Transplantation of mesenchymal stem cells (MSCs) derived from adult bone marrow has been proposed as a potential therapeutic approach for post-infarction left ventricular (LV) dysfunction. However, age-related functional decline of stem cells has restricted their clinical benefits after transplantation into the infarcted myocardium. The limitations imposed on patient cells could be addressed by genetic modification of stem cells. This study was designed to improve our understanding of genetic modification of human bone marrow derived mesenchymal stem cells (hMSCs) by polyethylenimine (PEI, branched with Mw 25 kD), one of non-viral vectors that show promise in stem cell genetic modification, in the context of cardiac regeneration for patients. We optimized the PEI-mediated reporter gene transfection into hMSCs, evaluated whether transfection efficiency is associated with gender or age of the cell donors, analysed the influence of cell cycle on transfection and investigated the transfer of therapeutic vascular endothelial growth factor gene (VEGF). hMSCs were isolated from patients with cardiovascular disease aged from 41 to 85 years. Optimization of gene delivery to hMSCs was carried out based on the particle size of the PEI/DNA complexes, N/P ratio of complexes, DNA dosage and cell viability. The highest efficiency with the cell viability near 60% was achieved at N/P ratio 2 and 6.0 μg DNA/cm2. The average transfection efficiency for all tested samples, middle-age group (<65 years), old-age group (>65 years), female group and male group was 4.32%, 3.85%, 4.52%, 4.14% and 4.38%, respectively. The transfection efficiency did not show any correlation either with the age or the gender of the donors. Statistically, there were two subpopulations in the donors; and transfection efficiency in each subpopulation was linearly related to the cell percentage in S phase. No significant phenotypic differences were observed between these two subpopulations. Furthermore, PEI-mediated therapeutic gene VEGF transfer could significantly enhance the expression level.
Efficient magnetic microactuators require a deposition and patterning of a permanent magnetic material. A material that can be deposited in the range of up to a couple of 10μm is sputtered SmCo. For the fabrication of magnetic microactuators, alternative substrate materials besides silicon are of great interest. Therefore, alumina-ceramic as well as B270-glass substrates were included in the investigation. A maximum energy product of 90kJ∕m3 was achieved for rather thick layers of 30μm deposited on glass or ceramic substrates. The latter substrates were found to be suitable for the deposition of SmCo layers up to a thickness of 50μm. Furthermore, the SmCo exhibits isotropic magnetic properties, thus a magnetization of the permanent magnetic layer can be performed in plane as well as perpendicular to the film plane. For the patterning of these thick SmCo layers ion beam etching and wet chemical etching were examined. For both methods, the suitability of patterning thick SmCo layers could be demonstrated. For the integration of a SmCo permanent magnet in a magnetic microactuator, the two technologies for deposition and patterning of the SmCo layer had to be combined. Two linear microactuators are presented utilizing different integration methods of the SmCo component as well as direction of magnetization.
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