Quasi-zwitterionic glow-discharge radio frequency plasma coatings

Abstract

Event Abstract Back to Event Quasi-zwitterionic glow-discharge radio frequency plasma coatings Marvin M. Mecwan1 and Buddy Ratner1 1 University of Washington, Bioengineering, United States Introduction: Glow discharge plasma-treated surfaces have been used to create non-fouling surfaces, and can be readily applied to implants. For successful plasma polymerization it is important that the monomer of interest be easily volatilized. Zwitterionic polymer hydrogels in mice have shown to resist foreign-body reaction[1]. However, zwitterionic polymer precursors, such as carboxybetaine methacrylate (CBMA) and sulfobetaine methacrylate (SBMA) are solids with high boiling points which would not make them ideal candidates for glow-discharge plasma treatment to coat surfaces. This study investigates the preparation of quasi-zwitterionic surfaces via glow-discharge plasma treatment prepared by the simultaneous deposition of a positively charged (N,N-dimethylaminoethyl methacrylate or DMAEMA), and negatively charged (methacrylic acid or MA) monomesr, and may lead to a new generation of non-fouling surfaces. Methods: Silicon substrates were cleaned with methanol in a sonication bath for 10 mins x2. Substrates were allowed to air dry in a chemical hood before plasma deposition. RF-Plasma deposition and delamination: Substrates were loaded into the plasma reactor, and argon etched (40W for 5 min). Using a caliper valve, the monomers of choice—DMAEMA and/or MA—was introduced into the chamber. DMAEMA monomer was heated to 550C and MA monomer was unheated. Plasma deposition was carried out at 250mT pressure; 20W for 30 secs (adhesion) followed by 5W for 15 mins (deposition). Substrates were quenched for 5 mins before venting the chamber and retrieving coated samples. Plasma-treated samples (n=3/group) were washed using DI water x 3 over 24 hrs to assess whether coatings would delaminate. ESCA analyses were done using an S-Probe ESCA (with monochromatic Al K-alpha X-rays focused to 800µm spot size) using survey and detailed C1s scans. Data was analyzed using ESCA analysis software. Results and Discussion: ESCA scans of plasma-treated substrates showed absence of substrate associated peaks (Si), suggesting that coatings did not delaminate. This also implies that plasma coatings on substrates are at least 10 nm thick—ESCA resolution is 100Å (coating thickness will be measured using ellipsometry). Furthermore, experimental and theoretical elemental compositions of the surfaces align well. From the detailed C1s scans for MA coatings we see two distinct peaks at 285.5 and 290 eV associated with hydrocarbon (-CH) and carboxyl (-COO) bonds respectively. For DMAEMA coatings, we see three peaks at 285.5, 287 and 289.5 eV associated with -CH, amine (-NH) and -COO bonds respectively. For the quasi-zwitterionic coatings, we also see three peaks associated with -CH, -NH, and -COO bonds respectively that have been slightly shifted to 286, 287.5 and 290.5 eV respectively when compared to just DMAEMA coatings. This shift can be attributed to the combination of both MA and DMAEMA in the quasi-zwitterionic coatings. Conclusions: The preliminary data demonstrates that quasi-zwitterionic surfaces can be successfully created by the simulataneous deposition of MA and DMAEMA. Ongoing studies include determining the amount of positive vs negative charge on the surfaces via derivitization chemistry, as well as their ability to prevent protein adsorption in order to determine the ability of these quasi-zwitterionic plasma coatings to efficaciously perform as a new generation of non-fouling surfaces. Shaoyi Jiang, PhD