Biomedical subjects

D J Beebe

Publications and source records attributed to D J Beebe.

13 recordsLinked to original sources

PubMed2007

Simulating mouse mammary gland development: cell ageing and its relation to stem and progenitor activity.

BACKGROUND: Somatic stem and progenitor cell division is likely to be an important determinant of tumor development. Each division is accompanied by a risk of fixing genetic mutations, and/or generating innately immortal cells that escape normal physiological controls. AIM: Using biological information, we aimed to devise a theoretical model for mammary gland development that described the effect of various stem/progenitor cells activities on the demographics of adult mammary epithelial cell populations. RESULTS: We found that mammary ductal trees should develop in juvenile mice despite widely variant levels of activity in the progenitor compartment. Sequestration (inactivation) of progenitor cells dramatically affected the aging-maturation of the population without affecting the total regenerative capacity of the gland. Our results showed that if stem and progenitor cells can be demonstrated in glands regenerated by serial transplantation, they originated in a canonical primary stem cell (providing a functional definition of mammary stem cells). Finally, when the probability of symmetric division of stem cells increased above a threshold, the mammary epithelial population overall was immortal during serial transplantation. CONCLUSIONS: This model provides, (1) a theoretical framework for testing whether the phenotypes of genetically modified mice (many of which are breast cancer models) derive from changes of stem and progenitor activity, and (2) a means to evaluate the resolving power of functional assays of regenerative capacity in mammary epithelial cell populations.

Analysis of Variance↗

PubMed2006

Gelatin based microfluidic devices for cell culture.

We have developed a technique for fabricating microfluidic devices from gelatin using a natural crosslinking process. Gelatin, crosslinked with the naturally occurring enzyme transglutaminase is molded to produce microchannels suitable for adherent cell culture and analysis. The autofluorescence of the material was shown to be minimal and within the range of typical background, ensuring utility with analyses using fluorescent dyes and labels would not be affected. Also, normal murine mammary epithelial cells were successfully cultured in the microchannels. The morphology of these adherent epithelial cells was shown to be significantly different for cells grown on rigid tissue culture plastic in either macro- or microscale cultures (even in the presence of a surface coating of gelatin) than those grown on the flexible crosslinked gelatin microchannels. Using these devices, the effects of both the extracellular matrix and soluble factors on cellular behavior and differentiation can be studied in microenvironments that more closely mimic the in vivo environment.

Animals↗

PubMed2004

A microfluidic method for removal of the zona pellucida from mammalian embryos.

Many in vitro procedures involve manipulation of the zona pellucida (chimerics, transgenics, biopsy). We have demonstrated a microfluidic channel network to precisely control (spatially and temporally) the delivery of chemical treatments for the removal of the zona pellucida. Building devices in polydimethylsiloxane (PDMS) with channel dimensions on the same order as that of the embryo diameter (approximately 120 microm) allows precise control of the local fluid environment. The system uses pressure driven flows to control embryo positioning, embryo movement, and plug formation. Zona removal is achieved by briefly washing a plug of lysing agent (acid Tyrode's medium) over the embryo.

Animals↗

PubMed2004

Early mammalian embryo development depends on cumulus removal technique.

Cumulus removal (CR) at the zygote stage is necessary for most mammalian in vitro production (IVP). Present techniques use high fluidic stresses (vortexing) or mechanical stress with enzymatic treatment (pipetting) to remove cumulus. Herein a recently developed microfluidic device for cumulus removal from zygotes is compared with traditional vortexing. Microfluidic CR (microFCR) increased development on day 2 (20 +/- 4% to 35 +/- 6%, p < 0.01) and blastocyst formation at day 8 (33 +/- 1% to 57 +/- 5%, p < 0.01) when compared to vortex CR. Vortexing effects on embryo development were studied; 15, 30 and 120 s vortex doses. Development at day 2 was inversely proportional to duration of vortexing. An in situ transcription assay was used to assess biochemical activity of zygotes after cumulus removal. There was a spike of RNA transcription of vortexed zygotes at 2 h post CR not seen in the microfluidic treatment. These results suggest the potential for microfluidic methods to enhance production efficiencies while providing insight into basic developmental mechanisms.

Animals↗

PubMed2001

An organic self-regulating microfluidic system.

In this paper we present an organic feedback scheme that merges microfluidics and responsive materials to address several limitations of current microfluidic systems. By using in situ fabrication and by taking advantage of microscale phenomena (e.g., laminar flow, short diffusion times), we have demonstrated feedback control of the output pH in a completely organic system. The system autonomously regulates an output stream at pH 7 under a range of input flow conditions. A single responsive hydrogel component performs the functionality of traditional feedback system components. Vertically stacked laminar flow is used to improve the time response of the hydrogel actuator. A star shaped orifice is utilized to improve the flow characteristics of the membrane/orifice valve. By changing the chemistry of the hydrogel component, the system can be altered to regulate flow based on hydrogels sensitive to temperature, light, biological/molecular, and others.

Journal Article↗

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↗