Rapid prototyping of arrayed microfluidic systems in polystyrene for cell-based assays.

Microfluidic cell-based systems have enabled the study of cellular phenomena with improved spatiotemporal control of the microenvironment and at increased throughput. While poly(dimethylsiloxane) (PDMS) has emerged as the most popular material in microfluidics research, it has specific limitations that prevent microfluidic platforms from achieving their full potential. We present here a complete process, ranging from mold design to embossing and bonding, that describes the fabrication of polystyrene (PS) microfluidic devices with similar cost and time expenditures as PDMS-based devices. Emphasis was placed on creating methods that can compete with PDMS fabrication methods in terms of robustness, complexity, and time requirements. To achieve this goal, several improvements were made to remove critical bottlenecks in existing PS embossing methods. First, traditional lithographic techniques were adapted to fabricate bulk epoxy molds capable of resisting high temperatures and pressures. Second, a method was developed to emboss through-holes in a PS layer, enabling creation of large arrays of independent microfluidic systems on a single device without need to manually create access ports. Third, thermal bonding of PS layers was optimized in order to achieve quality bonding over large arrays of microsystems. The choice of materials and methods was validated for biological function in two different cell-based applications to demonstrate the versatility of our streamlined fabrication process.

Image-based analysis of primary human neutrophil chemotaxis in an automated direct-viewing assay.

Multi-well assays based on the Boyden chamber have enabled highly parallel studies of chemotaxis-the directional migration of cells in response to molecular gradients-while direct-viewing approaches have allowed more detailed questions to be asked at low throughput. Boyden-based plates provide a count of cells that pass through a membrane, but no information about cell appearance. In contrast, direct-viewing devices enable the observation of cells during chemotaxis, which allows measurement of many parameters including area, shape, and location. Here we show automated chemotaxis and cell morphology assays in a 96-unit direct-viewing plate. Using only 12000 primary human neutrophils per datum, we measured dose-dependent stimulation and inhibition of chemotaxis and quantified the effects of inhibitors on cell area and elongation. With 60 parallel conditions we demonstrated 5-fold increase in throughput compared to previously reported direct-viewing approaches.

An automated high-content assay for tumor cell migration through 3-dimensional matrices.

High-content tumor cell migration assays in 3-dimensional (3D) extracellular matrix are a powerful tool for modeling and understanding the biology of this critical step in the process of metastasis. Currently available methods offer very limited throughput and are not amenable to studies of comparative pharmacology or small-scale screening. The authors present an automated approach to high-content tumor cell migration assays. A standard screening-sized plate with an array of microchannels was designed and constructed from common thermoplastics. After filling the channels with 3D matrix, cells were placed at one end of the channel, and migration into the channel was monitored via an imaging system. All liquid-handling steps were performed by standard liquid-handling robotics. Tumor cell migration in the channel was truly 3D and correlated with metastatic potential. The information-rich data from these assays were used to rank the potency of compounds inhibiting migration through 3D collagen as well as to gain additional insights into the compounds' activities related to cell health. This approach is compatible with a variety of multiparametric, morphological, and/or kinetic readouts.

Cellular observations enabled by microculture: paracrine signaling and population demographics.

The cellular microenvironment plays a critical role in shaping and directing the process of communication between the cells. Soluble signals are responsible for many cellular behaviors such as cell survival, proliferation and differentiation. Despite the importance of soluble signals, canonical methods are not well suited to the study of soluble factor interactions between multiple cell types. Macro-scale technology often puts cells into a convective environment that can wash away and dilute soluble signals from their targets, minimizing local concentrations of important factors. In addition, current methods such as transwells, require large numbers of cells and are limited to studying just two cell types. Here, we present data supporting the use of microchannels to study soluble factor signaling providing improved sensitivity as well as the ability to move beyond existing co-culture and conditioned medium paradigms. In addition, we present data suggesting that microculture can be used to unmask effects of population demographics. In this example the data support the hypothesis that a growth promoting subpopulation of cells exists in the mouse mammary gland.

Automated cell culture in high density tubeless microfluidic device arrays.

Microfluidics is poised to have an impact on life sciences research. However, current microfluidic methods are not compatible with existing laboratory liquid dispensing and detection infrastructure. This incompatibility is a barrier to adoption of microfluidic systems and calls for improved approaches that will enhance performance and promote acceptance of microfluidic systems in the life sciences. Ease of use, standardized interfaces and automation remain critical challenges. We present a platform based on surface tension effects, where the difference in pressure inside drops of unequal volume drives flow in passive structures. We show integration with existing laboratory infrastructure, microfluidic operations such as pumping, routing and compartmentalization without discrete micro-components as well as cell patterning in both monolayer and three-dimensional cell culture.

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.

High-throughput microfluidics: improved sample treatment and washing over standard wells.

Fluid flow in microchannels is used to treat or wash samples and can be incorporated into high-throughput applications such as drug screening, which currently use standard microtiter wells for performing assays. This paper provides theoretical and experimental data comparing microchannels and standard wells on the metrics of sample washing and experimental error in treatment concentrations. It is shown numerically and experimentally that microchannel concentration can be approximated with an inverse linear relationship to input volume. The experimentally supported mathematical approximation and error propagation methods are used to compare the accuracy and precision of treatments in microchannels vs. standard wells. Mathematical results suggest microchannels can provide 10 or more times the treatment precision of standard wells for volume ratios typical of high-throughput screening. Passive-pumping and diffusion are utilized to improve microchannel accuracy and precision even further in a treat-wait-treat method. The advantages of microchannels outlined here can have large-scale effects on cost and accuracy in screening applications.

Diffusion dependent cell behavior in microenvironments.

Understanding the interaction between soluble factors and cells in the cellular microenvironment is critical to understanding a wide range of diseases. Microchannel culture systems provide a tool for separating diffusion and convection based transport making possible controlled studies of the effects of soluble factors in the cellular microenvironment. In this paper we compare the proliferation kinetics of cells in traditional culture flasks to those in microfluidic channels, and explore the relationship between microchannel geometry and cell proliferation. PDMS (polydimethylsiloxane) microfluidic channels were fabricated using micromolding methods. Fall armyworm ovarian cells (Sf9) were homogeneously seeded in a series of different sized microchannels and cultured under a no flow condition. The proliferation rates of Sf9 cells in all of the microchannels were slower than in the flask culture over the first 24 h of culture. The proliferation rates in the microchannels then continuously decreased reaching 5% of that in the flasks over the next 48 h and maintained this level for 5 days. This growth inhibition was reversible and influenced only by the cell seeding density and the channel height but not the channel length or width. One possible explanation for the observed dimension-dependent cell proliferation is the accumulation of different functional molecules in the diffusion dominant microchannel environment. This study provides insights into the potential effects of the diffusion of soluble factors and related effects on cell behavior in microenvironments relevant to the emerging use of microchannel culture systems.