Electrical Coupling Between Cells and Graphene Transistors

In this work, both experimental data and a model are presented on the coupling between living cells and graphene solution‐gated field‐effect transistors. Modified HEK 293 cells are successfully cultured on graphene transistor arrays and electrically accessed by the patch clamp method. Transistor recordings are presented, showing the opening and closing of voltage‐gated potassium ion channels in the cell membrane. The experimental data is compared with the broadly used standard point‐contact model. The ion dynamics in the cell–transistor cleft are analyzed to account for the differences between the model and the experimental data revealing a significant increase in the total ionic strength in the cleft. In order to describe the influence of the ion concentration resulting from the cell activity, the ion‐sensitivity of graphene solution‐gated field‐effect transistors is investigated experimentally and modelled by considering the screening effect of the ions on the surface potential at the graphene/electrolyte interface. Finally, the model of the cell–transistor coupling is extended to include the effect of ion accumulation and ion sensitivity. The experimental data shows a very good agreement with this extended model, emphasizing the importance of considering the ion concentration in the cleft to properly understand the cell‐transistor coupling.     

Solar-Assisted District Heating Plants: Status of the German Programme Solarthermie-2000

Within the 10 year Programme “Solarthermie-2000” of the German Federal Ministry for Economics and Technology (BMWi), large-scale solar-assisted heating plants have been funded in Germany. Long-term monitoring programmes are carried out to prove the technical and economic feasibility of various solar system concepts with and without seasonal storage. The paper presents a summary and review of the present status and results of the activities in the Programme. Long-term monitoring programmes have shown that the design data of the solar plants can be achieved if realistic assumptions are made. The main obstacle for the implementation of the concepts on a broader scale without public subsidies is the high investment costs of the solar systems. The main goal of the Programme is the further improvement of the cost-effectiveness of the solar concepts.     

RF-induced heating of interventional devices at 23.66 MHz

Objective

Low-field MRI systems are expected to cause less RF heating in conventional interventional devices due to lower Larmor frequency. We systematically evaluate RF-induced heating of commonly used intravascular devices at the Larmor frequency of a 0.55 T system (23.66 MHz) with a focus on the effect of patient size, target organ, and device position on maximum temperature rise.

Materials and methods

To assess RF-induced heating, high-resolution measurements of the electric field, temperature, and transfer function were combined. Realistic device trajectories were derived from vascular models to evaluate the variation of the temperature increase as a function of the device trajectory. At a low-field RF test bench, the effects of patient size and positioning, target organ (liver and heart) and body coil type were measured for six commonly used interventional devices (two guidewires, two catheters, an applicator and a biopsy needle).

Results

Electric field mapping shows that the hotspots are not necessarily localized at the device tip. Of all procedures, the liver catheterizations showed the lowest heating, and a modification of the transmit body coil could further reduce the temperature increase. For common commercial needles no significant heating was measured at the needle tip. Comparable local SAR values were found in the temperature measurements and the TF-based calculations.

Conclusion

At low fields, interventions with shorter insertion lengths such as hepatic catheterizations result in less RF-induced heating than coronary interventions. The maximum temperature increase depends on body coil design.