In recent years, implantable drug delivery devices have been promising therapeutic systems for the treatment of chronic diseases. Chronic patients suffer from health problems as a result of permanent illness and/or organ failure. Therefore, medical methodology which can be effective for a long time has attracted a lot of attention. Implantable drug delivery devices are able to function in the human body for a long period. However, an improper amount of drug released from the device would cause uncomfortable side effect. To optimize the pharmacotherapy, drug release has to be well controlled in accordance with the remedy during a treatment course. An ideal drug delivery device is capable of releasing the desirable amount of drug to the targeted site for a required period of time. In order to achieve this goal, biodegradable polycaprolactone nanoporous membranes may be expected to control the drug release rate via tuning the porous structure.

In this study, biodegradable and biocompatible polycaprolactone (PCL) nanoporous membranes have been successfully prepared via the combination of thermally and nonsolvent induced phase separation techniques. The polymer solution with a specific composition was cast on a suitable plate. Then, the cast film of the solution was immersed into a lower temperature coagulation bath, i.e., both thermally and nonsolvent induced phase separations took place simultaneously. In the membrane preparation, the thermally induced phase separation could enhance porosity or avoid the formation of a dense top-layer. On the other hand, the nonsolvent induced phase separation could play a role on the formation and the dimension/size of nanoscale pores. Our results showed that the pore size reduced and the porosity increased as the coagulation bath temperature decreased. Also, the release rate of the model drug compound, lysozyme, into an aqueous solution was higher as a lower coagulation bath temperature was used. As a result, the drug release rate can be well controlled via adjusting the parameters for the membrane preparation, including coagulation bath temperature and casting solution composition. In addition, the nanoporous membrane provides a barrier for preventing the passage of cytotoxic cells, macrophages, antibodies and other immune substances.