Preparation and characterization of thermo-responsive PDMS surfaces grafted with poly(N-isopropylacrylamide) by benzophenone-initiated photopolymerization.

In the preparation of a thermo-responsive, poly(N-isopropylacrylamide) (PNIPAAm)-grafted polydimethylsiloxane (PDMS) surface by means of benzophenone-initiated photopolymerization, we observed that thick (>1 mm) PDMS substrates were much more difficult to be grafted with PNIPAAm than thin ones. Investigations revealed that the shortage of diffused benzophenone molecules in the surface region of the thick substrate might be the reason. By prolonging the time spent for treating the substrate with a benzophenone solution, PNIPAAm could be successfully grafted onto thick PDMS substrates. The PNIPAAm-grafted PDMS surface was highly thermo-responsive. The contact angle on a grafted surface increased from 38 to 91 degrees in response to the temperature increase from 20 to 38 degrees C. An electroosmotic flow (EOF) mobility of 5x10(-4) cm(2)/Vs was supported by a PNIPAAm-grafted PDMS channel at 50 degrees C, whereas negligible EOF was observed at 20 degrees C. Doxorubicin (DX), an anticancer drug, was adsorbed by the grafted surface at 40 degrees C, and the majority of the adsorbed DX was quickly released from the surface to a stripping solution at 5 degrees C. Osteoblast cells adhered onto the PNIPAAm-grafted PDMS surface and proliferated therein at 37 degrees C, while the cell sheet detached from the surface by lowering the temperature to 25 degrees C without using any enzymatic agent.