Brillouin imaging is increasingly recognized to be a powerful technique that enables noninvasive measurement of the mechanical properties of cells and tissues on a microscopic scale. This provides an unprecedented tool for investigating cell mechanobiology, cell-matrix interactions, tissue biomechanics in healthy and disease conditions and other fundamental biological questions. Recent advances in optical hardware have particularly accelerated the development of the technique, with increasingly finer spectral resolution and more powerful system capabilities. We envision that further developments will enable translation of Brillouin imaging to assess clinical specimens and samples for disease screening and monitoring. The purpose of this review is to summarize the stateof-the-art in Brillouin microscopy and imaging with a specific focus on biological tissue and cell measurements. Key system and operational requirements will be discussed to facilitate wider application of Brillouin imaging along with current challenges for translation of the technology for clinical and medical applications.
Culture medium is frequently modelled as water in computational fluid dynamics (CFD) analysis of in vitro culture systems involving flow, such as bioreactors and organ-on-chips. However, culture medium can be expected to have different properties to water due to its higher solute content. Furthermore, cellular activities such as metabolism and secretion of ECM proteins alter the composition of culture medium and therefore its properties during culture. As these properties directly determine the hydromechanical stimuli exerted on cells in vitro, these, along with any changes during culture must be known for CFD model accuracy and meaningful interpretation of cellular responses. In this study, the density and dynamic viscosity of DMEM and RPMI-1640 media supplemented with typical concentrations of foetal bovine serum (0, 5, 10 and 20% v/v) were measured to serve as a reference for computational design analysis. Changes in these properties during culture was investigated with H460 and HN6 cell lines. The density and dynamic viscosity of the media increased proportional to the % volume of added foetal bovine serum (FBS). Importantly, the viscosity of 5% FBS-supplemented RPMI-1640 was shown to increase significantly after 3 days of culture of NCI-H460 and HN6 cell lines, with distinct differences between magnitude of change for each cell line. Finally, measured values were applied in CFD analysis of a simple microfluidic device, which demonstrated clear differences in maximum wall shear stress and pressure between fluid models. Overall, these results highlight the importance of characterizing model-specific properties for CFD design analysis of cell culture systems.
Simulated microgravity (s-μg) devices provide unique conditions for elucidating the effects of gravitational unloading on biological processes and are increasingly being applied for mechanobiology studies. However, without proper characterization of the mechanical environment generated by these systems, the interpretation of results is confounded and limited. Furthermore, the cell culture approaches central to s-μg experimentation introduces new factors that can fundamentally affect results, but these are currently not addressed. It is essential to understand the complete culture environment and how constituent conditions can individually and synergistically affect cellular responses in order to correctly interpret results, otherwise outcomes may be misattributed to the effects of microgravity alone. For the benefit of the growing space biology community, this article critically reviews a typical s-μg cell culture environment in terms of three key conditions: fluid-mediated mechanical stimuli, oxygen tension and biochemical. These and the implications of other experimental variables for biological analysis are categorically discussed. A new set of controls is proposed to properly evaluate the respective effects of these conditions in s-μg culture, along with a reporting matrix and potential strategies for addressing the current limitations of simulated microgravity devices as a platform for mechanobiology research.
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