Comparison of nanostructure and nanomechanical properties of cast and air sides of polyimide films from different manufacturers.

Polyimide films are widely applied in harsh environments because of their outstanding performance. High-quality polyimide films are often manufactured through a two-step process. The complicated procedure results in different properties on the two sides, i.e., the air side and cast side of the films, and the quality of products from different manufacturers varies notably. In the present work, polyimide films with two thicknesses (1 and 2 mm) from four manufacturers were investigated. Atomic force microscope and FT-IR spectrometer were employed to monitor morphology, roughness, nanomechanical properties, and corresponding relative imidization degree on the two sides of each film. Statistical tools were applied to analyze the data. T-test suggests that the two sides of the same film were significantly different in roughness, DMT modulus, and relative imidization degree (p < 0.05). The roughness on the air side was consistently smaller than that of the cast side. ANOVA was used to compare differences among the manufacturers. Manufacturer B provided the smoothest films with the highest DMT moduli and imidization degrees. A positive correlation was found between the DMT modulus and imidization degree (r = 0.7330). Nanostructure and nanomechanical properties could affect the quality of the film. Striped morphology and adhesion were found on the cast side of the 2-mm film from manufacturer D, which compromised the film tension in the direction perpendicular to the strips. Investigations of morphology and mechanical properties of polyimide film at the nanoscale would help us better characterize the film, assure its quality, and select suitable film and side for proper applications.

Stabilization of liposomes with silicone layer improves their elastomechanical properties while not compromising biological features.

The liposomes are among the most promising types of drug delivery systems but low stability significantly limits their application. Some approaches proposed to overcome this drawback may affect the liposomes toxicity profile. It is assumed that developed by us and presented here stabilization method involving formation of silicone network within the liposomal bilayer will improve elastomechanical properties of vesicles while not deteriorating their biocompatibility. The silicone-stabilized liposomes were prepared by base-catalyzed polycondensation process of the 1,3,5,7-tetramethylcyclotetrasiloxane (D4H) within the liposomal bilayer. The systematic biological in vitro studies of vesicles obtained were carried out. Moreover, the elastomechanical features investigation employing atomic force microscopy (AFM) measurements was performed. These properties of the liposome membrane are of great importance since they define the nanocarriers' stability as well as play a significant role in their cellular uptake via endocytosis. Applying the Derjaguin-Muller-Toporov (DMT) model, the elastic modulus of the silicone-stabilized liposomes was determined and compared to that characteristic for the pristine liposomes. The in vitro biological evaluation of silicone-stabilized liposomes demonstrated that these vesicles are not toxic for blood cells isolated from healthy donors and they do not induce oxidative stress in HepG2 cells. AFM results confirmed the stabilizing effect of silicone and revealed that the silicone network improves the elastomechanical properties of the resulted liposomes. This is the first report demonstrating that the silicone-stabilized liposomes retain biocompatibility of pristine liposomes' while acquire significantly better elastomechanical features.