Ordered networks of rat hippocampal neurons attached to silicon oxide surfaces.

The control of neuronal cell position and outgrowth is of fundamental interest in the development of applications ranging from cellular biosensors to tissue engineering. We have produced rectangular networks of functional rat hippocampal neurons on silicon oxide surfaces. Attachment and network formation of neurons was guided by a geometrical grid pattern of the adhesion peptide PA22-2 which matches in sequence a part of the A-chain of laminin. PA22-2 was applied by contact printing onto the functionalised silicon oxide surface and was immobilised by hetero-bifunctional cross-linking with sulfo-GMBS. Geometric pattern matching was achieved by microcontact printing using a polydimethylsiloxane (PDMS) stamp. In this way the produced grid pattern ranged from 3 to 20 microm in line width and from 50 to 100 microm in line distances. As shown by atomic force microscopy (AFM), line widths and line distances of the peptide pattern differ less than 0.5 microm from the used PDMS stamp. The height of the layer of immobilised PA22-2 was approximately 3.5 nm implying the layer to be monomolecular. Immobilised PA22-2 was capable of binding anti-PA22-2 antibodies indicating that the function of the peptide was not compromised by immobilisation. Rat hippocampal neurons, cultured at low density in serum-free medium, were applied to the growth matrix of PA22-2-coated substrates and, within 1-3 h of culture, formed a network-like pattern that more or less matched the printed grid. Reliability and reproducibility of neuronal network formation depended on the geometry, line width and node diameter of the grid pattern. The immobilised neurons showed resting membrane potentials comparable with controls and, already after 1 day of culture, were capable of eliciting action potentials. The suitability of the immobilised neurons for the study of man-made neural networks and for multi-site recordings from a functional neuronal network is discussed.

Electrical recordings from rat cardiac muscle cells using field-effect transistors.

Extracellular electrophysiological recordings were made from cardiac cells cultured for up to seven days over microfabricated arrays of field-effect transistors. The recorded signals can be separated mainly into two types of cell transistor couplings: one that can be explained entirely by purely passive circuitry elements, and a second where voltage-gated ion channels contribute greatly to the measured extracellular signal.

Electrophysiological development of embryonic hippocampal neurons from the rat grown on synthetic thin films.

We have studied the electrophysiological properties of hippocampal neurons grown on surfaces of organic thin films formed on glass or silicon substrates and on microelectronic device surfaces in culture. Hippocampal neurons were dissociated from embryonic rats and plated on substrates chemically modified with laminin peptide in a chemically defined medium. The electrophysiological properties of the neurons were studied using patch-clamp amplifier technique. We observed that the neurons grown on these substrates develop resting membrane potentials more negative than -33 mV after 3 days in culture and are able to produce action potentials. More interestingly we found that the neurons when grown on the microelectronic surfaces develop similar electrophysiological characteristics as those on the glass surfaces. Passive electrical properties (Cm = 27 +/- 5 pF, Rm > or = 1 G omega) of the neurons studied by impedance spectroscopy did not change considerably during the first week in culture.

Field-effect transistor array for monitoring electrical activity from mammalian neurons in culture.

A field-effect transistor (FET) array has been fabricated and used for recording of electrical signals from neural cells. The array consists of p-channel FETs with non-metalized gates. The size of the gates of the 16 FETs are from 28 x 12 microns2 down to 10 x 4 microns2 and are arranged in a 4 x 4 matrix on 200 microns centers. For the device fabrication process we have especially focused on high sensitivity, good long-term stability in physiological conditions, and sufficient reduced signal-to-noise ratio. Special care was taken on the encapsulation technique of the device to allow surface modification based on the self-assembly technique. It can be shown that the microelectronic device surface can be modified with a synthetic peptide linked to the surface. Tailoring of the surface composition using this method allows hippocampal neurons to adhere and grow for days. More importantly, these cells develop typical electrical characteristics when cultured on this artificial surface. Using this approach neuron-FET couplings were recorded.