Hermann Schirra

Presentation of a new magnetic field therapy system for the treatment of human solid tumors with magnetic fluid hyperthermia

Magnetic fluid hyperthermia (MFH) selectively heats up tissue by coupling alternating current (AC) magnetic fields to targeted magnetic fluids, so that boundaries of different conductive tissues do not interfere with power absorption. In this paper, a new AC magnetic field therapy system for clinical application of MFH is described. With optimized magnetic nanoparticle preparations it will be used for target-specific glioblastoma and prostate carcinoma therapy.

Endocytosis of dextran and silan-coated magnetite nanoparticles and the effect of intracellular hyperthermia on human mammary carcinoma cells in vitro

Abstract To obtain more evidence for intracellular magnetic fluid hyperthermia (MFH), endocytosis and hyperthermia efficacy of silan and dextran magnetite was investigated. Differential endocytosis was observed in dependence of nanoparticle and cell type. Clonogenic survival was 3-fold lower after MFH versus waterbath hyperthermia. The selective “remote inactivation” of cancer cells by an AC magnetic field has been demonstrated in vitro.

Silica nanoparticles modified with aminosilanes as carriers for plasmid DNA

We synthesised silica nanoparticles (SiNP) with covalently linked cationic surface modifications and demonstrated their ability to electrostatically bind, condense and protect plasmid DNA. These particles might be utilised as DNA carriers for gene delivery. All nanoparticles were sized between 10 and 100 nm and displayed surface charge potentials from +7 to +31 mV at pH 7.4. They were produced by modification of commercially available (IPAST) or in-house synthesised silica particles with either N-(2-aminoethyl)-3-aminopropyltrimethoxysilane or N-(6-aminohexyl)-3-aminopropyltrimethoxysilane. All particles formed complexes with pCMVbeta plasmid DNA as evidenced by ratio dependent retardation of DNA in the agarose gel and co-sedimentation of soluble DNA with nanoparticles. High salt and alkaline pH did inhibit complex formation. Absorption onto the particles also decreased the hydrodynamic dimensions of plasmid DNA as shown by photon correlation spectroscopy. Complexes formed in water at a w/w ratio of Si26H:DNA (pCMVbeta) of 300 were smallest with a mean hydrodynamic diameter of 83 nm. For effective condensation a w/w ratio of Si26H:DNA of 30 was sufficient. Further, the absorbed DNA was protected from enzymatic degradation by DNase I.

Aqueous wet coatings for transparent plastic glazing

Abstract Electrostatically stabilized particulate sols, e.g. aqueous silica or alumina sols, have been surface-modified to reduce the particle/particle interaction and to obtain electrosterically stabilized sols. Epoxy functionalized alkoxysilanes were used as surface modifiers for alumina, silica or zirconia particles to achieve water dispersible nanoparticulate coating materials. After evaporating the organic solvent (produced by hydrolysis and condensation) aqueous sol-gel coatings have been prepared with organic solvent contents below 5%. The storage stability of these materials has been investigated by 29 Si-NMR. An amino functionalized alkoxysilane was used as condensation catalyst and the nanocomposite material was thermally cured at 130°C after flow or spray coating on pretreated polycarbonate substrates. The coatings show excellent adhesion which was shown by cross cut and tape test. After 1000 cycles Taber abrasion test (CS-10F, 500 g, DIN 52347) losses of transmittance due to scattering of 2–6% were achieved with a coating thickness of about 5 μm.

Organic-Inorganic Hybrid Materials Processing And Applications

Hybrid materials as inorganic-organic nanostructured composites require tailored surface chemistry in order to obtain a homogeneous distribution of the nanoparticles in the matrix. For this reason, nanoparticles with organic functions have been synthesized, first, to provide the desired ae-potential at a given pH value, second, to avoid irreversible agglomeration due to the spacing effect, and third, to provide the appropriate surface chemistry. I could be shown that using this approach, it is possible to switch the ζ-potential of SiO2 nanoparticles from a negative to a positive potential at neutral and to bind DNA fragments to the particles for an effective transfection into cells. Other examples show that nanoparticles (TiO2, SiO2) coated with epoxy and methacryloxy groupings can be used as coating sol for the fabrication of thin films with green densities up to 67% by volume only by photochemical crosslinking of the polymerizable groupings. Using this approach, interference layers have been fabricated on transparent plastics. In soft matrices, these particles permit to establish appropriate ζ-potentials and in electric fields by electrophoresis, it was possible to up-concentrate them to form gradient index optics. The investigations show that surface chemistry-tailored nanoparticles are a useful tool for the fabrication of nanocomposite hybrids.

Aqueous sol-gel derived nanocomposite coating materials

Sol-gel reactions, in general, have to take place in organic solvents in order to control the hydrolysis and condensation reaction. This leads to drawbacks in applications, since the organic solvent vapor concnetration has to be controlled for example in ocoating applications for environmental, health or security reasons. For this reason, a reaction route has been developed to produce coating precursors stable against water as solvent. To achieve this, conventional electrostatically stabilized sols obtained either by hydrolysis and condensation or commercially availabe sols (e.g. SiO2 sols) have been surface modified to reduce the particle-to-particle interaction and electrosterically stabilized precursors compatible to water have been obtained. By use of alkoxy silanes as surface modifiers, water-dispersable nanoparticulate liquid coating systems have been prepared, for example, with boehmite, SiO2 or TiO2 as nanoparticles to be crosslinked after coating thermally by inorganic condensation and organic condensation or polymerization reactions. Thus, aqueous sol-gel coating systems have been prepared with EtOH contents below 5%. In the paper, the basic reaction as well as material properties will be discussed.