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Biomedical subjects

Luke P Lee

Publications and source records attributed to Luke P Lee.

At least 19 recordsLinked to original sources

Dynamic single cell culture array.

It is important to quantify the distribution of behavior amongst a population of individual cells to reach a more complete quantitative understanding of cellular processes. Improved high-throughput analysis of single cell behavior requires uniform conditions for individual cells with controllable cell-cell interactions, including diffusible and contact elements. Uniform cell arrays for static culture of adherent cells have previously been constructed using protein micropatterning techniques but lack the ability to control diffusible secretions. Here we present a microfluidic-based dynamic single cell culture array that allows both arrayed culture of individual adherent cells and dynamic control of fluid perfusion with uniform environments for individual cells. In our device no surface modification is required and cell loading is done in less than 30 seconds. The device consists of arrays of physical U-shaped hydrodynamic trapping structures with geometries that are biased to trap only single cells. HeLa cells were shown to adhere at a similar rate in the trapping array as on a control glass substrate. Additionally, rates of cell death and division were comparable to the control experiment. Approximately 100 individual isolated cells were observed growing and adhering in a field of view spanning approximately 1 mm(2) with greater than 85% of cells maintained within the primary trapping site after 24 hours. Also, greater than 90% of cells were adherent and only 5% had undergone apoptosis after 24 hours of perfusion culture within the trapping array. We anticipate uses in single cell analysis of drug toxicity with physiologically relevant perfused dosages as well as investigation of cell signaling pathways and systems biology.

Cell Adhesion↗

Single-cell enzyme concentrations, kinetics, and inhibition analysis using high-density hydrodynamic cell isolation arrays.

High-quality single-cell data are required for a quantitative systems biology description of cellular function. However, data of this type are difficult and time-consuming to collect using traditional techniques. We present a robust and simple microfluidic method for trapping single cells in large arrays to address this problem. Ordered single-cell isolation arrays allow for high-density microscopic analysis with simplified image processing. Moreover, for fluorescent assays, on-chip sample preparation (e.g., fluorescent labeling, washing) can be performed, as opposed to manual intensive operations of incubation, centrifugation, and resuspension in previous techniques-saving time and reagents. This technology was applied to determine novel single-cell enzyme kinetics for three different cell types (HeLa, 293T, Jurkat). A kinetic model of this process predicted this varied response was due to variation in the concentration of carboxylesterase between cell types. Nordihydroguaiaretic acid (NDGA) was also characterized as an inhibitor of carboxylesterases. For HeLa cells, 20 nM of the 50 nM total carboxylesterases was unaffected by NDGA. This type of analysis could be directly applied to quantify a variety of intracellular enzymes with available fluorogenic substrates.

Carboxylesterase↗

Nanoliter scale microbioreactor array for quantitative cell biology.

A nanoliter scale microbioreactor array was designed for multiplexed quantitative cell biology. An addressable 8 x 8 array of three nanoliter chambers was demonstrated for observing the serum response of HeLa human cancer cells in 64 parallel cultures. The individual culture unit was designed with a "C" shaped ring that effectively decoupled the central cell growth regions from the outer fluid transport channels. The chamber layout mimics physiological tissue conditions by implementing an outer channel for convective "blood" flow that feeds cells through diffusion into the low shear "interstitial" space. The 2 microm opening at the base of the "C" ring established a differential fluidic resistance up to 3 orders of magnitude greater than the fluid transport channel within a single mold microfluidic device. Three-dimensional (3D) finite element simulation were used to predict fluid transport properties based on chamber dimensions and verified experimentally. The microbioreactor array provided a continuous flow culture environment with a Peclet number (0.02) and shear stress (0.01 Pa) that approximated in vivo tissue conditions without limiting mass transport (10 s nutrient turnover). This microfluidic design overcomes the major problems encountered in multiplexing nanoliter culture environments by enabling uniform cell loading, eliminating shear, and pressure stresses on cultured cells, providing stable control of fluidic addressing, and permitting continuous on-chip optical monitoring.

Bioreactors↗

Biologically inspired artificial compound eyes.

This work presents the fabrication of biologically inspired artificial compound eyes. The artificial ommatidium, like that of an insect's compound eyes, consists of a refractive polymer microlens, a light-guiding polymer cone, and a self-aligned waveguide to collect light with a small angular acceptance. The ommatidia are omnidirectionally arranged along a hemispherical polymer dome such that they provide a wide field of view similar to that of a natural compound eye. The spherical configuration of the microlenses is accomplished by reconfigurable microtemplating, that is, polymer replication using the deformed elastomer membrane with microlens patterns. The formation of polymer waveguides self-aligned with microlenses is also realized by a self-writing process in a photosensitive polymer resin. The angular acceptance is directly measured by three-dimensional optical sectioning with a confocal microscope, and the detailed optical characteristics are studied in comparison with a natural compound eye.

Animals↗

Microfluidics-based systems biology.

Systems biology seeks to develop a complete understanding of cellular mechanisms by studying the functions of intra- and inter-cellular molecular interactions that trigger and coordinate cellular events. However, the complexity of biological systems causes accurate and precise systems biology experimentation to be a difficult task. Most biological experimentation focuses on highly detailed investigation of a single signaling mechanism, which lacks the throughput necessary to reconstruct the entirety of the biological system, while high-throughput testing often lacks the fidelity and detail necessary to fully comprehend the mechanisms of signal propagation. Systems biology experimentation, however, can benefit greatly from the progress in the development of microfluidic devices. Microfluidics provides the opportunity to study cells effectively on both a single- and multi-cellular level with high-resolution and localized application of experimental conditions with biomimetic physiological conditions. Additionally, the ability to massively array devices on a chip opens the door for high-throughput, high fidelity experimentation to aid in accurate and precise unraveling of the intertwined signaling systems that compose the inner workings of the cell.

Animals↗

Microfluidic alignment of collagen fibers for in vitro cell culture.

Three dimensional gels of aligned collagen fibers were patterned in vitro using microfluidic channels. Collagen fiber orientation plays an important role in cell signaling for many tissues in vivo, but alignment has been difficult to realize in vitro. For microfluidic collagen fiber alignment, collagen solution was allowed to polymerize inside polydimethyl siloxane (PDMS) channels ranging from 10-400 microm in width. Collagen fiber orientation increased with smaller channel width, averaging 12+/-6 degrees from parallel for channels between 10 and 100 microm in width. In these channels 20-40% of the fibers were within 5 degrees of the channel axis. Bovine aortic endothelial cells expressing GFP-tubulin were cultured on aligned collagen substrate and found to stretch in the direction of the fibers. The use of artificially aligned collagen gels could be applied to the study of cell movement, signaling, growth, and differentiation.

Adsorption↗

Optofluidic control using photothermal nanoparticles.

Photothermal metallic nanoparticles have attracted significant attention owing to their energy-conversion properties. Here, we introduce an optofluidic application based on a direct optical-to-hydrodynamic energy conversion using suspended photothermal nanoparticles near the liquid-air interface. Using light beams with submilliwatt power, we can drive and guide liquid flow in microfluidic channels to transport biomolecules and living cells at controlled speeds and directions. Previously, a variety of methods for controlling microscale liquid flow have been developed owing to the increasing interest for microfluidics-based biochemical analysis systems. However, our method dispenses with the need for complex pump and valve devices, surface chemistry and electrode patterning, or any other further effort towards substrate fabrication. Instead, our optofluidic control method will allow the fabrication of all-optical large-scale integrated microfluidic circuits for biomolecular and cellular processing without any physical valve or mechanical pumping device.

Electrochemistry↗

Inspirations from biological optics for advanced photonic systems.

Observing systems in nature has inspired humans to create technological tools that allow us to better understand and imitate biology. Biomimetics, in particular, owes much of its current development to advances in materials science and creative optical system designs. New investigational tools, such as those for microscopic imaging and chemical analyses, have added to our understanding of biological optics. Biologically inspired optical science has become the emerging topic among researchers and scientists. This is in part due to the availability of polymers with customizable optical properties and the ability to rapidly fabricate complex designs using soft lithography and three-dimensional microscale processing techniques.

Animals↗

Mammalian electrophysiology on a microfluidic platform.

The recent development of automated patch clamp technology has increased the throughput of electrophysiology but at the expense of visual access to the cells being studied. To improve visualization and the control of cell position, we have developed a simple alternative patch clamp technique based on microfluidic junctions between a main chamber and lateral recording capillaries, all fabricated by micromolding of polydimethylsiloxane (PDMS). PDMS substrates eliminate the need for vibration isolation and allow direct cell visualization and manipulation using standard microscopy. Microfluidic integration allows recording capillaries to be arrayed 20 microm apart, for a total chamber volume of <0.5 nl. The geometry of the recording capillaries permits high-quality, stable, whole-cell seals despite the hydrophobicity of the PDMS surface. Using this device, we are able to demonstrate reliable whole-cell recording of mammalian cells on an inexpensive microfluidic platform. Recordings of activation of the voltage-sensitive potassium channel Kv2.1 in mammalian cells compare well with traditional pipette recordings. The results make possible the integration of whole-cell electrophysiology with easily manufactured microfluidic lab-on-a-chip devices.

Animals↗

Theoretical and experimental study towards a nanogap dielectric biosensor.

Theoretical and experimental studies of nanogap capacitors as potential label free biosensors are presented. The nanogap device is capable of detecting the existence of single stranded DNA (ssDNA) oligonucleotides (20-mer) in 100 nM aqueous solutions using a 20 nm gap of 1.2 pl in volume. While the dielectric properties of DNA solution have been widely investigated, early approaches are limited at low frequency by the parasitic noise due to the electrical double layer (EDL) impedance. Nanogap electrodes have the potential to serve as biomolecular junctions because their size (5-100 nm) minimizes electrode polarization effects regardless of frequency. In this paper, we modeled the effects of the EDL interaction between two parallel nanogap electrodes by solving the Poisson-Boltzmann (PB) equation for equilibrium state. When the gap size is smaller than the EDL thickness, the dependence of the nanogap capacitance on the ionic strength is insignificant. This is critical in using the capacitance change as an indicator of the existence of target molecules. The predicted capacitance of nanogaps filled with various ionic strength electrolytes was in quantitative agreement with the experimental measurements. The various concentrations of the target molecules in nanogap sensor were characterized. A capacitance change of a 20 nm x (10)1.5 microm x 4mm gap from 3.5 to 4.1 nF at 200 Hz was recorded between deionized water (DI) and 100 nM ssDNA solution (about 70,000 molecules inside the gap for equilibrium state).

Biosensing Techniques↗

Continuous perfusion microfluidic cell culture array for high-throughput cell-based assays.

We present for the first time a microfluidic cell culture array for long-term cellular monitoring. The 10 x 10 array could potentially assay 100 different cell-based experiments in parallel. The device was designed to integrate the processes used in typical cell culture experiments on a single self-contained microfluidic system. Major functions include repeated cell growth/passage cycles, reagent introduction, and real-time optical analysis. The single unit of the array consists of a circular microfluidic chamber, multiple narrow perfusion channels surrounding the main chamber, and four ports for fluidic access. Human carcinoma (HeLa) cells were cultured inside the device with continuous perfusion of medium at 37 degrees C. The observed doubling time was 1.4 +/- 0.1 days with a peak cell density of approximately 2.5*10(5) cells/cm(2). Cell assay was demonstrated by monitoring the fluorescence localization of calcein AM from 1 min to 10 days after reagent introduction. Confluent cell cultures were passaged within the microfluidic chambers using trypsin and successfully regrown, suggesting a stable culture environment suitable for continuous operation. The cell culture array could offer a platform for a wide range of assays with applications in drug screening, bioinformatics, and quantitative cell biology.

Cell Culture Techniques↗

Artificial ommatidia by self-aligned microlenses and waveguides.

We report the fabrication of artificial ommatidia, the imaging units of insects' compound eyes, by use of polymer integrated optics. These biomimetic structures are obtained by configuring microlenses to play dual roles for self-writing of waveguides (during the fabrication) and collection of light (during the operation). The artificial ommatidium, consisting of a microlens, a spacer, and a waveguide, directly resembles the structure of its biological counterpart. Optical characterizations reveal single-peak angular sensitivity with a +/- 0.75 degrees acceptance angle that is comparable to those found in nature. Using geometric and physical optics, we also investigate the relationship between angular sensitivity and the geometry of artificial ommatidia.

Animals↗

Alkaline hemolysis fragility is dependent on cell shape: results from a morphology tracker.

BACKGROUND: The morphometric analysis of red blood cells (RBCs) is an important area of study and has been performed previously for fixed samples. We present a novel method for the analysis of morphologic changes of live erythrocytes as a function of time. We use this method to extract information on alkaline hemolysis fragility. Many other toxins lyse cells by membrane poration, which has been studied by averaging over cell populations. However, no quantitative data are available for changes in the morphology of individual cells during membrane poration-driven hemolysis or for the relation between cell shape and fragility. METHODS: Hydroxide, a porating agent, was generated in a microfluidic enclosure containing RBCs in suspension. Automatic cell recognition, tracking, and morphometric measurements were done by using a custom image analysis program. Cell area and circular shape factor (CSF) were measured over time for individual cells. Implementations were developed in MATLAB and on Kestrel, a parallel computer that affords higher speed that approaches real-time processing. RESULTS: The average CSF went through a first period of fast increase, corresponding to the conversion of discocytes to spherocytes under internal osmotic pressure, followed by another period of slow increase until the fast lysis event. For individual cells, the initial CSF was shown to be inversely correlated to cell lifetime (linear regression factor R=0.44), with discocytes surviving longer than spherocytes. The inflated cell surface area to volume ratio was also inversely correlated to lifetime (R=0.43) but not correlated to the CSF. Lifetime correlated best to the ratio of cell inflation volume (Vfinal-Vinitial) to surface area (R=0.65). CONCLUSIONS: RBCs inflate at a rate proportional to their surface area, in agreement with a constant flux model, and lyse after attaining a spherical morphology. Spherical RBCs display increased alkaline hemolysis fragility (shorter lifetimes), providing an explanation for the increased osmotic fragility of RBCs from patients who have spherocytosis.

Cell Shape↗

Nanophotonic crescent moon structures with sharp edge for ultrasensitive biomolecular detection by local electromagnetic field enhancement effect.

We present novel gold nanophotonic crescent moon structures with a sub-10 nm sharp edge, which can enhance local electromagnetic field at the edge area. The formation of unconventional nanophotonic crescent moon structure is accomplished by using a sacrificial nanosphere template and conventional thin film deposition method, which allows an effective batch nanofabrication and precise controls of nanostructure shapes. Unique multiple scattering peaks are observed in a single gold nanocrescent moon with dark-field white light illumination. A 785 nm near-infrared (NIR) diode laser was used as the excitation source to induce the amplified scattering field on the sharp edge of the single gold nanocrescent moon. The Raman scattering spectrum of Rhodamine 6G molecules adsorbed on the single gold nanocrescent moon are characterized, and the Raman enhancement factor of single gold nanocrescent moon is estimated larger than 10(10), which suggests the potential applications of gold nanocrescent moons in ultrasensitive biomolecular detection and cellular imaging using surface enhanced Raman spectroscopy.

Electromagnetic Fields↗

High-density silver nanoparticle film with temperature-controllable interparticle spacing for a tunable surface enhanced Raman scattering substrate.

The formation of high-density silver nanoparticles and a novel method to precisely control the spacing between nanoparticles by temperature are demonstrated for a tunable surface enhanced Raman scattering substrates. The high-density nanoparticle thin film is accomplished by self-assembling through the Langmuir-Blodgett (LB) technique on a water surface and transferring the particle monolayer to a temperature-responsive polymer membrane. The temperature-responsive polymer membrane allows producing a dynamic surface enhanced Raman scattering substrate. The plasmon peak of the silver nanoparticle film red shifts up to 110 nm with increasing temperature. The high-density particle film serves as an excellent substrate for surface-enhanced Raman spectroscopy (SERS), and the scattering signal enhancement factor can be dynamically tuned by the thermally activated SERS substrate. The SERS spectra of Rhodamine 6G on a high-density silver particle film at various temperatures is characterized to demonstrate the tunable plasmon coupling between high-density nanoparticles.

Acrylic Resins↗

Time-resolved optical sensing of oligonucleotide hybridization via Au colloidal nanoparticles.

Au nanoparticles have distinctive absorption spectra whose peak position or particle plasmon resonance wavelength is highly sensitive to molecule adsorption on their surfaces. Spherical Au nanoparticles are surface-modified by amino-functionalized self-assembly-monolayer and used as optical probes in the fluorescence-label-free spectroscopic detection of sub-nanomole oligonucleotides. Time-resolved studies of the immobilization and hybridization of oligonucleotides on the surface of Au nanoparticles were carried out. By measuring peak shift of absorption spectra of the Au colloidal nanoparticles over time, the samples of 15 nM 20 mer target and mismatched oligonucleotides are distinguished by their different influences on the particle plasmon resonance wavelength. The approach presented in this paper extends the application of Au nanoparticles as the optical probe in oligonucleotide recognitions without prior sample labeling.

Biosensing Techniques↗

On-chip cell lysis by local hydroxide generation.

We present a novel method for on-chip cell lysis based on local hydroxide electro-generation. Hydroxide ions porate the cell membrane, leading to cell lysis. After lysis occurs, hydrogen ions, also generated on chip, react with excess hydroxide, creating a neutral pH lysate and eliminating the need for a wash step. Three different cell types are shown to be effectively lysed by this method: red blood cells, HeLa (human tumor line) and Chinese Hamster Ovary (CHO) cell lines. The release of cytoplasmic molecules from HeLa and CHO cells is demonstrated by monitoring the escape of a membrane impermeant dye from the cytoplasm. In the vicinity of the cathode, the hydroxide concentration is predicted by finite element simulations and shown to fit the lysis rates at different distances from the generating cathode. For flow-through experiments, a second device integrating a mechanical filter with hydroxide generation is fabricated and tested. The purpose of the filter is to trap whole cells and only allow lysate to pass through. The flow rate dependence of hydroxide concentration at the lysis filter is modeled and lysis efficiency is experimentally determined to be proportional to the hydroxide concentration for flow rates from 15 to 30 microl min(-1).

Animals↗

A novel high aspect ratio microfluidic design to provide a stable and uniform microenvironment for cell growth in a high throughput mammalian cell culture array.

We present a high aspect ratio microfluidic device for culturing cells inside an array of microchambers with continuous perfusion of medium. The device was designed to provide a potential tool for cost-effective and automated cell culture. The single unit of the array consists of a circular microfluidic chamber 40 microm in height surrounded by multiple narrow perfusion channels 2 microm in height. The high aspect ratio (approximately 20) between the microchamber and the perfusion channels offers advantages such as localization of the cells inside the microchamber as well as creating a uniform microenvironment for cell growth. Finite element methods were used to simulate flow profile and mass transfer of the device. Human carcinoma (HeLa) cells were cultured inside the device with continuous perfusion of medium at 37 degrees C and was grown to confluency. The microfluidic cell culture array could potentially offer an affordable platform for a wide range of applications in high throughput cell-based screening, bioinformatics, synthetic biology, quantitative cell biology, and systems biology.

Cell Culture Techniques↗