Synthesis and characterisation of organo-silica layers for the surface modification of chemical robots
The main aim of this thesis was to synthesise the “bodies” of artificial cell like particles (“chemical robots”) for the application as controlled-release and targeted delivery systems. The particles are composed of alginate gel core with encapsulated internal compartments (magnetic iron oxide nanoparticles and liposomes) and a porous silica (SiO2) shell.
The silica coated alginate macroparticles (1-2 mm) and microparticles (40-90 µm) were prepared by needle dropping and inkjet technology, respectively. The calcium alginate particles are widely used for the encapsulation and immobilization of various bioactives. However they are very porous and sensitive to harsh chemical and mechanical environments. To overcome the limitation of the alginate, a silica shell has been formed around the particles by a sol-gel process. The morphology, transport properties and encapsulation of internal compartments such as iron oxide nanoparticles and liposomes in the composite particles were investigated. Particles with and without the silica shell were always compared.
The silica shell was found to act as an efficient semi-permeable barrier that allows the diffusion of small and medium-sized molecules (vitamin B12, small enzyme lysozyme) but rejects larger objects such as larger proteins (BSA, ovalbumin) or liposomes. The benefits of the silica shell for the mechanical and chemical stability of composite alginate cores were also investigated. It has been found that the silica coating can provide a protection against chemical and mechanical stresses and does not negatively influence the stability of immobilized liposomes or the ability of composite particles to perform “on demand” release triggered by radiofrequency signal. An alternative method for silica coating of alginate particles was also studied. Specifically, the formation, stability and effective transport properties of a coating made by electrostatic Layer-by-Layer (LbL) assembly of silica nanoparticles on the surface of alginate hydrogel macroparticles were investigated. Finally the microparticle adhesion to cells in vitro was investigated. The interaction between magnetic microbeads modified by a specific antibody and live cells of the prostate carcinoma was studied.
It can be concluded that while the alginate hydrogel plays a role as the matrix for storage of internal components of chemical robots (magnetic iron oxide nanoparticles, enzymes and liposomes), the silica shell improved their functionality in three aspects. The silica shell provides a protection and improves mechanical and chemical stability of the chemical robots; it also acts as a diffusion barrier; finally, the ability of silica surface to be modified by antibodies makes it possible to achieve biologically specific adhesion properties of the chemical robots.