Study On The Interactions Between Polycation-modified Chitosan Materials And Cells

In this study, in order to improve the biocompatibility of chitosan, polycations were used to modify chitosan with blending method, and the interactions of the produced composite materials with cells were also explored.Firstly, poly-L-lysine was utilized to blend with chitosan and a series of composite film materials containing different contents of poly-L-lysine were obtained. With various assays, the surface characteristics of these composite films were investigated. It was found that the nanoscaled surface morphology, surface chemistry, and surface wettability of all the composite films were totally different. Among them, the composite films containing 0.25% and 0.5% (w/w) poly-L-lysine (PL-0.25 and PL-0.5) exhibited the nanofiber-dominant surface. Protein adsorption studies showed that the surface properties of these composite films could affect the adsorption of fibronectin on their surfaces. The nanofiber-dominant surfaces of PL-0.25 and PL-0.5 could induce greater fibronectin adsorption than pure chitosan control. Subsequently, the cell experiments with MC3T3-E1 osteoblast-like cells and PC12 cells were carried out to evaluate the cytocompatibility of all composite films. For these two types of cells, the overall morphology, cytoskeleton organization and structure, nuclei morphology, cell adhesion, proliferation, and differentiation on all composite films were systematically examined. On the surfaces of PL-0.25 and PL-0.5, MC3T3-E1 cells and PC12 cells both displayed better morphology, stronger cytoskeleton organization, and significantly higher levels of adhesion, proliferation, and differentiation when compared to chitosan control and other composite films. The results suggested that the nanofiber-dominant surfaces of PL-0.25 and PL-0.5 probably contributed to the promoted fibronectin adsorption and thereby enhanced the biocompatibility of these two composite films.In order to further verify the above results, we also used poly-L-lysine and the other two polycations, i.e. polyethyleneimine and poly-L-ornithine, to blend with chitosan at the same concentration of 0.25% (w/w) and produced three polycation-modified chitosan films. Although the polycation content in these three composite materials was identical, but their surface properties were also different. Chitosan blended with 0.25% poly-L-lysine still displayed the nanofiber-dominant surface. For the composite films modified with polyethyleneimine and poly-L-ornithine, however, their surfaces exhibited the nanoparticle topography. Protein adsorption and conformation studies demonstrated that the nanofiber-dominant surface of poly-L-lysine modified material could not only induce the maximum adsorption of fibronectin, but also maintain the conformation of bovine serum albumin closest to the natural state. Cell experiments showed that this surface promoted the growth of MC3T3-E1 cells and PC12 cells and caused the increased phosphorylation and gene expression levels of important functional proteins within MC3T3-E1 cells.In summary, in this thesis, the interactions between polycation-modified chitosan films and cells were systematically explored from three aspects including the surface properties of materials, protein adsorption, and cell behaviors. The results also showed that composite materials with nanofiber-dominant surfaces had good cytocompatibility with bone and nerve cells and exhibited potentials in the applications of bone and nerve regeneration in the near future.