Cellular microarrays for use with capillary-driven microfluidics

High-throughput screening paradigms in ecotoxicity testing: Emerging prospects and ongoing challenges

The rapidly increasing number of new production chemicals coupled with stringent implementation of global chemical management programs necessities a paradigm shift towards boarder uses of low-cost and high-throughput ecotoxicity testing strategies as well as deeper understanding of cellular and sub-cellular mechanisms of ecotoxicity that can be used in effective risk assessment. The latter will require automated acquisition of biological data, new capabilities for big data analysis as well as computational simulations capable of translating new data into in vivo relevance. However, very few efforts have been so far devoted into the development of automated bioanalytical systems in ecotoxicology. This is in stark contrast to standardized and high-throughput chemical screening and prioritization routines found in modern drug discovery pipelines. As a result, the high-throughput and high-content data acquisition in ecotoxicology is still in its infancy with limited examples focused on cell-free and cell-based assays. In this work we outline recent developments and emerging prospects of high-throughput bioanalytical approaches in ecotoxicology that reach beyond in vitro biotests. We discuss future importance of automated quantitative data acquisition for cell-free, cell-based as well as developments in phytotoxicity and in vivo biotests utilizing small aquatic model organisms. We also discuss recent innovations such as organs-on-a-chip technologies and existing challenges for emerging high-throughput ecotoxicity testing strategies. Lastly, we provide seminal examples of the small number of successful high-throughput implementations that have been employed in prioritization of chemicals and accelerated environmental risk assessment.

Plasma-induced covalent immobilization and patterning of bioactive species in microfluidic devices

Here, we present a straightforward technique to create bio-functional microfluidic channels using CO2 plasma to induce both carboxylic and hydroxyl groups onto the channel surface. Consequently, not only does the surface allow for irreversible covalent bonding to an oxygen plasma treated PDMS for microfluidic device fabrication, but it also provides functionality for biomolecular immobilization. Furthermore, we demonstrate integration of this technique with microcontact printing to covalently micropattern functional biomolecules inside microfluidic channels. The bio-functionality and efficacy of the microcontact printed antibodies is demonstrated for both bioassays as well as patterning and culturing different cell lines. Results show that the introduced method can be an excellent candidate for cell culture studies in microfluidics. With the new printing method, full cell confluency (∼400 cells per mm2) was achieved after incubation for only 1 day, which is significantly greater than other conventional cell culture techniques inside microfluidic devices. As a proof of concept, we demonstrated the endothelial cells functionality by stimulating von Willebrand Factor secretion under shear stress. This is done via perfusion of histamine through the channel and performing immunofluorescence labeling to observe the inflammatory response of the cells. The developed method eliminates the need for wet chemistry and significantly simplifies producing bio-functional chips which can be used for biosensing, organs-on-chips and tissue engineering applications.

Microtechnologies for Cell Microenvironment Control and Monitoring

A great breadth of questions remains in cellular biology. Some questions cannot be answered using traditional analytical techniques and so demand the development of new tools for research. In the near future, the development of highly integrated microfluidic analytical platforms will enable the acquisition of unknown biological data. These microfluidic systems must allow cell culture under controlled microenvironment and high throughput analysis. For this purpose, the integration of a variable number of newly developed micro- and nano-technologies, which enable control of topography and surface chemistry, soluble factors, mechanical forces and cell–cell contacts, as well as technology for monitoring cell phenotype and genotype with high spatial and temporal resolution will be necessary. These multifunctional devices must be accompanied by appropriate data analysis and management of the expected large datasets generated. The knowledge gained with these platforms has the potential to improve predictive models of the behavior of cells, impacting directly in better therapies for disease treatment. In this review, we give an overview of the microtechnology toolbox available for the design of high throughput microfluidic platforms for cell analysis. We discuss current microtechnologies for cell microenvironment control, different methodologies to create large arrays of cellular systems and finally techniques for monitoring cells in microfluidic devices.

Current Trends and Challenges in Biointerfaces Science and Engineering

The cellular microenvironment is extremely complex, and a plethora of materials and methods have been employed to mimic its properties in vitro. In particular, scientists and engineers have taken an interdisciplinary approach in their creation of synthetic biointerfaces that replicate chemical and physical aspects of the cellular microenvironment. Here the focus is on the use of synthetic materials or a combination of synthetic and biological ligands to recapitulate the defined surface chemistries, microstructure, and function of the cellular microenvironment for a myriad of biomedical applications. Specifically, strategies for altering the surface of these environments using self-assembled monolayers, polymer coatings, and their combination with patterned biological ligands are explored. Furthermore, methods for augmenting an important physical property of the cellular microenvironment, topography, are highlighted, and the advantages and disadvantages of these approaches are discussed. Finally, the progress of materials for prolonged stem cell culture, a key component in the translation of stem cell therapeutics for clinical use, is featured.

"One cell-one well": a new approach to inkjet printing single cell microarrays

A new approach to prepare arrays of sessile droplets of living single cell cultures using a liquid hydrophobic barrier prevents the samples from dehydrating, and allows for spatially addressable arrays for statistical quantitative single cell studies. By carefully advancing a thin layer of mineral oil on the substrate over the droplets during the printing, dehydration of the droplets can be prevented, and the vitality of the cells can be maintained. The net result of this confluence of submerged cell culturing and inkjet printing is facile access to spatially addressable arrays of isolated single cells on surfaces. Such single cell arrays may be particularly useful as high-throughput tools in the rapidly emerging "omics" fields of cell biology.

A self-pumping lab-on-a-chip for rapid detection of botulinum toxin

A robust poly(dimethylsiloxane) (PDMS) surface treatment was utilized for the development of a self-pumping lab-on-a-chip (LOC) to rapidly detect minute quantities of toxic substances. One such toxin, botulinum neurotoxin (BoNT), is an extremely lethal substance, which has the potential to cause hundreds of thousands of fatalities if as little as a few grams are released into the environment. To prevent such an outcome, a quick (<45 min) and sensitive detection format is needed. We have developed a self-pumping LOC that can sense down to 1 pg of BoNT type A (in a 1 microL sample) within 15 min in an autonomous manner. The key technologies enabling for such a device are a sensitive electrochemical sensor, an optimized fluidic network and a robust hydrophilic PDMS coating, thereby facilitating autonomous delivery of liquid samples for rapid detection. The stability, simplicity and portability of this device make possible for a storable and distributable system for monitoring bioterrorist attacks.

Stem cell plasticity, osteogenic differentiation and the third dimension

Different cues present in the cellular environment control basic biological processes. A previously established 3D microwell array was used to study dimensionality-related effects on osteogenic differentiation and plasticity of marrow stromal cells. To enable long-term culture of single cells in the array a novel surface functionalization technique was developed, using the principle of subtractive micro contact printing of fibronectin and surface passivation with a triblock-copolymer. Immunohistochemical stainings showed that when cultivated in 3D microenvironments, marrow stromal cells can be maintained in the wells for up to 7 days and be induced to commit to the osteogenic lineage. In conclusion, this work shows the modification of a 3D microwell array allowing the long term study of single stem cell plasticity and fate in controlled microenvironments.

Controlled deposition of cells in sealed microfluidics using flow velocity boundaries

We present a method for depositing cells in a sealed microfluidic device. The device consists of a poly(dimethylsiloxane) (PDMS) microfluidic network (MFN) sealed with a Si chip. The Si chip has vias and ports that are connected to high-precision motorized pumps. The surfaces of the PDMS MFN are homogeneously coated with fibronectin cell adhesion molecules (CAMs). Flow velocity boundaries are created between vicinal microfluidic structures to prevent or permit deposition of cells in specific regions of the MFN. In narrow flow paths, cells experience a wall shear stress from the fast-moving liquid that overcomes the initial adhesion of the cells with CAMs. Conversely, cells can adhere to CAMs in larger flow paths such as cell chambers inside which the velocity of the liquid and the shear stress are reduced. Interactively changing pumping rates makes the critical velocity (the velocity at which cells deposit in the chamber but not elsewhere) easy to find. The transparent PDMS MFN allows both real-time visualization of the deposition process and cellular assays. We illustrate this method using N9 mouse microglia cells. In one experiment, approximately 75 microglia are deposited per min in a approximately 0.5 microL chamber. The deposited cells remain viable, as assessed from staining and biofunctional assays. This method is simple, reliable, fast, and flexible, and therefore is an attractive technique for depositing cells in microfluidic systems for numerous applications.

Combining self-assembled monolayers and mass spectrometry for applications in biochips

Biochip arrays have enabled the massively parallel analysis of genomic DNA and hold great promise for application to the analysis of proteins, carbohydrates, and small molecules. Surface chemistry plays an intrinsic role in the preparation and analysis of biochips by providing functional groups for immobilization of ligands, providing an environment that maintains activity of the immobilized molecules, controlling nonspecific interactions of analytes with the surface, and enabling detection methods. This review describes recent advances in surface chemistry that enable quantitative assays of a broad range of biochemical activities. The discussion emphasizes the use of self-assembled monolayers of alkanethiolates on gold as a structurally well-defined and synthetically flexible platform for controlling the immobilization and activity of molecules in an array. The review also surveys recent methods of performing label-free assays, and emphasizes the use of matrix-assisted laser desorption/ionization mass spectrometry to directly observe molecules attached to the self-assembled monolayers.

Miniaturization of an Anoikis assay using non-adhesive micromolded hydrogels

Anoikis is a specific form of apoptosis resulting from the loss of cellular attachment to extracellular matrix or other cells. Challenges in simulating these conditions in vitro make it difficult to generate a controlled, efficient assay to study anoikis. We developed a microscale method for analysis and quantification of anoikis using micromolded, non-adhesive hydrogels. These hydrogels allow for isolation and observation of single, unattached cells in an ordered array, and controlled distribution. Cell distributions resulting from multiple seeding densities were compared to a mathematical probability model. Normal human fibroblasts, human umbilical vein endothelial cells, and Mandin-Darby canine kidney epithelial cells were seeded at low densities of approximately one cell/well. Because the hydrogel is made of non-adhesive agarose, attachment was negligible. Survival was monitored using fluorescent microscopy, and quantified by image analysis. The attachment and proliferative potential of cells after being held in a non-adherent environment was assessed with a companion attachment assay. The data from both methods revealed that cells were able to survive much longer than expected without attachment. When tested with H35 rat hepatoma cells we showed that single cancer cells could grow into three-dimensional spheroids, demonstrating the utility of this method in understanding the role of anoikis in cancer.