Generation of cell processes in a high frequency electric field

Electrical Stimulation of Human Mesenchymal Stem Cells on Conductive Substrates Promotes Neural Priming

Electrical stimulation (ES) within a conductive scaffold is potentially beneficial in encouraging the differentiation of stem cells toward a neuronal phenotype. To improve stem cell-based regenerative therapies, it is essential to use electroconductive scaffolds with appropriate stiffnesses to regulate the amount and location of ES delivery. Herein, biodegradable electroconductive substrates with different stiffnesses are fabricated from chitosan-grafted-polyaniline (CS-g-PANI) copolymers. Human mesenchymal stem cells (hMSCs) cultured on soft conductive scaffolds show a morphological change with significant filopodial elongation after electrically stimulated culture along with upregulation of neuronal markers and downregulation of glial markers. Compared to stiff conductive scaffolds and non-conductive CS scaffolds, soft conductive CS-g-PANI scaffolds promote increased expression of microtubule-associated protein 2 (MAP2) and neurofilament heavy chain (NF-H) after application of ES. At the same time, there is a decrease in the expression of the glial markers glial fibrillary acidic protein (GFAP) and vimentin after ES. Furthermore, the elevation of intracellular calcium [Ca2+ ] during spontaneous, cell-generated Ca2+ transients further suggests that electric field stimulation of hMSCs cultured on conductive substrates can promote a neural-like phenotype. The findings suggest that the combination of the soft conductive CS-g-PANI substrate and ES is a promising new tool for enhancing neuronal tissue engineering outcomes.

Cell manipulation and cultivation under a.c. electric field influence in highly conductive culture media

Extreme miniaturisation of electrodes enabled us to apply high-frequency electric fields (between 100 kHz and several hundred MHz) of field strengths up to 50 kV/m into cell suspensions of high conductivity (several S/m), such as original cell culture media. The active electrode areas were additionally decreased and modified by insulating the terminals and/or coating of the electrodes with thin dielectric layers. Micro scaled electrode structures were fabricated on glass or silicon wafers in semiconductor technology. It could theoretically and experimentally be shown that cells exhibit exclusively negative dielectrophoresis if suspended in highly conductive media. Therefore, they can be repulsed from surfaces by appropriate arrangements of electrodes and easily be manipulated in free solution. Adherently growing animal cells, like mouse fibroblasts (3T3, L929), were cultivated in Dulbecco's Modification of Eagle's Medium (DMEM) or RPMI 1640 under permanent field application (frequency: 10 MHz, field strength: 50-100 kV/m).

Radio-frequency microtools for particle and liver cell manipulation

Single particles can be manipulated by applying high frequencies to ultramicro electrode arrays fabricated on planar structures. Heat production can be reduced to the extent that intense electric fields can be applied even to unmodified cell culture media. Animal cells grow normally in the high field (up to 100 kV/m) between such continuously energized multielectrodes. As with laser tweezers [1-3], this technique can capture particles and cells in field traps, generate linear movement, and permit cell cultivation. It can also produce micropatterns of pH gradients, field-cast objects, and control cell adhesion. These microtools may be combined to develop cell separators, microsensors, and controlled-biocompatibility surfaces.

Experimental evidence for the involvement of the cytoskeleton in mammalian cell electropermeabilization

Chinese hamster ovary (CHO) cells and human erythrocytes were pulsed by using square-wave electric-field pulses. This treatment induced their permeabilization. This phenomenon appears to be a three-step process of creation, expansion and annihilation of permeated structures. Altering the cell cytoskeleton, either with drugs, such as colchicine, known to depolymerise the microtubules in CHO cells, or by high temperature shock to affect the spectrin-actin network in erythrocytes, induced no modification on the first two steps of the electropermeabilization process, but was associated with a dramatic decrease in the stability of the electro-induced permeated structures. These experimental observations support the hypothesis of an implication of cytoskeleton in electropermeabilization in agreement with thermodynamic conclusions.

Mechanism of cell protrusion formation in electrical field: the role of actin

An intense alternating current electrical field that imposes membrane-applied force on the cell surface can induce formation of cell protrusions (Popov, S.V. and Margolis, L.B. (1988) J. Cell Sci. 90, 379-389). This technique has been used to investigate the role of actin in the cell protrusion formation. Platinum replicas of the cytoskeleton were prepared to characterize the organization of the cytoskeleton in external force-induced protrusions. Bundles of microfilaments were found in the processes. A specific inhibitor of actin polymerization, cytochalasin B, as well as inhibitors of ATP synthesis (sodium azide and carbonyl m-chlorophenylhydrazone) did not change the morphology of electrical field-generated protrusions, revealed by scanning electron microscopy. However, organization of the cytoskeleton inside the processes changed drastically using these inhibitors. The results of these experiments demonstrate that (i) Membrane-applied force is sufficient to produce native-like cell protrusions, even in conditions where activity of the cytoskeleton is inhibited; (ii) Actin microfilaments can be organized into bundles directly under the action of membrane-applied force. The significance of these observations to cell protrusion formation under normal physiological conditions is discussed.

Local deformation of human red blood cells in high frequency electric field

A method of local and general deformation of single erythrocytes by external forces in high-frequency electric field is described. The method allows the avoidance of any mechanical contact of the cell with electrodes. Under the action of the forces applied human erythrocytes change their shape and produce various membrane structures: long filopodia-like processes, retraction fibers and lamella-like structures. These structures are never formed by erythrocytes under normal conditions, but are typical for fibroblasts, macrophages and epithelium cells. By the method developed the elastic properties of spicules on the membranes of echinocytes were also studied. Deformation of echinocyte in high-frequency electric field leads to the smoothing out of spicules. However, after the electric field is turned off, echinocyte restores its initial forms including the number and localization of all initial spicules on the cell surface.