The biocompatibility of materials used in printed circuit board technologies with respect to primary neuronal and K562 cells

Interdigitated aluminium and titanium sensors for assessing epithelial barrier functionality by electric cell-substrate impedance spectroscopy (ECIS)

Electric cell-substrate impedance spectroscopy (ECIS) enables non-invasive and continuous read-out of electrical parameters of living tissue. The aim of the current study was to investigate the performance of interdigitated sensors with 50 μm electrode width and 50 μm inter-electrode distance made of gold, aluminium, and titanium for monitoring the barrier properties of epithelial cells in tissue culture. At first, the measurement performance of the photolithographic fabricated sensors was characterized by defined reference electrolytes. The sensors were used to monitor the electrical properties of two adherent epithelial barrier tissue models: renal proximal tubular LLC-PK1 cells, representing a normal functional transporting epithelium, and human cervical cancer-derived HeLa cells, forming non-transporting cancerous epithelial tissue. Then, the impedance spectra obtained were analysed by numerically fitting the parameters of the two different models to the measured impedance spectrum. Aluminium sensors proved to be as sensitive and consistent in repeated online-recordings for continuous cell growth and differentiation monitoring as sensors made of gold, the standard electrode material. Titanium electrodes exhibited an elevated intrinsic ohmic resistance in comparison to gold reflecting its lower electric conductivity. Analysis of impedance spectra through applying models and numerical data fitting enabled the detailed investigation of the development and properties of a functional transporting epithelial tissue using either gold or aluminium sensors. The result of the data obtained, supports the consideration of aluminium and titanium sensor materials as potential alternatives to gold sensors for advanced application of ECIS spectroscopy.

Automatic system for electroporation of adherent cells growing in standard multi-well plates

In this study an automatic system is presented to perform electroporation, also known as electropermeabilization, on adherent cells. It is an intention of this system to apply electric field pulses directly to cells growing in standard multi-well plates as a step forward to include this technique in standard laboratory protocols. An interdigitated microelectrode assembly constructed with Printed Circuit Board (PCB) is placed closely above the cell monolayer, and in order to avoid direct contact with cells, small micro-separators were included in the structure. Additionally, distribution of current density was modified by filling the gap between adjacent electrodes with a non conductive material as predicted by electric field simulations. This modification helps to concentrate the electric field intensity in the region where cells are present. The device was tested using C2C12 cell line growing adhered in 24 multi-well plates and fluorescent labeled dextran FD20S as the molecule to be delivered. Successful transfection was observed with minimal invasiveness of the operation reducing the stress caused to cells.

Inverted open microwells for cell trapping, cell aggregate formation and parallel recovery of live cells

The inverted open microwell is a novel microstructure supporting isolation and trapping of cells, analysis of cell-cell and cell-molecule interactions and functional cell sorting. This work introduces the inverted open microwell concept, demonstrating successful isolation of K562 cells in 75 μm microwells fabricated on a flexible printed circuit board substrate, and recovery of viable cells onto standard microtiter plates after analysis and manipulation. Dielectrophoresis (DEP) was used during the delivery phase to control cell access to the microwell and force the formation of cell aggregates so as to ensure cell-cell contact and interaction. Cells were trapped at the air-fluid interface at the bottom edge of the open microwell. Once trapped, cells were retained on the meniscus even after DEP de-activation and fluid was exchanged to enable perfusion of nutrients and delivery of molecules to the microwell, as demonstrated by a calcein-staining protocol performed in the microsystem. Finally, cell viability was assessed on trapped cells by a calcein release assay and cell proliferation was demonstrated after multiple cells had been recovered in parallel onto standard microtiter plates.

Implantable polyimide cable for multichannel high-data-rate neural recording microsystems

To avoid or minimize postimplantation injury as a result of brain micromotion relative to the skull, a flexible multichannel polyimide (PI) cable was designed and microfabricated for data and power transmission between an intracranial IC recording from a neural probe array and an extracranial IC exchanging power and data wirelessly with an external unit. Surface characteristics, electrical properties, and cytocompatibility of the PI ribbon cable were investigated in this study. Scanning electron microscopic examination and atomic force microscopy analyses showed that the surface of the PI ribbon cable became significantly rougher due to the reactive oxygen ion etching process to open bonding pads. The enhanced surface roughness was also responsible for the increase in wettability and water absorption rate. However, water permeability measurement revealed that the micromachining fabrication process did not meaningfully affect the acceptable water vapor transmission rate of PI. Moreover, electrical properties, such as insertion loss, isolation between channels and data transmission capacity, were assessed for each channel of the PI ribbon cable on the basis of scattering parameter (S-parameter) measurement. Finally, 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay and live/dead intracellular staining tests were carried out to evaluate cell behaviors on the PI ribbon cable, indicating that the PI ribbon cable did not have acute cytotoxicity and appeared to be as cytocompatible as blank PI foils.

Horizontal nDEP cages within open microwell arrays for precise positioning of cells and particles

We present the structure of an open microwell, i.e. a microwell open at both the top and bottom ends, which enables single-cells to be handled, processed and recovered after the experiment. The microwell has a novel architecture which allows particles to be trapped and forced to interact by means of a cylindrical negative dielectrophoretic cage. Particles are aligned along a horizontal axis where the electric field minimum is placed. Arrays of open microwells are fabricated using flexible printed circuit board (PCB) technology providing cheap and disposable devices. Levitation and precise positioning of both polystyrene beads and K562 cells were experimented, confirming the results of physical simulations. Assessment of cell viability after 20 min exposure to the electric field was performed through a standard calcein-release assay.