Synthesis and characterization of porous carriers for controlled delivery systems
The present dissertation thesis deals with the synthesis and characterisation of spherical particles with a hollow interior and a porous silica shell. The particles should be able to encapsulate, store and after an external stimulus release an encapsulated chemical payload.
The silica particles were synthesised by a soft templating route using oil-in-water emulsion. The droplets of dispersed phase served as templates around which the silica was precipitated from the precursor tetraethyl orthosilicate. Further, the particles were modified with various materials to achieve desired properties. Modification with iron oxide nanoparticles introduced the heating ability in the presence of an external magnetic field and blocked the pores of silica shell to avoid diffusion of the encapsulated material. Modification with palm oil and poly(N-isopropylacrylamide) offered another way how to control the diffusion across the silica barrier. The size, morphology and stability of the composite particles were systematically investigated. The mass-transport properties of encapsulated chemical payload were studied and a mathematical model of diffusion from hollow particles was proposed. The external radiofrequency field was shown to be an effective trigger mechanism for remotely controlled diffusion of encapsulated material at an arbitrary on–off sequence.
In this thesis also a new approach to the preparation of hollow silica particles with a porous shell was introduced. The unicellular diatoms, which are a major group of algae, were cultivated to obtain hollow silica particles. The cultivation process, harvesting and post-treatment of harvested diatoms were investigated. The diatom shells were shown to be a promising source of silica microparticles with a highly ordered porous structure.