Analysis of Surface Sterilization and Properties of Medical Poly(tetrafluoroethylene) in Remote Argon Plasma

We have used a remote-argon-plasma reactor in which the active species can be separated at a special plasma field. Argon gas is used as the work gas. In this remote argon plasma, the distribution of electrons, ions, and radicals and germicidal effect (GE) of Escherichia coli on the surface of medical poly(tetrafluoroethylene) (PTFE) film are studied. Then surface properties of sterilized PTFE are investigated by water-contact- angle and mass-loss measurements, as well as scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. The results show that the concentration of electrons and ions decrease rapidly with increasing the sample position, which approximate to 0 at 30 cm, whereas the concentration of radicals change little within 40 cm. Relatively high-purity radicals are obtained in afterglow zone. GE values reach 4.633 in the active discharge zone (0 cm) and exceed 3.769 within 40 cm under the conditions of plasma RF-power of 100 W, exposure time of 120 s, and argon flux of 20 cm3/min. But remote-argon-plasma sterilization (40 cm) makes the PTFE surface higher hydrophilicity than the direct-argon-plasma sterilization (0 cm) and does not give remarkable degradation and damages in terms of mass-loss and surface morphology. Moreover, the remote argon plasma contributes more effectively to the defluorination (F/C = 2.24) from the PTFE than the direct argon plasma (F/C = 2.48), and thus, more oxygen functionalities (e.g., C = O) are formed on remote-plasma-sterilized PTFE surface. The essential reason is that remote argon plasma can enhance interactions between radicals and PTFE surface, which are inhibited in the active discharge zone. These experimental results show that the remote argon plasma is more appropriate to surface sterilization of medical PTFE in obtaining superior surface properties.