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Many biological processes are affected by hypoxia. For example, hypoxia has been suggested to be a driver of tendon degeneration especially in conjunction with mechanical stimulation. To better study the effects of both factors on tendon degeneration, tendon explant studies can be useful. However, such explant models are complicated by the need of an incubator to control the oxygen levels, limiting the types of experiments that can be done. In this paper, we describe the design of bubbler system to alter oxygen levels for experiments conducted in an open environment. The basin volume, basin surface area-to-volume ratio, total system volume, and pump flow rate were optimized to obtain the lowest possible oxygen level. Oxygen levels were most sensitive to the total system volume and pump flow rates with higher values for both parameters leading to lower oxygen readings. This bubbler system was able to reach and maintain hypoxic levels sufficient to conduct future tendon explant experiments to understand the mechanism driving tendinopathy. 

IntroductionFollowing early cell specification and tenocyte differentiation at the sites of future tendons, very little is known about how tendon maturation into robust load-bearing tissue is regulated. Between embryonic day (E)16 and E18 in the chick, there is a rapid change in mechanical properties which is dependent on normal embryo movement. However, the tissue, cellular and molecular changes that contribute to this transition are not well defined. MethodsHere we profiled aspects of late tendon development (collagen fibre alignment, cell organisation and Yap pathway activity), describing changes that coincide with tissue maturation. We compared effects of rigid (constant static loading) and flaccid (no loading) immobilisation to gain insight into developmental steps influenced by mechanical cues. ResultsWe show that YAP signalling is active and responsive to movement in late tendon. Collagen fibre alignment increased over time and under static loading. Cells organise into end-to-end stacked columns with increased distance between adjacent columns, where collagen fibres are deposited; this organisation was lost following both types of immobilisation. DiscussionWe conclude that specific aspects of tendon maturation require controlled levels of dynamic muscle-generated stimulation. Such a developmental approach to understanding how tendons are constructed will inform future work to engineer improved tensile load-bearing tissues. 

Abstract The 2021 Summer Biomechanics, Bioengineering, and Biotransport Conference (SB3C) featured a workshop titled "The Elephant in the Room: Nuclear Mechanics and Mechanobiology." The goal of this workshop was to provide a perspective from experts in the field on the current understanding of nuclear mechanics and its role in mechanobiology. This paper reviews the major themes and questions discussed during the workshop, including historical context on the initial methods of measuring the mechanical properties of the nucleus and classifying the primary structures dictating nuclear mechanics, physical plasticity of the nucleus, the emerging role of the linker of nucleoskeleton and cytoskeleton (LINC) complex in coupling the nucleus to the cytoplasm and driving the behavior of individual cells and multicellular assemblies, and the computational models currently in use to investigate the mechanisms of gene expression and cell signaling. Ongoing questions and controversies, along with promising future directions, are also discussed.