Study of plasma modified-PTFE for biological applications: relationship between protein resistant properties, plasma treatment, surface composition and surface roughness

Abstract

PTFE samples were treated by low-pressure, O₂ RF plasmas. The adsorption of BSA was used as a probe for the protein resistant properties. The exposure of PTFE to an O₂ plasma leads to an increase in the chamber pressure. OES reveals the presence of CO, CO₂ and F in the gas phase, indicating a strong etching of the PTFE surface by the O₂ plasma. Furthermore, the high resolution C1s spectrum shows the appearance of CF₃, CF and C-CF components in addition to the CF₂ component, which is consistent with etching of the PTFE surface. WCA as high as 160° were observed, indicating a superhydrophobic behaviour. AFM Images of surfaces treated at high plasma power showed a increase in roughness. Lower amounts of BSA adsorption were detected on high power, O₂ plasma-modified PTFE samples compared to low power, oxygen plasma-modified ones.

Keywords: biocompatibility; plasma treatment; polymer modification; polytetrafluoroethylene (PTFE); protein adsorption.

Figure 1

Schematic of the electrode and sample geometry.

Figure 2

Droplet of ultra pure water (V = 3 μL) deposited onto a oxygen plasma treated PTFE surface. Plasma treatment conditions were p = 6.66 Pa, DC-BIAS = −936 V, t = 120 sec. The water contact angle was >160°.

Figure 3

Comparison of the high resolution C1s spectra of oxygen plasma treated PTFE before (left) and after (right) BSA exposure for different plasma powers (p = 6.66 Pa). The peak assignments are: 1 CF₃ (294 eV), 2 CF₂ (292 eV), 3 CF (290 eV), 4 C-CF and/or C-O_x (287.4 eV), 5 CC (284.6 eV), 6 N-C=O (288.2 eV) and 7 C-O and/or C-N (286 eV).

Figure 4

Root mean squared surface roughness coefficient (triangle and square, left X axis) and water contact angle (star, right X axis) as a function of DC-BIAS for PTFE treated in an oxygen plasma at 6.66 Pa for 700s.

Figure 5

AFM images of a) as received PTFE; b) PTFE washed with isooctane; c) PTFE treated with a −250 V DC-bias oxygen plasma; d) PTFE treated with a −575 V DC-bias oxygen plasma; e) PTFE treated with a −750 V DC-bias oxygen plasma. The measured surface roughnesses of these surfaces are shown in Figure 3.

Figure 5

AFM images of a) as received PTFE; b) PTFE washed with isooctane; c) PTFE treated with a −250 V DC-bias oxygen plasma; d) PTFE treated with a −575 V DC-bias oxygen plasma; e) PTFE treated with a −750 V DC-bias oxygen plasma. The measured surface roughnesses of these surfaces are shown in Figure 3.

Figure 6

Optical emission spectra of the oxygen plasma without (dotted line) and with (solid line) a PTFE sample in the chamber. The DC-BIAS was −1000V and p(O₂) was 6.66 Pa. Spectra A were recorded in the plasma phase, spectra B were recorded close to the sample.

Figure 7

Comparison between HRC1s peak for PTFE sputtered with oxygen (left) or chemically etched by an oxygen plasma (right). Sputtering parameters: gas = O₂, E = 4 kV, I = 10 mA, P(in the ion gun) = 10 mPa, sputter time = 60 min. Chemical etching parameter: gas = O₂, DC-Bias = −936 V, p = 6.66 Pa, etching time = 2 min