Rate- and contractility-modulating drugs, such as adrenergic agonists and antagonists, are widely used in the treatment of cardiovascular conditions. Preclinical assessment of new modulators of rate, inotropy and metabolism can be aided by high-throughput (HT) methods for chronic measurements, coupled with scalable human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). Here, we evaluate the utility of long-term optical (label-free) measurements of pericellular oxygen in a HT format (96-well plates) for the assessment of the effectiveness of adrenergic drugs in hiPSC-CMs. Quantitative oxygen consumption metrics were derived and correlated to measurements performed in the same samples using all-optical electrophysiology. Adrenergic agonists significantly increased oxygen consumption rate (OCR), best seen in the kinetics of initial depletion of pericellular oxygen, i.e. time to reach 5%. Adrenergic antagonists decreased OCR, best quantified using steady-state values for pericellular oxygen after at least 5 h. OCR-based drug type identification correlated well with the acute spontaneous rate measurements in the same samples. Direct rate modulation with chronic optogenetic pacing sped up OCR in hiPSC-CMs. Blebbistatin, an excitation-contraction uncoupler, significantly reduced OCR. Computational modeling helped interpret our results by capturing the effects of pacing rate, adrenergic stimulation, and blebbistatin on oxygen consumption, thereby highlighting the key contribution of inotropy and mechanical contraction to OCR in hiPSC-CMs. We conclude that HT label-free optical oxygen measurements and the comprehensive in silico hiPSC-CM models, constrained by such measurements, represent valuable human-based approaches for non-invasive assessment of rate- and metabolism-modulating drugs in preclinical studies.

Adequate oxygen supply is crucial for proper cellular function. The emergence of high-throughput (HT) expansion of human stem-cell-derived cells and HT in vitro cellular assays for drug testing necessitate monitoring and understanding of the oxygenation conditions, yet virtually no data exists for such settings. We used HT label-free optical measurements and computational modeling to gain insights about oxygen availability (pericellular oxygen dynamics) in syncytia of human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CM) and human cardiac fibroblasts (cFB) grown in glass-bottom 96-well plates under static conditions. Our experimental results highlight the critical role of cell density and solution height (oxygen delivery path) in pericellular oxygen dynamics. The developed computational model, trained on the obtained comprehensive data set, revealed that time-variant maximum oxygen consumption rate, Vmax, is needed to faithfully capture the complex pericellular oxygen dynamics in the excitable hiPSC-CMs, but not in the cFBs. Interestingly, hypoxia (<2 % pericellular oxygen) developed within hours in the dense iPSC-CM cultures when the solution volume was sufficiently large. Conversely, hiPSC-CMs grown at low cell density or in smaller solution volume, as well as cFB under all studied conditions, were found to operate in hyperoxic (>7 %) conditions. Pericellular oxygen dynamics of the differentiated hiPSC-CMs evolved over days in culture, with the best improvement in respiration seen in samples operating close to normoxia. Our results and the developed computational model can be used directly to optimize cardiac cell growth in HT plates and achieve desired physiological conditions, which is important in cellular assays for cardiotoxicity, drug development, personalized medicine and heart regeneration applications.

Biofilm infections represent a major public health threat due to their high tolerance to antimicrobials and the lack of specific anti-biofilm drugs. To develop such drugs, it is crucial to have high-throughput biofilm growth systems that can emulate in vivo conditions without the cost and complexity of animal models. However, no current biofilm reactor can provide in vivo -like conditions in a high throughput standard microtiter format. This paper demonstrates a novel high-throughput (HT) microfluidic perfusion biofilm reactor (HT-μPBR) compatible with a standard 96-well microtiter plate for in situ optical analysis. A snap-on liquid-tight cover for standard microtiter plates was designed and fabricated with fluidic channels to provide closed-loop recirculating perfusion. Our system takes steps toward providing in vivo -like conditions with controlled shear stress and nutrient delivery. We describe the system fabrication and usage in optical analysis of biomass and viability of Escherichia coli ( E. coli ) biofilms. The HT-μPBR was set to perfuse at 1 mL/min corresponding to an average shear rate of approximately 5.7s^-1 on the bottom surface of a single well. Biofilms were detected on well plate bottoms and measured using a fluorescence microscope and plate reader to determine biomass and viability. Samples cultured in the HT-μPBR showed increased biomass while maintaining viability after 24 h. The HT-μPBR can further be combined with HT antibiotic susceptibility testing and additional optical techniques such as time-lapse imaging to improve understanding of the drug reaction mechanism as well as the optimization of drug combinations and delivery profiles.

Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) represent a scalable experimental model relevant to human physiology. Oxygen consumption of hiPSC-CMs has not been studied in high-throughput (HT) format plates used in pre-clinical studies. Here, we provide comprehensive characterization and validation of a system for HT long-term optical measurements of peri-cellular oxygen in cardiac syncytia (human iPSC-CM and human cardiac fibroblasts), grown in glass-bottom 96-well plates. Laser-cut oxygen sensors having a ruthenium dye and an oxygen-insensitive reference dye were used. Ratiometric measurements (409nm excitation) reflected dynamic changes in oxygen, as validated with simultaneous Clark electrode measurements. Emission ratios (653nm vs. 510nm) were calibrated for percent oxygen using two-point calibration. Time-dependent changes in the Stern-Volmer parameter, Ksv, were observed during the initial 40 min of incubation, likely temperature-related. Effects of pH on oxygen measurements were negligible in the pH range of 4 to 8, with a small ratio reduction for pH>10. Time-dependent calibration was implemented, and light exposure time was optimized (0.6 to 0.8s) for oxygen measurements inside an incubator. Peri-cellular oxygen dropped to levels < 5% within 3 -10 hours for densely-plated hiPSC-CMs in glass-bottom 96-well plates. After the initial oxygen decrease, samples either settled to low steady-state or exhibited intermittent peri-cellular oxygen dynamics. Cardiac fibroblasts showed slower oxygen depletion and higher steady-state levels without oscillations, compared to hiPSC-CMs. Overall, the system has great utility for long-term HT monitoring of peri-cellular oxygen dynamics in vitro for tracking cellular oxygen consumption, metabolic perturbations, and characterization of the maturation of hiPSC-CMs.

Lab-on-a-chip technologies and microfluidics have pushed miniaturized liquid handling to unprecedented precision, integration, and automation, which improved the reaction efficiency of immunoassays. However, most microfluidic immunoassay systems still require bulky infrastructures, such as external pressure sources, pneumatic systems, and complex manual tubing and interface connections. Such requirements prevent plug-and-play operation at the point-of-care (POC) settings. Here we present a fully automated handheld general microfluidic liquid handling automation platform with a plug-and-play 'clamshell-style' cartridge socket, a miniature electro-pneumatic controller, and injection-moldable plastic cartridges. The system achieved multi-reagent switching, metering, and timing control on the valveless cartridge using electro-pneumatic pressure control. As a demonstration, a SARS-CoV-2 spike antibody sandwich fluorescent immunoassay (FIA) liquid handling was performed on an acrylic cartridge without human intervention after sample introduction. A fluorescence microscope was used to analyze the result. The assay showed a limit of detection at 31.1 ng/mL, comparable to some previously reported enzyme-linked immunosorbent assays (ELISA). In addition to automated liquid handling on the cartridge, the system can operate as a 6-port pressure source for external microfluidic chips. A rechargeable battery with a 12 V 3000 mAh capacity can power the system for 42 h. The footprint of the system is 16.5 × 10.5 × 7 cm, and the weight is 801 g, including the battery. The system can find many other POC and research applications requiring complex liquid manipulation, such as molecular diagnostics, cell analysis, and on-demand biomanufacturing.

For metabolically active cells like cardiomyocytes, a balanced state of oxygen supply and demand is crucial for basic cell function. Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are a valuable experimental model due of their scalability and relevance to human physiology. Oxygen consumption and availability have not been characterized in high-throughput format (HT), used in pre-clinical studies. Here, we quantified pericellular oxygen in syncytia of hiPSC-CM and human cardiac fibroblasts, grown in glass-bottom 96-well plates ( Fig 1A-C ). We deployed Ruthenium-based oxygen sensors and a ratiometric optical oxygen measurement system ( Fig 1B ) to track pericellular oxygen over time across all wells. Measured ratios were calibrated to % oxygen using two-point calibration with 5% Na 2 SO 3 and upon saturation with ambient air. Solution height and cell density were varied (4 solution heights, 3 cell densities) to understand their role in oxygen diffusion and oxygen consumption rate (OCR) by the cells. Michaelis-Menten kinetics and the Thiele modulus were used to computationally simulate oxygen availability in matching conditions. Without active perfusion or mass transport, for all tested conditions in the hiPSC-CMs, oxygen was depleted to <5% within approximately an hour. The drop of oxygen occurred in two phases - a zero-order decrease phase, followed by Michaelis-Menten kinetic phase ( Fig 1D ). Increase in culture medium volume/ height was found to be a powerful determinate of oxygen availability in simulations and in experiments ( Fig 1E n = 5 per group). Higher cell density correlated with steeper slope in the first phase of decline in oxygen availability, n = 4 per group. Cardiac fibroblasts followed a similar pattern (n = 4 per group) with noticeably slower OCR. Overall, our results indicate that pericellular oxygen in HT glass-bottom plates may reach hypoxic levels quickly; solutions for active mass transport need to be considered.