hydrolytically degradable polymers have esters, orthoesters,
anhydrides, carbonates, amides, urethanes, ureas, etc. in their backbone [5]. Biodegradable polymers are chosen on the basis of various characteristics such as
degradability, solubility, permeability, and mechanical stability, which are adequate to influence the manufacturing and performance of polymeric devices. The
entrapment efficiency and drug release from the polymeric devices are the important parameters for the polymers to be used as vehicle [6]. Biodegradable polymers
are also highly preferred for the majority of biomedical applications in drug
delivery, preventive medicine, clinical inspection, surgical treatments of various
diseases, and tissue engineering scaffolds [7, 8]. The objective of this article is to
summarize the current status of biodegradable polymers for various biomedical
applications including transient implants, drug delivery vehicles, and tissue engineering scaffolds.
2 Polymer-Based Nanotechnology
Nanotechnology is a multidisciplinary area of applied science and technology
intended to create and fabricate devices or materials that lie within the nanometer
dimension. It has significant impact on the development of novel products at the
molecular or submicron level [9]. The unique properties of nanomaterials arise
from the nanoscale dimensions, which provide them with novel mechanical, thermal, and catalytic properties that are highly desirable for applications in commercial, medical, and environmental sectors. The application of nanotechnology for the
prevention and treatment of diseases and for the diagnosis, monitoring, and control
of biological systems is referred to as nanomedicine. Recently, the main goal of
nanomedicine is controlled delivery and targeting of pharmaceutical, therapeutic,
and diagnostic agents [10] with unique physicochemical and biological properties
that might be used to overcome the current limitations of molecular imaging and
gene/drug delivery [11, 12]. Significant efforts have already been employed in three
main areas: (1) drug delivery systems for active molecules, proteins, peptides, and
genes for localized or targeted delivery to the tissue; (2) application of
nanobiotechnology to the molecular imaging and therapy of the cardiovascular
system [8, 13]; and (3) targeted functional nanoparticles for cancer therapy and
diagnosis [14, 15]. Nanomaterial devices used for drug delivery should have certain
Biodegradable Polymers for Potential Delivery Systems for Therapeutics
171
polyorthoesters, polyurethanes, and polyacrylamides have been used to develop
various drug-loaded systems. Among them, thermoplastic aliphatic polyesters like
poly(lactic acid) (PLA), poly(glycolic acid) (PGA), and especially their copolymer
poly(lactic-co-glycolic acid) (PLGA), have generated great interest due to their
excellent biocompatibility, bioresorbability, and biodegradability [3, 4]. The most
commonly and extensively used biodegradable polymers are PLA, PLGA, poly
(E-caprolactone) (PCL), chitosan, gelatin, and poly(alkyl cyanoacrylates), which
are usually polymerized through condensation or other conventional polymerization reactions. Hydrolytically degradable polymers have esters, orthoesters,
anhydrides, carbonates, amides, urethanes, ureas, etc. in their backbone [5]. Biodegradable polymers are chosen on the basis of various characteristics such as
degradability, solubility, permeability, and mechanical stability, which are adequate to influence the manufacturing and performance of polymeric devices. The
entrapment efficiency and drug release from the polymeric devices are the important parameters for the polymers to be used as vehicle [6]. Biodegradable polymers
are also highly preferred for the majority of biomedical applications in drug
delivery, preventive medicine, clinical inspection, surgical treatments of various
diseases, and tissue engineering scaffolds [7, 8]. The objective of this article is to
summarize the current status of biodegradable polymers for various biomedical
applications including transient implants, drug delivery vehicles, and tissue engineering scaffolds.
2 Polymer-Based Nanotechnology
Nanotechnology is a multidisciplinary area of applied science and technology
intended to create and fabricate devices or materials that lie within the nanometer
dimension. It has significant impact on the development of novel products at the
molecular or submicron level [9]. The unique properties of nanomaterials arise
from the nanoscale dimensions, which provide them with novel mechanical, thermal, and catalytic properties that are highly desirable for applications in commercial, medical, and environmental sectors. The application of nanotechnology for the
prevention and treatment of diseases and for the diagnosis, monitoring, and control
of biological systems is referred to as nanomedicine. Recently, the main goal of
nanomedicine is controlled delivery and targeting of pharmaceutical, therapeutic,
and diagnostic agents [10] with unique physicochemical and biological properties
that might be used to overcome the current limitations of molecular imaging and
gene/drug delivery [11, 12]. Significant efforts have already been employed in three
main areas: (1) drug delivery systems for active molecules, proteins, peptides, and
genes for localized or targeted delivery to the tissue; (2) application of
nanobiotechnology to the molecular imaging and therapy of the cardiovascular
system [8, 13]; and (3) targeted functional nanoparticles for cancer therapy and
diagnosis [14, 15]. Nanomaterial devices used for drug delivery should have certain
Biodegradable Polymers for Potential Delivery Systems for Therapeutics
171