Formation And Characterization Of Natural Polysaccharide Hollow Nanocapsules Via Template Layer-by-Layer Self-assembly

From the whole organism to a tiny cell, each compartment in human body can beconsidered as a reactor or a container. Synthetic hollow capsules, similar to a tiny cell,permit the study of the influence of spatial confinement on chemical reactions andprovide an opportunity to perform chemical reactions in “exotic” environments, haveattracted much attention recently. An important feature of mirco-and nanocapsules isspatial control of individual reaction steps in various complex reaction cascades. Bothcarrageenan and chitosan are similar to Glycosaminoglycan （GAGs） in structurewhich is found largely in extracellular matrix （ECM）. From the biomimeticperspective, the nanoreactors or nanocontainers with carrageenan and chitosan as thecyst wall will have a perspective application in biomedicine.With natural polysaccharides carrageenan （Car） and chitosan （Cs） as thepolyanion and polycation respectively, multilayer hollow nanocapsules have beenfabricated via sequential layer-by-layer （LbL） electrostatic self-assembly from thesacrificed templates nanospheres （SiO₂-NH₂） with a diameter of100nm. TheLbL-assemebly SiO₂（Car/Cs）_xnanoshperes were treated with HF to etch SiO₂cores.The diameter of final （Car/Cs）_xnanocapsules were120nm.In the following research，we investigate the effect of reactant amount and makesure that the optimum amino-modification condition when APTES/TEOS is0.0238mol/mol. The optimum condition for LbL assembly is pH=3.41. The LbL assemblyprocess with the polysaccharides on SiO₂-NH₂core was followed by ζ-potential andsize analysis. The fabrication of （Car/Cs）_xnanocapsules and the removing of theSiO₂-NH₂core templates were confirmed by TG and EDS analysis. The morphology of SiO₂（Car/Cs）_xnanospheres and （Car/Cs）_xnanocapsules were observed by TEManalysis. The size analysis of （Car/Cs）_xnanocapsules indicated that the cyst wallthickness and cavity volume of the nanocapsules are pH and ionic strength dualresponsive. The average hydrodynamic diameters of the hollow nanocapsulesincreased by900nm with the increase in the salt concentration from0.01to0.20mol/L. With the increase in pH value of the dispersion media from2to12, thediameter of the （Car/Cs）5Car nanocapsules enhanced from344to757nm，whichsuggested that the interspace between chitosan and carrageenan will be more broaden（from18nm to53nm）. Finally, SiO₂（Car/Cs）_xwas used as a microreactor andhydroxyapatite （HA） was deposited by alternately deposition method onSiO₂（Car/Cs）_xnanospheres.Due to the biocompatibility of the natural polysaccharides carrageenan andchitosan and the responsiveness of nanocapsules to pH and ionic strength, the（Car/Cs）_xmultilayer nanocapsules are expected to be used as nanoreactors ornanocontainers to control the synthesis, encapsulation and releasing behaviors ofbioactive molecules.