In-situ Synthesis And Properties Of Polyvinyl Alcohol/Silica Composite Microspheres

Recently,sol-gel-derived silica xerogel has drawn extensive attentions from biomaterial researchers because of its good biocompatibility,biodegradability and biological activity.When used as a bone-repairing material,silica xerogel is favorable for the aggregation of calci?m and phosphate ions and the subsequent formation of bone-like hydroxyapatite layers.Polyvinyl alcohol?PVA?is one of the widely used synthetic polymers in various biomedical applications including bone tissue,articular cartilage,artificial cornea,drug delivery and other biological areas due to its good biocompatibility,biodegradability,inherent nontoxicity and desirable shape-forming ability.If we can combine silica xerogels with PVA,it is expected to obtain a multifunctional and highly efficient biomaterial.In this thesis,the PVA/SiO₂ composite microspheres were prepared in the Span 80-containing and Span 80-free water-in-oil systems by using an in-situ synthesis method.The influence of experimental parameters on the preparation of composite microspheres was discussed,and then the best experimental scheme for the preparation of composite microspheres was determined.The bioactivity,drug loading and release characteristics of the PVA/SiO₂ composite microspheres were evaluated.Based on the above research,The PVA/SiO₂/HA composite microspheres were successfully prepared in the micro-emulsion system,and their composition and morphology were preliminarily characterized.The main results of this paper are listed as follows:?1?The PVA/SiO₂ composite microspheres with a theoretical mass ratio of 4/1 were successfully prepared in a surfactant-free water-in-oil system.The results showed that the composite microspheres have a regular spherical shape,a high dispersity and a homogenous microstructure.Their average particle diameter was determined as 58.2 ?m.The inorganic phase of the composite microspheres was identified as amorphous SiO₂ with a condensation degree of about 62.4%,and its actual content was in close agreement with the theoretical value.The PVA/SiO₂ composite microspheres showed the good biological activity after being immersed in the simulated body fluid?1.5 SBF?.Therefore,the as-obtained PVA/SiO₂ composite microspheres is very promising to be used in bone tissue engineering as a bone repair material.?2?The PVA/SiO₂ composite microspheres with different SiO₂ contents were prepared in the Span 80-containing water-in-oil micro-emulsion system.The experimental results showed that the particle size of the PVA/SiO₂ composite microspheres is mainly ranged from 5 to 15 ?m,and their average particle size is about 11.6 ?m.The influence of different experimental parameters on the morphology of the PVA/SiO₂ composite microspheres was studied.It was found that when the concentration of PVA aqueous solution is 5%,the emulsification temperature is 50oC,the amount of surfactant is 2 g,the amount of catalyst HCl?1M?is 1.5 m L,and the amount of crosslinking agent GA?25%?is 0.5 m L,we can obtain the PVA/SiO₂ composite microspheres with a regular spherical shape,a high dispersity,small particle size and a homogenous microstructure.?3?The drug loading and release properties of the PVA/SiO₂ composite microspheres which were gained in a Span 80-containing micro-emulsion system were studied by using vancomycin hydrochloride as a model drug.The results showed that the encapsulation efficiency of the PVA/SiO₂ composite microspheres with 20% and 40% SiO₂ were 43.8% and 53.7% respectively,and the c?mulative drug release rates were 65.4% and 71.8% respectively.The drug release rate of the PVA/SiO₂ composite microspheres was significantly higher than that of pure PVA microspheres,and showed a sustained drug release performance.Therefore,the PVA/SiO₂ composite microspheres will desirably serve as a good drug carrier material in future.?4?In the Span 80-containing micro-emulsion system,the PVA/SiO₂/HA composite microspheres with a theoretical mass ratio of 7/2/1 were prepared using the best experimental parameters for preparing the PVA/SiO₂ composite microspheres.The resultant PVA/SiO₂/HA composite microspheres exhibited a regular spherical shape,a high dispersity and a homogenous microstructure.Their average particle diameter was determined as 10.8 ?m.