Biomedical subjects

A Offenhäusser

Publications and source records attributed to A Offenhäusser.

27 records · Page 2Linked to original sources

PubMed1999

Tailoring of surfaces with ultrathin polymer films for survival and growth of neurons in culture.

We have studied the adhesion, growth, and survival of dissociated cells of rat cerebellum onto glass surfaces derivatized with covalently bound ultrathin polymer layers. The surface coatings were prepared by growing polymer chains directly at the surfaces of solid substrates by using self-assembled monolayers of radical chain initiators. Methacrylate and acrylamide polymers with different polarities were covalently attached to the surfaces and the adhesion behaviour of the neuronal cells to these surfaces was studied. Best adhesion and neurite outgrowth properties were found using a positively charged polymer (poly(methacryloyl oxypropyl (trimethyl ammonium) bromide)). This 'grafting from' method for the generation of surface modifications can be used for tailoring the composition of the surface of the substrates. Our experiments demonstrate the potential of these layers for the design of polymeric surface coatings for long term stability of neuronal culture.

Animals↗

PubMed1998

Incorporation of the acetylcholine receptor dimer from Torpedo californica in a peptide supported lipid membrane investigated by surface plasmon and fluorescence spectroscopy.

The dimer species (M(r) 580,000) of the nicotinic acetylcholine receptor, isolated from the electric organ of Torpedo californica, was incorporated into a thiopeptide supported lipid bilayer. The incorporation was achieved by fusion of liposomes with reconstituted receptor onto a gold-supported thiopeptide lipid monolayer. Surface plasmon resonance spectroscopy (SPS) was used to monitor in real time the fusion process as well as the specific binding of the antagonist alpha-bungarotoxin. A recently developed extension of SPS offering enhanced sensitivity and specificity, surface plasmon fluorescence spectroscopy (SPFS), was then used to monitor subsequent binding of the monoclonal WF6 and polyclonal antibody, respectively. The latter was fluorescence labeled with Cy5. The different binding assays indicate the successful incorporation of the receptor in the lipid bilayer.

Animals↗

PubMed1997

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.

Action Potentials↗

PubMed1997

Electropolymerization of a phenol-modified peptide for use in receptor-ligand interactions studied by surface plasmon resonance.

The combination of surface plasmon resonance (SPR) with an electrochemical method for surface modification is presented. The SLP1 sequence of the sodium channel protein of rat cardiac muscle cells was N-terminally modified with an electropolymerizable group and immobilized on a gold-coated glass slide by oxidative polymerization. The resulting peptide-functionalized substrate was incubated with a polyclonal-specific anti-SLP1 serum. Growth of the peptide layer and the immunological reaction between ligand and receptor were detected on-line by SPR. The applicability of this approach for the rapid and selective analysis of receptor-ligand interactions is demonstrated.

Amino Acid Sequence↗

PubMed1997

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.

Animals↗

PubMed1996

Neural cell pattern formation on glass and oxidized silicon surfaces modified with poly(N-isopropylacrylamide).

Control over the adsorption of proteins and over the adsorption and spatial orientation of mammalian cells onto surfaces has been achieved by modification of glass and other silicon oxide substrates with poly(N-isopropylacrylamide) (PNIPAM). The functionalization of the substrates was achieved either by a polymer-analogous reaction of aminosilanes with reactive N-(isopropylacrylamide) (NIPAM)-copolymers and by copolymerization of NIPAM with surface-bound methacrylsilane. The obtained coatings were characterized by FT-1R, ellipsometry, and surface plasmon resonance measurements. The adsorption of two proteins-fibrinogen and ribonuclease A-on these surfaces was studied in situ by real time surface plasmon resonance measurements. The PNIPAM-grafted surfaces prepared by either chemical procedure inhibited the adsorption of both proteins. More importantly they prevented the adhesion of neuroblastomaXglioma hybrid cells cultured either in serum-free medium or in a medium containing serum proteins. Deep-UV irradiation was used to perform ablation processes and to create patterns permitting the examination of spatially controlled adhesion and growth of cells. This study showed that patterned ultrathin polymer films on glass are suitable substrates for controlling the interactions of cells with surfaces and are capable of directing the attachment and spreading of cells.

Acrylamides↗

PubMed1991

A neuron-silicon junction: a Retzius cell of the leech on an insulated-gate field-effect transistor.

An identified neuron of the leech, a Retzius cell, has been attached to the open gate of a p-channel field-effect transistor. Action potentials, spontaneous or stimulated, modulate directly the source-drain current in silicon. The electronic signals match the shape of the action potential. The average voltage on the gate was up to 25 percent of the intracellular voltage change. Occasionally weak signals that resemble the first derivative of the action potential were observed. The junctions can be described by a model that includes capacitive coupling of the plasma membrane and the gate oxide and that accounts for variable resistance of the seal.

Action Potentials↗

PubMedDate not supplied

Validation of the use of field effect transistors for extracellular signal recording in pharmacological bioassays.

The use of field effect transistors (FETs) in biomedical research has been in rapid progression in recent years. The present study aims to demonstrate a quantitative use of these devices in pharmacological bioassays. FETs were made as a 4 x 4 matrix of gates with a width of 200 microm separating each gate. The surface of the FETs (silicon oxide), covered with a layer of laminin, fibronectin, or nitro cellulose was suitable for cell adhesion. The cultured dissociated cardiac myocytes were spontaneously active within 24 to 48 h after initial plating. Simultaneous intracellular patch clamp recordings were used to verify the electrophysiological signals of cells that were coupled to the gates. All positive chronotropes (isoproterenol, norepinephrine) and negative chronotropes (verapamil, carbamylcholine, SDZ PCO400) showed their characteristic effects on heart cells in terms of changes of beat frequency. As the myocytes were in a complete syncitium on each FET, the cells need not be directly coupled to the gate in order to detect any ionic changes. This enables global cellular responses to be analyzed. The system also offers an opportunity to study the interconnections and communications between different cells. Furthermore, the changes of signal shapes in the presence of different agents could also be detected. The present study demonstrates how versatile and sensitive this recording system is in distinguishing different ionic signal shapes. The authors believe that this system has the potential to replace some currently employed in vitro methods, offering an alternative, which can substantially reduce animal use in pharmacological experiments.

Action Potentials↗

PubMedDate not supplied

Connectivity patterns in neuronal networks of experimentally defined geometry.

Experimental control over the position and connectivity pattern of neurons on a surface is of central interest for applications in biotechnology, such as cell-based biosensors and tissue engineering. By restricting neuronal networks to a simple grid pattern, a drastic reduction of network complexity can be achieved relative to networks on homogeneous substrates. Therefore, patterned neuronal networks are also a valuable tool in research on neuronal signal transduction. Microcontact printing has emerged as a simple and efficient method for surface patterning to direct cellular attachment. Although the formation of synaptic contacts in networks of rat cortical cells on such surfaces has been demonstrated, evidence of more complex circuits has been lacking. Triple patch-clamp measurements were performed to analyze connectivity in neuronal networks complying with a grid-shaped micropattern. Cells adhered stringently to the pattern and interconnected to a range of different types of circuits: linear connections, feedback loops, as well as branching and converging pathways. We conclude that in spite of the severe geometric restrictions, a complex repertoire of different connectivity patterns can form along the provided pathways. At the same time, network complexity is kept low enough to allow the study of these patterns at the resolution of single cell-cell contacts.

Animals↗