Synthesis of hollow SiO2 stimuli-responsive microparticles
The possibility to control the release of active substances represents one of the most important attributes of targeted drug delivery. The purpose of this thesis is to design and characterize microscopic, synthetically created particles from composite material based on silica, thermoresponsive polymer poly-N-isopropylacrylamide (PNIPAM) and magnetite nanoparticles, which could be used as a means of such delivery. All of the materials mentioned above provide the desired microparticles with unique characteristics such as endurance and hardness of silica, the ability of thermoresponsive polymers to change its volume in dependence on temperature and the possibility of induction heating as a result of the presence of magnetite nanoparticles.
Synthesis of such microparticles consists of several steps. Firstly, it is essential to prepare macroporous hollow silica microparticles using solid template method. One of the numerous advantages of silica is the wide range of the ways to modify it. This attribute was exploited in order to create silica/Fe3O4, silica/PNIPAM and finally silica/PNIPAM/Fe3O4 composite microparticles. There are few methods available to use in the synthesis of similar microparticles and in this thesis, some of them were studied in order to choose the most suitable one. Products of every process performed were characterized in terms of its composition, morphology and induction heating properties. Considering the results of these measurements, the final method for the synthesis of silica/PNIPAM/Fe3O4 composite microparticles was chosen. By regarding the intended application of the microparticles obtained, it was necessary to perform several release experiments with different model substances. These experiments were meant to prove the dependence of substance’s diffusion on its molecular weight and temperature and served as a means of acquiring the notion of diffusion characteristics of silica/PNIPAM/Fe3O4 composite microparticles.