Iridium oxide films deposited on stimulation electrode wires by rf sputtering exhibit markedly different surface morphologies and charge capacities in response to variations in deposition conditions. The films sputtered on the composite wire specimens are comprised of closely packed ellipsoidal platelets in varying degrees of alignment. The film appearance and electrochemical properties are strongly dependent on the water-to-oxygen ratio in the sputter gas. Increasing this ratio from 0 to 0.22 results in a marked rotation of the direction of net alignment of the sputtered iridium oxide film (SIROF) platelets and reduced anodic and cathodic charge capacities. The anodic charge capacities of the SIROF films were remarkably linear with respect to the logarithm of the cyclic voltammetry sweep rate.
Here we describe of an 'Interrogator' instrument that uses liquid-handling robotics, a custom software package, and an integrated mobile microscope to enable automated culture, perfusion, medium addition, fluidic linking, sample collection, and in situ microscopic imaging of up to 10 Organ Chips inside a standard tissue culture incubator. The automated Interrogator platform maintained the viability and organ-specific functions of 8 different vascularized, 2-channel, Organ Chips (intestine, liver, kidney, heart, lung, skin, blood-brain barrier (BBB), and brain) for 3 weeks in culture when fluidically coupled through their endothelium-lined vascular channels using a common blood substitute medium. When an inulin tracer was perfused through the multi-organ Human Body-on-Chips (HuBoC) fluidic network, quantitative distributions of this tracer could be accurately predicted using a physiologically-based multi-compartmental reduced order (MCRO) in silico model of the experimental system derived from first principles. This automated culture platform enables non-invasive imaging of cells within human Organ Chips and repeated sampling of both the vascular and interstitial compartments without compromising fluidic coupling, which should facilitate future HuBoc studies and pharmacokinetics (PK) analysis in vitro.Vascularized human Organ Chips are microfluidic cell culture devices containing separate vascular and parenchymal compartments lined by living human organ-specific cells that recapitulate the multicellular architecture, tissue-tissue interfaces, and relevant physical microenvironments of key functional units of living organs, while providing vascular perfusion in vitro 1,2 . The growing recognition that animal models do not effectively predict drug responses in humans 3-5 and the related increase in demand for in vitro human toxicity and efficacy testing, has led to pursuit of time-course analyses of human Organ Chip models and fluidically linked,
Iridium oxide films deposited on Ti-alloy stimulation electrode wires by rf sputtering exhibit markedly different surface morphologies and redox capacities in response to variations in applied substrate bias potential. Films deposited with a −20 volt bias were relatively smooth and featureless whereas those sputtered with a +20 volt bias were comprised of closely packed 1 micron long platelets. Intermediate substrate biases revealed a gradual progression from the smooth surface to one sparsely populated with particles to a morphology comprised of tightly packed platelets. The electrochemical properties of the films are strongly dependent on the substrate bias employed during deposition. As the DC bias was increased from −20 volts to +20 volts the anodic and cathodic charge capacities determined by cyclic voltammetry decreased linearly from 36 to 12 mC/cm2.
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