5.4 Dialysis
Dialysis provides an easy and efficient way for the preparation of small, finely
distributed polymeric nanoparticles [73, 74]. In this process, polymer is dissolved in
an organic solvent and placed inside a dialysis tube with proper molecular weight
cutoff and dialysis performed against a non-solvent that is miscible with the
solvent. The displacement of the solvent inside the dialysis membrane causes the
progressive aggregation of polymer due to a loss of solubility and the construction
of a homogeneous suspension of nanoparticles. The mechanism of the dialysis
process is based on similar phenomena to that of nanoprecipitation [65].
6 Biodegradable Polymers and Their Applications
The most extensively used biodegradable polymers are PGA, PLA,PLGA, PCL,
poly(alkyl cyanoacrylates), chitosan, and gelatin. The therapeutic applications and
preparation methods of these polymeric nanoparticles, with entrapment and release
of various drugs are described below and summarized in Table 1.
6.1 Poly(glycolic acid)
PGA was the first biodegradable synthetic semicrystalline polymer (glass transition
temperature, T g ~40
C; melting temperature, T m >200
C) to be considered for
biomedical applications. PGA has been used in bone internal fixation devices due to
its good mechanical properties. The good fiber-forming ability and scaffolding
ability of PGA, together with cell viability, were used to develop resorbable devices
and for tissue regeneration [119]. PGA is being used as a biocompatible durable
substitute and as an excellent skin-closing suture material. It also has the ability to
help regenerate biological tissue [120]. However, PGA is hydrolyzed in few
months, indicating a high degradation rate. It is broken down into glycine under
physiological conditions, which can be excreted from the body or converted into
carbon dioxide and water via the citric acid cycle [121]. Due to the high rate of
degradation and low solubility of PGA, its biomedical and pharmaceutical
applications are limited. Therefore, several copolymers containing glycolide units
are being developed to overcome the disadvantages of pure PGA.
184
S.K. Pandey et al.
Dialysis provides an easy and efficient way for the preparation of small, finely
distributed polymeric nanoparticles [73, 74]. In this process, polymer is dissolved in
an organic solvent and placed inside a dialysis tube with proper molecular weight
cutoff and dialysis performed against a non-solvent that is miscible with the
solvent. The displacement of the solvent inside the dialysis membrane causes the
progressive aggregation of polymer due to a loss of solubility and the construction
of a homogeneous suspension of nanoparticles. The mechanism of the dialysis
process is based on similar phenomena to that of nanoprecipitation [65].
6 Biodegradable Polymers and Their Applications
The most extensively used biodegradable polymers are PGA, PLA,PLGA, PCL,
poly(alkyl cyanoacrylates), chitosan, and gelatin. The therapeutic applications and
preparation methods of these polymeric nanoparticles, with entrapment and release
of various drugs are described below and summarized in Table 1.
6.1 Poly(glycolic acid)
PGA was the first biodegradable synthetic semicrystalline polymer (glass transition
temperature, T g ~40
C; melting temperature, T m >200
C) to be considered for
biomedical applications. PGA has been used in bone internal fixation devices due to
its good mechanical properties. The good fiber-forming ability and scaffolding
ability of PGA, together with cell viability, were used to develop resorbable devices
and for tissue regeneration [119]. PGA is being used as a biocompatible durable
substitute and as an excellent skin-closing suture material. It also has the ability to
help regenerate biological tissue [120]. However, PGA is hydrolyzed in few
months, indicating a high degradation rate. It is broken down into glycine under
physiological conditions, which can be excreted from the body or converted into
carbon dioxide and water via the citric acid cycle [121]. Due to the high rate of
degradation and low solubility of PGA, its biomedical and pharmaceutical
applications are limited. Therefore, several copolymers containing glycolide units
are being developed to overcome the disadvantages of pure PGA.
184
S.K. Pandey et al.