Page 36 - Biodegradable Polyesters

14 1 Biodegradable Polyesters: Synthesis, Properties, Applications

Table 1.4 Thermal and mechanical properties of poly(glycolide) [21, 50].

Property PGA
∘
T ( C) 40
g
∘
T ( C) 225–230
m
−3
Density(g cm ) 1.5–1.69
Tensile strength (GPa) 0.08–1
Young’s modulus (GPa) 4–14
Elongation at break (%) 30–40
Applications Currently, polyglycolide and its copolymers (poly(lactic-co-glycolic
acid), poly(glycolide-co-caprolactone), and poly(glycolide-co-trimethylene car-
bonate)) are widely used as materials for the synthesis of absorbable sutures
[82–88]. In most cases, PGA is copolymerized with other organic acids such
as with PLA to make a PLA–PGA copolymer for improving its property [89].
PGA–PLA copolymers have been known to be biodegradable and histocom-
patible for the past 40 years. Their physicochemical and biological properties
have been found suitable, in many instances, for sustaining drug release in vivo
for days or months [89, 90]. Microencapsulation technique is chosen frequently
for its unique properties because microcapsules can be made using different
traditional and nontraditional techniques containing core materials ranging
from biological proteins to synthetic drugs [90]. Lima and Rodrigues Junior [91]
reviewed the development of a biocompatible delivery system using poly(-DL-
lactide-co-glycolide) microspheres as a controlled release antigen for parenteral
administration offers several advantages in terms of immune adjuvanticity over
other compounds. It was found that, in contrast to other carriers, microspheres
are more stable, thus permitting administration by the oral or parenteral route.
Nanotechnology has been applied in drug delivery system in recent years using
biodegradable polymer as key carrier materials. Biodegradable nanoparticles
formulated from biocompatible poly(D,L-lactide-co-glycolide) has shown the
potential for sustained intracellular delivery of different therapeutic agents
[92]. Drug delivery into the brain using poly(lactide-co-glycolide) microspheres
attracted attention. For brain drug administration, locally controlled drug release
by way of an implantable polymeric device was developed as macroscopic
implants needing open surgery for implantation. To avoid surgery implantation,
poly(lactide-co-glycolide) microspheres were shown to be safe and promising
for drug delivery into the brain. Poly(lactide-co-glycolide) is biodegradable and
biocompatible with brain tissue. Owing to their size, these microspheres can be
easily implanted by stereotaxy in discrete, precise, and functional areas of the
brain without causing damage to the surrounding tissues. Brain tumor treatments
were developed using this approach [93]. Biodegradable nano/microparticles of
poly(DL-lactide-co-glycolide) and PLGA-based polymers are widely investigated
as carriers for controlled delivery of macromolecular therapeutics such as
proteins, peptides, vaccines, genes, antigens, and growth factors. These devices