Functional and responsive surfaces via initiated chemical vapor deposition (iCVD)

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2011.Cataloged from PDF version of thesis.Includes bibliographical references.Stimuli-responsive polymers provide a method to control system behavior through the use of an external stimulus, such as temperature, pH, or electric fields among others. Temperature-responsive polymers, especially those based on N-isopropylacryalmide (NIPAAm), are of particular research interest due the ease of implementation of temperature changes to systems as well as the large accessible range of hydrophilic / hydrophobic switching. Initiated chemical vapor deposition (iCVD) is shown to be a useful technique for surface modification with NIPAAm-based polymers due to its ability to provide complete functional retention and applicability to "real world" substrates, which many times have varying compositions and / or micro- or nano-structured surfaces. The novel copolymer thin film of iCVD poly(NIPAAm-co-di(ethylene glycol) divinyl ether) (p(NIPAAm-co-DEGDVE)) is shown to exhibit a sharp lower critical solution temperature (LCST) transition, better-than or equivalent to other surface modification techniques, while also being able to achieve a wider range of thicknesses from the nano- to micro-scale, which is especially useful for flow control, actuator or sensor applications. The bottom-up film growth of iCVD allows for compositional gradients throughout the thickness of a polymer film. A novel NIPAAm-based copolymer with a NIPAAm-rich surface layer is developed which exhibits both fast swelling and deswelling kinetics. Quartz crystal microbalance with dissipation monitoring (QCM-D) is used to study the transition behavior of these films. These data provide valuable information relating to the polymer conformational changes throughout the transition region and help elucidate thermodynamic and mesh characteristics of the films. Finally, an application is developed which utilizes both iCVD and a complementary technique, oxidative CVD (oCVD), to create self-heating membranes with responsive permeability characteristics.by Mahriah E. Alf.Ph.D

Fabrication and characterization of a porous silicon drug delivery system with an initiated chemical vapor deposition temperature-responsive coating

This paper reports on the fabrication of a pSi-based drug delivery system, functionalized with an initiated chemical vapor deposition (iCVD) polymer film, for the sustainable and temperature-dependent delivery of drugs. The devices were prepared by loading biodegradable porous silicon (pSi) with a fluorescent anticancer drug camptothecin (CPT) and coating the surface with temperature-responsive poly(N-isopropylacrylamide-co-diethylene glycol divinyl ether) (pNIPAM-co-DEGDVE) or non-stimulus-responsive poly(aminostyrene) (pAS) via iCVD. CPT released from the uncoated oxidized pSi control with a burst release fashion (similar to 21 nmol/(cm(2) h)), and this was almost identical at temperatures both above (37 degrees C) and below (25 degrees C) the lower critical solution temperature (LCST) of the switchable polymer used, pNIPAM-co-DEGDVE (28.5 degrees C). In comparison, the burst release rate from the pSi-pNIPAM-co-DEGDVE sample was substantially slower at 6.12 and 9.19 nmol/(cm(2) h) at 25 and 37 degrees C, respectively. The final amount of CPT released over 16 h was 10% higher at 37 degrees C compared to 25 degrees C for pSi coated with pNIPAM-co-DEGDVE (46.29% vs 35.67%), indicating that this material can be used to deliver drugs on-demand at elevated temperatures. pSi coated with pAS also displayed sustainable drug delivery profiles, but these were independent of the release temperature. These data show that sustainable and temperature-responsive delivery systems can be produced by functionalization of pSi with iCVD polymer films. Benefits of the iCVD approach include the application of the iCVD coating after drug loading without causing degradation of the drug commonly caused by exposure to factors such as solvents or high temperatures. Importantly, the iCVD process is applicable to a wide array of surfaces as the process is independent of the surface chemistry and pore size of the nanoporous matrix being coated