Effects of chitosan solution concentration and incorporation of chitin and glycerol on dense chitosan membrane properties.

The aim of this work was to perform a systematic study about the effects induced by chitosan solution concentration and by chitin or glycerol incorporation on dense chitosan membranes with potential use as burn dressings. The membrane properties analyzed were total raw material cost, thickness, morphology, swelling ratio, tensile strength, percentage of strain at break, crystallinity, in vitro enzymatic degradation with lysozyme, and in vitro Vero cells adhesion. While the use of the most concentrated chitosan solution (2.5% w/w) increased membrane cost, it also improved the biomaterial mechanical resistance and ductility, as well as reduced membrane degradation when exposed for 2 months to lysozyme. The remaining evaluated properties were not affected by initial chitosan solution concentration. Chitin incorporation, on the other hand, reduced the membranes cost, swelling ratio, mechanical properties, and crystallinity, resulting in thicker biomaterials with irregular surface more easily degradable when exposed to lysozyme. Glycerol incorporation also reduced the membranes cost and crystallinity and increased membranes degradability after exposure to lysozyme. Strong Vero cells adhesion was not observed in any of the tested membrane formulations. The overall results indicate that the majority of the prepared membranes meet the performance requirements of temporary nonbiodegradable burn dressings (e.g. adequate values of mechanical resistance and ductility, low values of in vitro cellular adhesion on their surfaces, low extent of degradation when exposed to lysozyme solution, and high stability in aqueous solutions).

Analysis of cellular morphology, adhesion, and proliferation on uncoated and differently coated PVC tubes used in extracorporeal circulation (ECC).

The biggest challenge to improve extracorporeal circulation (ECC) circuits lays on avoiding platelet adhesion to their surfaces, because this contributes to thrombus formation, resulting in the activation of blood coagulation. One approach to minimize this effect is to improve the biocompatibility of ECC circuits by modifying their surfaces. This can be achieved by coating them with heparin or phospholipids. The present study investigated the adhesion and morphology characteristics of fibroblastic and blood cells cultured on uncoated poly (vinyl) chloride PVC tubes as well as on heparin, phosphatidylcholine (DMPC), and phosphatidylethanolamine (DMPE) -coated tubing. The results showed the importance of uniform coating regardless of the substance used, because the coatings cover the grooves on PVC surfaces, which favor cell adhesion. The comparison among the three different coatings showed the best biocompatibility results for the PVC tubes coated with heparin, followed by the coating with DMPE and with DMPC. For all coated tubes, cells did not spread on the PVC surfaces and, consequently, did not adhere to their surfaces, increasing the overall biocompatibility of PVC tubes. However, possible DMPE's alkylation, caused by sterilization, resulted in increased material hydrophobicity, which explains the decrease in fibroblastic adhesion. Furthermore, sterilization of DMPC-PVC improves its hydrophilic character, also decreasing adhesion. Based on these results, coating PVC with the phospholipids DMPC and DMPE seems to be a promising technique to improve the biocompatibility of PVC tubes, and is worthy of further investigation.

The cytotoxicity in vero cells of a perfluorocarbon used in vitreoretinal surgery

Perfluoro-n-octane is a high-density liquid perfluorocarbom used as a long-term vitreous replacement in vitreoretinal surgery. In this study, we assessed the toxicity of perfluoro-n-octane (PFOC) on Vero cells using and indirect toxicity test, scanning electron microscopy and immunocytochemistry. For indirect toxicity test, Vero cells were cultured for 12 h with PFOC extracts in 96-well plates and the plates were, then, read at 540 nm. for direct toxicity, Vero cells were incubated with 0.1 ml of perfluoro-n-octane alone. Glass coverslips were used as inert control for weight, to produce mechanical compression similar in weight and area to that caused by perfluoro-n-octane. Cells cultured without PFOC were used as a negative control. Silicone bands with a weight and area similar to those of perfluoro-n-octane served as a positive control for toxicity. The indirect toxicity test showed that perfluoro-n-octane did not release soluble toxic substances that affected cell growth. In the direct toxicity test, the cells in the control group had homogenously distributed actin filaments, althougth scanning electron microscopy revealed some vesicles on the cell surface. In the controls for weight, cytoplasmic retraction and the formation of thin cellular prolongations were seen. Cells incubated with perfluoro-n-octane showed greater changes compared to those seen in cells under a similar control weight. Silicone-treated cells had an irregular or fragmented morphology. These results show that, in addition to its compressive action on cultured cells, perfluoro-n-octane may also exert a toxic effect.