Pavel Kovačík – Diploma thesis summary

Synthesis and characterisation of hollow silica microparticles for targeted delivery systems

The aim of this work is to fabricate hard porous micro-particles based on silica (SiO2) to
create bodies of so-called chemical robots. Porous SiO2 shells or micro-skeletons are
ubiquitous in nature – in particular in marine microorganisms (diatoms). It is envisaged that a
chemical robot will be a simple fully synthetic “unicellular organism”, with main attributes
similar to those of living organisms, such as the ability to move in its environment, exchange
matter with its surroundings or accumulate or excrete reaction products, except reproduction
and evolution. The size range of the micro-particle entities will be in order of 10-100 μm.
There are several methods how these particles can be prepared such as precipitation of silica
around a template. This method was used for creating porous micro-particles in this work.
The procedure based on the Stöber method was used for preparing hollow silica microparticles.
The hollow core was obtained by a sol – gel process of tetraethyl orthosilicate
(TEOS) in non-ionic W/O emulsion containing kerosene, sorbitan monooleate (Span80) and
water. The second way was to use liquid template (droplets of octylamine) which was
subsequently removed to create hollow core. The experimental conditions affecting the microparticles
properties (size, thickness, permeability) were investigated in order to precisely
control characteristics of the chemical robot’s body. We will show that particle size can be
systematically varied in the range of 10 – 100 μm. The particle size distribution was measured
by the laser scattering method and the microstructure of the porous particles was visualized by
scanning electron microscopy (SEM) and confocal microscopy. The permeability of the silica
shell was characterized indirectly by measuring the uptake/release kinetics of a model
substance (methylene blue) using UV/VIS spectrophotometry. The porosity of silica shell was
characterized by BET analysis and the density of silica shell was measured by the helium
pycnometry.