Efficient formation of uniform-sized embryoid bodies using a compartmentalized microchannel device

A student team in a University of Michigan biomedical engineering design course constructs a microfluidic bioreactor for studies of zebrafish development

The zebrafish is a valuable model for teaching developmental, molecular, and cell biology; aquatic sciences; comparative anatomy; physiology; and genetics. Here we demonstrate that zebrafish provide an excellent model system to teach engineering principles. A seven-member undergraduate team in a biomedical engineering class designed, built, and tested a zebrafish microfluidic bioreactor applying microfluidics, an emerging engineering technology, to study zebrafish development. During the semester, students learned engineering and biology experimental design, chip microfabrication, mathematical modeling, zebrafish husbandry, principles of developmental biology, fluid dynamics, microscopy, and basic molecular biology theory and techniques. The team worked to maximize each person's contribution and presented weekly written and oral reports. Two postdoctoral fellows, a graduate student, and three faculty instructors coordinated and directed the team in an optimal blending of engineering, molecular, and developmental biology skill sets. The students presented two posters, including one at the Zebrafish meetings in Madison, Wisconsin (June 2008).

Microfluidic culture of single human embryonic stem cell colonies

We have developed a miniaturized microfluidic culture system that allows experimentation on individual human embryonic stem cell (hESC) colonies in dynamic (flow applied) or static (without flow) conditions. The system consists of three inlet channels that converge into a cell-culture channel and provides the capability to spatially and temporally deliver specific treatments by using patterned laminar fluid flow to different parts of a single hESC colony. We show that microfluidic culture for 96 h with or without flow results in similar maintenance of hESC self-renewal, the capability to differentiate into three germ cell lineages, and to maintain a normal karyotype, as in standard culture dishes. Localized delivery of a fluorescent nucleic acid dye was achieved with laminar flow, producing staining only in nuclei of exposed cells. Likewise, cells in desired regions of colonies could be removed with enzymatic treatment and collected for analysis. Re-coating the enzyme treated area of the channel with extracellular matrix led to re-growth of hESC colonies into this region. Our study demonstrates the culture of hESCs in a microfluidic device that can deliver specific treatments to desired regions of a single colony. This miniaturized culture system allows in situ treatment and analysis with the ability to obtain cell samples from part of a colony without micromanipulation and to perform sensitive molecular analysis while permitting further growth of the hESC colony.

Engineering the embryoid body microenvironment to direct embryonic stem cell differentiation

Embryonic stem cells (ESCs) are pluripotent cells capable of differentiating into all somatic and germ cell types. The intrinsic ability of pluripotent cells to generate a vast array of different cells makes ESCs a robust resource for a variety of cell transplantation and tissue engineering applications, however, efficient and controlled means of directing ESC differentiation is essential for the development of regenerative therapies. ESCs are commonly differentiated in vitro by spontaneously self-assembling in suspension culture into 3D cell aggregates called embryoid bodies (EBs), which mimic many of the hallmarks of early embryonic development, yet the 3D organization and structure of EBs also presents unique challenges to effectively direct the differentiation of the cells. ESC differentiation is strongly influenced by physical and chemical signals comprising the local extracellular microenvironment, thus current methods to engineer EB differentiation have focused primarily on spatially controlling EB size, adding soluble factors to the media, or culturing EBs on or within natural or synthetic extracellular matrices. Although most such strategies aim to influence differentiation from the exterior of EBs, engineering the microenvironment directly within EBs enables new opportunities to efficiently direct the fate of the cells by locally controlling the presentation of morphogenic cues.

Microfluidic system for formation of PC-3 prostate cancer co-culture spheroids

The niche microenvironment in which cancer cells reside plays a prominent role in the growth of cancer. It is therefore imperative to mimic the in vivo tumor niche in vitro to better understand cancer and enhance development of therapeutics. Here, we engineer a 3D metastatic prostate cancer model that includes the types of surrounding cells in the bone microenvironment that the metastatic prostate cancer cells reside in. Specifically, we used a two-layer microfluidic system to culture 3D multi-cell type spheroids of fluorescently labeled metastatic prostate cancer cells (PC-3 cell line), osteoblasts and endothelial cells. This method ensures uniform incorporation of all co-culture cell types into each spheroid and keeps the spheroids stationary for easy tracking of individual spheroids and the PC-3's residing inside them over the course of at least a week. This culture system greatly decreased the proliferation rate of PC-3 cells without reducing viability and may more faithfully recapitulate the in vivo growth behavior of malignant cancer cells within the bone metastatic prostate cancer microenvironment.

Embryoid body morphology influences diffusive transport of inductive biochemicals: a strategy for stem cell differentiation

Differentiation of human embryonic stem (hES) cells into cells for regenerative medicine is often initiated by embryoid body (EB) formation. EBs may be treated with soluble biochemicals such as cytokines, growth factors and vitamins to induce differentiation. A scanning electron microscopy analysis, conducted over 14 days, revealed time-dependent changes in EB structure which led to the formation of a shell that significantly reduced the diffusive transport of a model molecule (374 Da) by >80%. We found that the shell consists of 1) an extracellular matrix (ECM) comprised of collagen type I; 2) a squamous cellular layer with tight cell-cell adhesions associated with E-cadherin; and 3) a collagen type IV lining indicative of a basement membrane. Disruption of the basement membrane, by either inhibiting its formation with noggin or permeabilizing it with collagenase, resulted in recovery of diffusive transport. Increasing the diffusive transport of retinoic acid (RA) and serum in EBs by a 15-min collagenase digestion on days 4, 5, 6 and 7 promoted neuronal differentiation. Flow cytometry and quantitative RT-PCR analysis of collagenase-treated EBs revealed 68% of cells expressing neural cell adhesion molecule (NCAM) relative to 28% for untreated EBs. Our results suggest that limitations in diffusive transport of biochemicals need to be considered when formulating EB differentiation strategies.

Cell culture models in microfluidic systems

Microfluidic technology holds great promise for the creation of advanced cell culture models. In this review, we discuss the characterization of cell culture in microfluidic systems, describe important biochemical and physical features of the cell microenvironment, and review studies of microfluidic cell manipulation in the context of these features. Finally, we consider the integration of analytical elements, ways to achieve high throughput, and the design constraints imposed by cell biology applications.

A microwell array system for stem cell culture

Directed embryonic stem (ES) cell differentiation is a potentially powerful approach for generating a renewable source of cells for regenerative medicine. Typical in vitro ES cell differentiation protocols involve the formation of ES cell aggregate intermediates called embryoid bodies (EBs). Recently, we demonstrated the use of poly(ethylene glycol) (PEG) microwells as templates for directing the formation of these aggregates, offering control over parameters such as size, shape, and homogeneity. Despite these promising results, the previously developed technology was limited as it was difficult to reproducibly obtain cultures of homogeneous EBs with high efficiency and retrievability. In this study, we improve the platform by optimizing a number of features: material composition of the microwells, cell seeding procedures, and aggregate retrieval methods. Adopting these modifications, we demonstrate an improved degree of homogeneity of the resulting aggregate populations and establish a robust protocol for eliciting high EB formation efficiencies. The optimized microwell array system is a potentially versatile tool for ES cell differentiation studies and high-throughput stem cell experimentation.

Measurement of gene expression from single adherent cells and spheroids collected using fast electrical lysis

The cytosol of a single adherent cell was collected by the electrical cell lysis method with a Pt-ring capillary probe, and the cellular messenger RNA (mRNA) was analyzed at a single-cell level. The ring electrode probe was positioned 20 microm above the cultured cells that formed a monolayer on an indium-tin oxide (ITO) electrode, and an electric pulse with a magnitude of 40 V was applied for 10 micros between the probe and the ITO electrodes in an isotonic sucrose solution. Immediately after the electric pulse, less than 1 microL of the lysed solution was collected using a micro-injector followed by RNA purification and first strand cDNA synthesis. Real-time PCR was performed to quantify the copy numbers of mRNA encoding glyceraldehyde-3-phosphate dehydrogenase (GAPDH) expression inside the single cell. The average copy numbers of GAPDH mRNA collected by the electrical cell lysis method were found to be comparable to those obtained by a simple capillary suction method. Although single-cell analysis has already been demonstrated, we have shown for the first time that the fast electrical cell lysis can be used for quantitative mRNA analysis at the single-cell level. This electrical cell lysis method was further applied for the analysis of mRNA obtained from single spheroids-the aggregated cellular masses formed during the three-dimensional culture -- as a model system to isolate small cellular clusters from tissues and organs.