The scientific focus in Bioelectrics is the interaction of pulsed electric fields (PEF) with biological cells and tissue. In general, for PEF exposure, the biological material is suspended in aqueous solution between two electrodes, which are connected to a high voltage pulse generator.
Basically, the effect of PEFs on biological cells and tissue can be subdivided into two regimes:
For slowly rising and low-amplitude field pulses, only the plasma-membrane of the cells, which can be considered as an electrical isolator, is affected. The electric field in the cell interior is zero. Due to the external electric field, the cell´s plasma-membrane is charged. Elevated transmembrane voltages cause a structural reorganization of membrane constituents, i.e. the phospolipid molecules, which results in an increase of membrane permeability by formation of aqueous pores. This process is called electroporation. It is applied for exchanging water-soluble substances across the cell membrane.
When applying fast-rising and high amplitude electric field pulses, large displacement currents across the membrane can access the cell interior and affect intracellular structures. The resulting intracellular electric field interacts with polar molecules and charges organelle membranes. Most prominent reactions of biological cells on this so called ultra-short pulse exposure are calcium emission from intracellular stores (mitocondria) and release of apoptosis. Several nanoseconds into the pulse, the plasma-membrane responds by generation of a large number of very small and subsequently fast resealing pores.
R&D topics:Pulsed electric field treatment of microalgae biomass for extraction of valuable intracellular substances
Microalgae biomass is a promising alternative to agriculturally produced biomass for energetic use. The yield of microalgae biomass per footprint and year is at least twice and the lipid content 10 times higher.
This activity in the framework of the Helmholtz programme „Renewable Energies“ focuses on downstream processing of microalgae biomass for energetic use. Key objective is to improve extraction of intracellular lipids and other valuable substances from microalgae by PEF treatment. The work includes photobioreactor cultivation of microalgae at IHM as feedstock for experiments and implementation of fluorescence-optical and biochemical diagnostics for lipid and cell content monitoring.
This work is embedded into the KIT-microalgae-platform (link auf C. Posten site)
Investigations so far demonstrated that yield of lipids and water-soluble substances can be increased by PEF treatment by a factor of 2-4. Current work deals with parameter studies on treatment energy optimization and with the implementation of pilot processes for biomass treatment up to a mass-flow of some 100 litres per hour.Stimulation of cellular stress responses by sublethal pulsed electric fields
In general, a pulsed electric field treatment for extraction purposes causes a lethal degree of membrane permeabilization.
By shortening the pulse duration and treatment energy cells and organisms respond with stress reactions, like Calcium emission or cytoskeleton reorganization. most probable, membrane perturbations or field impact on polar molecules are responsible for these effects.
Basic effects of ultra-short nanosecond pulse exposure on cytoskeleton are subject of collaborative research with Botanical Institute I. (link auf peter nick seite)
Nanosecond time resolved measurement of the membrane charging
Besides intracellular single cell reactions, sublethal PEFs can stimulate growth of organisms. A pulsed electric field treatment of seedlings of Arabidopsis thaliana with 10 ns pulses resulted in increased leaf area growth of more than a factor of 2. Current work focuses on basic mechanisms for growth stimulation and on possible applications to proliferate growth of single cell suspensions.
Membrane charging is a necessary condition for subsequent membrane permeabilization. The time constant of membrane charging is on the order of 100 ns demanding for a diagnostics like pulsed laser fluorescence microscopy (PLFM) exhibiting a temporal resolution of 5 ns.
For measurement the cell membrane is stained by a voltage sensitive dye. The cells are located in a micro electrode arrangement and illuminated by a 5 ns long laser pulse in the course of the applied electric field pulse. Membrane voltage changes due to membrane charging are indicated by intensity changes of the fluorescent light emitted from the dye molecules. Current basic research deals with charging properties during the first hundred of nanoseconds of a pulse and with molecular dynamics of voltage sensitive dyes.