The purpose of this study was to determine the effect of atomic oxygen (AO) exposure on the hydrophilicity of nine different polymers for biomedical applications. Atomic oxygen treatment can alter the chemistry and morphology of polymer surfaces, which may increase the adhesion and spreading of cells on Petri dishes and enhance implant growth. Therefore, nine different polymers were exposed to atomic oxygen and water-contact angle, or hydrophilicity, was measured after exposure. To determine whether hydrophilicity remains static after initial atomic oxygen exposure, or changes with higher fluence exposures, the contact angles between the polymer and water droplet placed on the polymer’s surface were measured versus AO fluence. The polymers were exposed to atomic oxygen in a 100-W, 13.56-MHz radio frequency (RF) plasma asher, and the treatment was found to significantly alter the hydrophilicity of non-fluorinated polymers.
Pristine samples were compared with samples that had been exposed to AO at various fluence levels. Minimum and maximum fluences for the ashing trials were set based on the effective AO erosion of a Kapton witness coupon in the asher. The time intervals for ashing were determined by finding the logarithmic values of the minimum and maximum fluences. The difference of these two values was divided by the desired number of intervals (ideally 10). The initial desired fluence was then multiplied by this result (2.37), as was each subsequent desired fluence. The flux in the asher was determined to be approximately 3.0 × 1015 atoms/cm2 sec, and each polymer was exposed to a maximum fluence of 5.16 × 1020 atoms/cm2.
It was determined that after the shortest atomic oxygen exposure (fluence of 2.07 × 1018 atoms/cm2), non-fluorinated polymer samples became significantly more hydrophilic than their pristine counterparts. This may be due to either surface texture changes or oxidation functionality surface changes. Despite long-term exposure (fluence of 5.16 × 1020 atoms/cm2), the water contact angles remained relatively unchanged after the initial exposure. This implies that increasing the atomic oxygen fluence after an initial short exposure did not further affect the hydrophilicity of the polymers. Rather, polymers were affected by a very short exposure (19 atoms/cm2). This indicates that oxidation functionality is more likely the contributor to increased hydrophilicity than texture, as texture continues to develop with fluence. The water contact angles of fluorinated polymers were found to change significantly less than non-fluorinated polymers for equivalent atomic oxygen exposures, and two of the fluorinated polymers became more hydrophobic.
Significant decreases in the post-exposure water contact angle were measured for non-fluorinated polymers. The majority of change in water contact angle was found to occur with very low fluence exposures, indicating potential cell culturing and other biomedical benefits with very short treatment time.
This work was done by Kim de Groh of Glenn Research Center; Lauren Berger and Lily Roberts of Hathaway Brown School; and Bruce Banks of Alphaport.
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