Reversible and irreversible rotating field-induced membrane modifications

Tumor treating fields: a new frontier in cancer therapy

Tumor treating fields (TTFields) is a noninvasive, regional antimitotic treatment modality that has been approved for the treatment of recurrent glioblastoma by the U.S. FDA and has a CE mark in Europe. TTFields therapy delivers low-intensity (1-3 V/cm), intermediate-frequency (100-300 kHz), alternating electric fields to the tumor using transducer arrays placed on the skin around the region of the body containing the tumor. TTFields therapy affects metaphase, by disrupting mitotic spindle formation, and anaphase, by dielectrophoretic dislocation of intracellular constituents, resulting in apoptosis. TTFields therapy is frequency tuned to specific cancer cell types. The antimitotic effect of TTFields therapy has been demonstrated in multiple cell lines when the appropriate frequency was utilized. A phase III trial of TTFields monotherapy compared to active chemotherapy in recurrent glioblastoma patients established that TTFields therapy is associated with minimal toxicity, better quality of life, and comparable efficacy to chemotherapy. Ongoing and future trials will evaluate TTFields in newly diagnosed glioblastoma, solid tumor brain metastases, nonsmall cell lung cancer, and ovarian and pancreatic cancers.

A new microsystem for automated electrorotation measurements using laser tweezers

We have developed a new microsystem for fast, automated studies of reactions and kinetics of single cells with biochemical or pharmacological agents. A cell spins in an external rotating electric field and the frequency dependence characterises the passive dielectric properties of membrane and cytoplasm. We use a planar microelectrode chip with microchannel (easily covered with a removable slip) for the application of frequencies exceeding 250 MHz to determine cytoplasmic properties in low and high conductivity electrolyte solutions. The laser tweezers serve as a bearing system, rotation is induced by microelectrodes and rotation speed is recorded automatically. This opens up new possibilities in biotechnology, e.g. for drug screening as demonstrated by measuring the influence of ionomycin on the passive dielectric properties of T-lymphoma cells. Additionally, a possible infrared-induced long-term cell damage could be observed by electrorotation and is discussed.

Nystatin-induced changes in yeast monitored by time-resolved automated single cell electrorotation

A widespread use of electrorotation for the determination of cellular and subcellular properties has been hindered so far by the need for manual recording of cell movements. Therefore a system has been developed that allows the automatic collection of electrorotation spectra of single cells in real time. It employs a hardware based registration of image moments from which object orientation is calculated. Since the camera's video signal is processed without intermediate image storage a high data throughput of about two recordings per second could be achieved independently of image resolution. This made it possible to monitor changes in cell membrane and cytoplasm of the yeast Saccharomyces cerevisiae under the influence of the antibiotic nystatin with a temporal resolution of 3 min. Up to 20 electrorotation spectra of an individual cell could be collected in the frequency range between 1 kHz and 1 GHz. Two distinct events 7 and 75 min after addition of nystatin were observed with a fast increase in membrane permeability accompanied by a nearly simultaneous drop in cytoplasmic conductivity.

A traveling-wave micropump for aqueous solutions: comparison of 1 g and microgram results

The operation of a micro-chip-based fluid circulator based on the interaction of a high-frequency traveling wave with a thermally generated inhomogeneity in an aqueous medium is investigated. The profiles of the electric field, the thermal gradient and the driving force within the device are derived numerically, and the dependence upon applied voltage under different experimental conditions is derived. The importance of convection in the operation of the device is assessed by operating it in various orientations, as well as under microgravity, and also by investigating the reversal and turn-on characteristics. The pump showed the unexpected ability to trap microparticles present in the driven fluid.