We used plasma formed in mixtures of SO2 and O2 for surface modification of PET polymer. X-ray photoelectron spectroscopy and atomic force microscopy showed functionalization of samples with sulfur-containing groups and revealed highly altered morphology of plasma-treated samples. The samples were then incubated with human umbilical vein endothelial cells (HUVEC) and various biological tests were performed. The biocompatibility demonstrated a well-pronounced maximum versus gas composition, which correlated well with the development of the surface morphology. The best proliferation was observed in the case of nearly the same amounts of both mentioned gasses what was explained by formation of –SOx radicals on the surface of polyethylene terephthalate – similar to the groups in heparin. Such a surface finish seems to be stable so the innovative treatment with SO2/O2 plasma represents an interesting alternative to classical heparin coatings.
COBISS.SI-ID: 30276647
Excitation of sulfur plasma in the inductively-coupled RF plasma was investigated. Plasma may be sustained in two different discharge modes. If the electric field in the coil has a capacitive component, then plasma is in so called “E-mode”. If there is an inductive component, which develops inside the coil due to the induced electric field, plasma is in “H-mode”. The E-mode is characterized by low electron density, whereas the H-mode is characterized by a high electron density causing substantial gas dissociation. The appearance of these modes depends on a discharge power and pressure. The transition between these modes may be very abrupt. Such effects were studied for the case where plasma was created in SO2. It was found that SO2 molecules partially dissociate upon plasma conditions already when the discharge power is low (plasma in the E-mode). The most intensive radiation arises from transitions of SO radicals. As the power increases the radiation slightly increases until the transition to the H-mode appears. At this power the plasma luminosity increases abruptly for three orders of magnitude. Simultaneously the emission from both atomic species (S and O) prevails over the emission of SO radicals indicating a high dissociation of parent molecules in the H-mode. When decreasing the power, the transition occurs at a lower power thus a hysteresis is observed. This is the first report on the hysteresis observed in the SO2 plasma.
COBISS.SI-ID: 29911847
A process for modifying the surface properties of polytetrafluoroethylene (PTFE) polymer using sulfur-containing gaseous plasma is presented in this paper. Samples of PTFE foils were treated in pure H2S gaseous plasma sustained by an electrode-less radio-frequency discharge in the E-mode. The samples were kept at a floating potential. X-ray photoelectron spectroscopy, secondary ion mass spectrometry and atomic force microscopy were used to determine the evolution of the surface functionalities and morphology. An extremely thin film of chemically bonded sulfur was formed on the surface after a few seconds of plasma treatment, whereas a treatment duration of more than a minute resulted in the deposition of pure sulfur. The deposited film remained as thin as a few nanometers, even after half an hour of treatment.
COBISS.SI-ID: 28983591
In this scientific paper we have investigated interaction of H2S plasma with the PET polymer surfaces. We found substantial amounts of sulfur on the polymer, which was deposited to the surface. At longer treatment time the amount of sulfur was reduced due to sample heating, meaning that the deposit is not stable. Large spherical aggregates were also observed on the surface, which were not attributed to the sulfur deposit but rather due to etching. Rich surface morphology as well as chemical state of the modified surface may have substantial effect on biological response of this material.
COBISS.SI-ID: 29265703
In this paper we compared formation of SO3 functional groups on polymer surface treated in SO2 or H2S plasma which was mixed with oxygen, or we performed subsequent treatment in H2S followed by O2. Oxygen added to H2S does not help in formation of SO3 groups from deposited sulfur, because sulfur was still in non-oxidized state. Formation of oxygen rich functional groups was formed only at subsequent treatment in H2S and O2, but their concentration was much smaller than using pure SO2 plasma. Thrombogenicity of plasma treated surfaces was tested by investigating platelet adhesion. Surprisingly, the best results were obtained for polymer subsequently treated in H2S and O2 plasma and not for polymer treated in SO2 plasma, which had the highest concentration of SO3 groups.
COBISS.SI-ID: 29420583