Surface modification of high-performance polymeric fibers by an oxygen plasma. A comparative study of poly(p-phenylene terephthalamide) and poly(p-phenylene benzobisoxazole)

Effect of non-oxidative plasma treatments on the surface properties of poly(p-phenylene terephthalamide) (PPTA) and poly(p-phenylene benzobisoxazole) (PBO) fibres as measured by inverse gas chromatography

It has been shown in previous works that the interfacial adhesion in PPTA- and PBO-epoxy composites can be improved by modifying the surface properties of these high-performance fibres upon exposure to non-oxidative plasma treatments. In this work, the effects developed on both types of polymer surface were examined as a function of treatment gas nature (He or N₂) and exposure time (one or four minutes) using inverse gas chromatography at infinite dilution (IGC). From the adsorption of n-alkanes, it has been proved that non-oxidative plasma treatments led to energetically heterogeneous surfaces in the case of PPTA, and to low-energy surfaces in the case of PBO. Nevertheless, it was proved with the 1-min plasma treatments (either under helium or under nitrogen) that chemical reactivity was enhanced on the PBO surface. Such a behaviour was ascribed to the presence of low-molecular weight oxidized materials. The mechanisms involved in surface activation of PPTA were not equivalent under He or N₂ exposure. Nitrogen plasma exposure led to a PPTA surface that is chemically reactive as a result of polarity enhancement. Helium plasma-treated PPTA surface was characterized by the presence of branched arrangements that intensified the number of chemical contacts onto reactive sites. Finally, for both fibre sets, if the purpose is to enhance the chemical surface reactivity, it makes no sense to increase the plasma exposure time from 1 to 4 min.

Dose-dependent enhancement of bone marrow stromal cells adhesion, spreading and osteogenic differentiation on atmospheric plasma-treated poly(l-lactic acid) nanofibers

Although poly(l-lactic acid) nanofibers are known to promote osteogenic differentiation of bone marrow stromal cells, their relative hydrophobicity and surface inertia tend to hinder their biomedical application. We explored a feasible and effective technique to improve the bioactivity and biocompatibility of poly(l-lactic acid) fibers for further application in regenerative medicine. A low-temperature atmospheric plasma was used to treat poly(l-lactic acid) nanofibers for 1, 5, and 10 min, and the surface properties and dose-dependent effects on the behavior of bone marrow stromal cells were studied. Both the amino group content and surface hydrophilicity of the nanofibers increased with treatment time, whereas the spreading and proliferation of bone marrow stromal cells were greatest on nanofibers which had been treated for 5 min, followed by samples treated for 1 and 10 min. The quantitative reverse transcription–polymerase chain reaction analysis of the bone marrow stromal cells on the 5-min-treated nanofibers had the highest expression level of osteogenic marker genes including RUNX2, BMP2, ALP, COL1A1, OPN, and OCN. The nanofibers treated for 5 min also promoted the high levels of alkaline phosphatase activity. These results suggest the exertion of dose-dependent effects by atmospheric plasma treatment on the surface of poly(l-lactic acid) nanofibers, and that this treatment is a feasible and effective technique to improve biomaterial biocompatibility and promotion of osteogenic differentiation of bone marrow stromal cells.