In situ micropatterning technique by cell crushing for co-cultures inside microfluidic biochips

Online Measurement of Glucose Consumption from HepG2 Cells Using an Integrated Bioreactor and Enzymatic Assay

Hepatocytes help to maintain glucose homeostasis in response to a variety of signals, including pancreatic hormones such as insulin. Insulin is released from the pancreas with variable dynamics, yet the role that these play in regulating glucose metabolism in the liver is still unclear. In this study, a modular microfluidic system was developed to quantitatively measure the effect of insulin dynamics on glucose consumption by a human hepatocarcinoma cell line, HepG2. A microfluidic bioreactor that contained 10⁶ HepG2 cells was cultured for up to 10 days in an incubator. For glucose consumption experiments, the bioreactor was removed from the incubator and connected with reagents for an enzymatic glucose assay. The mixed components were then delivered into a droplet-based microfluidic system where the intensity of the fluorescent product of the enzyme assay was used to quantify the glucose concentration. By optimizing the mixing time of the reagents, the dynamic range of the enzymatic assay was adjusted to 0–12 mM glucose and had a time resolution of 96 ± 12 s. The system was used to observe rapid changes in insulin-induced glucose consumption from HepG2 cells. This assay format is versatile and can be expanded to measure a variety of hepatic metabolites, such as lactate, pyruvate, or ketone bodies, which will enable the correlation of pancreatic hormone dynamics to liver metabolism.

An optimized procedure to develop a 3-dimensional microfluidic hydrogel with parallel transport networks

The development of microfluidic hydrogels is an attractive method to generate continuous perfusion, induce vascularization, increase solute delivery, and ultimately improve cell viability. However, the transport processes in many in vitro studies still have not been realized completely. To address this problem, we have developed a microchanneled hydrogel with different collagen type I concentrations of 1, 2, and 3 wt% and assessed its physical properties and obtained diffusion coefficient of nutrient within the hydrogel. It is well known that microchannel geometry has critical role in maintaining stable perfusion rate. Therefore, in this study, a computational modeling was applied to simulate the 3D microfluidic hydrogel and study the effect of geometric parameters such as microchannel diameters and their distance on the nutrient diffusion. The simulation results showed that the sample with 3 channels with a diameter of 300 μm has adequate diffusion rates and efficiency (56%). Moreover, this system provides easy control and continuous perfusion rate during 5 days of cell culturing. The simulation results were compared with experimental data, and a good correlation was observed for nutrient profiles and cell viability across the hydrogel.

The Use of Microfluidics in Cytotoxicity and Nanotoxicity Experiments

Many unique chemical compounds and nanomaterials are being developed, and each one requires a considerable range of in vitro and/or in vivo toxicity screening in order to evaluate their safety. The current methodology of in vitro toxicological screening on cells is based on well-plate assays that require time-consuming manual handling or expensive automation to gather enough meaningful toxicology data. Cost reduction; access to faster, more comprehensive toxicity data; and a robust platform capable of quantitative testing, will be essential in evaluating the safety of new chemicals and nanomaterials, and, at the same time, in securing the confidence of regulators and end-users. Microfluidic chips offer an alternative platform for toxicity screening that has the potential to transform both the rates and efficiency of nanomaterial testing, as reviewed here. The inherent advantages of microfluidic technologies offer high-throughput screening with small volumes of analytes, parallel analyses, and low-cost fabrication.

Online monitoring of hepatic rat metabolism by coupling a liver biochip and a mass spectrometer

A microfluidic liver biochip was coupled with a mass spectrometer to detect in real time the drug metabolism of hepatocytes.

A Review of the Application of Body-on-a-Chip for Drug Test and Its Latest Trend of Incorporating Barrier Tissue

High-quality preclinical bioassay models are essential for drug research and development. We reviewed the emerging body-on-a-chip technology, which serves as a promising model to overcome the limitations of traditional bioassay models, and introduced existing models of body-on-a-chip, their constitutional details, application for drug testing, and individual features of these models. We put special emphasis on the latest trend in this field of incorporating barrier tissue into body-on-a-chip and discussed several remaining challenges of current body-on-a-chip.

Standing surface acoustic wave based cell coculture

Precise reconstruction of heterotypic cell-cell interactions in vitro requires the coculture of different cell types in a highly controlled manner. In this article, we report a standing surface acoustic wave (SSAW)-based cell coculture platform. In our approach, different types of cells are patterned sequentially in the SSAW field to form an organized cell coculture. To validate our platform, we demonstrate a coculture of epithelial cancer cells and endothelial cells. Real-time monitoring of cell migration dynamics reveals increased cancer cell mobility when cancer cells are cocultured with endothelial cells. Our SSAW-based cell coculture platform has the advantages of contactless cell manipulation, high biocompatibility, high controllability, simplicity, and minimal interference of the cellular microenvironment. The SSAW technique demonstrated here can be a valuable analytical tool for various biological studies involving heterotypic cell-cell interactions.

A microfluidic device mimicking acinar concentration gradients across the liver acinus

The acinus-mimicking microfluidic chip, which simulates the in vivo condition of the liver, was developed and reported in this paper. The gradient microenvironment of the liver acinus is replicated within this proposed microfluidic chip. The advantage of this acinus-mimicking chip is capable of adjusting the concentration gradient in a relatively short period of time at around 10 s. At the same instance the non-linear concentration gradient can be presented in the various zones within this microfluidic chip. The other advantage of this proposed design is in the convenience of allowing the direct injection of the cells into the chip. The environment within the chip is multi-welled and gel-free with high cell density. The multi-row pillar microstructure located at the entrance of the top and bottom flow channels is designed to be able to balance the pressure of the perfusion medium. Through this mechanism the shear stress experienced by the cultured cells can be minimized to reduce the potential damage flow from the perfusion process. The fluorescence staining and the observations of the cell morphology verify the life and death of the cells. The shear stress experienced by the cells in the various zones within the chip can be effectively mapped. The serum glutamic oxaloacetic transaminase (SGOT) collected from the supernatants was used to determine the effects of the degassing process and the shear stress of the medium flow on the cultured cells.

Biomechanical regulation of vascular smooth muscle cell functions: from in vitro to in vivo understanding

Vascular smooth muscle cells (VSMCs) have critical functions in vascular diseases. Haemodynamic factors are important regulators of VSMC functions in vascular pathophysiology. VSMCs are physiologically active in the three-dimensional matrix and interact with the shear stress sensor of endothelial cells (ECs). The purpose of this review is to illustrate how haemodynamic factors regulate VSMC functions under two-dimensional conditions in vitro or three-dimensional co-culture conditions in vivo. Recent advances show that high shear stress induces VSMC apoptosis through endothelial-released nitric oxide and low shear stress upregulates VSMC proliferation and migration through platelet-derived growth factor released by ECs. This differential regulation emphasizes the need to construct more actual environments for future research on vascular diseases (such as atherosclerosis and hypertension) and cardiovascular tissue engineering.

Heterotypic cell-cell interaction on micropatterned surfaces

PURPOSE

The aim of this paper was to study the influence of chemical and topographical signals on cell behavior and to obtain a heterotypic cell-cell interaction on microstructured domains.

METHODS

The polysaccharide hyaluronic acid (Hyal) was photoimmobilized on glass surfaces in order to obtain a pattern with squares and rectangles of different dimensions and chemistry. The microstructured surfaces were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The behavior of human coronary artery endothelial cells (HCAEC) and human tumoral dermal fibroblasts (C54) was investigated on these micropatterned surfaces by adhesion studies. Moreover heterotypic interaction among C54 and HCAEC adherent on patterned surfaces was evaluated by time-lapse video microscopy

RESULTS

Surface analysis revealed the presence of a pattern consisting of alternating glass and Hyal microstructures whose dimensions decreased from the center to the edge of the sample. Neither HCAEC nor C54 adhered to the immobilized Hyal but both adapted their shape to the different sizes of the glass squares and rectangles. The number of adherent cells depended on the dimensions of both the glass domains and the nuclei of the cells. Co-cultured C54 on HCAEC patterned surfaces showed a heterotypic cell-cell interaction in the same chemical and topographic domain.

CONCLUSIONS

A heterotypic cell-cell interaction occurred in the same chemical and topographic micro-domains but in narrow areas only. Moreover, the number of cells adhering to the glass domains and cell morphology depended on the dimensions of both adhesive areas and cell nuclei.

A method for patterned in situ biofunctionalization in injection-molded microfluidic devices

We developed a method to modify the surface in injection molded polymer microdevices prior to bonding and to pattern biomolecules in the completed microsystem in situ by a sequence of simple perfusion steps directly before utilization of the device. This method is compatible with production technology such as injection molding and bonding processes currently employed in the fabrication of polymer microsystems. It solves the problem of the inherent incompatibility of biomolecules with microfabrication technology as it allows for the biofunctionalization step to be performed after completion of the microsystem. Injection molded cyclic olefin copolymer (COC) microfluidic chips were modified by irradiating the surface with UV-light at lambda = 185 nm. This results in the formation of stable acidic groups which were further modified by binding of the extracellular matrix protein collagen type I. Non-irradiated surfaces were modified by binding of Pluronic® F-127 to become non-adhesive. Density of acid groups decreases to 50% within 45 days and to 25% within 19 weeks after irradiation. However, even then the remaining density of functional groups was shown to be sufficient to bind proteins and promote cell adhesion. Selective adhesion of primary hepatocytes on surfaces patterned by UV-irradiation and a biofunctional coating with collagen type I were demonstrated in injection molded microsystems.

Microfluidic biochip for the perifusion of precision-cut rat liver slices for metabolism and toxicology studies

Early detection of kinetic, metabolic, and toxicity (ADME-Tox) profiles for new drug candidates is of crucial importance during drug development. This article describes a novel in vitro system for the incubation of precision-cut liver slices (PCLS) under flow conditions, based on a poly(dimethylsiloxane) (PDMS) device containing 25-microL microchambers for integration of the slices. The microdevice is coupled to a perifusion system, which enables a constant delivery of nutrients and oxygen and a continuous removal of waste products. Both a highly controlled incubation environment and high metabolite detection sensitivity could be achieved using microfluidics. Liver slices were viable for at least 24 h in the microdevice. The compound, 7-ethoxycoumarin (7-EC), was chosen to test metabolism, since its metabolism includes both phase I and phase II metabolism and when tested in the conventional well plate system, correlates well with the in vivo situation (De Kanter et al. 2004. Xenobiotica 34(3): 229-241.). The metabolic rate of 7-EC was found to be 214 +/- 5 pmol/min/mg protein in the microdevice, comparable to well plates, and was constant over time for at least 3 h. This perifusion system better mimics the in vivo situation, and has the potential to significantly contribute to drug metabolism and toxicology studies of novel chemical entities.

Co-culture of epithelial cells and bacteria for investigating host-pathogen interactions

The human gastrointestinal (GI) tract is a unique environment in which intestinal epithelial cells and non-pathogenic (commensal) bacteria co-exist. This equilibrium is perturbed by the entry of pathogens into the GI tract. A key step in the infection process is the navigation of the pathogen through the commensal bacterial layer to attach to epithelial cells. It has been proposed that the microenvironment that the pathogen encounters in the commensal layer plays a significant role in determining the extent of attachment and colonization. Current culture methods for investigating pathogen colonization are not well suited for investigating this hypothesis as they do not enable co-culture of bacteria and epithelial cells in a manner that mimics the GI tract microenvironment. Here we report the development of a microfluidic co-culture model that enables independent culture of eukaryotic cells and bacteria, and testing the effect of the commensal microenvironment on pathogen colonization. A pneumatically-actuated system was developed to form reversible islands that allow development of bacterial biofilm along with culture of an epithelial cell monolayer. The co-culture model used to develop a commensal Escherichia coli biofilm among HeLa cells, followed by introduction of enterohemorrhagic E. coli (EHEC) into the commensal island, in a sequence that mimics the sequence of events in GI tract infection. Using wild-type E. coli and a tnaA mutant (lacks the signal indole) as the commensal bacteria, we demonstrate that the commensal biofilm microenvironment is a key determinant of EHEC infectivity and virulence. Our model has the potential to be used in fundamental studies investigating the effect of GI tract signals on EHEC virulence as well as for screening of different probiotic strains for modulating pathogen infectivity in the GI tract.

Integrating polyurethane culture substrates into poly(dimethylsiloxane) microdevices

Poly(dimethylsiloxane) (PDMS)-based microdevices have enabled rapid, high-throughput assessment of cellular response to precisely controlled microenvironmental stimuli, including chemical, matrix and mechanical factors. However, the use of PDMS as a culture substrate precludes long-term culture and may significantly impact cell response. Here we describe a method to integrate polyurethane (PU), a well-studied and clinically relevant biomaterial, into the PDMS multilayer microfabrication process, enabling the exploration of long-term cellular response on alternative substrates in microdevices. To demonstrate the utility of these hybrid microdevices for cell culture, we compared initial cell adhesion, cell spreading, and maintenance of protein patterns on PU and PDMS substrates. Initial cell adhesion and cell spreading after three days were comparable between collagen-coated PDMS and PU substrates (with or without collagen coating), but significantly lower on native PDMS substrates. However, for longer culture durations (> or = 6 days), cell spreading and protein adhesion on PU substrates was significantly better than that on PDMS substrates, and comparable to that on tissue culture-treated polystyrene. Thus, the use of a generic polyurethane substrate in microdevices enables longer-term cell culture than is possible with PDMS substrates. More generally, this technique can improve the impact and applicability of microdevice-based research by facilitating the use of alternate, relevant biomaterials while maintaining the advantages of using PDMS for microdevice fabrication.