Preparation And Characterization Of Polyelectrolyte Composite Microspheres Based On Chitosan

In recent years,the preparation of inorganic/organic composite microspheres has gained much interest for its unique properties combined the robust properties from polymers and special characters from inorganic nanoparticles.Representatively, functional composite microspheres have great potentials in magnetic separation and enzyme immobilization,environmental remediation,biomagnetics,therapeutic and diagnostic biomedical fields.In practice,for further improving the adaptability of magnetic microspheres in the physical environment and decreasing the side effect of composite materials to human,the design and preparation of biocompatible and biodegradable functional composite microspheres become more important.In this context,based on the research on the electrostatic interaction between polyelectrolyte and inorganic nanoparticles,various of composite assembly and composite microsphere were prepared with various functions.These factors which influenced the formation of the composite structure have been investigated,and the mechanism of the interaction between polyelectrolyte and nanopariticles has been further discussed.The results of each part are listed as follows:(1)CdTe quantum dots stabilized by Mercaptoproponic acid(MPA) were prepared by hydrothermal method.Through the electrostatic interaction between the amino groups from chitosan and the carboxyl groups from MPA,CdTe/CS composite assemblies were formed.During the increased amount of CdTe QDs,the morphology of composite assembly has showed the transition from no assembly to irregular assembly,and then the flocculation occurred.Correspondingly,the CdTe/CS composite assemblies were easily formed between large-sized CdTe QDs and CS.In the further research,EDC was introduced into the CdTe/CS system.By activating the carboxyl groups of MPA,the condensation occurred between the amino groups and carboxyl groups.And the spherical assemblies were formed with stable photo luminescent property.(2)A simple approach was presented to prepare functional inorganic/organic composite microspheres in which the inorganic nanoparticles were encapsulated into the polyelectrolyte complexes between chitosan(CS) and poly(aspartic acid) sodium salt(PAsp).The magnetic microspheres were prepared via electrostatic interaction between the citrate groups stabilizing Fe₃O₄ nanoparticles and the amino groups of CS. Being taken as a kind of special polyelectrolyte with high molecular weight,the inorganic nanoparticles presented strong interaction with polyelectrolyte.By tuning the unit molar ratio of the opposite charged polyelectrolyte and the amount of Fe₃O₄ nanoparticles,the structure of the composite microspheres could be controlled,and then the approach was extended to prepare luminescent-magnetic CS-PAsp microspheres by encapsulated Fe₃O₄ nanoparticles and CdTe quantum dots synchronously,which exhibited superior pH stability and remained strong photoluminescence properties after crosslinking.(3)The magnetic CS-PAsp microspheres were used to encapsulate hydrophilic drugs(5-Fu and DOX),the drug-loaded composite microspheres showed favorable morphology with the relative lower encapsulation efficiency and loading capability. That was attributed to the strong interaction between inorganic nanoparticles and CS, which occupied most interspaces between polyelectrolyte.Thus,the drug molecular was hard to adsorb onto the CS chains.The magnetic CS-PAsp microspheres also showed lower cyctoxcity,and exhibited the favorable capability for complex with plasmid DNA with preferably efficiency,which is important for the potential application as targeted gene vector.