Biomedical subjects

Bruce C Wheeler

Publications and source records attributed to Bruce C Wheeler.

9 recordsLinked to original sources

PubMed2006

Neuronal network structuring induces greater neuronal activity through enhanced astroglial development.

The confluence of micropatterning, microfabricated multielectrode arrays, and low-density neuronal culture techniques make possible the growth of patterned neuronal circuits overlying multielectrode arrays. Previous studies have shown synaptic interaction within patterned cultures which was more active on average than random cultures. In our present study, we found patterned cultures to have up to five times more astrocytes and three times more neurons than random cultures. In addition, faster development of synapses is also seen in patterned cultures. Together, this yielded greater overall neuronal activity as evaluated by the number of active electrodes. Our finding of astrocytic proliferation within serum-free culture is also novel.

Action Potentials↗

PubMed2006

Epoxy-silane linking of biomolecules is simple and effective for patterning neuronal cultures.

Surface chemistry is one of the main factors that contributes to the longevity and compliance of cell patterning. Two to three weeks are required for dissociated, embryonic rat neuronal cultures to mature to the point that they regularly produce spontaneous and evoked responses. Though proper surface chemistry can be achieved through the use of covalent protein attachment, often it is not maintainable for the time periods necessary to study neuronal growth. Here we report a new and effective covalent linking approach using (3-glycidoxypropyl) trimethoxysilane (3-GPS) for creating long term neuronal patterns. Micrometer scale patterns of cell adhesive proteins were formed using microstamping; hippocampal neurons, cultured up to 1 month, followed those patterns. Cells did not grow on unmodified 3-GPS surfaces, producing non-permissive regions for the long-term cell patterning. Patterned neuronal networks were formed on two different types of MEA (polyimide or silicon nitride insulation) and maintained for 3 weeks. Even though the 3-GPS layer increased the impedance of metal electrodes by a factor of 2-3, final impedance levels were low enough that low noise extracellular recordings were achievable. Spontaneous neural activity was recorded as early as 10 days in vitro. Neural recording and stimulation were readily achieved from these networks. Our results showed that 3-GPS could be used on surfaces to immobilize biomolecules for a variety of neural engineering applications.

Animals↗

PubMed2006

Neural recording and stimulation of dissociated hippocampal cultures using microfabricated three-dimensional tip electrode array.

There is increasing interest in interfacing dissociated neuronal cultures with planar multielectrode arrays (MEAs) for the study of the dynamics of neuronal networks. Here we report on the successful use of three-dimensional tip electrode arrays (3D MEAs), originally developed for use with brain slices, for recording and stimulation of cultured neurons. We observed that many neurons grew directly on protruding electrode surface, appearing to make excellent contact. A larger than usual portion of extracellular spikes had large positive peaks, while most of the spikes from conventional two-dimensional electrode arrays had large negative spikes. This may be due to the direct capacitive coupling situation provided by relatively large electrode surface area.

Action Potentials↗

PubMed2006

Application of a PDMS microstencil as a replaceable insulator toward a single-use planar microelectrode array.

Here we present a novel idea for a replaceable insulator, and thus advance toward the goal of a single-use planar microelectrode array (MEA) for the study of electrogenic tissues. The concept of a replaceable insulator is motivated by insulator degradation after repeated usage of an MEA. Instead of fabricating a more durable insulator for repeated MEA usage, we propose replacing the insulator and effectively producing a fresh MEA for each experiment. We chose a polydimethylsiloxane (PDMS) microstencil as a candidate for the replaceable insulator as it is biocompatible, shows reversible adhesion to surfaces, and can be easily and controllably fabricated. As a proof-of-concept, we demonstrate two applications using microstencils: the rejuvenation of an old MEA and the fabrication of a single-use MEA. These MEAs were tested with dissociated neural cell cultures and neural recordings were performed at 14 days in vitro. Inexpensive and quick supply of insulators with micrometer-sized holes provides a way of constructing an MEA that can be treated as a disposable component in high throughput cell-based biosensor applications.

Animals↗

PubMed2004

Gold-coated microelectrode array with thiol linked self-assembled monolayers for engineering neuronal cultures.

We report the use of a gold coating on microelectrode arrays (MEAs) to enable the use of the relatively reliable surface modification chemistry afforded by alkanethiol self-assembled monolayers (SAMs). The concept is simple and begins with planar MEAs, which are commercially available for neuronal cell culture and for brain slice studies. A gold film, with an intermediate adhesive layer of titanium, is deposited over the insulation of an existing MEA in a manner so as to be thin enough for transmission light microscopy as well as to avoid electrical contact to the electrodes. The alkanethiol-based linking chemistry is then applied for the desired experimental purpose. Here we show that polylysine linked to alkanethiol SAM can control the geometry of an in vitro hippocampal neuronal network grown on the MEA. Furthermore, recordings of neuronal action potentials from random and patterned networks suggest that the gold coating does not significantly alter the electrode properties. This design scheme may be useful for increasing the number of neurons located in close proximity to the electrodes. Realization of in vitro neuronal circuits on MEAs may significantly benefit basic neuroscience studies, as well as provide the insight relevant to applications such as neural prostheses or cell-based biosensors. The gold coating technique makes it possible to use the rich set of thiol-based surface modification techniques in combination with MEA recording.

Action Potentials↗

PubMed2004

Performance of time- and frequency-domain binaural beamformers based on recorded signals from real rooms.

Extraction of a target sound source amidst multiple interfering sound sources is difficult when there are fewer sensors than sources, as is the case for human listeners in the classic cocktail-party situation. This study compares the signal extraction performance of five algorithms using recordings of speech sources made with three different two-microphone arrays in three rooms of varying reverberation time. Test signals, consisting of two to five speech sources, were constructed for each room and array. The signals were processed with each algorithm, and the signal extraction performance was quantified by calculating the signal-to-noise ratio of the output. A frequency-domain minimum-variance distortionless-response beamformer outperformed the time-domain based Frost beamformer and generalized sidelobe canceler for all tests with two or more interfering sound sources, and performed comparably or better than the time-domain algorithms for tests with one interfering sound source. The frequency-domain minimum-variance algorithm offered performance comparable to that of the Peissig-Kollmeier binaural frequency-domain algorithm, but with much less distortion of the target signal. Comparisons were also made to a simple beamformer. In addition, computer simulations illustrate that, when processing speech signals, the chosen implementation of the frequency-domain minimum-variance technique adapts more quickly and accurately than time-domain techniques.

Algorithms↗

PubMed2003

A modified microstamping technique enhances polylysine transfer and neuronal cell patterning.

Macromolecular microstamping with polydimethylsiloxane (PDMS) stamps has been demonstrated to transfer proteins onto glassy substrates for antigen or antibody detection and for cell patterning. For many applications, including neuronal cell patterning, it is important to assure reliable transfer of sufficient quantity of protein. Research has shown that protein transfer is enhanced with the selection of the proper protein-stamp-substrate combination. In addition, detergent studies have shown that detergent-protein complexes detach from surfaces to a greater extent than proteins alone. Therefore, we hypothesized that stamp surface modification (termed here a release layer) can enhance polylysine transfer and benefit cell growth on microstamped substrates. We found unmodified stamps to transfer insufficient polylysine to support good cell survival of hippocampal neurons in a widely used serum-free, reduced-glia cell culture system. However, with modified stamps neuronal growth was reliably good. This enhanced cell growth can be attributed to the increased polylysine transfer due to the release layer rather than increased loading onto the stamp. This enhancement was found to be even greater for two-month old stamps that were stored in water. Furthermore, the physicochemical properties of the release layer can modulate the loading process. Thus, our data supports the conclusions that the release layer: (1) modulates polylysine loading, (2) enhances polylysine transfer, (3) enhances cellular growth on microstamped substrates, and (4) extends the durability (defined as the number of times a stamp can be reused) of PDMS microstamps.

Animals↗

PubMed2003

Blind estimation of reverberation time.

The reverberation time (RT) is an important parameter for characterizing the quality of an auditory space. Sounds in reverberant environments are subject to coloration. This affects speech intelligibility and sound localization. Many state-of-the-art audio signal processing algorithms, for example in hearing-aids and telephony, are expected to have the ability to characterize the listening environment, and turn on an appropriate processing strategy accordingly. Thus, a method for characterization of room RT based on passively received microphone signals represents an important enabling technology. Current RT estimators, such as Schroeder's method, depend on a controlled sound source, and thus cannot produce an online, blind RT estimate. Here, a method for estimating RT without prior knowledge of sound sources or room geometry is presented. The diffusive tail of reverberation was modeled as an exponentially damped Gaussian white noise process. The time-constant of the decay, which provided a measure of the RT, was estimated using a maximum-likelihood procedure. The estimates were obtained continuously, and an order-statistics filter was used to extract the most likely RT from the accumulated estimates. The procedure was illustrated for connected speech. Results obtained for simulated and real room data are in good agreement with the real RT values.

Acoustics↗

PubMed2002

Microcontact printing: a versatile technique for the study of synaptogenic molecules.

During synaptogenesis information exchanged locally between synaptic partners results in precise alignment of morphological and molecular specializations. For example, agrin derived from motoneurons induces localized postsynaptic differentiation at the neuromuscular synapse. Similar information molecules are thought to act at other synapses; however, techniques for directly evaluating synaptogenic activities of such molecules are lacking. Here we use agrin-induced differentiation as a model system to validate a novel approach for characterizing synaptogenic molecules. Proteins are patterned with micron scale resolution on glass coverslips by covalent microcontact printing and these substrates are used for cell culture. Postsynaptic molecules accumulate specifically at sites of contact between muscle cells and patterned agrin: a response which is quantifiable. Our results demonstrate that microcontact printing is applicable to the analysis of cellular response to locally immobilized information molecules.

Agrin↗