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Abstract

In this work, close attention has been devoted to assessing the effects of cold atmospheric pressure plasma treatment on standard polypropylene microcentrifuge tubes. After successful optimization of plasma parameters an automatic plasma treatment device was constructed for repeatable treatment of the tubes’ inner surface. Once the effects of plasma treatment on the tubes’ inner surface were thoroughly examined and described, the microbiological response of microvesicles and proteins to these surfaces was studied.
Our aim was therefore to optimize plasma treatment parameters for the tubes’ inner surface modification, to make such treatment fast, effective, repeatable and applicable in biomedicine. Main hypothesis was, that plasma treatment improves the microvesicle isolation process. Each of the fields involved, plasma technology, polymer sciences and biomedicine, is complex and challenging by itself. Plasma treatment of inner surface of long narrow tubes is almost non-existent in the literature, partially due to difficulties of analyzing curved surfaces and partially due to plasma jet restrictions. Further on, polypropylene is known for its poor functionalization by plasma treatment compared to other polymers like PET for example. It also has to be taken into consideration that polypropylene blends and fillers differ greatly amongst various manufacturers. Three of them were compared in this work. Moreover, plasma treatment has to be homogeneous and repeatable if we tend to use it for biomedical or other delicate applications. This brings us to the last major issue, the repeatability and unknown factors in biomedical experiments. Especially in the microvesicle isolation technique there are numerous variables and the protocol is rather new and still in the process of development and optimization.
Methods used in this work can be divided into three categories, those for plasma characterization, those for polypropylene characterization and those for characterization of biomedical experiments. In the first category, plasma is characterized by optical emission spectroscopy (OES), electric current and voltage measurements. Polypropylene is characterized by water contact angle (WCA) and surface free energy measurements, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and differential scanning calorimetry (DSC). In the end, for biomedical experiment, flow cytometry, dynamic light scattering (DLS) and atomic force microscopy (AFM) are involved in microvesicle characterization and adsorption measurements by ultraviolet-visible spectrophotometry (UV-Vis) for proteins.
It was found that atmospheric pressure plasma jet can uniformly alter polypropylene tubes’ inner surface if the plasma jet parameters and position are chosen appropriately. Further on, large variations were found between tubes made by different manufacturers. It was once again confirmed that plasticware can affect laboratory results in a significant manner. It was also confirmed that microvesicle isolation yields were noticeably improved when plasma-treated tubes were used, even though the process of isolation deviates greatly.