Ordered Aggregating And Self-assembling Of Lactic Copolymers And Chitosan Derivates

Chitosan and its derivatives, showing excellent biological properties such as biodegradation in the human body, immunological, antibacterial, and wound-healing activity, are useful as carriers in drug delivery systems, as antibacterial agents, cell culture, and in other medical applications. Meanwhile, properties especially in strength could be improved through being mingled with other biomaterials. Poly(lactic acid) or its copolymers with other oligomers have been being used in such diverse biomedical fields as tissue engineering, implantation of medical devices and artifical organs, bone repair, et al, because of their biodegradable, biocompatible and self-assembling when the block copolymers are used for the prepration of nanoparticles. New muti-biomaterials nanoparticles with better biological properties can obtained throught the complexing of chitosan or its derivates with poly(lactic acid) or its copolymers, but we could not bring about the aim just throught simple complexing. So we have synthesized some peculiar structure derivates of chitosan and poly(lactic acid) in order to prepare muti-biomaterials nano-objects throught the ordered aggregating and self-assembling of these molecules. The main results are as follows:The length of the block PLA(hydrophilic) and the hydrophilic or hydrophobic property make the copolymers amphiphilic or not. Star-shaped polymers including PLA-PTOL(Poly[(lactic acd)-co-(pentaerythritol)]),PLA- GLU(Poly[(lactic acid)-co-(glutamic acid)]), and PLA-LYS(Poly[(lactic acid)- co-(lysine)]), show hydrophobic attribute to the block PLA; Poly[(lactic acid)-co-(butanedioic anhydridel))-co-(polyethylene glycol-2000l)](PLA-BDC- PEG-2000)as a typical block copolymer shows amphiphilic attribute to the block PLA and PEG-2000(hydrophilic); copolymers with taurinic or triethylaminic functional groups at side chains including Poly[(lactic acid)-co-(butanedioic anhydridel))-co-(2,2-ditaurinic-Methyl-1,3-propanediol)] (PLA-BDA-DTMPDOL) and Poly[(lactic acid)-co-(butanedioic anhydridel))- co- (2,2-ditriethylaminic-methyl-1,3-propanediol)](PLA-BDA-DTEAMPDOL) are typic- al polyelectrolyte; Poly[(lactic acid)-co-(butanedioic anhydridel))-co- (2,2- dilinoleonyl-1,3-propanediol)](PLA-BDA-DLPDOL) with linoleonyl fun- ctional groups at side chains is a hydrophobic combed polymer. Chitosan derivates modified by taurinic or triethylaminic functional groups at the C2 position show better polar than chitosan and can be dissolved in many polar solvents; chitosan derivates modified by linoleonyl functional groups at the C2 position called as combed polymer show better hydrophobic than chitosan and can be dissolved in many nonpolar solvents.The ordered molecular aggregates with different sorts of image and size, including PLA-PTOL/CS, PLA-GLU/CS, and PLA-LYS/CS have been prepared by slow evaporation of solvent in different sorts of solvents, such as CHCl3/CH3OH-AcOH, and CHCl3/CH2Cl2-CCl3CO2H. There are big differences in image and size because of solvents and molecular weight of these star-shaped polymers; but the density of polymers could not impact on the size of these ordered molecular aggregates; the aggregates grows larger with the increasing of molecular weight. It states that there are strong hydrogen bonds between C=O of PLA-PTOL and H-O of CS from FT-IR spectrums. The thermopositive values are 8.6kj/mol, 5.6kJ/mol, and 5.6kJ/mol in the self-assembling process of these three ordered molecular aggregates.Amphiphilic block copolymer (PLA-BDA-PEG-2000) can self-assemble and becomes solid and hollow balls in polar solvents such as H2O, THF, EtOH, and DMF. The size of balls grows larger with the increasing of the length of arms (PLA); density could not impact on the size of balls, but balls grow more irregular when density turns lower. The auto process of self-assembly is thermopositive and the value is 20.666kJ/mol. The ordered molecular aggregates can be obtained by self-assembly of combed polymers themselves and each other including PLA-BDA-DLPDOL, (N-linoleonyl)CS, and (N-butanoyl,N-linoleonyl ) CS. The graft ratio of linoleonyl to combed polymers and the types of solvents have effects on the images of ordered molecular aggregates, and density does not. The process is thermopositive and there are blue-shifts of covalent bond in FT-IR spectrums after self-assembling.Three polyelectrolyte membranes, including PLA-BDA-DTMPDOL/(N-(2- Hydroxyl-3-Trimethylamino)Propanyl)CS,PLA-BDA-DTEAMPDOL/(N-butanedioic)CS, and PLA-BDA-DTEAMPDOL/2-Hydroxyl-3-SulfoPropanyl)CS, have been prepared by molecular deposition. The surface images of these membranes have some changers with the changers of ion ratios and densities of polyelectrolyte molecules. Tight membranes can be obtained by increasing ion ratios and adjusting densities; the self-assembly process of these membranes is a lay-lay molecular self-assembly of polyelectrolytes with contrary electric charges. The process is thermopositive and there are blue-shifts of covalent bond in FT-IR spectrums after self-assembling.In a word, these different types of the derivatives of chitosan and poly(lactic acid), despite there are different molecular structures, all can do ordered gather and self-assemble automatically at a special condition. The forces of self-assembly include hydrogen bond, hydrophobic-lipophilic interaction, static electricity interaction, and et al. The images of the ordered aggregates differ from one another attributing to the type of polymer molecules and solvent, and et al. At same time, the ordered aggregates are biodegradable and have a fast biodegradation rate.