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In this work we propose time-deniable signatures (TDS), a new primitive that facilitates deniable authentication in protocols such as DKIM-signed email. As with traditional signatures, TDS provide strong authenticity for message content, at least {\em for a sender-chosen period of time}. Once this time period has elapsed, however, time-deniable signatures can be forged by any party who obtains a signature. This forgery property ensures that signatures serve a useful authentication purpose for a bounded time period, while also allowing signers to plausibly disavow the creation of older signed content. Most critically, and unlike many past proposals for deniable authentication, TDS do not require interaction with the receiver or the deployment of any persistent cryptographic infrastructure or services beyond the signing process ( e.g., APIs to publish secrets or author timestamp certificates.) We first investigate the security definitions for time-deniability, demonstrating that past definition attempts are insufficient (and indeed, allow for broken signature schemes.) We then propose an efficient construction of TDS based on well-studied assumptions. 

Despite the crucial role of lymphangiogenesis during development and in several diseases with implications for tissue regeneration, immunity, and cancer, there are significantly fewer tools to understand this process relative to angiogenesis. While there has been a major surge in modeling angiogenesis with microphysiological systems, they have not been rigorously optimized or standardized to enable the recreation of the dynamics of lymphangiogenesis. Here, a Lymphangiogenesis‐Chip (L‐Chip) is engineered, within which new sprouts form and mature depending upon the imposition of interstitial flow, growth factor gradients, and pre‐conditioning of endothelial cells with growth factors. The L‐Chip reveals the independent and combinatorial effects of these mechanical and biochemical determinants of lymphangiogenesis, thus ultimately resulting in sprouts emerging from a parent vessel and maturing into tubular structures up to 1 mm in length within 4 days, exceeding prior art. Further, when the constitution of the pre‐conditioning cocktail and the growth factor cocktail used to initiate and promote lymphangiogenesis are dissected, it is found that endocan (ESM‐1) results in more dominant lymphangiogenesis relative to angiogenesis. Therefore, The L‐Chip provides a foundation for standardizing the microfluidics assays specific to lymphangiogenesis and for accelerating its basic and translational science at par with angiogenesis.

 

BACKGROUND: Almost 95% of the venous valves are micron scale found in veins smaller than 300μm diameter. The fluid dynamics of blood flow and transport through these micro venous valves and their contribution to thrombosis is not yet well understood or characterized due to difficulty in making direct measurements in murine models. OBJECTIVE: The unique flow patterns that may arise in physiological and pathological non-actuating micro venous valves are predicted. METHODS: Computational fluid and transport simulations are used to model blood flow and oxygen gradients in a microfluidic vein. RESULTS: The model successfully recreates the typical non-Newtonian vortical flow within the valve cusps seen in preclinical experimental models and in clinic. The analysis further reveals variation in the vortex strengths due to temporal changes in blood flow. The cusp oxygen is typically low from the main lumen, and it is regulated by systemic venous flow. CONCLUSIONS: The analysis leads to a clinically-relevant hypothesis that micro venous valves may not create a hypoxic environment needed for endothelial inflammation, which is one of the main causes of thrombosis. However, incompetent micro venous valves are still locations for complex fluid dynamics of blood leading to low shear regions that may contribute to thrombosis through other pathways. 

The lymphatic vascular function is regulated by pulsatile shear stresses through signaling mediated by intracellular calcium [Ca 2+ ] i . Further, the intracellular calcium dynamics mediates signaling between lymphatic endothelial cells (LECs) and muscle cells (LMCs), including the lymphatic tone and contractility. Although calcium signaling has been characterized on LEC monolayers under uniform or step changes in shear stress, these dynamics have not been revealed in LMCs under physiologically-relevant co-culture conditions with LECs or under pulsatile flow. In this study, a cylindrical organ-on-chip platform of the lymphatic vessel (Lymphangion-Chip) consisting of a lumen formed with axially-aligned LECs co-cultured with transversally wrapped layers of LMCs was exposed to step changes or pulsatile shear stress, as often experienced in vivo physiologically or pathologically. Through real-time analysis of intracellular calcium [Ca 2+ ] i release, the device reveals the pulsatile shear-dependent biological coupling between LECs and LMCs. Upon step shear, both cell types undergo a relatively rapid rise in [Ca 2+ ] i followed by a gradual decay. Importantly, under pulsatile flow, analysis of the calcium signal also reveals a secondary sinusoid within the LECs and LMCs that is very close to the flow frequency. Finally, LMCs directly influence the LEC calcium dynamics both under step changes in shear and under pulsatile flow, demonstrating a coupling of LEC–LMC signaling. In conclusion, the Lymphangion-Chip is able to illustrate that intracellular calcium [Ca 2+ ] i in lymphatic vascular cells is dependent on pulsatile shear rate and therefore, serves as an analytical biomarker of mechanotransduction within LECs and LMCs, and functional consequences. 

Background Organ‐on‐chip technology has accelerated in vitro preclinical research of the vascular system, and a key strength of this platform is its promise to impact personalized medicine by providing a primary human cell–culture environment where endothelial cells are directly biopsied from individual tissue or differentiated through stem cell biotechniques. However, these methods are difficult to adopt in laboratories, and often result in impurity and heterogeneity of cells. This limits the power of organ‐chips in making accurate physiological predictions. In this study, we report the use of blood‐derived endothelial cells as alternatives to primary and induced pluripotent stem cell–derived endothelial cells. Methods and Results Here, the genotype, phenotype, and organ‐chip functional characteristics of blood‐derived outgrowth endothelial cells were compared against commercially available and most used primary endothelial cells and induced pluripotent stem cell–derived endothelial cells. The methods include RNA‐sequencing, as well as criterion standard assays of cell marker expression, growth kinetics, migration potential, and vasculogenesis. Finally, thromboinflammatory responses under shear using vessel‐chips engineered with blood‐derived endothelial cells were assessed. Blood‐derived endothelial cells exhibit the criterion standard hallmarks of typical endothelial cells. There are differences in gene expression profiles between different sources of endothelial cells, but blood‐derived cells are relatively closer to primary cells than induced pluripotent stem cell–derived. Furthermore, blood‐derived endothelial cells are much easier to obtain from individuals and yet, they serve as an equally effective cell source for functional studies and organ‐chips compared with primary cells or induced pluripotent stem cell–derived cells. Conclusions Blood‐derived endothelial cells may be used in preclinical research for developing more robust and personalized next‐generation disease models using organ‐on‐chips.