The Preparation Of Biocompatible Microgels And Its Structure And Properties

In order to improve the treatment efficiency of disease and the quality of life, more and more biocompatible materials have been developed, studied and applied. Especially, for the treatment of cancer and other disorders, targeting and controlled release of drug earriers play a significant supporting role. Microgels have excellent dispersion stability and could respond to certain external stimuli and entrap the drug molecules with their three-dimensional cross-linked network, which could be released in a particular environment. For example, poly(N-isopropylacrylamide) (PNIPAm) microgels have been intensively investigated as a drug carriers in many reports. However, the physiological toxicity of NIPAm severely limits the real biological applications of PNIPAm microgels.In this thesis, biocompatible monomers N-vinylpyrrolidone (NVP) and N-vinylcaprolactam (VCL) were selected as the main monomers in order to prepare biocompatible microgel. The morphologies, structures and properties as well as their potential applications as drug carriers were systematically investigated by combining techniques. The poly(N-vinylpyrrolidone) microgel (PNVP microgels) were prepared by using surfactant free emulsion polymerization (SFEP) with NVP as the monomer and ethylene glycol dimethacrylate (EGDMA) as the crosslinker. The PNVP microgels had hydrodynamic diameters of about 200 nm with a narrow distribution. The results of dynamic and static light scattering (DLS & SLS) indicated that the PNVP microgels had relatively dense internal structures. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that the PNVP microgels had rough surface morphologies. Cytotoxicity and phagocytosis experiments showed that the PNVP microgels were biocompatible and could be swallowed by living cells. The PNVP microgels could be used to load and release the model drugs isoniazid and 5-fluorouracil. The experimental results indicated that the PNVP microgels had better controlled release properties for hydrophilic drugs isoniazid.Poly(N-vinyl caprolactam) microgel is a kind of quaternary crosslinked biocompatible microgel, which was prepared by SFEP with VCL as the main monomer,4-vinylpyridine (4VP) as the quaternizable comonomer and 1,6-dibromo hexane (6Br) as the quaternary crosslinking agent. Furthermore, hydrophilic NVP monomer was also introduced into the microgels in order to adjust the phase transition temperature (VPTT) of the resultant microgels to be close to the physiological temperature. The obtained PVCL microgels had spherical shape with sizes of about 200-400 run and inhomogeneous network structures as revealed by DLS & SLS. The results of cytotoxicity and hemolysis indicated that these series of PVCL microgels had good biocompatibility. Because the PVCL microgels contained quaternized nitrogen atoms, the microgels also exhibited certain antibacterial capability. These PVCL microgels could entrap and release model hydrophilic drug of sodium salicylate by ion exchange with a high encapsulation efficiency and a low release ratio of drug.