Study Of Synthesis Of Amphiphilic Polymer And Its Self-assemble Behavior And Surface Modification Of Nanoparticles

Polysaccharides were hydrophobically modified by cholesterol. Its self-assemblebehavior in aqueous solution and its surface modification of PLA nanoparticles werestudied.Amphiphilic polymer composed of dextran and cholesterol was synthesized by reactingof cholesterol succinic acyl chlorine with the hydrocyl groups on dextran main-chain. Theresultants were characterized by FT-IR and 1H NMR, the results show thatdextran-cholesterol conjugate with different degree of substitute can be obtained. The higherthe degree of substitute, the lower the critical aggregate concentration was comfirmed by theresults of Fluorescence spectrum and viscosity measurement. TEM and PCS resultsdemonstrated that the aggregates were spherical and the diameter was mainly within100-300nm.Dextran was oxidated by Sodium Periodate to investigate the influence of main-chainstructure on the self-aggregate, and the higher the degree of oxidation , the lower the criticalaggregate concentration investigated by fluorescence spectrum and viscosity measurement.The results of TEM and PCS show the decrease in diameter of aggregates.The chitosan was hydrophobically modified by cholesterol-succinis ester, usinghydrophilic EDC. The results of 1H NMR show that cholesterol conjugate with main-chainof chitosan and the degree of substitute was 4.63/100 Ugl. The influence of differentpreparation methods on the self-aggregate was measured by fluorescence spectrum andviscosity measurement. It is confirmed that frozen-drying process would lower the criticalaggregate concentration of resultants and increase the average diameter of aggregates.Based on the above investigation, the function of surface modification with amphiphilicpolymer was also studied. The results of XPS and Zeta potential show that the content ofcholesterol modified chitosan on the surface of PLA nanospheres is direct proportion to theconcentration of cholesterol modified chitosan in the water, though the content is lower thanprevious expectation. As shown by TEM and PCS results, diameter of PLA nanoparticaleswith surface modification of cholesterol modified chitosan increases with the decrease ofcholesterol modified chitosan in the water. The structure of self-aggregate of amphiphilicpolymer in water would influence the effect of surface modification of PLA nanoparticles.PLA nanoparticles surface modified by cholesterol modified dextran have obvious core-shellstructure with nanoprecipitation method, as proved by TEM and PCS. The diameter of PLAnanoparticles surface modified by cholesterol modified dextran increases as theconcentration of cholesterol modified dextran decrease and the concentration of PLAincrease.