Development of controlled releasing surfaces by plasma deposited multilayers

This work deals with the use of plasma technology for the creation of a controlled release multilayer structure. At first, polypropylene (PP) films were modified by vapour phase plasma-induced graft-polymerization of acrylic acid. The physico-chemical properties of the plasma-modified films were evaluated by means of contact angle measurements and Attenuated Total Reflectance Infrared (ATR/FT-IR) spectroscopy analyses. The acrylic acid functionalization was found to be stable in aqueous environments. Due to the acidic characteristics of their surface, acrylic acid modified films (PP-AAc) are able to absorb positively charged molecules by ion–exchange reaction. We studied the absorption and the release in Phosphate Buffer Saline (PBS) and HCl 0.1 N of a cationic dye (methylene blue, MB), which was used as model compound. In order to control the release rate of the dye, a barrier coating was deposited over the MB loaded acrylic acid layer. This barrier coating was deposited by plasma polymerization of hexamethyldisiloxane (HMDSO). We found that the HMDSO coating strongly decreases the release rate of MB, both in PBS and HCl solutions. Moreover, the variation of the barrier coating thickness allowed us to tune the release rate of the cationic dye.