Biomedical subjects

D J Beebe

Publications and source records attributed to D J Beebe.

8 recordsLinked to original sources

PubMed2001

Surface-directed liquid flow inside microchannels.

Self-assembled monolayer chemistry was used in combination with either multistream laminar flow or photolithography to pattern surface free energies inside microchannel networks. Aqueous liquids introduced into these patterned channels are confined to the hydrophilic pathways, provided the pressure is maintained below a critical value. The maximum pressure is determined by the surface free energy of the liquid, the advancing contact angle of the liquid on the hydrophobic regions, and the channel depth. Surface-directed liquid flow was used to create pressure-sensitive switches inside channel networks. The ability to confine liquid flow inside microchannels with only two physical walls is expected to be useful in applications where a large gas-liquid interface is critical, as demonstrated here by a gas-liquid reaction.

Journal Article↗

PubMed2001

Handling individual mammalian embryos using microfluidics.

We have designed, built, and tested microfluidic systems capable of transporting individual, preimplantation mouse embryos (100-microm to 150-microm diameter) through a network of channels. Typical channels are 160 to 200 microm deep, 250 to 400 microm wide at the top, and narrower at the bottom (0 to 250 microm wide) due to the fabrication process. In these channels, a pressure gradient of 1 Pa/mm causes the medium to flow on the order of 10(-10) m3/s (100 nl/s), with an average speed of 1 to 2 mm/s. Under these flow conditions the embryos roll along the bottoms of the channels, traveling at 1/2 the speed of the fluid. By manipulating the pressure at the wells connected to the ends of the channels, the embryos can be transported to (and retained at) specific locations including culture compartments and retrieval wells.

Animals↗

PubMed2000

Microfluidic tectonics: a comprehensive construction platform for microfluidic systems.

A microfluidic platform for the construction of microscale components and autonomous systems is presented. The platform combines liquid-phase photopolymerization, lithography, and laminar flow to allow the creation of complex and autonomous microfluidic systems. The fabrication of channels, actuators, valves, sensors, and systems is demonstrated. Construction times can be as short as 10 min, providing ultrarapid prototyping of microfluidic systems.

Journal Article↗

PubMed2000

Microfabricated elastomeric stencils for micropatterning cell cultures.

Here we present an inexpensive method to fabricate microscopic cellular cultures, which does not require any surface modification of the substrate prior to cell seeding. The method utilizes a reusable elastomeric stencil (i.e., a membrane containing thru holes) which seals spontaneously against the surface. The stencil is applied to the cell-culture substrate before seeding. During seeding, the stencil prevents the substrate from being exposed to the cell suspension except on the hole areas. After cells are allowed to attach and the stencil is peeled off, cellular islands with a shape similar to the holes remain on the cell-culture substrate. This solvent-free method can be combined with a wide range of substrates (including biocompatible polymers, homogeneous or nonplanar surfaces, microelectronic chips, and gels), biomolecules, and virtually any adherent cell type.

Animals↗

PubMed2000

Integrating microfabricated fluidic systems and NMR spectroscopy.

The philosophy of miniature total analysis systems (mu-TAS) hinges on the integration of multiple chemical processing steps and the means of analyzing their results on the same miniaturized system. We have constructed chip-based capillary electrophoresis (CE) devices equipped with an integrated planar radio-frequency detector coil used for nuclear magnetic resonance spectroscopy (NMR). Separations were accomplished in the devices, but satisfactory NMR spectra could only be obtained from samples of high concentration. The relative sensitivity is explained and the scaling law dichotomy of CE and NMR explored.

Electrophoresis, Capillary↗

PubMed1998

A silicon-based tactile sensor for finger-mounted applications.

This paper presents a silicon-based force sensor packaged in a flexible package and describes the sensors performance on human subjects. The sensing element consists of a circular silicon diaphragm (200-micron thick with a 2-mm radius) over a 10-micron sealed cavity with a solid Torlon dome providing force-to-pressure transduction to the diaphragm. Two dome heights (0.5 and 1.5 mm) were compared. The sensor with the taller dome showed improved sensitivity. Dynamic calibration and tracking experiments are performed with the sensor mounted on the dominant thumb of five human subjects. Both force and loading direction are statistically significant (P < 0.05). Subject variability accounted for 8.7% of the variance, while loading direction accounted for 1.9% of the variance. Average errors for the tracking experiment range from-2.8 to 1.0 N and are subject dependent. Three out of four subjects showed increasing negative error with increasing load.

Adult↗

PubMed1998

A microfabricated electrostatic haptic display for persons with visual impairments.

An electrostatic haptic display with three 7 x 7 electrode arrays of three different sizes was fabricated on a 4-in wafer using lithographic microfabrication techniques. The display utilizes electrostatic stimulation to generate a tactile sensation of texture on a scanning finger. The tactile sensation appeared to be a result of increased friction and vibration due to the electrostatic forces between the finger skin and the electrodes. Various spatial tactile patterns (lines, circles, squares, and triangles, etc.) can be presented on the display. Experiments of threshold, line separation, and pattern recognition were performed on subjects with visual impairments to study the spatial resolution and information transmission on arrays of variant electrode size and spacing. Two columns with two-column spacing can be resolved with 80% accuracy on the small array, for a spatial resolution of 5.8 mm in terms of edge-to-edge electrode distance. The overall percentages of correct recognition for the patterns were 68.3, 72.1, and 71.3% on the small, medium, and large arrays, respectively. While subject is an important factor for both threshold and pattern recognition, electrode size was statistically significant for threshold only. Frequency and duty cycle of the stimulation waveform did not show statistical significance.

Adult↗

PubMed1997

Electrothermal branding for embryo labeling.

A novel embryo labeling technique based on electrothermal branding is developed. Two types of micro branding irons are fabricated and tested. One utilizes 25 microns tungsten wire as the heating element. The other utilizes surface micromachining techniques to fabricate polysilicon branding irons. The thermal behavior of the branding irons and the heat distributions in the embryos are analytically modeled. Micron-scale labels on unfertilized bovine embryos are achieved.

Animal Identification Systems↗