NAMS 2002 Workshop - ICOM 2008

Asymmetric Polymeric Membrane Formation – 2
Tuesday July 15, 9:30 AM-10:00 AM, Wai’anae
Synthesis and Characterization of Nanoporous Polycaprolactone
Membranes for Controlled Drug Release
C. Yen (Speaker), The Ohio State University, Columbus, OH, USA
H. He, Nanoscale Science and Engineering Center for Affordable Nanoengineering of, Columbus,
OH, USA
L. Lee, The Ohio State University, Columbus, OH, USA
W. Ho, The Ohio State University, Columbus, OH, USA
Polycaprolactone (PCL) has recently drawn a lot of attention in the biomedical
applications. PCL, a semicrystalline polymer, has several advantages including
low cost, biocompatiblitiy, and biodegradability. Moreover, PCL is a U.S. Food
and Drug Administration approved material for implantable devices, such as
suture. Thus, PCL is a superior material to fabricate an affordable and
implantable drug delivery device.
The porous membranes play an important role in a variety of drug delivery
systems. Several factors, including porosity, turtuosity, and pore size, have
critical effects on controlling the rate of drug diffusion through the membranes.
Currently, porous PCL membranes can be prepared by solvent-cast-leaching
method, bi- axial stretching, thermally-induced phase separation, and
nonsolvent-induced phase separation. However, state-of-the-art, porous PCL
membranes which are prepared via above methods have pore size still on a
micron scale that is too large. The mechanism governing diffusion phenomena
could be free diffusion, leading to an undesirable burst effect. Therefore, micronsize
porous membranes might not be a proper means to achieve the desirable
zero-order drug release rate. It appears that nanoporous PCL membranes could
be an ideal system to achieve the desirable release rate for implantable drug
delivery devices.
In this study, nanoporous PCL membranes have been prepared successfully via
the combination of thermally and nonsolvent induced phase separations. In the
membrane formation, the effects arisen from the thermally-induced phase
separation on the membrane formation have been investigated. In the membrane
preparation, the cast-film on a glass plate was immersed into a coagulation
(water) bath at a different constant temperature. When water bath temperature
was 5° C, the pore size at membrane top side was approximately 50 nm, and the
porosity was about 73%. However, while water temperature increased, the pore
size would also increase but the porosity would decrease. As coagulation bath
temperature increased to 35°C, the pore size at top side of the membrane would
be about 1 µm, and the porosity was about 56%. Lower coagulation