In this work, non-invasive high-spatial resolution three-dimensional (3D) X-ray micro-computed tomography (μCT) of healthy mouse lung vasculature is performed. Methodologies are presented for filtering, segmenting, and skeletonizing the collected 3D images. Novel methods for the removal of spurious branch artefacts from the skeletonized 3D image are introduced, and these novel methods involve a combination of distance transform gradients, diameter-length ratios, and the fast marching method (FMM). These new techniques of spurious branch removal result in the consistent removal of spurious branches without compromising the connectivity of the pulmonary circuit. Analysis of the filtered, skeletonized, and segmented 3D images is performed using a newly developed Vessel Network Extraction algorithm to fully characterize the morphology of the mouse pulmonary circuit. The removal of spurious branches from the skeletonized image results in an accurate representation of the pulmonary circuit with significantly less variability in vessel diameter and vessel length in each generation. The branching morphology of a full pulmonary circuit is characterized by the mean diameter per generation and number of vessels per generation. The methods presented in this paper lead to a significant improvement in the characterization of 3D vasculature imaging, allow for automatic separation of arteries and veins, and for the characterization of generations containing capillaries and intrapulmonary arteriovenous anastomoses (IPAVA).

We created a transient computational fluid dynamics model featuring a particle deposition probability function that incorporates inertia to quantify the transport and deposition of cells in mouse lung vasculature for the re-endothelialization of the acellular organ. Our novel inertial algorithm demonstrated a 73% reduction in cell seeding efficiency error compared to two established particle deposition algorithms when validated with experiments based on common clinical practices. We enhanced the uniformity of cell distributions in the lung vasculature by increasing the injection flow rate from 3.81 ml/min to 9.40 ml/min. As a result, the cell seeding efficiency increased in both the numerical and experimental results by 42 and 66%, respectively.

The adverse effects of global warming have made it critical to transition our reliance on fossil fuels to more sustainable energy sources. Polymer electrolyte membrane fuel cells (PEMFCs) can facilitate this transition by providing on-demand power with zero local carbon emissions. However, the high cost and poor durability of fuel cells hinder their widespread adoption. Particularly, PEMFC performance is strongly dependent on the flow fields which should be designed to optimize the transport of reactants and byproducts while maintaining uniform compression with subsequent layers. An important flow field design parameter is the channel aspect ratio which directly influences compression and the transport of reactants and products. Although novel flow field configurations have been studied previously, a comprehensive investigation on the effects of channel aspect ratio on cell performance has yet to be performed. In this study, we compared the electrochemical performance across varying flow field channel aspect ratios (channel width by height) from 0.5-2.0 with a fixed active area. The ohmic and mass transport resistances were quantified using electrochemical impedance spectroscopy. Operando X-ray imaging was performed to spatially resolve water saturation under the land and channel regions of the flow fields. We observed that lower channel aspect ratios (or higher number of channels for the given active area) led to lower ohmic resistance but resulted in higher mass transport losses at higher current densities due to significant water saturation under the hydrophilic ribs of the flow field. Notably, from these results we elucidated that there exists an ideal channel to rib width ratio to facilitate efficient mass transport and effective contact between the porous microstructures.

In polymer electrolyte membrane (PEM) fuel cells, the bipolar plates (BPPs) are responsible for the transport of reactants (via embedded flow fields), heat, and electrons, and account for 18-28% of the cost of fuel cell systems1. Thus, there is a great opportunity to improve the energy density of PEM fuel cells by improving the functions of BPPs, such as providing liquid water management, which affects reactant delivery and heat distribution. Previous work has shown that mass transport losses due to liquid water accumulation under the lands and channels of PEM fuel cell flow fields limit the power density of fuel cells2. Previous work has demonstrated that water will preferentially flow in a desired direction by implementing biomimetic wicking structures3; however, such wicking structures have not been previously implemented into a fuel cell. Furthermore, the design of BPPs has not been tailored to target areas of water accumulation. In this work, biomimetic geometries that promote passive unidirectional water wicking were implemented in a PEM fuel cell flow field to enhance liquid water removal and the distribution of reactant gases. The BPPs were characterized via constant current electrochemical testing and electrochemical impendence spectroscopy (EIS) to elucidate the dominant losses observed during operation. Operando synchrotron X-ray radiography was performed during the electrochemical testing in order to quantify the liquid water accumulation on the cathode side of the PEM fuel cell. The spatial distribution of liquid water was combined with EIS characterizations to explain the performance of the designs at high current densities, where mass transport losses typically dominate. The results from this work can be used to further optimize the design of PEM fuel cell bipolar plates in order to produce more efficient fuel cell stacks and drive PEM fuel cells into the global energy market. References Y. Wang, D. F. Ruiz Diaz, K. S. Chen, Z. Wang, and X. C. Adroher, Materials Today, 32, 178–203 (2020). N. Ge et al., Electrochimica Acta, 328, 135001 (2019). J. Feng and J. P. Rothstein, Journal of Colloid and Interface Science, 404, 169–178 (2013).

Mr. HUNTINGTON said the question of tramways had taken such a footing in English construction that it was quite time to have a fair and deliberate discussion concerning it. Tramways would in