Biomedical Engineering Reference
In-Depth Information
Fig. 3 Typical in vitro drug release profile for drug-loaded PLA/PLGA
nanoparticles. Initial burst release is characterized by dissolution of drug
molecules (in red) present on or near the nanoparticle (in blue) surface,
diffusion phase is characterized primarily by drug molecules diffusing from the
polymer matrix, and degradation phase is characterized by drug molecules
primarily being released following bulk degradation of the polymer matrix
packaged in the dry formwith glycerine as the preservative or in
the wet form with 0.05 % w/v sodium azide as the preservative.
It is recommended that the wet membranes must not be allowed
to dry out as drying can lead to an irreversible collapse of the pore
structure; hence, they should be kept wetted in 0.05 % w/v
sodium azide during storage. Before using the dialysis membrane
for the in vitro release study, the membrane should be soaked in
distilled and de-ionized water for 15-30 min to remove the
preservative. Soaking should be followed by thorough rinsing
in running distilled and de-ionized water.
5. Volume of DCM for dissolving the polymer is based on the
amount of polymer weighed, the type of polymer, and the
molecular weight of the polymer. In general, PLA polymers
have a lower solubility than PLGA polymers in most solvents.
Further, as the intrinsic viscosity of the polymer increases,
the molecular weight increases and the solubility decreases
[
29
,
30
]. In the methods described, while 100 mg PLGA of
0.32-0.44 dl/g intrinsic viscosity was dissolved in 1 ml DCM,
200 mg
L
-PLA which had a higher intrinsic viscosity of
0.95-1.2 dl/g was dissolved in 5 ml of DCM. About 5 min
of vortexing can help dissolve the polymers in DCM.
6. PLA/PLGA particles designed for sustained release are char-
acterized by a triphasic drug release profile as depicted in Fig.
3
[
31
]. The initial burst release is due to dissolution of the drug
present on or near the particle surface. The burst release is
followed by a slow release phase that is controlled by diffusion
of the drug from the polymer matrix [
14
,
15
,
32
]. The diffu-
sion phase is followed by a more rapid drug release due to bulk
degradation of the polymer matrix [
14
,
15
]. It has been
