We present a highly parallel microfluidic approach for contacting single cell pairs. The approach combines a differential fluidic resistance trapping method with a novel cellular valving principle for homotypic and heterotypic single cell co-culturing. Differential fluidic resistance was used for sequential single cell arraying, with the adhesion and flattening of viable cells within the microstructured environment acting to produce valves in the open state. Reversal of the flow was used for the sequential single cell arraying of the second cell type. Plasma stencilling, along the linear path of least resistance, was required to confine the cells within the trap regions. Prime flow conditions with minimal shear stress were identified for highly efficient cell arraying ($99%) and long term cell culture. Larger trap dimensions enabled the highest levels of cell pairing ($70%). The single cell co-cultures were in close proximity for the formation of connexon structures and the study of contact modes of communication. The research further highlights the possibility of using the natural behaviour of cells as the working principle behind responsive microfluidic elements.

In this paper we present compartmentalized neuron arraying (CNA) microfluidic circuits for the preparation of neuronal networks using minimal cellular inputs (10-100-fold less than existing systems).The approach combines the benefits of microfluidics for precision single cell handling with biomaterial patterning for the long term maintenance of neuronal arrangements. A differential flow principle was used for cell metering and loading along linear arrays. An innovative water masking technique was developed for the inclusion of aligned biomaterial patterns within the microfluidic environment. For patterning primary neurons the technique involved the use of meniscus-pinning micropillars to align a water mask for plasma stencilling a poly-amine coating. The approach was extended for patterning the human SH-SY5Y neuroblastoma cell line using a poly(ethylene glycol) (PEG) back-fill and for dopaminergic LUHMES neuronal precursors by the further addition of a fibronectin coating. The patterning efficiency E patt was .75% during lengthy in chip culture, with y85% of the outgrowth channels occupied by neurites. Neurons were also cultured in next generation circuits which enable neurite guidance into all outgrowth channels for the formation of extensive inter-compartment networks. Fluidic isolation protocols were developed for the rapid and sustained treatment of the different cellular and sub-cellular compartments. In summary, this research demonstrates widely applicable microfluidic methods for the construction of compartmentalized brain models with single cell precision. These minimalistic ex vivo tissue constructs pave the way for high throughput experimentation to gain deeper insights into pathological processes such as Alzheimer and Parkinson Diseases, as well as neuronal development and function in health.

We report the use of thin film poly(dimethylsiloxane) (PDMS) prints for the arrayed mass production of highly uniform 3-D human HT29 colon carcinoma spheroids. The spheroids have an organotypic density and, as determined by 3-axis imaging, were genuinely spherical. Critically, the array density impacts growth kinetics and can be tuned to produce spheroids ranging in diameter from 200 to 550 µm. The diffusive limit of competition for media occurred with a pitch of ≥1250 µm and was used for the optimal array-based culture of large, viable spheroids. During sustained culture mass transfer gradients surrounding and within the spheroids are established, and lead to growth cessation, altered expression patterns and the formation of a central secondary necrosis. These features reflect the microenvironment of avascularised tumours, making the array format well suited for the production of model tumours with defined sizes and thus defined spatio-temporal pathophysiological gradients. Experimental windows, before and after the onset of hypoxia, were identified and used with an enzyme activity-based viability assay to measure the chemosensitivity towards irinotecan. Compared to monolayer cultures, a marked reduction in the drug efficacy towards the different spheroid culture states was observed and attributed to cell cycle arrest, the 3-D character, scale and/or hypoxia factors. In summary, spheroid culture using the array format has great potential to support drug discovery and development, as well as tumour biology research.

Inspired by complex multifunctional leaves, in this study, we created robust hierarchically wrinkled nanoporous polytetrafluoroethene (PTFE) surfaces that exhibit superhydrophobic properties by combination of PTFE micellization and spontaneous surface wrinkling on a commercially available thermoretractable polystyrene (PS) sheet. A PTFE dispersion was coated onto the PS sheet, followed by thermal treatment to remove the surfactants surrounding the PTFE particles, and surface wrinkling was induced through a dynamic thermal contraction process. Thermally induced contraction from the PS sheet provided the driving force for developing and stabilizing micrometer-sized wrinkle formation, whereas the nanometer-sized PTFE particle aggregation formed a rigid nanoporous film, providing its intrinsic hydrophobic character. By combining the hierarchical interfacial structure and chemical composition, hierarchically wrinkled nanoporous PTFE surfaces were fabricated, which exhibited extremely high water repellence (water contact angle of ∼167°) and a water rolling-off angle lower than 5°. The wrinkled patterns could intimately bind the nanoporous PTFE layer through enhanced adhesion from their curved surface and viscous liquid surfactants, making these surfaces mechanically robust and offering potentially extendable alternatives with self-cleaning, antifouling, and drag-reducing properties.

In this report, we focus on the microfabrication and cell seeding issues of artificial blood capillaries for tissue engineering. Two different fabrication methods (stainless steel electroforming and silicon electroforming) and a number of materials (PC, Polycarbonate and biocompatible material PLGA, poly lactide-co-glycolides) are implemented to build the vascular network. The vascular network is then used as the scaffold to cultivate the bovine endothelial cell (BEC). During the period of cell cultivation, oxygen and nutrient need to be continuously delivered by a circular pressurizing system. In cell culture, encouraging results are obtained through the dynamical seeding of the BEC on the scaffolds. A systematic cell culture process has been developed after repeated experiments. Successful seeding efficiencies are obtained by using the developed systematic cell culture process

Three-dimensional (3D) cell cultures and organs-on-a-chip have been developed to construct microenvironments that resemble the environment within the human body and to provide a platform that enables clear observation and accurate assessments of cell behavior. However, direct observation of transendothelial electrical resistance (TEER) has been challenging. To improve the efficiency in monitoring the cell development in organs-on-a-chip, in this study, we designed and integrated commercially available TEER measurement electrodes into an in vitro blood-brain barrier (BBB)-on-chip system to quantify TEER variation. Moreover, a flowing culture medium was added to the monolayered cells to simulate the promotion of continuous shear stress on cerebrovascular cells. Compared with static 3D cell culture, the proposed BBB-on-chip integrated with electrodes could measure TEER in a real-time manner over a long period. It also allowed cell growth angle measurement, providing instant reports of cell growth information online. Overall, the results demonstrated that the developed system can aid in the quantification of the continuous cell-pattern variations for future studies in drug testing.

A pinched-flow deflection technology was developed for rapid single cell switching between biochemical microenvironments.Millisecond switching was used to stimulate and preserve epidermal growth factor receptor (EGFR) autophosphorylation transitions. Intramolecular phosphorylation initiates signal transduction, is silenced by phosphatase activity until EGFR dimerization enables intermolecular phosphorylation to initiate downstream signalling.

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